Accelerating New Product Deployment with
Manufacturability Guidelines
by
Wern-Lirn Wang
M.S. Chemical Engineering
Pennsylvania State University (1986)
Submitted to
the Alfred P. Sloan School of Management
and the Department of Materials Science and Engineering
in Partial Fulfillment of the Requirements for the Degrees of
Master of Science in Management
and
Master of Science in Materials Science and Engineering
in conjunction with the Leaders for Manufacturing Program
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
May 1994
© Massachusetts Institute of Technology, 1994
ALL RIGHT RESERVED
Signature of Author
-M1riSloan School of Manage ý
Department of Materials Science and Engineering
May, 1994
Certified by
Deborah Ancona, Thesis Supervisor
Ase~te Professor of Organization Studies
Certified by
Don P. C
, Thes u sor
Bernard M. Gordon Professor of Engineerin[t 1ov
a ioI(nd4aractice
aE
Accepted by
--.-
I Jeffrey A. Barks
d11
Associate Dean, Sloan Master's and Bachelor's Programs
Accepted by
g •rlncnp
Carl V. Thompson II,
airman
MASSACHUSETrS Q
1 1partmental Committee on Graduate Students
OF TECHNOLOGY
WJUN 08 1994
-2-
Accelerating New Product Deployment with
Manufacturability Guidelines
by
Wern-Lirn Wang
Submitted to the Alfred P. Sloan School of Management and
the Department of Materials Science and Engineering
on May 6, 1994, in Partial Fulfdllment of the Requirements for the degrees of
Master of Science in Management
Master of Science in Materials Science and Engineering
Abstract
A manufacturability guidelines approach is employed in this research to accelerate
new product deployment process of thin-film-head. The design-lead product development
practices in this industry suggest a traditional design rules approach is inadequate. The
manufacturability guidelines take into account the dynamics between design and
manufacturing activities. Through enhancing constructive interactions between design and
manufacturing engineers, these manufacturability guidelines render product designers
flexibility to explore product technology envelope while ensure the manufacturability of
the designs. The guidelines is a knowledge database linking design parameters with
manufacturability issues. With their knowledge structure based on physical phenomena of
the manufacturing process, the manufacturability guidelines provide likely directions for
disciplined design decisions even though the knowledge involved is not thoroughly
verified. This research proposed an application of the manufacturability guidelines as a
vigilant information system in the design review process. It was also found that the
guidelines can be used as a communication tool to facilitate concurrent engineering.
Several organizational and cultural issues were found to be the obstacles for applications
of the guidelines. An organization that promotes information sharing and organizational
learning is essential for the manufacturability guidelines to deliver their full potentials.
Engineering resources allocation was a concern among the management for a full scale
design and manufacturing integration. A pilot product development team approach was
then suggested to disseminate experience of team-based product deployment process and
rally support from the rest of the organization and upper management.
Thesis Supervisors:
Thesis Reader:
Professor Deborah Ancona
Associate Professor of Organization Studies
Professor Don P. Clausing
Bernard M. Gordon Professor of Engineering Innovation
and Practice
Professor Stuart Brown
Associate Professor of the Department of Materials Science
and Engineering
-3-
-4-
Acknowledgment
This thesis would not have been possible without the help and encouragement of several
people. Mr. Arthur L. Keigler guided me through the study of thin-film-head
manufacturing process and provided constant support for my work. I would like to thank
Mr. Mike Collver and Mr. Larry Neumann for their support and suggestions which have
become a integral part of this thesis.
The support and cooperation from people of Mr. Arthur's and Mr. Neumann's groups are
specially appreciated. It would be impossible for this research to proceed without the
patience and helps from many people in the organization.
The guidance of my faculty advisors, Prof. Deborah Ancona and Prof. Don P. Clausing,
has helped me throughout the internship and the preparation of this thesis. I like also to
thank for the support of my thesis reader, Prof. Stuart Brown of the Department of
Materials Science and Engineering for his special attention on the technical part of this
thesis.
Finally, I would like to dedicate this thesis to my wife, Vicki, who have encouraged me
through my two years at the Leaders for Manufacturing Program.
-5-
TABLE OF CONTENTS
1. INTRODUCTION
13
PART I SMART HEAD BUSINESS (SHB)
2. BACKGROUND
21
2.1 THIN-FILM-HEAD INTRODUCTION
21
2.2 DISK DRIVE AND DISK DRIVE HEAD INDUSTRY
26
2.3 SMART HEAD BUSINESS' MARKET POSITION
30
2.4 CHALLENGES IN NEW PRODUCT DEPLOYMENT
33
3. TFH WAFER PRODUCT DEPLOYMENT PROCESS
35
3.1 OLD PRODUCT DEPLOYMENT PROCESS
35
3.2 REORGANIZATION
39
3.3 NEW PRODUCT DEPLOYMENT PROCESS
41
3.4 CURRENT ISSUES IN PRODUCT DESIGN
45
3.5 CURRENT ISSUES IN NEW DESIGN MANUFACTURING
47
3.6 CURRENT ISSUES IN VOLUME PRODUCTION
49
3.7 THE SCOPE OF THIS RESEARCH
50
PART H TECHNICAL ISSUES
4. MANUFACTURABILITY ISSUES OF TFH WAFER MANUFACTURING
53
4.1 WAFER MANUFACTURING PROCESS
53
4.2 PHOTORESIST COATING
57
4.3 PHOTORESIST PATTERNING
65
4.4 PHOTORESIST HARD-BAKE
69
4.5 REGISTRATION
72
4.6 PHOTORESIST NOTCHING
74
4.7 CRITICAL DIMENSION CONTROL
76
-7-
5. DESIGN FOR MANUFACTURING
79
5.1 DESIGN-PUSH VERSUS DESIGN FOR MANUFACTURING
79
5.2 CURRENT MISMATCH BETWEEN PRODUCT DESIGN AND MANUFACTURING
PROCESS CAPABILITY
81
5.3 INTEGRATION OF DESIGN AND MANUFACTURING
6. MANUFACTURABILITY GUIDELINES
85
89
6.1 A KNOWLEDGE ISSUE
89
6.2 THE PROCESS OF DERIVING MANUFACTURABILITY GUIDELINES
92
6.2.1 Process Characterization
92
6.2.2 Fault Tree Analysis
92
6.2.3 Critical Design Parameters
97
6.2.4 Critical Design Parameter Database
97
6.2.5 Manufacturability Guidelines
98
PART III MANAGERIAL ISSUES
7. APPLICATIONS OF THE MANUFACTURABILITY GUIDELINE
7.1 A TOOL FOR DESIGN REVIEW
99
99
7.1.1 Design Review
99
7.1.2 A Tool for Design Review
101
7.1.3 A Model
106
7.2 CONCURRENT ENGINEERING
109
8. IMPLEMENTATION OF MANUFACTURABILITY GUIDELINES
APPLICATIONS
115
8.1 RESISTANCE OVER IMPLEMENTATION
115
8.1.1 The Resistance
115
8.1.2 The Hypothesis
116
8.1.3 The Survey
117
8.1.4 The Conclusion
120
122
8.2 ORGANIZATION DYNAMICS
-8-
9. PRODUCT TEAM APPROACH
127
9.1 PRODUCT DEPLOYMENT PROCESS INTEGRATION WITH CONCURRENT
ENGINEERING
127
9.2 PRODUCT DEVELOPMENT TEAM APPROACH
130
9.2.1 Team Definition
130
9.2.2 Product Development Team in SHB
133
9.2.3 The Pilot Team Approach
136
10. SUGGESTIONS FOR FUTURE STUDY
139
10.1 FURTHER REFINEMENT AND UPDATES OF THE MANUFACTURABILITY
GUIDELINES
139
10.2 OTHER GUIDELINE FOR DESIGN PURPOSES
141
10.3 ORGANIZATIONAL STUDY
143
APPENDIX A
145
APPENDIX B
151
APPENDIX C
155
APPENDIX D
157
APPENDIX E
159
REFERENCE
165
-9-
LIST OF FIGURES
FIGURE 2-1: TFH MAGNETIC WRITING AND RECORDING PROCESS
FIGURE 2-2: HARD DISK DRIVE MARKET SHARE OF 1992
FIGURE 2-3: TFH OEM MARKET SHARE
FIGURE 3-1: OLD PRODUCT DEPLOYMENT PROCESS
FIGURE 3-2: NEW PRODUCT DEPLOYMENT PROCESS
FIGURE 3-3: SYSTEM DYNAMICS VIEW OF THE ISSUES
FIGURE 4-1: A TYPICAL TFH STRUCTURE
FIGURE 4-2: TFH DEVICE TOPOGRAPHY
FIGURE 4-3: DEVICE ORIENTATION VERSUS PHOTORESIST FLOW
FIGURE 4-4: COIL PATTERNING AND FOCAL OFFSET
FIGURE 4-5: SHADOWING EFFECT
FIGURE 4-6: IMPACT OF FEATHERING SCHEME ON SHADOWING EFFECT
FIGURE 4-7: NOTCHING MECHANISM
FIGURE 5-1: MISMATCH BETWEEN DESIGN AND MANUFACTURING
FIGURE 5-2: REDUCING THE GAP BETWEEN DESIGN AND
MANUFACTURING
FIGURE 5-3: SYSTEM DYNAMICS VIEW OF DESIGN AND MANUFACTURING
INTERACTIONS
FIGURE 6-1: FAULT TREE ANALYSIS
-A] EXAMPLE OF FTA
FIGURE 6-2: AN EXAMPLE OF FTA
-10-
FIGURE 7-1: A DESIGN REVIEW MEETING
100
FIGURE 7-2: REINFORCING LOOP THAT CAUSES DISINTEREST
103
FIGURE 7-3: CONCURRENT PROCESS
112
FIGURE 7-4: A MODEL OF CONCURRENT ENGINEERING
114
FIGURE 8-1: SHIFTING ENGINEERING RESOURCES TO DESIGN ACTIVITY 123
FIGURE 8-2: A SYSTEM DYNAMIC MODEL
124
FIGURE 9-1: A MODEL FOR INTEGRATED PRODUCT DEPLOYMENT
PROCESS
128
FIGURE 9-2: TEAM STRUCTURES
134
-11-
-12-
CHAPTER
1. INTRODUCTION
A thin-film-head (TFH) is a miniature electromagnet transducer mounted on a computer
disk drive to record or to reproduce digital signals with magnetic media. With disk drive
industry demanding an annual storage density growth of 30 to 35 percent, the product life
cycle of TFH has been shrinking to one year or less. It is projected that the annual growth
rate of storage density will accelerate to 60% in the near future while an annual 7 percent
price erosion is expected. As a result, TFH manufacturers have to accelerate their product
deployment processes and increase wafer yield in order to stay competitive in the market.
Design for manufacturing (DFM) seems to be the answer for both. However, traditional
design rule approach is not adequate in this industry where product designers continuously
pushing product technology envelope to meet performance demand. A new approach that
takes into account the dynamics between manufacturing process capability and product
performance requirement is needed. This research develops a new approach employing
the manufacturability guidelines to enhance the interactions between design and
manufacturing. The manufacturability guidelines is a knowledge database built upon a
structure that is based on physical phenomena of TFH manufacturing process. With the
physical phenomena structure, the manufacturability guidelines provide linkages between
fragmented manufacturing knowledge and critical design parameters. The
manufacturability guidelines are proposed to serve as a vigilant information system for
product design review process as well as a communication framework for concurrent
-13-
engineering. This study found several organizational and behavioral issues associated with
the changes associated with the proposed applications of the guidelines. To take full
advantage of the benefit of the guidelines, a pilot product development team approach is
suggested to move SHB product deployment process to a product development team
approach. The manufacturability guidelines can serve as a common communication tool
between engineers of different discipline. Finally, this thesis wraps up with several
suggestions for future studies to farther explore the potentials of the manufacturability
guidelines.
Chapter 2. Background
This Chapter provides a brief history of TFH technology evolvment along with summaries
of computer disk drive and disk drive head industries. Current market position of SHB,
the facility where this study took place, is then discussed. Being the number four OEM
supplier in the TFH industry, SHB has to be innovative to prosper among competitors
many times its size. The discussion draws a conclusion that SHB has to improve its
product deployment process to reduce time-to-market as well as to increase its wafer yield
to achieve competitive advantage.
Chapter 3. TFH Wafer Product Deployment Process
A close examination of the product deployment processes of SHB is provided in this
Chapter. The author suggested functional organization and sequential product
deployment process are the two reasons for excess design iterations and low wafer yield.
-14-
SHB's product team did not improve the deployment process as expected because the
message from the management was not clear and people naturally fell back to old
functional practices. A system dynamics analysis is provided to incorporate issues in
product design, new design manufacturing, and volume production. This analysis shows
that product designs with little attention to process manufacturability and lack of adequate
technical resources in manufacturing engineering group are the internal causes for current
product deployment problems. Outside factors such as shrinking product life cycle and
corporate demand for higher revenue put further pressure to this strained system To
break this vicious cycle manufacturing engineering resources have to shifted to the design
activities to produce product designs with manufacturability. The end of this Chapter
outlines the scope of this research---o develop a structured design tool to address
manufacturability issues of photolithography process.
Chapter 4. Manufacturability Issues of TFH Wafer Manufacturing
A review of the complex TFH wafer process is provided in this Chapter. This review
covers topics of coating, patterning, hard-bake, registration, notching, and critical
dimension control. This study found the intertwining relationships between different
process steps render discrete manufacturing knowledge useless in solving wafer yield
problems. The physical phenomena and the related knowledge discussed in this Chapter
are used later to form the knowledge structure of the manufacturability guidelines.
Chapter 5. Design for Manufacturing
The competitive environment of TFH industry is re-examined from a technical view point.
-15-
It is recognized that the demand for higher storage density has forced TFH designers to
lead process designers in pushing technology envelope. As a result, any structured design
tool has to take into account the dynamics between design and manufacturing activities.
Because of this reason, the traditional design rule approach is not adequate for TFH
product deployment process. The second issue is the low wafer yield. Through several
benchmark analyses, this research concluded a mismatch between product design and
manufacturing process capability is the reason for low wafer yield. The existence of this
problem also suggests the need for better collaboration between design and manufacturing
engineers. Accordingly, the scope of this research was expanded from delivering
information of the process capability to the design engineers to integrating the design and
the manufacturing activities through the manufacturability guidelines.
Chapter 6. Manufacturability Guidelines
To enhance the integration of design and manufacturing activities, the manufacturability
guidelines will have to be able to facilitate compromises as well as stimulate creativity to
exploit the technology envelope of both design and manufacturing disciplines. For this
reason, the guidelines must serve as a knowledge tool to reveal the connections between
design attributes and manufacturing issues and a communication tool to enhance
information exchanges. With this in mind, the author employed process characterization
and fault tree analysis to derive a knowledge structure that links design attributes and
manufacturing issues based on physical phenomena of TFH fabrication process. The
critical design parameters were then identified. To tailor the knowledge database for
-16-
easier use in design activities, the information was resorted by design parameters to form
the manufacturability guidelines. Although most of the manufacturing knowledge
available was drawn from experience without much precise verification, the
manufacturability guidelines provide a feasible structure to facilitate disciplined design
decisions based on the existing understanding of the TFH process.
Chapter 7. Applications of the Manufacturability Guidelines
The author suggested the manufacturability guidelines can be used as a vigilant
information system to remind manufacturing engineers about possible manufacturability
issues in a design review meeting. A model of using the manufacturability guidelines in
current design review setting was proposed. Feedback from product group manager
suggested another model of using the guidelines to solicit inputs of manufacturability in
the early phase of design activities. Since the guidelines provide a knowledge structure
between design parameters and manufacturing issues, this study found the guidelines can
be used to facilitate concurrent engineering. As each design parameter is set, its
implications on manufacturability can be obtained from the guidelines. Manufacturing
engineers can then start to work on process and manufacturing issues of a new design
before the design is completed.
Chapter 8. Implementation of Manufacturability Guidelines Applications
This Chapter focuses on the cultural and organizational issues related to the changes
suggested in the last Chapter. A survey was conducted to solicit opinions from design
-17-
engineers about the applications of the manufacturability guidelines. The feedback
showed design engineers were afraid of the uncertainty associated with changes. The
author argued that the key nature of the manufacturability guidelines-information
sharing-is incompatible with current organizational culture and performance measuring
system In other words, to gain the benefits of the manufacturability guidelines the culture
and supporting structure have to be changed. Another concern over the higher level of
manufacturing engineers' involvement in design activities is the resource allocation. The
management was afraid that a full scale design and manufacturing integration would mean,
in the initial phase, fewer resources for production support. They argued that it is risky to
pull engineering resources away from fire-fighting activities under corporate pressure for
higher revenue. However, staying at current position is not a viable option either. SHB
needs to change in order to meet current and future market challenges.
Chapter 9. Product Team Approach
To fully explore the potential of the manufacturability guidelines, a product development
team (PDT) approach is necessary. Not only because the PDT is the best format for
concurrent engineering, but also because the PDT provides a cross-functional environment
where the manufacturability guidelines can be used as the common communication tool to
create synergy. By analyzing the characteristics of true PDT, the author argued the
current product teams in SHB are not true PDTs. Changes in organizational culture and
individual behavior are necessary to change these product teams to true PDTs. With the
constraints mentioned in the last Chapter in mind, a pilot team approach was suggested.
-18-
In short, the pilot team is a true PDT used as a showcase and knowledge dissemination
center for the PDT approach. Through its success, the pilot team provide good insight of
a PDT to the rest of the organization and rally support from corporate executives.
However, to ensure the success of this pilot team, a knowledgeable team-building
specialist and a strong team sponsor are necessary to nurture the growth of the team.
Chapter 10. Suggestions for Future Study
To ensure that the manufacturability guidelines are used to achieve their full potential, they
have to be constantly updated and refined. Other factors inproduct design, such as
performance requirements, magnetic requirements, plating issues, and vacuum issues need
to have a similar knowledge database established to provide a balance inputs for design
engineers in making trade-off decision.
-19-
-20-
PART I SMART HEAD BUSINESS (SHB)
CHAPTER
2. BACKGROUND
2.1 THIN-FILM-HEAD INTRODUCTION
A thin-film-head (TFH) is a miniature electromagnet that records (in writing mode) digital
signals onto magnetic media and reproduces (in reading mode) digital signals from the
magnetic patterns stored on the media. In the writing mode, an electrical current passes
through the coil of a TFH and creates a magnetic field which produces magnetic flux
around the pole tip (gap of magnetic head) area. The magnetic flux penetrates the
medium and induces a magnetization pattern on the recording medium as the TFH moves
across it. In the reading mode, the changes of the magnetic field around the pole tip
created by the magnetization patterns of medium as a result of the TFH moving across the
medium create electric volts in the coil which reproduce the digital signals that were
originally stored. A graphic representation of the writing and reading process is provided
in Figure 2-1 [Bertram 1986]. In digital recording, a bit of recorded information is defined
by a reversal of the magnetization state of the active layer of the medium.
Magnetic recording technique was first developed by Valdemar Poulsen to capture and
record the human voice and sound in general [Ciureanu 1990]. The Poulsen telegraphon,
he patented in 1898, consisted of a steel wire wound on a drum set between the poles of a
permanent magnet. Once it was connected to a telephone, the head magnetized the wire
-21-
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according to the variations of the current in the telephone. Over the years, different
magnetic heads and recording media were developed in response to the growing needs for
audio, video, and digital recording. The TFH, or thin-film inductive transducer, was
developed to fulfill the need for a miniaturized, highly sensitive and accurate transducer
for various scientific and technical applications. Early research concerning the use of thinfilm structures for data recording dates back to the 1960s. The first experimental model
of a TFH device was invented a decade later, and the first commercially available storage
device using TFH technology was the IBM 3370/3380 disk drive. Over the years, the
market share of TFH transducers in the hard disk drive market has steadily increased to 50
percent (mainly in the high-end segment) [Belden 1993]. The advantage of the TFH over
traditional ferrite heads stems from the differences in the manufacturing process. Adopted
from the semiconductor thin film technology, this manufacturing process renders a much
more compact structure that results in device miniaturization and lower production cost.
The read operation of TFH is based on Faraday's Law, with the output signal amplitude
depending directly on the rate of the magnetic flux change through the media surface. As
a result, the control of the relative speed between TFHs and the recording medium (the
spin speed of the medium) is of vital importance to the performance of storage devices,
such as the computer disk drive. New technology development in the area of
galvanomagnetic sensors (which measure the strength of the magnetic field
-23-
straightforwardly) has resulted in the magneto-resistive head (MR) where the output
signal does not depend on the rate of change of the input signal (the rate of change of the
medium spin). One advantage of the MR head is that it allows higher storage density on
magnetic medium because it provides a stronger signal. The newest invention inthis area,
the giant magneto-resistance head (GMR) by IBM will increase disk-drive density by a
factor of 50. Even though the MR head is generally perceived inthe industry as the next
generation storage device, it is facing difficulties in competing with the TFH because of
high cost and lower yield which are typical for new technologies intheir early stage of
development. Another factor to consider inthe future development of MR technology is
that the MR head needs a thin-film inductive head for writing purposes. Because the MR
head is basically a read head, it needs a thin film inductive head to do the writing. This
constraint offers current TFH manufacturers an opportunity for gradual transition from
TFH to future MR technology.
Thin-film inductive heads can be classified into different performance categories based on
their geometric structures (the number of coil layers). The geometric structure is generally
determined by the winding scheme of the coil. A higher number of coil turns increases
signal strength and, as a result, increases storage density on the recording media as less
area is required for each bit of information. However, TFH designs with more coil turns
and more layers pose additional challenges to the wafer fabrication process. Although the
feature sizes of a TFH themselves are not particularly difficult to make with the current
-24-
process, there are other factors conspiring against conventional lithography, including
thick resist, reflective metal surfaces, and rough metal surfaces [Bond 1993]. Because of
these factors, the competitiveness of the wafer fabrication process has become increasingly
important for TFH manufacturers in the highly competitive market.
-25-
2.2 DISK DRIVE AND DISK DRIVE HEAD INDUSTRY
Disk Drive Industry
The demand for disk drives (hard disk drives) grew rapidly in 1992 as a result of the price
reduction of the personal computers. However, in early 1993 the growth fell. Several
disk drive vendors who saw the high growth the year before increased production sharply
in anticipation of sustained growth in market volume or market share. Aggregate disk
drive production grew faster than demand, leading to excess inventories and severe pricing
pressures. While the hard drive business has always been a roller-coaster ride of price
wars, product gluts, and shortages, this latest turmoil signaled that the market has been
increasingly commoditized by slim profit margins and stiff competition [Schroeder 1993].
The current hard disk drive market is divided between several large vendors and smaller
players targeted at the high-end niche of the market (Figure 2-2). Total disk drive unit
sales can be segmented into drives installed at the system factory (OEM, original
equipment manufacturer), drives installed into new systems by dealers, and add-on drives
sold into the installed base of systems. For drives sold with new systems, the pendulum
has swung from OEM to dealer installed units and back again [Casey 1993]. Due to the
personal computer (PC) price war, first-tier PC makers (IBM, Apple, Compaq, etc.) are
gaining market share at the expense of the low-priced clone makers. As the first-tier
system vendors continue to gain market share, certain disk drive makers will benefit more
than others. As for the add-on portion, 26 percent of the drives sold by U.S. dealers in
March 1993 were add-ons to the installed base of PCs. That is twice the amount three
-26-
IBM 10%
Maxtor 10%
Quantum 15,
nner 24%
Seagate
Western Digital
9%
Source: INFOCORP
Figure 2-2: Hard disk drive market share of 1992
to four years ago. The reasons behind these increases have been new software
applications (provoking a desire for increased storage) and low-priced disk drives.
However, many industry analysts do not believe the growth trend is sustainable. New
data-compression software and network storage devices will take away potential add-on
drive expenditures.
Because of over-capacity and market shifts, some consolidations among independent drive
makers are likely to occur. On the other hand, new technologies will increase the pace of
changes as well. Historically, disk drive vendors have increased areal density (amount of
information per unit surface area of the medium) at a rate of 30 to 35 percent per year.
-27-
New head technology, such as MR,can accelerate that pace to 60 percent annually. This
technology evolution will lead to shorter product life cycles and faster price erosion. With
a 60 percent annual increase in areal density, a 38 percent annual drop in the cost per
Mbyte of hard disk storage can be predicted [Casey, 1993]. Disk drive companies will
have to learn to cope with this price erosion, to manage more frequent product changes,
and ramp up new technologies much more quickly.
Disk Drive Head Industry
The disk drive head industry is cyclical in nature. There are currently ten major TFH
manufacturers with capacities ranging from 1.8 million to 84 million units per year. Each
has a different customer base. Two of the biggest producers, IBM and Seagate, ship a
major portion (over 80 percent) of their products to internal customers. Other vendors
target mainly in the OEM market with each one serving several hard disk drive
manufacturers. Between the drive and head industries, it is common for a disk drive
maker to source from several TFH vendors at the same time to ensure a steady supply of
this critical component.
Though the disk drive industry is under pricing pressure due to over-capacity, the TFH
market is expected to grow continuously at the expense of the ferrite and the MIG (metalin-gap) heads which employ older technologies. Some marketing researches [Laetz 1992]
predicted the TFH market would grow at a compounded annual rate of 28 percent in the
US and 68 percent in the non-US market. However, the low profitability of the disk drive
-28-
industry has put pressure on the price of the TFH. Currently, the gross margin for head
makers is 2 percent on average [Citta 1993]. Projected price erosion of the TFH is 7
percent annually. On the other end, although the TFH devices have equal or better
performance characteristics than that of ferrite and MIG technologies, the lack of head
supplies and higher price have resulted in many disk drive companies continuing to look
for alternatives. Continuous improvement in the ferrite and the MIG technologies has
been able to fill the performance gap. This situation will also increase the pricing pressure
on TFH products until the designs of TFH devices can push head performance farther
ahead of other designs.
Demands for increasing areal density from the hard disk drive industry will keep pressure
on the miniaturization of TFH. Several new technologies in head designs, such as virtual
contact recording, increasing coil turn with lower impedance, and MR, will be employed
to push the technology envelope. Other factors that influence TFH performance may
impact the future development of the industry as well. New wafer materials for TFH
(glass and silica) are under investigation to reduce costs or increase the strength of
transducers. Designs of circuit channels which handle signals between the TFH and the
disk drive controller will pose a major obstacle in further improvement of head
capabilities. A new read channel design, partial response, maximum likelihood (PRML),
promises thirty percent improvement in area density and it is believed it will be widely
adopted in the near future.
-29-
2.3 SMART HEAD BUSINESS' MARKET POSITION
Smart Head Business (SHB), being part of one leading computer manufacturer in the
country, started as a captive supplier of TFH devices for its internal customer-the disk
drive division which supplies hard disk drives for the computer systems this company
produced. In 1990, the demand for this company's main product--the computerstarted to fall off and the corporation went through a close scrutiny with each business
unit demanding that every subsidiary become profitable by its own means. It was clear to
the management of SHB, at that time, that this business unit would begin to have
difficulties along with its disk drive sibling unless new markets for its TFH devices could
be developed. Top management took the initiative by exploiting its business opportunity
as an OEM head supplier. A cadre of engineers was assembled to develop the first
product for outside customers. This venture became a huge success and established SHB
as one of the major suppliers of TFH devices in the OEM market.
Among the OEM suppliers of TFH devices, SHB ranks fourth, after Seagate and Read
Rite. It has an annual capacity of twelve million units which is one seventh of that of the
largest competitor in the market. However, SHB has established, starting with its first
OEM product, a reputation of high-quality products and good customer services. To
many of SHB's customers, those were the reasons that they filled SHB's production
schedule while other TFH producers suffered under-utilization of their capacities.
Another advantage of SHB is the small market presence of its internal customer. The
sister division of SHB makes drives mainly for the high end market which does not
-30-
OTHERS
6%
S
SEGATE/PCI
46%
AMC
8%
Source: TrendFOCUS, Press Releases
Figure 2-3: TFH OEM market share
overlap with the market segment of most of SHB's customers.
As the OEM business expanded and market competition intensified, several bottle-necks in
operations started to surface. Higher production cost was identified as the main problem,
and lack of economy of scale and low wafer yield were believed to be the reasons. New
product deployment has been under pressure as well, since the old deployment process
could not keep pace with shrinking product life cycles. These problems have created an
-31-
impasse within SHB, since most of them are rooted within the SHB organizational
structure which is basically a small-scale laboratory-type production facility, and none of
the symptoms can be changed easily.
-32-
2.4 CHALLENGES IN NEW PRODUCT DEPLOYMENT
To address the competitiveness of SHEB in the OEM market, the product deployment
process is critical not only because it is the means for SHEB to carry out its product
strategy, but also because the product and process designs have a great impact on future
product cost (yield) and quality. The current new product deployment process takes more
than a year from concept initiation to volume production. With product life cycle running
at one year on average, this lengthy process would render the new design obsolete before
it hit the market in volume, not to mention that the low turn-around of engineering
resources associated with the longer process retards SHB's ability to deal with a wider
product line for its expanding business. However, short deployment cycle time (time-tomarket) demands more than faster design activities. It is generally believed within SHB
that costly design iteration is one of the main reasons for the long deployment process. In
order to shorten the deployment process, the number of design iterations has to be
reduced. In other words, product and process designs have to be better matched with the
current fabrication process so that fewer efforts would be needed to fine-tune the designs.
Since more than eighty percent of product life cycle cost is determined in the new product
deployment process [The Economist 1994], it is important to take manufacturing issues
into consideration in this process. Low wafer yield, which is the number one problem in
TFH fabrication, could be traced back to the design of the products as well. Instead of
treating the yield problems as an issue that continuous process improvement has to tackle,
it is much more effective to design into the products the manufacturability of the current
-33-
process. This effort is crucial for SHB from an organizational stand-point. An entrenched
attitude of blaming wafer manufacturing engineering group for low wafer yield has
derailed the group's morale over the years. To be a successful OEM manufacturer, SHB
needs a strong manufacturing engineering group to tackle the problems associated with
increasingly complicated product designs and processes. To restore morale and improve
the technical capability of wafer engineering, it is essential to give manufacturing
engineering more sayings in the designs of product and process that will be ultimately
its responsibility to maintain.
However, both challenges demand more than just changes in product deployment
procedures. Changes in people's attitude, the organizational structure, the incentive
system, the technical capability, and the process knowledge are required to facilitate a
better deployment process. Because of the complexity involved, there is a need to better
understand the TFH product deployment process.
-34-
CHAPTER
3. TFH WAFER PRODUCT DEPLOYMENT PROCESS
3.1 OLD PRODUCT DEPLOYMENT PROCESS
The old product deployment process dates back to when SHB was just a captive supplier.
Following the work flow, the whole process was divided into several stages that linked
together sequentially (Figure 3-1). With this arrangement, the market opportunity or
customer's demand for a new product was first perceived by either the marketing group or
the application group which interacted closely with customers, each of which was assigned
to a specific application engineer at SHB. The performance requirements for the new
product were then specified by the application group and were given to the magnetic
modeling group. Magnetic modeling was an essential step in linking performance
requirements to dimensional requirements that designers needed in order to carry out
structural design. The physical and structural designs of the TFH and wafer layout were
done by the design engineer group which also worked closely with the CAD engineers to
finalize the details of photolithography masks that were used in the manufacturing
process. Generally, each new product design was assigned to one designer and he was
expected to work together with process designers (or engineers) to devise the
manufacturing process for the new TFH design. In practice, it was hard to draw a line
between the work of design engineers and process engineers since many design engineers
had expertise in both product and process and would engage heavily in process design
work as well. Since both design and process engineers reported to the same manager,
-35-
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the intermingling of these two functions did not cause any organizational problem. There
was a validation procedure after the process design was completed to prove the feasibility
of the process before it was given to manufacturing engineering. This procedure called for
a small sample production of the new product and was generally carried out by technicians
who worked for process designers. After the process was proved workable, a design
review meeting was held by product designers, process designers, and manufacturing
engineers. It was generally accepted that the responsibility of the design group ended after
designs, both product and process, were handed over to manufacturing engineering. From
there on, manufacturing engineers took over and were responsible to ramp up the
production and take ownership of the process in volume production. The production
group, led by a wafer fabrication production manager, was responsible for wafer
throughput. There was also an advanced research group which was given the charter to
do longer-term TFH technology development. The advanced research group engaged in a
new product deployment process by bringing in new product design concepts, such as the
B-type TFH design. This functionally organized process worked well for SHB when the
product life-cycle was long, the product line was small, and the emphasis of the new
product was head performance. During the period of being a captive supplier, SHB had
successfully provided its internal customers with high-performance heads since the
division of labor rendered head designers, through collaboration with the advanced
research group, able to push head performance to the limits of technology.
-37-
Because head performance was the top priority of the business, the product design group
was given more attention from top management than other groups in the deployment
process. The consequence of this imbalance was an organizational culture that regarded
head design as the leading activity in SHB, and other functions, such as manufacturing, as
just an implementation of product design. To a very large degree, the emphasis on design
activity reflected on the career paths of many design engineers. Most of the head
designers started with manufacturing when they joined SHB. After demonstrating their
capabilities in mastering the technology over the years, they were promoted to process or
product design positions which kept them away from the "mundane" manufacturing
activity. Their background in manufacturing did provide an advantage to SHB in the early
days. In the development of the first OEM product, the intimate understanding of process
and manufacturing played a critical role in bringing out the product in a very short period
of time with a small group of people. The down-side of this organizational mentality was
the deterioration of manufacturing engineering capability. Since most engineers have
shied away from making a career out of manufacturing, SHB has not established the
strong manufacturing engineering organization that is critical to the success of its OEM
venture.
-38-
3.2 REORGANIZATION
The problems did not surface until SHB engaged itself in the OEM market where
customers' demands varied and costs became critical. Furthermore, the product life cycle
had continued shrinking over the years as a result of technological advancement and
demands for higher storage density. All these factors had direct impacts on the new
product deployment process. To meet these challenges, product designers at SHB came
up with a full line of products to satisfy different customers, pushed product technology
further to its limit, and rushed new product design in a shorter period of time. However,
the consequences of these changes created tremendous difficulties in wafer manufacturing
operations.
To stay competitive in the OEM market, SHB had to increase the efficiency of
manufacturing and reduce production costs. Wafer throughput and wafer yield, as a
result, became the focal points of top management. It was believed by management that
the way to increase throughput was to push more wafers through the production line.
However, as throughput increased, wafer yield started to suffer. Management reacted to
this situation by putt:ng more pressure on wafer engineering. Without looking at the yield
problem from a system point of view, manufacturing engineers started to pull more
resources into fighting frequent wafer yield problems (fire-fighting). The results were
disappointing since many problems recurred. Since manufacturing engineering had been
short on technical expertise compared to other engineering groups, its inability to improve
wafer yield was regarded as the source of the yield problem by the rest of SHB.
-39-
At the same time, as a stream of new TFH designs poured into wafer fabrication facility
(wafer fab.), the first-time-yield started to decrease as manufacturing problems grew.
Manufacturing engineering, under pressure to push capacity and improve wafer yield of
volume products, had few resources to spare for new product and process refinement. As
a result, the number of design iterations as well as the time-span for each iteration
increased. Gradually, the deadline for new product introduction began to slip while the
competition and price pressure of the market intensified.
The problems in product deployment and low wafer yield finally deteriorated to the point
that the customer base of SHB started to erode. As a result, top management decided a
reorganization of engineering groups was necessary to address these problems. Starting in
the fourth month of this research, news on organizational change started to spread around
SHB without any detailed information. Rumors proliferated about the final structure and
who the new managers would be. Some design engineers got so excited about the rumor
of engineering groups' consolidation that they expressed strong objection to management
in fear that they might be asked to work on manufacturing assignments as well as shift
work in the future. Despite the anxiety in the engineering groups, the final organizational
structure and new managers' assignments were not settled until one and half months later.
-40-
3.3 NEW PRODUCT DEPLOYMENT PROCESS
The new engineering organization is made up of two groups: the product and process
groups. By putting magnetic modeling, advanced research, and design engineering under
the control of one product group manager, top management believed that the productspecified resources could be better coordinated. Based on this same philosophy, the
process design group and the manufacturing engineering group were combined to form
the new process group. It was perceived by management that the fusion of process design
engineering resources with manufacturing engineering could greatly improve the technical
capability of the manufacturing function. The product group is now headed by a senior
design engineer in the belief that his intimate knowledge of design activities can forge
better collaboration among different designers. The process group, on the other hand,
falls under the responsibility of the previous manufacturing engineering manager.
Besides the functional structure of this new organization, a product team approach (Figure
3-2) was adopted in the hope of improving new product deployment process. All
engineering resources of these two groups are divided into four permanent product teams
that each support one product platform. The office area is divided into several clusters
with members of each product team located close to one other. Within the cluster of
cubicles that the product team occupies, there is a meeting area dedicated for team
activities. Both managers agreed in the beginning that one design engineer within each
team would be assigned as the team leader and be responsible for the performance of the
team. However, they did not reach an agreement on the charter of the product teams.
-41-
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The product group manager believed the teams were basically design (both product and
process designs) units since they were led by design engineers and were organized by the
product platforms. On the other hand, the process group manager wanted the teams'
charter to cover process maintenance (production support) as well. Without a consensus,
the part of teams' responsibility on process maintenance has not been clearly defined. As
a result, the team leaders have been reluctant to take on initiative to tackle wafer yield
problems. In response to this situation, the process group manager started to pull process
and manufacturing engineers out of product teams to do fire-fighting. This measure
strained the dynamics of the teams as team leaders found they did not have control over
the team resources. To some team leaders, this was enough reason to fall back to old
functional practices.
The first new product deployment initiative after the reorganization was the B product.
Led by one senior design engineer, the B team did a wonderful job in planning and
executing each stage of the deployment process. The decisive factor for the success,
based on feedback from team members, was the leadership and process knowledge of its
team leader. With his expertise in both product and process, he brought many
manufacturability issues into the design process. The final result pleased management and
was regarded as the model for the product team approach. Even then, however, the team
leader commented during the final design review that there were still three things that did
not go well. One was the slow decision-making process, which caused delays in making
design changes. The second was insufficient supports from wafer manufacturing. Too
-43-
many fire-fighting activities pulled engineering resources from concentrating on the pilot
runs. Finally, even with the photolithography knowledge of all team members, including
the leader himself photo process problems still occurred during pilot production and
resulted in a couple of design iterations.
The C product initiative, however, provided a different example of the product team
dynamics. Proceeding parallel to B initiative after the reorganization, the C project was
known within SHB as the next generation product after B. As a result, resource allocation
for the C project fell behind activities that were perceived to be of higher priority, such as
fire-fighting and the B project. Without being able to motivate and coordinate his team
members to advance the design process as he desired, the team leader of C complained
that the product team activities were not on the top of the priority list of his team
members. Another disadvantage for the C team was that its team leader did not possess as
great a depth of process and manufacturing expertise as the leader of the B team. Under
these two constraints, this team leader started to retrench to his old practices-ffmishing
designs himself and giving them to the process group. Though the project was not
finished at the end of this research, the initial feedback on design was not favorable. The
process group manager believed little consideration had been given to the
manufacturability issues and he expected several design iterations would be necessary to
work out the bugs.
-44-
3.4 CURRENT ISSUES IN PRODUCT DESIGN
The most pressing issue in the new product design process is the need to shorten design
cycle time. The most recent B design took close to a year to finish, and the current C
design has already taken more than a year before samples have been sent to the customers.
With a one-year product life cycle in the market, it is difficult to maintain a leadership
position with a design cycle time of more than a year. Many design engineers attributed
the long cycle time to the inability of the management to make prompt decisions as well as
the lack of supports from manufacturing engineering (resulting in delays in pilot runs and
excessive design iterations). Under the current organizational structure, design engineers
will take the initiative to try various design features to ensure the performance
requirements of the product being met. Frequently, design changes have been required to
achieve that goal. Design changes have also been necessary to accommodate new
performance requirements initiated by market dynamics or customers' demands. In either
case, management has to approve such changes, and this process takes time. Design
engineers also complain about the lack of engineering support in the pilot runs of new
designs. The pilot runs of a new design are important because they provide information
regarding manufacturing difficulties and final product performance. Several pilot runs are
generally required to fine-tune the designs. Since new designs in SHB generally call for
different manufacturing steps than those of existing products, it is desirable to have
manufacturing engineering nurture the wafers of the pilot runs through the fabrication
process. However, the fire-fighting activities in wafer fab. absorb much of the engineering
resources, and to manufacturing engineering, they take first priority.
-45-
The second issue is new process technology. Until recently, SHB has been regarded in the
TFH industry as a leader in bringing new product designs to the market. Currently,
several new designs on the market brought out by competitors are fabricated with new
process technologies of which SHB has no prior experiences. With the manufacturing
engineering (and the new process group) fully occupied with fire-fighting activities and not
being able to exploit new process technologies, design engineers feel they are restricted
with fewer design options. They believe under the current situation, it is hard for SHB to
supply comparable products to its customers in a timely manner.
-46-
3.5 CURRENT ISSUES IN NEW DESIGN MANUFACTURING
For the manufacturing engineering, which is plagued with insufficient engineering
resources to support production, multiple design iterations are something they need least.
The manufacturing engineering manager believes excessive design iterations are a sign of
the lack of discipline on the part of the design engineers. He pointed out several new
product design cases where the same manufacturing problems reoccurred. It seemed to
him that little attention was given by designers to incorporate organizational knowledge,
especially the knowledge related to the manufacturability of new designs. The
consequence, he argued, was a waste of time and resources as well as potential yield
problems if the design became a volume product.
The latter concern is the biggest problem the wafer manufacturing engineering has to deal
with every day. The pressures to solve reoccurring wafer yield upsets and demands for
ever higher wafer yields exhaust all engineering resources and hinder the development of
new process capability. The common view shared by manufacturing engineers is that all
the fire-fighting work they have done has just been a Band-Aid measure which has little
chance of solving the underlying problems.
Another issue at the top of wafer manufacturing engineering's list is operator errors. The
general perception among engineers is that lack of discipline and training in production
personnel has been among the top three reasons for wafer scrap. Many procedures were
installed with the intention of preventing mistakes and problems in the manufacturing
-47-
process. It was only found later, in many cases, that the problems occurred because the
proper procedures were not followed. With no control over operators, manufacturing
engineers believe the only option they have is to install more safe-guard procedures to
counteract the situation.
-48-
3.6 CURRENT ISSUES IN VOLUME PRODUCTION
Complaints from manufacturing engineering about the lack of discipline and training of the
operators has caused the production group to feel frustrated. Having been given the
charter to increase the throughput of the wafer fab., they feel powerless with regard to the
low wafer yield problem Since most production employees do not have much technical
background, the fabrication process is always regarded as being the responsibility of
manufacturing engineering. With incidents of wafer yield upsets increasing, the
production group manager claims there is insufficient engineering support for production
activities. He believe the problems generally take too long to solve and that the
throughputs suffer accordingly. Product proliferation is another problem since the
chances for operator errors increase as new production procedures multiply. Many errors
occur because of unclear instructions or inadequate coordination between manufacturing
engineers and production supervisors. In short, the production manager believes that
manufacturing engineering owns the process and should be available whenever there is a
problem and should solve the problem promptly.
-49-
3.7 THE SCOPE OF THIS RESEARCH
A system dynamics view of all issues mentioned above is provided in Figure 3-3. This is a
reinforced loop which means the situation would only get worse by itself. External factors
such as inadequate technical resources in manufacturing engineering, little attention to
manufacturability in designs, long decision-making process, lack of technical capability in
operators, and lack of discipline fuel the reinforced loop. It is apparent that this is a very
complicated system and no simple answer can be given to solve all the problems. Some
ideas, however, can be inferred from the theory of system dynamics to tackle this system
[Hinds 1994]. The most effective way to stop this vicious cycle is to break the cycle apart
and to prevent the loop from reinforcing itself again. One way to do that is to adopt a
conservative product strategy, give manufacturing engineering and production some extra
breathing space while improving technical capability and designing new products with
manufacturability. Another alternative is to increase the manufacturing engineering
resources or squeeze current resources with more capacity to effectively break the rightside loop. To achieve long-term success, this approach must be accompanied by measures
to improve the technical capability of engineers, the process capability, and the process
technologies.
Taking into account the six-months limitation of LFM internship, it was decided to focus
this research on a certain part of the system, described in Figure 3-3. At that time, the
process group manager (former manufacturing engineering manager) argued that the lack
-50-
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of manufacturability in product designs was the major reason for excessive design
iterations and low wafer yields. He believed there was an imperative need for a structured
tool to deliver the information of manufacturability to the design engineers to assist them
in designing new products with manufacturing issues in mind. The design engineers
welcomed this suggestion because additional information about manufacturability could be
very helpful in design activities.
The only controversy was the format of this information system (tool). An initial proposal
of a design-rule type of information system was opposed by many design engineers as the
name seemed to suggest posing constraints on design options. In the end, it was decided
that the project would investigate the manufacturability information for photolithography
process as well as a proper format to present the information to address the excess design
iteration and low wafer yields issues.
-52-
PART IITECHNICAL ISSUES
CHAPTER
4. MANUFACTURABILITY ISSUES OF TFII WAFER
MANUFACTURING
4.1 WAFER MANUFACTURING PROCESS
The current multilayered TFH was first proposed by Lazzari and his coworkers in 1970
[Ciureanu 1990]. Its structure consists of the thin ferromagnetic poles (NiFe), the
dielectric insulation (hard-baked photoresist), and the conducting coil (copper) layers
(Figure 4-1). TFH manufacturing process starts with a three-inch (in diameter) wafer and
builds on it layers of device features with vacuum, photolithography, and plating
processes.
The manufacturing process of all layers of the TFH wafer basically starts with a
photoresist patterning process to transfer device features from the photo masks to the
photoresist patterns on the wafer. The patterning process of the TFH wafer fabrication is
carried out through a process that is similar to that used in the semiconductor industry.
Coated wafers are first transferred to a pr-bake oven to dry out the photoresist (get rid of
solvent) before they are processed in the aligners. The aligners are optical exposure
machines that shine ultraviolet light-UV (or high UV-through photo masks to expose
the photoresist. Because there can be only one focal plane for every exposure, the best
condition for patterning is when the photoresist surface is flat and every point on the wafer
-53-
el
can be brought into focus. Finally, exposed wafers are transferred to developers where
exposed photoresist is washed out to develop specific patterns on the wafers. Different
aligners are used in different steps of wafer processing depending on machine capacity and
the precision requirements of the specific pattern developed. A vacuum deposition step is
required for a pole or coil layer before the patterning process is started. The thin layer of
metal deposited under the photoresist patterns serves as the base where plating process
can be started. After the patterns are established, the plating process for poles or coil can
then be carried out.
In addition to serving as a patterning material for other process steps, photoresist is also
used as a building material for the TFH devices. The bulk part of a TFH device stack is a
sandwich structure of photoresist and copper coils. To incorporate photoresist into the
permanent structure of the TFH, the photoresist must have a solid characteristic that can
withstand high temperatures generated during the read/write process [Monson 1984]. In
order to transform photoresist into a solid material, all of its solvent has to be dried out
and its polymer molecules cross-linked. Photoresist hard bake is designed for these
purposes. Wafers that go through the patterning process are moved into a hard bake oven
where the temperature goes through a preset warm-up scheme to dry out solvent and
induce cross-linkage reaction to solidify the photoresist.
The overall process starts with the pole 1 layer plus a thin deposition layer. This is
followed by a series of repetitive steps to build a sandwich structure of the insulation and
-55-
the coil layers. Finally, the pole 2 layer is built on top of the final insulation layer. Wiring
studs are then plated before a protective encapsulation layer is deposited.
The finished wafers are then electrically tested and transferred to the slider department
which is under the slider group. In the slider operation, each wafer is cut down to the size
of individual TFH and each TFH is polished to meet specific requirements. The TFHs are
then moved to the assembly and testing area. All TFHs are then examined for their critical
dimensions and flying characteristics before they are mounted on to the actuator arms to
form head gimbal assemblies (HGAs) which are the final products SHB sell to its
customers.
-56-
4.2 PHOTORESIST COATING
The topography of the TFH device poses a unique challenge to the photoresist coating
process of wafer fabrication. The traditional spin-on process is designed for coating a flat
surface where the centrifugal force (as a result of wafer spinning), the viscous force of
photoresist, the surface tension of photoresist [Peurrung 1993] and the affinity force
between photoresist and wafer surface reach a balance and a photoresist coating with
uniform thickness is formed. For the TFH wafer, the device topography has a height
differential (between the top of stack, and the base) of up to 30 microns (Figure 4-2),
which is much larger than the photoresist coating thickness itself (three microns). During
the spin-on process, the photoresist flowing over the wafer surface under the influence of
centrifugal force, accumulates in the front side of the device stack (lumping effect) and on
the back side of the device stack (snow fence effect). Since devices on wafers (all pointed
to the same direction) have different orientations relative to the photoresist flow (radiated
out from the center of the wafer), the degree of photoresist accumulation due to both
effects will vary depending on the device position on a wafer (Figure 4-3). Furthermore,
the coating thickness around the stack shoulder tends to be thinner as centrifugal force
reduces the amount of coating in that area because of the orientation of the device surface
versus photoresist flow. All these factors make a uniform coating thickness, the premise
for the current patterning (pattern transferring) technique, impossible in TFH wafer
manufacturing.
Besides, from a processing standpoint, different process steps in wafer fabrication
-57-
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-59-
emphasize different coating characteristics. For patterns used in the plating process, a
uniform coating thickness (conformal coating) is desired since it provides good
dimensional definition and renders easier control of exposure energy in the patterning
steps. In contrast, for patterns used in the insulation and the coil layer processes, planar
coating (flat over the whole wafer) would be desired since it provides a flatter surface on
the stack top. However, a planar coating creates tremendous difficulties for patterning
because the photoresist thickness would vary drastically over the wafer surface and
different exposure energies would be required to pattern a single layer. For this reason,
planar coating is not used in the TFH process. This dilemma illustrates the fundamental
difficulty in the photolithography process of TFH manufacturing--dealing with
topography with a flat surface coating technique.
Several process parameters can be used to fine-tune the coating characteristics of
photoresist. The coating process is divided into two steps. In the first step, photoresist is
dispensed on the wafer and then the wafer is spun at low speed to let photoresist spread
over the entire wafer. The next step is to speed up the spinning and get rid of excess
photoresist on the wafer. Generally, in semiconductor processing, it is the final spin speed
that determines the coating thickness [Meyerhofer 1978]. However, since the TFH
process requires a much thicker coating (3 microns versus 1 micron or less in
semiconductor processing), it is not enough to rely solely on the high-speed spinning to
produce the desired thickness. Instead, the low-speed spinning is much more emphasized
in TFH fabrication. One technique is to spin the wafer at much lower speed for a longer
-60-
period of time in step one. The reason for this technique is to start the drying process of
photoresist before the second step where excess photoresist is spun out. With photoresist
in higher viscosity (drying out), the final coating can be thicker.
One hypothesis argues that the same approach can produce conformal coating as well.
The reasoning behind this theory is that the drying process in step one would create a layer
of"photoresist crust" which constitutes the main part of the final coating. Since the
drying process proceeds uniformly across the wafer, it is expected that the crust should be
of uniform thickness and therefore so should the final coating. Although this coating
scheme is widely used in SHB,there is little coating thickness data available to verify this
hypothesis.
Coating with Topography
As discussed above, manufacturability issues in the coating process include photoresist
lumping in front of and behind the device stack, thinning around the stack shoulder, and
non-flat coating on top of the stack. Each issue has a number of design attributes
associated with it. Lumping of photoresist is the result of the existence of photoresist flow
obstacles-the device stack. Parameters related to the stack shape, such as the ramp
angle (the larger the angle, the more likely the lumping), the stack shape (stacks with
shapes that block more photoresist flow will cause more lumping), and the number of
layers (the higher the stack and the higher number of layers, the more likely the lumping)
will have a direct impact on the accumulation of photoresist. Device orientation relative
-61-
to photoresist flow is another factor that could impact on the amount of accumulation.
Finally, throat height (the distance between the tip of pole 2 and the ramp) is a factor that
can affect the degree of impact from photoresist lumping on the most critical area of the
TFH device--the pole tip. Larger throat heights keep the pole tip away from areas where
photoresist accumulates and is desired to prevent excessive photoresist from affecting the
dimensional control of the pole tip.
Photoresist Thinning around the Stack Shoulder
The thinning effect around the stack shoulder, as explained before, has a lot to do with the
shoulder's surface orientation with photoresist flow. Factors that affect the shape of the
stack shoulder, such as the shoulder curvature (degree ofphotoresist reflow), the
feathering scheme (layer terracing), the number of layers, and the ramp angle for fourthlayer definition (the fourth layer defines shoulder as well as ramp angle) are the design
attributes that can impact the degree of thinning.
Non-Uniform Photoresist Coating on the Stack Top
As mentioned above, it is difficult to achieve a uniform and flat photoresist coverage on
the top of the stack where successive coil and insulation layers build up because of huge
height differentials between device features on the wafer. The number of layers and the
degree ofphotoresist reflow (explained in the photoresist patterning section, page 65) can
influence the flatness of the stack top, and as a result, the uniformity ofphotoresist as well.
Another important factor here is the size of the stack area. With larger stack sizes, the top
-62-
surfaces are generally flatter than stacks with smaller areas. The shape of a stack can also
be affected by misalignment of the insulation layer. In other words, stacks with successive
insulation layers out of alignment would be less likely to provide a flat surface and a
uniform photoresist coverage.
Edge Bead
Photoresist has a tendency to accumulate around the rim of wafers (the edge bead effect)
during the spin-on coating process; this effectively renders the devices on the edge of the
wafer useless by reducing the size of active array. Designs with active array (the array
that defines the devices for final TFH products) that extends closer to the edge of the
wafer would have lower device yield as a result. Because of this reason, smaller arrays are
desired from a manufacturability stand-point. There is, however, another way to reclaim
as many good devices as possible from a processed wafer. Taking advantage of the fact
that most process variations of wafer fabrication are distributed radially from the center of
the wafer, designs with active areas that can reclaim devices on the lateral sides of the
arrays would produce more devices per wafer without any change in the fabrication
process.
Coil Coverage
After each coil layer is plated and the remaining seed removed, insulation layers are laid
down on top of the coil layer to form a protection for the coil and a base for successive
processing. In some cases, the insulation layers do not provide full coil coverage and
-63-
circuit shortages occur. To improve the robustness of insulation coverage for the coil,
two factors should be analyzed. First is the coil height. Even though the coil heights of
current designs have never been increased to a degree where photoresist coating could not
cover under normal coating conditions, areas around the rim of the stack top can have
exposed coil from time to time because of the coating thinner effect mentioned earlier.
Designs with lower coil height would have less chance of having the coil exposed.
Another related factor is the over-exposure budget for via blasting. In order to clear all
residual photoresist in via, an extra exposure step, via blasting, is taken. Depending on the
design of the process, sometimes via blasting not only clears residual photoresist but also
damages the insulation layer. To prevent via blasting from attacking the insulation layer,
extra mask bias-the over-exposure budget-is added to the blasting mask. From a
manufacturability standpoint, it is desired to have a larger budget to ensure the integrity of
the insulation layer.
Coating for Pole 2 Plating
Since pole 2 extends from pole tip to via, the photoresist pattern for pole 2 plating must
cover the low point as well as the high point on the wafer. Areas with thin photoresist
coating, such as the stack shoulder, present a serious challenge for achieving adequate
coating thickness for plating purposes. To make this photoresist coating process more
robust, a smaller pole 2 height is an advantage for manufacturing.
-64-
4.3 PHOTORESIST PATTERNING
The first issue in the patterning process stems from the fact that the top surface of each
individual TFH device stack is not flat. Because each insulation layer (photoresist
coating) that makes up the stack has gone through a hard-bake process during which
photoresist reflow takes place, the device stack has a natural tendency to form a round
shoulder. With a non-flat stack top, succeeding layers (such as the coil layer) that lie on
top of it will experience UV light intensity variation during the patterning process (Figure
4-4). As a result, under-exposure or over-exposure can occur and feature dimension can
vary. Variable mask bias (different portions of the coil have different mask biases) has
been used to counteract this problem. The center part of the device feature generally has a
larger mask bias so that higher dosages of UV light can be used to ensure proper exposure
at the rim of the stack top where sagging surfaces cause UV light to lose focus.
However, as mentioned in the last section, due to the differences in the orientation relative
to photoresist flow in the coating process (the coating for the insulation layer), the coating
thickness of devices varies for each layer. Manifesting this effect through multi-layers, the
shape of the stack is different from one to the other. Using the same mechanism
mentioned previously, random variation in stack shapes makes focusing UV light on every
point of the device features on top of the stack impossible. This variation in stack shape
introduces a process variation affecting successive patterning steps that even variable
mask bias cannot abate.
-65-
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The second problem in the patterning process involves the topography of the wafer. Since
the height differential between stack top and wafer base can be as large as 20 to 30
microns, it is impossible to bring into focus both the top and the base. As a consequence,
the feature dimension changes with altitude. The situation is especially difficult in the pole
2 alignment process during which patterns on the stack top and wafer base have to be
established with a single exposure. To alleviate the extent of this problem, the focal plane
(every point on the plane is of equal distance to the UV light source) for pole 2 alignment
is usually set at the middle level. Variable mask bias technique is applied, as well, to
compensate for the remaining out-of-focus effect. However, as stated before, the stack
shape difference between devices causes additional dimensional variation that is hard to
control.
Patterning with a Non-flat Stack Top
To deal with the problem of a non-flat stack top, several design parameters can be
adjusted to make the patterning process more robust. The size of the device stack (the
larger the stack, the flatter the stack top will be), the degree of reflow (a lower degree of
reflow retains the flatness of the stack top), sensible alignment target (reducing the chance
of misalignment, less chance for rough stack top), and the number of layers (the lower the
stack, the more likely to have a flat stack) are parameters that should be considered to
improve manufacturability.
-67-
Patterning with Topography
Since this problem originated with the height differential of device features, the most
effective way to make the patterning process easier is to reduce the stack height. Since
the number of layers is the biggest factor in determining stack height, it is desirable from a
manufacturing standpoint to have fewer layers in the design.
-68-
4.4 PHOTORESIST HARD-BAKE
One undesirable side effect of the hard-bake process is photoresist reflow. As the
temperature ofphotoresist increases inside the hard-bake oven, it first rises to a flowing
temperature at which photoresist starts to reform itself under the influence of surface
tension and gravity. As its temperature exceeds the glass transition temperature, a crosslinking reaction takes place and the photoresist structure solidifies. The result of
photoresist reflow between these two temperatures is the rounding of the device stack. A
round stack creates problems for successive layer processing since it is more difficult to
bring a non-flat surface into focus, as discussed in last section.
There are two different hard-bake processes: one with oxygen and one without. During
an oxygen bake, the oven chamber is pressurized with an atmosphere consisting of a
gaseous mixture of a specific oxygen and nitrogen composition. With the presence of
oxygen, it is believed that the cross-linking reaction takes place at a lower temperature and
therefore has the effect of reducing the degree of reflow, since the time span for
photoresist to reform itself is reduced. As a result, the device stack experiences less
rounding effect. In contrast, in a regular bake (without oxygen) where nitrogen fills the
oven, reflow occurs to its full extent and rounder stacks are produced.
Variation of Stack Height and Stack Flatness
Since photoresist reflow alters the shape of the device stack, factors affecting the
photoresist flow characteristic during that temperature window (between flowing
-69-
temperature and glass transition temperature), such as photoresist coating thickness,
ambient temperature distribution in the hard-bake oven, and the relative position of the
device on the wafer, can have impacts on final stack shape as well. Since these factors can
vary from device to device, they introduce additional variation of stack shape (height and
flatness) and the range of variation is proportional to the degree of the photoresist reflow.
Residual P2 Seed in Via
Products that do not have the pole 2 covering the whole via are subject to a problem
called residual P2 seed. The seed layer is laid down as the base for pole 2 plating and
should be removed after pole 2 patterning to avoid circuit shortage or signal noise.
However, the effectiveness of the process employed to remove P2 seed-ion beam
etching-is hindered by the shadowing effect (Figure 4-5). Device stacks with a higher
degree of reflow have less chance to form shadows for ion beam etching and are less likely
to have residual P2 seed. Another factor that can impact residual P2 seed is the feathering
ion beam
I
I
ion beam
I
via area
(photoresist)
area
shadow (unetched P2 seed)
insulation (photoresist)
Higher Degree of Reflow
Lower Degree of Reflow
Figure 4-5: Shadowing effect
-70-
scheme of insulation layers (Figure 4-6). Stacks with less feathering can form larger
shadows in via during ion beam etching and are likely to have residual P2 seed.
ion beam
ion beam
via area
(photoresist)
via area
(unetched P2 seed)
insulation (photoresist)
(photoresist)
insulation (photoresist)
shadow
(unetched P2 seed)
Less Feathering
More Feathering
Figure 4-6: Impact of feathering scheme on shadowing effect
Ramp Angle Control
The ramp angle of pole 2 is determined by the structure of the insulation layer underneath,
and the structure of the insulation layer is determined by the degree of photoresist reflow
in the hard-bake process. A flatter ramp angle requires a higher degree ofreflow, and all
factors mentioned previously that could affect reflow would also have their impacts on the
final ramp angle and the range of its variation. As a result, products with lower angles can
have a larger range of ramp angle variation. In addition, the layer of insulation upon
which pole 2 is built can also affect ramp angle. As each layer of processing introduces
additional structural variation to the device, the insulation layer built at the early stage of
the fabrication process (first layer, for example) has a smaller range of variation between
devices. Products with pole 2 built on these insulation layers, as a consequence, have
better ramp angle control.
-71-
4.5 REGISTRATION
Registration is the alignment of device features over different layers of processing. Since
the device features are transferred from photo masks to wafers through UV light
exposure, registration is established through the alignment between photo masks and the
targeted wafer. To facilitate this alignment process before UV light exposure, "crosses"
are built on the wafer. By optically lining special windows on masks with these crosses,
alignment of the pattern with the device features on the wafer can be ensured. Currently,
alignments of less critical layers (features with less stringent alignment and dimension
specifications) are done manually, while critical layers are aligned automatically (steppers).
Both processes are subject to alignment errors. Errors of manual alignment stem from
individuals' judgment on the lining of mask windows and wafer targets. Misalignments on
steppers, however, are generally caused by undetectable wafer crosses. Residual
photoresist of early process steps could accidentally cover wafer alignment crosses and
prevent laser scanners on steppers from accurately locating the targets. To account for
process-related misalignments, a registration budget is usually established in the design of
products. Devices with a certain registration budget can tolerate feature misalignment
within budget withoat compromising the device's functional performance.
Layer to Layer Registration
Because registration is established through the alignment, measures that improve the
alignment process are desired from a registration point of view. Easily detectable wafer
targets, such as targets that have more distinguishable boundaries (for manual alignment)
-72-
or that can be identified even with residual photoresist (for automatic alignment) would
greatly enhance the efficiency of the alignment process. Larger registration budgets,
which place extra constraints on product designers, could render a more robust alignment
operation since device tolerance for misalignment increases.
Throat Height and Ramp Angle Control
For first-layer ramp angle definition (the ramp angle built on the first layer of insulation),
better alignment means better throat height (determined by the registration between pole 2
and first insulation layer patterning) control. On the other hand, ramp angles of products
with fourth-layer definition (the ramp angle built on the fourth layer of insulation) are
greatly affected by the registration of insulation layers. As each subsequent insulation
layer is built on top of the previous layer, misalignment of any layer will have its impact on
the final stack shape, and as a result, the ramp angle. Because the extra chance of ramp
angle variation, first-layer definition is more desirable for ramp angle control.
-73-
4.6 PHOTORESIST NOTCHING
Notching is the undesirable exposure of photoresist due to reflection of UV light over a
reflective surface during photoresist patterning. The most likely reflective surface is the
seed layer. As a result, notching usually happens in pole 2 patterning where the seed layer
under photoresist is reflective and curved.
Pole 2 Photoresist Notching
There are two kinds of notching in the pole 2 patterning process. One involves notching
in the pole yoke area, and the other involves notching on top of the via. The pole yoke is
the place where yoke width suddenly narrows down. Since the pole yoke is located on
top of the ramp, UV light that hits the cleared photoresist area would be reflected by the
underlying seed layer at an angle to the adjacent photoresist (Figure 4-7). To reduce the
extent of this reflection, design parameters such as yoke neck height (the distance from
pole tip to yoke neck) and the widening angle of the pole yoke can be adjusted. Larger
yoke neck height means the yoke neck is higher up the ramp where the geometry is
generally flatter. A flatter surface reduces the degree of reflection to adjacent photoresist.
Another advantage of larger yoke neck height is that a greater distance between pole yoke
and pole tip reduces the impact of notching as it moves away from the most critical area
for head performance. A smaller pole yoke widening angle can also help since reflective
light has less chance to hit directly on the photoresist pattern.
-74-
TOP VIEWI
LUV LIGHT
1TF'TChTINTAT
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Figure 4-7: Notching mechanism
The via notching occurs for products that do not have pole 2 covering the whole via. The
photoresist pattern that defines pole 2 in via would be subjected to reflection by the
underlying seed layer inside the via, and therefore notching occurs. The situation is worse
around the top of the via where reflection from one side of the via shoulder hits
photoresist of the other side of the via shoulder. Certain new designs have reduced the
degree of via notching by minimizing the area of pole 2 inside the via to reduce reflective
surface. Another effective way of eliminating via notching is to cover the whole via area
with pole 2, and therefore no photoresist pattern is necessary inside the via. Both
approaches have proven to be effective and should be employed whenever possible.
-75-
4.7 CRITICAL DIMENSION CONTROL
Pole Tip Width Control
A device feature with stringent dimensional specifications is called critical dimension
(CD). Widths and thicknesses of both poles (at pole tip) fall into this category because of
their close relationship with head performance. In most cases, dimensions of pole 2 are
where efforts are concentrated since they are smaller (critical in terms of performance
constraints) and are made at a later stage of wafer manufacturing (accumulated variations
from prior process steps). Pole 2 widths are defined by photoresist patterns, so they are
subjected to variations related to photoresist coating and patterning processes. One of
these variations is created by the photoresist lumping in front of the ramp as discussed in
the coating section. To reduce the effect of this, one can increase throat height and move
the pole tip away from the photoresist lumping area. An additional complication related to
width control is the measurement scheme. Every wafer is checked either before
(photoresist pattern dimension) or after (plated pole width) plating to prevent out of
specification wafers from further processing. These checks are done automatically
through a machine by sampling pre-specified devices on a wafer and optically measuring
their dimensions. As TFH design pushes for smaller poles, pole width has shrunk to a
degree where the current machine has difficulty in providing accurate measurement. New
equipment is under investigation to solve this problem while design engineers explore
designs with even narrower pole widths.
-76-
Pole Tip Thickness Control
The thicknesses of pole 2 are established during the plating process. In the plating
process, the amount of plated material is controlled through control of plating. In other
words, such a plating control scheme ensures a constant amount of material being plated
on every wafer. For this reason, final pole thickness becomes a function of pole width.
Factors affecting pole width can influence final pole thickness through the current plating
procedure.
-77-
-78-
CHAPTER
5. DESIGN FOR MANUFACTURING
5.1 DESIGN-PUSH VERSUS DESIGN FOR MANUFACTURING
With the demand from the disk drive industry to increase storage density at a rate between
35 to 60 percent per year, there is a constant pressure on the TFH designers to push the
limits of the technology envelope. That means that the designers must push the state of
the art while they learn how to use the new technology. Since new product technology
generally require different processing procedures, manufacturing engineering has to
advance along the new process learning curve quickly to deliver the products. Design
iterations could become necessary for both design and manufacturing engineers to search
for the best product-process combination. As a result, the new product deployment
process moves toward the direction of design-push [Costlow 1994] instead of design-formanufacturing (DFM). It is undesirable from a manufacturing standpoint to have new
product features on the TFH device with little knowledge about their associated
implications for the manufacturing process. However, with market demands and
competition pushing in the direction of improving head performance, SHB must balance
its design and manufacturing to maintain a competitive line of products and low
production costs (higher wafer yield).
In order to bring issues of manufacturing into the design process earlier to prevent costly
design iterations, many companies have implemented DFM methods. Early efforts in the
area of DFM concentrated on the method of design rules and later, on the method of
-79-
"rules of thumb" [Whitney 1988]. Both methods have been widely used in a variety of
industries. Design rules express the boundaries within which the manufacturing process
operates in terms of the issues confronting product designers [Wheelwright 1992]. The
idea behind design rules is to establish a boundary within which the manufacturing process
is capable of meeting design requirements. However, in a dynamic market such as the
TFH industry, companies employing such an approach may miss crucial opportunities to
change the manufacturing process in order to enhance the performance of the
manufacturing system to produce competitive products.
-80-
5.2
CURRENT MISMATCH BETWEEN PRODUCT DESIGN AND
MANUFACTURING PROCESS CAPABILITY
In addition to the excessive design iterations, low wafer yield is another issue that is
closely related to product designs and manufacturing activities. The chronic low wafer
yield problem SHB is suffering is a result of the mismatch between product designs and
manufacturing process capability (Figure 5-1). In other words, the low wafer yield
problem is a direct result of an imperfect product deployment process. There is
information available from several benchmark studies indicating that several of SHB's
TFH designs demand higher sophistication in the manufacturing process than do designs
of products of similar performance from the competitors. At the same time, information
about production cost and manufacturing technology reveals that the wafer manufacturing
process of SHEB is not as efficient as that of some competitors and is incapable of
producing current SHB designs with a comparable wafer yield. If the status of the designmanufacturing system is used as a benchmark, this information seems to suggest there is a
gap between the designs and the current process capability, and the size of the gap can be
an indication of the degree of yield loss. The gap is a result of the lack of communication,
the lack of collaboration, and the over-the-wall syndrome that is typical in a functional
organization. Apparently, the easiest way to reduce the gap, and improve wafer yield, is
to move product designs and manufacturing process capability closer to each other (Figure
5-2). However, moving designs and process to match each other requires comprehensive
knowledge of the interactions between these two activities. It is also necessary to install a
-81-
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of engineers in order to match both together more effectively.
-84-
5.3 INTEGRATION OF DESIGN AND MANUFACTURING
Recognizing the ineffectiveness of the design rules approach in coping with fast changing
technology and market dynamics, recent researches of DFM have pointed to an
interactive, integrative design process in which product and process engineers create a
joint product-process design [Wheelwright 1992]. In such a setting, product design
choices comprehend key process restraints, but the process itself may also changethrough process development and investment--to enhance capability and provide what the
emerging design requires. A summary of the desired interactions between the design and
manufacturing activities is provided in Figure 5-3. Such an approach tackles not only the
excessive design iteration issue (by designing in the manufacturabiltiy of the design
attributes) but also the wafer yields issue (by designing in the capability of the process)
discussed in the previous section. The integration mentioned above suggests a new set of
activities and interactions, a new way to frame and solve problems. Several structured
tools have been proposed to integrate detailed product and process design with
manufacturing, such as house of producibility [Wheelwright 1992] and lifetime cost
analysis [Ulrich 1991]. A structured tool creates a common framework and language. If
properly executed, it could reveal important tradeoffs and conflicts early and thus save
valuable time and resources. The structured tools also make holes in the organization's
knowledge about critical relationships apparent and provide a basis for capturing and
using knowledge important in making choices about design.
-85-
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Because of the reasons mentioned in the last two sections and the benefits associated with
the integration of design and manufacturing, the goal of this research gradually evolved
from developing a design-rule type of information database to a manufacturabilityknowledge oriented information system-the manufacturability guidelines. Accordingly,
the scope of this research was expanded from delivering information of the process
constraints to the design engineers to integrating the design and the manufacturing
activities through the manufacturability guidelines.
-87-
-88-
CHAPTER
6. MANUFACTURABILITY GUIDELINES
6.1 A KNOWLEDGE ISSUE
Since one of the goals of integrating design and manufacturing is to match the product
design with the manufacturing process, it is clear that one piece of information that the
manufacturability guidelines have to provide is where the current process capability lies.
On the other hand, from a competitiveness standpoint, the manufacturability guidelines
have to take into account the dynamics between manufacturing process capability and
product performance requirement; the content of these guidelines will have to be able to
facilitate compromises as well as to stimulate creativity to exploit the technology envelope
of both disciplines. In short, manufacturability guidelines must serve as a knowledge tool
to reveal the connections between design attributes and manufacturing issues as well as a
communication tool to enhance information exchanges.
As a matter of fact, these two pieces of information are closely related to each other. A
fair assessment of the current process capability will not be possible until the knowledge
linking design and manufacturing is established. Due to the intertwining nature of the
interactions between different processing steps, the process capability cannot be judged
from the capability of individual steps. For example, the control of the critical dimensions
has more to do with the photoresist coating thickness than the capability of the aligner
which patterns the dimensions. For years, design engineers at SHB have argued that if
manufacturing engineering could provide them with information about process capability,
-89-
they would incorporate the constraints of the manufacturing process into product designs
more readily. However, the problem is that the knowledge does not exist.
Organizational barriers confine efforts within each group to serve its best interest-to
focus all intelligence within the group on the deliverables. For designers, the tangible
results are product designs, while for manufacturing engineering, it is higher wafer yields.
Operating with the perception that the goal of manufacturing is to strive for higher wafer
yields, knowing how far the manufacturing process can be pushed to support new designs
has not been much of an issue. Under this kind of organizational structure, there is little
incentive for individuals to cross over the organizational barriers and to understand
various activities and the relationships between them. Knowledge gaps are formed and
further propagate as each group stretches for higher efficiency. With that knowledge gap
unfilled, frustration pervades because incremental efforts from each individual group do
not bring lasting results.
If the manufacturability guidelines are to achieve the goals of this research outlined in
Chapter 2, they have to incorporate information on the process capability and the
relationships between design and manufacturing. They also have to be formatted as a tool
for engineers of both product and process groups in order to encourage collaboration. In
other words, the manufacturability guidelines have to be compiled as a knowledge-based
information system incorporating a model of interaction of both product and process
groups. To put matters into proper perspective, this chapter will concentrate on the
development of manufacturability guidelines, while in the next chapter the model for
-90-
interaction will be proposed and managerial measures needed to facilitate the kind of
collaboration the model suggests will be discussed.
-91-
6.2 THE PROCESS OF DERIVING MANUFACTURABILITY GUIDELINES
6.2.1 Process Characterization
To construct a knowledge-based information system, it is necessary to amass the
knowledge involved. Since manufacturability is the main issue in the guidelines, the
process group naturally becomes the first source for information. A process
characterization was carried out first among several manufacturing engineers to identify
critical issues in wafer manufacturing. The whole photolithography operations in the
wafer fabrication were divided into consecutive steps and all steps were categorized into
four basic steps with a process block diagram drawn for each of them (Appendix A). The
idea was to study the input and output attributes of each process step and to have the
cause-and-effect relationship between the input and output attributes investigated. It was
found that there is little knowledge within manufacturing engineering to link these
attributes to product designs. As a result, a different approach was devised to derive the
guidelines from basic photolithography operations. However, it turned out that the
knowledge gained through this process characterization had laid the foundation for the
fault tree analysis that will be discussed next.
6.2.2 Fault Tree Analysis
The final manufacturability guidelines include four parts: the fault tree analysis, the critical
design parameters, the critical design parameter database, and the manufacturability
guidelines. Each part is listed in the Appendix and will be discussed separately. The fault
-92-
tree analysis (FTA) has been widely used in product design team activity (PDT) as a tool
to induce the root causes of problems and has been proved to be highly productive in
leading to the optimization of robust functionality. It provides a visual and connective
method to bring out and integrate team members' collective experiences [Clausing 1994].
The idea of employing FTA stemmed from the understanding that it is the device features,
and so the design of TFH, that introduce the non-ideal conditions for the photolithography
operations. Most photolithography operations in TFH wafer fabrication are borrowed or
derived from the semiconductor manufacturing process. Those technologies were
originally designed for processing flat wafers where device topography was not an issue.
However, as TFH designs strove for miniaturization and pushed for higher sensitivity
(more coils, and higher stack as a result), the height differential became so huge that the
technologies were stretched to the limits and variations from ambient factors multiplied.
With this perspective, FTA could be used to derive critical design parameters from current
manufacturing difficulties. Current manufacturing difficulties were summed up by several
manufacturing engineers during the exercise of process characterization (the previous
section) and were translated into the non-ideal conditions for the photo process. Related
non-idea conditions were then grouped together under different basic photo operations.
FTA was then applied to the non-ideal conditions to find out the photo issues involved in
every non-ideal condition. Further induction brought causes (or physical phenomena) for
each photo issue and the design parameters associated with each cause (Figure 6-1 and
Figure 6-2). Along with the induction of the design parameters, the cause-and-effect
relationships between the design parameters and non-ideal conditions were established
-93-
Fault Tree Analysis
PHOTO OPERATION KNOWLEDGE,
MANUFACTURING DIFFICULTIES
Non-Ideal ConditionsInduced by Wafer
Features
Photo Issues Related to the Non-Ideal
Conditions
Causes for These Photo Issues
Wafer Design Parameters Associating
with These Causes or Photo Issues
4
CriticalDesign Parameters,
Interactionsbetween Design Parameters
& Manufacturability
Figure 6-1: Fault tree analysis
-94-
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This piece of information turned out to be very important for the manufacturability
guidelines.
The results from this FTA are listed in Appendix B. Before taking on the effort, I decided
to broaden the knowledge base to incorporate several design engineers as well. In the
process of the fault tree analysis, it was recognized by the people involved that most parts
of the induction were based on individuals' inference of their knowledge about wafer
manufacturing process rather than solid evidence or experimental results. This deficiency
was a direct result of the lack of such information in the organization. It was expected
that there would be controversies over certain parts of this analysis. Arguments arose
even between the engineers involved in the FTA process. However, to gain precise
knowledge of these manufacturing issues means extensive research in current
manufacturing process and it is prohibitive expensive for SHB to embark on such an
effort. Clausing argued that it is important to make disciplined decisions based on the
existing understanding of nature [Clausing 1994]. In a highly competitive market,
designers have to make design decisions based on current available information to catch
the market opportunity window. The manufacturability guidelines, through its knowledge
structure which is based on physical phenomena of the manufacturing process, link design
parameters with manufacturing issues. Although the knowledge involved is not
thoroughly verified, the guidelines provide likely directions for design engineers to make
design trade-off decisions based on existing understanding of the manufacturing process.
-96-
6.2.3 Critical Design Parameters
The design parameters derived from the FTA were then compiled to form a critical design
parameter list. The list was constructed with the intent to single out these parameters
among other design parameters. It gave design engineers a first glance impression of
which parts of product design could impact manufacturability. The complete list of critical
design parameters is provided in Appendix C.
6.2.4 Critical Design Parameter Database
One consensus among those people who were involved in this research was the need for a
baseline of the current manufacturing process. However, without information regarding
process capability in terms of critical design parameters, the process baseline could not be
established. The closest available information, without embarking on massive design
experiments, was product design specifications for active products (Appendix D). People
who use this database as the baseline for the current process have to be cautious about
two things. First, the specifications do not equal the process capabilities. As stated
before, wafer engineering does have problems in maintaining wafer yield at the targeted
level. In other words, for those products having recurring wafer yield problems, the
product specifications are tighter than what the current process can provide. Second,
while the specifications could be viewed as the upper bound of process capability, the
database provides no information as to which critical design parameters are on the
technology envelope (the limiting parameters under current process capability).
-97-
6.2.5 Manufacturability Guidelines
On the premise that one of the main user groups of this knowledge system will be the
product designers, it is necessary to reassemble the information into a format that could
readily help design activities. Since the designers are basically dealing with various design
parameters, it makes sense to re-sort all the information based on the critical design
parameters. The results from FTA were then recompiled with each critical design
parameter listed along with the non-ideal conditions associated with it (Appendix E).
Knowledge of the cause-and-effect relationships between each parameter and non-ideal
conditions was sorted into two categories. The two categories stand for two directions
toward which the value of this critical design parameter can move. Under each category
the associated benefits in manufacturability (reduction of non-ideal conditions) are listed.
For example, under the 4th design parameter-reflow scheme--there are two categories
listed. Under the "more reflow" category, the two listed statements, less PR thinning in
ramp shoulder and less residual P2 seed on B product, indicate that higher degree of
reflow will improve the situations of should PR thinning and residual P2 seed. Similarly,
less degree of reflow will produce flatter stack coating, better stack patterning, better
reflow control, and better ramp angle control as listed under the category of'less reflow".
This setup was devised for the convenience of the designers since parameters with only
one category filled require no need for trade-off in design from a manufacturing
standpoint. Those with both categories filled would call for special attention when
changes in design are required.
-98-
PART III MANAGERIAL ISSUES
CHAPTER
7. APPLICATIONS OF THE MANUFACTURABILITY
GUIDELINE
7.1 A TOOL FOR DESIGN REVIEW
7.1.1 Design Review
One immediate application of the manufacturability guidelines is to use them as a checklist
for the design review mentioned in Chapter 2. The purpose of the design review is to
evaluate candidate designs (of product and process) simultaneously from multiple
viewpoints [Ishii 1988]. The design review of SHB takes place in a format of a "round
table" meeting between design engineers, process engineers, and manufacturing engineers
(including photo, plating, and vacuum engineers). Each participant presents his view of
the compatibility between the candidate design and his field of expertise. Suggestions for
modifications of the candidate design or re-specifications of the fabrication process are
made by the participants based on their understanding of the design and their knowledge
of the manufacturing process. I attended two design review meetings during the period of
this study. A typical setup of the review meeting is depicted in Figure 7-1. With copies of
the description of the new fabrication process distributed, the meeting proceeded as the
product designer went over the manufacturing process of the new design step-by-step and
asked for questions and input. The atmosphere was casual and the manufacturing
-99-
Mc
Figure 7-1: A design review meeting
engineers occasionally gave input based on their reactions to the particular step or
operation under discussion. The discussion was dominated by the product designer and
the manufacturing engineer of a specific field (plating, vacuum, or photo) since each step
of the process was generally considered the jurisdiction of the engineer of that particular
field. In another words, there was little group-work involved in the design review
process. The CAD engineer, who sat in front of a workstation terminal, brought up the
mask drawing (a two dimensional CAD drawing) whenever there was a photolithography
operation invoh .... There were a few times when concerns about the manufacturability of
a particular step were raised; compromises were then made between the product designer
and the manufacturing engineers on the spot with the aid of the CAD engineer to change
the mask drawing. However, most conversations were clarifications of the details of the
fabrication process. There were no questions asked specifically about the reasons behind
-100-
the designs. An atmosphere of compliance prevailed. The need for affiliation and the
desire to avoid confrontation as suggested by Morley [Hosking 1991], prevent participants
from challenging the design. One interesting observation of the meeting was that the CAD
engineer seemed to be more knowledgeable about the manufacturability of the photo mask
designs than the photo engineer. Being the only CAD engineer at SHB, he was involved
with every mask design in the manufacturing of TFH and as a result learned a great deal
about the manufacturability of mask designs. Few photo engineers have as broad a
knowledge about different mask designs because there is no system to record the
knowledge gained by an individual engineer for later dissemination to the rest of the
group.
7.1.2 A Tool for Design Review
Although the design review meeting provides a forum for interaction between design and
manufacturing engineers before the new design is handed over to the manufacturing group
(the process group in the new organization), the lack of a systematic approach for
examining the designs impairs the function of the meeting for investigating the
manufacturability issues of the new designs. Certain areas of weakness can be
summarized to illustrate the inefficiency of the design review process:
1. There is no vigilant information system to remind engineers of possible
manufacturability issues.
2. An information system for relating manufacturability issues between different
process steps does not exist.
-101-
3. Manufacturability knowledge is based on the production results of previous
designs instead of on an understanding of the process capability.
4. There is no tool or record for disseminating the manufacturabiltiy knowledge.
Each of these areas of weakness will be addressed in the following paragraphs and a
model for the use of the manufacturability guidelines in the design review will be
proposed.
1.
Vigilant information system
The manufacturability issues of TFH wafer fabrication are very complicated (as shown in
Appendix A). The manufacturability guideline's system listed in Appendix E exemplifies
the large number of design parameters and compromises involved. A manufacturing
engineer would have difficulty remembering all this information and applying them in
evaluating a new product design. Without a structured problem-solving tool, it is difficult
for any person to have an adequate understanding of the complexity involved. According
to research done by Keigler [Keigler 1994], dealing with complex systems without a
vigilant information system could disinterest behavior through a mechanism which is
described in Figure 7-2. The manufacturability guidelines listed in Appendix E can be
used as a vigilant information system not only because of the broad manufacturability
knowledge they contain, but also because of the format which allows them to be readily
used in a design review setting. Since all manufacturability knowledge is categorized
according to critical design parameters, the impacts and trade-offs of those design
parameters can be studied in the design review meeting.
-102-
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2.
Manufacturability issues between different process steps
The most difficult aspect of studying the manufacturability issues of the TFH fabrication
process is the intertwining nature of different process steps. Because the TFH has a
layered structure, the device feature functionality depends on how well the underlying
layers are built as well as how well the geometrical dimensions of the underlying layers fit
with each other. As a consequence, small imperfections of the lower layers could result in
large physical or functional variations at the higher layers. For this reason, it is important
to examine the designs of each device layer with a device structure perspective, instead of
focusing only on the operation used to build a particular layer. The cause-and-effect
relationships between different layers are also complicated, and it is impossible for an
engineer to remember them all. The manufacturability guideline system developed in this
research can be used as a vigilant information system to reveal the linkages among the
effects of different fabrication steps. This is because the system was established through a
fault tree analysis which exhausted all the factors that contributed to each specific nonideal process condition. The manufacturing engineers can start with a specific operation
difficulty (non-ideal condition) and trace back those factors of the different process steps
involved (information in the fault tree analysis). Alternatively, they can look at a specific
critical design parameter and find out which non-ideal conditions (process difficulties)
could be affected by changing the value of this parameter (manufacturability guidelines).
3.
Manufacturability knowledge
Because of the intertwining nature of the operations of different process steps, it is
-104-
dangerous to attach a manufacturability issue solely to one apparent design parameter
without a full understanding of the mechanism that creates the problem inthe first place.
For example, it is widely accepted that the mask bias (to counteract the non-ideal
condition of patterning with topography) of each coil layer should depend upon which
layer the coil is built. However, a simple check of the fault tree analysis (listed in
Appendix B) reveals that there are six design parameters involved in this non-ideal
condition-patterning with topography. A simple reflow scheme change or a design with
different rail size (stack size) could easily change the patterning characteristics for which
simple adjustments based on the number of the coil layer just would not compensate. For
this reason, it is better to hand over the responsibility ofjudging the manufacturability of a
new design to manufacturing engineers who understand the mechanisms behind process
difficulties to provide them with the manufacturability guidelines system as a tool for
facilitating the design review process.
4.
Dissemination of manufacturability knowledge
The manufacturability knowledge should be disseminated to the whole engineering
organization to enhance organizational learning. The knowledge and information of the
manufacturability guidelines bring up engineers' awareness over the manufacturability
issues. An individual engineer exposed to this guidelines can be motivated to validate the
knowledge or be inspired to prove otherwise. Either way, adopting the framework of the
manufacturability guidelines can align the efforts of the individual engineer toward the
goal of reducing design iterations and increasing wafer yield. The structured knowledge
-105-
will also induce dialogues and discussions that are essential to the advancement of process
technologies [Senge 1990]. A good example of the manufacturability guidelines in
bringing engineer's attention on manufacturability issues is the "snow-fence effect." The
photoresist lumping effect was initially perceived as a result of resist flowing against the
device ramp. This piece of information, cited in the manufacturability guidelines, caught
the attention of the design engineer for the C product. As a consequence, he made an
extra effort to verify the existence of this effect on the new C wafer (product with the
highest stack height, presumably having the most severe lumping effect). To people's
surprise, the results showed the photoresist was actually lumping on the back side of the
stack, as snow accumulates at the back side of the fence. It is a good lesson for the
management about the momentum that can be generated when the proper framework is
installed and intellectual challenges are directed to achieve the goals of the organization.
Finally, the manufacturability guidelines contain structured manufacturability knowledge
and can be readily used as a tool to disseminate the knowledge in the organization.
7.1.3 A Model
A model of the usage of the manufacturability guidelines can be outlined to remedy the
four areas of weakness just mentioned above. The guidelines can be used as a vigilant
information system by the participants in a design review meeting. As they go over each
step of the fabrication process the guidelines will remind them about the possible
manufacturability issues and the relationships between the operations of different
processing steps. Used as an information system, it carries the manufacturing knowledge
-106-
that is based on completed understanding of the fabrication process and as a result, can be
used as a communication tool to inspire dialogues and discussions between engineers.
One drawback of the design review meeting is that the inputs come after the designs are
done. It generally takes more to change the designs after they are done, plus it could
invoke a defensive attitude among product designers in a design review meeting. A much
better arrangement would be to use the manufacturability guidelines to solicit inputs
before the design process takes place. Generally, several critical design parameters (such
as the number of layers) are set during the product concept phase so their impacts on
current fabrication process can be evaluated before the design activity starts. A pre-design
meeting can be institutionalized to assemble the design, process, and manufacturing
engineers in discussing the manufacturability and product performance issues. The
manufacturability guidelines can be used in this meeting to solicit inputs and opinions
related to the new product concept. Feedback collected in this pre-design meeting can
guide design engineers through their work in avoiding manufacturing difficulties that they
be forced to deal with later.
One main benefit of the design review meeting is that it provides a platform where
collectively interactions among all engineers involved can take place. To induce the
interactions, group-work skills are as important as cross-functional knowledge.
Participants of the meeting need to know how to ask questions and how to engage a
discussion constructively to do brain-storming. They also have to have an attitude of
-107-
focusing on issues, instead of relating issues to individuals. However, people who used to
work under a functional organization have a tendency to confine individual efforts to a
specific area and attribute the result of those efforts to the person in charge. The
management has to recognize the difficulties involved for people to change from a
functional mode to a group-work mode. One way to facilitate the change is providing
training and consulting resources. These experts can train people and serve as groupwork facilitators to monitor the progress. Having those experts in place send a strong
message of management's commitment to change and make global changes easier to
install.
-108-
7.2 CONCURRENT ENGINEERING
As mentioned in the last section, adopting the knowledge framework of the
manufacturability guidelines would promote awareness of the manufacturability issues
among engineers. As a result, it would redirect the engineering focus from fire-fighting
the symptoms to studying the manufacturability of the process. Indeed, a major advantage
of the manufacturability knowledge system developed in Chapter 5 is that it was derived
from the non-ideal conditions of the basic process operations. Starting from the root
causes of the manufacturing problems, the guidelines give manufacturing engineers a new
framework and dimension to think about the cause-and-effect relationships of process
problems. Looking at the problems from a manufacturability point of view, enables
engineers to install more robust solutions to prevent problems from reoccurring. It would
create the awareness that the wafer yields are designed, not fabricated, into the products.
This awareness would encourage interactions among design, process, and manufacturing
engineers.
After the manufacturability guidelines were developed, it was found that the
manufacturability issues of the wafer fabrication process were modularized around the
critical design parameter involved in the fourth part of the manufacturability guidelines
system---the manufacturability guidelines (Appendix E). Since assigning proper values to
all design parameters constitutes the main tasks of TFH design, a design-parameterspecific manufacturability knowledge system, such as the manufacturability guidelines,
-109-
provides the manufacturing engineers with the ability to investigate the impacts of new
product design before the design is completed.
Both the old and new product deployment processes described in Chapter 2 are divided
into several distinct process blocks because the traditional thinking about the deployment
process is that the task defined in each block is independent and that it takes the
completed results from the previous block to start the work for the next block. The
manufacturability guidelines change both of these perceptions. First, since the
manufacturability issues can be traced back to certain design parameters, the
manufacturing and process development are not independent from other steps of the
deployment process where the design parameters are set. The moment a specific design
parameter is decided, its impacts on manufacturing are set and the impacts can be
deciphered through the applications of the manufacturability guidelines. In other words,
the tasks within different blocks of deployment process can be closely related.
Second, because the issues of manufacturability are modularized according to specific
critical design parameters, potential difficulties in the fabrication process can be identified
once the parameter is decided. Efforts to design a robust process or other manufacturing
measures to counteract the processing difficulties can be started before the whole design
is completed. The most significant example of this early warning effect of future
fabrication problems is the issues related to "the number of layers". This design parameter
is set in the very first phase of the product deployment process. It is the main part of
-110-
product concept. According to the guidelines listed in Appendix E, there are six
manufacturability issues linked directly to this parameter. That means the process and
manufacturing engineers can expect that certain process changes or process innovations
are needed in the early phase of this deployment process. Development of techniques in
overcoming the potential problems in the coating and patterning (focusing in specific)
process can be started much earlier than that of the current practices.
Concurrent Engineering Models
Both implications of the manufacturability guidelines suggest the direction of concurrent
engineering [Clausing 1994]. The guidelines serve to enhance knowledge and information
flow, a concept similar to the technology stream that Clausing proposed (Figure 7-3). All
participants in the new product deployment process--application group, marketing group,
magnetic group, product group, process group, and production group--can use the
guidelines to communicate manufacturability information. Since the basic knowledge
framework developed by the guidelines is accepted by everybody involved, confusions and
misunderstandings can be reduced. For example, while the number of layers requirement
is perceived by the application group in the product concept phase, specific issues in
coating and patterning operations cited in the guidelines can be communicated to other
groups for inputs. Guided by the manufacturability guidelines, people of other functions,
such as product, process, and production groups, will know exactly what the implications
are with the specific value of the number of layers. By focusing on manufacturability
issues, the application of the guidelines ensure the awareness of manufacturability
-111-
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Figure 7-3: Concurrent process
issues among members of the deployment process and provide a vehicle for delivering the
knowledge to the early phase of deployment where the root cause of the manufacturing
difficulties originated.
Beyond serving as a common language and communication tool for information
concurrence, the modularized characteristics of the manufacturability guidelines provide
the linkages between different activities in the product deployment process. With the
linkages well documented and understood by the members involved, deployment work at
different steps can proceed in a parallel manner. The overlapping of different deployment
steps can be illustrated by the integrated problem-solving model of Wheelwright and Clark
-112-
[Wheelwright 1992]. The model they proposed is presented in Figure 7-4. Through
intensive communication, information of product design is shared by design, process, and
manufacturing engineers. Although the product design activities are always ahead of the
process development and manufacturing problem-solving, different tasks in the
deployment process can proceed with some degree of parallelism. This overlapping of
various deployment activities reduces deployment cycle time and shortens time-to-market.
A more detailed discussion about concurrent engineering is provided in Chapter 8.
-113-
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CHAPTER
8. IMPLEMENTATION OF MANUFACTURABILITY
GUIDELINES APPLICATIONS
8.1 RESISTANCE OVER IMPLEMENTATION
8.1.1 The Resistance
The first test of the manufacturability guidelines was to introduce them to the design
engineers as a design review tool. The intent was to illustrate the benefits of the
guidelines and to rally the designers' support for this application. Since the goal of the
design review tool is to bring manufacturability issues to design process, the support from
design engineers is critical to the success of the guidelines. Early responses from design
engineers were very favorable. They viewed the manufacturability guidelines as an
interesting tool for their design work. Because the guidelines incorporated the knowledge
of senior designers, design engineers with less knowledge were excited about the
information in the guidelines. The first sign of resistance came when I wrote a report
commenting on a new C design with the help of the manufacturability guidelines. The
designer for the C product strongly rejected the idea of distributing the report for
demonstration (a design review tool) purpose. He argued that those comments in the
report could be used by somebody in the organization to question the quality of his work.
A couple of days later, this design engineer set up a meeting with the process and
manufacturing engineers on the C product team to evaluate the manufacturability
guidelines. The group came to the conclusion that the information in the guidelines was
invalid for there was no data to support most of the guidelines. He argued that the
-115-
information incorporated in the guidelines came from a limited number of engineers. As a
result, the guidelines were not objective enough to serve as a judgment tool despite my
explanation that this report was used as a demonstration of an application of the
guidelines, not as a performance matrix. His fear of exposing his work under the focus of
the guidelines was so entrenched that the suggestion of incorporating his counterpoints in
this report was not accepted either.
8.1.2 The Hypothesis
This incident raised the question about the degree of resistance over the idea of a design
review tool. My company supervisor and I started to recognize that there was structural
resistance in the organization that was incompatible with the application of the
manufacturability guidelines. I then proposed a hypothesis for the resistance based on my
experience of working with the design engineers. The hypothesis argued the knowledgesharing nature of the manufacturability guidelines was not compatible with the established
design practices, which define the design as an individual's project.
The product design (physical and structural designs) activity is generally regarded as the
domain of the designer in charge. It is '"hisjob" to complete the design within a prespecified time span. Though the designer takes responsibility for the final result of the
design, the functional disjoints between various activities of the deployment process render
him significant freedoms to make design trade-off decisions without disclosing the reasons
behind them. Since the designer will be judged by the final result of the new design, he
-116-
has every reason to keep the design trade-off information to himself to avoid exposure to
criticism. This is a comfort zone the designers enjoy even in the new engineering
organization described in Chapter 2. The product team arrangement does bring process
and manufacturing engineers into the design process. However, without knowledge of
how the product design affects TFH performance, few process or manufacturing engineers
are able to challenge the design effectively.
The manufacturability guidelines change the dynamics of the design process. With
manufacturability issues listed and organized by the design parameters involved, the
guidelines become a questionnaire that design engineers have to answer. Not only does
the design engineer have to defend his design decisions but also he has to put them on the
record for later verification (after the pilot production run). It is a new rule of the game
and is potentially threatening to design engineers since the quality of the design is their
responsibility.
8.1.3 The Survey
To better understand the resistance from design engineers, I conducted a survey asking
design engineers the following four questions:
* What is the advantage or disadvantage, in your opinion, of a design process
done by an individual designer over a process done by a work group?
-117-
* In your opinion, is there any benefit to having several engineers review a new
design with a structured checklist or a set of guidelines, such as the
manufacturability guidelines?
* Do you think the wafer designers should feel comfortable about sharing with
other engineers the trade-off decisions they make inthe design?
* In your opinion, why hasn't SHB used a structured design review tool similar
to the manufacturability guidelines before?
The survey was carried out after my introduction of the manufacturability guidelines to the
engineering groups. Taking advantage of the fresh memory of my interviewees, I was
hoping that the survey could elicit opinions based on what the guidelines really are.
Results were positive. All participants concurred on the potential of the guidelines, with
some concerns expressed over the difficulties of implementation. The results from this
survey are summarized below.
All engineers, except one expressed their support for a work group type of design process,
although some engineers expressed concern over the implementation of the process in the
current organizational structure. The engineer with the different opinion believed it would
be time consuming and ineffective to have design decisions made among multiple
engineers.
"The management has to buy in first, otherwise it will never work." '"his
organization is composed of groups with different responsibilities, different boxes,
everyone tries to do his best, but the communication between the boxes is a
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problem. People of different boxes do not understand issues of other boxes.
Working together requires mutual understanding. ...we need education and
training..." "...the current performance measurement is still not in line with
encouraging people to broaden up their skills..." " ...the design activity is evolving
toward more of an individual's work because the technology has become more
complex so that one person can understand only his area of expertise..." "Ido
believe the virtue of having the design done by an individual designer. With a wide
distribution of the degree of understanding about product design issues among
engineers, there is no way to do the design work with consensus."
Everyone agreed with the idea of having somebody else review the design with a
structured checklist. Several engineers questioned, however, how valid is the information
in the guidelines to judge the quality of a design.
"I like the idea of the manufacturability guidelines. But the best way to do it is to
use the guidelines in soliciting input in the early phase of design activity as well as
to use it in reviewing the final design." "I have no problem having somebody else
review my designs as long as he is non-biased and knows what he is talking
about." 'The problem is different design engineers have different opinions on how
to do designs. It is hard to say who is right and who is wrong."
-119-
Again, every engineer believed that the trade-off decisions should be shared by other
engineers, but many engineers believed there would be resistance in implementation due to
the political situation of the organization.
"I agree that the trade-off information should be revealed to the organization. ...I
do not want to be the first to do that. There could be some people who would
want to use this information against me." 'The information is an asset. People like
to keep it to themselves. That keeps them in a status of being the experts."
There were a variety of opinions about why SHB has not used a structured design review
tool until now.
'We haven't have such a tool before, ...we are so busy doing our jobs that nobody
has time to work on developing it..." "I guess there is an ego issue in preventing us
from adopting a design review tool. ...the design work is still a domain of the
individual designer..." "I have my own set of design rules. It has served me well in
the past. ...I would not want to fall into a position where I have to defend those
rules. Everybody can have their own opinions."
8.1.4 The Conclusion
According to the results of this survey, the design engineers do perceive the value of
adopting a structured design review tool. However, they are concerned because of the
uncertainty of changes. Certain arrangements, such as using the guidelines to solicit input
at the beginning of the design process, can smooth the impact of the changes since the
-120-
design is still the domain of a design engineer. However, the key nature of the
manufacturability guidelines is information sharing. The guidelines need an environment in
which people believe in the value of organizational learning and share a mutual trust
among the members. Only in such an environment can the guidelines be maintained to
serve their purpose-disseminating the knowledge. Because this environment is much
different from the current engineering organization, changes in people's mentalities and
behaviors are necessary if the guidelines are to be used properly. Nevertheless, the design
engineers do not know how the changes will affect them. Nobody wants to be the first to
try the new practice, especially when the performance matrix is still in favor of individual
excellence. That was the reason the C designer discredited the information contained in
the guidelines as being non-verified. He thought there were two options for him. He
could argue that the comments in my report were based on invalid information; or he
could admit he did not consider manufacturability issues in his design, which was not to
his favor under current organizational structure. Apparently, the management has to take
the leadership to facilitate these changes. Without a strong commitment from the
management and a supporting structure (performance measurement system, incentive
system, etc.) in place, it is difficult to ask designers to commit to the changes that are
necessary for the success of the design review process.
-121-
8.2 ORGANIZATION DYNAMICS
The management is in a key position to institutionalize the manufacturability guidelines as
a tool to bring manufacturability concerns to the design process. Beyond being committed
to the guidelines and being the leader in their implementation, the management has to
resolve the inertia of the organization against changes. Among the obstacles that need to
be removed in order to apply the guidelines, the issue of engineering resource allocation is
the most critical one. Since the new approach emphasizes the early involvement of
manufacturing engineers in the design process, they will have to spend more time working
with designers instead of solving process problems. Although improvements in product
designs will reduce the needs for engineering resources in fire-fighting activities, there is a
time-lag between the onset of shifting resources to design and the resulting reduction of
wafer yield problems. The main reason for this time lag is the learning curve effect for
both design and manufacturing engineers. They need to learn how to work together
effectively in integrating manufacturability with the design of products. This process takes
time. The second reason for the time lag is multiple product platforms. It takes many new
product introductions for products with manufacturability to significantly reduce the level
of fire-fighting activities in the wafer fab. As a result, this applications of
manufacturability guidelines will initially weaken the capability of wafer manufacturing
engineering in supporting production. Since SHB is currently under corporate pressure to
increase throughput, any measure that could adversely affect production activity is not
welcomed from a management point of view. As a consequence, to transform the current
product deployment process from a fire-fighting mode to a proactive design-with-
-122-
manufacturability mode, extra manufacturing engineering resources are needed in the
transition period (Figure 8-1). Without additional engineering resources, a vicious cycle
of trying to cover both areas-the design process and production--with the same amount
transition
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Figure 8-1: Shifting engineering resources to design activity
of resources will occur (Figure 8-2). If the management increases the level of involvement
of manufacturing engineers in design activities, fewer efforts will be made in process
problem solving. As a result, process upsets would last longer or there would simply be
more process problems. Either way, the revenue will decrease as the wafer yield
deteriorates. Lower revenue will induce more corporate pressure for improvement, and
the management will have to shift manufacturing engineers back to production support.
These cause-and-effect relationships are contained in the upper loop of the model. Being a
balanced loop, the system has a strong tendency to stay at current status. Changes or
disturbances will be counteracted until the original status is restored.
-123-
Lower wafer outputs
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More process problems
Lower revenues
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Figure 8-2: A system dynamic model
(The organization has to ride through the delays to bear the fruit of designs with
manufacturability)
The lower loop is the mechanism that can transform SHB to a manufacturability-focused
organization. However, one key element in this reinforced loop is the delays. Though the
design engineer admitted no difficulty of adjustment for individuals in my survey, the
process engineering manager believes they will have to learn new skills and adjust their
mentalities for working in an environment in which the design information is shared. Both
-124-
of them take time. There is also a delay before new designs take over the existing
products, so less engineering resource is tied up in the production support. As a
consequence, the organization has to ride through the delays before the lower loop takes
over and gains the benefits of design with manufacturability.
All three engineering managers-managers of the product and process groups and their
boss, the engineering manager-share the concern over the resource allocation issue
discussed above. Options such as adding new engineers and increasing the work-loads of
every engineer have been seriously considered. However, new engineers generally need
extensive training before they can contribute, which would effectively lengthen the delays
mentioned above. Loading the engineers with extra work does not work well either,
especially when they know nothing about the reason behind this measure and see no end
to the extra demands.
Steering the whole organization head-on with problems might have some risks involved,
staying at current status is not an option for SHB either. With market rapidly changing
and competitors improving their products, SHB would not be able to compete with their
current practices. Re-engineering of product deployment process is the only solution for
SHB to get out of the downward spiral of fire-fighting activities, and design with
manufacturability is the key. There is an alternative for the full scale change, however. A
pilot team model will be proposed in the next chapter. By highly leveraging the influence
-125-
of star performers, this model facilitates the changes with little disruption in the current
organization.
-126-
CHAPTER
9. PRODUCT TEAM APPROACH
9.1 PRODUCT DEPLOYMENT PROCESS INTEGRATION WITH
CONCURRENT ENGINEERING
To further accelerate the product deployment process, SHB engineering groups have to
go beyond the concurrence of design and manufacturing. The goal is real time
coordination between upstream and downstream groups so that costly mistakes can be
avoided and time-to-market reduced. The integrated problem-solving model discussed in
section 6.2 can be extended to incorporate the whole product deployment process. The
work of application, marketing, magnetic modeling, product, process, and production
groups can start with certain degree of parallelism (Figure 9-1). Downstream engineers
not only participate in a preliminary and ongoing dialogue with their upstream
counterparts, but they use that information and insight to get a flying start on their own
[Wheelwright 1992]. This changes the content of the downstream work inthe early
phases of upstream design and is also likely to change fundamentally the content of
communication between the two groups as suggested by Clausing [Clausing 1994].
Communication that is rich, bilateral, and intense is essential. This does not mean the
absence of conflict but rather the honest, open consideration of alternatives, and
resolutions based on data, analyses, and a joint creative product deployment process.
For early and frequent exchange of constraints, ideas, and objectives, the integration of
product deployment process relies on a style of problem solving that is broader and more
-127-
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comprehensive than one experiences in a traditional functional organization. To capture
the detail important for the interconnection between the upstream and downstream
groups, face-to-face discussion, direct observation, and interaction with physical
representations (physical or computer-based) are needed. The manufacturability
guidelines can be very helpful in this high band-width communication. Because of the
complex nature of the interactions among results from different deployment steps, it is
difficult for individual engineers to remember all the cause-and-effect relationships which
his part of the work affects. The guidelines can serve as a knowledge database to provide
a framework of the interactions between the results from different activities. In this
function, the manufacturability guidelines are similar to the DAISlE (Designers Aid for
Simultaneous Engineering) system developed by Liou and Miller [Liou 1991] and the
Real-Time Constraint Checking System proposed by Kameyama [Kameyama 1993].
-129-
9.2 PRODUCT DEVELOPMENT TEAM APPROACH
The concurrent engineering model mentioned above in its best form can be carried out by
a multifunctional product development team, PDT [Clausing 19941. In a situation where
the real-time combination of multiple skills, experiences, and judgments is required, a team
approach inevitably gets better results than a collection of individuals operating within
confined job roles and responsibilities. This is because traditional hierarchical and
functional mechanisms are inadequate to address the coordination needs of highly complex
organizations in a timely and cost-effective manner. Some of the most dramatic stories in
the popular press related to fast-cycle turnaround and time-based competitive advantage
have attributed success to effective team organizations and project leadership [Clark
1991]. Regarded as the best organizational format for a small group of people
undertaking a specific task, the team (or work team) organization has been studied
intensively. However, the names of work team, high power work team, or autonomous
team have become such buzz words that the names are often misused to represent groups
of people who are loosely organized. To suggest a work-team approach in the new
product deployment process, it is necessary to clarify the meaning of "team" used in this
thesis.
9.2.1 Team Definition
According to the definition given by Katzenbach & Smith [Katzenbach 1993], the team is
"a small number of people with complementary skills who are committed to a common
-130-
purpose, performance goals, and approach for which they hold themselves mutually
accountable." From this definition, clearly there are five characteristics of a real workteam organization.
* Small Number
The team has to keep the number of its members small to facilitate constructive
interaction. As the number of members increases, the logistical issues, such as
finding a large meeting room and time for everybody to meet, become difficult
to resolve. Large groups tend to settle on less clear statements of purpose that
get set by the hierarchical leaders. Larger numbers of people usually cannot
develop the common purpose, goals, approach, and mutual accountability of a
real team Katzerbach & Smith suggested that teams of less than ten members
constituted the majority of the successful stories they had studied.
* Complementary Skills
Katzerbach & Smith claimed there are three types of skills the teams must
develop-functional expertise, problem-solving and decision-making skills, and
interpersonal skills. A team cannot be started without some minimum
complement of skills, and no team can achieve its goal without developing all
the skill levels required.
* Committed to a Common Purpose and Performance Goals
-131-
A common and meaningful purpose sets the tone and aspiration of the team
The best teams invest a tremendous amount of time and effort exploring,
shaping, and agreeing on a common purpose. Specific goals provide clear and
tangible footholds for teams. They facilitate clear communication and
constructive conflict within the team, and their attainability helps teams
maintain their focus on getting results. The purpose and goals depend upon
each other to stay relevant and vital. The specific performance goals help a
team track progress and hold itself accountable; the broader aspirations in a
team's purpose supply both meaning and emotional energy.
* Committed to a Common Approach
Teams also need to develop a common approach that defines how they will
work together to accomplish their purpose. When individuals approach a team
situation in a business setting, each has pre-existing job assignments as well as
strengths and weaknesses reflecting a variety of backgrounds, talents,
personalities, and prejudices. Only through mutual discovery and
understanding of how to apply all its human resources to a common purpose
can a group really develop and agree on the best team approach to achieve its
goal.
-132-
* Mutual Accountability
No group ever becomes a team until it can hold itself accountable as a team.
Team accountability is the sincere promises the team members make to each
other, promises that underpin two critical aspects of teams: commitment and
trust. Mutual promises and accountability cannot be coerced any more than
people can be made to trust one another. Nevertheless, mutual accountability
does tend to grow as a natural counterpart to the development of team
purpose, performance goals, and approach.
Work teams can have different organizational structures. Wheelwright and Clark
described several common team structures [Wheelwright 1992]. Among them (Figure 92), the heavyweight team and the autonomous team are more in line with the work team
discussed here. The four structures provide a full spectrum of work-team setups available.
They also reveal an evolution path for transformation from a traditional functional
organization to a totally autonomous work team.
9.2.2 Product Development Team in SHB
Considering the five characteristics of teams, apparently there are huge differences
between the product teams at SHB and the true teams described above. The product
teams at SHB generally do not have a clear common purpose or common performance
goals. The story of the C product team discussed in section 2.3 exemplifies the problems.
-133-
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The purpose of the C product team-to develop the C product--was simply given by the
management. To all of its members except the team leader, the team work was just one of
their many responsibilities. Many of them perceived that their performances in the product
team were not the first priority in the mind of their superiors. Under this kind of
condition, it takes the initiative of the team leaders to set performance goals to clearly
define and monitor the teams' activities. That was the reason why the B product team
delivered better results than that of the C team The leadership of the B team leader,
through his meticulous record-keeping and incremental goal-setting, held the group
together. There is little emphasis on the common approach among the members of the
product teams. Since every team member is still attached to a functional organization and
is still under his functional supervisor's jurisdiction in terms of performance evaluation,
there is little incentive for team members to work out painstakingly the best approach for
the team to achieve its goal. As a result, the activities of the product team have never
reached a level where a thorough re-examination of the current deployment process takes
place. Basically, the team members believed the purpose of the product team approach
was to facilitate people "to do a better job," so every team went through meeting after
meeting doing the same things they did before, only faster. The accountability of product
team members is unclear. Beyond the understanding that team leaders--the design
engineer-hold the full responsibility for the design, there is no clear definition of how the
rest of the teams will be accountable for the design or to each other. As a matter of fact,
certain engineers argued that the broad statement-'"the design is the responsibility of the
whole team"--actually diffuses the accountability of the team leader.
-135-
9.2.3 The Pilot Team Approach
Judging from the current status of SHB engineering, clearly to build a true product team
organization to a scale as suggested in Figure 9-2 requires a major undertaking if not an
impractical one. However, for SHB to stay competitive in the marketplace and maintain
agility against its larger opponents, the work-team approach is necessary. SHB has to
have shorter time-to-market and higher wafer yield than those of its competitors to
establish a competitive edge. None of them can be achieved through just working harder
with current practices as discussed in Chapter 8.
A possible alternative to a full-scale product team re-engineering is the pilot-team
approach. This strategy leverages the influence of a star PDT in demonstrating the
advantage of the team approach while keeping the rest of the organization intact. The star
PDT will exchange its members with the rest of the organization to disseminate the
knowledge and experience of working in a true team environment. With little disruption
of the current organization, the dilemma mentioned in section 8.2 can be relieved. Since
there is only one team to nurture, the management can concentrate its resources to ensure
the success of the PDT.
The most critical factor in the success of the pilot-team approach is that the team has to be
a true work team and it has to be successful. Since the pilot team serves as the showcase
of the team approach, it has to be set up correctly from the beginning so that people can
have a clear idea of what the product team is. To rally future support for the PDT
-136-
approach, the management needs the success of the pilot team to convince people and top
management. Since the PDT is very different from current product team setups, the pilot
PDT will need helps from a team-building specialist to guide its members in developing a
common purpose, performance goals, a common approach, and establishing mutual
accountability. It is important that this team expert understands the organizational
dynamics (organizational politics) of current operations and be knowledgeable about the
difficulties people will experience in a change process. For this reason, the organizational
consulting group of the corporate service should be the best resource for this purpose.
The expert has to serve as an organizational consultant for cultural and behavioral
changes. With those difficulties in mind, the pilot team should adopt the heavyweight
team structure. The autonomous team, though an ultimate goal of the team approach, has
the disadvantage of little thing as given. As a result, the team members are likely to lose
focus and direction. Without discipline of looking for opportunities to utilize existed
designs, they are likely to reinvent the wheel without emphasizing that the project be
folded up on time and the manufacturability of product be properly ensured. The project
manager (team sponsor) of the heavyweight team is in a key position to ensure the success
of the team. They are "heavyweighted" in two respects [Wheelwright 1992]. First, they
are senior managers within the organization. Not only do they have expertise and
experience, they also wield significant organizational clout. Second, these leaders have
primary influence over the people working in the team. This is especially important if the
team members have secondary responsibilities in areas outside of the team's activity. In
this case, the project manager has to give these team members clear descriptions of his
-137-
expectation and the priority between different responsibilities to prevent any confusion.
With adequate resource allocation, insulation over other organizational demands, and
direct supervision, an adequate heavyweight sponsor can be critical to the success of the
pilot PDT.
Though the pilot team serves as the showcase of product team approach, there is no need
to have all star performers in the team. On the contrary, a pilot team with a group of
mixed-level performers will make its success more persuasive to the rest of the
organization. So long as the skills of the members can complement each other to perform
the work, the team dynamics will provide a setting for team and individual learning which
is another important aspect of the team dynamics.
In the process of installing PDT, the role of manufacturability guidelines can be
complementary rather than be just a subset of the PDT approach. The guidelines can
provide an initial knowledge framework for the team's common approach. It creates an
organizational awareness of the manufacturability issues and leads to a new methodology
in product deployment process. In summary, the manufacturability guidelines, concurrent
engineering, and the PDT are three tools to improve the product deployment process.
Each has its distinctive features in advancing the capability of an organization, and all
three reinforce each other. A successful company will need to master all three tools to
harness the potential of its people and their intelligence in order to establish a long-term
competitive advantage in a fast changing market.
-138-
CHAPTER
10. SUGGESTIONS FOR FUTURE STUDY
10.1 FURTHER REFINEMENT AND UPDATES OF THE
MANUFACTURABILITY GUIDELINES
To ensure that the manufacturability guidelines are used to achieve their full potential,
there has to be a system established to constantly update and refine the contents of the
guidelines. Feedback from design and manufacturing engineers indicated that the
guidelines covered most manufacturability issues and related knowledge available within
SHB. However, the guidelines are by no means a complete source of information.
Individual engineers might possess specific knowledge of a particular product that is not
known by others. It will be the whole engineering organization's benefit to have that
knowledge studied and incorporated into the guidelines.
As new product and process technologies evolve, their impact on manufacturability will
have to be studied. With an organization-wide awareness of the guidelines, more
engineers will be conscientious about manufacturability issues when they apply new
product or process technologies. Knowledge or experience gained through these new
developments should be incorporated in the guidelines in a timely manner so the same
lesson does not have to be learned again.
The most important extension of this research is a systematic study of the mechanisms
behind the cause-and-effect relationships in the guidelines. As suggested by many design
-139-
engineers, the lack of experimental data in supporting the information in the guidelines
warrants a serious study. A systematic knowledge of the reasons behind the
manufacturability issues can be an effective competitive advantage for SHB. For example,
the knowledge of the snow fence effect described in Chapter 6 led to several design
changes to reduce the variation of critical dimensions. If proved to be effective, these
changes can render SHB the capability to increase the storage density of its TFH devices
without additional investment. In a market with many larger competitors, the most
effective weapons SHB possesses are its engineers and the knowledge they amass. Using
knowledge as leverage, SHB can be flexible and effective-having superior product
performance without advanced manufacturing process or maintaining the same
performance with higher wafer yield. The key to SHB's competitive strategy is not to do
something others cannot, but to do the same thing, only better.
-140-
10.2
OTHER GUIDELINE FOR DESIGN PURPOSES
Due to the time limit, this research focused only on the manufacturability of the
photolithography process. However, wafer design requires information in other areas as
well. Concentrating only on the manufacturability issues listed in the guidelines can bias
the designer's trade-off decisions. To provide a balanced information structure to the
product deployment process, guidelines of other disciplines have to be established.
Product performance and magnetic requirements are two key design inputs. The design
engineers have to deliver a design that can satisfy both requirements. Over years of
experience, most designers have established an adequate understanding of the linkages
between design parameters and the two requirements. However, the relationships are so
complicated that some trial-and-error is still necessary in the current design process.
Guidelines that provide systematic knowledge of the cause-and-effect relationships in
these two areas will be very helpful to designers in meeting both performance and
magnetic requirements.
Manufacturability guidelines of the other parts of wafer manufacturing-plating and
vacuum-are of great importance to product design as well. Since the wafer
manufacturing process is a combination of all three operations (photo, plating, and
vacuum), a discussion of process manufacturability would not be complete without all
three operations included. It is also important to integrate all three guidelines in a single
set of manufacturability guidelines. For years, the manufacturing engineering group has
-141-
been divided into the three disciplines. However, there is no difference between an issue
of photo operation and an issue of plating operation from a process manufacturability
point of view. The design trade-off decision should be made according to the impact on
process manufacturability, regardless of the operation involved. In other words, the
process group has to establish cross-discipline knowledge to accurately assess the
manufacturability of the whole fabrication process. Only when such an integration occurs
can a complete list of process manufacturability guidelines be constructed.
-142-
10.3 ORGANIZATIONAL STUDY
The implementation phase of the manufacturability guidelines warrants additional studies.
Discussions in Chapter 7 revealed the structural resistance and difficulties involved in
organizational changes. An action plan and execution strategies for transforming the
engineering groups to a true product-team type of organization are still not available,
despite the model proposed in Chapter 8. This opportunity provides a challenging topic
for LFM research. An internship project can be set up to study the SHB engineering
organization and devise a plan for organizational re-engineering. Depending on the
amount of time and resources involved, the student can participate in the initial phase of
the changes while monitoring the dynamics of the organization. Though the main focus of
this research will be on organizational issues, the student will still have to establish a good
understanding of the technical issues in TFH design and manufacturing. I believe this
project will provide the student with good experience in planning and implementing
changes that are not adequately addressed in the current LFM curriculum. After all, no
change will ever succeed unless we know how to implement it correctly.
-143-
-144-
APPENDIX A
-145-
INPUT & OUTPUT ATTRIBUTES
OF POLE 1 PHOTO PROCESS
Coater Spread IV:
mne
d2
Coater
Spin
Spee
Photo-Speed,
Photoresist
% solid, and mole. weight
IOir-
set
Foca
Exposure Energy
(pellicle transm.)
Mask Bias
Developer Wash Tim
ýI
F
L
F
F
K
L
o Side Wall Angle
(
~~-
P1 PHOTO
PROCESS
-~
_1
CD
*- CD Ranee
Photoresist Thickness
* Photoresist Uniformity
--
o Photoresist Residue
P1 to 0 Layer Registration
MONITORINGL
1
1
--
A l
"I•
NII]
&I`
ATb 1ITnT]Xfi'NT
T
11~1~1~1
~YC·VU
-146-
INPUT & OUTPUT ATTRIBUTES
OF COIL PHOTO PROCESS
Coater Spread Time
Coater Spin Speed
Photoresist Photo-Speed,
% solid, and mole. weight
Focal Offset
Exposure Energy
Mask Bias
Developer Wash Time
Coil Shape
Overlay Tolerance
Coil Setback (front)
Water Contact-
ý
Side Wall Angle
•
Stack Height ---Shape of Stack --P1 to 0 Layer
Registration
COIL PHOTO
PROCESS
Coil to P1 Placement--*
MONITORING
ADJUSTMENT
-147-
Photoresist Thickness
" Photoresist Uniformity
-Photoresist Residue
-j
Edge Bead
-.Ream PR Residue
- *Dummy Coil
--Coil Displacement
------ Seed Oxidation
------ PR Adhesion
INPUT & OUTPUT ATTRIBUTES
OF INSULATION PHOTO PROCESS
r4c,
C
uaterI •ple•i
Ar~r
rprm__
Coater Spin
Photoresist Phc
% solid, and m
Focal Offs
Exposure Ei
Mask Bia
Developer Wa
Ramp Angle
Bake Temp. (;
Bake Tin
Bake Atmos
Magnetism of
;tack Height
Coil Shape
(through PR th
hape of Stack
Ramp Angle
Stack Heig
a Ramp Angle
Shape of St;
resist Residue
-oat)
P1 to 0 Lay
Registratiol
Throat Def.
ELG Def.
Coil Registra
(Placement)
R Curement
MONITORING
&
I
ADJUSTMEN T
-148-
INPUT & OUTPUT ATTRIBUTES
OF POLE 2 PHOTO PROCESS
Coater Spread Time Coater Spin Speed Photoresist Photo-Speed,
% solid, and mole. weight
Focal Offset
Exposure Energy
(pellicle transm.)
Mask Bias
Developer Wash Time +
|I
r
rl
r.
-
k..
-
Stack Height
Side Wall Angle
)
Shape of Stack
I ()
Via Ramp Angle
Ramp Angle
(through PR thickness)
Coil Shape
P2 PHOTO
PROCESS
I
CD
CD Range
- iVia Notching
Zero-Throat Notching
, Photoresist Thickness
O Photoresist Uniformity
- Photoresist Residue
P2 to P1
Registration
(through PR thickness)
P1 to 0 Layer
Registration
MONITORING L
E
ADJUSTMENT
-149-
-150-
APPENDIX B
-151-
SECTION 1. FAULT TREE ANALYSIS
(The analysis is presented in term of relieving the cause that related to particular photo
issue. For example, less ramp angle reduces the Snow Fence Effect and relieves the
problem of excess PR in front of ramp)
COATING (C)
=5 COATING WITH TOPOLOGY
Issues:
PR Lumping in front ofRamp
Stack Shield (Snow Fence Effect)
ramp angle
LESS
distance between pole & ramp (throat height)
MORE
stack shape
ROUND
no. of layer (thinner insulation layer)
LESS
variation of device orientation (relative to PR flow)
LESS
Stack
Shoulder
in
PR Thinning
PR flow characteristic & surface tension
MORE
shoulder curvature (reflow)
feathering scheme (terracing)
MORE
ramp angle (for 4th layer definition only)
LESS
no. of layer (thinner insulation layers)
LESS
Non-uniform coating of PR on top of Stack
Small stack area
rail size
MORE
Non-flat stack surface
reflow (original PR shape)
LESS
no. of layer (thinner insulation layer)
LESS
registration budget
LESS
detectable alignment target (easily detected sites)
BETTER
-= EDGE BEAD
Heavy coating near the edge of wafer
SMALLER active array size (keep slider away from edge)
slider bar arrangement on wafer (increase yield
BETTER
too!)
-= COIL COVERAGE
Robustness of insulation coverage
overexposure budget for via blasting
LARGE
Robustness of coatingcoveragefor coilplating
coil height
SMALL
-152-
=
COATING FOR POLE 2 PLATING
Robustness of coating coveragefor pole 2 plating
SMALL
P2 pole height
PATTERNING (P)
=- PATTERNING WITH TOPOLOGY
Issues:
Focus on non-flat stack top
MORE
rail size
LESS
reflow (original PR shape)
registration budget
LESS
BETTER
sensible alignment target (easily sensed sites)
LESS
no. of layer (thinner insulation layer)
Focal offset for topology
LESS
no. of layer (thinner insulation layer)
PR HARD BAKE (PR)
=· VARIATION OF STACK HEIGHT AND STACK FLATNESS
Issues:
Reflow process control
LESS
reflow
- RESIDUAL P2 SEED IN VIA OF B PRODUCT (AFTER SEED ETCH)
Issues:
Steep ramp angle
MORE
reflow
Lack offeathering
MORE
feathering
-= RAMP Aý IGLE CONTROL
Issues:
Ramp angle definition layer
1st layer definition
MORE
Reflow process control
LESS
reflow
REGISTRATION (R)
-= LAYER TO LAYER REGISTRATION
Issues:
Ease of manufacturing
-153-
detectable alignment target
BETTER
Robustness of alignment design
LARGE
registration budget
- RAMP ANGLE CONTROL (4TH LAYER DEFINITION ONLY)
Issues:
Ramp angle variation
MORE
1st layer definition
NOTCHING (N)
=: P2 PR NOTCHING
Issues:
PR notching on ramp (affecting P2 CD)
LARGE
P2 yoke neck height
SMALL
P2 yoke widening angle
PR notching on top of via
MORE
Pseudo-RPM or RPM design
LARGE
P2 coverage on via (covering whole via)
CD CONTROL (CD)
:= P1 & P2 WIDTH CONTROL
Issues:
PR sidewall angle control
SMALL
no. of layer
IVS measurement accuracy
LARGE
P2 width (track width defined by pole 2)
CD variation control
LARGE
P2 width variation tolerance
=: P2 THICKNESS CONTROL
Issues:
Pole 2 thickness variation control
ramp angle
SMALL
throat height
LARGE
-154-
APPENDIX C
-155-
SECTION 2. TFII CRITICAL DESIGN PARAMETERS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
ramp angle (reflow scheme, temp. & time)
throat height
stack shape
reflow scheme (reflow temp. & time)
feathering scheme (layer to layer recess)
no. of layer
layer thickness
transducer size (rail size)
registration budget
ramp angle definition layer
device orientation (standard)
detectable alignment target (standard)
active array size (standard)
slider bar arrangement on wafer (standard)
B product via feathering
P2 yoke neck height
P2 yoke widening angle
P2 coverage on via
overexposure budget for via blasting (or blast mask bias)
20.
P1 width - P2 width
21.
22.
23.
24.
P1 & P2 width
P1 & P2 width variation tolerance (standard)
coil height
P2 pole height
-156-
APPENDIX D
-157-
C
am
)
a)
E
b-
e
h.
a
',,,
a)
CL
a)
0 0
a)
I.
0
.
0
_
0
0
0
_
•0
6
APPENDIX E
-159-
SECTION 3. MANUFACTURABILITY GUIDELINE
1.
RAMP ANGLE
LARGER
2.
SMALLER
less PR lumping in front of ramp (C)
less PR thinning in ramp shoulder (C)
** 4th layer definition
especially
less pole 2 height variation (CD)
** with same lapping
tolerance
THROAT HEIGHT
LARGER
better coating uniformity in pole (C)
** caused by flow of PR
less pole 2 variation (CD)
** better PR coating uniformity
3.
STACK SHAPE
ROUND
less PR lumping in front of ramp (C)
4.
SMALLER
OTHER SHAPE
REFLOW SCHEME (reflow temp. & time)
MORE REFLOW
less PR thinning in ramp shoulder (C)
LESS REFLOW
flatter stack surface (C)
flatter stack surface (P)
better reflow control (PR)
less residual P2 seed on B product (PR)
better ramp angle control (PR)
** better reflow control
-160-
5.
FEATHERING SCHEME (TERRACING)
MORE
less PR thinning in stack shoulder (C)
** terrace hold more PR
LESS
NO. OF LAYER (or stack height)
LAYER THICKNESS
MORE
8.
LESS
more conformal coating on pole (C)
more conformal coating on shoulder (C)
more uniform coating on stack (C)
** flatter stack
easier focus on stack (P)
**flatter stack
easier focus for topology (P)
**smaller focal offset
difference for features on top
and below the stack
easier pole width control (CD)
** steeper side wall
TRANSDUCER SIZE
LARGER
uniform coating on stack (C)
easier coil patterning on stack (C), ** flatter
9.
SMALLER
REGISTRATION BUDGET
LARGER
SMALLER
uniform stack coating (C), ** flatter
easier coil patterning (P), ** flatter
easier overlay pattering (R)
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10.
RAMP ANGLE DEFINITION LAYER
1ST LAYER
OTHER LAYER
less PR thinning in stack shoulder (C)
** shallower angle around shoulder
better ramp angle control (PR)
** only involve Ist layer insulation
difficult ramp angle control
** good overlay among
layers (R)
11.
DEVICE ORIENTATION (standard)
NEW
NORMAL
uniform coating (C)
** PR under same flow path for every transducer
12.
DETECTABLE ALIGNMENT TARGET (standard)
LARGER
uniform stack coating (C), ** flatter
easier coil patterning (P), ** flatter
easier overlay patterning (PR)
13.
SMALLER
ACTIVE ARRAY SIZE (relative to size of wafer) (standard)
LARGER
SMALLER
less edge bead effect (C)
14.
SLIDER BAR ARRANGEMENT ON WAFER (standard)
NEW
NORMAL
less edge bead effect (C)
** higher yield
15.
B PRODUCT VIA FEATHERING
MORE
LESS
less residual P2 seed (PR)
** easier for seed etch
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16.
P2 YOKE PULL-BACK OR NECK HEIGHT (B product only)
LARGER
SMALLER
less P2 width problem (N), notch away from tip
17.
P2 YOKE WIDENING ANGLE
SMALLER
LARGER
less reflective notching on P2 ramp
18.
P2 COVERAGE ON VIA
SMALLER
LARGER
less P2 reflective notching on via
19.
OVEREXPOSURE BUDGET FOR VIA BLASTING
(OR BLAST MASK BIAS)
SMALLER
LARGER
exposed coil problem less likely (C)
21.
P1 & P2 WIDTH
LARGER
SMALLER
easier IVS measurement (CD)
22.
P1 & P2 WIDTH VARIATION TOLERANCE (standard)
LARGER
easier CD control (CD), ** higher yield
23.
SMALLER
COIL HEIGHT
LARGE
SMALL
robust PR coating for coil plating (C)
24.
P2 POLE HEIGHT
LARGE
SMALL
robust PR coating for P2 plating (C)
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