Background Statement for SEMI Draft Document 5269A
NEW STANDARD: TERMINOLOGY FOR THROUGH SILICON VIA
GEOMETRICAL METROLOGY
Notice: This background statement is not part of the balloted item. It is provided solely to assist the recipient in
reaching an informed decision based on the rationale of the activity that preceded the creation of this Document.
Notice: Recipients of this Document are invited to submit, with their comments, notification of any relevant
patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this
context, “patented technology” is defined as technology for which a patent has issued or has been applied for. In the
latter case, only publicly available information on the contents of the patent application is to be provided.
Background
This document provides a starting point for standardization of geometrical metrology for selected dimensions of
through silicon vias (TSVs). This document is needed because different technologies can measure various
geometrical parameters of an individual TSV, or of an array of TSVs, such as pitch, top CD, top diameter, top area,
depth, taper (or sidewall angle), bottom area, bottom CD, bottom diameter, and possibly others. However it is
currently difficult to compare and/or correlate results from the various measurement technologies for various TSV
dimensions. In some cases certain parameters may be described by similar names, but are actually different aspects
of the TSV geometry. Other characteristics of TSV metrology, such as electrical metrology, could be addressed in
future activity.
The creation of this document was authorized by Committee 3DS-IC on July 12, 2011. It was first balloted in Cycle
1 of Calendar Year 2012, and the results were adjudicated at the SEMI Spring Standards Meeting. It will be
reballotted in Cycle 4 of Calendar Year 2012, and the results will be adjudicated at the SEMI standards meeting at
SEMICON West, San Francisco, CA in July, 2012.
Review and Adjudication Information
Task Force Review
Committee Adjudication
Inspection & Metrology Task Force
North America 3DS-IC Committee
July 10, 2012
July 10, 2012
8:00 AM to 10:00 AM, Pacific Time
3:00 PM to 5:00 PM, Pacific Time
San Francisco Marriott Marquis Hotel
San Francisco Marriott Marquis Hotel
San Francisco, California
San Francisco, California
David Read (NIST, david.read@nist.gov)
Urmi Ray (Qualcomm)
Victor Vartanian (SEMATECH)
Sesh Ramaswami (Applied Materials)
Yi-Shao Lai (ASE)
Richard Allen (SEMATECH)
Chris Moore (Semilab)
Chris Moore (Semilab)
Paul Trio (SEMI NA)
Paul Trio (SEMI NA)
Standards Staff:
408.943.7041 /ptrio@semi.org
408.943.7041 / ptrio@semi.org
This meeting’s details are subject to change, and additional review sessions may be scheduled if necessary. Contact
SEMI Standards staff for confirmation.
Group:
Date:
Time & Timezone:
Location:
City, State/Country:
Leader(s):
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SEMI Draft Document 5269A
NEW STANDARD: TERMINOLOGY FOR THROUGH SILICON VIA
GEOMETRICAL METROLOGY
1 Purpose
1.1 Clear and commonly accepted definitions are needed for efficient communication and to prevent
misunderstanding between buyers and vendors of metrology equipment and manufacturing services. The purpose of
this document is to provide a consistent terminology for the understanding and discussion of metrology issues
important to through silicon vias (TSV).
2 Scope
2.1 The scope of this document is limited to the definitions of terms used to specify measured quantities that
characterize TSV. This document does not describe measurement procedures, but rather attempts to define the
measurands clearly, usefully, and unambiguously.
2.2 The focus of this document is on geometry-related metrology and measurands important for definition and
control of fabrication and inspection operations on structures that include openings for TSV.
2.3 This document is intended for TSVs in silicon.
2.4 This document does not attempt to discuss statistical considerations, which are covered in SEMI E89 and
elsewhere.
2.5 This document adapts structure and wording from other SEMI documents, particularly SEMI P35.
NOTICE: SEMI Standards and Safety Guidelines do not purport to address all safety issues associated with their
use. It is the responsibility of the users of the Documents to establish appropriate safety and health practices, and
determine the applicability of regulatory or other limitations prior to use.
3 Referenced Standards and Documents
3.1 SEMI Standards and Safety Guidelines
SEMI P35 — Terminology for Microlithography Metrology
SEMI E89 — Guide for Measurement System Analysis (MSA)
3.2 SEMI Documents
SEMI International Standards: Compilation of Terms (Updated 0811)1
3.3 NIST Documents2
NBSIR 79-1758 — The Calibration of a Roundness Standard (http://emtoolbox.nist.gov/Publications/NBSIR791758.pdf)
3.4 Other Documents
International Technology Roadmap for Semiconductors, 2009 Edition, Chapter on Interconnect
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
4 TSV Metrology Issues
4.1 Geometrical measurements — any measurement of length or position contains an unknown error, the influence
of which on subsequent application of the measurement data is best described by numerical measurement
uncertainty. The problem of measuring geometric dimensions on TSV is complicated by the fact that the TSV is a 3-
1
http://semi.org/en/sites/semi.org/files/docs/CompilationTerms0811.pdf
National Institute of Standards and Technology, 100 Bureau Drive, Stop 3460, Gaithersburg, MD 20899-3460, USA; Telephone: 301.975.6478,
http://www.nist.gov
2
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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dimensional object with (usually) an irregular and complex shape. The metrology problem is further complicated
because TSV are microscopic, and only magnified images can be measured.
4.2 In efficient practice, TSV opening geometry is specified using only a few selected parameters, because the
additional data needed to fully describe the complex TSV shape can be considered immaterial to the subsequent
applications of the measurement data, and are seldom available.
4.3 The first rule of metrology is to define exactly what is to be measured. The approach used here, in light of the
previous paragraphs, is to define specific applications of widely used terms such as depth and diameter for TSV.
These definitions will rely on standard geometrical constructions such as straight lines, circles, ellipses, etc. as
needed for clarity. The differences between the ideal and the actual shape of a TSV opening may contribute to the
overall measurement variability or uncertainty of some dimension of the TSV being characterized.
4.4 Challenges from the ITRS Roadmap — The International Technology Roadmap for Semiconductors, 2010
Update, anticipates minimum TSV diameters ranging from 8 to 0.8 µm in global and intermediate interconnect
levels in 3D-SICs from 2009 to 2015. Among the five most critical challenges beyond the 16 nm node is a practical
approach for 3D chip stacking; Table INTC5 states that engineering manufacturable solutions that meet cost targets
for this technology is key. Addressing this challenge will require advances in metrology. This document is part of
the groundwork for that metrology.
5 Definitions
5.1 through silicon via opening (TSV) — a hole or recess in a silicon wafer that begins at the wafer top surface and
may or may not: a) extend fully through the wafer from one surface to the other; b) contain a conductor; c) contain
additional layers such as an insulator between the conductor and the silicon, a diffusion barrier on the silicon surface
within the hole, or others. (Discussion: The International Technology Roadmap for Semiconductors defines a
through-silicon-via as an electrical conductor. Here we are defining specifically terms for the metrology of the TSV
opening, within which the complete electrical conducting TSV will be constructed.)
5.2 wafer top surface — the wafer surface where the TSV opening is initially created and where the excavation of
the TSV begins. This surface is defined to be horizontal; its perpendicular is defined to be vertical. Figure 1 shows a
sketch of a TSV at the wafer top surface.
5.3 wafer bottom surface — the wafer surface opposite the wafer top surface.
5.4 area — geometrical area of the TSV opening in a particular horizontal plane. In figure 1, the area of the TSV
opening is the area covered by the light upward diagonal line pattern.
5.4.1 top area — area of the TSV opening at the top surface of the wafer.
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Figure 1
TSV with sidewall at top wafer surface.
5.5 depth — the distance, measured from the wafer top surface vertically toward the wafer bottom surface, between
the top surface and the deepest point of the TSV opening.
5.5.1 intermediate depth — the distance measured from the wafer top surface to a selected level less than the full
depth of the TSV opening. For example, the TSV opening area at an intermediate depth of 50 % of the wafer
thickness might be of interest.
5.5.2 full depth TSV — a TSV opening that extends from the top surface to the bottom surface of the wafer.
5.6 reported horizontal dimensions — The scheme and numerical values used to specify the breadth of a TSV. The
breadth of a TSV may be specified in a variety of ways depending on circumstances such as the fabrication method
and the measurement tools that are available. This standard adopts the major and minor diameters, as defined below,
as the reference geometrical construction for the horizontal dimensions of the TSV opening. Other possible
examples of reference dimensions, not defined in this standard, include the diameter of a circle in a horizontal plane
that can be inscribed in the TSV opening, the side of a square that can be inscribed in the TSV opening, etc. The
geometrical terms and definitions herein are intended to be consistent, to the extent feasible, with their standard
usage in the literature on geometry, in order to promote the use of existing mathematical methods and software and
to minimize confusion.
5.6.1 center — the center of a TSV opening in any horizontal plane is the centroid (“center of gravity”) of the area
of the TSV.
5.6.2 chord — A straight line that extends from one point on the sidewall of the TSV opening in a specific
horizontal plane to another such point in the same plane.
5.6.3 major diameter — the length of the longest chord of the TSV opening in any particular horizontal plane.
There is no requirement that this diameter pass through any geometrical center or centroid of the TSV opening.
There is no relationship implied between the length of the major diameter and the area of the TSV opening. Figure 2
indicates the major and minor diameters of a TSV opening. The unit for this dimension shall be the micrometer.
Discussion: This definition implies that all diameters of the TSV are observable within the field of view of the
measurement instrument. If only a subset of the TSV diameters is within the field of view, for instance, by use of a
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline.
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vertical cross section, the reported diameter value will be affected by the geometrical relationship between the
measurement plane and the TSV.
5.6.3.1 center point of the major diameter — the point on the major diameter equidistant from its ends.
5.6.4 minor diameter — the length of the shortest chord that passes through the center point of the major diameter.
Figure 2 shows an example. Under this definition the minor diameter need not be at 90° to the major diameter, and
no relationship is specified or assumed between the length of the minor diameter and the area of the TSV opening.
The unit for this dimension shall be the micrometer.
Figure 2
TSV opening showing major and minor diameters as defined here. The minor diameter is the shortest
diameter that passes through the center point of the major diameter.
5.6.5 Diameters of TSV openings may be of interest in planes at various intermediate depths along the TSV.
Whenever a diameter is given, the plane in which it is measured should be specified. Some examples follow.
5.6.5.1 top major diameter — the major diameter of the TSV opening being characterized, measured at the top
surface of the wafer.
5.6.5.2 bottom major diameter — the major diameter of the TSV opening being characterized, measured at the
bottom surface of the wafer.
5.6.5.3 90 % depth major diameter — the major diameter of the TSV opening being characterized, measured in the
horizontal plane at 90 % of the depth of the TSV.
5.6.5.4 top minor diameter — the minor diameter of the TSV opening being characterized, measured at the top
surface of the wafer.
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5.6.5.5 bottom minor diameter — the minor diameter of the TSV opening being characterized, measured at the
bottom surface of the wafer.
5.6.5.6 90 % depth minor diameter — the minor diameter of the TSV opening being characterized, measured in the
horizontal plane at 90 % of the depth of the TSV.
5.7 CD — critical dimension. This document defines all the CDs of the TSV opening based on the length of the
minor diameter at various depths within the TSV opening. Whenever a CD is given, the plane in which it is
measured shall be specified. Some examples follow.
5.7.1 top CD — CD (length of minor diameter) of the TSV opening at the top wafer surface.
5.7.2 CD at 90% depth — CD (length of minor diameter) at an intermediate depth of 90% of the depth of the TSV.
5.7.3 bottom CD — CD (length of minor diameter) of the TSV opening at the bottom wafer surface. Use of this
term implies that the TSV opening is a full thickness TSV.
5.8 roundness — ratio of the length of the minor diameter to the length of the major diameter in the same plane.
Because of the use of the term ‘aspect ratio’ in the International Technology Roadmap for Semiconductors (ITRS) in
connection with the depth of the TSV opening, the use of the term ‘aspect ratio’ in connection with the in-plane
dimensions of the TSV opening is deprecated. A definition of aspect ratio that is intended to be consistent with the
ITRS usage is given below in 5.13.
NOTE 1: See the NIST document listed in section 3.3, above, on calibration of a roundness standard, for an example of a
treatment of roundness. This document treats roundness as “…radial deviations of the workpiece from the center of rotation…”,
although it does not state a formal definition of roundness.
5.8.1 top roundness — roundness at the top surface of the wafer.
5.8.2 bottom roundness — roundness at the bottom surface of the wafer.
5.8.3 roundness at 90 % depth — roundness at the an intermediate depth of 90% of the depth of the TSV.
5.9 sidewall surface texture — the local character of the surface formed by the sidewall of a TSV opening.
5.9.1 scallop — a periodic sidewall feature created by certain etch processes
5.9.2 scallop size — the peak to valley distance perpendicular to the TSV sidewall at a particular scallop (see Fig.
3a).
5.9.3 sidewall topography, ST — the quantitative measure of the sidewall surface texture. Wikipedia indicates that
topography is concerned with surface shape and features, local detail, and the three-dimensional quality of the
surface. The term is used in that sense here.
5.9.3.1 For scallop-based etch processes, the sidewall topography is given by Equation (1)
𝑆𝑇 =
𝑠𝑐𝑎𝑙𝑙𝑜𝑝 𝑠𝑖𝑧𝑒
𝑇𝑜𝑝 𝑚𝑖𝑛𝑜𝑟 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟
(1)
5.9.3.2 For other etch processes, the sidewall surface topography is determined by use of idealized geometrical
shapes that are drawn within and outside of the representation of the TSV sidewall. The ellipse is expected to be the
most useful such shape for measurements in horizontal planes through the TSV. The circle is a special case of the
ellipse. The rectangle may be chosen for TSV openings that conform better to this shape. The rectangle or the
trapezoid may be the most useful such shape for measurements on vertical planes through the TSV. The sidewall
topography is defined by Equation (2) for rectangles or trapezoids truncated at the top and bottom (Fig. 3a) and
Equation (3) for circles or ellipses (Fig. 3b), where ST is the sidewall topography, Aouter is the area of the
circumscribed ellipse or rectangle, and Ainner is the area of the inner ellipse or rectangle.
𝑆𝑇 =
𝐴𝑜𝑢𝑡𝑒𝑟 −𝐴𝑖𝑛𝑛𝑒𝑟
2 𝐴𝑖𝑛𝑛𝑒𝑟
(2)
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𝐴𝑜𝑢𝑡𝑒𝑟 −𝐴𝑖𝑛𝑛𝑒𝑟
(3)
4 𝐴𝑖𝑛𝑛𝑒𝑟
5.9.3.2.1 Discussion: Figure 3a shows circumscribed and inscribed rectangles for a TSV opening as measured in a
vertical plane through the TSV. Figure 3b shows circumscribed and inscribed ellipses for a TSV opening as
measured in a horizontal plane through the TSV. There is no requirement for any particular geometrical relationship
between the two constructed reference geometries. Their centers, orientations, and values of roundness may be the
same or different.
Top minor
diameter
Scallop size
Figure 3a
TSV showing scallop size and inscribed and circumscribed rectangles in a vertical plane through a TSV.
These are examples of geometrical constructions that may be used in evaluating sidewall topography.
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Figure 3b
TSV with inscribed and circumscribed ellipses, for use in evaluating sidewall topography in a horizontal
plane through the TSV
5.10 pitch — distance between the centroid of a TSV and the centroid of an adjacent TSV.
5.10.1 pitch, average — average spacing between centroids of a specified group of TSV arranged along a line.
5.10.2 pitch, minimum — minimum spacing between centroids of any two neighboring TSV within a group of TSV
arranged along a line.
5.10.3 tilt — angle in degrees between the top surface normal of the wafer and the line connecting the center of the
TSV at the top wafer surface with the deepest point of the TSV. Discussion: An angle of 0º indicates an absence of
tilt.
5.11 sidewall angle — angle in degrees between a line through the edge of the TSV and the horizontal plane.
Discussion: Sidewall tilt is the same as sidewall angle. Considerations about the effect of the plane of the cross
section on the measured result, as discussed in 5.6.3 (as revised) apply here as well, if a vertical cross section is used.
An angle less than 90º indicates a TSV diameter that decreases with increasing depth, while an angle of more than
90º indicates a TSV with a diameter that increases with depth. The line should accurately track the direction of the
top 90%, or more, of the sidewall of the TSV.
5.12 reveal — Distance remaining between the deepest point within a TSV opening and the bottom surface of the
wafer. This dimension may be calculated as the difference between the wafer thickness and the TSV depth.
5.13 aspect ratio — ratio of the depth of a TSV opening to its top major diameter.
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NOTICE: Semiconductor Equipment and Materials International (SEMI) makes no warranties or representations as
to the suitability of the Standards and Safety Guidelines set forth herein for any particular application. The
determination of the suitability of the Standard or Safety Guideline is solely the responsibility of the user. Users are
cautioned to refer to manufacturer’s instructions, product labels, product data sheets, and other relevant literature,
respecting any materials or equipment mentioned herein. Standards and Safety Guidelines are subject to change
without notice.
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rights or copyrights asserted in connection with any items mentioned in this Standard or Safety Guideline. Users of
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and the risk of infringement of such rights are entirely their own responsibility.
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