Summary of Introduction
• MEMS (U.S.) Sometimes Microsystems in Europe.
• MEMS=MicroElectroMechanical Systems
• Very broad definition in practice: Mechanical, Electrical,
Optical, Thermal, Fluidic, Chemical, Magnetic.
• Generally systems created using microfabrication that are
not integrated circuits. Many (but not all) of the
microfabrication techniques were borrowed from the IC
industry.
• Market is smaller than IC market, but more diverse and
growing faster.
Some Examples
• Accelerometer
– Electrical/Mechanical
•
mTAS or Micro Total Analysis System
– Purifies, amplifies, and detects DNA, for example.
– Fluids/Biochemistry/Optical/Electrical
• TI DLP
– Optical/Mechanical/Electrical/Surface Science
• Microrelay
– Mechanical/Electrical/Surface Science
• Microplasma Source
– Electrical/Electromagnetic/Plasma
• What do you need to know for MEMS?
• Everything!!!???
• Truly an interdisciplinary field.
What are we going to do?
• Learn a useful subset of techniques needed for designing MEMS
devices. Not all!!
• We will design MEMS devices.
– Project teaming survey is due Monday – see web site.
– Project assignment to be posted on the web site.
• We will discuss examples of MEMS devices and use the techniques we
have developed.
• First we will look at microfabrication and process integration.
• Other notes:
– First homework is due Thursday. We will try to have all students consolidated to
one section to make the discussion board and the electronic turn-in (for video
streaming students) in one place by Thursday.
– Second homework is due Thursday, Sept. 23 (but you will have everything you
need to do the work over the weekend). Homework 3 will probably be due on
Monday, Sept. 27. The homework load will decrease as the project load increases
(generally).
Microfabrication:
Types of Micromachining for MEMS
• Bulk Micromachining
– Etch away large parts of the silicon wafer.
– Traditionally, KOH or other chemical etch.
– Recently DRIE (Deep Reactive Ion Etch), an anisotropic plasma etch.
Microfabrication:
Types of Micromachining for MEMS
• Surface micromachining
– On surface of wafer/substrate
– Sometimes can be a post-process on top of CMOS wafer
for process integration with electronics.
– Typically much thinner structures than bulk
micromachining, but metal structures can be fairly thick.
Microfabrication: Types of Micromachining for MEMS
• LIGA
– X-ray lithographie, galvanoformung, abformtechnik (or lithography,
electrodeposition, and molding).
– A special type of surface micromachining, not much used in its original form.
– Now sometimes refers to using very thick photoresist to make thick electroplated
structures.
Packaging
• Ideally, part of fabrication process, then just use a cheap plastic
package.
• Often, a surface micromachined device is bonded to a bulk
micromachined package (the cavity to contain the device is etched
from the wafer using bulk micromachining).
• Sometimes the package is the most expensive part of the device
(pressure sensors, microfluidics). Especially true when the device
interacts with the outside environment.
References: Text (brief), Campbell or other IC fabrication
text (generally good, but incomplete for MEMS), Madou
(specific to MEMS).
Silicon wafer fabrication
•
Taken from www.egg.or.jp/MSIL/english/index-e.html
Silicon wafer fabrication – slicing and
polishing
•
Taken from www.egg.or.jp/MSIL/english/index-e.html
ECE 1233 PMOS Fabrication Sequence
N-type Si wafer <100>
Pre-diffusion clean
Pad oxidation
Week 1
SiO2
O2
Deposit LPCVD nitride
Si3N4
SiH2Cl2
NH3
Week 2
Spin photoresist
PR
Week 2
Expose PR with
active area mask
and develop
Reactive ion etch
nitride layer
Strip PR
CHF3
O2
Week 3
Pre-diffusion clean
Field oxidation
O2
H2O
Strip nitride and pad oxide
Sacrificial oxidation
O2
Week 3
Strip sac ox
Gate oxidation
O2
Deposit LPCVD polysilicon
Poly
Week 4
SiH4
PR/etch gate mask
Strip PR
SF6
O2
LPCVD Systems
Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/
Ion implant BF2
+
P doped areas
Week 5
Pre-diffusion clean
Drive-in/oxidation
O2
H2O
PR/etch contact mask
Strip PR
Clean
Sputter deposit Al/1%Si
Week 6
Ar
Al/Si
PR/etch metal mask
Strip PR
Gate (contact not shown)
Anneal
Week 6
Source
Drain
ECE 1233 PMOS Fabrication Sequence
N-type Si wafer <100>
Pre-diffusion clean
Pad oxidation
Week 1
SiO2
O2
Deposit LPCVD nitride
Si3N4
SiH2Cl2
NH3
Week 2
Spin photoresist
PR
ECE 1233 PMOS Fabrication Sequence
N-type Si wafer <100>
Pre-diffusion clean
Pad oxidation
Week 1
SiO2
O2
Deposit LPCVD nitride
Si3N4
SiH2Cl2
NH3
Week 2
Spin photoresist
PR
Week 2
Expose PR with
active area mask
and develop
Reactive ion etch
nitride layer
Strip PR
CHF3
O2
Week 3
Pre-diffusion clean
Field oxidation
O2
H2O
Strip nitride and pad oxide
Sacrificial oxidation
O2
Week 3
Strip sac ox
Gate oxidation
O2
Deposit LPCVD polysilicon
Poly
Week 4
SiH4
PR/etch gate mask
Strip PR
SF6
O2
Ion implant BF2
+
P doped areas
Week 5
Pre-diffusion clean
Drive-in/oxidation
O2
H2O
PR/etch contact mask
Strip PR
Clean
Sputter deposit Al/1%Si
Week 6
Ar
Al/Si
Ion implant BF2
+
P doped areas
Week 5
Pre-diffusion clean
Drive-in/oxidation
O2
H2O
PR/etch contact mask
Strip PR
Clean
Sputter deposit Al/1%Si
Week 6
Ar
Al/Si
PR/etch metal mask
Strip PR
Gate (contact not shown)
Anneal
Week 6
Source
Drain
Electrodeposition/Electroplating
Surface Micromachined
Post-Process Integration with CMOS
20-100 V Electrostatic Actuation
~100 Micron Size
Gate
Drain
Beam
Beam
Drain
Gate
Source
Gate
Drain
SEM of NEU microswitch
Source
Source
IBM 7-Level Cu Metallization (Electroplated)
Packaging
• Ideally, part of fabrication process, then just use a cheap plastic
package.
• Often, a surface micromachined device is bonded to a bulk
micromachined package (the cavity to contain the device is etched
from the wafer using bulk micromachining).
• Sometimes the package is the most expensive part of the device
(pressure sensors, microfluidics). Especially true when the device
interacts with the outside environment.
•Adhesives
•Organics
•Glass (Glass Frit)
•Metals (~Solders, Metal/Semiconductor Eutectics)
•Thermal Compression Bonding
•Au-Au/Clean/300 C
•Why?
NUMEM Microrelay Process
sourc e
gate
drain
sourc e
gate
drain
sourc e
gate
drain
NUMEM Microrelay Process
sourc e
gate
drain
sourc e
gate
drain
Residual stress gradients
Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/
More tensile on top
More compressive on top
Just right! The bottom line: anneal
poly between oxides with similar
phosphorous content. ~1000C for
~60 seconds is enough.
Residual stress gradients
Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/
A bad day at MCNC (1996).
DRIE structures
Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/
• Increased capacitance
for actuation and
sensing
• Low-stress structures
– single-crystal Si only
structural material
Thermal Actuator
Comb-drive Actuator
• Highly stiff in vertical
direction
– isolation of motion to
wafer plane
– flat, robust structures
2DoF Electrostatic actuator
Scalloping and Footing issues of DRIE
Top wafer surface
cathode
Top wafer surface
anode
ew
Sc
sid
ped
o
l
l
a
all
Tip precursors
<100 nm silicon nanowire
over >10 micron gap
1 µm
microgrid
Footing at the bottom of
device layer
Milanovic et al, IEEE TED, Jan. 2001.
Taken from: http://www.imm-mainz.de/english/sk_a_tec/basic_te/liga.html
Sub-Micron Stereo Lithography
New Micro Stereo Lithography for Freely Movable 3D Micro Structure
-Super IH Process with Submicron ResolutionKoji Ikuta, Shoji Maruo, and Syunsuke Kojima
Department of Micro System Engineering, school of Engineering, Nagoya University
Furocho, Chikusa-ku, Nagonya 464-01, Japan
Tel: +81 52 789 5024, Fax: +81 52 789 5027 E-mail: ikuta@mech.nagoya-u.ac.jp
Fig. 6 Schematic
diagram of the
super IH process
Fig. 1 Schematic diagram of IH Process
Fig. 5 Process to make movable gear and shaft
(a) conventional micro stereo lithography needs base layer
(b) new super IH process needs no base
Micro Electro Mechanical Systems
Jan., 1998 Heidelberg, Germany
Sub-Micron Stereo Lithography
New Micro Stereo Lithography for Freely Movable 3D Micro Structure
-Super IH Process with Submicron ResolutionKoji Ikuta, Shoji Maruo, and Syunsuke Kojima
Department of Micro System Engineering, school of Engineering, Nagoya University
Furocho, Chikusa-ku, Nagonya 464-01, Japan
Tel: +81 52 789 5024, Fax: +81 52 789 5027 E-mail: ikuta@mech.nagoya-u.ac.jp
Fig. 10 Micro gear and shaft make of solidified polymer
(b) side view of the gear of four teeth
(d) side view of the gear of eight teeth
Micro Electro Mechanical Systems
Jan., 1998 Heidelberg, Germany
Simple Carbon Nanotube Switch
Diameter: 1.2 nm
Elastic Modulus: 1 TPa
Electrostatic Gap: 2 nm
Binding Energy to Substrate:
8.7x10-20 J/nm
Length at which adhesion = restoring force: 16 nm
Actuation Voltage at 16 nm = 2 V
Resonant frequency at 16 nm = 25 GHz
Electric Field = 109 V/m or 107 V/cm + Geom.
(F-N tunneling at > 107 V/cm)
Stored Mechanical Energy (1/2 k x2 ) = 4 x 10-19 J = 2.5 eV
Extras
Micromachining Ink Jet Nozzles
Microtechnology group, TU Berlin
Bulk micromachined cavities
Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/
• Anisotropic KOH etch
(Upperleft)
• Isotropic plasma etch (upper
right)
• Isotropic BrF3 etch with
compressive oxide still showing
(lower right)
Surface Micromachining
Taken from http://www-bsac.EECS.Berkeley.EDU/~pister/245/
Deposit sacrificial layer
Deposit/pattern structural layer
Pattern contacts
Etch sacrificial layer
Packaged Plasma Source
Top View
Die in Hybrid Package
Side View
Fabrication
PR
Cr/Au/TiW
Glass Wafer
Expose/Dev.
TiW etch
Electroplate
Gold
PR strip
TiW/Au/Cr etch
spiral coil
Bond to 10 mm diam.
glass chamber
interdigitated capacitor
to vacuum system
SEM of Interdigitated
Capacitor Structure