Transcript Introduction to Polysilicon Micromachining

An Introduction to
Polysilicon
Micromaching
Robert W. Johnstone
www.sfu.ca/~rjohnsto/
www.sfu.ca/immr/
Personal Information
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Robert W. Johnstone
Graduate Student at
Simon Fraser University
School of Engineering
Science
Simon Fraser University
8888 University Drive,
Burnaby, BC
Canada V5A 1S6
Tel: (604) 291-4971
Fax (604) 291-4951
An Introduction to Polysilicon Micromachining
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Outline
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Introduction
Fabrication
MEMS Technology
Sensors
Actuators
Packaging Issues and
Integration
MUMPs Examples
Design Issues
Evaluations and
Questions
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Introduction
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Introduction: Terminology
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Micromachining
Microfabrication
Microelectromechanical
Systems (MEMS)
Microsystems Technology
(MST)
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Introduction
Microfabrication
Micromachining
Bulk
Micromachining
LIGA Process
Microelectronics
Surface
Micromachining
Raised
Structures
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Introduction: Features of MEMS
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Miniature mechanical
systems
Batch fabrication
approach
Utilizes microelectronic
manufacturing base
Common technology for
sensors, actuators and
systems
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Introduction: Why Miniaturize?
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System Integration
Avoid assembly of discrete components
 Better reliability
 Lower costs
 Better Performance
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Better Response
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Smaller devices have less inertia, less thermal
mass, less capacitance, etc.
Increased Reliability
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Mass decreases faster than structural strength
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Introduction: Systems-on-a-Chip
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Traditional
Hundreds of components
Manual/semi automated
assembly
Plenty of solder joints
Sensitive to shock and vibration
Future
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Single chip
No assembly
Minimal solder joints
Batch fabrication
Insensitive to shock & vibration
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Introduction: Growth Prediction
Technologies experiencing growth.
 Hard disk drive heads
 Inkjet print heads
 Heart pacemakers
 In vitro diagnostics
 Hearing aids
 Pressure sensors
 Chemical sensors
 Infrared imagers
 Accelerometers
 Gyroscopes
 Machine monitoring
 Micro fluidics
 Magnetoresistive sensors
 Microspectrometers
 Micro optical systems
 Military systems
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Introduction: Growth Prediction
MEMS Device Revenues
Source: SEMI
MEMS use in existing systems
Source: MST News
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Introduction: Applications
Relevant Examples
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Telecommunication relies on routing optical
signals
Present systems use large and centralized
networks
A low cost optical switch can revolutionize
telecommunications technology
MEMS enables practical, low cost micro-mirrors
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Introduction: Applications
Inertial Measurement
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MEMS enables low cost
chips that can monitor
motion and position
Enables integration of
inertial measurement in
systems not possible with
traditional technology
Applications in air bags,
skid control, machine
tools, sports equipment
etc
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Introduction: Applications
Micro Fluidics
 Ink jet printing
 mTAS – Micro Total Analysis
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System (chemical analysis)
Environmental monitoring:
Detection of pollutants and
pathogens
Biomedical devices: heart/lung
and kidney Dialysis machine,
dosing systems etc
DNA analysis systems for
diagnostic, therapeutic
And forensic studies
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Introduction: Applications
Development Strategy
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Strategy #1
Build the best one possible to
meet the most stringent
requirements
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Strategy #2
Build them cheap and worry about
performance later
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Introduction: Applications
Industry’s Interest in MEMS
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New products in old fabs
Seamless integration into existing
fabrication plants
Minimal additional investment
Risk is low
Logical next step
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Introduction: Major Challenge
Technology Standards
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Application specific technologies
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Differently tuned technology for
different devices/applications
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Presently low synergy or
cooperation in formulating a
common technology
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Fabrication
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Fabrication: Technology
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Basic fabrications
processes based on IC
technology
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Fabrication: Spectrum
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IC technology
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Bipolar
CMOS
BiCMOS
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MEMS related technology
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Bulk micromachining
Surface micromachining
LIGA, LIGA-like
Micro EDM
3D stereo lithography
Laser micromachining
Focused ion beam milling
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Fabrication: Basic Processes
Silicon Processing
 Lithography
 Oxidation
 Diffusion
 Thin film deposition
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CVD process
Thermal evaporation
Sputtering
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Fabrication: Lithography
Lithography is the process of transferring a pattern
from a mask to a photoresist using a
photographic tool (mask aligner), and to the
silicon substrate using etching techniques.
PATTERN TRANSFER
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Fabrication: Lithography
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Coat the wafer with an adherent and etchresistant photoresist
Selectively remove the resist to leave the desired
pattern by exposure and development steps
Etch to transfer the mask pattern to the
underlying material
Remove (strip) the photoresist and clean the
wafer
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Fabrication: Lithography
Mask Pattern
UV Light
Transparent
region
Opaque
region
Photomask
Photoresist
Oxide
Silicon substrate
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Fabrication: Lithography
Positive Photoresist
Silicon substrate
Expose and develop
Silicon substrate
Strip resist
Silicon substrate
Etch oxide
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Fabrication: Lithography
Negative Photoresist
Silicon substrate
Expose and develop
Silicon substrate
Strip resist
Silicon substrate
Etch oxide
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Fabrication: Lithography
Subtractive vs. Additive Pattern Transfer
Film
Mask
Mask
After
lithography
Film
Etch
After mask
removal
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Fabrication: Lithography
Spin Coating of Photoresist
Dispense
resist
Spin
PR Spinner
Spin
complete
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Fabrication: Lithography
Types of Lithographic Tools
Mask and wafer in direct contact
Very high resolution
1X magnification
Proximity Printers Mask and wafer separated by a few micron gap
Moderate resolution
Contact Printers
Projection Printers
Accomplished via mirror and lenses
Step and Repeat
Projection Printers
High resolution
5X and 10X reduction possible
Relaxes reticle tolerances and defect requirements
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Fabrication: Lithography
Contact Printing
Wafer and mask
out-of-contact
during alignment
Wafer and mask
in-contact
during exposure
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Fabrication: Lithography
Projection Printing (using Wafer Stepper)
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Fabrication: Oxidation
Thermal oxidation is a high
temperature process used
to grow a continuous layer
of high-quality silicon
dioxide on silicon
substrate
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Dry oxidation: oxidizing
species is oxygen
Wet oxidation: oxidizing
species is water vapour
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Fabrication: Oxidation
After oxidation
Oxidation process
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Fabrication: Oxidation
Ref: Fundamentals of Silicon Integrated Device Technology
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Fabrication: Oxidation
Ref: Fundamentals of Silicon Integrated Device Technology
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Fabrication: Oxidation
Oxidation Through a Window in the Oxide
Oxidation complete
Oxidation process
Oxide removed
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Fabrication: Oxidation
Local Oxidation
Silicon nitride deposition
Oxidation complete
Oxidation
Silicon nitride removed
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Fabrication: Oxidation
Oxide Layer Color Chart
Film
Thickness
(Microns)
0.05
Color and Comments
Tan
Film
Thickness
(Microns)
0.60
Color and Comments
Carnation pink
0.07
Brown
0.58
Light orange or yellow to pink borderline
0.10
Dark violet to red violet
0.57
0.12
Royal blue
0.56
Yellow to "yellowish" (At times it appears to
be light creamy gray or metallic)
Green yellow
0.15
Light blue to metallic blue
0.54
Yellow green
0.1
Metallic to very light yellow green
0.52
Green (broad)
0.20
Light gold or yellow - slightly metallic
0.50
Blue green
0.22
Gold with slight yellow orange
0.49
Blue
0.25
Orange to melon
0.48
Blue violet
0.27
Red violet
0.47
Violet
0.30
Blue to violet blue
0.46
Red violet
0.31
Blue
0.44
Violet red
0.32
Blue to blue green
0.42
Carnation pink
0.34
Light green
0.41
Light orange
0.35
Green to yellow green
0.39
Yellow
0.36
Yellow green
0.37
Green yellow
Silicon Processing for the VLSI Era: Volume 1- Process Technology
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Fabrication: Diffusion
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Diffusion is a process by which atoms of impurities (eg.,
B, P, As, Sb) move into solid silicon as a result of the
presence of a concentration gradient and high
temperatures.
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Fabrication: Diffusion
Diffusion Through an Oxide Window
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Fabrication: Diffusion
Diffusion Profiles
Diffusion from
unlimited source
Diffusion from
limited source
Diffusion from
concentration step
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Fabrication: Diffusion
Resistivity of Diffused Layers in Silicon
Irvines’s
Curves
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Fabrication: Diffusion
Oxidation/Diffusion Furnace
Separate furnaces
for oxidation and
diffusion processes
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Fabrication: Thin Film Deposition
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Chemical Vapor Deposition (CVD) Processes
Physical Vapor Deposition (PVD) Processes
Thermal evaporation
 Sputtering
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Fabrication: Thin Film Deposition
CVD is the formation of a solid film on a substrate by the reaction
of vapour phase chemicals which are decomposed or reacted on
or near the substrate.
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Fabrication: Thin Film Deposition
Reaction Energy
Thermal
Photons
Electrons
Reaction Types
Heterogeneous reaction
Chemical reaction takes place
Very close to the surface
Good quality films
Homogeneous reaction
Processes
APCVD – Atmospheric pressure CVD
LPCVD – Low pressure CVD
PECVD – Plasma enhanced CVD
Chemical reaction takes place
In the gas phase
Poor quality films
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Fabrication: Thin Film Deposition
Deposition Conditions
Mass Transport Limited
Reaction Rate Limited
Temperature not critical
Regulation of reactant
Temperature sensitive
Reactant flux not critical
species on wafer surface is
important
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Fabrication: Thin Film Deposition
Crystallographic Forms
Deposition condition and
reaction chemistry
determine the crystalline
nature of the film
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Fabrication: Thin Film Deposition
APCVD
 Atmospheric pressure
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chemical vapor deposition
Large volume of carrier
gases needed
Poor step coverage
Low throughput
Primarily used for LTO
Process gases
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Fabrication: Thin Film Deposition
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LPCVD
Low-pressure chemical
vapor deposition
Reaction rate limited
operation
Operates at 0.1 to 1Torr
pressure
Good quality films
Conformal coverage
Typically used for HTO,
Poly-silicon, some metal
films and nitride
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Fabrication: Thin Film Deposition
PECVD
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Plasma enhanced chemical vapor
deposition
Low temperature operation
Good conformal step coverage
Primarily used for passivation and
inter-level dielectrics
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Fabrication: Thin Film Deposition
CVD Chemistry
Film
Reactant Gases
(Carrier)
Temp
°C
Deposition Rate
nm/min
APCVD
Epitaxial Si
Cold Wall (CW)
SiCl4H2 (H2)
SiHCl3 / H2 (H2)
SiH2Cl2 (H2)
SiH4 (H2)
1125 – 1200
1100 – 1150
1050 – 1100
1000 - 1075
500 – 1500
500 – 1500
500 – 1000
100 - 300
Poly Silicon
(CW)
SiH4 (H2)
850 - 1000
100
Si3N4
(CW)
SiH4 / NH3 (H2)
900 - 1100
20
SiO2
SiH4 / O2 (N2)
200 - 500
100
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Fabrication: Thin Film Deposition
Film
Epitaxial Silicon
Poly Si
Reactant Gases
Temp
(Carrier)
°C
LPCVD
SiH2Cl2 (H2)
1000 - 1075
(30 – 80 Torr)
Deposition Rate
nm/min
100
100% SiH4
(0.2 Torr)
23% SiH4 (N2)
(1.0 Torr)
620
10
640
19
Si3N4
SiH2Cl2 / NH3
(0.3 Torr)
800
4
SiO2
SiH2Cl2 / N2O
(0.4 Torr)
900
8
SiO2
SiH4 / O2
SiH4 / PH3 / O2
(0.7 Torr)
450
450
10
12
300
10
Si3N4
PECVD
SiH4 / NH3 (N2)
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Fabrication: Thin Film Deposition
PECVD Systems
Parallel plate PECVD
(Low throughput)
High throughput PECVD
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Fabrication: Thin Film Deposition
Physical Vapor Deposition (PVD)
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Physical vapor deposition
is a process in which the
material to be deposited is
converted from a solid
phase into vapor phase,
then moved through a
region of low pressure,
with the vapor condensing
on the substrate, to form a
solid thin film.
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Evaporation: Source
material is converted into
liquid phase and next into
vapour phase usually by
thermal process
Sputtering: Physical
dislodging of atoms from a
target
Primarily used for
interconnect metal
deposition
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Fabrication: Thin Film Deposition
Thermal Evaporation
Evaporator
Evaporation Sources
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Fabrication: Thin Film Deposition
Electron Beam Evaporation
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Provides
very clean
and high
purity metal
films
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Fabrication: Thin Film Deposition
Sputtering Systems
DC Sputtering DC voltage between target and substrate,
used for conductive targets (metal films)
RF Sputtering RF voltage between target and substrate,
used for insulators (dielectrics)
Magnetron
Sputtering
Magnetic field confines electrons near the target,
increasing the number of electrons causing
ionization collisions and, thereby, deposition rates
Reactive
Sputtering
Sputtering a target material in presence of a
reactive gas, thereby, depositing a compound
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Fabrication: Etching Thin Films
Typically photoresist is used as a masking layer
Wet Etch
Liquid phase wet chemical etch
Under
cut problems
Not useful for fine dimension control
Dry Etch
Use of a gas plasma to abrasively etch the
thin film
Excellent dimension control
Reactive Ion Etch
Use of a reactive gas species that reacts with
the thin film and produce a gaseous by product
Fluorine, Chlorine Excellent dimension and sidewall control
based chemistry
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Fabrication: Planarization
 Chemical mechanical polishing (CMP)
 Planarization process used in IC technology
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Non planarized surface micromachining produces stringers and
non-flat surfaces
Yield and reliability problems
Not suitable for micro-optics
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Fabrication: Planarization
Non CMP
Stringers
Non uniform staple
Non planar link
Non planar hinge
CMP Sandia National labs
Uniform and flat staple
Planar link
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Planar hinge
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MEMS Technology
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MEMS Technology
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Major MEMS technologies
Bulk micromachining
 Surface micromachining
 LIGA
…
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MEMS Technology
Historically:
Silicon Micromachining
3-D Sculpting of silicon and silicon
compounds
Offshoot of IC fabrication technology
Uses lithography & mass production
Modern:
Non silicon MEMS
Electroforming
Molding
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MEMS Technology: Roots
IC Technology
Micromachining
Silicon wafer
Silicon wafer
Oxidize
Oxidize
Lithography
Lithography
Diffuse impurity
Etch the substrate
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MEMS Technology: Roots
Basic Etching Processes
Isotropic Etching
Anisotropic Etching
Etch cavity bound by the crystal planes
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MEMS Technology: Roots
Micromachining Classification
Bulk Micromachining
Deposit thin films on substrate
Pattern thin films lithographically
Selectively etch away a portion of
Surface Micromachining
Deposit thin films on substrate
Pattern thin films lithographically
Selectively etch away one (or
the substrate to form a free
standing 3D microstructure bound
by a cavity
more) of the intermediate thin films
to form a free standing 3D structure
standing on top of the substrate
surface
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MEMS Technology: Bulk
Relies mostly on anisotropic etching
(wet as well as dry etch)
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MEMS Technology: Bulk
Silicon Anisotropic Etchants
Etchant
Mask
Etch Stop
Etch Rate
mm/hr
Etch Ratio
(100):(111)
Potassium
Hydroxide
(KOH)
SiO2, SiN
Boron > 1020
cm-3 reduce
etch rate by
20
~85
~400
Ethylene
Diamine
Pyrocatechol
(EDP)
SiO2, SiN, Au
Boron >
5x1019 cm-3
reduces etch
rate by 50
~70
~35
Tetramethyl
Ammonium
Hydroxide
(TMAH)
SiO2, SiN
Boron > 1020
cm-3 reduce
etch rate by
40
~60
~10
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MEMS Technology
MEMS Specific Etching
Etch Stop Techniques
 Heavily boron doped
silicon can act as an etch
stop
 For more precise
thickness control use
electrochemical
techniques
 Technology developed for
silicon pressure sensors
and single crystal silicon
resonators
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MEMS Technology
Deep Reactive Ion Etching (DRIE)
STS, Alcatel, Trion, Oxford Instruments …
Unconstrained geometry
Uses high density plasma to alternatively
90o side walls
etch silicon and deposit a etch-resistant
High aspect ratio 1:30
polymer on side walls
Easily masked (PR, SiO2)
BOSCH Patent


Polymer
Polymer deposition
Process recipe depends on
geometry
Silicon etch using
SF6 chemistry
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MEMS Technology: LIGA
X-Rays
High aspect ratio
X-Ray mask
Thick
Photoresist
(PMMA)
Electroplate
metal
Metallic microstructures
Suitable for magnetic
actuation and sensing
Enables micro assembly
Dissolve resist
Liga-like technique
uses thick photoresist and
UV lithography
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MEMS Technology: Surface
Sacrificial and Structural Layers
Structural Layer: Must have good mechanical and electrical
properties
Sacrificial Layer: Must be stable during deposition and
processing should etch quickly during
release step
Both layers should be IC process compatible and
should have excellent etch selectivity
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MEMS Technology: Surface
Sacrificial and Structural Layers
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Sacrificial Materials
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Silicon dioxide
Doped silicon oxides
Photoresist
Polyimides
Carbon and few metals

Structural Materials

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

Polysilicon
Aluminium
Silicon nitride
Silicon carbide
Nickel
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MEMS Technology: Surface
 Prototypical surface

micromachining process
Three structural layers



Polycrystalline silicon
(polysilicon)
First layer is not
moveable
Often called zero layer
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MEMS Technology: Surface
Metal
Silicon
Dioxide
Polysilicon
Silicon
Nitride
Substrate
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MEMS Technology: Surface
Metal
Silicon
Dioxide
Polysilicon
Silicon
Nitride
Substrate
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MEMS Technology: Surface
Silicon
Dioxide
Polysilicon
Silicon
Nitride
Substrate
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MEMS Technology: Surface
Polysilicon
Silicon
Nitride
Substrate
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MEMS Technology: Surface
A combination of sacrificial and structural layers
Micro bridge
Rotating part
Structural Layer (Poly)
Sacrificial
Layer
Isotropic Etching
Isotropic Etching
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MEMS Technology: Surface
Micro bridge
Rotating part
Structural Layer (Poly)
Isotropic Etching
Isotropic Etching
Sacrificial Layer
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MEMS Technology: Surface
Silicon Nitride
Wafer (Silicon)
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MEMS Technology: Surface
Silicon Dioxide
Silicon Nitride
Wafer (Silicon)
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MEMS Technology: Surface
Poly-silicon
Silicon Dioxide
Silicon Nitride
Wafer (Silicon)
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MEMS Technology: Surface
Photolithography
Poly-silicon
Silicon Dioxide
Silicon Nitride
Wafer (Silicon)
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MEMS Technology: Surface
Silicon Dioxide
Photolithography
Poly-silicon
Silicon Dioxide
Silicon Nitride
Wafer (Silicon)
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MEMS Technology: Surface
Photolithography
Silicon Dioxide
Photolithography
Poly-silicon
Silicon Dioxide
Silicon Nitride
Wafer (Silicon)
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MEMS Technology: Surface
Photolithography
Poly-silicon
Photolithography
Silicon Dioxide
Photolithography
Poly-silicon
Silicon Dioxide
Silicon Nitride
Wafer (Silicon)
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MEMS Technology: Surface
Photolithography
Metal
Photolithography
Poly-silicon
Photolithography
Silicon Dioxide
Photolithography
Poly-silicon
Silicon Dioxide
Silicon Nitride
Wafer (Silicon)
An Introduction to Polysilicon Micromachining
89
MEMS Technology: Surface
Release
Photolithography
Metal
Photolithography
Poly-silicon
Photolithography
Silicon Dioxide
Photolithography
Poly-silicon
Silicon Dioxide
Silicon Nitride
Wafer (Silicon)
An Introduction to Polysilicon Micromachining
90
MEMS Technology: Surface
An Introduction to Polysilicon Micromachining
91
MEMS Technology: Surface
An Introduction to Polysilicon Micromachining
92
MEMS Technology: Surface
State-of-the-Art Surface Micromachining
Number of structural layers determine the
complexity/advancement
2-Level
3-Level
4-Level
Actuator
Actuator
Gear Hub
Drive link
Gear
5-Level
Actuator
Hub
Drive link
Gear Hub
Actuator
Movable plate
Simple sensors &
actuator
Gears
gear train
CRONOS and various
university technology
Pin-joints,
gear train
Multilevel
gears and
advanced MEMS
Sandia’s SUMMiT
technology
An Introduction to Polysilicon Micromachining
93
MEMS Technology: Surface
State-of-the-Art Surface Micromachining
2-Level
3-Level
5-Level
Pin-joints,
gear train
Multilevel
gears and
advanced MEMS
40mm
20mm
Simple sensors &
actuator
4-Level
Gears
gear train
CRONOS and various
university technologies
Sandia’s SUMMiT
technology
An Introduction to Polysilicon Micromachining
94
Sensors
An Introduction to Polysilicon Micromachining
95
Sensors: Transduction Principles
Physical Sensors
 Accelerometer
 Gyroscope
 Pressure sensor
 Mass flow sensor
 Temperature sensor
 Proximity sensor
 Magnetic sensor
Chemical Sensors
 Gas detector
 pH Detector


Micro-fluidics
Bio-analysis
An Introduction to Polysilicon Micromachining
96
Sensors: Acceleration
Transduction:
Piezoresistive
Capacitive
Resonance based
Analog Devices ADXL-50
integrated Accelerometer
with on board electronics
(BiCMOS)
Based on comb structure
and capacitive pick-up
Translation direction
180° out-of-phase signals
fed to this pair of
stationary electrodes
An Introduction to Polysilicon Micromachining
97
Sensors: Pressure




Piezoresistive
Bulk micromachining
Electrochemical etching
Anodic bonding to a
PYREX base
An Introduction to Polysilicon Micromachining
98
Sensors: Pressure
Cross-Sectional and Side Views of a commercial Bulk Micromachined
Pressure Sensor
An Introduction to Polysilicon Micromachining
99
Sensors: Gas


Adsorption


Foreign chemical species
enter interstitial or
bonding sites at or near
the surface
Changes the interface
properties
Absorption


Foreign chemical species
enter interstitial or
bonding sites within the
bulk material
Changes the materials
bulk properties
An Introduction to Polysilicon Micromachining
100
Sensors: Gas Concentration
Gas Sensor Principles
Metal Oxide Gas sensor
FET Gas Sensor
Adsorbed gas molecule
alters the conductivity
Adsorbed gas molecule
alters the threshold voltage
An Introduction to Polysilicon Micromachining
101
Sensors: Sandia Developments
An Introduction to Polysilicon Micromachining
102
Sensors: 3-axis Acceleration Sensor
Sandia National Labs
An Introduction to Polysilicon Micromachining
103
Sensors: Surface Micromachined Pressure Sensor
Sandia National Labs
An Introduction to Polysilicon Micromachining
104
Sensors: Combustible Gas Sensor
Sandia National Labs
An Introduction to Polysilicon Micromachining
105
Actuators
An Introduction to Polysilicon Micromachining
106
Actuators

Microactuators are the special contribution of
MEMS technology

Actuation Mechanisms
Electrostatic
 Thermal
 Magnetic
 Piezoelectric

Can be easily implemented
using most of the surface
micromachining technology
Silicon is neither piezoelectric
nor magnetostrictive, therefore,
additional thin films have to be
added to the microstructures
An Introduction to Polysilicon Micromachining
107
Actuators: Electrostatic
In surface micromachining, often popularly known as comb
drives.
Plate-1
V (volts)
d
Principle
y
Plate-2
x
Plate-3
Consider parallel plate 1 & 2
Force of attraction (along y direction)
Fp = ½ eA(V2/d2)
Consider plate 2 inserted between plate 1 and 3
Force of attraction (along x direction)
Fc = e (t/d) V2
Constant with x-directional translation
An Introduction to Polysilicon Micromachining
108
Actuators: Electrostatic
Comb Drives
CRONOS comb drive
Sandia cascaded comb drive
(High force)
An Introduction to Polysilicon Micromachining
Close-up view
of the shuttle
109
Actuators: Electrostatic
Squeeze Film: Texas Instruments DMD
An Introduction to Polysilicon Micromachining
110
Actuators: Thermal



Uses thermal expansion
for actuation
Small thermal expansion
is mechanical amplified
Very effective and high
force output per unit area
An Introduction to Polysilicon Micromachining
111
Actuators: Thermal
Cold arm
Direction of
actuation
Current
output
terminal
Ground
plane
Current
output pad
Hot arm
An Introduction to Polysilicon Micromachining
112
Actuators: Thermal
Acknowledging ZYVEX (www.zyvex.com)
An Introduction to Polysilicon Micromachining
113
Actuators: Motors
Electrostatic Micromotor
Wobble Micromotor
(also electrostatic)
Stator
Rotor
Stator
Hub
Hub
Rotor
An Introduction to Polysilicon Micromachining
114
Actuators: Motors
Sandia’s wedge
stepping motor
LIGA – electro-magnetic
microactuator
An Introduction to Polysilicon Micromachining
115
Actuators: Motors
Acknowledging Sandia National Labs (www.sandia.gov)
An Introduction to Polysilicon Micromachining
116
Actuators: Motors
Acknowledging Rotary Stepper Motor (www.zyvex.com)
An Introduction to Polysilicon Micromachining
117
Actuators: Motors
Linear Stepper Motor
An Introduction to Polysilicon Micromachining
118
Actuators: Motors
Vibromotor
An Introduction to Polysilicon Micromachining
119
Actuators: Steam Engine
Sandia National Labs
Vapour
Pvapour
Heater Element
Piston
Liquid
Cylinder




Structure immersed in working fluid (DI water)
Vapor bubble formed at right end
Vapor condenses at the piston end
Expansion of vapor bubble moves the piston
An Introduction to Polysilicon Micromachining
120
Actuators: Steam Engine
Sandia National Labs
Single piston
Multi piston
An Introduction to Polysilicon Micromachining
121
Actuators: Fluidics
Glass
micromachined
DNA purification
system
DRIE etched fluidic
handling system
An Introduction to Polysilicon Micromachining
122
Actuators: Fluidics


Muscle-cell
analysis
Plant pathogen
detector
 Dr. Paul Li,
2 cm
department of
chemistry, Simon
Fraser university
An Introduction to Polysilicon Micromachining
123
Actuators: Fluidics
Phase Transformation Fluid Pump
An Introduction to Polysilicon Micromachining
124
Actuators: Photonics
Fresnel Zone Plate and Laser Diode (UCLA)
UC Berkeley micromirror
Sandia micromirror
Clip-on and virtual retinal displays
An Introduction to Polysilicon Micromachining
125
Actuators: Movies
Acknowledging Sandia National Labs (www.sandia.gov)
An Introduction to Polysilicon Micromachining
126
Packaging
An Introduction to Polysilicon Micromachining
127
Packaging: Process








Wafer dicing (diamond saw)
Release and dry
Die attach
Wire bonding
Multi-chip modules and flip-chip bonding
Hermetic sealing (for physical sensor)
Potting to protect from shock
Orientation of sensors (inertial sensors)
An Introduction to Polysilicon Micromachining
128
Packaging: Release



Normal drying after deionized (DI) water rinse
creates a meniscus between the substrate and
microstructure
This process collapses the freestanding
microstructure
In general, want to avoid surface coming into
contact to avoid adhesion
An Introduction to Polysilicon Micromachining
129
Packaging: Release
Supercritical CO2 Drying
Solutions
 Make structures stiffer in Zdirection (high aspect ratio)
 Add dimples to reduce surface
contact area
 Treat surfaces to make them
hydrophobic
 Avoid creating the meniscus by
drying in supercritical CO2
 Freezing and sublimating
the solvent
An Introduction to Polysilicon Micromachining
130
Packaging: Electronics
CMOS Compatible Micromachining
Technique
Use an existing industrial CMOS technology as a base
Introduce special layout design techniques
Perform micromachining step as a post-process
Advantages
No need for a in-house fab
Can integrate microstructure and
electronics on the same chip
Disadvantages
Limited assortment of microstructures
A CMOS Micromachined
integrated IR emitter pixel
An Introduction to Polysilicon Micromachining
131
Packaging: Why Integrate?
Cost: Batch fabrication
Performance: Reduced parasitics
Manufacturability: Integrated contacts have higher yield
than wire bonds and flip-chip bonds
Reliability: Integrated systems are more reliable
than hybrids
Size: Offers the ultimate level of
miniaturization
An Introduction to Polysilicon Micromachining
132
MUMPs Examples
An Introduction to Polysilicon Micromachining
133
MUMPs Examples
Design
Layout Generation
Layout Tool
 L-Edit (Tanner Tools)
 Cadence
 AutoCAD
Masks for fabrication
Output File Format
 CIF
 GDS II
 DXF
An Introduction to Polysilicon Micromachining
134
MUMPs Examples




The Multi-User Micromachining Process
(MUMPs) is a polysilicon surface-micromachining
process
Provided to public by Cronos
Uses three structural layers
Uses two sacrificial layers
An Introduction to Polysilicon Micromachining
135
MUMPs Examples
Process Layers
 Nitride
 Polysilicon-0
 1st Oxide
 Polysilicon-1
 2nd Oxide
 Polysilicon-2
 Metal
Design Layers
 POLY0
 ANCHOR1
 POLY1
 ANCHOR2
 P1P2VIA
 POLY2
 METAL
An Introduction to Polysilicon Micromachining
136
MUMPs Examples
Design layers’ functions
Poly-0
Defines the geometry of Polysilicon-0
Anchor-1
Attaches Poly-1 to Poly-0 or attaches Poly-1 to
Nitride
Poly-1
Defines the geometry of Poly-1
Anchor-2
Attaches Poly-2 to Poly-0 or attaches Poly-2 to
Nitride
Poly1-Poly2-Via
Attaches Poly-2 to Poly-1
Poly-2
Defines geometry of Poly-2
Metal
Defines geometry of metal.
Preferably on top of Poly-2
An Introduction to Polysilicon Micromachining
137
MUMPs Examples
Design layers’ functions
Poly-0
First-Oxide
Anchor-1
Poly-1
Second-Oxide
Silicon Nitride
Anchor-2
Poly1-Poly2-Via
Poly-2
Silicon Substrate
Metal
An Introduction to Polysilicon Micromachining
138
MUMPs Examples
Sample Design: Hinge
Hinge
Poly-1
Anchor-2
Poly-2
Metal
An Introduction to Polysilicon Micromachining
139
MUMPs Examples
Dimples

Rotor without dimples

Rotor with dimples
When flat structures are
released the surface
contact will glue parts
together and prevent
movement
Very small indentations
(bumps) created on Poly1 and Poly-2 so that when
structures are released
they rest on the bumps
An Introduction to Polysilicon Micromachining
140
MUMPs Examples
Sample Design: Thermal Actuator
Poly-0
Anchor-1
Dimple
Poly-1
P1-P2 Via
Poly-2
Metal
An Introduction to Polysilicon Micromachining
141
MUMPs Examples
Sample Design: Gear Train
Anchor-1
Dimple
Poly-1
P1-P2 Via
An Introduction to Polysilicon Micromachining
Poly-2
142
MUMPs Examples
Sample Design: Gear Train
An Introduction to Polysilicon Micromachining
143
MUMPs Examples
Sample Design: Why double thickness structures
Pawl can slip
underneath
gear teeth
An Introduction to Polysilicon Micromachining
144
MUMPs Examples
Sample Design: Why double thickness structures
Teeth between
gear and motor
can slip
An Introduction to Polysilicon Micromachining
145
MUMPs Examples
Sample Design: Tower
Poly-0
Dimple
Anchor-1
P1P2V
Poly-1
Poly-2
Anchor-2
An Introduction to Polysilicon Micromachining
Metal
146
MUMPs Examples
Simulation



At device level, simulation
requires building 3D
model.
Layout  3D model
www.sfu.ca/immr/



ANSYS
Cif-input to 3D output.
Ansys
VRML
 MEMS Pro
 Intellisuite
An Introduction to Polysilicon Micromachining
147
MUMPs Examples
Mirrors
An Introduction to Polysilicon Micromachining
148
MUMPs Examples
Bistable Mechanism
An Introduction to Polysilicon Micromachining
149
MUMPs Examples
Bistable Mechanism
An Introduction to Polysilicon Micromachining
150
Design Issues
An Introduction to Polysilicon Micromachining
151
Design Issues: Topography



In the MUMPs process, all
growth is conformal
Processing steps depend
heavily on the preceding
steps
Managing topology is an
important
An Introduction to Polysilicon Micromachining
152
Design Issues: Topography
 Thin films conform closely to


the topology of the previously
deposited and patterned layers
Topology can trap a structure
that was intended to move
freely
Unless the preceding layers are
designed to ensure the upper
structural layers are flat where
needed, the induced topology
can have detrimental effects on
device operation
An Introduction to Polysilicon Micromachining
153
Design Issues: Topography



Topography can create
structural weaknesses
Topography provides
stress concentration
points and beam thinning
may occur due to variation
in film thickness across
steps
Problems are
compounded since
lithography is more
difficult along height
changes
An Introduction to Polysilicon Micromachining
154
Design Issues: Topography
 Both actuators are composed




of a wide arm and narrow arm
Differential heating due to an
applied current causes
differential thermal expansion
This was supposed to cause
the arm to curve upwards
However, the wide arm has
conformed and is no longer flat
The wide arm’s bending
stiffness is thus significantly
higher, reducing any motion
An Introduction to Polysilicon Micromachining
155
Design Issues: Residual Stresses
 
 Uniform stress is the average stress through the thickness of the film
 For singly supported structures, one should expect a dimensional


change as the structure relaxes to a non-stressed state
Doubly supported structures can be more reliable, in that their length
will remain fixed
Over a critical compressive stress they will buckle
An Introduction to Polysilicon Micromachining
156
Design Issues: Residual Stresses


A non-uniform stress is a
residual stress with a
gradient
Non-uniform stresses are
both more difficult to
handle theoretically and
more difficult to measure.
An Introduction to Polysilicon Micromachining
157
Design Issues: Ground Planes
 Ground planes are necessary



to electrically shield devices
from the wafer
Conducting bodies at different
potentials will experience an
attractive force; this includes
surface micro-machined
devices and the substrate
If the attractive force is strong
enough, the device will be
pulled down to the substrate
surface
Even if the device does not
adhere, significant friction will
be present
An Introduction to Polysilicon Micromachining
158
Design Issues: Double-thickness


Contact surfaces should
be avoided in surface
micro-machined devices .
Where contact surface are
needed, double-thickness
parts will often be needed


Because they are so thin,
surface micromachined
devices will have
significant vertical
flexibility
There may be bowing.
An Introduction to Polysilicon Micromachining
159
Design Issues: Tethers




Free moving structures
will flap around during
release
This can damage the
device itself as well as
nearby devices
The device should be
tethered to the wafer
surface
These tethers are broken
after release
An Introduction to Polysilicon Micromachining
160
Design Issues: Dimples



Dimples are small bumps
on the underside of the
first structural layer
A short wet etch is used to
isotropically etch small
cavities the first sacrificial
layer
The first structural layer
will then have bumps, as it
will conformally fill the
holes
Dimple
Dimple
An Introduction to Polysilicon Micromachining
Dimple
161
Design Issues: Raised Structures


Hinges allow parts to
rotate
Properly design parts can
rotate off the wafer
surface
An Introduction to Polysilicon Micromachining
162
Design Issues: Raised Structures
An Introduction to Polysilicon Micromachining
163
Design Issues: Raised Structures
An Introduction to Polysilicon Micromachining
164
Design Issues: Raised Structures
An Introduction to Polysilicon Micromachining
165
Design Issues: Raised Structures
An Introduction to Polysilicon Micromachining
166
Please fill out the course
evaluation
Thank-you
An Introduction to Polysilicon Micromachining
167
Selected References






















S. Wolf and R. N. Tauber, Silicon Processing for the VLSI Era, Volume 1 – Process Technology,
California, Lattice Press 1986.
S. Ghandi, VLSI Fabrication Principles, Silicon and Gallium Arsenide, Second Edition, John Wiley &
Sons, Inc., New York, 1994.
S. M. Sze, VLSI Technology, McGraw-Hill, 1983.
Madou M., Fundamentals of Microfabrication, CRC Press, New York, 1997.
M. Parameswaran, M. Paranjape, Layout Design Rules for Microstructure Fabrication Using
Commercialy Available CMOS Technology, Sensors and Materials, 5, 2, 1993, pp. 113-123.
How Semiconductors are Made, Harris Semiconductor
Ernest Garcia, Jeff Sniegowski, Surface Micromachined Microengine, Sensors and Actuators A 48
(1995), pp2O3-214.
Kurt E. Peterson , Silicon as a Mechanical Material, Proc. of IEEE, vol 70 no 5, May 1982.
Joseph Shigley , Mechanical Engineering Design, 1989, ISBN 0-07-056899-5
S.M. Sze , Semiconductor Sensors, 1994, John Wiley & Sons, ISBN 0-471-54609-7
J. J. Sniegowski and E. J. Garcia, Surface Micromachined Gear Trains Driven by an On-Chip
Electrostatic Microengine, IEEE Electron Device Letters, Vol. 17, No. 7, 366, July 1996.
J. J. Sniegowski, S. M. Miller, G. F. LaVigne, M.S. Rodgers and P.J. McWhorter, Monolithic GearedMechanisms Driven by a Polysilicon Surface-micromachined On-Chip Electrostatic Microengine,
Solid-State Sensor and Actuator Workshop, Hilton Head Is., South Carolina, June 2-6, 19969 pp. 178182.
J. J. Sniegowski, Moving the World with Surface Micromachining, , Solid State Technology, Feb.
1996, pp. 83-90.
An Introduction to Polysilicon Micromachining
168
WWW MEMS References

















http://www.mems.sandia.gov
http://www.onixmicrosystems.com/
http://www.siliconsense.com/
http://www.intellisense.com/index.html
http://www.siliconlight.com/
http://www.css.sfu.ca/sites/immr/
http://www.memsrus.com/
http://www.zyvex.com/Research/MEMS/M
EMS.html
http://mems.engr.wisc.edu/liga.html
http://www.biomems.net/
http://bsac.eecs.berkeley.edu/
http://www.cmc.ca/beams.html
http://www.ece.cmu.edu/~mems/
http://www.mech.kuleuven.ac.be/
http://mishkin.jpl.nasa.gov/CSMT_PAGE
http://muresh.et.tudelft.nl/dimes/index.html
http://wwwbsac.eecs.berkeley.edu/~ptjones/databas
e.html
















http://dolphin.eng.uc.edu/index.html
http://mems.eeap.cwru.edu
http://www.ida.org/MEMS/
http://www-mtl.mit.edu/home.html
http://synergy.icsl.ucla.edu/index.html
http://www.rgraceassoc.com
http://cdr.stanford.edu/
http://www.shef.ac.uk/uni/projects/mesu/
http://www.mems.ecs.soton.ac.uk/title.htm
http://www.trimmer.net/
http://www-mtl.mit.edu/semisubway.html
http://www2.ncsu.edu/eos/project/erl_html
/erl_damemi.html
http://www.laas.fr/mc2_Europractice/
http://www.tanner.com/
http://www.omminc.com/
http://www.microsensors.com/
An Introduction to Polysilicon Micromachining
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An Introduction to Polysilicon Micromachining
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An Introduction to Polysilicon Micromachining
171