Transcript A brief history of MEMS fabrication

A brief history of MEMS fabrication
Chang Liu
Micro Actuators, Sensors, Systems Group
University of Illinois at Urbana-Champaign
Chang Liu
MASS
UIUC
To Do …
• Get a better diagram of MOS process flow.
Chang Liu
MASS
UIUC
Outline
• Traditional silicon micromachining technology
– Common microfabrication technology for IC
– Bulk micromachining
• Etching, bonding, planarization
– Surface micromachining
• Suspended structures, antistiction methods, 3D microstructures
– Methods for merging micromechanics and IC
• Extended microfabrication technology in 90’s
– LIGA
– Deep reactive ion etching
– Polymer based microfabrication
• Future foundry based processes
Chang Liu
MASS
UIUC
A Standard IC Process
• Draw a diagram of a circuit.
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http://www.chips.ibm.com/gallery/
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UIUC
Basic Fabrication Processes
• Deposition (Material addition)
– spin coating, evaporation, electroplating, reactive growth, CVD,
sputtering
• Lithography
– various wavelengths, mask making, alignment, exposure
• Etching (Material removal)
– wet chemical etching, dry plasma etching, gas phase etching,
• Wafer bonding
– Silicon on insulator wafers (SOI)
• Packaging
– adhesion, wire bonding
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MASS
UIUC
From wafer to device
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MASS
UIUC
Chang Liu
MASS
UIUC
Processing Equipments
A tour of lab is arranged in the middle of semester
Wafer aligner
and exposure tool
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Metal Evaporator
Plasma etcher
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UIUC
Micro Fabrication Technology
start
Cycle 1
Cycle 2
Starting
wafer
Cycle 3
Cycle 4
Cycle 5
Cycle 6
MEMS
subtracting
(etching)
pattern
Adding
(deposition)
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MASS
UIUC
Silicon Bulk Etching
• Anisotropic Etching
• Isotropic etching
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MASS
UIUC
Chang Liu
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UIUC
Chang Liu
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UIUC
First Idea for Surface Micromachining …
• Physicist Richard Feynman
– “There is plenty of room at the bottom”
• Excerpt
– How can we make such a device? What kind of manufacturing
processes would we use? One possibility we might consider, since
we have talked about writing by putting atoms down in a certain
arrangement, would be to evaporate the material, then evaporate
the insulator next to it. Then, for the next layer, evaporate another
position of a wire, another insulator, and so on. So, you simply
evaporate until you have a block of stuff which has the elements--coils and condensers, transistors and so on---of exceedingly fine
dimensions.
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MASS
UIUC
Polysilicon as a Mechanical Material
• Invented by Dr. Muller and Dr. Howe of Berkeley
• Established sacrificial etching process using
– polysilicon as a mechanical structural material
– oxide as a sacrificial material
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MASS
UIUC
Surface Micromachining
Fabrication Process for Micro Motor
(1st pass description)
Learning objectives:
How to represent process using cross-sectional view?
Build ability to correlate mask and sideviews.
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MASS
UIUC
Step 1: Starting wafer
• Mask top view
• Side view
mask
Start with blank silicon wafer (one side polished with optical finish). Wafer orientation is
not critical. The thickness of the wafer is not drawn to scale- the typical thickness of 0.30.5 mm.
Chang Liu
MASS
UIUC
Step 2: Deposition of sacrificial layer
• Top view (mask)
• Side view
mask
Deposit silicon oxide film (with phosphorous doping) as the sacrificial layer.
- conformal coating
- thickness 1-3 micrometers
Chang Liu
MASS
UIUC
Step 3: Deposition of structural layer
• Top view (mask)
• Side view
mask
Deposit polycrystalline silicon film (without phosphorous doping) as the structural layer.
- conformal coating
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MASS
UIUC
Step 4: Pattern the top polysilicon layer
• Top view (mask)
• Side view
Pattern the silicon layer with the first mask to form the shape of the rotor and the hole for
the anchor.
Chang Liu
MASS
UIUC
Step 5: Deposit a second sacrificial layer
• Mask top view
• Side view
mask
Conformal deposition of P-doped oxide again.
Chang Liu
MASS
UIUC
Step 6: Pattern and Etch the sacrificial layers
• Top view (mask)
• Side view
Pattern the wafer with the photoresist layer and the first mask.
Using HF solutions to etch through the two oxide layers. Lateral etching will occur and the
dimension control is critical.
Chang Liu
MASS
UIUC
Step 7: Deposit polysilicon structural layer.
• Top view (mask)
• Side view
mask
Conformal deposition of polysilicon again.
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MASS
UIUC
Step 8: Pattern Polysilicon.
• Top view (mask)
• Side view
mask
Pattern the top layer polysilicon to form the confinement structure and anchor.
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MASS
UIUC
Step 9: Sacrificial layer removal and freeing of
structures
• Top view (mask)
• Side view
mask
Remove the oxide using 49% HF solutions, which etches oxide fast (1 micron/minute) and
the polysilicon slowly.
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MASS
UIUC
High Aspect Ratio Devices
Thick photoresist
*:
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Lithographie, galvanoformung, abformung
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UIUC
New Materials and Processes
Inorganic Materials and processes
• High temperature materials
processing (SiC)
• Silicon Ge (SiGe)
• Diamond (electrical
conductance and mechanical
toughness)
Organic Materials
• Silicone elastomer
• Elastic polymer
• Chemical vapor deposition of
plastic films (Parylene)
• Electroactive Materials
• …
•
•
•
•
•
Laser Micromachining
Deep Reactive Ion Etching
Focused ion beam etching
Chemical mechanical polishing
Permanent magnet and
electromagnetic materials
• Rapid prototyping
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MASS
UIUC
Micro guitar – Cornell University
Sandia
Photonic lattice
IBM Supercone
tip
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MASS
UIUC
Man-made Submarine … in your artery
MicroTEC Inc.
• RMPD is a micro stereo lithography method for rapid creation
of 3-D micro structures of any shape as prototypes or for series
production
Das micro-U-Boot, das kleinste U-Boot der Welt!
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www.microTEC-D.com Duisburg, Germany
MASS
UIUC
Chang Liu
MASS
UIUC
Focused Ion Beam Etching
•
http://www.iis-b.fhg.de/en/arb_geb/technology_an_fib.htm
• energy: 30 keV
• current: 6 pA - 7 nA
• resolution: 16 nm
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MASS
UIUC
FIB process (continued)
•
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http://www.msm.cam.ac.uk/dmg/research/fib/micromachine/index.html
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UIUC
Ferrari MEMS vs. Suzuki MEMS
Ferrari 348 1989
Suzuki Swift 1997
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MASS
UIUC
MUMPS
• 3 poly surface micromachining
• Process
• One process, different devices.
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MASS
UIUC
MEMS Foundry MEMS Exchange
• Distributed, Virtue fab
– UC Berkeley
– Cornell Nanofabrication
Facility (CNF)
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www.mems-exchange.org
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UIUC
Polymer MEMS
• Polymer materials as substrate
–
–
–
–
Replaces silicon
Lower costs
Examples: liquid crystal polymer, polyimide, glass
Drawbacks: cannot integrate circuitry. However, circuits can be
wire-bonded to the polymer chip
• Polymer as structures
– Replaces silicon, silicon nitride, silicon oxide, etc
– Lower costs, greater mechanical flexibility
– Examples: Parylene, photoresist, polyimide
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MASS
UIUC
LCP for MEMS packaging
• Copper-LCP laminates for
flexible circuit boards
• LCP thermal bonding for
environmental encapsualtion
• LCP substrates for robust
devices
15mm
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MASS
UIUC
Tactile Sensor Fabrication
• Double-sided alignment,
deposition and patterning of NiCr
Strain gauges and Al RIE mask
on 2mil (50μm) thick LCP
• Dry etching (RIE O2 plasma) of
35μm deep, 500μm square
backside cavity, remove Al
• Deposition and patterning of Au
interconnects
• Spin and pattern 20μm tall
polyimide tactile bumps
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MASS
UIUC
Tactile Sensor Operation
• Converts normal applied load into
change in resistance
• Array can image tactile contact
• Similar fabrication techniques can
provide shear data
Applied Load
Tactile Bump
Membrane
Perimeter
Compressive Strain (x-dir)
Strain Gauge
Area
Tensile Strain (x-dir)
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MASS
UIUC
Conclusions
• Microfabrication technology is a dynamically advancing field.
– Technology push
• New microfab processes and materials are developed in response to
application needs
– Technology pull
• New fabrication techniques enables new devices and new applications
• Micromachining involves silicon, glass, and polymer materials,
not just silicon alone.
• The microfabrication process is an integral part of the device
design and material selection. The capability and practicality of
microfabrication must be taken into consideration when
considering candidate designs.
Chang Liu
MASS
UIUC