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Prof P.S. Gandhi, ME, IIT Bombay

Lecture 7: Silicon Micromachining

Prasanna S. GandhiAssistant Professor,Department of Mechanical Engineering,Indian Institute of Technology, Bombay,

MEMS: Fabrication

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Prof P.S. Gandhi, ME, IIT Bombay

Recap: Last Class

Plasma fundamentals Processes

Material removalEtchingReactive Ion Etching

Material additionSputtering

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Prof P.S. Gandhi, ME, IIT Bombay

Today’s Class

SFB + DRIE Surface micromachiningLift-off processLIGAFabrication examples:

Pressure sensor

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Prof P.S. Gandhi, ME, IIT Bombay

DRIE

Etch-deposition alternate cycles: patent by Robert Bosch GmbH in inductively coupled plasma (ICP)-RIELimitation: etch rates dependent on aspect ratioComparison of dry vs wet etching for Si and other materials

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Prof P.S. Gandhi, ME, IIT Bombay

Silicon Fusion Bonding (SFB)

Silicon on Insulator (SOI) technologyProcess

CleaningNaOH solution at 100o (hydration step OH groups on bond surface hydrophilic)Hold together at 800-1100o

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Prof P.S. Gandhi, ME, IIT Bombay

Silicon Fusion Bonding + DRIE

Combination of CMOS electronics with MEMS structure

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Prof P.S. Gandhi, ME, IIT Bombay

Surface Micromachining

Combination of lithography and etchingDefined with respect to deposited films instead of Si substrate

List process detailsAny problems??

Wafer

U-V RAYS

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Prof P.S. Gandhi, ME, IIT Bombay

Surface Micromachining

At DARPA, USA

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Prof P.S. Gandhi, ME, IIT Bombay

Electroplating

SUBSTRATE

ADHESION LAYERCOPPER LAYER

U V LIGHT

OPTICAL MASK

CHROMIUM LAYER

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Prof P.S. Gandhi, ME, IIT Bombay

LIGA

Combined Lithography, electroplating and molding process for high aspect ratio (depth/width) structures

SUBSTRATE

PMMA RESIST

MASK

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Prof P.S. Gandhi, ME, IIT Bombay

LIGA

Micromotor fabricated using LIGA

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Prof P.S. Gandhi, ME, IIT Bombay

Pressure Sensor

Process??

Applications

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Prof P.S. Gandhi, ME, IIT Bombay

Conclusions

Surface micromachiningDeep RIE + Silicon fusion bondingLIGAFabrication of pressure sensor

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Prof P.S. Gandhi, ME, IIT Bombay

Next class

Extra class: Electronic Packaging

Non-conventional machining processes at micro-scale

Electro discharge machining