Overview of MEMS and Microtechnology Fall 2014

Kevin M. Walsh, PhD

ECE543

Overview of Microtechnology

and MEMS

1

• BACKGROUND -MEMS definition,

introduction, history, market survey, and

references

• MATERIAL ISSUES

• uFAB and uMACHINING PROCESSES

• APPLICATIONS and EXAMPLES

• CLEANROOM CONSIDERATIONS

• FUTURE DIRECTIONS

Outline

2

Micro-Electro-Mechanical Systems (MEMS) is the

integration of mechanical elements, sensors, actuators, and

electronics on a common substrate through the utilization of

microfabrication technology or “microtechnology”.

So what exactly is MEMS?

3

“Micromachining” formally refers to the bulk

anisotropic etching of crystalline silicon using

traditional batch fabrication techniques.

“Micromachining” informally refers to the complete

combination of processing technologies used to

fabricate miniature MEMS-based devices and systems,

such as LOC systems.

…and how about micromachining?

source: Sandia NL

Source: UofL Source: UofL 4

MEMS and Micro-

machining Examples

pressure sensors

accelerometers

flow sensors

inkjet printers

deformable mirror devices

gas sensors

micromotors

microgears

lab-on-a-chip systems (LOC)

5

MEMS - the next evolutionary step on the microtechnology

ladder.

Microtechnology - refers to the “miniaturization” technology

that was originally developed for the fabrication of electronic

integrated circuits (ICs)

MEMS - resulted when microtechnology was applied to the

production of devices, structures, and systems that were

more than just electronic in functionality (1980)

Source: UW Source: UofL

6

USA - MEMS (micro-electro-mechanical systems)

[name officially adopted in 1989 by a group of 80 researchers at Salt

Lake City for the Micro-Tele-Operated Robotics Workshop]

Europe - MST (micro-systems technology)

Japan - Micromachines

A ROSE is a rose !!

7

Why use micromachining?

• miniaturization

• cost/performance advantages (due to batch fabrication)

• integration with electronics

• faster devices (speed usually scales with size)

• lower power consumption

• improved accuracy, reliability, and reproducibility

• new effects and products due to miniaturization/microfab

8

MEMS/Micromachining Texts

Micromechanics and MEMS: Classic and Seminal Papers to 1990 by W.

Trimmer (editor)

Micromachined Transducers Sourcebook by G. Kovacs

Fundamentals of Microfabrication by Marc J. Madou

Microsensors by Richard S. Muller, Roger T. Howe, Stephen D.

Senturia, R. Smith (editors)

An Introduction to MEMS Engineering by Nadim Maluf

Silicon Micromachining by Elwenspoek and Jansen

MEMS WWW Bookstore: http://mems.isi.edu/bookstore/

Handbook of Microlithography, Micromachining and

Microfabrication (Vol. 2) by P. Rai-Choudhury (editor)

9

MEMS/Micromachining Journals

Sensors and Actuators by Elsevier Science, Netherlands

Journal of MEMS by ASME and IEEE, USA

Sensors Magazine by Helmers Publishing, USA

Journal of Micromechanics and Microengineering by Institute of

Physics, United Kingdom

Micromachine Devices, a companion to R&D Magazine, by Cahners

Business Information, USA

IEEE Sensors Journal by IEEE, USA (new)

10

Dedicated MEMS/Micromachining Issues

Forbes ASAP, April 2, 2001

MRS Bulletin, Vol. 26, No. 4, April 2001

Proceedings of the IEEE, August 1998

Microengineering and MEMS by Dr. Daniel Banks

http://www.dbanks.demon.co.uk/ueng/

UofL MEMS Resources

http://mitghmr.spd.louisville.edu/mems_links.html

MEMS Clearinghouse – http://mems.isi.edu/

MEMS Exchange - http://www.mems-exchange.org/

Various LOC Web Sites

Dedicated MEMS/Micromachining Web Sites

11

Traditional Microelectronic Fabrication Texts

Semiconductor Devices: Physics and Technology by S. M. Sze

Semiconductor Integrated Circuit Processing Technology by W. R.

Runyan and K. E. Bean

Introduction to Microelectronic Fabrication by Richard C. Jaeger

Silicon Processing for the VLSI Era: Volume 1 – Process Technology

by S. Wolf and R. N. Tauber

The Science and Engineering of Microelectronic Fabrication by S.

A. Campbell (includes a chapter on MEMS)

Modern Semiconductor Fabrication Technology by P. Gise and R.

Blanchard

Microchip Fabrication by Peter Zant

12

MEMS…

…evolved from the Microelectronics Revolution

IC Industry Timeline

1999

10 million transistors

1947

single transistor

1958

first IC

History

13

MEMS Timeline 1980

2030

1999

(1.3 million micro-mirrors) TI DMD ?

Bulk micromachined

pressure sensor

14

The Opportunity for MEMS Technology

15

MEMS compared to ICs

Source: Madou

2001 $14B (5% of IC market) $300B

2009 $100B Source: Forbes

- 2000 BMW 740i has over 70 MEMS sensors - 16

MEMS Sectors and Forecast

Source:

Maluf

17

MEMS Technology: Materials Issues

Source: Madou 18

MEMS Technology: Materials Issues

Source: Madou 19

The MicroTechnology/MEMS Tool Set …

cleanroom plus microfab processes

+

So, you’re interested in MEMS; what do you need?

20

Standard IC Processes

Source:

CWRU

Source: Jaeger

1

2 3

21

Standard IC Processes

• Sputtering

• Evaporation

• Thermal Oxidation

• CVD (chemical vapor deposition)

• Spinning

• Epitaxy

(1) Deposit/Grow Thin Films oxidation

spinning sputtering sputtering 22

Standard IC Processes

• Photolithography

• Etching Techniques (wet, dry/RIE)

(2) Pattern Thin Films

RIE system photolithography

patterned wafer

23

• thermal diffusion

• ion implantation

(3) Introduce Dopants - to form electrically-active

regions for resistors, diodes, transistors, etc.

thermal diffusion furnaces solid source doping

Standard IC Processes

24

Example of Deposition

Thermal Oxidation

• dry oxide – slower growth, denser, better quality

• wet oxide – faster growth rate (~10x)

• MEMS applications – barrier masks for etching

and doping, dielectrics for devices

dry

wet

Source:

Jaeger

dry oxidation 25

Oxidation Kinetics

Source: Jaeger

Wet oxidation is faster because water

vapor has a higher solubility in

silicon dioxide than gaseous oxygen

(i.e larger N0 in graph to right and

therefore larger flux, J)

26

Dry Oxidation

Source: Sze

note crystal orientation dependence

(111) Si has highest packing density 27

Wet Oxidation

Source: Sze

28

Techniques for Determining Oxide Thickness

Source: Campbell

• ellipsometry – laser polarization technique (expensive)

• profilometry – mechanical stylus technique (requires a step)

• color chart - inexpensive

29

Sputtering

Thin film deposition technique in which energetic ions, typically Ar+,

bombard a target and displace atoms which are then transported to the

wafer surface, where deposition occurs. Both conductive and insulating

materials can be sputtered.

Source: Jaeger 30

Evaporation

Thin film deposition technique in which material is evaporated

from a solid source in a high vacuum environment using thermal

or e-beam energy.

Source: Sze (Semi Sensors)

31

Comparison of Evaporation and

Sputtering Deposition

Source: Gise

32

Spinning

Thin film deposition technique used for polymers (such as

photoresists), spin-on dopants and SOG (spin-on glass). Low

cost capital equipment $5-10K.

Source: Sze (Semi Sensors)

33

a) oxidation

b) spin resist

c) align/expose

d) develop

e) oxide etch (wet

or dry/RIE)

f) strip resist

g) patterned oxide

“Photolithography”

Source:

Jaeger

Thin Film Patterning

Typical Photolithographic

Steps

34

Photoresist Types

Source:

Zant

• positive – better resolution, less

pinholes, liftoff compatible

• negative – faster exposure, better

adhesion, cheaper

IR mask aligner

35

Other Photolithographic Issues

• photomask polarity – light or dark field

• photoresist polarity – positive or negative

• etch vs liftoff

• aligners - contact vs proximity vs projection (steppers)

• aligners – frontside vs backside (IR)

• non-optical lithography – e-beam, x-ray, soft

IR mask aligner Liftoff 36

Example of Impurity Doping

Thermal Diffusion

• liquid, solid, or gaseous dopant sources

• highest doping concentration at surface

• high temp process – oxide masks

• deep junction depths possible

• MEMS applications – piezoresistive

elements and p+ etch stops

Source:

Jaeger

diffusion furnaces

37

Source:

Jaeger

Thermal Diffusion Process

• MEMS applications – piezoresistive elements and p+ etch stops 38

Example of Impurity Doping

Ion Implantation

Source:

Jaeger

39

Ion Implantation

• precise control of doping profile (through specie, dose, energy)

• low temp process (can use resist as mask)

• buried peak concentrations

• expensive capital equipment

• MEMS applications – piezoresistive elements, p+ etch stops, SIMOX

Source: Jaeger Source: Sze

40

Micromachining Processes

Source: Maluf

41

Micromachining Processes

• subtractive (etching) process

• wet vs dry etching

• isotropic vs anisotropic etching

Bulk Micromachining

42

Typical Micromachining

Etch Profiles

Source: Maluf

“RIE”

RIE - reactive ion etch 43

• Using (100) silicon wafer with SiO2 mask

Bulk Micromachining

44

Typical Bulk Micromachining

Etching Setup

45

Bulk Micromachining

using (100) silicon

Examples

Source: Maluf

Source: Madou

46

Bulk Micromachining Rules for (100) Si – Rule 1 “Features misaligned to the <110> wafer flat will be undercut”

Source: UofC 47

Source: Elwenspoek

Bulk Micromachining Rules for (100) Si – Rule 1b “Any feature will eventually result in the largest inverted pyramidal

rectangular pit that can be circumscribed around that feature”

48

Source: Ristic

Bulk Micromachining Rules for (100) Si – Rule 1b “Any feature will eventually result in the largest inverted pyramidal

rectangular pit that can be circumscribed around that feature”

Source: UofL

49

Bulk Micromachining Rules for (100) Si – Rule 2 “Convex (outside) corners will be undercut due to fast-etching

exposed secondary planes”

Source: Elwenspoek 50

Source: Ristic

Source: Ristic

Source: Ristic Source: Wise

51

Micromachining Processes

Bulk Micromachining – Corner Compensation

Source: Maluf Source: UofL

• Technique for minimizing corner erosion by adding

additional mask features at the corners. Can result in near

perfect mesa structures.

52

• Isotropic

• HNA (hydroflouric, nitric and acetic acid)

• also called “poly-etch”

Most Popular Silicon Bulk

Micromachining Wet Etchants

• Anisotropic

• Potassium Hydroxide (KOH)

• EDP

• Hydrazine

• TMAH

53

Comparison of Silicon Micromachining Etchants

Source: Maluf

54

Etchants for Other MEMS Thin Films

Source: Maluf

55

Micromachining software

ACES – PC based Micromachining Simulation Software

(http://galaxy.ccsm.uiuc.edu/aces/)

56

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

Micromachining Processes

• Timed etch stop

• Boron (p+) etch stop

• Electrochemical (pn junction) etch stop

• Buried oxide etch stop (BESOI, SIMOX)

Bulk Micromachining Etch Stop Techniques

57

Micromachining Processes

Boron (p+) Etch Stop Technique

Source: Sze (Semiconductor Sensors)

58

Boron (p+) Etch Stop Examples

Source: Sze (Semi Sensors)

59

Boron (p+) Etch Stop Examples

Source: Kovacs 60

Micromachining Processes

Electrochemical (pn junction) Etch Stop Technique

Source: Kovacs

61

Electrochemical Etch Stop Example

Source: Kovacs

Source: Maluf

62

Micromachining Processes

• Similar to electrochemical etch stop process except the

p+ region is replaced with a buried oxide layer, which

functions as an etch stop to most anisotropic etchants.

• Bonded and Etched-back Silicon On Insulator (BESOI)

• Separation by Ion Implantation of Oxygen (SIMOX)

• Requires no voltage bias.

Buried Oxide Etch Stop Technique

Source: Kovacs

oxide

63

Micromachining Processes

• additive process

• structural & sacrificial layers

Surface Micromachining

Source: Sandia

64

• MUMPS (Cronos)

• SAMPLES (Sandia)

Surface Micromachining Process

Source: Sze (Semi Sensors)

MEMS Foundries

65

Micromachining Processes

• glass-Si anodic bonding

• si-si fusion bonding (SFB)

• eutectic bonding

• low temp glass bonding

• thermal compression

Wafer-Level Bonding

Source: EV

Source: Maluf

Source: UofL

66

• glass-Si field assisted bonding technique

• requirements

• similar TCEs (Corning 7740)

• clean & smooth surfaces

• <1um rms roughness

• slightly conductive glass

• elevated temperature (200-500C)

• high voltage (200-1000V)

Anodic or Electrostatic (ES) Bonding

Source: Sze

Source: UofL

67

Silicon Fusion Bonding (SFB)

Source: Sze

(Semi Sensors)

hydrophilic

surfaces

68

Micromachining Processes

• Single Crystal Reactive

Etching and Metalization

• CMOS compatible

• used by EG&G IC for

accelerometers

• 20-30 um depth limit

SCREAM

Source: Maluf Source: Elwenspoek 69

Micromachining Processes

• high density ICP plasma

• high aspect ratio Si structures

• cost: $500K

• vendors: STS, Alcatel, PlasmaTherm

Deep Reactive Ion Etching (DRIE)

Source: LucasNova

Source: AMMI Source: STS Source: STS 70

DRIE Etching Process – Gas Cycling

Source:

Kovacs

71

Micromachining Processes

• electroless plating and electroplating

techniques for producing thick films

• thick patterned resists used as molds

Plating

Source: Carl Suss

Copper

structures

72

Micromachining Processes

• uses x-ray lithography (PMMA resist), electrodeposition and molding to

produce very high aspect ratio (>100) micro-structures up to 1000 um tall

(1986)

LIGA (lithographie, galvanoformung, abformtechnik)

Source: Madou

Source: Kovacs 73

Micromachining Processes

• uses optical epoxy negative-resist developed by IBM to produce high

aspect ratio micro-structures (1995)

Poor Man’s LIGA

Source: Maluf

UofL Micro-reaction wells: 150 um wide,

120 um tall, 50 um wall thickness

74

Ultra- High-Precision Micromilling

and Microdrilling

Vibration isolated

• 1 ton block of granite

• Hydraulic suspension system

Computer-controlled laser-guided positioning system

• Air bearings

• X-Y stage resolution < 10 nm

• Z-axis resolution >50 nm

• (Linear Encoder)

Spindle speed = 20,000 rpm

G-code programming language

Tools – High Speed Tool Steel or Tungsten Carbide

Source: Dover Instruments 75

Materials Micro-milled/drilled

Plastics:

• PMMA (Top), Lexan,

Teflon, nylon, Epoxy, etc.

Metals:

• Molybdenum (Bottom),

aluminum, copper,

stainless steel, mild steel,

gold, titanium, tantalum,

tungsten, graphite, etc.

Others:

• PZT, silicon, Pyrex.

Source: Dover Instruments 76

• bulk micromachining

• silicon fusion bonding (SFB)

• DRIE

Combining uMachining

Processes

Source: LucasNova

Source: Maluf 77

Micromachining Tricks

Source: Kovacs

78

Other Micromachining Processes

• Chemical Vapor Deposition (CVD, LPCVD, PECVD)

• Epitaxy

• Vapor Phase Etching – xenon diflouride non-plasma

isotropic dry etch

• Laser Machining – laser ablation process for primarily

polymers

• Porous Silicon Formation

• Chemical Mechanical Polishing (CMP)

• Micro-embossing and Micro-stamping

• Inkjet Printing

• Soft Lithography with SAMs

79

MEMS Examples

Conventional Pressure Sensor

Source: Maluf 80

MEMS Examples

Conventional Pressure Sensor

Source: NovaSensor

0

10

20

30

40

50

60

0 20 40 60 80 100 120

Pressure (PSI)

Ou

tpu

t V

olt

ag

e (

mV

)

UofL uFab Course Sensors 81

MEMS Examples

Conventional Pressure Sensor Packaging

Source: Madou

82

MEMS Examples

Pressure Sensor (ultra-miniature)

Source: NovaSensor 83

MEMS Examples

Pressure Sensor (ultra-miniature)

Source: UofL 84

MEMS Examples

• Accelerometers

Source: UofL

85

MEMS Examples

Accelerometers

Sources: Analog Devices, Lucas NovaSensor, and EG&G IC Sensors 86

MEMS Examples

• Flow Sensors

Source: UofL

87

MEMS Examples

• Gas Sensors • MicroMotors

Source: UofL

Source: Berkeley

88

MEMS Examples

Inkjet Technology – “side shooter”

Source: Elwenspoek

(Microsensor)

89

MEMS Examples

Inkjet Technology – “top shooter”

Source: Maluf 90

MEMS Examples

Micromotors

Source: MIT and Berkeley 91

MEMS Examples

Micro-structures using LIGA

Source: UW 92

MEMS Examples

Micro-Grippers

Source: Berkeley 93

MEMS Examples

Micro-Tweezers

Source: MEMS Precision Instruments 94

MEMS Examples Neural Probes

Source: Mich (K. Wise) 95

MEMS Examples

Neural Interface Chip

Source: Stanford 96

MEMS Examples

Lab-on-a-Chip Systems

Source: Caliper

• separation

• dilution

• mixing and dispensing

• analysis

Source: Maluf

97

UofL NSF Lab-on-a-Chip Project

GOAL

Develop true portable microchip analysis systems

with electrochemical detection for broad practical

use

BACKGROUND

Current microanalysis devices with laser induced

fluorescence detection are successful but are neither

fully “micro” nor fully “integrated”

Electrodes can be fabricated directly on a microchip

in almost any size, shape, location, or composition

RESULTS

Developed portable electronics for CE/EC device

Fabricated and tested working CE/EC micro-chips

Modeled microfluidic flow using MEMCAD

TECHNOLOGICAL IMPACT

Produce self-contained lab-on-a-chip instruments

that fully utilize microfabrication technology for

optimum miniaturization, structural sophistication,

and ease of construction

Identify and define optimum chip configuration

Portable Electronics, DataAcquisition and Display Unit

Disposable Micro-CE/ECPlug- In Module

Micromachined GlassWafer

Microfabricated Glass Substrate with Patterned Electrodes

Electrical Connections

Sample Inlet Reservoir

Sample WasteReservoir

Buffer Inlet Reservoir

Buffer Waste Reservoir

PC Interface

“An Integrated Monolithic Capillary Electrophoresis (CE)

System with Electrochemical Detection (ECD)”

98

Operation

Injection mode Separation mode

A

A

A

Injection

Waste Sample

CE

Detection

A

A

Separation

A

Waste

CE

Sample

Detection

99

Results

• Analyte

– Dichlorofluorescein (60 μM, 420.1 g/mole)

• Buffer

– Phosphate (10mM – pH = 6.0)

• Comments

– Injection and separation both at 1 kV (250 V/cm)

– Average plug speed 372 ± 13 um/sec (n=7)

– Higher injection voltages decreased the volume of the plug – did not affect the speed. Spectra Physics 770 Argon-Ion laser (514 nm) at 2.5 W through a 2mm/5mm diverging tip.

injection separation

simulation

100

Separation and EC Detection

• On-chip separation and

electrochemical detection

has been realized

• Photolithographically

patterned Pt electrodes

• Dopamine and Catechol

used as analytes

• Integrated with

miniaturized custom-

made power supply and

detection circuit

101

MEMS Examples

Channels, Nozzles, Flow Structures, and Load Cells

Source: EG&G IC Sensors 102

MEMS Examples

Micromachined Tips for FEDs and AFMs

Source: IBM Source: Micron Technology 103

MEMS Examples

Optical MEMS (MOEMS)

Source: NIST, Simon Fraser, UCLA, and MCNC 104

MEMS Examples Optical MEMS (MOEMS)

Source: IMC (Sweden), Maluf and TI

TI’s DMD

105

• physical sensors: pressure, acceleration, flow

• lab-on-a-chip systems: uTAS using CE/EC

• micro-pumps

• bio-MEMS devices

• RF MEMS for wireless communication

• chemical and CNT sensors

• microhotplates

• MEMS-based microphones

• inkjet microtechnology

• MEOMS: optical MEMS

• smart sensors

• energy harvesting

• nanotechnology

UofL MEMS Group

Research Areas

106

Future Direction

Commercial Successes Emerging Technologies

• pressure sensors

• accelerometers

• gyros

• flow sensors

• radiation sensors

• MEMS microphones

• gas sensors

• ink jet printheads

• DMD micro-mirrors for

projection systems

• LOC

• optical switches

• RF MEMS

• microfluidics

• micro pumps, valves and mixers

• gnat robots

• drug delivery

• tissue engineering

• micro-motors

• NEMS

• new fab technologies

2000 BMW 740i contains

over 70 MEMS sensors !

107

Cleanroom

Standards

Source: Zant

Class 100 – no more than 100

particles of diameter .5 microns or

larger per cubic foot of air space.

Source: Zant

108

Cleanroom Configuration and Activities

Source: Zant

Table from Zant illustrating

increase in particle count due to

various cleanroom activities 109

The End

110