Process Technology to Fabricate High Performance MEMS on Top of Advanced LSI

1

Shuji TanakaTohoku University, Sendai, Japan

2

Mor

e M

oore

: Min

iatu

rizat

ion

Integrated inertia

sensors Integrated health care

devices

3 µm

0.8 µm DMD

~202

0

~202

5

One-chip multiband/ tunable

wireless chips

Implantable devices

~201

5 Self-controlled one-chip sensors

Pre

sent

High performance integrated sensors

SmallerMore inteillentMore distributed

JSAP Integrated MEMS Technology Roadmap

Nanoelectronics

More than Moore: Diversification

W-LANW-LAN

Digital TVDigital TVW-CDMAW-CDMA

PHSPHS WiMAXWiMAX

GSM/PDCGSM/PDC5.16～5.35 GHz2.4～2.48 GHz

470～770 MHz

2.5～2.7 GHz

1.92～1.98 GHz UL2.11～2.17 GHZ DL

800 MHz 900 MHz1.9 GHz

4th Gen.4th Gen.

1.88～1.92 GHz

Multiband Wireless Communication

3

Tx

RxMulti-band wireless communication chip for W-CDMA + GSM/GPRS/EDGE(Qualcomm, QSC6240)

Integration of Wireless Communication System

LNA 0/90 ºA/D

A/D

Digital signalprocessor

FilterMixer

Discrete devicesIntegrated devices based on RF CMOS technology

Frequency tuning circuit

Unimplemented system

Real one-chip solution enables not only advanced mobile communication systems but also ubiquitous network sensors, wireless healthcare chips etc.

Integration of advanced LSI and “mechanical” devices (SAW/BAW filters, clock oscillators, RF MEMS switches, variable capacitors) is a key.

Rx

4

ADXRS150 2-axis gyro

Inertia Sensors (Analog Devices)

Detection circuit

G sensor

Safety steel ball sensor

125 μm

1.3 μm

2 μm

5

A tiny capacitance change (12 zF) corresponding to 1.6×10-4 Å displacement is detectable by the embedded integrated circuit in the gyro.

Integrated Accelerometer (Analog Devices)

Poly-Si sensor structure on 3 µm-ruled, W-metalized BiCMOSPoly-Si annealing at 1100 °C for 30 min, Impossible to fabricate in LSI foundry

Circuit(NPN, NMOS)

Poly Si sensor structure

On-CMOS structure

SOI MEMS structureSensor structure release from this trench Sensor structure Circuit

Single crystal Si sensor structure beside 0.6 μm-ruled, Al-metalized CMOSCompatible with advanced LSI from LSI foundry, Low space efficiency

Judy et al., Hilton Head Island WS 2004, 27

SOI

Trench isolation

6

Digital Micromirror Device (TI)

• 10~16 μm square micromirrors• ~2 μs response time• 8.5 V driving voltage• ±12 ° tilt angle• 848×600 = 508800 pixels for SVGA

~ 1280×1024 = 1310720 pixels for SXGA

Hornbeck, IEDM 2007, 17-24

7

Applications of DMD

Rear-projection television

Panasonic

Projector for cinema complex

NEC

Mobile projector

NEC Weight: 1 kg

8

Metal Surface Micromachining for DMD (TI)

0.8 µm CMOS

address circuit

(SRAM) Al SiO2

SiO2 Al

AlResist

Kessel et al., Proc. IEEE, 86 (1998) 1687

1. Sacrificial resist layer

2. Al and SiO2 mask for hinges

3. Al and SiO2 mask for beams

4. Al etching for beams and hinges

5. Sacrificial resist layer and Al mirror

6. Sacrificial resist etching

Resist

Hornbeck, IEDM 2007, 17-249

MEMS-LSI Integration using Ge Sacrificial Layer

Ge

Al

Au/Cr

AlN

1. Ge patterning and SiO2 deposition

2. Metal patterning and AlN deposition

3. AlN and Au/Cr patterning

4. Ge sacrificial etching

SiO2

Mo

LSI

Collaboration with NDK• Multi-freq. AlN Lamb wave resonator monolithically integrated with LSI

• Application to one-chip high-speed communication devices

100 μm

310 MHz

LSI

10

Electrostatic-Actuated Capacitive Shunt Switch

Ni bridgeDielectric layer(SiO2)

-30

-25-20

-15-10

-5

0

510

1520

1 3 5 7Freqency（GHｚ）

-0.5

-0.45-0.4

-0.35-0.3

-0.25

-0.2

-0.15-0.1

-0.050

Insert loss

Isolation

Frequency (GHz)

Isol

atio

n (d

B)

Inse

rtion

loss

(dB

)

Off state

On state

Signal

Ground

Actuation pad Ground

200 µm

Notches for close contact

GND GNDSignal

Sacrificial PR (3.5 µm)

Sacrificial PR (1.5 µm)

Driving voltage: 38 V

Yuki et al., Sensor Symposium 2007

11

Wafer-Level Packaging of RF MEMS Switch

DC in (Au/Cr)

CPWCPW

Dry film resistCavity

RF MEMS switch packaged by dry film resist

Exposed part

Polyolefin moldDry film resist

1. Molding dry film resist

3. Laminating molded dry film resist and exposing

4. Developing and over-coating

Device wafer

2. Exposing dry film resist

Exposed part

Yuki et al., Sensor Symposium 2007

12

Phase Shifter Using RF MEMS Switches

Z0

Z 1

Z0

Z 2

Capacitive shunt SW

Reflection typeSwitching line type

SW downReflect here

SW upReflect here

Capacitive shunt SW

0°

90°

22.5°

180°

45°

Reflection-type phase shifter using RF MEMS switch

(Taiko Denki & Tohoku Univ.)13

Memory Effect of Metal Hinges in DMDA. B. Southeimer, IEEE 40th Annual International Reliability Physics Symposium, Dallas, TX, 2002

50 % / 50% 5 % / 95%

Shi

ft (%

) of

bia

s vo

ltage

at

whi

ch a

hal

f of m

irror

s la

nd o

n th

e le

ft si

de

Duty cycle in accelerating test

Simulating random image Simulating static image

Test duration Mirrors exhibiting hinge memory

14

Wafer Bonding-based MEMS-LSI Integration

1. Preparation of a device layer on a support wafer Adhesion layer

Device layere.g.) Single crystal Si, Piezoelectric materials, Diamond, Compound semiconductors

Support wafer

Interlayer

2. Fabrication of a LSI wafer

3. Low temperature bonding of the device layer and the LSI wafer

LSI wafer

e.g.) SiO2, Polymer

15

4. Removal of the support wafer/Thinning of the device wafer

5. Fabrication of MEMS (e.g. RF MEMS switch, variable capacitor) or SAW/BAW devices

6. Release of the device by sacrificial etching

LSI wafer

Electrical connection

Polymer

Single Crystal RF MEMS Switch on Top of LSI

Actuation electrode

Metal anchor

Single crystal Si cantilever

Signal line

RF MEMS switches on a dummy LSI wafer

Metal anchor

200 μm Single crystal Si cantilever

200 μm

Metal anchor

Single crystal Si bridge0

5

10

15

20

25

0 200 400 600 800 1000

Hig

ht (μ

m)

Lateral length (μm)

OFF (Vdrive = 0 V)

ON (Vdrive = 8 V)

OFF ON

16

Single-Crystal-Si-on-LSI (SOL) Technology

1. Fabrication of metal padson a (dummy) LSI wafer

2. Bonding a SOI wafer onthe LSI wafer usingpolymer interlayer

3. Etching of the handle andBOX layers

4. Patterning of metalelectrodes

5. Shape formation of thedevice by reactive ionetching

6. Cu electroplating usingphotoresist molds for electrical connection

7. Removal of thephotoresist molds

8. Sacrificial polymer etchingby O2 ashing to releasethe device

LSI wafer

SOI wafer

Polymer

Cu

Photoresist mold17

200 μm

AlN/Si Composite Resonators on Top of LSI

18

1. Electrically-coupled AlN/Si composite thickness-mode filter

2. Mechanical-coupled AlN/Si composite disk array filter

Si

In Out

GND

Coupling Beam4λ

Si

In Out

GND

SiO2

Out-of-phase mode In-phase mode

Collaboration withMr. Matsumura (NiCT)

AlNSi

AlNSi

Single-Crystal-Si-on-LSI (SOL) Technology

19

1. Wafer bonding using polymer

PolymerLSI

SOI wafer

3. Metal patterning

5. Metal patterning

6. Si etching

7. Sacrificial polymer etchingRu Au/Cr

Al Au/Cr

Au/Ti

2. Handle layer and BOX layer etching

4. AlN deposition and patterningAlN

Resist

SiO2

AlN/Si Composite Resonators on Top of LSI

20

Unpublished data

Share Wafer System in Tohoku University

Given process→ Call for devicesGiven process→ Call for devices

Registration from A corp., B univ. …Registration from A corp., B univ. …

A B CD E FG H I

A

B

Group ASensor circuitGroup ASensor circuit

Group BDriver circuitGroup BDriver circuit

Group COscillator circuitGroup COscillator circuit

Coordination with LSI foundry

Coordination with LSI foundry

A B

CD

A B

CD

A B

CD

Is there a common process?

Is there a common process?

Multiple devices in each shot

Group DActuator circuitGroup DActuator circuit

Delivery after chip separation

Delivery after chip separation

Full wafers to each groupFull wafers to each groupProject members (NDA is concluded.)

Shuttle service

Share wafer system

MEMS fabrication by each groupMEMS fabrication by each group21

Summary

• There is strong demands for monolithic integration of advanced LSI and “mechanical” devices such as clock oscillators, mechanical filters, switches and sensors. “More than Moore” with “Moore Moore” and “Biyond CMOS”

• There are varieties of existing MEMS-LSI integration technology, but they are not suitable for the above applications.

• We have developed new versatile microprocess technology for the monolithic integration of high-performance MEMS on top of advanced LSI.

• Using the developed technology, we fabricated RF MEMS switches/variable capacitors, RF mechanical resonators and filters etc.Acknowledgement: This study was partly supported by Special Coordination Funds for Promoting Science and Technology.22