Silicon Carbide Electronic Device Processingfor Power Devices and I.C.’s

Melissa Spencer, Dept of ECEEMRL

Why SiC?

• SiC devices are needed by DoD and Industry– High-temperature, power and frequency electronics

– Critical future technology to replace silicon microchips

• EMRL is a device fabrication research

laboratory focusing on SiC technology

• Reactive Ion Etching (RIE) is one of the key

manufacturing steps in semiconductor

technology– SiC 3rd strongest material, only RIE can etch it to make devices

Reactive Ion Etching

RF energy strikes a plasma which etches the SiC material

Plasma ChemistryPlasma Chemistry

Etch: SF6+He, H2, O2

Ash: O2

RF PowerRF Power

10-100 W typical

PressurePressure

100-600 mT

These SiC samples were etched using our RIE process

Etched Devices*

*G. E. Carter, J. B. Casady, M. Okhuysen, J. D. Scofield, and S. E. Saddow, ICSCRM’99

Problem

• Changes in plasma dielectric constant, P,

plasma impedance, ZP, variation

• This changes the RF power transfer to the plasma

Pin = Preflected + Pplasma

• The etch rate is a sensitive function of Pplasma

• Manual impedance matching makes the etching

process highly operator dependent

• Therefore RIE process variations unavoidable

RIE Etch Rate

SEMICONDUCTOR DEVICE CROSS-SECTION

Each one of these layers are very thin so

etching is critical!

• RIE etch rate recipes are critical in forming devices– Devices are fabricated by forming, patterning, and etching layers

– Each layer must be precisely etched for the device to function properly

2.5 m

Each layer is patterned and etched

Power Dependence*

Etch rate is a sensitive function of plasma power

10 Percent power change

20% etch rate variation

*J. Bonds, G. E. Carter, J.B. Casady and J.D. Scofield, Spring MRS Meeting, April 2000

SF6 :O2 (5:10 sccm)Pressure = 100 mTElectrode to sample spacing = 25.4 cm

Power (W) vs Etch rate (A/min)

Etc

h r

ate

(An

gstr

oms/

min

ute

)

Power (W)

1600

1400

1200

1000

800

600

400

200

00 5 10 15 20 25 30 35 40

Automated RF Tuner

• Detects load impedance, ZP, changes

• Automatically matches ZP, making the

RIE process more repeatable

• Allows more precise RIE recipes to be performed

• Devices with finer features may be fabricated

Impedance Matching

The load impedance is matched to the source impedance by a “T” network:

X1 X2

X3

X1, X2 variable capacitors and X3 variable inductanceControl algorithm to minimize PR vs. ZP

PForward

PReflected

RF Source =ZS

ZP

Implementation• Hardware

– Variable Impedance Devices

– Detection Circuitry for PForward and PReflected

– Micro-Controller

– Servo Motors (impedance device tuning)

– AC to DC Converter– A/D Converters

• Software– Impedance Tuning Algorithm

– Monitoring Software

Schematic

vcc -cs20 1

7 Vin-

6 Vin+

9 Vref/ 2

ADC0804

7 Vin-

6 Vin+

9 Vref/ 2

ADC0804

vcc20

D3 15

D0 18

D2 16D1 17

D6 12D5 13D4 14

-WR 3-RD 2

D7 11

-intr 5-cs

1

-

+

For Voltageinput

inputRefl Voltage

5V

5V

2k

10k 1uF

1uF

5V

24PWRGND 23RES 22+5V 21P15 20P14 19P13 18P12 17P11 16P10 15P9 14P8 13

56789101112

234

1

P5

P7P6

P4P3P2P1P0

TX

GNDATNRX

Serial

Moto

r 3

Moto

r 2

Moto

r 1

Au

to O

ut p

ut

Au

to I

np

ut

Cable 5V SwitchReset

LM358

LT1029

-intr 5

D6 12

D1 17D0 18

D4 14D3 15D2 16

D5 13

-RD 2

D7 11-WR 3

Automated RF Tuner

Matching Algorithm

Vary Impedance

Vary Impedance

?

Detect Reflected

Power

System Block Diagram

Monitoring PC

Monitoring PC

Micro-Controller

Micro-Controller

ServoMotor/Driver

ServoMotor/Driver

ServoMotor/Driver

ServoMotor/Driver

ServoMotor/Driver

ServoMotor/Driver

Detection Circuitry for Forward and

Reflected Power

Detection Circuitry for Forward and

Reflected Power

RF inRF in

RF outRF out

Goal: Maintain constant power transfer

MFJ-962D

Future Work

• Modular Device– Feedback circuitry can be replace with other detection

devices

• Communication with computer– Reflected Power could be compensated with RF source

• Automate other power related parameters– Electrode spacing could be varied automatically to

utilize optimal spacing

LAM 9400 EtcherAIXTRON SiC Reactor

• Multi Wafer SiC Epi• Sub-micron lithography• Multi Wafer Plasma Etching• Multi Wafer PECVD• Multi Wafer Metal Deposition

Prototyping

Systems Production• Northrop Grumman• GE/Lockheed Martin

Component Production• Mississippi Small Business • SBIR’s

EMRL• SiC CVD Epi Research

• Materials Characterization

Research Impact

• Device Design & Fab

• This project has been a collaborative effort by members of the Emerging Materials Research Laboratory at MSU and would not have been possible without the assistance of the EMRL researchers and staff.

• Dr. Mazzola and Dr. Casady for their support of this project• Janna Bonds and Geoff Carter for their RIE assistance• Dr. Donohoe for his help on RF concepts and impedance matching theory• Dr. Saddow my project advisor

Acknowledgements

Silicon Carbide Electronic Device Processingfor Power Devices and I.C.’s

Melissa Spencer, Dept of ECEEMRL