1. GaAs MESFET Process Flow
Wafer Cleaning
Device Processing

2. Wafer Cleaning Degreasing (grease)
Boil the substrate in Trichloroethane (TCE – 80 C) for 10 minutes (hard grease)
Soak in warm Acetone (50 C) for 10 minutes (light grease and polymers)
Soak in IPA (2-propanol) for 10 minutes
Flush with cold IPA
Blow dry with N2
RCA cleaning (oxides, metal contaminants)
Immerse GaAs in 1:1 solution of HCL:DI-water for 5 minutes
Immerse GaAs in 1:1 solution of NH4OH:DI-water for 5 minutes
Immerse GaAs in DI-water for 5 minutes

3. Photoresist (positive)
GaAs MESFET Process Flow
Start with a n-GaAs / SI-GaAs wafer
Apply positive-Photoresist (S-1813)
Photoresist (positive)
n-GaAs
SI-GaAs

4. Apply 1st mask to form the S/D ohmic contact pattern
GaAs MESFET Process Flow
Apply 1st mask to form the S/D ohmic contact pattern
Apply UV-light
Exposed PR will become softer
Develop (MF sec.) the photoresist and remove soft parts
hard PR
soft PR
n-GaAs
SI-GaAs

5. hard PR n-GaAs SI-GaAs AuGeNi GaAs MESFET Process Flow
S/D ohmic contact deposition (AuGeNi) – deposit them first and then thermal
annealing – thicknesses ???
Lift-off (with acetone and ultrosonic agitation)
AuGeNi
Apply PR to form the gate
Apply the mask and expose the wafer to UV light
hard PR
n-GaAs
SI-GaAs

6. n-GaAs SI-GaAs AuGeNi TiPtAu GaAs MESFET Process Flow
Develop the photoresist
Evaporate TiPtAu
AuGeNi
Lift off
TiPtAu
n-GaAs
SI-GaAs

7. n-GaAs SI-GaAs AuGeNi TiPtAu TiAu GaAs MESFET Process Flow
First metallization
AuGeNi
Develop the PR
TiPtAu
Evaporate TiAu
Lift-off
TiAu
n-GaAs
SI-GaAs

8. n-GaAs SI-GaAs AuGeNi TiPtAu TiAu GaAs MESFET Process Flow
Silicon-Nitride for electrical isolation
TiPtAu
TiAu
n-GaAs
SI-GaAs

9. * Optical lithography, feat.res. ~ 0.5-1 µm
Final Device
AuGeNi
* Optical lithography, feat.res. ~ µm
TiPtAu
* Ti( 250 A) / Au (1500 A)
TiAu
Source
Drain
Gate
2.5µm
TiAu
~ 2.5µm
TiPtAu
AuGeNi
n-GaAs
1.5 µm
SI-GaAs
1-2 µm