In order to reduce chemical waste in the lab, a simple technique for defining aluminum
contacts is used: lift-off.
Prior to evaporation of metal, Mask 5 is used to delineate areas on the wafer where
aluminum will form the contacts and interconnects.
Al will adhere to the surface of the wafer during evaporation. Afterwards the PR
is removed, lifting off any aluminum that deposited onto the PR, leaving Al only
in the open areas of PR film.
- 6" diameter petri dish
- ultrasonic bath (optional)
time: until all PR is removed
- Solvent hood: room 50S (wet lab)
- Ultrasonic bath: solvent hood from above
PR, acetone, and ipa are volatile and flammable. Keep away from flame. Possible
biological hazards: only use in a fume hood.
- Place the wafer into the container marked Lift-off Acetone.
- Make sure the wafer is covered entirely with acetone and soak for 10 minutes (if
the ultrasonic bath is available, place the container and wafer into the sump -
make sure it has water in it).
The aluminum will begin to ‘peel off.’ Slight agitation
of the container will help lift-off the metal. If the aluminum has not completely
lifted off after 10 minutes, take a swab and gently wipe the wafer to remove the
- Degrease your wafer after all excess aluminum has lifted off.
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