Aluminum Lift-Off

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.

Equipment

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• 6" diameter petri dish
• ultrasonic bath (optional)

Supplies

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• acetone
• Texwipe swab

Operating parameters

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time: until all PR is removed

Equipment/controls/tools locations

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• Solvent hood: room 50S (wet lab)
• Ultrasonic bath: solvent hood from above

Operating precautions

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Chemical hazard

PR, acetone, and ipa are volatile and flammable. Keep away from flame. Possible biological hazards: only use in a fume hood.

Operating procedure

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1. Place the wafer into the container marked Lift-off Acetone.
   
   
2. 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 metal.
   
   
3. Degrease your wafer after all excess aluminum has lifted off.