Liftoff Recipe

Liftoff patterning is the standard way to pattern materials that are difficult to etch (e.g., the noble metals Au, Pt).

Expose and develop photoresist. A special liftoff resist is available on svgcoat3 or headway.
Evaporate or sputter metal on top.
Remove photoresist, usually with asap-liftoff.

Useful Notes

Don't hard bake photoresist. This makes it much more difficult to remove (at least 10x longer in asap-liftoff)
High temperature evaporation (e.g., Pt) can make the wafers hot enough to melt photoresist; the photoresist tends to flake (“reticulate”) and unwanted metal can be deposited in the cracks. To fix this, (a) minimize evaporation time by using thin layers or high deposition rates, (b) run evaporation in steps allowing wafers to cool in between, (b) use temperature-resistant photoresist.

Date	Person	Data
10 Dec 2020	Daniel	Accidentally UV hard baked standard 2um MiR701 with axcelis recipe U for 26nm Cr + 282nm Au liftoff. Had to run recipe 17 (high intensity 6“ wafer with soak) 13 times (!) to complete liftoff, but it worked in the end. Lesson: don't hard bake liftoff photoresist.
12 Jul 2021	Daniel	Learned that LOR liftoff resist may be resistant to higher temperatures than MiR701 and so may work much better for high temperature metal deposition (e.g., Pt).