I defined an interdigitated grating of indium tin oxide on gallium arsenide by electron beam lithography using pmma a2 (120nm) and sputtering 40nm ITO. Unfortunately I see that the largest parts of the pattern easily liftoff while small parts in the interdigitated regions are much harder to liftoff, probably because of proximity effects or limited surface exposed to the stripper.
So far, I used warm acetone and warm NMP in a gentle sonication bath at 60°C, but PMMA is still there and is only slowly removed after 40mins.
Any suggestion on how to do it faster?
Dear Francesco Todisco , PMMA bonds can be broken by UV irradiation ( I used 365nm UV light), after some minutes of exposure it was a lot easier to remove with acetone. I had thinner films, but it should work for your 120nm thick film too. If some material still remains, you can reply the process: exposure x mins followed by acetone development.
Hope it helps.
Thanks guys (and ciao Brunooooo)...at the end it worked continuously sonicating at 60°C in NMP and checking the sample every 10min. Unfortunately the GaAs substrate is pretty fragile and it does not survive long sonications. Manuel Gómez next time I'll give it a try with UV exposure ;)
You are welcome! Glad that Bruno Paulillo ´s answer worked!
All the best.
Manuel
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