Firstly, I'm unsure about the scope of this stack, but let's try.
I'm doing electron beam lithography on semi-insulating GaAs wafer pieces. And I have a hard time getting the PMMA to stick onto the GaAs. It detaches from the surface, and makes EBL possible.
My initial approach was cleaning in U/S acetone, then rinse with IPA. Secondly, I tried rather long cleaning steps (30 minutes of sonication time), and longer solvent bake of the PMMA (solvent: chlorobenzene).
I've had limited success with 60s etch in ammonia, followed by a 3 hour solvent bake, after spin coating. Limited success means that the thin film did not entirely peel off, in the vacuum of the SEM.
I'm aiming for a 100nm PMMA layer, and I need to produce features of down to 200nm in linewidth.
Do you have any pointers, or ideas for surface cleaning/etching? I'm contemplating the standard RCA cleaning procedure, but it's also a rather significant step up in complexity and work safety considerations.