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.

  • $\begingroup$ Hey, have you tried a plasma treatment? $\endgroup$ – John H. K. Mar 8 '17 at 18:08
  • $\begingroup$ Hi @JohnH.K., No I haven't. That is a great idea, but unfortunately that is not available in my lab. $\endgroup$ – C.Buhl Mar 10 '17 at 10:58

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