Hi Everyone,

I am new. Nice to meet you all.

I am trying to write a pattern on my GaAs coated with
PMMA, and then evaporate gold on it.

If I coat it with only one layer of 6% PMMA with
molecular weight 350k, then evaporate Cr first
(thickness 50A), and then Au 200A, the result is good.
But when I tried Cr 50A and Au 400A, I got difficulty
during lift-off. The desired region and the unwanted
region of the metal are connected.

Could anyone suggest some methods to solve this
problem? (say, switch to PMMA with higher molecular
weight?) I prefer single layer. If  double layers are
needed, I prefer double PMMA instead of 1 PMMA and
another kind of polymer. It would be a great help if
you provide details of your parameters.

Thank you.

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