Hello, MEMS.
Thank you for your mail for my problem.
And I have another problem in my experiment.
 My experiment using the PMMA , KOH  is somewhat poor.
I used the 20 % KOH etchant with IPA, H2O.
After etching,(I made the pattern E-Beam lithography.)
I removed the PMMA with ACETON, but there is no pattern.
So I guess the substrate is not etched the KOH etchant.
Do you know what's the problem?
I etched the substrate about 2 min.
I guess two reason. Is it right? Or another problem?

1). Etch rate is so small that the substrate is not etched.

2). The nature oxide on the substrate is prohibit the
    etching of the substrate.

Please let me know the problem.
That is very big problem to me.
Thank you for reading my mail.
Sincerely.
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