Dear Li,

Do you need PMMA as resist for E-Beam-lithography?

In that case, I suggest to try a more capable resist like ZEP520A
instead of PMMA.

Believe me or not, PMMA doesn't work proper.

In addition, you can hardening ZEP by UV radiation to obtain a better
selectivity.

Best regards,

Philipp



Am 12.08.2011 17:43, schrieb Li. Zhang:
> Hi all,
>
> I'm looking for a RIE recipe for silicon etching using PMMA mask. The PMMA
> mask is about 20nm thick and spin-coated on silicon substrate. The etching
> depth into silicon is expected to be 20nm~30nm. I tried different recipes
> but didn't get decent results.
>
> The recipes I tried include
> 1) SF6 15sccm + O2 7.5sccm, 40W, 30mTorr -- mask degraded making silicon
> surface very rough.
> 2) SF6 15sccm, 40W, 30mTorr for 2min -- etching rate for this one is very
> high, the features expanded and I got an etching depth of 70nm. Degraded
> mask and rough surface. Selectivity is not yet measured.
> 3) CH4 25sccm, 90W, 50mTorr -- selectivity PMMA/Si is around 6:1, the mask
> film barely survived.
>
> Does anyone have suggestions for my situation? Thanks!
>
> Li
>