I am trying to fabricate free standing PMMA micro structures on Silicon substrate, which requires isotropic, selective silicon etching leaving large undercut. I've tried wet etching with KOH, however the selectivity was poor. Reactive ion etching with SF6+C4H8 yields better results, but longer etching time towards desired undercut (~20um) partially destroys PMMA.
Could someone please suggest different recipe with RIE or an alternate approach? (XeF2 would have been promising option, unfortunately we don't have it)
Thank you very much.
You may want to check the following discussion, where I have mentioned some options for the wet etching of amorphous silicon. There are chemical resistance charts available on-line for PMMA (or equivalent commercial designations), such as the one signalled below, that may be of some assistance while selecting among silicon wet etching options for their selectivity against PMMA: https://www.researchgate.net/post/What_kind_of_solution_can_be_used_to_etch_amorphous_silicon
http://www.sdplastics.com/acryliteliterature/1554BChemResistanceChart.pdf
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