Hello,

I am having some difficulty etching 100 wafers using 30% KOH at 80 °C.

Rather than the expected 54.7° angle, I am experiencing a rough surface
with a ~45° between the top of the wafer and my sidewall, with some
rounding as well. Additionally, in a ~1.5 hour etch I lost all 6000
angstroms of thermally grown SiO2.

I am using a bit older KOH (unknown grade) and a slightly lower
concentration than is typical, with no IPA. I am using few polypropylene
holders to position my wafer in a beaker on a hotplate with stir bar.

It seems like I am getting some sort of contamination that is effecting
selectivity of the planes but it does not make much sense. Should I use a
commercial etchant from Transene to be safe like PSE-200?

Thanks,
Dave C.
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