You could try photosensitive Polyimide if the resolution is good enough. It is
far more chemically resistive to attack. If you need help baking the Polyimide
send it to us for free test. Bill Moffat

Sent from my iPad

> On May 6, 2017, at 5:58 PM, Andreas K. Huettel  wrote:
>
> Dear all,
>
> we need to etch deep holes into a Si wafer (with a 500nm surface oxide) that
> already has sensitive Nb structures on top.
>
> The etching alone works mostly fine with first RIE through the oxide and then
> hot KOH. However, the KOH also dissolves our photoresist and then attacks the
> niobium.
>
> We already tried placing a baked-out PMMA layer between niobium and
> photoresist, but that didn't help too much.
>
> Do you have any advice for this?
> Are there any photoresists around that are KOH-stable?
> What other protective could be used that later are easily removed?
>
> Best,
> Andreas
>
> --
> PD Dr. Andreas K. Huettel
> Institute for Experimental and Applied Physics
> University of Regensburg
> 93040 Regensburg
> Germany
>
> tel. +49 151 241 67748 (mobile)
> tel. +49 941 943 1618 (office)
> fax +49 941 943 1670
> e-mail andreas.huettel@ur.de
> http://www.akhuettel.de/
> http://www.physik.uni-r.de/forschung/huettel/
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