Hi,
   If I understand your question clearly, you need one side etch in KOH.
I know black wax can protect one side of wafer if coat it. I do not have the
black wax source company information at hand, but I think you find it on web.

hope it helpful

JL

Li Song  wrote:
Dear friends,

I am fabricating gas sensor by using SOI wafer.
Because not having suitable chuck for one side
etching, I try to passivate one side, then put whole
wafer in KOH. Considering etch rate for room temp., I
should use 600C  KOH, please recommend one suitable
passivation chemicals.

Thanks a lot.

Sincerely yours

Li Song


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