I dealt with this KOH business last week. I found the article below very
helpful. Best regards.

http://www.virginiasemi.com/pdf/siliconetchingandcleaning.pdf

--
Engin Pehlivanoğlu
Research Assistant
Wireless Microsystems Group
EECS @ CWRU




>From: Vinay 
>Reply-To: General MEMS discussion 
>To: [email protected]
>Subject: [mems-talk] KOH etching
>Date: Tue, 10 Jan 2006 22:55:30 -0600
>
>Hello all,
>I am trying to etch Si using KOH. I tried various concentrations at
>different temperatures and it looks 40% KOH [40gms KOH, 100ml water,
>25ml IPA] at 80 degrees C works the best [15 mins of etching resulted
>in a depth of 15um]. But i am unable to get a smooth surface. I see
>black spots scattered all over the wafer. I was wondering if any of
>you have experienced this before. Is there any other etchant or
>another concentration of KOH that could be used as a 2nd step to
>smoothen the surface, once the target depth is reached? Any
>suggestions would be greatly appreatiated.