I never tried PDMS as an etch mask against KOH. That is an interesting
idea. However, PDMS is permeable. Is it possible that KOH is
penetrating the PDMS mask and slowly attacking your substrate, leaving
a white residue?


On Tue, Jan 21, 2014 at 3:27 PM, Abhinav Jain  wrote:
> Hello all!
>
> I am using PDMS to protect one side of the wafer during 8 hour KOH etch at
> 85C. I am using Sylgard 170.
>
> I am having problems having a clean surface after wet-etching of PDMS. I am
> using Dynasolve 217, but its not dissolving it completely (even after hours
> of dipping in solution). I am even using Q-tip sometimes to remove PDMS in
> the Dynasolve solution. There is always this white residue/layer left.
>
> 1. Am I missing something? Is there a better way to wet etch PDMS? How
> about TBAF and NMP mixture? Is this more efficient than Dynasolve to remove
> the residual PDMS?
>
> 2. Is there an inexpensive and quick way to protect the other side of the
> wafer? (Other than protek and parylene coating. I am looking for something
> which is easy to coat and easy to remove). How about Apezion W wax? Is it
> stable at 85C?  How do you apply solid wax to the whole wafer?
>
> (There is LPCVD silicon nitride film on the other-side but there are always
> some pinholes and defects and it cant stand 8 hour etch.)
>
> I would really appreciate the inputs.
>
> Thanks
> Abhinav Jain
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