Brewer Science sells a spin-on polymer coating that is designed to
protect from KOH, and removes easily from the wafer in an acetone
bath afterwards.  It is called B1-18.   I've used it with limited success,
as sometimes it de-laminates from my wafers.   I am trying to protect
an oxide, though.   You might have better luck with adhesion to your
poly-Si surface.    I have also found that B1-18 works better for me
if I use it to bond my sample wafer to another 'scrap' wafer.   This
minimizes
the exposure of B1-18 to KOH etching to just the edges of the spin-on
coat, and seems to solve my de-laminating problem (so far...).

good luck.

-Jed Ley

Li Wang wrote:

> Hello,
>
> I want to protect my front side during KOH etching because there is
> polysilicon on it. I designed a jig which seal the wafer with O-ring
> and sandwiched the wafer in between two plastic pieces, fastened with
> six screws. But my problem is that the forces on the screw is kind of
> difficult to control and the wafers were broken several times in
> testing when the wafers were etched thinner. Another way I tried is
> PDMS protection. I put PDMS on the front side. The problem I met is
> that the PDMS will be detached from the wafer after I put the wafer
> into hot KOH for 2 hours. Anyone has any idea of KOH protection,
> please email me to help me out. Thanks a lot.
>
> Li Wang
>
>
>
>
>
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