I have a problem with adhesion of PDMS to LPVCD SiN.

The "cross section" is like this:

1. 300nm LPCVD SiN  mask on wafer backside, used for through wafer KOH etching
2. 300nm LPCVD SiN mask on front side that together with the mask from backside
defines Si islands
3. 50 microns PDMS spin coated on front side


The idea is to fabricate Si islands stuck on the PDMS membrane. It
worked fine 2 years ago but now, no matter what I do, the moment KOH
reaches the PDMS-SiN interface from the wafer front side, the islands
peel off instead of remaining attached to the PDMS membrane. Same thing
happens if I completely remove the Sin from the front side.

I have tried cleaning the wafer, O2 plasma treatment for increasing PDMS
adhesion but nothing works. I have reviewed my processing steps but
found nothing that causes this.

For better understanding of my process, you can check an old paper on my
first successful results, from EPTC 2008, "Mesh Interconnects for
Silicone Embedded Stretchable Silicon Electronics".

Can anyone help me with this?

Sincerely yours,

Sebastian Sosin