Hello all,

I am using XeF2 to release my Silicon devices.
The top of my devices are covered with a reflown (at 170C, for 90
minutes) photoresist (S1813), and side walls of the devices are covered
with oxide that acts as a passivation layer against XeF2 for the side walls.
When I start the isotropic etching process, XeF2 penetrates from the
"device-photoresist" interface at the top part of the devices, and my
devices are etched by XeF2.

I do not know the reason for that, and I wonder if there is somebody who
has an experience with that or has helpful comments how to solve that issue.

In case you are wondering:

I am using P20 as adhesion promoter before I spin the photoresist
(S1813). And, before I do the isotropic etching, I am reflowing S1813
for 90 minutes at 170C.

I tried the same isotropic etching process without reflowing the same
photoresist, unfortunately I had the same issue.

I checked if it can be related with misalignment issues. The optical
microscope pictures say that I do not have serious misalignment issues
that will cause an opening on top of my device where XeF2 can attack
Silicon without having any difficulties.

I did not try to clean my wafer before I apply P20, that is what I am
going to try next, but I wanted to ask you in case this will not help me...

Best regards,


Mehmet Yilmaz
Mechanical Engineer