Hello Maryla,

I was following the discussion regarding your membrane fabrication issues. I
think that all the responses so far have been right concerning stress
related problems. I have a different suggestion / question. If your goal is
to fabricate SiN membranes (this is what I understand) why do you use SiO2?

SiN (low stressed)  is an excellent etch mask in KOH. Now, if your goal is
to fabricate a membrane out of SiO2, you might want to consider starting out
with a thicker layer of SiO2 and after KOH etching your predefined membrane
thickness should remain. (start thickness: original SiO2 thickness + Etch
rate SiO2 in KOH * KOH etch time) If you goal is to fabricate a membrane in
SiO2 and SiN then the stress problem stays and I would certainly follow the
advice of the MEMS-talk community. Take into account that if you reduce your
membrane area you might just as well succeed without further problems.


Hope to be of use,

Regards,

Marc van den Boogaart,
PhD-student, EPFL-LMIS1