Hi Daxiang,

I sounds like you are using PECVD nitride which is not a dense enough film
to withstand long KOH etch. We have successfully used a 25nm Low Stress
LPCVD Nitride Film for a though wafer KOH mask.  I would recommend Low
Stress LPCVD Nitride for you application.

Jessica Gomez
Rogue Valley Microdevices

-----Original Message-----
From: D. Zhou [mailto:[email protected]]
Subject: [mems-talk] Au/Cr(or Ti) as the KOH mask

I deposited a 250nm-thick Si3N4 layer as the mask of KOH but it could not
provide sufficient protection during the KOH ething. This is partly because
SiN deposited in our group is not pure Si3N4, but contains a large amout of
oxygen. The patterns are not well difined using this SiN as the mask.

Now I am going to try some metals as the masking layer, say Au/Cr or Au/Ti
(Cr or Ti works as the adhesive layer). Is there anybody who has any
experiences in this? How thick should the Au layer be so that it can be
strong enough during a very long etch time (9~10 hours in KOH @80c.) Any
suggestions? Thanks a lot.