Andreas,
        The TMAH process leaves a wafer with moisture in the Si02.  If your HMDS
process does not do a good job of dehydrating the wafer the HMDS reacts with the
moisture leaving an easy to remove adhesion molecule.  If you use vacuum vapor
prime, the wafer is totally dehydrated and the HMDS can only react with hydroxyl
ions on the wafer.  This produces a tight bond that moisture can not break.
This is almost identical to a process I ran back at AMD, 15,000 Angstroms of
SiO2, wet etch in buffered HF for 17 minutes.  With my old bake then spray HMDS
process I had problems with adhesion if I went more than 4 hours between bake
and HMDS.  With vacuum vapor prime I ran tests up to 7 days old with no
problems.  Contact me directly and I will give you some more ides.  Bill Moffat.

-----Original Message-----
From: Andreas Jahn [mailto:[email protected]]
Sent: Tuesday, March 04, 2003 1:36 PM
To: [email protected]
Subject: [mems-talk] Adhesion problems after etching with TMAH


To all,

does anyone know, what could cause adhesion problems of photoresist on SiO2
after etching in TMAH?
I oxidize a Si-wafer (double polished) and pattern the SiO2 on the backside.
Then I etch it in TMAH. If I want to pattern the
same SiO2 on the frontside, the HF undercuts the photoresist even with the
use of HMDS as an adhesion promoter.
It is the same procedure than the backside. Thanks for your help.
-Andreas


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