When you say using HMDS, are you talking about wet HMDS which has
adhesion problems or vapor prime?  Bill Moffat

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On
Behalf Of Denis Petrov
Sent: Monday, May 09, 2011 2:13 AM
To: General MEMS discussion
Subject: [mems-talk] Problem BOE SiON underetching too high

Dear colleagues,

We have the following problem here. The underetching rate of SiON
(silicon
oxinitride) during the etching with BOE at room temperature is too high.
Normally, it must be in the range of 1:1 or minimally 1:2 with respect
to the profile depth, but we have 1:6. And the slope shape is very
unstable, always different.

We suspect that our photoresist (HIPR) has bad adhesion to the SiON. We
use HMDS for better adhesion, but it seem to be of very little help.

Does anyone know how to solve the problem?