Some questions.

1. When you do the vapor prime, do you use heat? You need to have heat
so you don't leave a film of excess HMDS molecules. There are two
theories out there how HMDS works, but you need to bake the wafer for
either theory.

2. In the vacuum bake you run a risk of the surface of the resist
"crusting." That is you desolvate the top layer and that film blocks the
further loss of solvent from the bulk of the film.

3. Finally without heat, you will have low internal diffusion of
solvents from the bulk and I would think that your vacuum baking might
have to go for a long time, too long for a practical process.

4. I don't understand why you think softbaking would cause a charge
build up. A hot plate shouldn't build up charge and a largely
atmospheric oven bake shouldn't build up charge.


Ed

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Andrew Sarangan
Sent: Thursday, August 13, 2009 10:39 PM
To: General MEMS discussion
Subject: [mems-talk] Adhesion promoter for LiNbO3?


I am having adhesion problems of photoresist on LiNbO3 substrate. I've
tried HMDS (vapor prime) but it is not clear to me if HMDS works on
LiNbO3. Furthermore, my problem is exacerbated by the fact that I am not
doing any soft-bake or PEB, in order to avoid charge build-up on the
substrate. Instead I've been drying the resist films in a vacuum at room
temperature. This is Shipley 955 resist.