Martin--
You're right that the thermal contact is not very good with photoresist, but
of course it's a lot better than air.
One solution is start by etching most of the way through the wafer. This is
bit tricky as the perimeter etches around 10% faster than the center (this
varies a lot by recipe).
Next, coat both the "handle" wafer and the "product" wafer back side with
thin coatings of photoresist. This gives better coating and therefore a
better thermal contact than just coating the handle wafer, but the top of
the product wafer usually touches the chuck on the resist spinner and can
stratch it or leave particles.
A way of getting around this is using a manual spinner with four small
clamps only at the wafer perimeter.
Next, press the wafers together. As with any other bonding, apply pressure
at the center first in an effort to push all of the air out.
Finally, complete the etch.
    --Kirt Williams

----- Original Message -----
From: "Martin J Prest" 
To: 
Sent: Wednesday, January 11, 2006 8:16 AM
Subject: [mems-talk] temporary wafer bond?


Can anybody suggest a good way to temporarily bond a silicon wafer to a
handle wafer when through wafer etching with a DRIE system?

Ideally, this should be something that can be spread on the handle to a
uniform thickness and make a good thermal contact. It should also be easy to
remove afterwards using heat and/or solvent, leaving no residue on the
wafer.

I've tried photo-resist, but I'm worried that the thermal contact is not
very good.

Regards,

Martin.