This is experience from about a decade ago with an STS DRIE system.

Electrostatically clamped chucks may have trouble completely nulling out the
charge holding the wafer to the chuck, resulting in sticking to the chuck,
then breakage when the wafer handler tries to pick up the wafer.

Mechanically clamped chucks don't have the sticking problem. They hold the
wafer down with eight fingers connected to a ring-shaped weight. The weight
is necessary due to the helium backside pressure, required for a good
thermal contact. Because the weight of the fingers bows the wafer upward in
the center, the chuck must be domed slightly upward in the center. If the
chuck is not domed, the wafer gets hot rapidly and the photoresist is
damaged (guess how I know this). One issue with the mechanical clamp is that
the areas under the clamp are not etched, leaving little hills around the
wafer edge. This can be a problem if you want to bond the wafer to another
on.

I got really good at cleaning broken wafers out of our system!

You can visually monitor the wafer temperature with liquid-crystal
"temperature dots" that permanently change color when the wafer temperature
gets above transition temperature. Cover them with a little Kapton tape and
punch a hole with a razor blade to let the air out.

I'd say that a mechanically clamped chuck is better for research, and
electrostatic is better for production.

   --Kirt Williams

-----Original Message-----
From: mems-talk-bounces+kirt_williams=sbcglobal.net@memsnet.org
[mailto:mems-talk-bounces+kirt_williams=sbcglobal.net@memsnet.org] On Behalf
Of Tepper-Faran Tamar
Sent: Thursday, June 09, 2011 12:24 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] DRIE chuck

DRIE chuck - what is better: mechanical or electrostatic?

Please advise pro's and con's of each type of chuck from your own
experience.

Thanks!