I think you need to have the sample go onto a dummy wafer with travel
stops. The travel stops could be silicon sections affixed to the edge of
the wafer. That way the mask is physically prevented from getting too
close to your small sample that you are exposing. Or you could have two
fused wafers, one of which has a center section cut out, and  the rest
of the remaining wafer acts as a travel stop or as a contact surface for
the proximity check for some types of contact/proximity aligners.

The critical thing would be that the wafer piece that acts as a travel
stop be close to the same thickness as your sample, so you proximity
settings for exposure acting on the wafer piece would work for your
sample and not be out of the control range of the machine.

If you have only a simple contact machine, the travel stop pieces should
be thicker.

Ed Sebesta



-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of alim polat
Sent: Thursday, February 07, 2008 11:14 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] Problems on lithography exposing small samples on
MA/BA6 Mask and Bond Aligner

Hello, everyone
Recently I found out that conducting photo lithography procedure on
small samples is quite challenging. For example, we have MA/BA 6 Mask
and Bond Aligner in our lab to expose samples with photoresist on them.
However, exposing small samples brings great challenge. I usually put
the small samples on top of a dummy wafer and expose.
Sometimes after finishing exposure the small samples are stuck to the
mask when the wafer holder goes down if the thickness of the samples is
thicker, which also brings damage to the expensive mask. I wonder if
anyone has some good ideas about this tricky problem. I will really
appreciate some good ideas.
Alim Polat, PhD student
Linkoping University
Sweden