Just one thin more to add.
When you spin small samples, you usually and with thicker resist on the
edges. Try to actually clean them, and if this is too crude, spin then while
on a dummy wafer with other wafer pieces touching each edge so the resist
can flow of the edges while spinning.
shay

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Edward Sebesta
Sent: Thursday, February 07, 2008 11:41 PM
To: General MEMS discussion
Subject: RE: [mems-talk] Problems on lithography exposing small samples
onMA/BA6 Mask and Bond Aligner

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