Lei,

      At least 2 companies built the answer in the 90's.  The problem
lies in the air vortexes above the substrate during spin.  Mask makers
hit it first with square substrates.  The cure was another square
substrate above and close the substrate to reduce air vortexes above the
treated substrate.

Bill Moffat

________________________________

From: mems-talk-bounces@memsnet.org on behalf of Robert MacDonald
Sent: Thu 2/11/2010 11:08 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] Help for photoresist coating



Lei,

it is possible to put a uniform coating on a rectangular substrate, or
at least to improve performance. You turn off the exhaust to your
spinner, and saturate the spinner environment with the solvent used in
the resist (sometimes by putting clothes soaked in it in there), and
close the lid. Then spin your resist. After the spin/spread cycle is
done, turn the exhaust on to initiate drying. this should help.

If your spinner doesn't have all these features automatically, you
should be able to rig something manual up. I did this years ago on small
rectangular substrates and got good improvement.

Good luck.

Rob MacDonald
Shearwater Scientific
www.shearwaterscientific.com