A good way to see if this is the source of the problem is to put the resist
coated wafer under 100X objective with a yellow filter and while observing -
remove the filter. If after few seconds the resist pops into the objective
and leaves a hole in the surface - this is it. F this is the case split the
exposure into 2 or three sorter exposures with few seconds in between.

Shay

-----Original Message-----
From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org]
On Behalf Of Bill Moffat
Sent: Thursday, January 14, 2010 12:36 AM
To: General MEMS discussion
Subject: Re: [mems-talk] Lithography on LTO

One possibility that comes to mind.  Very early technical paper by Mary Long
in the 80's on bubble formation in thick resist at exposure.  17 microns is
pretty thick.  During exposure the heat of the exposure lamp causes bubble
formation inside the resist.  If there is a bubble  partially on the expose
section it will give a half circle in the resist line that is developed
away.  Mary was at Motorola or Arizona University in Tucson when she gave
the paper.  My colleague and I would have thought the problem would have
been reversed, mouse bites in the aluminum because of the reflectivity of
the aluminum.  Try longer gentler exposure.  Also when we got mouse bites in
aluminum we increase the prime time from 5 minutes to 20 minutes.  The lower
number of hydroxyl ions on metal require longer HMDS exposure for the same
contact angle. Bill Moffat