Matteo,
       Soft bake, you are trying to remove solvent from the resist or Polymer
without desentisising the sentitiser.  The sensitiser can be activated by U.V.
light or heat.  At 90 degrees C the sensitiser is not affected at all for hours.
So stay at 90 or below.  A hot plate is best for 1 wafer as it will bake from
below and drive the solvent out at the top of the resist.  The best of all would
be a vacuum hot plate to suck out the solvent and bake at the same time.  An
oven is a poor choice but sometimes effective because a number of wafers can be
treated at once.  The oven heats by radiation, not a lot at 90 C.  By convection
not a lot until the surrounding gas gets to 90 C and conduction, if you use
Teflon cassettes, not a lot because the cassette is in an insulator.  Luckily
the sensitser is not hurt at 90 for hours so you can spend a long time in the
oven to achieve the solvent removal.  Hard bake you have completed all the
definition of the resist dimensions so you do not need a lot of temperature
uniformity.  Aim for 150 degrees.  A higher temperature oven or hot plate will
encourage resist flow and reduction or scum at the bottom of opened holes.  I
manufacture specialized ovens for lithography work so I will send you a
commercial to your direct email  Bill Moffat

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Matteo Dainese
Sent: Thursday, November 11, 2004 7:01 AM
To: [email protected]
Subject: [mems-talk] oven/hot plate bake


Hello all,
I would like to increase my awareness
when I'm processing with the different
polymers I'm using. I have this small question:
what is the difference between
curing/soft baking/hard baking a photoresist,
or a polymer in general, on a hotplate or
in a normal oven (same temperature)?
Is there any reason why I should choose either
one or the other?
I would be happy if any of you can give an opinion.
Thank you

Matteo Dainese

Graduate student
KTH - Royal Institute of Technology
Stockholm
Sweden
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