The temperature for a hard bake, that is a post develop bake, for a
positive resist (Novolak resist) could be anywhere from 120 deg. C to
160 deg. C. If on a hot plate they could be just a few minutes, in an
oven probably 20 to 30 min. Depends how much process control you want
for an oven bake. It will take about 30 to 40 minutes to reach
temperature in an oven.

The key thing is that with the higher temperatures the resist becomes
more difficult to remove post etch or post implant. Depending whether
you want to remove the resist with O2 plasma, solvents, resist stripper,
or sulfuric peroxide will depend on your substrate and the temperature
of the bake.

Also, it depends what you are trying to accomplish. For ion implant, you
just want to get the solvent out of the resist and not have your
implanter coated on the inside with tar so 120 to 130 deg. C would work
fine. For wet etch you want good adhesion. For plasma etch you are
concerned with etch erosion. If your substrate is going to get hot, a
higher temperature bake might be useful. If you have resist popping in a
plasma a higher temperature might be better.

If the temperature is too high the edges of the resist can round off.
This might be something you want or want to avoid.

There are two condensation reactions with positive resist. One at 130
degrees which gives off water and another at 160 to 170 degrees which
gives off another organic. At higher temperatures you are creating a
thermoset plastic and can plan to use really hot sulfuric peroxide or
plasma to remove it.

So see if you can bake at lower temperatures for whatever your process
is.

Not knowing your process it is difficult to make a recommendation.
However, if you had an AZ resist you could call someone and get help.
1813, good luck!

Incidentally, a post exposure bake is also useful, but if you are doing
features of 3 microns or less.

Edward H. Sebesta
Independent MEMS and Semiconductor Process Engineer



-----Original Message-----
From: mems-talk-bounces@memsnet.org
[mailto:mems-talk-bounces@memsnet.org] On Behalf Of Evelyn B
Sent: Saturday, February 07, 2009 9:48 AM
To: General MEMS discussion; Evelyn Benabe
Subject: [mems-talk] Resist 1813 post development bake


I have heard that for improved etch resistance 1813 resist should be
post-develop baked.  Does any one know the recommended post development
bake temperature and duration for 1813 resist?  I understand that both
the temperature and duration should be larger than that of the
soft-bake.