Fusion UV bake system
rissman at stanford.edu
Thu Jan 11 11:53:50 PST 2007
UV bake is a standard industry process for hardening of resist used
in harsh conditions, e.g. aggressive plasma etch processes and high
dose implants. This process uses a short UV exposure to create a
skin on the resist to fix the profile, followed by an extended bake
of up to 200 degrees with UV exposure. The efficacy of this process
can be found in the literature in papers such as Allen, ECS, 1982:
SNF has a Fusion UV bake system and Cesar Baxter has gotten the
system operational. I have done some preliminary testing and have
found the following:
1. I verified that resist could be baked to 200 degrees with no
pattern flow using the standard process.
2. With Nancy Latta's help, we were able to demonstrate increase in
selectivity for two kinds of etches. On stsetch, Nancy ran a 10
minute "deep" program. The consumption of resist on the UV baked
resist was about 70 nm (1 um starting film) and the consumption of
resist on an unbaked wafer was 620 nm, or about a 9 times
decrease. On the amtetcher, Nancy ran a 40 minute oxide etch. This
consumed about 400 nm of resist on a UV baked sample and totally
consumed the resist on the control, unbaked wafer.
3. Since the Fusion is a broad spectrum UV source, we can use it to
expose PMMA. A 30 second exposure with the bulb on low was
sufficient to expose a standard PMMA film, which developed away in
I have to this point had the following negative results.
1. Ed Myers ran the "shallow" program on stsetch2 for 10 minutes (120
cycles), and the resist consumption for the control and UV baked
sample were comparable.
2. I have been unable to crosslink PMMA with UV exposure. The PMMA
is consumed (either sublimation or oxidation) at a dose which should
be sufficient from crosslinking.
I am presently looking for a few users who would like to try the
Fusion with their processes. As we get more data on the system, we
can turn it over to general use. Please contact me if you have
processes which you think will benefit from using the Fusion system
so we can arrange for a time to work together.
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