Bake problem with SVGDEV track 2

Arash Hazeghi ahazeghi at
Tue Sep 28 23:01:02 PDT 2010



In the past three weeks I have had issues with my lift off process, after
calibrating exposure and focus with ASML many times, I still had
inconsistent results, the outer dies on the wafer showed artifacts after
liftoff. My devices have min CD (0.5um) lines and spaces, this happened for
both 1um and 1.6um 3612 PR. The inner dies were perfect at the same time. A
few times I could see a circular trace on the wafer with the center of the
wafer looking a bit brighter than the edges. Mahnaz suggested that this was
a result of underexposure for the outer dies. However after consulting with
ASML engineers and carefully inspecting leveling for each die it was
determined that all dies are exposed consistently. Last night I noticed a
wafer showing the same circular trace when it went through post exposure
bake on SVGDEV track #2 (front). Since the wafer had not been developed,
only the track hot plate could have caused this visually-apparent artifact .
Today I checked temperature uniformity for track 2 hot plate with an IR
sensor, to my surprise it seems that the hot plate is not even sitting at
110C but it is about 50C and only when you hit "start" it is warmed up to
the bake temperature. The hot plate on track 2 seems to be sitting at ~120C
all the time. 

There is also a huge temperature gradient on this track with top side  as
high as 120C and the lower and right side falling to about 40C, here you can
see how the temperature changes as I move the laser spot around the wafer.


This is very problematic for people who want to resolve near min CD features
across a whole wafer. Perhaps it is better to devote a separate hot plate
with a clean and even surface for post exposure bake which the users will
not use for braining samples that have resist/contamination on the bask







Arash Hazeghi


PhD Candidate

Stanford Center for Integrated Systems

CIS-X 300, 420 Via Palou Mall, 

Stanford, CA 94305


phone: +1-650-725-0418



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