Bake problem with SVGDEV track 2
Gary J Sosa
gsosa at stanford.edu
Wed Sep 29 15:38:48 PDT 2010
I measured the hotplate temperature on both developer tracks with our test instruments. Everything looks good. I also made sure that the hotplate vacuum was working properly and that wafers were held in firm contact to the hotplate surface. Here are the results of the measurements:
Target temperature set at 110 Deg. C.
Developer #2(Front): 110.2 Deg C. Uniformity: 0.23%
Developer #1(Back): 109.9 Deg C. Uniformity: 0.23%
Used a thermocouple wafer to measure the target temperature at the center of the hotplate. Used a surface contact thermometer to measure the hotplate uniformity . Both hotplates are within <.5 degrees of setpoint and within .3 degrees of each-other.
----- Original Message -----
From: "Linda Ohara" <linda.ohara at asml.com>
To: "Gary J Sosa" <gsosa at stanford.edu>
Sent: Wednesday, September 29, 2010 10:31:56 AM
Subject: FW: Bake problem with SVGDEV track 2
From: Arash Hazeghi [mailto:ahazeghi at stanford.edu]
Sent: Tuesday, September 28, 2010 11:01 PM
To: 'Mary Tang'; Mahnaz Mansourpour; 'Thumser, Uli'
Cc: Ping Ding; svgdev2 at snf.stanford.edu
Subject: Bake problem with SVGDEV track 2
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 side.
Stanford Center for Integrated Systems
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Stanford, CA 94305
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