Nitrogen is released when the resist is exposed. If your rather high temp
softbake creates a crust on the resist surfaces, the nitrogen might not have
a way to escape.
You might want to reduce the SB temp to 95 deg.
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Wei Cheng
Sent: Friday, February 01, 2013 6:25 AM
To: General MEMS discussion
Subject: [mems-talk] AZ5218 PR issue in Metal Lift off process
I use AZ5218 in metal lift off process. I have seen lots of bubbles in the
PR sometimes. See pictures below. Lots of bubbles form a line in the center
of the scribe-line. The bubble line lies at exactly where two exposure
fields overlap. So the PR in this 10um width strip sees double exposure. And
this strip is where I can find most of the bubbles. This bubble issue does
not happen always. On some other wafers or even some other portion of the
same wafer, I can only find much less bubble.
One time I did inspection right after post exposure bake (PEB) I saw the
bubbles on the wafer already.
This is a mystery to me. Anyone has any idea what could be wrong?
Spin speed of ~1000rpm=20
Soft bake: 110C/90"=20
~3.7um film thickness
Exposure: 55~70mj in Canon i1 stepper
PEB: 115C / 75"~90"
Flood exposure 300" in Quintel aligner
Develop: diluted AZ400K / 100"
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