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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