hi all

 I spin coated 15-20nm 950k PMMA on Si chip, baked at 200c for 2min, made
some pattern and then evaporated 5nm Cr on top. But when I tried to lift
off it was very difficult. I used acetone, ultrasonic and even oxygen
plasma. Finally PMMA was lift off but some part of Cr pattern was damaged.
I guess that was because ultrasonic destroyed the adhesion between Si and
Cr. I don't know why the lift off can be so difficult. Is that because Cr
is high-melting-point metal? Can someone tell me? Many thanks.

Cheers

Jiang