1. If you evaporated the Cr with e-beam, the e-beam may affect the PMMA.
2. Or in case of  thermal evaporation, substrate must be cool.
3. You'd better try to use thicker PMMA about 100nm and sputtering process.

hope this helpful...


Lee, Duhyun
========================================
----- Original Message -----
From: "Z. Jiang" 
To: 
Sent: Friday, September 10, 2004 9:22 PM
Subject: [mems-talk] pmma lift off problem


> 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
>
>
>