help with evaporating tungsten

Charis Quay Huei Li cquayhl at
Mon Dec 11 18:40:18 PST 2006

Dear all,

     Recently we have been trying in our lab to evaporate tungsten as 
e-beam alignment marks. We are encountering some problems with poor 
adhesion during liftoff and we were wondering if ay of you who do a 
similar process would mind sharing your steps?
     Our smallest feature size is about 100nm and we are using either 
200K/950K or 495K/950K PMMA bilayer.
     Initially, after just soaking in acetone, squirting and heating up 
the acetone (and squirting again) one chip came out with extra metal all 
over the place. I then tried sonicating in larger and larger time 
increments, starting with 10s and finally going up to minutes at a time. 
It looked like the metal wouldn't come off and wouldn't come off, and then 
suddenly a lot of it came off at once at t = 20 minutes roughly.
     Please let me know if you have any insight into this.
     Thanks very much.


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