Tips for Iontech uniformity?

[sjo at stanford.edu]

Hello,

Does anyone have some good tips how the etch uniformity can be  
improved in Drytek 1? I am using the resist strip O2 plasma, 500  
mTorr, 100 sccm O2, 83 Watts, and the etch rate at the center of my 4"  
wafer always seems vastly different different from the etch rate at  
the wafer edge.

Any suggestions?

Thanks!
Sebastian