Dear all,

I have questions about DC-bias in dry etching.

Conditions:
I use the same recipe, size of carrier wafer and Therma plasma (dry etching
machine),
only slight difference may be the size of the samples (on the carrier wafer).

Results:
for example, the DC bias for the first sample is 90 V,  the bias for the second
sample is 10 V
sometime it is 0. Etching results are very different.

My questions:
what are the parameters affecting the DC bias?
why are there so much difference of the bias in my etching condictions.

Anyone had this kind of experience?

Thanks.

Xiaodong