Xiaodong,

How different are the sizes of the samples? (10%, 50%, etc) Also, what is the
size of your sample vs the carrier wafer and how are you holding them together?
If your DC bias is changing, I assume you are fixing your RF power, right?  The
DC bias depends on the RF power and the chemical reaction so, if the small
sample is the one with the 10V bias, it sounds like your sample size is small
enough that the reaction products for the small sample barely produce a bias.

Ramon Figueroa

----- Original Message -----
From: xiaodong wang 
Subject: [mems-talk] Questions about DC-bias in dry etching
> 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?