Ramon,

Thank you for your reply.

The size difference of the samples are less than 30%.

The samples are very small compared to the carrier wafer (8 inch wafer). The
size of samples

are about 2 cm wide and 4 cm long.

I use PR to hold the samples.

Yes, the RF power is fixed.

Xiaodong

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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.