Yilei, are you sure about your etching gas?
O2 is mixed with CF4 to avoid the formation of
the polymer layer (O2 reacts with C).

How much power do you use, for RIE?
Is it possible that the polymer layer already presents
on the sample could be "sputtered" away and deposit
all over the oxide?
You can do a pure O2 etching before extracting the sample
from the RIE system.

Or try to exchange the power connection
to the electrodes of the system, if you can:
the sample connected to ground and the other electrode to power,
then go with lower power and longer time than RIE:
it is only a chemical etching without ions mechanical bombardment.

Paolo Tassini

-----Messaggio Originale-----
Da: "yilei zhang" 
Oggetto: [mems-talk] residues on RIE etched sio2

> Hello colleagues:
> I used rie (10% O2, 90% CF4) to etch silicon with a polymer layer and a
sio2
> mask, but found the left sio2 cannot be further etched away with HF. I
> searched the archive and found the RIE may generate a polymer layer or
> fluorocarbon, and a layer of fluorinated si. I want to know is there any
> way to remove the left sio2 mask? Thanks.
>
> Regards,
> Yilei Zhang