It could due to the residue stress of your SOI wafers. You might need to ask
the vendor first to rule out this possibility.

Was ur 2nd DRIE done after you performed one time of DRIE on that wafer or
you started with another new patterned wafer? And did you notice the
distortion after releasing (I mean etching away the Buried OX) or right
after DRIE?

Jie

On Tue, Jan 13, 2009 at 9:06 AM, Jungwook Choi  wrote:

> Dear all,
>
> We had performed DRIE to etch the 20 um thick silicon layer on SOI wafer.
> However, the silicon layer was not fully etched, so the silicon was
> remained
> at the bottom (on top of buried oxide).
>
> For the perfect etching of silicon, we had performed second DRIE process on
> same layer. We realized that the many compliant beams were distorted (it
> looks like distortion after releasing the residual stress between two
> layers) after second DRIE process and became thin compared to the result of
> first DRIE process.
>
> We think that the high temperature during DRIE would be one of candidate
> for
> distortion.
>
> It will be highly appreciated if anybody knows or guesses the reasons and
> possibilities of distortion after second DRIE process. The solution to
> avoid
> the distortion of beams will be very helpful to us.
>
> Regards,
>
> Jungwook Choi
>

*  Zou Jie (Jay)
*  Department of Physics
*  University of Florida
*  Tel: +1-352-846-8018
*  Email: zoujiepku@gmail.com
*  Homepage: http://plaza.ufl.edu/zoujie/