How did you fix your sample? Why would the liquid get your top Si layer? By
vapor?

It should be easy to dry etch (e.g. DRIE) through your handle layer of the
SOI. If you work with a whole wafer, the top (device) layer will face down
to the Helium flow and should be intact during DRIE. If you are working with
a small piece of SOI, I think it is pretty difficult to protect your top Si
layer if you couldn't spin photoresist or grow oxide on it. Then you might
want to do the dry etch to open the through holes before you pattern the top
layer.

Hope it helps.

Jie

On Wed, May 5, 2010 at 11:25 AM, weiquan yang  wrote:

> I want to etch away the Si base substrate of SOI wafer from back side and
> remain the top thin Si layer and buried oxide layer.  I try the wet etching
> in both ways (using TMAH or KOH solution). The SiO2 or Si3N4 deposited by
> PECVD were used as protection mask layers (both side: top and back).
> However
> SiO2 or Si3N4 can not survive very well in the hot sulution for long term
> (several hours). Some local areas of top Si layer of SOI was etched
> away. Could you guys kindly give me some suggestions? Is this due to the
> quality of SiO2 or Si3N4 layer? The quality of SiO2 or Si3N4 by PECVD may
> be
> not very good , so the SiO2 or Si3N4 can not survive.
> Some dry etching suggestion is aslo welcome.
>
> Thank you!
>
> Weiquan Yang

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