Can you provide more details about your cryo-etching? like what gases, bias,
pressure, temperature...

blackness could be a good sign for you. You could check the "black silicon
method" on the scholar google. In their case, that blackness basically is
the Si needle on the bare Si area. It could work as a sign that tells you
got good aspect-ratio.

Good luck,
Jie

On Fri, Nov 28, 2008 at 6:01 PM,  wrote:

> Hi all,
>
> I am doing a silicon cryo-etch process. My processes before the final
> cryo-etch step are as follows:
>
> 1- start with a silicon wafer that has about 500 nm thermal oxide layer on
> its surface.
> 2- lithography steps using positive resist(HPR 504)
> 3- RIE to remove sio2
> 4- Branson etching
> 5- final step cryo-etching
>
> I get my wafer covered with a black gunck in the middle of it at the end of
> cryo step.
> In my wafer I don't have too many objects or features and a lot of it is
> bare silicon to be etched. I suspect this is the source of my problem. Does
> anybody have an idea how to solve this issue? I greatly appreciate your
> suggestions and comments.
>
> Thank you
>
> Syd

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