Hi Shimul,

I got the same problem years ago. I have solved it simply by changing
the flow ratio between SF6 and C4F8. You can find more information in
my paper:

Fei Wang, Xinxin Li, Nanxiang Guo, Yuelin Wang, and Songlin Feng, “A
silicon cantilever probe card with tip-to-pad electric feed-through
and automatic isolation of the metal coating,” Journal of
Micromechanics and Microengineering, Volume 16, Issue 7, pp.
1215-1220, 2006.

Hope it helps.

Fei

2009/5/19, shimul saha :
> Hello,
>
> I am using BOSCH process for deep dry etching of silicon. The gases are SF6,
> O2 during etching cycles and C4F8 during deposition cycles.. At present I am
> getting slightly negative sidewall, but I want a positive sidewall. Can you
> please provide any hint, probably changing gas ratio (incerase or decrease
> any of the gas content) or power to get a positive sidewall in etching. Any
> suggestions will be greatly helpful for me. Thanking you in advance.
>
> Best regards,
> Shimul

--
Best regards,
Yours sincerely
Fei Wang
______________
Postdoctoral researcher, Dr
MIC - Department of Micro and Nanotechnology
Technical University of Denmark (DTU)
Building 344, 1st floor, Room no. 130
DK-2800, Kgs. Lyngby
Denmark
Tel:  +45 4525 6311
Fax:  +45 4588 7762
Email: fei.wang@nanotech.dtu.dk
       http://www.nanotech.dtu.dk