I would like to thank everyone for your kind help. Thanks to your
suggestions we have modified our process and now it is working fine.
We did not see Si grass at the trench bottom anymore. So we agree with
you that the main problem here was the passivation was so strong which
dominated the etching. Nevertheless, some vertical striations still
remain so we will vary our process a bit to see how it works.

Greetings,
Nam Le, graduate student
Ritsumeikan University, Japan

On Thu, Dec 11, 2008 at 5:44 PM, 汪飞  wrote:
> Hi Nam Le,
>
> If you are doing through wafter DRIE, it would not matter since you
> will not have a bottom surface. But for the etched depth of 100um, you
> will get more or less grass effect. Try to lower the passivation gas
> flow to 50sccm, and check the profile. It would probably be helpful to
> weaken the grass effect while may be harmful for the verticality.
>
> You can also get some further informations about how to control the
> etching profile and grass effect from following references:
>
> 1.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, 2006(16): 1215-1220.
>
> 2. A.A. Ayón, R. Braff, C.C. Lin, H.H. Sawin, and M.A. Schmidt,
> Characterization of a time multiplexed inductively coupled plasma
> etcher, Journal of the Electrochemical Society, 1999(146): 339-349.
>
> Hope it helps, Good luck!
>
> Yours,
> Fei
>