Hi， Yu Chen,

Do you mean that the TMAH etch the <111> silicon a little about 2nm just
under the MASK?

 i'm not sure if i got your point.

The selectivity between <111> and <100> is about 1:10 in my experience (9
part 25% +1Part IPA +80 DegreeC),  The selectivity of  your recipe must be
small than 1:10 but it still have maybe 1:100. After 2.5min etching, the
several nms undercutting is  inevitable.

BR，

YanXin


On Thu, Mar 3, 2011 at 9:29 AM, Yu Chen  wrote:

> I am not sure I explained my questions clear last time.
> I understand TMAH etch is anisotropic etch.
> the question are the  notches "<" and "> " I drew in the picture which is
> ~2nm.
>
> of course if the silicon was etched during mask definition before TMAH
> etching, such structure can formed,
> my questions are
> is this normal or because the way I did it?
> how to avoid this?
>
> Thanks
>
> Best
>
> YU CHEN

--
Yan Xin
-Pen-Tung Sah MEMS Research Center,
-Xiamen University, CHINA
XMU HOME:
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