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

On Thu, Mar 3, 2011 at 12:21 AM, mail.wafer-bumping <
jjhreche@wafer-bumping.com> wrote:

> Why don't you read about silicon crystal structure and etchants? This is
> very basic.
> John Reche
>
>
> On 12:59 PM, Yu Chen wrote:
>
>> Dear all,
>>
>> when I was using TMAH to etch silicon, I noticed a notch under the mask(~2
>> nm). roughly like below
>>        _______________________________
>>               >                                   <
>>              /                                      \
>>             /                                        \
>>            /                                          \
>>
>>
>> does anybody know why it happens? is there any way to avoid this?
>> mask is SiN, TMAH(25%) 50 oC. I only etched 2.5 min as I do not want to
>> much
>> undercut.
>>
>> any information are welcome.
>>
>> sincerely
>>
>> Yu CHEN
>>
>>