Dear Yanjun,
WE had a simillar case lately - if the LPCVD nitride comes highly stressed, it
cracks on sharp corners and around pinholes, the oxide undercuts and the nitride
lifts of an curls. This causes long "v-gooves" shapes to be etched in the
silicon
from sharp corners and pinholes.

Shay

"Yanjun(David) Tang" wrote:

> Hi, MEMS folks:
>
>      This is David Tang, a graduate student in Louisiana Tech University. I'm
> doing (100) Silicon deep etching (500mm). The Si wafer is coated with 0.6mm
> SiO2 layer and 0.2mm Silicon Nitrate layer is coated on SiO2 layer(Silicon
> Quest company). The etchant is KOH, temp 800C, stirring 220RPM and Silicon
> Nitrate layer is used for masking. During the etching, I found Silicon Nitrate
> stripped at some edge area, leading to the severe distortion of expected
> pattern. Was it because 0.2mm Silicon Nitrate isn't sufficient to mask against
> KOH etchant? Could you help me to improve process to obtain best pattern? Did
> someone ever deposit Au/Cr layer on Silicon Nitrate layer to help mask against
> KOH etchant? Thank you for any help.
>
> Best regards
>
> Yanjun(David) Tang
>
> Graduate student
> Institute for Micromanufacturing
> Louisiana Tech University
>
> 1401 Tech Farm Rd. Apt. #238, Ruston, LA 71270, USA
> Email: yta001@coes.latech.edu
>           tang_yanjun@yahoo.com
> Homepage: http://www.latech.edu/~yta001/index.htm
> Tel: 1-318-255-5133
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