Dear Yanjun,
As  a general rule, reducing the temperature and the concentration of the KOH
will increase your selectivity. However, the etch rate will go down too.
Ýou didn't mention the concentration of your KOH mixture, if it's greater than
30 wt %, reduce it. Also, reduce the temperature to 60 degree-C. As a rule of
thumb, the etch rate halves for every 10 degrees-C you reduce the temperature,
so you'll have to etch about 4 times longer.
If you still don't have the required selectivity, you might try to go down in
concentration before you go below 60 degrees-C. (Just a hunch, not based on
facts that I know of.)
Good luck,
Sjoerd Haasl


> Message: 5
> From: "Yanjun(David) Tang" 
> To: 
> Date: Mon, 16 Sep 2002 02:52:25 -0700
> Subject: [mems-talk] Si/SiO2 KOH etching selectivity
> Reply-To: [email protected]
>
> Hi, MEMS folks
>      I've been working on releasing SiO2 cantilever beams from Si with KOH wet
etching. SiO2 beams was attached to Si layer at one side. The temperature is 80
degree-C and stirring is 220RPM. The etching time is about 15mins. By
caculation, only 15um Si layer needs to be etched away to release cantilever
beam. I didn't get satisfactory etching selectivity on Si/SiO2 etching rate.
SiO2 beams began to be etched even before Si was cleaned. The resulted
cantilever beam wasn't integrated. Do you have some suggestions about how to
increase the etching selectivity or any ideas about releasing SiO2 cantilever
beams from Si. Thanks.
>
> Best regards
>
> Yanjun(David) Tang
>
> Graduate student
> Institute for Micromanufacturing
> Louisiana Tech University
>
> 1401 Tech Farm Rd. Apt. #238, Ruston, LA 71270, USA
> Email: [email protected]
>           [email protected]
>
> Tel: 1-318-255-5133
>
> --__--__--
>