Just a note:
   Looking at my reference (H. Seidel) I see that 30% KOH @ 80C should give
you a silicon to oxide selectivity of ~115 not the 300-400 you mention,
could your ref. be stating the silicon (100/110) selectivity? Typically the
lower the KOH concentration and temperature the better the Si/Ox
selectivity, while sacrificing Si etch rate i.e. 22% KOH @ 68C 35um/hr w/
Si/Ox Selectivity ~333

                eric




> Message: 1
> Date: Fri, 19 Jul 2002 17:22:52 -0400
>
> Message: 7
> Date: Mon, 22 Jul 2002 09:12:43 -0400 (EDT)
> From: Peng Yao 
> To: mems-talk@memsnet.org
> Subject: [mems-talk] KOH etch stop
> Reply-To: mems-talk@memsnet.org
>
> Hi,
> I planed to stop the KOH wet etching by the buried oxide layer of SOI
> wafer. But every time when I did the experiment, KOH just etched through
> the oxide layer. The oxide layer is about 1 micron thick, with 2 or 10
> micron 100 silicon on top. According to some references, it should be
equal
> to 300-400 microns silicon in 30wt% KOH solution @80 degree. But everytime
> I did the experiment, I just saw the reaction kept going and going, and
> suddenly etch through the wafer. (By seeing the bubble of reaction. I
> assume that the bubbling will decrease or even disappear when reaction
> reached to the oxide)
> Any explain or suggestion will be really appreciated.
>
> Thanks a lot!
>
> Peng Yao
> DOEs lab
> Electrical Engineering Dept.
> Univeristy of delaware
> Newark D.E 19716