One micron of buried oxide should be more than sufficient as an etch "stop"
under these conditions. I suggest that you measure the Si etch rate, then
calculate the time required to etch to the Si-SiO2 interface. Allow for
some time for overetch, but not long enough to go through the oxide.
If you want to further improve the etch selectivity of the Si to SiO2, try
lowering the KOH concentration to 20% and the temperature to 70 degC.
Roger Shile
-----Original Message-----
From: Peng Yao [mailto:[email protected]]
Sent: Monday, July 22, 2002 6:13 AM
To: [email protected]
Subject: [mems-talk] KOH etch stop
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
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