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:yaopeng@UDel.Edu] Sent: Monday, July 22, 2002 6:13 AM To: mems-talk@memsnet.org 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 _______________________________________________ MEMS-talk@memsnet.org mailing list: to unsubscribe or change your list options, visit http://mail.mems-exchange.org/mailman/listinfo/mems-talk Hosted by the MEMS Exchange, providers of MEMS processing services. Visit us at http://www.memsnet.org/ "This email and any attachments may contain information that is confidential and proprietary information of Veeco Instruments Inc. and are intended only for the use of the addressee. Unauthorized use, distribution or copying is forbidden. If you have received this email in error, please notify the sender immediately by return email and delete all copies of this message and any attachments from your computer. Thank you."