Hi Grace, I would also recommend trying the etch without the ammonium persulfate. However, I am not sure what that will do to your oxide to aluminum selectivity. A typical recipe is listed below. 250ml TMAH (25% from Aldrich) 375 ml H2O 22g of silicic acid 90C with an etch rate ~1.0um Phil Tabada -----Original Message----- From: gracekuo [mailto:super511_1028@yahoo.com.tw] Sent: Sunday, August 18, 2002 10:13 PM To: mems-talk@memsnet.org Cc: gracekuo@gct.com.tw Subject: [mems-talk] RE: Contamination issue of additive in THAH etching Hi Philipe and Mike, thank you for your reply, let me describe the contamination more specific, after we add the AP (2.5g dissolved in DI water, add into the etchant per 15 min. ) into the heated etchant (2L ; include TMAH, AP, SA, and DI water), we can see white particulates float over the etchant immediately, the particulate size is quite big (~2x1x1 cm3), and it can dissolve into the etchant after 10~15min. And after the etching, we just clean the sample with DI water, but as we observe the etched sample, there are plenty of particles over the sample surface, and the particulates is especially big stored in etched cavity, as we analysis the particle with EDAX, it just have Si and O composition, i dont know if it is just the silicic acid that precipitated out of solution, and could anyone give us some suggestion to prevent this particulates, thank you for your help, grace Email:super511_1028@yahoo.com.tw ----------------------------------------------------------------- < (C$Q3# Yahoo!)_ www.yahoo.com.tw _______________________________________________ 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/ DISCLAIMER: Unless expressly stated otherwise, this message is confidential and may be privileged. It is intended for the addressee(s) only. Access, copying, disclosure or re-use of the e-mail or any information contained therein by any other person is not authorized. If you are not the intended recipient please notify the sender immediately by returning the e-mail to the originator.