Dear Peng, A possible explanation for your observation of increased etch rate with higher He addition to SF6 etch gas could be, that the He increases the concentration of free radicals (eigher ionized or non-ionized). Since SF6 alone doesn't etch anything at all, the etch rate is primarily controlled by the number (and kind) of reactive species in the process chamber at a time and the bias voltage at the substrate. The He is easily ionized and thus can enhance ionization of SF6 itself. Best regards, Joern Koblitz ****************************** Joern Koblitz microFAB Bremen GmbH - the MEMS Wafer Foundry Universitaetsallee 5 D-28359 Bremen, Germany Phone: +49 421 24 100 0 Fax: +49 421 24 100 99 eMail: koblitz@microfab.de website: www.microfab.de ****************************** -----Original Message----- From: Peng Yao [mailto:yaopeng@UDel.Edu] Posted At: Thursday, March 28, 2002 9:48 PM Posted To: MEMS-talk Conversation: [mems-talk] Helium's role in RIE Subject: [mems-talk] Helium's role in RIE Hi all, I am using SF6+He to etch silicon. I thought He will be helpful to get a smother surface. I fixed all the other parameters like pressure, power, etching time... and only change the flow rate of SF6 and He. The strange thing is that the etching speed of SF6:He=10:20 was larger than that of SF6:He=20:20. (They were etched in same machine and at same day, one after the other) And also I found that if I fix the gas flow of SF6 and only change the persentage of He, the etching rate will increase with increasing the persentage of He. All these seem to indicate that He can not only cool the photoresist, but also will help the etching. Does anyone else has similar experience. And I am not sure what kind effect of He to side wall, will it make the process more isotropic or more anisotropic? 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.mems-exchange.org/