Hi William, Can you consider using a metallic backside coating prior to your photo process? I would suggest sputtering 300 Ang TiW on the backside of the wafer, the reflectivity of TiW is relatively poor, and it can be removed very easily after photo using a wet etch in peroxide. Justin C. Borski MEMS Program Manager Advanced MicroSensors Inc. jborski@advancedmicrosensors.com -----Original Message----- From: William Lanford-Crick [mailto:wlanford@uiuc.edu] Sent: Friday, May 14, 2004 11:28 PM To: General MEMS discussion Subject: [mems-talk] Photlith on transparent materials Hi Group, I am having difficulty patterning wide-bandgap semiconductors which are transparent to the 436 nm in our g-line stepper. The incident radiation seems to be reflecting off the wafer chuck and back up into the photoresist. The causes the entire die to be somewhat exposed. How can I prevent this? I have found some improvement by additionally spinning photoresist onto the backside of the wafer (AZ5214E at 2k rpm--I have not measured the thickness at that speed). I suspect that using a very thick PR layer would solve the problem (by absorbing the radiation) but I would need to remove it immediately after developing the patterns, and I don't see an easy way to do that. Any suggestions? Are there any spin-on materials that have high absorption at 436 nm and are easy to remove (without disturbing PR)? Thanks for any suggestions, William B Lanford-Crick Micro and Nanotechnology Lab, UIUC _______________________________________________ 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/ **********************AMS CONFIDENTIAL AND PROPRIETARY INFORMATION***************************** This e-mail communication and any attachments are confidential and intended only for the use of the designated recipients named above.