They made a metal cage that held the resist coated mask face up and a blank mask about 1/4" away from it. This trapped air between the masks and there was little if any turbulence, during spin. This was particularly important in the case of mask blanks. Because the masks were square the corners were particularly affected by turbulence. One French company tried to patent the technique years ago. Bill -----Original Message----- From: mems-talk-bounces+bmoffat=yieldengineering.com@memsnet.org [mailto:mems- talk-bounces+bmoffat=yieldengineering.com@memsnet.org] On Behalf Of Yingtao Tian Sent: Thursday, June 28, 2012 4:42 AM To: General MEMS discussion Subject: Re: [mems-talk] Ultrathick SU8 photoresist processing Hi Bill, Thanks for the suggestion. Did you mean they used to put the second blank mask during soft bake process and will the two masks remain parallel to each other ? I tried to put a petri dish set up with a tweezer on one side, but it does help very much. Could you suggest some literature to read more details please? Thanks a lot! Regards, Yingtao -----Original Message----- From: mems-talk-bounces+y.tian=bham.ac.uk@memsnet.org [mailto:mems-talk- bounces+y.tian=bham.ac.uk@memsnet.org] On Behalf Of Bill Moffat Sent: 27 June 2012 20:54 To: General MEMS discussion Subject: Re: [mems-talk] Ultrathick SU8 photoresist processing Air turbulence can be the answer. When engineers were experimenting with super thick resist on photo masks they used to put a second blank mask a short distance above the mask being coated. This protected the resist surface from air turbulence. You may want to use a variation of this. Bill Moffat -----Original Message----- From: mems-talk-bounces+bmoffat=yieldengineering.com@memsnet.org [mailto:mems- talk-bounces+bmoffat=yieldengineering.com@memsnet.org] On Behalf Of Yingtao Tian Sent: Wednesday, June 27, 2012 9:36 AM To: mems-talk@memsnet.org Subject: [mems-talk] Ultrathick SU8 photoresist processing Dear All, I am trying to make very thick SU8 photoresist on silicon wafer, however, I found that, even the resist was spun coated, the surface will not be flat. I tried to put over 200 um thick resist but the thickness can vary between 180 - 220 across the whole wafer. I have tried to adjust the levelness of the hotplate by using an inclinometer and it was almost perfectly levelled. Somebody suggested that the air turbulence in the cleanroom does matter for such very thick resist. But, I have no evidence to doubt it. Anybody has ideas? Thanks, Yingtao _______________________________________________ Hosted by the MEMS and Nanotechnology Exchange, the country's leading provider of MEMS and Nanotechnology design and fabrication services. Visit us at http://www.mems-exchange.org Want to advertise to this community? See http://www.memsnet.org To unsubscribe: http://mail.mems-exchange.org/mailman/listinfo/mems-talk _______________________________________________ Hosted by the MEMS and Nanotechnology Exchange, the country's leading provider of MEMS and Nanotechnology design and fabrication services. Visit us at http://www.mems-exchange.org Want to advertise to this community? See http://www.memsnet.org To unsubscribe: http://mail.mems-exchange.org/mailman/listinfo/mems-talk _______________________________________________ Hosted by the MEMS and Nanotechnology Exchange, the country's leading provider of MEMS and Nanotechnology design and fabrication services. Visit us at http://www.mems-exchange.org Want to advertise to this community? See http://www.memsnet.org To unsubscribe: http://mail.mems-exchange.org/mailman/listinfo/mems-talk _______________________________________________ Hosted by the MEMS and Nanotechnology Exchange, the country's leading provider of MEMS and Nanotechnology design and fabrication services. Visit us at http://www.mems-exchange.org Want to advertise to this community? See http://www.memsnet.org To unsubscribe: http://mail.mems-exchange.org/mailman/listinfo/mems-talk