We had similar problems with a thick photoresist (9.7 um) due to trapped air that would explode upon heating up the resist post-coat. What seemed to help the most was to redesign the alignment marks - keep them narrow and short. The second thing that helped was to let the PR settle for a few minutes after spinning before exposing it to any kind of heat. Hope this helps. Regards, -Deep Sent from Windows Mail From: Bill Chow Sent: Wednesday, May 14, 2014 9:14 AM To: General MEMS discussion Dear all, Recently, I am working on a two layer SU-8 structure. All the process are followed with the suggested procedures. However, the problem appeared when I try to look for the alignment mark, after I have spin coated and prebaked the second layer of SU-8, it is difficult to locate the first layer exposed features. First layer thickness : 3.7um Second layer thickness : 17 - 20um I found that it is extremely difficult to locate the first layer pattern under the microscope after I have coated the second layer, despite it can be seen be naked eye.... Sometimes if there are some defect or bump in the 2nd layer above the alignment mark, then it can be seen clearly. However, it is a random process and will affect my pattern. Are there any ways to improve the visiblity of the alignment mark after I have coated the 2nd layer? Thanks. Regards, Bill _______________________________________________ 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