Amani, STR 1075 is nominally intended for ~10 µm features, and as such, is not the best possible choice for a 100 µm thick coat (although 30 µm is not too bad). With a similar resist, AZP4620 (which has a slightly lower solids content, at ~41% rather than ~44%), the thickest I was able to achieve in a single coat was 65 µm. In order to achieve a 100 µm coat with the STR 1075, you would need to perform a double coat at least, and perhaps a triple coat or more (I had a few advantages in the resist processing system I used - an EVG150, which is designed for thick resist applications). In general, for all thick resists, there are a few general guidelines to keep in mind: 1. For the softbake, make sure not to expose the wafer too rapidly to too high a temperature. A hot plate with ramped proximity pins, which can allow a gradual approach to the hot plate, is ideal. If you expose the wafer too quickly, the solvent in the resist closest to the wafer will flash to vapor without being able to escape, and will cause bubbles in the coat. 2. Edge bead is going to be a major issue as well. A good edge bead removal process will help improve later exposure characteristics. 3. Thick resists have one unifying characteristic - they are all high solids (and thus low solvent) content. This provides its own challenges. Basically, the resist is so thick, and the solvent content so low, that, during the initial stages of the spin, the solvent of the top layer of resist evaporates sufficiently to significantly increase the viscosity, while the resist in the under-layer remains at the same, lower viscosity. This causes irregular flow velocities between top and bottom, which can lead to "wrinkling" of the resist. The EVG150 integrates an automated cover for the coating module, which allows for coating in a solvent rich environment, preventing the drying of the resist, and allowing improved resist uniformity. For the thicker regions of the range you are looking at, you may also want to look at another material - AZ50XT from Clariant. This material is nominally for 50 - 75 µm films, and can be stretched to 100 µm without too much trouble. Best Regards, Chad Brubaker EV Group invent * innovate * implement Technology - Tel: (602) 437-9492, Fax: (602)437-9435 e-mail: C.Brubaker@EVGroup.com, www.EVGroup.com This message and any attachments contain confidential or privileged information, which is intended for the named addressee(s) only. If you have received it in error, please notify the sender immediately and then delete this e-mail. Please note that unauthorized review, copying, disclosing, distributing or otherwise making use of the information is strictly prohibited. -----Original Message----- From: mems-talk-bounces@memsnet.org [mailto:mems-talk-bounces@memsnet.org] On Behalf Of Amani Salim Sent: Friday, August 06, 2004 7:48 PM To: mems-talk@memsnet.org; amanis@ece.umn.edu Subject: [mems-talk] tips for making thick 1075 photoresist Dear Colleagues, I am trying to make a very thick photoresist (using 1075 positive thick PR) and eventually will exposed it using a clear field mask, the thickness am looking so far is from 30-100 microns, if anyone has any tips for me to make this process a success (exposure time, soft bake and post bake temp and time, ect..), that'll be great, thanks Amani Salim ****************************************** Research Assistant Department of Electrical and Computer Eng. U of Minnesota,T.C. UMBM Lab Office phone: 612 626-0590 Lab phone: 612-626-7188 _______________________________________________ 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/