Qing, I see two possible issues with the method you are using. First, I can almost guarantee you are performing an insufficient softbake. The idea of the short soft-bakes in between coats isn't bad (bear in mind, for a 10 um thick coat of AZ P4620, you will typically need a bake in excess of 3 min). However, you need to bear in mind that a cured layer of photoresist becomes a heat resistance film, so, as you get thicker, its important to eventually increase the bake time. Your best bet would be on the final coat, when you'll probably want a bake of ~ ten minutes. Even better would be to try to get the proper film thickness in fewer coats (AZP4620 should easily be capable of a 20 - 25 um coat, if your spinner is good enough; even >50 is possible). That way, you are not over-curing (and making harder to expose/develop) the lower layers. The second issue has to do with the exposure method. For good sidewall performance, its necessary to use a collimated light source, which most flood expose systems are not. Based on the exposure source, its possible to create a light angle of several tens of degrees, which directly translates to sidewall profile. You'd be better off using a proximity/contact mask aligner such as an EVG620. 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+c.brubaker=evgroup.com@memsnet.org [mailto:mems-talk- bounces+c.brubaker=evgroup.com@memsnet.org] On Behalf Of Qing Yao Sent: Monday, February 16, 2004 10:19 AM To: MEMS-talk Subject: [mems-talk] thick photoresist development Hi, I have difficulty in patterning thick photoresist. The following is what I did: 1> coat a 4" Si wafer with 5 layers of AZ4620 using a spinner. The thickness of each layer is about 10 microns and the total thickness of PR is about 50 microns. Bake the wafer at 110 degree centigrade for 1 min. after the deposition of each single layer. 2> print the image pattern on a transparency (emulsion down) using a 5080-dpi laser printer. put the transparency mask on top of the PR layer and put a 4" quartz plate on top of the mask. Then do Fusion Flood exposure. the dose is about 3300 mJ/cm2. Lots of bubbles are generated during the exposure process. 3> use 1:4 AZ400K to develop the PR for about 9 minutes. I used both optical microscope and surface profilometer to measure the side wall. The slope angle is about 50 degrees. However, I need the slope angle to be close to 90 degrees (at least larger than 80 degrees) so that it is almost perpendicular to the substrate. What can I do to achieve it? Would you please give me any suggestions? by the way, the thick photoresist layer is sort of mold (for electroless plating of Ni on Si substrate). Best Regards, Qing Yao ___________________ M&IE @ 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/