Tom, To determine whether the 4 um high structures would be considered "high aspect ratio" structures, you'd really have to consider the width of the structures, and the resist film thickness. If your structures are 4um high, but 100 um across in width and length, then, no they are not high aspect. On the other hand, if they are 4um across or less (i.e. aspect ratio of 1:1 or less), they may be. If you are trying to coat them with a 1- um resist, then yes, they would be considered such. If you are coating them with 10 um, then not really (although you may still see some non-uniformity to your coat). However, even if they are 100 um wide, and 100 um long, they could still be considered to be "topographically challenged" if you are trying to coat them with a 1 um resist. In this case, most of the surface may coat okay, but at the edges of the structure, and in the "shadow" of the structure (that is, the side of the structure away from the center of the wafer), you will see severe non- uniformities, and perhaps even compromised coverage. If you are trying to do a 1-2 um coat, I would tend to recommend a process like spray coating, which can perform a conformal coating of the surfaces. As to exposure, a 1x, full field, contact/proximity mask aligner such as an EVG620 would be able to expose these structures just fine. Since the exposure system uses a collimated light source, and so does not rely on precise focus, the 4 um height difference will cause little to no problem with the exposure, allowing production of features as small as 2-3 um wide.. 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: Tom Fan [mailto:Tom.Fan@asu.edu] Sent: Tuesday, August 12, 2003 5:16 PM To: mems-talk@memsnet.org Subject: [mems-talk] Electrodes in Microchannel On the same topic, would 4-um high structures (serving as electrodes) standing on otherwise flat substrates be considered "high-aspect-ratio" structures? Would conventional resist spin coating process do the job? And also can the lithographic tool handle a height difference of 4 um (if exposures on and off the structures are desired)? Thanks, Tom _______________________________________________ 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/