One method that has been of use to us in coating of square or rectangular substrates is by using an EVG100 series spray coater. When a standard spin coating process is used to deposit resist on a non-circular substrate, the center of the substrate, in the form of an inscribed circle, will remain very uniform. However, a marked non-uniform pattern can be seen at the corners of the substrate. The primary reason for this issue you've been seeing has to do with the turbulence at the edges of the substrate. This turbulence causes an increased evaporation rate, causing the resist at the corners to dry out more quickly, and so the continual flow of resist from the center of the substrate begins to overlap this dried resist, creating a buildup. With spray coating, the use of a low rpm spin means that the relative movement between the substrate and the air is nearly the same. The resist at the edges does not dry out appreciably faster than that at the center. Additionally, resist does not flow in any traditional manner (i.e. radially) during spray coating, so there is no problem with resist buildup at the corners. In this manner, the full surface uniformity is the same, regardless of the overall shape of the substrate. As an added side benefit, the appearance of an edge bead, or thickened layer of resist at the edge of a substrate, is nearly non-existent as well. 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 Zheng Xia Sent: Friday, February 27, 2004 9:30 AM To: mems-talk@memsnet.org Subject: [mems-talk] resist on rectangular shape slides Hi, Does anyone have suggestion on how to apply uniform resist on rectangular shape glass slides (1 x 3 inch)? I tried to spin them with full coverage of resist on slides, but the result is not good. Resist sometimes cannot reach corners, and it shows certain interference pattern under light, indicating the unevenness of resist thickness. Thank you. Best, ------------------------- XIA, ZHENG Microfluidics and BioMEMS Lab Interdisciplinary Microsystems Group Department of Mechanical and Aerospace Engineering University of Florida ------------------------- _______________________________________________ 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/