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:
[email protected], www.EVGroup.com
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-----Original Message-----
From: [email protected] [mailto:mems-talk-
[email protected]] On Behalf Of Zheng Xia
Sent: Friday, February 27, 2004 9:30 AM
To: [email protected]
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
-------------------------
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