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:
[email protected], www.EVGroup.com
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-----Original Message-----
From: Tom Fan [mailto:[email protected]]
Sent: Tuesday, August 12, 2003 5:16 PM
To: [email protected]
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
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