I have to disagree on one point, just for clarity's sake.

By and large, the majority of front-to-back lithography processes performed
these days (especially in MEMS) are performed using a front-to-back mask aligner
such as the EVG620, which uses backside microscopes for visible light alignment.
This does allow front to back lithography with SSP wafers. Even automated
alignment (via image recognition) is possible.

We have seen this application in cases where alignment keys are being patterned
on the backside for future bond alignment, and also for the patterning of gross
etch features (such as large cavities).

However, fine feature definition is impossible, due both to the random height
differences, which will create various proximity distances and thus various line
widths, and to the fact that the surfaces are not normal to the exposure
radiation, causing random reflection, again making line widths vary (this effect
is even more pronounced with thicker films). If this manner of patterning is
required, DSP wafer are also likewise required.



Best Regards,

Chad Brubaker



EV Group-Technology, Tel: (602) 437 9492 x 119, Fax: (602) 437 9435
E-mail: [email protected],  Web: www.EVGroup.com,

 -----Original Message-----
From:   beaton@npphotonics (Bill Eaton) [mailto:[email protected]]
Sent:   Thursday, July 03, 2003 10:25 AM
To:     'General MEMS discussion'
Subject:        RE: [mems-talk] DSP vs SSP

For most microelectronics applications, people tend to use single side
polished (SSP) wafers. These are wafers with a mirror finish on one side and
a rougher, lapped or etched surface on the other side. Double side polished
(DSP) wafers have a mirror finish on both sides. They are useful for certain
MEMS processes that require doing operations on both sides of the wafer.
Most photolithographic processes and many deposition processes will not
yield very good results on the rough side of an SSP wafer. Furthermore,
processes that require front to backside alignment typically rely on using
an infrared camera to see through the wafer to see a pattern. The rough side
of an SSP wafer typically is too great for IR alignment.

Regards,

Bill Eaton, Ph.D.
Materials & Analysis Manager
NP Photonics

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of Tom Fan
> Sent: Wednesday, July 02, 2003 12:17 PM
> To: [email protected]
> Subject: [mems-talk] DSP vs SSP
>
>
>
>
> Wafers have two polishing options: Double Side Polished or
> Single Side
> Polished. I am wondering whats the particular applications
> for these two types
> of wafers? Why are they differentiated?
> Anybody could enlighten me?
>
> Thanks,
> Tom Fan
>
>
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