[mems-talk] DSP vs SSP

[Brubaker Chad]

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: C.Brubaker at evgroup.com,  Web: www.EVGroup.com, 

 -----Original Message-----
From: 	beaton at npphotonics (Bill Eaton) [mailto:beaton at npphotonics.com] 
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: mems-talk-bounces at memsnet.org
> [mailto:mems-talk-bounces at memsnet.org]On Behalf Of Tom Fan
> Sent: Wednesday, July 02, 2003 12:17 PM
> To: mems-talk at memsnet.org
> 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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