if you are looking to have an even etch rate on both sides, the best
solution to your problem  is to use wafers with both sides of wafer
polished so that the surface roughness is similar. This would be easier
than trying to manage the oxide thickness or change the oxide methods (
compensating with higher thickness oxide on back)
If the base wafers are single side polished with a KOH etch backside and
depending on the lapping compound and the original etch method/process
(time/temp), the backside will be extremely rough reducing the oxide
thickness uniformity on the back. With your controlled etch of the front
side, the high points (low oxide) areas of the back will etch through
much faster.
Another base wafer alternative would be to use a good a acid etched
substrate instead of a caustic etched one. The problem here is obtaining
acid etch wafers which fewer suppliers can provide and this will only
improve, but still not be as good as using double side polished wafers.

Ken

Soumen Das wrote:
>
> Hello
> We are doing the silicon etching through windows simultaneously from both,
> front and back sides using KOH solution. The masking material for silicon
> etching is thermally grown 1 micron thick silicon dioxide. We observed that
> front side oxide remains for very long time in KOH soluton. However, back side
> oxide does not stay for long time. It etch out very fast than front side
> oxide.
> The wafer backside roughness is much higher than frontside surface. How can we
> improve the backside oxide quality to be used as masking material for KOH
> etching
> Do anyone has any solution?
> Thanks
> Dr. Soumen Das
> Sr. Scientific Officer
> Microelectronics Centre
> Dept. of Electronics & ECE
> Indian Institute of Technology
> Kharagpur 721 302, India
> email: [email protected]
> Phone: +91-3222-81914 (O)
>             +91-3222-81475 (Lab)
>             +91-3222-81915 (R)
> Fax: +91-3222-755303/777190
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