Appeal No. 2001-2590
Application No. 09/449,063
an oxide layer thicker in one region as opposed to another by
using oxygen ions. (Examiner’s Answer, page 4, lines 6-8).
The examiner then concludes that it would have been obvious
to one of ordinary skill in the art at the time the invention was
made to replace the nitrogen ions in Hsu with the oxygen ions of
Wristers because it would allow Hsu to produce the desired goal of
forming gate oxides with different thicknesses in a single
processing step. (Examiner’s Answer, page 4, lines 8-12).
The appellants note that Hsu uses nitrogen to depress the
oxidation rate, and fluorine to increase the oxidation rate of a
silicon layer, but not oxygen. Wristers, it is urged, is
concerned only with the provision of a gate dielectric layer of
uniform thickness within an isolation structure with the oxide
thickness in the isolation structure being thicker to reduce the
electric field across the guard ring. Consequently, it is
reasoned, that Wristers is not concerned with providing gate oxide
layers of different thicknesses for different transistors in a
semiconductor chip. (Appeal Brief, page 6, lines 5-20).
We note that it is not in dispute that Hsu is almost
identical to the instantly claimed invention. The only
discernable difference between the claimed subject matter and Hsu
is the passage at column 2, lines 44-50 which states:
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