Appeal No. 1997-3688
Application 08/113,887
a silicon dioxide mask 11, conformably depositing oxidization resistant layer 13 on the mask,
anisotropically etching the oxidation resistant layer to leave sidewalls 13 and etching the silicon
substrate 10 to form a trench adjacent the sidewalls. Saito shows the oxidation mask consisting
of oxide 11 plus sidewalls 12 as being unchanged during the growth of oxide 14.
Upon our review of Koto we find that the silicon nitride layers 3a and 3b sandwiching a
polysilicon layer 6 do not have a sidewall. Koto's invention relies on growing of the oxide 4 in the
substrate to also oxidize the end portions of polysilicon 6 to form oxide 10. The oxidation of the
end portions of polysilicon 6 increases its volume and thereby increases the downward pressure
on the bird's beak 5 of the growing oxide 4. This pressure retards oxide growth and results in a
smaller bird's beak 5. This is shown in Figures 2a, 2b, 3a and 3b.
We note that Koto relies on the lack of the sidewalls to have the polysilicon 6 oxidized and
expand to control the bird's beak 5 growth. Furthermore, we note that Saito relies on a
completely different approach of using an oxide mask plus oxidation resistant sidewalls as an
oxidation mask for growing the oxide. We fail to find any suggestion in Koto or Saito to use the
Saito' method in the sidewall structure of Koto. Furthermore, upon our review of Bryant and Wolf,
we fail to find these references suggest the combination as proposed by the Examiner.
In view of the foregoing, we have not sustained the rejection of claims 27, 31 and 32 under
35 U.S.C. § 103. Accordingly, the Examiner's decision is reversed.
REVERSED
5
Page: Previous 1 2 3 4 5 6 Next
Last modified: November 3, 2007