Appeal No. 1997-3162
Application 08/540,961
LOCOS isolation region. We understand the Examiner's position
that Kikuchi's gate structure is exactly the same as
Appellants' gate structure. The issues are: (1) whether it
would have been obvious to use this gate structure with a
surrounding shallow trench isolation instead of LOCOS
isolation; and, if so, (2) whether it would have been obvious
to select the lengths "such that a threshold voltage, V , at
t
said shallow trench edges is substantially equal to V between
t
said shallow trench edges," as claimed.
The Examiner's sole motivation for modifying Kikuchi to
use trench isolation is the finding that Shimizu teaches that
trench isolation is better than LOCOS (EA3). Appellants argue
that Shimizu discloses that while trench isolation solves
certain difficulties associated with the conventional LOCOS
isolation method, it explains that trench isolation has
problems with edge sidewall leakage, among other things, and
therefore ultimately indicates that trench isolation is
inferior to LOCOS (Br8). As Appellants note (Br8-9), Shimizu
implements the invention with non-trench isolation.
The relative weight of the advantages versus
disadvantages of trench isolation, i.e., whether trench
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