Appeal No. 1999-2347
Application 08/892,560
discloses that the interconnect may be aluminum or polysilicon
which indicates that the interchangeability of these materials
was known to those of ordinary skill in the art. Thus, we
conclude that it would have been obvious to one of ordinary skill
in the art to use metal interconnections as taught by Erie and
Kim in place of the polysilicon interconnections in Barber. One
of ordinary skill in the art would have been motivated to etch
the silicon nitride etch stop layer so as to not form
non-conductive back-sputtered compounds of the metal
interconnections in view of the teachings of Erie that the etch
stop layer should be etched to avoid sputtering of the underlying
metallization.
Alternatively, we conclude that it would have been obvious
to modify Erie in view of Barber to arrive at the subject matter
of claim 21. Erie teaches that other materials than titanium
oxide can be used for the etch stop layer (col. 4, lines 5-7).
Barber teaches silicon nitride as an etch stop layer in the same
environment of making contact vias. One of ordinary skill in the
art would have been motivated to substitute silicon nitride for
the titanium oxide etch stop layer in Erie because silicon
nitride was a known alternative etch stop material, as taught by
Barber.
Appellants argue that the Examiner's assertion that it would
have been obvious to use silicon nitride in place of the Ti xOy in
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