Appeal No. 1999-0874
Application 08/726,733
As specifically applicable to independent claim 7, the discussion at column 5,
lines 45-63 of Teng indicates to the artisan that silicon nitride would have had a
relatively lesser etching rate than the silicon oxide in the interlevel dielectric discussed.
Thus, in accordance with the feature of the second insulation level having a higher
etching selectivity with respect to the first insulation layer, the silicon oxide layer
discussed in this portion of Teng would have a higher etching selectivity as suggested
by this discussion than the silicon nitride layer. These are the same corresponding
materials associated with the claimed first insulation layer and the second insulation
layer in appellants’ representative prior art Figures 38 and 39.
Moreover, in discussing the formation of insulating films such as silicon dioxide
and silicon nitride beginning at the bottom of page 96 of Muller, the statement is made
at the top of page 97 that silicon nitride layers do not oxidize as readily as do silicon
oxide layers. This suggests again relative, selective etching or oxidation capabilities
between the two materials. Selective oxidation is specifically taught at the top of page
638 of the section of Kirk-Othmer indicating that silicon nitride is an ideal material for
such selective oxidation since it too has an extremely slow rate of oxidation. The
discussion at the top of page 639 indicates that the selection of relative etch rate
selectivity is important in the fabrication of integrated circuit structures and may for
example be controlled by the nature of the etching material such as in corresponding
Table 3 at page 640. This table indicates that silicon dioxide and silicon nitride may
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