Appeal No. 1999-2576
Application 08/836,960
on the exposed parts of the base layer at the bottom of the
holes, after which the silicon nitride layer at the bottom of
the holes is converted to silicon oxide and removed using a
fluoride type solution. Transl.
at 6-7. The next step, shown in Figure 2(c), is to deposit
the polysilicon film 108 of which polysilicon layers 108a and
108b will be formed.
Inasmuch as Yorikane fails to disclose forming a silicon
nitride diffusion barrier layer between the base layer and its
associated polysilicon layer, as required by claim 1, the
question is whether it would have been obvious in view of
Yorikane to replace McFarlane's diffusion barrier layer 18b
with a layer of silicon nitride. However, even assuming for
the sake of argument that such a substitution would have been
obvious, we agree with Appellant that the references
collectively fail to suggest making the silicon nitride layer
thin enough to allow charge carriers to pass therethrough.
Nor is this an inherent result of combining the teachings of
McFarlane and Yorikane in the foregoing manner. Whereas
Appellant's silicon nitride layer is "typically about 2 nm"
(Specification at 3, l. 6), which is equivalent to about 20 D,
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