Appeal No. 94-0809
Application 07/707,365
Nishizaka teaches that by burying polycrystalline silicon
layer 10 in trenches encased by an oxidation film 9, substrate 20
is effectively held at the ground potential in a stable manner
(Nishizaka, col. 5, l. 28-33). Nishizaka nowhere suggests that
his process causes the impurities with which the polycrystalline
silicon layer 10 “may be doped” to diffuse into the substrate
to form source/drain regions of a field-effect transistor (Ans.,
p. 5, first full para.). To the contrary, Nishizaka expressly
states (col. 5, l. 44-58):
Therefore, [the (sic)] following advantages are obtained
in the invention.
. . . . .
(2) A short circuit is avoided between digit lines,
because no charge is accumulated in a polycrystalline
silicon layer which is buried into element separating
trenches. Furthermore, if the polycrystalline silicon
layer is connected to a semiconductor substrate, and
connected through a source electrode to the ground
potential, the semiconductor substrate is easily connected
to the ground potential, so that the transistor operates
with a stable characteristic.
It is difficult for this panel to understand how the
polycrystalline silicon layers buried into the separating
trenches can “form source/drain regions of a field effect
transistor” and impart the advantage of functional stability to
Nishizaka’s invention when doping the buried polycrystalline
silicon layers with impurities is entirely optional.
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Last modified: November 3, 2007