Appeal No. 1998-0970
Application 07/995,325
The boron layer is deposited on a silicon substrate
or in an opening provided in an insulation layer mounted
on the silicon substrate by vacuum evaporation,
sputtering, CVD (Chemical Vapor Deposition), etc. The
deposition of the boron layer should preferably be made
after the natural oxide layer settled on the silicon
substrate is etched off by dilute fluoric acid or by the
argon sputtering process in a vacuum.
The deposited boron is later diffused by heat treatment
(annealing) (claim 12, step i) and the contact hole is filled
with an electrically conductive aluminum wire layer 118
(claim 12, step j). The purpose of diffusing boron into the
silicon or the impurity diffusion region is to ensure good
ohmic contact between the p-type impurity layer 113 and the
aluminum wire layer 118 (col. 5, lines 3-7), which is the same
as Appellants' reason of reducing the contact resistance
(specification, p. 1, lines 6-7).
The differences between Tsunashima and the subject matter
of claim 12 are that Tsunashima does not disclose:
(1) specifically removing a natural oxide film from a surface
of the impurity diffusion (Tsunashima discloses removing a
natural oxide layer from the silicon substrate surface, but
does not express mention removing the oxide from the surface
of the impurity diffusion region); (2) the specific process
step of removing the natural oxide film recited in step g);
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