Appeal No. 2003-2107
Application No. 09/429,283
obviousness inquiry when the modification render[s] the prior art
reference inoperable for its intended purpose." In re Fritch,
972 F.2d 1260, 1265-66, n.12, 23 USPQ2d 1780, 1783, n.12, citing
In re Gordon, 733 F.2d 900, 902, 221 USPQ 1125, 1127 (Fed. Cir.
1984). Thus, it would not have been obvious to modify Chishima
to include doping the n-channel MOSFET.
Choi discloses two different transistors on the same chip
and, as recognized by the examiner (Answer, page 5), discusses
nitrogen implantation for the p-type MOSFET (to reduce the
penetration of boron through the gate oxide layer). However,
Choi teaches (column 2, lines 2-3) that "nitrogen incorporation
degrades p-channel mobility which is also undesirable."
Nonetheless, Choi discloses (column 8, lines 16-18) an embodiment
which includes nitrogen implantation, but with no suggestion to
implant nitrogen in the n-type MOSFET with a different
concentration than that used for the p-type MOSFET. Further, as
with Chishima, no impurity other than nitrogen is discussed with
respect to both transistors.
Gardner (column 10, lines 21-26) states generally that the
amount of dopant in the gate affects the threshold voltage.
However, Gardner does not specify how the amount of dopant
affects the threshold voltage, and particularly how nitrogen
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