Appeal No. 2001-2590
Application No. 09/449,063
Nitrogen ions 14 are implanted through the sacrificial
silicon oxide layer 12 into the semiconductor substrate
10 in the planned 3 V transistor region not covered by the
photoresist. The ions are implanted at a dosage of between
about 1 E 14 to 3 E 14 atoms/cm2 and energy of between about
30 to 50 KeV. The nitrogen ions within the semiconductor
substrate will depress the oxidation rate of the substrate.
In other words, Hsu teaches that a nitrogen implanted area
will grow an oxide layer more slowly, resulting in a thinner gate
oxide layer. Hsu also teaches an alternative means for increasing
the oxidation rate using fluorine in a so-called second preferred
embodiment discussed at column 3, lines 11-20:
Fluoride ions 15 are implanted through the sacrificial
silicon oxide layer 12 into the semiconductor substrate
10 in the planned 5 V transistor region not covered by the
photoresist. The ions are implanted at a dosage of between
about 7.5 E 15 to 3 E 16 atoms/cm2 and energy of between about
25 to 45 KeV. The fluoride ions within the semiconductor
substrate will increase the oxidation rate of the substrate
so that the resulting silicon oxide layer is between about 10
to 20 Angstroms thicker in the implanted region than in the
non-implanted region.
Thus, the overall teaching of Hsu is that oxidation can be
increased or inhibited by implanting various ions.
Wristers teaches the implantation of oxygen is known to
increase the oxidation rate in implanted portions. (Column 2,
lines 19-23). Wrister’s goal, however, is thicker regions and a
concomitant reduction in electric field.
It is well-settled that a prior art reference is relevant for
all that it teaches to those of ordinary skill in the art. In re
Fritch, 972 F.2d 1260, 1264, 23 USPQ2d 1780, 1782 (Fed. Cir.
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