Ex parte IWAMURO - Page 7
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Board of Patent Appeals and Interferences > 1997 > Ex parte IWAMURO - Page 7
Appeal No. 95-4159
Application 08/151,055
whereas the typical PT IGBT has life-time-killers in the
substrate.
Although the examiner proposes to use Laska to teach
nothing more than the fact that the P- and/or P+ layers of Fay
could be created by using a doping technique, this position
ignores specific language of claim 1 which Fay cannot meet.
The examiner reads the substrate of claim 1 on layers 13 and
14 of Fay which are epitaxially grown layers of N-doped
silicon. The examiner asserts that one can look to the
average concentration of layers 13 and 14 and consider it as a
single substrate layer of that concentration. However,
replacing layers 13 and 14 in Fay with a single layer having
the average concentration would destroy the Fay device. The
heavily doped layer 13 is necessary in Fay to provide a buffer
layer between the N-type epitaxial layer and the lightly doped
P-type layer so the device can operate as a PT IGBT.
Claim 1 also recites that the substrate is “produced
from a single silicon crystal prepared by a zone melting
method and substantially free of lifetime killers.” We fail
to see how the epitaxially grown layers of Fay can meet this
recitation. As noted above, the PT IGBT of Fay would be
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Last modified: November 3, 2007
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