Ex parte Iwamuro

Board of Patent Appeals and Interferences

Dec 15, 1997

08151055 (B.P.A.I. Dec. 15, 1997)

Application for patent filed November 12, 1993. 1
According to appellant, the application is a continuation of
07/829,262, filed February 3, 1992.
1
THIS OPINION WAS NOT WRITTEN FOR PUBLICATION
The opinion in support of the decision being entered today (1)
was not written for publication in a law journal and (2) is
not binding precedent of the Board.
Paper No. 29
UNITED STATES PATENT AND TRADEMARK OFFICE
_____________
BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
_____________
Ex parte NORIYUKI IWAMURO

_____________
Appeal No. 95-4159
Application 08/151,0551
______________
ON BRIEF
_______________
Before HAIRSTON, JERRY SMITH and TORCZON, Administrative
Patent Judges.
JERRY SMITH, Administrative Patent Judge.
DECISION ON APPEAL
Appeal No. 95-4159
Application 08/151,055
2
This is a decision on the appeal under 35 U.S.C. § 134
from the examiner's rejection of claims 1-3, 6 and 7. Claims
4 and 5 stand withdrawn from consideration by the examiner as
being directed to a nonelected invention.
The claimed invention pertains to the structure of a
semiconductor element, particularly an insulated gate bipolar
transistor (IGBT).
Representative claim 1 is reproduced as follows:
1. A semiconductor element, comprising:
a substrate of first conductivity type having an
impurity concentration of not less than 4.0 x 10¹³/cm³, said
substrate being produced from a single silicon crystal
prepared by a zone melting method and substantially free of
lifetime killers;
a first diffused region of second conductivity
type in a first surface of the substrate;
a second diffused region of first conductivity
type in the first region such that a channel region is formed
between the second region and the substrate through the first
region;
an insulating film on the first surface of the
substrate over the channel region;
a gate electrode on the insulating film;
a source electrode on the first surface of the
substrate in contact with the first and second regions;
Appeal No. 95-4159
Application 08/151,055
3
a third diffused region of second conductivity
type formed in an opposite second surface of the substrate and
having a depth of at least 2 microns; and
a drain electrode in contact with said third
region.
The examiner relies on the following references:
Fay et al. (Fay) 5,237,183 Aug. 17, 1993
(filed Dec. 14,
1989)
T. Laska et al. (Laska), “A 2000 V-Non-Punch-Through-IGBT with
Dynamical Properties like a 1000 V-IGBT,” International
Electron Devices Meeting, December 9-12, 1990, pages 32.6.1-
32.6.4.
Claims 1-3, 6 and 7 stand rejected under 35 U.S.C. §
103. As evidence of obviousness the examiner offers Fay in
view of Laska.
Rather than repeat the arguments of appellant or the
examiner, we make reference to the brief and the answer for
the respective details thereof.
OPINION
We have carefully considered the subject matter on
appeal, the rejection advanced by the examiner and the
evidence of obviousness relied upon by the examiner as support
for the rejection. We have, likewise, reviewed and taken into
consideration, in reaching our decision, the appellant’s
Appeal No. 95-4159
Application 08/151,055
4
arguments set forth in the brief along with the examiner's
rationale in support of the rejection and arguments in
rebuttal set forth in the examiner's answer.
It is our view, after consideration of the record
before us, that the collective evidence relied upon and the
level of skill in the particular art would not have suggested
to one of ordinary skill in the art the obviousness of the
invention as set forth in claims 1-3, 6 and 7. Accordingly,
we reverse.
In rejecting claims under 35 U.S.C. § 103, it is
incumbent upon the examiner to establish a factual basis to
support the legal conclusion of obviousness. See In re Fine,
837 F.2d 1071, 1073, 5 USPQ2d 1596, 1598 (Fed. Cir. 1988). In
so doing, the examiner is expected to make the factual
determinations set forth in Graham v. John Deere Co., 383 U.S.
1, 17, 148 USPQ 459, 467 (1966), and to provide a reason why
one having ordinary skill in the pertinent art would have been
led to modify the prior art or to combine prior art references
to arrive at the claimed invention. Such reason must stem
from some teaching, suggestion or implication in the prior art
as a whole or knowledge generally available to one having
Appeal No. 95-4159
Application 08/151,055
5
ordinary skill in the art. Uniroyal Inc. v. Rudkin-Wiley
Corp., 837 F.2d 1044, 1051, 5 USPQ2d 1434, 1438 (Fed. Cir.),
cert. denied, 488 U.S. 825 (1988); Ashland Oil, Inc. v. Delta
Resins & Refractories, Inc., 776 F.2d 281, 293, 227 USPQ 657,
664 (Fed. Cir. 1985), cert. denied, 475 U.S. 1017 (1986); ACS
Hospital Systems, Inc. v. Montefiore Hospital, 732 F.2d 1572,
1577, 221 USPQ 929, 933 (Fed. Cir. 1984). These showings by
the examiner are an essential part of complying with the
burden of presenting a prima facie case of obviousness. Note
In re Oetiker, 977 F.2d 1443, 1445, 24 USPQ2d 1443, 1444 (Fed.
Cir. 1992).
We consider first the rejection as it applies to
independent claim 1 and claims 2, 6 and 7 which depend
therefrom. These claims stand or fall together [brief, page
5]. The examiner has read claim 1 on Fay, and concludes that
Fay only lacks the teaching of the third diffused region on
the backside of the substrate [final rejection, pages 2-3].
The examiner cites Laska as a teaching that it was
conventional to form a third region of an IGBT by doping the
backside of a silicon substrate to form the emitter of the
device [Id., page 3]. The examiner concludes that the
Appeal No. 95-4159
Application 08/151,055
6
collective teachings of Fay and Laska would have suggested the
invention as recited in claim 1.
Appellant argues that there is no motivation to
combine the teachings of Fay with Laska [brief, pages 6-7].
According to appellant, the IGBTs of Fay and Laska operate so
differently that the artisan would not selectively pick and
choose elements from the two devices to arrive at the claimed
invention. The examiner responds that appellant’s arguments
are not commensurate in scope with the invention of claim 1.
Although the examiner is correct to note that
arguments of nonobviousness must be commensurate in scope with
the claimed invention, the examiner must still consider the
propriety of combining prior art teachings based on what would
have been suggested to the artisan who has this prior art
before him. The Fay IGBT has a buffer layer which makes it a
punch-through (PT) type device. Laska discloses a non-punch-
through (NPT) IGBT which is designed to have operating
characteristics similar to a PT IGBT. While PT IGBTs and NPT
IGBTs operate to achieve similar results, they achieve these
results in an entirely different manner. Laska notes that an
NPT IGBT is fabricated using no life-time-killing steps
Appeal No. 95-4159
Application 08/151,055
7
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
Appeal No. 95-4159
Application 08/151,055
8
expected to have lifetime killers in order to operate as a PT
device. Although the examiner attempts to dismiss features of
claim 1 as being directed to the process of making the
product, the presence or absence of lifetime killers in the
device is a structural distinction which is known to affect
the performance of the device. Therefore, Fay’s epitaxial
layers 13 and 14 cannot simply be equated with a single
substrate having the properties recited in claim 1.
Appellant also argues that the collective teachings of
Fay and Laska do not teach or suggest that a third diffused
region of at least 2 microns should be implanted on the
backside of the substrate [brief, pages 7-9]. It is the
examiner’s position that since the P-type collector region of
Fay is thicker than 5 microns, if the P-type region of Fay
were created by diffusion as taught by Laska, then this
diffused P-type region would also have a thickness greater
than 5 microns. Appellant notes that Laska discloses no
dimensions for his third diffused region, and the Laska
teachings of an NPT IGBT would not have been combined with the
Fay PT IGBT for determining dimensions of layers in two
disparate devices such as this. We agree with appellant.
Appeal No. 95-4159
Application 08/151,055
9
While we do not disagree with the examiner that the P-
type collector region of Fay can be achieved by a diffusion
process, we agree with appellant that the dimensions of the
Fay PT IGBT device cannot simply be interchanged with the
Laska NPT IGBT device. The examiner cannot simply combine
selected teachings from disparate devices to support the
position that the combined teachings would have been obvious
to the artisan.
For all the reasons discussed above, we do not sustain
the rejection of claims 1, 2, 6 and 7.
With respect to independent claim 3, it is
significantly broader than independent claim 1. Nevertheless,
claim 3 recites the same substrate limitations that we
considered in claim 1 as well as a diffused region in the
substrate having a depth of at least 2 microns. Since we find
the same deficiencies in combining the teachings of Fay with
Laska that we discussed above, we again fail to see how the
invention as recited in claim 3 is suggested by the applied
prior art. Therefore, we do not sustain the rejection of
claim 3.

Appeal No. 95-4159
Application 08/151,055
10
In summary, we have not sustained the examiner’s
rejection of the claims under 35 U.S.C. § 103. Therefore, the
decision of the examiner rejecting claims 1-3, 6 and 7 is
reversed.
REVERSED
)
KENNETH W. HAIRSTON )
Administrative Patent Judge )
)
)
) BOARD OF PATENT
JERRY SMITH )
Administrative Patent Judge ) APPEALS AND
Appeal No. 95-4159
Application 08/151,055
11
)
) INTERFERENCES
)
RICHARD TORCZON )
Administrative Patent Judge )

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