Achim Trautmann et al.

Patent Trials and Appeals Board

Oct 16, 2019

14917009 - (D) (P.T.A.B. Oct. 16, 2019)

UNITED STATES PATENT AND TRADEMARK OFFICE
UNITED STATES DEPARTMENT OF COMMERCE
United States Patent and Trademark Office
Address: COMMISSIONER FOR PATENTS
P.O. Box 1450
Alexandria, Virginia 22313-1450
www.uspto.gov
APPLICATION NO. FILING DATE FIRST NAMED INVENTOR ATTORNEY DOCKET NO. CONFIRMATION NO.
14/917,009 03/05/2016 Achim Trautmann 2178-1394 9985
10800 7590 10/16/2019
Maginot, Moore & Beck LLP
One Indiana Square, Suite 2200
Indianapolis, IN 46204
EXAMINER
VU, DAVID
ART UNIT PAPER NUMBER
2818
MAIL DATE DELIVERY MODE
10/16/2019 PAPER
Please find below and/or attached an Office communication concerning this application or proceeding.
The time period for reply, if any, is set in the attached communication.
PTOL-90A (Rev. 04/07)

UNITED STATES PATENT AND TRADEMARK OFFICE
____________

BEFORE THE PATENT TRIAL AND APPEAL BOARD
____________

Ex parte ACHIM TRAUTMANN and CHRISTIAN TOBIAS BANZHAF
____________

Appeal 2018-004383
Application 14/917,009
Technology Center 2800
____________

Before MARK NAGUMO, DONNA M. PRAISS, and
MERRELL C. CASHION, JR., Administrative Patent Judges.

PRAISS, Administrative Patent Judge.

DECISION ON APPEAL1
Appellant2 appeals under 35 U.S.C. § 134(a) from the Examiner’s
decision rejecting claims 1–5 under 35 U.S.C. § 103. We have jurisdiction
over the appeal under 35 U.S.C. § 6(b).
We REVERSE.

1 Our Decision refers to the Specification (“Spec.”) filed Mar. 5, 2016, the
Examiner’s Final Office Action (“Final Act.”) dated May 23, 2017,
Appellant’s Appeal Brief (“Appeal Br.”) filed Oct. 19, 2017, the Examiner’s
Answer (“Ans.”) dated Jan. 24, 2018, and Appellant’s Reply Brief (“Reply
Br.”) filed Mar. 21, 2018.
2 We use the word “Appellant” to refer to “applicant” as defined in 37
C.F.R. § 1.42. Appellant is Robert Bosch GMBH, which is also identified as
the real party in interest. Appeal Br. 2.
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STATEMENT OF THE CASE
The invention relates to a method for producing a substrate. Spec.
1:9–10. According to the Specification, substrates comprising a silicon
carbide layer are used increasingly in standard components such as power
semiconductors, which are produced as trench metal oxide semiconductor
field-effect transistors (trench MOSFETs). Id. 1:17–22. The Specification
discloses that power semiconductors block voltages up to more than 1.2 kV
and are used in electro-mobile applications such as motor vehicles with
batteries as well as microelectromechanical systems. Id. at 1:19–27.
According to the Specification, the trench of the prior art structures is coated
with a gate oxide and a doped implantation may be subsequently carried out
in the bottom of the trench. Id. at 2:27–31. The transition from the side wall
of the trench to the bottom of the trench is said to lead to very high field
strengths in this region which can exceed the breakdown threshold of the
oxide layer, leading to component damage. Id. at 2:36–3:1. The
Specification discloses a trench with a step that can be produced in a self-
aligning manner. Id. at 3:23–24. Claim 1, reproduced below from the Claims
Appendix to the Appeal Brief, is illustrative (emphases added).
1. A method for producing a substrate for a metal oxide
semiconductor field-effect transistor or a micro-
electromechanical system, the substrate including a first silicon
carbide layer having a hexagonal crystal structure, a
moderately p-doped silicon carbide layer arranged on the first
silicon carbide layer, and a heavily n-doped silicon carbide
layer arranged on at least a part of the moderately p-doped
silicon carbide layer, the method comprising:
dry etching a temporary trench into the first silicon
carbide layer by using a structured first masking layer, the dry
etching being carried out in such a way that a residue of the first
structured masking layer remains;
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applying a second masking layer at least on walls of the
temporary trench; and
dry etching by using the residue of the first masking layer
and the second masking layer as masks so as to form a trench
having a step located in the first silicon carbide layer.

ANALYSIS
We review the appealed rejections for error based upon the issues
Appellant identifies, in light of the arguments and evidence produced
thereon. Ex parte Frye, 94 USPQ2d 1072, 1075 (BPAI 2010) (precedential)
(cited with approval in In re Jung, 637 F.3d 1356, 1365 (Fed. Cir. 2011)
(“[I]t has long been the Board’s practice to require an applicant to identify
the alleged error in the examiner’s rejections.”)). After considering the
argued claims in light of the case law presented in this Appeal and each of
Appellant’s arguments, we are persuaded of reversible error in the
Examiner’s rejections.

Rejection 1: Claims 1, 2, and 5
The Examiner rejects claims 1, 2, and 5 under 35 U.S.C. § 103 over
the combination of Blanchard3 and Takeuchi4 for the reasons stated on pages
2–4 of the Final Office Action.
Appellant asserts that the Examiner failed to clearly articulate reasons
why it would have been obvious to modify Blanchard to arrive at the method
claimed in claims 1, 3, and 5. Appeal Br. 4. Appellant also asserts that the
Examiner erred in rejecting claim 5 over Blanchard and Takeuchi because

3 US 2003/0181010 A1, published Sept. 25, 2003.
4 US 5,744,826, issued Apr. 28, 1998.
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claim 5 depends from claim 4, which is separately rejected over an
additional secondary reference. Id. at 11.
Appellant acknowledges that the Examiner finds Blanchard lacks a
silicon carbide layer having a hexagonal crystal structure and combines
Takeuchi’s SiC device to improve channel mobility, but asserts that the
proposed modification to Blanchard would not have been made by one of
ordinary skill in the art due to “substantial differences in the structure of the
Blanchard and Takeuchi MOSFETs.” Id. at 6–7. Appellant asserts that
Blanchard teaches forming a trench into which a p-type region is inserted
while Takeuchi teaches a substrate that already includes the P-type region
prior to the trench formation. Id. at 8. Thus, Appellant argues that the
combination of the references would duplicate the P-type regions as the p-
type doped columns, resulting in a MOSFET unsuitable for Takeuchi’s
intended purpose. Id. Appellant also contends that Blanchard’s layering of
the p-type body region causes on-resistance of the device to increase rapidly
as the breakdown voltage increases and, therefore, teaches away from
Takeuchi’s substrate structure. Id. at 9.
The Examiner responds that both Blanchard and Takeuchi are trench
gate-type power MOSFETs with the difference being the substrate materials:
Blanchard’s device is formed in the silicon substrate, while Takeuchi’s
device is formed in the hexagonal crystal based single crystal silicon carbide
substrate. Ans. 2 (citing Blanchard Fig. 5(a), N-501; Takeuchi Fig. 4, SiC 2,
3). The Examiner responds that the required three-layered substrate is taught
by Takeuchi, not by Blanchard, namely, first silicon carbide layer 2 having a
hexagonal crystal structure, moderately p-doped silicon carbide layer 3
arranged on first silicon carbide layer 2, and heavily n-doped silicon carbide
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layer 5 arranged on at least a part of the moderately p-doped silicon carbide
layer 3. Id. at 3 (quoting Final Act. 3, citing Takeuchi Fig. 4, items 2, 3, 5).
The Examiner finds that the combination of Blanchard and Takeuchi
would have produced a terraced-trench gate-type power MOSFET taught by
Blanchard, with the trench formed by etching through the three-layer SiC
substrate which is a hexagonal crystal based single crystal silicon carbide
substrate taught by Takeuchi. Id. at 3–4. The Examiner determines that
modifying the silicon substrate of Blanchard’s device by using the SiC
substrate taught by Takeuchi would have been obvious to one of ordinary
skill at the time of the invention because Takeuchi teaches that the
modification would have improved channel mobility. Id. at 4 (citing
Takeuchi 4:16–22). The Examiner also finds that Takeuchi teaches
employing such a crystal structure results in reduced on-resistance during
periods of high-voltage application. Id. (citing Takeuchi 1:20–25).
Regarding Appellant’s position that the combination would duplicate the p-
type regions and that Blanchard’s p-type doped columns formed in the p-
type region of Takeuchi would result in the MOSFET functioning
improperly, the Examiner states that the whole gate structure shown in
Blanchard’s Figure 4 is not relied upon for the rejection, but only
Blanchard’s teaching of multiple dry etching temporary trenches to form a
terraced-trench. Id. at 4–5.
The Examiner also responds that Blanchard’s Figure 5 is relied upon
rather than Blanchard’s Figure 1, therefore a comparison of Blanchard’s
Figure 1 with Takeuchi’s Figure 4 is not appropriate and does not teach
away from using Takeuchi’s structure because both Takeuchi’s structure and
Blanchard’s Figure 5 are trench gate-type power MOSFETs, which are
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vertical channel devices, while Blanchard’s Figure 1 is a conventional lateral
MOSFET. Id. at 5–6 (citing Blanchard ¶ 33).
Based on the cited record in this Appeal, we are persuaded that the
Examiner reversibly erred in combining the teachings of Blanchard and
Takeuchi. Because claims 2 and 5 depend from claim 1 either directly or
indirectly, our discussion focuses on claim 1.
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 (Fed. Cir. 1988). In so
doing, the Examiner must make the factual determinations set forth in
Graham v. John Deere Co., 383 U.S. 1, 17 (1966) (noting that 35 U.S.C.
§ 103 leads to three basic factual inquiries: (1) the scope and content of the
prior art; (2) the differences between the prior art and the claims at issue;
and (3) the level of ordinary skill in the art). Furthermore, the Examiner’s
obviousness rejection must be based on
“some articulated reasoning with some rational underpinning to
support the legal conclusion of obviousness” . . . . [H]owever,
the analysis need not seek out precise teachings directed to the
specific subject matter of the challenged claim, for a court can
take account of the inferences and creative steps that a person
of ordinary skill in the art would employ.
KSR Int’l Co. v. Teleflex, Inc., 550 U.S. 398, 418 (2007) (quoting In re
Kahn, 441 F.3d 977, 988 (Fed. Cir. 2006)).
If the Examiner’s burden is met, the burden then shifts to the
Appellant to overcome the prima facie case with argument and/or evidence.
Obviousness is then determined on the basis of the evidence as a whole and
the relative persuasiveness of the arguments. See In re Oetiker, 977 F.2d
1443, 1445 (Fed. Cir. 1992).
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Although the Examiner identifies the benefit of channel mobility for
selecting Takeuchi’s single crystal hexagonal silicon carbide semiconductor
substrate comprising a stack having the three layers required by claim 1
(Ans. 2), the Examiner does not adequately rebut Appellant’s assertions
(Appeal Br. 8–9) that the combination of Blanchard’s terraced trenching
method with Takeuchi’s silicon carbide substrate “would not be functional”
and “would be [for]5 a superfluous p-doping of Takeuchi’s p-doped layer.”
Claim 1 is directed to a method of producing a substrate for a MOSFET by
performing dry etching and masking steps on a layered substrate that
includes a moderately p-doped silicon carbide layer. As Appellant points out
and the record supports, Blanchard teaches etching trenches to form a
terraced trench for the purpose of inserting a p-type region. Appeal Br. 8;
Blanchard ¶¶ 23, 34, Fig. 4. Appellant’s position that a skilled artisan would
not have modified Blanchard’s device with Takeuchi’s stacked silicon
carbide semiconductor substrate because fulfilling the purpose of
Blanchard’s terraced trench method steps would have duplicated the p-type
regions by forming Blanchard’s p-type doped columns in the p-type region
of Takeuchi is therefore reasonable and supported by the record.
Absent a reason for utilizing Blanchard’s method of forming a p-
doped region in Takeuchi’s stacked substrate, the combination of Blanchard
with Takeuchi is simply picking and choosing elements of claim 1 from the
references based on knowledge gleaned only from Appellant’s disclosure.
Consequently, the Examiner’s selection of only Blanchard’s multiple dry

5 More precisely, we understand Appellant to argue, not that the stepped
trenching itself is p-doping, but that the subsequent p-doping is the only
reason Blanchard gives to engage in step-trenching. That is, Blanchard step
trenches in order to p-dope the substrate in a particular way.
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etching temporary trenches to form a terraced-trench in Takeuchi’s device
without regard to Blanchard’s gate structure or purpose for forming a
terraced-trench constitutes impermissible hindsight. See KSR, 550 U.S. at
421 (“A factfinder should be aware, of course, of the distortion caused by
hindsight bias and must be cautious of arguments reliant upon ex post
reasoning.”).
For these reasons, we reverse the Examiner’s rejection of claims 1, 2,
and 5 under 35 U.S.C. § 103 over Blanchard and Takeuchi.

Rejections 2 and 3: Claims 3 and 4
The Examiner rejects claim 3 over the combination of Blanchard and
Takeuchi in further view of Blanchard ’188.6 The Examiner rejects claim 4
over the combination of Blanchard and Takeuchi in further view of Tseng.7
Final Act. 4–5.
Appellant relies on the same arguments presented with respect to
claim 1 in asserting the patentability of dependent claim 4, therefore we
affirm the rejection of claim 4 for the same reasons discussed above in
connection with claim 1. Appeal Br. 13.
Appellant additionally argues that the Examiner erred in rejecting
dependent claim 3 because a person having ordinary skill in the art would
have been discouraged from using the repetitive trenching and doping steps
of Blanchard ’188 based on Blanchard’s teaching that such a process is
expensive to perform. Id. at 12–13 (citing Blanchard ¶ 11); Reply Br. 6.

6 US 2003/0122188 A1, published July 3, 2003.
7 US 5,741,741, issued Apr. 21, 1998.
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Because the Examiner does not rely on the secondary references to
cure the deficiencies of the combination of Blanchard and Takeuchi
discussed above in connection with claim 1, we reverse the rejections of
claims 3 and 4 for the same reasons.

CONCLUSION
In summary:
Claims
Rejected
35 U.S.C.
§ Reference(s)/Basis Affirmed Reversed
1, 2, 5 103 Blanchard and Takeuchi 1, 2, 5
3 103
Blanchard,
Takeuchi, and
Blanchard ’188
3
4 103
Blanchard,
Takeuchi, and
Tseng
4
Overall
Outcome
1–5

REVERSED