Court Opinion

ID: 4519339
Source: CourtListenerOpinion
Date Created: 2020-03-25 16:00:34.645728+00
Date Added: 2024-06-11T11:53:11.416369
License: Public Domain

Case: 19-1669    Document: 55     Page: 1   Filed: 03/25/2020

        NOTE: This disposition is nonprecedential.

   United States Court of Appeals
       for the Federal Circuit
                  ______________________

     LONE STAR SILICON INNOVATIONS LLC,
                   Appellant

                             v.

     ANDREI IANCU, UNDER SECRETARY OF
   COMMERCE FOR INTELLECTUAL PROPERTY
    AND DIRECTOR OF THE UNITED STATES
      PATENT AND TRADEMARK OFFICE,
                   Intervenor
             ______________________

                        2019-1669
                  ______________________

     Appeal from the United States Patent and Trademark
 Office, Patent Trial and Appeal Board in No. IPR2017-
 01566.
                  ______________________

                 Decided: March 25, 2020
                 ______________________

    TIMOTHY P. MALONEY, Fitch, Even, Tabin & Flannery,
 Chicago, IL, argued for appellant. Also represented by
 NICHOLAS T. PETERS, DAVID ALLEN GOSSE.

     DANIEL KAZHDAN, Office of the Solicitor, United States
 Patent and Trademark Office, Alexandria, VA, argued for
 intervenor. Also represented by MAI-TRANG DUC DANG,
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 2                    LONE STAR SILICON INNOVATIONS     v. IANCU

 THOMAS W. KRAUSE, BRIAN RACILLA, FARHEENA YASMEEN
 RASHEED, MEREDITH HOPE SCHOENFELD.
               ______________________

     Before LOURIE, SCHALL, and CHEN, Circuit Judges.
 LOURIE, Circuit Judge
     Lone Star Silicon Innovations LLC (“Lone Star”) ap-
 peals from the final written decision of the Patent Trial and
 Appeal Board (“Board”) holding claims 2 and 7 of U.S. Pa-
 tent 6,388,330 (the “’330 patent”) unpatentable as obvious.
 For the reasons described below, we affirm.
                         BACKGROUND
      Lone Star is the owner of the ’330 patent, which is di-
 rected to semiconductor etch stop layers with low dielectric
 constants. An etch stop layer is made of material that is
 resistant to the process used to etch other layers of a semi-
 conductor device and is deposited between two other layers
 to allow those layers to be etched separately. The invention
 of the ’330 patent reduces capacitive coupling between lay-
 ers of metal interconnects by reducing the dielectric con-
 stant of the etch stop layers to below 5.5, in contrast to the
 prior art dielectric constants of 7.5 or higher.
      Independent claims 1 and 6, which are not at issue in
 this appeal, are directed to integrated circuits comprising
 an “etch stop layer of silicon nitride . . . having a dielectric
 constant below 5.5.” ’330 patent col. 6 ll. 62–64, col. 7 ll.
 22–24, col. 8 ll. 4–6. Dependent claims 2 and 7, which are
 at issue in this appeal, are directed to the integrated cir-
 cuits of claims 1 and 6 respectively, wherein the silicon ni-
 tride etch stop layer is a “multilayer structure.” Id. col. 7
 ll. 3–4, col. 8 ll. 12–13.
     Micron Technology, Inc. (“Micron”) petitioned for inter
 partes review of claims 1, 2, 5, 6, 7, and 10. Micron asserted
 a single ground in its petition, namely, that the challenged
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 LONE STAR SILICON INNOVATIONS   v. IANCU                    3

 claims were obvious over Watatani 1 in view of Tanaka. 2
 The petition stated: “The Ground is explained below and is
 supported by the Declaration of Dr. Richard B. Fair.”
 J.A. 70.
      Within that single ground, Micron asserted two sepa-
 rate theories regarding the prior art’s teaching of the “mul-
 tilayer structure” limitation in claims 2 and 7. In its first
 theory, Micron contended that “Watatani expressly de-
 scribes an etch stop layer that includes ‘three or more lay-
 ers’ of silicon nitride.” J.A. 105 (citing Watatani col. 7 ll.
 54–55). In its second theory, Micron contended that “[s]uch
 multilayer silicon nitride layers were well known in the
 prior art,” and Micron supported this second theory with
 declaration testimony from its expert as well as prior art
 references Watatani, SST 1987, 3 and Wang. 4 See J.A. 105–
 07; see also J.A. 81–82 (“It Was Well Known In The Prior
 Art To Form Multilayer Silicon Nitride Etch Stop Films”).
     The Board instituted review of the challenged claims.
 J.A. 209. For the “multilayer structure” of claims 2 and 7,
 the Board rejected Micron’s first theory, i.e., the theory
 based on the description in Watatani. J.A. 224 (“On this
 record, we agree with Patent Owner that Watatani does
 not describe an etch stop layer that includes three or more
 layers of silicon nitride.”). But the Board expressly

     1  U.S. Patent 6,153,511.
     2  Masayuki Tanaka et al., Low-k SiN Film for Cu In-
 terconnects Integration Fabricated by Ultra Low Tempera-
 ture Thermal CVD, in 1999 SYMPOSIUM ON VLSI
 TECHNOLOGY, DIGEST OF TECHNICAL PAPERS, 47–48 (Bus.
 Center for Acad. Societies Japan, 1999).
     3  Novellus Sys., Continuous Process CVD System, 30
 SOLID STATE TECH., no. 10, Oct. 1987, at 49–50.
     4  U.S. Patent 6,017,791.
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 4                    LONE STAR SILICON INNOVATIONS   v. IANCU

 acknowledged that Micron had asserted a second inde-
 pendent theory for the “multilayer structure” limitation:
     Petitioner’s contentions regarding claims 2 and 7
     are not, however, based solely on Watatani’s disclo-
     sure of multilayer etch stops. Petitioner also con-
     tends that “multilayer silicon nitride layers were
     well known in the prior art.”
 J.A. 225. The Board found that Micron’s evidence—includ-
 ing the teachings of SST 1987 and Wang—was “sufficient
 to support its contention that multilayer silicon nitride lay-
 ers were known in the art.” J.A. 226.
     Lone Star filed a request for rehearing, arguing that
 the Board exceeded its authority by instituting review of
 claims 2 and 7 “based on a new ground not asserted in the
 Petition.” J.A. 241. The Board denied Lone Star’s request,
 finding that the institution decision relied on additional
 prior art references “in the same way” that Micron’s peti-
 tion did, namely, “as evidence of the knowledge of a person
 of ordinary skill in the art.” J.A. 258. The Board noted
 that Lone Star “cites no authority for the proposition that
 a reference relied upon to show that a claim limitation is
 within the knowledge of a [person of ordinary skill in the
 art] must be expressly included in the list of references that
 denominate the ground.” J.A. 259; see J.A. 258 (“Our reli-
 ance on SST 1987, however, does not transform the insti-
 tuted ground into a ‘new ground,’ as argued by Patent
 Owner.”).
     In its patent owner response, Lone Star again raised
 its contention that the Board had exceeded its authority
 and also addressed the merits of the obviousness challenge.
 Micron argued in reply that the instituted ground based on
 Watatani, Tanaka, and the knowledge of a person of ordi-
 nary skill had been asserted in the petition. J.A. 378–80.
 Micron also submitted a second declaration from its expert
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 LONE STAR SILICON INNOVATIONS   v. IANCU                   5

 declarant, Dr. Fair, who cited yet another reference, Yota, 5
 to support his opinion that that multilayer silicon nitride
 films were well-known in the art. See J.A. 890–94.
     Lone Star believed that portions of Micron’s reply im-
 properly relied on new evidence, particularly those por-
 tions that relied on Dr. Fair’s citations to additional
 exhibits, such as Yota, that were not previously submitted
 with Micron’s petition. See J.A. 1483–85. The parties
 jointly requested permission from the Board to submit ad-
 ditional briefing, which the Board allowed. Id. Lone Star
 thus had the opportunity to submit a sur-reply in which it
 addressed Dr. Fair’s second declaration, including his reli-
 ance on Yota. See J.A. 397–99.
      In its final written decision, the Board held all of the
 challenged claims, including claims 2 and 7, obvious over
 Watatani in view of Tanaka. J.A. 2. The Board again re-
 jected Lone Star’s argument that the Board had exceeded
 its authority and again emphasized that its institution de-
 cision and final written decision properly relied on addi-
 tional references like SST 1987 “in the same way as it was
 relied upon in the Petition: as evidence that multilayer sil-
 icon nitride layers were known in the prior art.” J.A. 42.
 On the merits, the Board held that Micron proved by a pre-
 ponderance of the evidence that a person of ordinary skill
 in the art would have been motivated to use a multilayer
 silicon nitride structure when forming an etch stop layer
 and would have had a reasonable expectation of success in
 achieving the subject matter of claims 2 and 7. J.A. 38–39.

     5   Jiro Yota et al., Comparison between HDP CVD
 and PECVD Silicon Nitride for Advanced Interconnect Ap-
 plications, in PROC. OF THE IEEE 2000 INT’L INTERCONNECT
 TECH. CONFERENCE, 76–78 (IEEE Electron Devices Soc’y,
 2000).
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 6                   LONE STAR SILICON INNOVATIONS   v. IANCU

      Lone Star appealed the Board’s final written decision
 only with respect to claims 2 and 7. Micron declined to par-
 ticipate in the appeal because it had already reached a set-
 tlement with Lone Star. The Director of the United States
 Patent and Trademark Office (“Director”) intervened pur-
 suant to 35 U.S.C. § 143. We have jurisdiction under
 28 U.S.C. § 1295(a)(4)(A).
                        DISCUSSION
      Our review of a Board decision is limited. In re Baxter
 Int’l, Inc., 678 F.3d 1357, 1361 (Fed. Cir. 2012). We review
 the Board’s legal determinations de novo, In re Elsner, 381
F.3d 1125, 1127 (Fed. Cir. 2004), but we review the Board’s
 factual findings underlying those determinations for sub-
 stantial evidence, In re Gartside, 203 F.3d 1305, 1316 (Fed.
 Cir. 2000). A finding is supported by substantial evidence
 if a reasonable mind might accept the evidence as adequate
 to support the finding. Consol. Edison Co. v. NLRB, 305
U.S. 197, 229 (1938). “Where there is adequate and sub-
 stantial evidence to support either of two contrary findings
 of fact, the one chosen by the board is binding on the court
 regardless of how we might have decided the issue if it had
 been raised de novo.” Mishara Constr. Co. v. United States,
 230 Ct. Cl. 1008, 1009 (1982) (citing Koppers Co. v. United
 States, 186 Ct. Cl. 142, 151 (1968), and Nat’l Concrete &
 Found. Co. v. United States, 170 Ct. Cl. 470, 478 (1965)).
     Lone Star raises two challenges on appeal. First, Lone
 Star contends that the Board exceeded its authority when
 it reviewed claims 2 and 7 and held them unpatentable
 based on a ground of obviousness that was not asserted in
 Micron’s petition for inter partes review. Second, Lone
 Star contends that the Board’s obviousness conclusion for
 claims 2 and 7 is not supported by substantial evidence.
 We address Lone Star’s challenges in turn.
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                               I
      Lone Star argues that the petition set forth a single
 ground of obviousness based solely on the combination of
 Watatani and Tanaka, but the Board held the claims un-
 patentable based on an unasserted ground that included a
 combination of those two references with at least three ad-
 ditional references—SST 1987, Wang, and Yota. According
 to Lone Star, the Board exceeded its authority, as set forth
 in 37 C.F.R. § 42.108(a), to authorize review to proceed on
 “all or some of the grounds of unpatentability asserted for
 each claim.” Appellant Br. 37 (quoting and adding empha-
 sis to the regulation).
     The Director responds that Lone Star is attempting to
 challenge the Board’s institution decision, which is a non-
 appealable issue pursuant to 35 U.S.C. § 314(d). The Di-
 rector further argues that, even to the extent that Lone
 Star’s challenge is appealable, the Board did not abuse its
 discretion or exceed its authority in this case.
     We agree with the Director that Lone Star’s challenge
 is directed to the Board’s institution decision, which is not
 appealable. The relevant statutory language is the “No Ap-
 peal” clause in Section 314(d):
     (d) No Appeal.—The determination by the Direc-
     tor whether to institute an inter partes review un-
     der this section shall be final and nonappealable.
 In Cuozzo Speed Techs., LLC v. Lee, 136 S. Ct. 2131, 2141
 (2016) (“Cuozzo III”), the Supreme Court held that “[t]he
 text of the ‘No Appeal’ provision, along with its place in the
 overall statutory scheme, its role alongside the Adminis-
 trative Procedure Act, the prior interpretation of similar
 patent statutes, and Congress’ purpose in crafting inter
 partes review, all point in favor of precluding review of the
 Patent Office’s institution decisions.”
     We recently addressed a challenge similar to the one
 presented here. See Koninklijke Philips N.V. v. Google
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 8                    LONE STAR SILICON INNOVATIONS   v. IANCU

 LLC, 948 F.3d 1330 (Fed. Cir. 2020). In that case, the pe-
 tition presented a single obviousness ground based on the
 SMIL reference but also relied on the Hua reference as ev-
 idence of what was known in the art. Id. at 1333–34. Alt-
 hough the petition asserted only one obviousness ground,
 the Board instituted review on two obviousness grounds—
 (1) SMIL in view of Hua and (2) SMIL “in light of the gen-
 eral knowledge of the skilled artisan.” Id. at 1334. Regard-
 ing the first instituted ground, we concluded that it was
 error for the Board to institute review based on a ground of
 obviousness over SMIL and Hua because that ground was
 not presented in the petition. Id. at 1337. But regarding
 the second instituted ground, we found no error in the
 Board’s decision to institute review based on obviousness
 over SMIL in view of the knowledge of a person of ordinary
 skill. Id. at 1338. Notably, the evidence presented to sup-
 port the knowledge of a person of skill relied in part on
 other references, including Hua.
     Here, like the second instituted ground in Koninklijke
 Philips, the Board instituted inter partes review based on
 the ground of obviousness that was presented in Micron’s
 petition—Watatani in view of Tanaka. The petition undis-
 putedly asserted only one obviousness ground. The Board
 was not, however, obligated to “ignore the skilled artisan’s
 knowledge when determining whether it would have been
 obvious to modify the prior art.” Id. at 1337. Indeed, the
 statutory definition of obviousness expressly depends on
 what would have been known to a person having ordinary
 skill in the art. 35 U.S.C. § 103.
     Lone Star focuses entirely on the listed references.
 Lone Star insists that the instituted ground was not actu-
 ally presented in the petition because it relies on additional
 references beyond Watatani and Tanaka that were not pre-
 sented in the petition and the Board lacked authority to
 sua sponte add its own ground of unpatentability. Lone
 Star argues that the mere fact that the Board failed to ex-
 plicitly acknowledge this as a “new ground” is insufficient
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 LONE STAR SILICON INNOVATIONS     v. IANCU                     9

 to distinguish this case from the first instituted ground in
 Koninklijke Philips, which we found to be instituted in er-
 ror. 948 F.3d at 1337. But here, the Board repeatedly
 made clear that the instituted ground was based on Wa-
 tatani and Tanaka, and that the additional references were
 being relied on exclusively for their teachings about what
 was well-known in the art. J.A. 225; see also J.A. 42, 258.
 And the Board only did so after it expressly interpreted the
 petition to have presented that argument. E.g. J.A. 225
 (quoting “[p]etitioner’s contention[] . . . that ‘multilayer sil-
 icon nitride layers were well known in the prior art.’” (em-
 phasis added)); J.A. 226 (“Petitioner’s evidence is sufficient
 to support its contention . . . .”). Under Section 314(d), the
 Board’s decision to institute review based on its interpre-
 tation of the petition is not appealable. See Cuozzo III, 136
S. Ct. at 2139 (holding that the Board’s interpretation of
 the petition to have implicitly presented a challenge was
 unreviewable).
      Lone Star attempts to avoid the “No Appeal” clause by
 arguing that its challenge in this case is not to the Board’s
 institution decision, but rather to the scope of the Board’s
 statutory and regulatory authority throughout the pro-
 ceeding, which is reviewable. Lone Star relies heavily on
 the Supreme Court’s acknowledgment that the petition is
 “the centerpiece of the proceeding both before and after in-
 stitution.” SAS Inst., Inc. v. Iancu, 138 S. Ct. 1348, 1358
 (2018). Lone Star argues that the “No Appeal” clause in
 Section 314(d) pertains only to the “preliminary patenta-
 bility [decision]” based on the “patentability merits of par-
 ticular claims,” and is thus inapplicable in this case. See
 Reply Br. 6 (quoting Wi-Fi One, LLC v. Broadcom Corp.,
 878 F.3d 1364, 1372 (Fed. Cir. 2018) (en banc)). According
 to Lone Star, the controlling authority in this case is 37
 C.F.R. § 42.108, which allows the Board to institute review
 “on all or some of the grounds of unpatentability asserted.”
 Lone Star also argues that 35 U.S.C. § 311(b) limits the
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 10                   LONE STAR SILICON INNOVATIONS   v. IANCU

 scope of the Board’s authority to a ground on which a peti-
 tioner asks for review.
     We disagree with Lone Star’s characterization of both
 its challenge and the Board’s institution decision. In
 Cuozzo III, the Supreme Court held that the “No Appeal”
 clause applies to attacks that are “closely tied” to the
 Board’s “decision to initiate inter partes review.” 136 S. Ct.
 at 2141. We find that this is such a case. In order to grant
 the relief that Lone Star requests, we would have to un-
 wind the Board’s institution decision and compare it to the
 particular language used in Micron’s petition regarding the
 “multilayer structure” limitation, which is precisely the
 kind of analysis the Supreme Court cautioned against. Id.
 at 2139. In essence, Lone Star’s argument that a specific
 theory was not within “the grounds of unpatentability as-
 serted” under 37 C.F.R. § 42.108 “is little more than a chal-
 lenge to the Patent Office’s conclusion, under § 314(a), that
 the ‘information presented in the petition’ warranted re-
 view.” Id. at 2142.
      In an attempt to distinguish Cuozzo III, Lone Star
 points to a number of cases in which this court has re-
 viewed institution-stage issues. But in each such case the
 reviewable issue was not closely tied to substantive patent-
 ability requirements. See Arista Networks, Inc. v. Cisco
 Sys., Inc., 908 F.3d 792, 799 (Fed. Cir. 2018) (reviewing as-
 signor estoppel); Wi-Fi One, 878 F.3d 1364, 1374 (review-
 ing time bar); see generally Applications in Internet Time,
 LLC v. RPX Corp., 897 F.3d 1336 (Fed. Cir. 2018) (review-
 ing the real party in interest requirement). And while the
 Supreme Court itself acknowledged that the “No Appeal”
 clause does not extend to appealable constitutional or stat-
 utory violations, Cuozzo III, 136 S. Ct. at 2141–42, that
 acknowledgement is not applicable here, where Lone Star’s
 challenge is to the evidentiary basis underpinning the
 Board’s interpretation of the petition in its institution de-
 cision.
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     We also note that that this court has entertained chal-
 lenges to the Board for exceeding its authority in violation
 of the Administrative Procedure Act (“APA”) by, for exam-
 ple, failing to give “notice of and a fair opportunity to meet
 the grounds of rejection.” In re NuVasive, Inc., 841 F.3d
966, 971 (Fed. Cir. 2016) (quoting Belden Inc. v. Berk-Tek
 LLC, 805 F.3d 1064, 1080 (Fed. Cir. 2015)). But, im-
 portantly, Lone Star has not raised such a challenge under
 the APA in this case. Indeed, the crux of Lone Star’s argu-
 ment is that the Board exceeded its authority notwith-
 standing the undisputed fact that Lone Star did have
 notice of the full scope of the inter partes review and an
 adequate opportunity to respond in its patent owner re-
 sponse and its sur-reply. In the context of challenges under
 the APA, we have found that the Board is within its au-
 thority to institute review and consider even arguments
 that were not asserted in the petition “after giving [the pa-
 tent owner] a full opportunity to submit additional evi-
 dence and arguments on that point.” NuVasive, 841 F.3d
 at 975 (citing In re Kumar, 418 F.3d 1361, 1367–69 (Fed.
 Cir. 2005)). All the more so here, where the Board put Lone
 Star on notice of its finding that the “multilayer structure”
 theory was presented in the petition, there is nothing in the
 patent statute or the regulations that limits the Board’s
 authority to include that theory within the scope of its re-
 view. 6

     6   Although not cited in the petition, Yota was not
 needed for the petition to establish, on the basis of SST
 1987 and Wang, that multilayer silicon nitride structures
 were well known. To the extent that the Board relied on
 Yota to rebut specific arguments made by Lone Star
 against reasonable expectation of success, the Board was
 within its authority to do so where Lone Star was given
 ample opportunity to respond.
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     At bottom, the Board interpreted the petition to have
 presented a specific theory for the “multilayer structure”
 limitation. The Board instituted an inter partes review
 that includes that theory. Lone Star asks us to review that
 institution decision. Under the “No Appeal” clause, as in-
 terpreted by the Supreme Court in Cuozzo III, that decision
 is not reviewable.
                               II
     We turn now to Lone Star’s challenge on the merits of
 the Board’s obviousness conclusion for claims 2 and 7. Ob-
 viousness is a question of law based on underlying facts,
 including the scope and content of the prior art, differences
 between the prior art and the claims at issue, the level of
 ordinary skill, and relevant evidence of secondary consid-
 erations. Graham v. John Deere Co., 383 U.S. 1, 17–18
 (1966). Whether a skilled artisan would have been moti-
 vated to combine prior art references is also a question of
 fact. Wyers v. Master Lock Co., 616 F.3d 1231, 1238–39
 (Fed. Cir. 2010).
     Lone Star challenges a number of the facts underlying
 the Board’s obviousness conclusion. Lone Star contends
 that, even accepting that a multilayer structure of silicon
 nitride was well-known in the art, the record is devoid of
 evidence that such a multilayer structure was known to be
 used as an etch stop layer, which is what claims 2 and 7
 actually require. Lone Star also challenges the Board’s
 conclusions regarding motivation to combine and reasona-
 ble expectation of success. Lone Star argues that the two
 alleged motivations to use a multilayer structure—layer
 uniformity and avoiding pinholes—are divorced from the
 overall context of the claims, which require that the etch
 stop layer have a dielectric constant below 5.5. And Lone
 Star argues that the evidence in the record demonstrates
 that a person of skill would have expected a multilayer
 structure to increase the dielectric constant of the etch stop
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 LONE STAR SILICON INNOVATIONS   v. IANCU                  13

 layer, which is the opposite of the claimed invention di-
 rected to lower dielectric constants.
     The Director responds that the multilayer structure
 limitation of claims 2 and 7 adds no patentable significance
 to the obvious integrated circuit of claims 1 and 6. Said
 differently, the Director argues that claims 2 and 7 are di-
 rected to nothing more than starting with an obvious inte-
 grated circuit and adding a well-known multilayer
 structure that has well-established benefits for integrated
 circuits. The Director further argues that Lone Star’s mo-
 tivation to combine argument is contrary to law, and that
 substantial evidence from both parties’ experts and multi-
 ple prior art references supports the Board’s findings re-
 garding reasonable expectation of success.
      We agree with the Director. The Supreme Court has
 made clear that “if a technique has been used to improve
 one device, and a person of ordinary skill in the art would
 recognize that it would improve similar devices in the same
 way, using the technique is obvious unless its actual appli-
 cation is beyond his or her skill.” KSR Int’l Co. v. Teleflex
 Inc., 550 U.S. 398, 417 (2007). For purposes of this appeal,
 it is not disputed that multilayer structures were known to
 improve integrated circuits by improving layer uniformity
 and decreasing pinholes. And the record contains substan-
 tial evidence that using the multilayer structure of silicon
 nitride recited in claims 2 and 7 would improve the etch
 stop layers in the integrated circuits of claims 1 and 6 in
 the same way. Thus, the multilayer structure does not ren-
 der nonobvious the otherwise obvious integrated circuits of
 claims 1 and 6.
      Furthermore, regarding a motivation to combine, we
 reject Lone Star’s contention that the known advantages
 that would have motivated a person of skill to use multi-
 layer structures must be shown to directly impact the
 claimed lower dielectric constant. On the contrary, the law
 is clear that “the motivation to modify a prior art reference
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 14                  LONE STAR SILICON INNOVATIONS   v. IANCU

 to arrive at the claimed invention need not be the same mo-
 tivation that the patentee had.” Monsanto Tech. LLC v.
 E.I. DuPont de Nemours & Co., 878 F.3d 1336, 1347 (Fed.
 Cir. 2018) (citation omitted, emphasis added). Here, there
 is substantial evidence that a person of skill would have
 been motivated to use a multilayer structure of silicon ni-
 tride as an etch stop layer to improve layer uniformity and
 avoid pinholes. And, having been motivated to use a mul-
 tilayer structure, the person of skill would have thus ar-
 rived at the claimed invention of claims 2 and 7.
      Finally, regarding the reasonable expectation of suc-
 cessfully achieving a low dielectric constant with a multi-
 layer structure, the Board relied on the testimony of both
 parties’ expert witnesses regarding the relationship be-
 tween density and dielectric constants when stacking mul-
 tiple thin layers to achieve thickness. J.A. 41–42 (citing
 both Dr. Fair and Dr. Bottoms). And simply put, the
 Tanaka prior art reference teaches a silicon nitride layer
 with a dielectric constant that is below 5.5 as required by
 the claims, see J.A. 41, and Micron’s expert, Dr. Fair,
 pointed to multiple references to support his opinion that
 the low dielectric constant could be maintained using a
 multilayer structure. J.A. 893–94. Lone Star challenged
 Dr. Fair’s opinions below with the same factual arguments
 it now raises on appeal, but the Board rejected Lone Star’s
 challenges based on the teachings of the prior art refer-
 ences, the background of the ’330 patent itself, and incon-
 sistencies within Lone Star’s positions. J.A. 47–48. We are
 not in a position to second-guess the Board’s evaluation of
 expert witnesses’ credibility or its reconciliation of per-
 ceived inconsistencies in their testimony. Yorkey v. Diab,
 601 F.3d 1279, 1284 (Fed. Cir. 2010) (“We defer to the
 Board’s findings concerning the credibility of expert wit-
 nesses.” (citing Velander v. Garner, 348 F.3d 1359, 1371
 (Fed. Cir. 2003))). On this record, the Board’s finding that
 a person of skill would have had a reasonable expectation
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 LONE STAR SILICON INNOVATIONS   v. IANCU                 15

 of successfully achieving the invention of claims 2 and 7 is
 supported by substantial evidence.
                        CONCLUSION
      We have considered Lone Star’s remaining arguments,
 but we find them to be unpersuasive. Accordingly, the de-
 cision of the Board holding unpatentable claims 2 and 7 of
 the ’330 patent is affirmed.
                        AFFIRMED