Case: 23-1397 Document: 45 Page: 1 Filed: 02/06/2025

United States Court of Appeals for the Federal Circuit ______________________

HD SILICON SOLUTIONS LLC, Appellant

v.

MICROCHIP TECHNOLOGY INC., Appellee ______________________

2023-1397 ______________________

Appeal from the United States Patent and Trademark Office, Patent Trial and Appeal Board in No. IPR2021- 00752. ______________________

Decided: February 6, 2025 ______________________

SARAH S. BROOKS, Venable LLP, Los Angeles, CA, ar- gued for appellant. Also represented by JUSTIN J. OLIVER, Washington, DC.

BRETT M. SCHUMAN, Goodwin Procter LLP, San Fran- cisco, CA, argued for appellee. Also represented by RACHEL M. WALSH; SANJEET DUTTA, Redwood City, CA; ROHINIYURIE TASHIMA, Washington, DC. ______________________

Before LOURIE, STOLL, and CUNNINGHAM, Circuit Judges. Case: 23-1397 Document: 45 Page: 2 Filed: 02/06/2025

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LOURIE, Circuit Judge. HD Silicon Solutions LLC (“HDSS”) appeals from a fi- nal written decision of the United States Patent and Trade- mark Office Patent Trial and Appeal Board (“the Board”) holding claims 1–7 and 9–17 of U.S. Patent 6,774,033 (“the ’033 patent”) unpatentable as obvious. Microchip Tech. Inc. v. HD Silicon Sols. LLC, No. IPR2021-00752, 2022 WL 16748547 (P.T.A.B. Nov. 7, 2022) (“Decision”). For the fol- lowing reasons, we affirm. BACKGROUND The ’033 patent is directed to a local interconnect layer in an integrated circuit. ’033 patent, col. 1 ll. 49–50. To connect transistors within an integrated circuit, a local in- terconnect layer “provide[s] relatively short electrical paths between” the transistors. Id. col. 1 ll. 31–32. The challenged claims include independent claims 1 and 15. Claim 1 recites: 1. A method of forming a local interconnect layer in an integrated circuit, the method comprising: depositing a first film over an oxide layer, the first film comprising titanium nitride; and depositing a second film over the first film, the second film comprising tungsten, the first film and the second film forming a metal stack of the local interconnect layer. Id. col. 5 l. 55–col. 6 l. 4 (emphasis added). The dependent claims add limitations specifying the technique used to de- posit the films, the thickness of one or both of the films, and the type of etchant used to etch the films. See generally id. col. 6 ll. 5–56. Microchip Technology Inc. (“Microchip”) petitioned for inter partes review (“IPR”), arguing that all claims of the ’033 patent would have been obvious over U.S. Patent Case: 23-1397 Document: 45 Page: 3 Filed: 02/06/2025

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5,847,463 (“Trivedi”). Trivedi is directed to a method of forming a local interconnect structure that has “tungsten silicide and titanium nitride layers, or has a tungsten layer covered on opposite sides thereof with titanium nitride.” Trivedi, col. 1 ll. 10–12. At the Board, the parties disputed the construction of the term “comprising tungsten,” found in all challenged claims. Based on the text of the claims, the specification, and extrinsic evidence, the Board construed “comprising tungsten” to mean any form of tungsten, including both el- emental tungsten and tungsten compounds. Decision at *3–6. The Board then held that Microchip had met its bur- den to show that all claims of the ’033 patent, except claim 8, are unpatentable, based on either Trivedi alone or Trivedi in combination with one or more secondary refer- ences. Id. at *6–32. HDSS timely appealed. We have jurisdiction under 28 U.S.C. § 1295(a)(4)(A). DISCUSSION HDSS presents two main arguments on appeal. The principal argument is that the Board improperly construed the phrase “comprising tungsten.” In the alternative, HDSS separately challenges the Board’s motivation to combine findings as to certain dependent claims. Although we conclude that the Board’s claim construc- tion was erroneous, we determine that that error was harmless. We further reject HDSS’s challenges to the Board’s motivation to combine findings. I We interpret claim terms from the perspective of a per- son of ordinary skill in the art at the time of the invention, who is “deemed to read the claim term not only in the con- text of the particular claim in which the disputed term ap- pears, but in the context of the entire patent, including the Case: 23-1397 Document: 45 Page: 4 Filed: 02/06/2025

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specification.” Phillips v. AWH Corp., 415 F.3d 1303, 1313 (Fed. Cir. 2005) (en banc). Evidence extrinsic to the patent may also be useful in construing claim terms, but is gener- ally viewed as “less reliable than the patent” itself. Id. at 1318. “Claim construction is ultimately a question of law, de- cided de novo on review . . . [b]ut we review any underlying fact findings about extrinsic evidence . . . for substantial- evidence support when the appeal comes from the Board.” Intel Corp. v. Qualcomm Inc., 21 F.4th 801, 808 (Fed. Cir. 2021). The ’033 patent claims use precise language, i.e., the recitation of another element, when referencing materials in their compound form. Specifically, claim 1 recites that the first film of the local interconnect “compris[es] titanium nitride.” ’033 patent, col. 5 l. 58 (emphasis added). Com- pare that to how claim 1 recites the composition of the sec- ond film, that it “compris[es] tungsten,” without the presence of another element. Id. col. 6 l. 2. This suggests that the ’033 patent uses explicit language to refer to a com- pound when a compound is intended, and when no such language is included, only the elemental form is intended. A claim to “tungsten,” on its own, therefore refers to ele- mental tungsten. Furthermore, the specification exclusively refers to tungsten as a singular component, i.e., as an element. E.g., id. col. 3 ll. 8–10 (“Additionally, titanium nitride may serve as a barrier and adhesion layer for a subsequently depos- ited tungsten film.”). And when referencing the properties of tungsten that make it a desirable material for use in a local interconnect, the specification refers to properties unique to tungsten itself—not compounds of tungsten— such as low resistivity and chemical stability. Id. col. 3 ll. 41–42 (“Tungsten also has a relatively low resistivity compared to titanium nitride.”); id. col. 3 ll. 47–48 (“Rela- tively speaking, tungsten is also a chemically stable Case: 23-1397 Document: 45 Page: 5 Filed: 02/06/2025

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material.”). Indeed, at oral argument, Microchip’s counsel conceded that when “the specification refers to a layer of tungsten . . . that is referencing elemental tungsten.” See Oral Arg. at 15:50–16:03, available at https://oralargu- ments.cafc.uscourts.gov/default.aspx?fl=23-1397_1106202 4.mp3. Not once is a tungsten compound mentioned in the specification, let alone in the prosecution history. Consistent with this understanding, the ’033 patent uses an open-ended modifier when referring to materials that include both compounds and elements. Dependent claim 12 refers to a “chlorine-based etchant,” ’033 patent col. 6 ll. 36 (emphasis added), which the specification de- fines as including both chlorine compounds and elemental chlorine, id. col. 4 ll. 13–16. (“In one embodiment, a chlo- rine-based etchant, such as boron trichloride (BCl3) or chlo- rine (Cl2), is employed to etch a film 103 of titanium nitride stopping on oxide layer 102.”). See also id. col. 6 ll. 33 (“flu- orine-based etchants”). That further demonstrates that when the ’033 patent references “tungsten” on its own, it is referring to tungsten in its elemental form. The Board’s core reasoning in coming to its construc- tion was based on one sentence in the ’033 patent: “The first film may comprise titanium nitride, while the second film may comprise tungsten, for example.” Id. col. 1 ll. 53–54; see Decision at *5. According to the Board, the phrase, “for example,” means that elemental tungsten is just “one ex- emplary embodiment” of a “second film comprising tung- sten,” and therefore the limitation cannot be so narrowed. Decision at *5. We agree with the Board that this sentence refers to tungsten as an exemplary embodiment of a “second film comprising tungsten.” Nevertheless, the Board’s reasoning is flawed because it assumes that there are only two forms of tungsten—purely elemental tungsten and tungsten com- pounds. But that is not the case. As explained by HDSS’s expert, “[b]y using the terminology of comprising tungsten, Case: 23-1397 Document: 45 Page: 6 Filed: 02/06/2025

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[the claim] allows for the possibility of unintentional impu- rities that might be incorporated during the deposition pro- cess.” J.A. 3069 ¶ 48; see also Oral Arg. at 2:04–2:06, 4:08– 4:13 (counsel for HDSS explaining that the phrase “com- prising tungsten” includes elemental tungsten attached to other “minute particles” or “minute elements.”). The incor- poration of minute materials with elemental tungsten does not constitute a tungsten compound. Thus, when read in accord with the understanding that elemental tungsten may include additional minute materials, yet still not be a compound, the description of elemental tungsten as an “ex- ample” is not inconsistent with the ’033 patent’s disclo- sures indicating that the patent requires elemental tungsten. The Board also relied on European Patent Application Publication 0463373 (“Gunturi”) in coming to its construc- tion. Decision at *6. Gunturi recites “forming [a] local in- terconnect structure using a material comprising tungsten,” Gunturi col. 4 ll. 28–29, and discloses that such material may be “a thin layer of tungsten silicide,” a tung- sten compound. Id. col. 3 l. 39. Accordingly, the Board rea- soned that Gunturi “teaches that the phrase ‘comprising tungsten’ includes” tungsten compounds. Decision at *6. While the Board’s interpretation of Gunturi is certainly reasonable, Gunturi is insufficient to support the Board’s construction because it conflicts with the specification, claims, and prosecution history of the ’033 patent, which indicate that “comprising tungsten” requires elemental tungsten. See Bell Atl. Network Servs., Inc. v. Covad Commc’ns Grp., Inc., 262 F.3d 1258, 1269 (Fed. Cir. 2001) (“[E]xtrinsic evidence may be used only to assist in the proper understanding of the disputed limitation; it may not be used to vary, contradict, expand, or limit the claim lan- guage from how it is defined, even by implication, in the specification or file history.”). Case: 23-1397 Document: 45 Page: 7 Filed: 02/06/2025

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For the foregoing reasons, the Board’s claim construc- tion was erroneous. The term “comprising tungsten,” as recited in the challenged claims, requires elemental tung- sten. II A We next consider how the Board’s obviousness deter- minations are impacted by our rejection of the Board’s claim construction. Obviousness is a question of law based on underlying findings of fact. KSR Int’l Co. v. Teleflex Inc., 550 U.S. 398, 427 (2007). We review the Board’s legal con- clusion on obviousness de novo and its findings of fact for substantial evidence. HTC Corp. v. Cellular Commc’ns Equip., LLC, 877 F.3d 1361, 1369 (Fed. Cir. 2017). What a reference teaches and the presence or absence of a motiva- tion to combine references are questions of fact. PAR Pharm., Inc. v. TWI Pharms., Inc., 773 F.3d 1186, 1196–97 (Fed. Cir. 2014). HDSS asserts that reversal or vacatur of the Board’s obviousness findings is required because the findings were dependent on the Board’s incorrect construction of “com- prising tungsten,” which is recited in each of the challenged claims. HDSS Br. 28. Microchip argues the contrary, that even under an elemental tungsten-requiring construction, the Board’s findings should be affirmed because the main prior art reference, Trivedi, discloses both elemental tung- sten and tungsten-silicide layers, and the Board found that both layers would have rendered the “second film compris- ing tungsten” limitation obvious. Oral Arg. at 22:10–22:52 (Microchip counsel asserting that HDSS’s claim construc- tion argument does not “matter” because Trivedi also “teaches [elemental] tungsten as the second film and the [Board] relied on that” disclosure). We agree with Microchip. The Board found that Trivedi discloses both a tungsten-silicide and an elemental Case: 23-1397 Document: 45 Page: 8 Filed: 02/06/2025

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tungsten layer, and either disclosure would render the “second film comprising tungsten” limitation of claim 1 ob- vious: “Trivedi itself teaches that either tungsten silicide or elemental tungsten may be used to form the [second] lo- cal interconnect layer” of claim 1. Decision at *9. That finding is consistent with what Trivedi discloses and is therefore supported by substantial evidence. Trivedi col. 1 ll. 10–12. (“[T]he local interconnect has tungsten silicide and titanium nitride layers, or has a tungsten layer covered on opposite sides thereof with titanium nitride.” (emphasis added)). Further recall that the dependent claims only add limitations with respect to the technique used to deposit the films, the thickness of one or both of the films, and the type of etchant used to etch the films. See generally ’033 patent, col. 6 ll. 5–56. The Board’s obviousness findings are equally supported regardless whether Trivedi’s elemental tungsten or tungsten-silicide layers are used to render claim 1 obvious. HDSS presents no argument in response. Therefore, although the Board erred in construing “comprising tungsten,” that error was harmless. B Finally, we address HDSS’s arguments challenging the Board’s findings of obviousness with respect to certain de- pendent claims. HDSS contends that some of the Board’s obviousness findings were not supported by substantial evidence be- cause the Board: (1) misinterpreted Trivedi’s disfavor of certain deposition and etching techniques disclosed by the other references, and (2) did not explain why a person of ordinary skill in the art would combine Trivedi and the other references to meet certain dependent claims’ specific thicknesses. We disagree on both counts. The Board thoroughly considered HDSS’s arguments as to Trivedi’s purported disfavor of certain deposition and etching techniques and reasonably rejected them. See, e.g., Case: 23-1397 Document: 45 Page: 9 Filed: 02/06/2025

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Decision at *17 (“While Trivedi may have expressed a pref- erence for [a non-sputtering process for the tungsten layer] . . . Trivedi also teaches [a] [sputtering] process to form lay- ers in the local interconnect.”). Moreover, the Board pro- vided thorough and well-reasoned explanations, relying on the testimony of Microchip’s expert, for why a person of or- dinary skill in the art would be motivated to combine Trivedi with one or more of the other references to arrive at the specific thicknesses of the challenged dependent claims. See, e.g., Decision at *21 (a person of ordinary skill in the art would be motivated to “apply [another refer- ence’s] thicknesses to Trivedi’s local interconnect” because such a combination was a “predictabl[e]” combination of known features). At bottom, HDSS asks us to reweigh the evidence, which we decline to do. Roku, Inc. v. Universal Elecs., Inc., 63 F.4th 1319, 1326 (Fed. Cir. 2023) (“An ap- pellate court does not and should not reweigh evidence or make factual findings.” (cleaned up)). CONCLUSION We have considered HDSS’s remaining arguments and find them unpersuasive. For the reasons provided, we af- firm. AFFIRMED