The US Court of Appeals for the Federal Circuit affirmed a Patent Trial & Appeal Board obviousness determination even though it found the Board had improperly construed a claim term, because the Court found the error harmless in the context of the prior art. HD Silicon Solutions LLC v. Microchip Technology Inc., Case No. 23-1397 (Fed. Cir. Feb. 6, 2025) (Lourie, Stoll, Cunningham, JJ.)
During a 2022 inter partes review (IPR), the Board determined that all but one of the 17 challenged patent claims were unpatentable as obvious in light of a prior patent (Trivedi) and other secondary prior art. The patent described methods of creating “a local interconnect layer in an integrated circuit” using two films. The independent claim recited a first film composed of titanium nitride and a second film as “comprising tungsten.” The Board construed “comprising tungsten” to include either elemental tungsten or tungsten-based compounds. The Board also found that the Trivedi patent disclosed films comprising either elemental tungsten or tungsten compounds. Thus, the Board held that all claims except one were obvious in light of Trivedi and that a person of ordinary skill in the art would have been motivated to combine Trivedi with other prior art. The patent owner appealed, arguing that the Board’s obviousness finding was dependent on the Board’s incorrect construction of the phrase “comprising tungsten.”
The Federal Circuit agreed that the Board’s claim construction was erroneous, because the term “comprising tungsten” required elemental tungsten. The Court explained that the claims explicitly used compound names when referring to compounds, such as “titanium nitride.” Thus, when the drafters wrote “comprising tungsten” without more, they clearly intended to exclude non-elemental tungsten options. The Court also noted that the patent specification used “tungsten” to reference only elemental tungsten and used the word “based” to encompass both elements and their compounds. For example, the patent discussed “chlorine-based” and “fluorine-based” components. Thus, the Court concluded that the claim drafters knew how to delineate when terms should include compounds, and that there was no such delineation in the term “comprising tungsten.”
The Board relied on a single sentence in the patent that stated: “the second film may comprise tungsten, for example,” to support its construction. The Federal Circuit rejected such a broad reading of this language, explaining that it only provided for impurities mixed among the elemental tungsten in the second film, rather than the film comprising a tungsten compound. The Board also cited a European Union (EU) patent in support of the construction that “comprising tungsten” explicitly included tungsten compounds. The Court stated that such extrinsic evidence was insufficient to overcome the asserted patent’s intrinsic teachings.
The Federal Circuit analyzed whether the Board’s obviousness holding could stand given its erroneous construction. The Court found that because the Board determined that Trivedi disclosed layers made of a tungsten compound and elemental tungsten, the patent claims were obvious when the disputed term was properly construed to be limited to elemental tungsten. Thus, the Board’s error was harmless.
