Elementary, My Dear Watson: How Claiming ‘Comprising’ Might Not Be So Compound After All

5.6.25

On February 6, 2025, the Federal Circuit clarified that claims describing a structure with an element may exclude its compounds if, given the specification, those skilled in the art would interpret the structure as pertaining solely to the elemental form. Those tasked with drafting claims to such structure should recognize where reliance on elemental forms will be advantageous to distinguishing over similar compounds in the prior art.

In HD Silicon Solutions LLC v. Microchip Technology Inc., the Court of Appeals for the Federal Circuit affirmed the Patent Trial and Appeal Board’s (PTAB) ruling that declared claims 1–7 and 9–17 of U.S. Patent No. 6,774,033 (“the ’033 patent”) unpatentable for obviousness. The patent at issue focuses on a method of forming a local interconnect layer in integrated circuits, specifically through the sequential deposition of a titanium nitride film and a tungsten film. Illustrative claim 1 is recited below:

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.

The crux of the appeal centered on the PTAB’s interpretation of the term “comprising tungsten” within the patent claims. The PTAB had broadly construed this phrase to include any form of tungsten, both elemental and compound. This interpretation played a key role in the board’s decision, as it matched the patent claims against prior art that described similar methodologies using both forms of tungsten.

However, the Federal Circuit critiqued this broad interpretation, finding the ’033 patent’s language and specification clearly limited “tungsten” to its elemental form. In particular, the specification exclusively referred to tungsten as a singular component. Also, 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. The disclosures in the specification, along with the prosecution history and statements of counsel at oral argument, led the court to conclude “the ’033 patent uses an open-ended modifier when referring to materials that include both compounds and elements.”

Despite identifying this error in claim construction, the Federal Circuit deemed the error harmless because the prior art referenced in the case, specifically Trivedi, included disclosures of both elemental tungsten and tungsten compounds, which would still render the patented method obvious.

The court’s decision here highlights the need to be cognizant of limitations directed to elements, where other such compounds that include various elements are similarly recited and disclosed. This includes situations where both elemental forms and compound variants are disclosed in the patent’s disclosure. Where a POSITA might also recognize that element-only compositions of various structures provides certain advantages over compounds, then claims reciting such elements may very well be limited to such.

Sam Raque | Associate Attorney