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Patent cancellation upheld despite PTAB claim construction error
What if the Patent Trade and Appeal Board (PTAB) improperly interprets a claim term in evaluating patentability? It often leads to a reversal or reconsideration of the board’s decision. That’s not always the case, though, as one patent holder recently learned the hard way in a decision by the U.S. Court of Appeals for the Federal Circuit.
Layering the facts
HD Silicon Solutions owned a patent that described a method for creating a local interconnect layer (used in semiconductors) using two films — a first film “comprising titanium nitride” and a second film “comprising tungsten.” The second is deposited over the first to form a metal stock of the layer.
Microchip Technology Inc., a semiconductor supplier, sought inter partes review (IPR) of the patent by the PTAB. Under IPR, the board can reconsider and cancel an already-issued patent based on certain types of “prior art” that made the invention obvious and thus unpatentable.
Microchip contended that all of the patent claims were obvious based on a previous patent. That patent related to a method of forming a local interconnect structure with “tungsten silicide and titanium nitride layers” or “a tungsten layer covered on opposite sides thereof with titanium nitride.”
Before the PTAB, the arguments revolved around the proper construction (or interpretation) of the term “comprising tungsten,” which appeared in all of the challenged patent claims. The PTAB construed it to mean any form of tungsten, including both elemental tungsten and tungsten compounds based on a sentence in the patent that said “[t]he first film may comprise titanium nitride, while the second film may comprise tungsten, for example” (emphasis added). It reasoned that elemental tungsten was just “one exemplary embodiment” of a second film.
The PTAB therefore found all but one of the claims unpatentable because they were obvious based on the prior art. HD Silicon Solutions appealed.
Conducting claim construction
As the Federal Circuit explained, patent claim terms should be interpreted from the perspective of a person of ordinary skill in the relevant field at the time of the invention. The person is deemed to read the term in the context of the particular claim where it appears as well as the entire patent. Evidence outside of the patent can be useful, but it’s generally considered less reliable than the patent itself.
The Federal Circuit found that the PTAB had misinterpreted the term “comprising tungsten,” though. The court noted the claims’ “precise language.” For example, the first film is described as comprising titanium nitride, while the second film comprises tungsten, without any other element. This suggests, the court said, that the patent uses explicit language to refer to a compound when a compound is intended. Where no such language is included, only the elemental form is intended.
In addition, when referring to the properties of tungsten that make it a desirable material in a local interconnect, the patent specification refers to properties unique to the element itself — properties not found in tungsten compounds. In fact, a tungsten compound is never mentioned in the specification or anywhere in the prosecution history.
The appellate court also faulted the PTAB’s reliance on a European patent application publication in its construction. The publication, the board found, taught that the phrase “comprising tungsten” includes tungsten compounds. But, the court pointed out, the publication conflicts with the contested patent’s specification, claims and prosecution history. Extrinsic evidence can’t be used to vary, contradict, expand or limit claim language from how it’s defined in the specification or prosecution history.
Nonetheless, the Federal Circuit affirmed the PTAB’s ruling because the board determined that the earlier patent disclosed both elemental tungsten layers and tungsten-silicide layers. Either disclosure would have made the “second film comprising tungsten” limitation obvious. The court concluded that the board’s erroneous construction of the claim term was ultimately harmless.
Hazard zone
The case highlights how a patent examiner’s improper construction of patent claims can lead to rejection of a patent. In this case, the misinterpretation was “harmless,” but sometimes it can cause great harm.
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