Holding: Extrinsic evidence may only be used to assist with a proper understanding of a disputed claim limitation and should not be used for claim construction when it conflicts with the specification, claims, and prosecution history for the disputed claim limitation. An error in claim construction does not necessarily lead to reversal if the error is harmless.
Microchip Technology petitioned for inter partes review (IPR) against US Pat. No. 6,774,033 owned by HD Silicon Solutions. The ‘033 Patent is directed to a local interconnect layer for an integrated circuit. The local interconnect layer forms a relatively short electrical connection between transistors on the circuit. Claim 1 of the ‘033 Patent recites a method of forming a local interconnect layer that includes depositing a first film comprising titanium nitride over an oxide layer. A “second film comprising tungsten” is deposited over the first film to form a metal stack of the local interconnect layer. The PTAB found claims 1-7 and 9-17 of the ‘033 Patent to be unpatentable as obvious over US Pat. No. 5,847,463 to Trivedi.
During the IPR proceeding, the PTAB construed the term “comprising tungsten” to mean any form of tungsten, including both elemental tungsten and tungsten compounds. The Federal Circuit found this construction to be erroneous for several reasons. First, the claims of the ‘033 Patent used explicit language when referring to an element or an elemental compound. When a compound was intended, the compound was specifically named, such as with the use of “titanium nitride” in claim 1. Second, the specification of the ‘033 Patent only referred to the tungsten film with tungsten as a singular element and gave no examples of tungsten compounds that could be used for the second film. The specification further referenced the tungsten layer as having desirable properties of elemental tungsten that are unique from properties of compounds of tungsten. Lastly, other claims in the ‘033 Patent used an open-ended qualifier for terms that are meant to include both elements and compounds. As an example, dependent claim 12 recites a “chlorine-based etchant” when referring to an etchant that may be elemental chlorine or chlorine compounds.
Claim terms are interpreted in the context of the claim, but also in the context of the entire patent, including the specification. Extrinsic evidence may be used to construe claim terms, but this evidence holds less weight than the intrinsic evidence included in the patents itself. When determining its construction of “comprising tungsten,” the district court relied on third party European Patent Application Publication 0463373 to Gunturi as extrinsic evidence. The Gunturi reference recited that a “local interconnect structure using a material comprising tungsten” may include “a thin layer of tungsten silicide.” However, the Federal Circuit found this to be insufficient to support the PTAB’s construction since this construction of “comprising tungsten” conflicts with the specification, claims, and prosecution history of the ‘033 Patent. Extrinsic evidence may only be used to assist with a proper understanding of the disputed claim limitation. It may not be used to vary, contradict, expand, or limit the claim language from how it is defined in the specification or prosecution history.
Although the Federal Circuit found the PTAB’s construction of the phrase “comprising tungsten” to include tungsten compounds to be erroneous, it found this error to be harmless and upheld the PTAB’s decision of obviousness. The Federal Circuit found that the Trivedi reference discloses that either a tungsten compound or elemental tungsten layer may be used to form the second interconnect layer. Therefore, the Federal Circuit’s narrower construction of the term “comprising tungsten” to only include elemental tungsten was still met by the Trivedi reference.
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