Federal Circuit Affirms PTAB Despite Erroneous Claim Construction

The Federal Circuit has found that the Patent Trial and Appeal Board (PTAB or Board) construed patent claims erroneously but that the error was harmless.

HD Silicon Solutions LLC (“HDSS”) appealed from a decision of the PTAB holding claims 1–7 and 9–17 of its US Patent 6,774,033 (“Metal Stack for Local Interconnect Layer”) unpatentable as obvious.

The ’033 patent is directed to a local interconnect layer in an integrated circuit.

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.

[Emphasis added by court.]

Microchip Technology Inc. (“Microchip”) petitioned for inter partes review (“IPR”), arguing that all claims of the ’033 patent would have been obvious over US patent 5,847,463 (“Trivedi”).

As the US Patent and Trademark Office (USPTO) notes, under 35 U.S.C. 103

A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains.

The court noted, "Obviousness is a question of law based on underlying findings of fact.”

Further, said the court,

What a reference teaches and the presence or absence of a motivation to combine references are questions of fact.

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.”

At the PTAB, the parties disputed the construction of the term “comprising tungsten.”

The Board construed the term “comprising tungsten” to mean any form of tungsten, including both elemental tungsten and tungsten compounds.

Microchip argued that even under an elemental tungsten-requiring construction, the Board’s findings should be affirmed because Trivedi discloses both elemental tungsten and tungsten-silicide layers, and the Board found that both layers would have rendered the “second film comprising tungsten” limitation obvious.

The PTAB then held that Microchip had met its burden 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 references.

On appeal, HDSS argued that the Board improperly construed the phrase “comprising tungsten.”

The court concluded that the Board’s claim construction was erroneous but determined that the error was harmless.

The court noted that

We interpret claim terms from the perspective of a person of ordinary skill in the art at the time of the invention, who is “deemed to read the claim term not only in the context of the particular claim in which the disputed term appears, but in the context of the entire patent, including the specification.”

Also, noted the court,

Evidence extrinsic to the patent may also be useful in construing claim terms, but is generally viewed as “less reliable than the patent” itself.

In this case, said the court,

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.” … Compare that to how claim 1 recites the composition of the second film, that it “comprises tungsten,” without the presence of another element. This suggests that the ’033 patent uses explicit language to refer to a compound 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 refers to elemental tungsten.

Also, “the specification exclusively refers to tungsten as a singular component, i.e., as an element.”

In addition, “Not once is a tungsten compound mentioned in the specification, let alone in the prosecution history.”

The Board’s reasoning on construction 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.”

According to the Board, the phrase “for example” means that elemental tungsten is just “one exemplary embodiment” of a “second film comprising tungsten,” and therefore, the limitation cannot be so narrowed.

The court asserted the Board’s reasoning was flawed because it assumes that there are only two forms of tungsten—purely elemental tungsten and tungsten compounds.

“But that is not the case,” said the court.

HDSS’s expert had explained at trial that “[b]y using the terminology of comprising tungsten, [the claim] allows for the possibility of unintentional impurities that might be incorporated during the deposition process.”

According to the court,

The incorporation 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 “example” is not inconsistent with the ’033 patent’s disclosures indicating that the patent requires elemental tungsten.

The court concluded that the term “comprising tungsten,” as recited in the challenged claims, requires elemental tungsten.

The court then turned to the Board’s obviousness determinations.

The Board found that Trivedi discloses both a tungsten-silicide and an elemental tungsten layer, and either disclosure would render the “second film comprising tungsten” limitation of claim 1 obvious.

The court noted the Board’s finding that

“Trivedi itself teaches that either tungsten silicide or elemental tungsten may be used to form the [second] local interconnect layer” of claim 1.

In fact, said the court,

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.

The court thus affirmed the PTAB’s decision that the ‘033 patent was unpatentable as obvious.