Federal Circuit Affirms PTAB’s Refusal To Import Limitation, And Finding Of Obviousness
On May 14, 2020, the Court of Appeals for the Federal Circuit (CAFC) issued an opinion affirming a final decision by the U.S. Patent and Trademark Office’s Patent Trial and Appeal Board (PTAB) that appellant’s patent claims are unpatentable. Lone Star Silicon Innovations LLC v. Iancu, __ F.3d __ (Fed. Cir. May 14, 2020). In its affirmance, the CAFC found that the PTAB had correctly construed a disputed claim term and that substantial evidence supported the PTAB’s finding of obviousness.
The challenged ’061 patent relates to a MOS transistor having a trenched gate. Conventional MOS transistors include a semiconductor substrate having a channel region between source and drain regions, and a gate electrode, disposed above the channel region, for switching the channel region’s electrical conductivity. According to the patent, forming the gate in a trench in the substrate, rather than on the substrate, improves performance and manufacturability.
Claim 1 states: “A semiconductor transistor comprising . . . a channel region formed in the semiconductor substrate . . . beneath the bottom surface of the trench and . . . a trenched gate electrode . . . .”
A petition for inter partes review (IPR) was filed challenging certain claims of the ’061 patent as obvious. The PTAB instituted the IPR and issued a decision, finding all challenged claims obvious. Specifically, the PTAB found, inter alia, that independent claims 1 and 11 would have been obvious over certain prior art, and that claims 6 and 16 would have been obvious over the combination of patents to inventors Tanaka and Ooka.
The PTAB’s obviousness determination hinged on the meaning of the claim term “a channel region formed in the semiconductor substrate.”
Patent owner had proposed to construe this term as “a channel region defined by the presence of dopants that are separate or additional relative to the semiconductor substrate of a first conductivity type.” The PTAB rejected this construction, and found that, while the claims encompassed a channel region implanted with an additional or separate dopant relative to the substrate, as in patent owner’s proposed construction, neither the claim language itself nor the specification required such additional doping. Rather, the PTAB concluded, the term “channel region . . .” should be given its well-established ordinary meaning, as provided in textbooks, which does not require additional or separate doping of the region. The PTAB further noted that patent owner’s own expert agreed with this ordinary and customary meaning.
The PTAB acknowledged that the specification of the ’061 patent describes examples in which the channel region is implanted with additional or separate dopant. However, because those examples are consistently described as “one embodiment” or a “preferred embodiment” of the invention, the PTAB found these references to be only “exemplary in nature,” and declined to read the limitation of implanting a dopant into the claimed “channel region.”
On appeal, patent owner argued that the specification required a construction of “channel region” that included the additional doping. The CAFC first acknowledged that the claim language and specification are always the most important sources of evidence in construing claims. However, in this case, the CAFC agreed with the PTAB that this intrinsic evidence lacked the needed clarity to import a dopant implantation requirement, where the well-understood meaning of the term “channel region” in the MOS transistor art did not so require.
The CAFC also rejected patent owner’s argument that the PTAB’s construction rendered the subsequent claim term—“the channel region forming a contiguous region beneath the bottom surface of the trench”—superfluous. To the contrary, the CAFC found that this term at least clarifies, in the context of the assertedly novel trenched gate, that the inventors defined the “channel region” to have the customary attribute of being contiguous with the source and drain regions, despite the existence of a trench.
Finally, while acknowledging that each of the examples in the specification include additional channel region doping, the CAFC found that this was not sufficient to redefine the meaning of “channel region,” at least in part because the examples are not characterized as part of the patent’s inventive contribution.
With respect to challenged claims 6 and 16, the CAFC also rejected patent owner’s assertion that Tanaka and Ooka were incompatible as contrary to the evidence presented.