IPR2015-01368
`U.S. Patent No. 8,525,138
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`UNITED STATES PATENT AND TRADEMARK OFFICE
`_____________
`
`BEFORE THE PATENT TRIAL AND APPEAL BOARD
`_____________
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`ASML NETHERLANDS B.V., EXCELITAS TECHNOLOGIES CORP., AND
`QIOPTIQ PHOTONICS GMBH & CO. KG,
`Petitioners
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`v.
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`ENERGETIQ TECHNOLOGY, INC.,
`Patent Owner
`_____________
`
`Case IPR2015-01368
`U.S. Patent No. 8,525,138
`_____________
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`PATENT OWNER’S RESPONSE
`UNDER 37 C.F.R. § 42.120
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`TABLE OF CONTENTS
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`IPR2015-01368
`U.S. Patent No. 8,525,138
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`I.
`II.
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`C.
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`INTRODUCTION ........................................................................................... 1
`STATE OF THE ART ..................................................................................... 2
`A. Arc Lamp Technology........................................................................... 2
`B.
`Energetiq’s Laser Sustained Plasmas .................................................... 3
`III. CLAIM INTERPRETATION ......................................................................... 4
`A.
`“Light source” ....................................................................................... 5
`B.
`“Sustain” ................................................................................................ 6
`IV. THE DEFINITION OF AN ORDINARY ARTISAN IN THE FIELD .......... 8
`A. Active Workers In The Field And The Inventor ................................... 9
`B.
`Problems In The Art, Prior Art Solutions, Rapidity with Which
`Innovations are Made, and Sophistication of the Technology ............ 10
`Petitioners Provide No Factual Support for their Definition and
`Do Not Rely On Any Of The Relevant Factors .................................. 10
`V. OBVIOUSNESS UNDER § 103 BY GÄRTNER IN VIEW OF BETEROV11
`A. Overview Of Gärtner ........................................................................... 11
`B. Overview of Beterov ........................................................................... 12
`C. An Ordinary Artisan Would Not Have Redesigned Gärtner By
`Replacing Its Continuous Long Wavelength Laser With A
`Short Wavelength Laser Such As Disclosed In Beterov Or As
`Otherwise Available At The Time Of The Invention ......................... 14
`1.
`At the time of the invention, it was believed that a short
`wavelength laser would have led to energy being absorbed less
`efficiently, resulting in lower brightness light .......................... 14
`At the time of the invention, it was believed that a short
`wavelength laser would have led to larger plasma, resulting in
`lower brightness light ................................................................ 21
`Energetiq’s recognition of an unexpected physical result led to
`the claimed invention ................................................................ 23
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`2.
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`3.
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`IPR2015-01368
`U.S. Patent No. 8,525,138
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`D.
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`b.
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`Petitioners Fail To Demonstrate Why An Ordinary Artisan
`Would Have Combined Gärtner With Beterov ................................... 25
`1.
`Petitioners do not demonstrate why no one combined Gartner
`with a short wavelength laser, despite the wide availability of
`such lasers at least as early as Gärtner ...................................... 25
`a.
`Suitable short wavelength lasers existed long before the
`’138 priority date ............................................................ 26
`The years-long commercial availability of suitable short
`wavelength lasers before the invention, coupled with the
`teachings away from the use of such, shows that the
`invention was not obvious when made ........................... 27
`Petitioners have failed to demonstrate that an ordinary artisan
`would have been motivated to replace Gärtner’s long
`wavelength laser with a short wavelength laser........................ 28
`Replacing Gärtner’s long wavelength laser with a short
`wavelength laser would not have been a “simple substitution”30
`a.
`There would have been no expectation of success ......... 30
`b.
`The resulting device would have been inoperative for its
`intended purpose ............................................................. 30
`Beterov Undermines Petitioners’ Suggestion That One Having
`Ordinary Skill Would Find Any Teaching, Suggestion Or
`Motivation To Combine Gärtner With Beterov ........................ 31
`VI. CONCLUSION .............................................................................................. 34
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`2.
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`3.
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`4.
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`iii
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`IPR2015-01368
`U.S. Patent No. 8,525,138
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`I.
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`INTRODUCTION
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`This case is about a light source so much brighter than anything that
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`preceded it that it has essentially replaced its predecessors in the semiconductor
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`manufacturing field. Previously, state of the art light sources for semiconductor
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`wafer inspection, lithography, and metrology tools were arc lamps – e.g., Xenon or
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`Mercury arc lamps. Energetiq patented a fundamentally new approach that uses a
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`laser to provide energy to a gas in a chamber—at a wavelength within 10
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`nanometers of a strong absorption line of the gas—to produce a light that was
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`brighter than any previous technology could achieve.
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`Critically, Petitioners concede that the invention was novel. They advance
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`no anticipation arguments in this proceeding, instead relying on factually
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`incorrect and legally insufficient obviousness arguments that are guided by
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`hindsight reconstruction and undermined by the very references upon which they
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`rely. For the reasons set forth below, the ‘138 claims are not obvious over Gärtner
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`in view of Beterov, at least because there would have been no motivation to
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`combine Gärtner and Beterov, and because contemporaneous references taught
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`away from such a combination.1
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` 1
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` Energetiq does not discuss Petitioners’ other proposed rejection—obviousness
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`over Gartner in view of Wolfram—because the Board denied institution on this
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`basis.
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`Because Petitioners have not met their burden of proof, the ‘138 patent
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`IPR2015-01368
`U.S. Patent No. 8,525,138
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`claims must be confirmed.2
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`II.
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`STATE OF THE ART
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`A. Arc Lamp Technology
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`For at least a decade prior to the invention, the semiconductor industry used
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`xenon or mercury arc lamps to produce a light for use in wafer inspection and
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`metrology systems. (See Smith Declaration at ¶ 8 (Ex. 2016); ’138 patent (Ex.
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`1001), 1:33-35 (“The state of the art in, for example, wafer inspection systems
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`involves the use of xenon or mercury arc lamps to produce light.”).) Arc lamps use
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`an anode and cathode to provide an electrical discharge to a gas within the lamp
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`that excites the gas, causing it to emit light. (See ’138 patent (Ex. 1101), 1:33-49.)
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`However, they suffer from a number of shortcomings that constrain the accuracy
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`and efficiency of the equipment that uses them, including instability of the arc,
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`undesirable time to failure, and limits on how bright such sources can get (the
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`spectral brightness of arc lamps is limited by the maximum current density—if too
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`high, it would melt the arc lamps’ electrodes). (See, e.g., Smith Decl. at ¶ 8 (Ex.
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`2016).)
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` 2
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` This response is supported by the Declaration of Dr. Donald K. Smith. Patent
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`Owner did not submit a preliminary response in this proceeding.
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`2
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`Over time, the industry demanded improvements in the brightness level of
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`IPR2015-01368
`U.S. Patent No. 8,525,138
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`light sources beyond that which could be met by traditional xenon and mercury arc
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`lamps (ordinarily in the range of about 1 to 9 mW/mm2-sr-nm). (Smith Decl. at ¶¶
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`8-9 (Ex. 2016).) For instance, in 2005, Energetiq was approached by an industry
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`leader to see whether Energetiq could use a plasma to develop a high brightness
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`light source. (Id. at ¶ 10) The industry required light that was at least many times
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`higher brightness than that of existing arc lamps. Petitioner ASML agrees that
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`“[s]ignificant . . . brightness improvements” are necessary over arc lamps. (U.S.
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`Pub. No. US 2013/0329204 A1 at ¶ 0008 (Ex. 2009).) Energetiq’s patented Laser
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`Driven Light Source technology delivers a light source for these applications that
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`provides brightness that is greater than Mercury or Xenon arc lamps.
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`B.
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`Energetiq’s Laser Sustained Plasmas
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`To satisfy the industry’s need for a higher brightness light source, Energetiq
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`developed a laser-driven light source that uses fundamentally different technology
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`and physics principles than arc lamps. Energetiq’s invention is directed at a light
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`source comprising a chamber, an ignition source for ionizing a gas within the
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`chamber, and at least one laser for providing energy to the ionized gas, which
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`produces a high brightness light. Energetiq’s patented laser-driven light source
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`produces light that is several times brighter than can be achieved by arc lamps. For
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`example, an experiment described in the patent showed a brightness of 8 to
`3
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`18W/(mm2-sr) over the 200-400 nm wavelength band, which is equivalent to a
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`U.S. Patent No. 8,525,138
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`spectral brightness of 40 to 90 mW/(mm2-sr-nm)—i.e., four to ten times the
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`brightness of existing xenon or mercury arc lamps. (‘138 Patent Fig. 3 (Ex. 1001);
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`Smith Decl. at ¶ 12 (Ex. 2016).)
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`III. CLAIM INTERPRETATION
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`In inter partes review, claims are given their broadest reasonable
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`interpretation consistent with the patent specification. 37 C.F.R. § 42.100(b); In re
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`Cuozzo Speed Techs., LLC, 793 F.3d 1268, 1276 (Fed. Cir. 2015), cert granted, 84
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`U.S.L.W. 3562 (U.S. Jan. 15, 2016) (No. 15-446). Within this framework, terms
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`generally are given their ordinary and customary meaning. See In re Translogic
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`Tech., Inc., 504 F.3d 1249, 1257 (Fed. Cir. 2007). The relevant consideration in
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`claim construction is the meaning that would be assigned a claim term by an
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`ordinary artisan at the time of the invention. Phillips v. AWH Corp., 415 F.3d
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`1303, 1313 (Fed. Cir. 2005) (en banc). “Even under the broadest reasonable
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`interpretation, the Board’s construction ‘cannot be divorced from the specification
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`and the record evidence.’” See Microsoft Corp. v. Proxyconn, Inc., 789 F.3d 1292,
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`1298 (Fed. Cir. 2015) (citation omitted).
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`Petitioners proposed a construction for the term “light source.” (IPR ’1368
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`Petition at 13.) In its Institution Decision, the Board adopted Petitioners’ proposed
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`construction based on the record evidence available at the time. (Institution
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`Decision at 5.) Energetiq disagrees with the construction proposed by Petitioners
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`U.S. Patent No. 8,525,138
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`and adopted by the Board and instead proposes a new construction below. In
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`addition, Energetiq proposes one further construction of a term not considered by
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`the Board or by Petitioners (“sustain”). Each of these constructions reflects the
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`broadest reasonable interpretation of each claim term in light of the specification
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`and evidence now of record.
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`A.
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`“Light source”
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`In its Institution Decision, the Board determined that Petitioners’ proposed
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`construction of “light source” was consistent with the broadest reasonable
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`construction, and adopted the following construction:
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`Claim Term
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`“light source”
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`Construction
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`a source of electromagnetic radiation in the
`ultraviolet (“UV”), extreme UV, vacuum UV,
`visible, near-infrared, middle infrared, or far
`infrared regions of the spectrum, having
`wavelengths within the range of 10 nm to
`1,000 μm.
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`Institution Decision at 5. While Energetiq asserts that the term “light source”
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`should more properly be construed to mean “a source of electromagnetic energy,”
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`Energetiq’s positions on the challenged claims do not turn on the meaning of the
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`IPR2015-01368
`U.S. Patent No. 8,525,138
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`term “light source,” and the adopted construction is applied where appropriate.
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`B.
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`“Sustain”
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`Neither Petitioners nor Energetiq proposed a construction for the term
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`“sustain” prior to institution—and the Board did not construe it in its Decision.
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`But given some of the arguments Petitioners have made confusing “initiating” or
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`“generating” a plasma with “sustaining” a plasma, it is believed the Board should
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`define the term, and make clear that it is used according to its ordinary and
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`customary meaning. That is, the Board should define “sustain” to mean in the
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`context of a plasma, “maintain without interruption.”
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`The term “sustain” is used in the claims to contrast the behavior of the
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`plasma, from other terms relating to the plasma, such as “generate” or “initiate.”
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`An illustrative use of this term appears in claim 1, which states: “[a] laser
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`configured to provide energy … to sustain a plasma…” (’138 patent, claim 1 (Ex.
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`1001).) The ’138 patent discusses that “the light source 700 includes an ignition
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`source…that, for example, generates an electrical discharge in the chamber
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`728…to ignite the ionizable medium. The laser source 704 then provides laser
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`energy to the ionized medium to sustain the plasma 732 which generates the high
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`brightness light 736.” (Id. at 20:64-21:4 (emphases added) (Ex. 1001); Smith
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`6
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`Decl. at ¶ 22. (Ex. 2016)).
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`The distinction between “igniting” or “generating” a plasma and
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`U.S. Patent No. 8,525,138
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`“sustaining” a plasma is brought into sharper focus with reference to other
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`embodiments in the ’138 patent, in which laser energy is both “igniting” and
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`“sustaining” the plasma. In those instances, each term, i.e., ‘ignite’ and ‘sustain,’
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`has independent meaning with respect to the effect that the laser is having on the
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`plasma. See ’138 patent, claim 1 at 20:58-62 (“The laser beam 724 passes through
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`the chamber 728…where the plasma 732 exists (or where it is desirable for the
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`plasma 732 to be generated by the laser 724 and sustained)…[T]he ionizable
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`medium is ignited by the laser beam 724.”). Similarly, claim 1 requires “an
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`ignition source” and a “laser…to sustain a plasma within the chamber…” (Id. at
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`claim 1; Smith Decl. at ¶ 23 (Ex. 2016).)
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`An ordinary artisan would understand that to “sustain a plasma” means to
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`maintain the plasma without interruption. (Smith Decl. at ¶ 24 (Ex. 2016).)
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`Petitioners’ expert acknowledges he understood the term “sustain” to mean “to
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`maintain the existence of” such that the “plasma would continue to exist.” (Eden
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`Tr. 66:16-19; 68:18-21 (Ex. 2006).) This understanding is also reflected in
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`common technical references in the field. (See, e.g., Keefer at 169 (“With the
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`advent of continuous, high-power carbon dioxide lasers, it became possible to
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`sustain a plasma in a steady-state…”) (Ex. 2082).) The term “laser sustained
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`plasma” is frequently used in the art to describe a plasma that generates steady-
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`state light output, in contrast to plasma sources that exhibit other modes of
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`U.S. Patent No. 8,525,138
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`operation, such as “pulsed” plasmas existing only transiently, and to which the
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`term sustain would not be not applied. (See id. at 172 (“High-energy pulsed lasers
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`can generate plasma breakdown directly within a gas that results in a transient
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`expanding plasma similar to an explosion.”) (Ex. 2082).) The customary and
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`ordinary meaning of the term is also reflected in and consistent with dictionary
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`definitions. Webster’s Third New International Dictionary (2002) defines
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`“sustain” to mean “to cause to continue (as in existence or a certain state or in
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`force or intensity): to keep up esp. without interruption, diminution, or flagging :
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`maintain.” (Webster’s Third New Int’l Dict. of the English Language, Unabridged,
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`“Sustain,” 2304 (2002) (Ex. 2023); see also The Merriam-Webster Dictionary 722
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`(2004) (sustain, “to keep going: prolong”) (Ex. 2024); The American Heritage
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`Dictionary of the English Language 1744 (4th ed. 2006) (sustain, “To keep in
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`existence; maintain.”) (Ex. 2025).) (Smith Decl. at ¶¶ 25-26 (Ex. 2016).)
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`Thus, Energetiq submits that “sustain” should be construed to mean
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`“maintain without interruption.”
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`IV. THE DEFINITION OF AN ORDINARY ARTISAN IN THE FIELD
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`Here, the level of ordinary skill is a master of science degree in physics,
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`electrical engineering or an equivalent field, and 4 years of work or research
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`experience in plasmas and a basic understanding of lasers; or a Ph.D. degree in
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`physics, electrical engineering or an equivalent field and 2 years of work or
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`U.S. Patent No. 8,525,138
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`research experience in plasmas and a basic understanding of lasers. (Smith Decl.
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`at ¶ 13 (Ex. 2016).)
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`The main difference between Energetiq’s definition and Petitioners’
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`(adopted in the Institution Decision) is that Petitioners’ definition requires
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`expertise in lasers—knowledge that the active workers in the field did not have.3
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`Not surprisingly, Petitioners provide no factual support. To the contrary,
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`Energetiq’s definition is fully supported, taking into account the experience of
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`active workers in the field, and further informed by other pertinent factors that
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`determine the level of skill of an ordinary artisan (see Daiichi Sankyo Co., Ltd. v.
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`Apotex, Inc., 501 F.3d 1254, 1256 (Fed. Cir. 2007)).
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`A. Active Workers In The Field And The Inventor
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`Energetiq’s R&D staff at the time of the invention typifies the educational
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`level of active workers in the field. (Smith Decl. at ¶ 15 (Ex. 2016).) At the time
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`of the invention, when they were hired, 4 out of 7 individuals in Energetiq’s R&D
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`staff had a basic understanding of lasers, which is consistent in scope with
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`Energetiq’s proposed definition—the rest had no experience in lasers. Importantly,
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` 3
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` Petitioners’ proposed definition is “a Ph.D. in physics, electrical engineering, or
`an equivalent field, and 2–4 years of work experience with lasers and plasma, or a
`master’s degree in physics, electrical engineering, or an equivalent field, and 4–5
`years of work experience with lasers and plasma.
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`none had the lasers expertise Petitioners propose. A definition that ignores the
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`IPR2015-01368
`U.S. Patent No. 8,525,138
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`active works in the field, in favor of one that is divorced from all facts, is improper.
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`B.
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`Problems In The Art, Prior Art Solutions, Rapidity with Which
`Innovations are Made, and Sophistication of the Technology
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`The problems encountered in the art included the need for a high brightness
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`light source for applications such as semiconductor manufacturing. (See ’000
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`patent, at 1:38-59. (Ex. 1001).) Prior art solutions used by ordinary artisans
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`consisted of arc lamps which used electrodes to excite gas in a chamber and
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`produce light – they did not use lasers. (Smith Decl. at ¶ 16 (Ex. 2016).) Indeed,
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`Energetiq’s invention enabled the sale of the first commercial laser driven light
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`source—a market that did not exist prior to the invention. Innovations had been
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`slow and incremental, consisting of improvements to existing arc lamps. (Id.)
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`Thus, requiring laser expertise—as proposed by Petitioners—is incorrect and
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`unsupported.
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`C.
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`Petitioners Provide No Factual Support for their Definition and
`Do Not Rely On Any Of The Relevant Factors
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`Petitioners’ proposed definition relies solely on their expert’s equally
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`conclusory statement. Petition at 3. Indeed, when Petitioners’ expert was
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`questioned as to how he arrived at his definition, Petitioners’ expert acknowledged
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`a failure to consider any of the pertinent factors and was incapable of providing
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`specific factual support. (Eden Tr. 191:23-192:6 (“Q: Can you explain for me how
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`you came to this definition? A: Basically, it’s just based on almost 40 years of
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`working in the field, Ms. Reed. I tried to capture in the definition of one skilled in
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`the art the credentials, if you will, the training, that one would most likely find in
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`someone skilled in the art.”) (Ex. 2006).) In fact, Petitioners’ expert conceded he
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`failed to consider the knowledge of active workers in the field, instead improperly
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`focusing on “those who have made major contributions” in the field of lasers,
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`naming as models of those “of ordinary skill,” experts such as Dr. William Silfvast
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`and Dr. Howard Milchberg – that is, those who possess knowledge well beyond a
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`person having ordinary skill in the art. (Id. at 192:11-193:19 (emphasis added).)
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`Indeed, the entirety of Petitioners’ expert declaration is suspect, given that
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`he improperly applied the knowledge and skill of experts in lasers in deciding
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`obviousness, rather than the knowledge that would be possessed by one having
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`ordinary skill in the art, despite the words he parroted from Petitioners’ brief.
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`V. OBVIOUSNESS UNDER § 103 BY GÄRTNER IN VIEW OF
`BETEROV
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`A. Overview Of Gärtner
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`Gärtner is a 1985 French patent application that describes an incomplete
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`system which appears to relate to a radiation source for optical devices. (Gärtner at
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`1:1-5 (Ex. 1004); Smith Decl. at ¶ 17 (Ex. 2016).) As far as can be determined,
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`Gärtner is a standalone reference that was never developed into a commercial
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`product. (Id. at ¶ 18.) Indeed, Gärtner is so far removed from mainstream
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`commercial light source R&D that it had never been cited by the Patent Office
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`before Petitioners identified it to Energetiq; yet, it has since been overcome in two
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`subsequent patent proceedings in this patent family. (Smith Decl. at ¶ 18 (Ex.
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`2016).)
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`Gärtner describes using a CO2 laser to try to generate a plasma discharge. It
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`is patentably important that Gärtner uses a CO2 laser, because while Gärtner does
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`not expressly disclose its wavelength, it is well-known that CO2 lasers produce
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`energy at a wavelength between 9,400 and 10,600 nm—which far exceeds the
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`wavelength ranges contemplated by Energetiq’s patents (e.g., within 10
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`nanometers of certain strong absorption lines of xenon at 980 nm, 895 nm, 882,
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`nm, or 823 nm). (Compare Gärtner at 5 (Ex. 1004) with ‘138 Patent at 34:7-30
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`(Ex. 1001).) Gärtner does not describe or suggest using any other laser, let alone a
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`short wavelength laser, to sustain a plasma. (Smith Decl. at ¶ 20 (Ex. 2016).) The
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`wavelength is important to the invention – this is not a technology where one
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`would just swap one type of laser for any other type, where wavelength is
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`irrelevant. (Id.) At the time of the invention, those of ordinary skill would not
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`have expected the results Energetiq obtained by using a short wavelength laser.
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`B. Overview of Beterov
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`12
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`(Id.)
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`Beterov is an academic article that considers the role of atomic resonance in
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`forming plasmas. Beterov shows the manner in which a plasma may be formed in
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`an atomic vapor, such as a sodium metal vapor, by tuning a laser to a resonant
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`excitation frequency for the atoms, and then allowing the resonantly excited atoms
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`to ionize via the process of collisions between excited atoms (a process called
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`“associative
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`ionization”).
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` Beterov discusses multiple
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`lasers using short
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`wavelengths. For example, Petitioners discuss in detail Beterov’s use of a
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`continuous dye laser “tuned in resonance with the 3p-4d transition (λ = 568.8 or
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`568.2) of the Na [sodium] atom.” Petition at 17.
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`Notably, Beterov’s disclosure is devoid of any discussion that would connect
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`plasmas that are generated, to any application for which a bright broadband light
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`source would be required. (See generally Beterov (Ex. 1006); Smith Decl. at ¶ 28
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`(Ex. 2016).) Instead, the discussion in Beterov appears to be directed to
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`“realization and application of the optogalvanic effect” and to “study the kinetics
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`of nonequilibrium plasma, to study elementary processes in a plasma and in a gas,
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`[and] to detect radiation having a certain wavelength, etc.” (Beterov at 552 (Ex.
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`1006); Smith Decl. at ¶ 28 (Ex. 2016).) A person of ordinary skill in the art,
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`seeking to improve on the brightness of prior art light sources (e.g., arc lamps)
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`would not have turned to Beterov’s academic disclosure directed to disparate
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`applications. (Smith Decl. at ¶ 28 (Ex. 2016).)
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`C. An Ordinary Artisan Would Not Have Redesigned Gärtner By
`Replacing Its Continuous Long Wavelength Laser With A Short
`Wavelength Laser Such As Disclosed In Beterov Or As Otherwise
`Available At The Time Of The Invention
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`Petitioners fail to recognize that the state of the art expressly taught away
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`from using short wavelength lasers, such as those discussed in Beterov, to sustain a
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`plasma and produce bright light—which is the purpose of the ‘138 invention.
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`(Smith Decl. at ¶ 29 (Ex. 2016).) In particular, Petitioners allege that such a
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`combination would have been obvious based on an example from Beterov that
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`utilizes a continuous dye laser “tuned in resonance with the 3p-4d transition (λ =
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`568.8 or 568.2) of the Na atom.” Petition at 17. This laser has a wavelength that is
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`more than an order of magnitude lower than that of Gärtner’s 10.6 μm CO2 laser.
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`As set forth in detail below, it would not have been obvious to make such a
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`substitution. Thus, Petitioners cannot carry their burden to demonstrate that one of
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`ordinary skill in the art would have been motivated to combine the teachings of
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`Gärtner and Beterov to arrive at the claimed combination.
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`1.
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`At the time of the invention, it was believed that a short
`wavelength laser would have led to energy being absorbed
`less efficiently, resulting in lower brightness light
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`In 2006, when this invention was disclosed, an ordinary artisan would not
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`have been motivated to replace Gärtner’s CO2 laser with a short wavelength laser
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`such as Beterov’s, because doing so would have been contrary to the conventional
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`understanding in the field of the “inverse bremsstrahlung” absorption mechanism.
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`U.S. Patent No. 8,525,138
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`(Smith Decl. at ¶ 30 (Ex. 2016); see Arkie Lures, 119 F.3d at 958 (“conventional
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`wisdom that a combination should not be made is evidence of unobviousness”); In
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`re Hedges, 783 F.2d at 1041.) Indeed, Energetiq was the first to discover that the
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`industry’s understanding of laser plasma heating was incomplete. (Smith Decl. at ¶
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`31 (Ex. 2016).)
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`The “inverse bremsstrahlung” absorption mechanism, which governed the
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`traditional understanding of laser-sustained plasma interactions before Energetiq’s
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`invention, is “one of the fundamental interactions in optical physics” that an
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`ordinary artisan at the time of the invention would have been aware of. (Eden Tr.
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`at 97:6-14.4 (Ex. 2006); Smith Decl. at ¶ 31 (Ex. 2016).) According to the
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` 4
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` Inverse bremsstrahlung is a process in which free electrons in plasma absorb
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`energy from an incident laser beam during collisions with ions and neutral atoms.
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`(D. Keefer, “Laser Sustained Plasmas,” Chapter 4, in Radziemski et al., Laser-
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`Induced Plasmas and Applications 173 (1989) (Ex. 2082) (“Keefer”).) The
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`amount of energy absorbed by the plasma is based on the absorption coefficient,
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`Eq. (1)
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`which is given by:
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`𝛼=�𝜋𝜋𝜔�2𝑛𝑆0𝐺𝑘𝑘 �1−𝑒−ℏ𝜔/𝑘𝑘ℏ𝜔/𝑘𝑘 �
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`15
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`“inverse bremsstrahlung” absorption mechanism, it was believed at the time of the
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`U.S. Patent No. 8,525,138
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`invention that the laser wavelength played a significant role in sustaining the
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`plasma. (Smith Decl. at ¶ 32 (Ex. 2016).) According to Petitioners’ expert,
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`“[o]ne of the critical aspects of [laser-produced plasma] is that the plasma absorbs
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`the laser light.” (Eden Tr. at 89:17-90:1 (Ex. 2006).) Because energy absorbed by
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`the plasma is proportional to the square of the wavelength (λ2) of the light being
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`absorbed, it was believed that as the wavelength became shorter, the energy
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`absorbed by the plasma would decrease. (Smith Decl. at ¶ 32 (Ex. 2016).) Less
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`energy absorbed means lower brightness. (Id.)
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`Similarly, because the absorption length of the plasma is approximately
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`proportional to 1/(λ2) of the light being absorbed, it was believed that as the laser
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`wavelength became shorter, the absorption length (and resulting plasma size)
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`would increase. (Id. at ¶ 33.) Because brightness is a measure of power radiated
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`by a source per unit surface area, longer (and larger) plasma again means lower
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`brightness. (Id. at ¶ 33.)
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`
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`wherein ω, frequency, is given by ω=(2πc)/(λ) and c is the speed of light. (Keefer
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`at 173 (Ex. 2082); Smith Decl. at ¶ 32 (Ex. 2016).) Relatedly, the absorption
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`length of the plasma is equal to 1/α. (Smith Decl. at ¶ 32 (Ex. 2016).)
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`For many years, these principles guided the work in the field and, as a result,
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`long wavelength CO2 lasers, as in Gärtner, which have a wavelength λ=10,600 nm,
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`were the preferred source for laser-sustained plasmas – because they had a long
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`wavelength. (Id. at ¶ 34.) By the time of the invention, numerous references
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`recognized the inverse bremsstrahlung mechanism, and expressly taught away
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`from using a short wavelength laser. (Id. at ¶ 34.) For example, a 1991 textbook
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`by Raizer—re-printed in 1997 and used by Petitioners’ expert today to teach a
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`class on plasma fundamentals—warned that a short wavelength laser is
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`“clearly…not advantageous for sustaining a plasma.” (Raizer 1991 at 308 (Ex.
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`2007); Raizer, Gas Discharge Physics 308 (Corrected 2nd Printing 1997) (Ex.
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`2011) (“Raizer 1997”); ECE 523 Syllabus (Spring 2016) (Ex. 2012).) Similarly, a
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`1985 article by Cremers (Ex. 2081) reported “unsuccessful attempts” to sustain
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`plasma using a short wavelength laser. (Cremers at 671.) According to Cremers,
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`“[b]ecause laser heating of a plasma via inverse [b]remsstrahlung varies as λ2…,
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`the failure to form the [plasma] was probably due to the 100 times lower
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`absorption of the plasma at 1.06 μm [1,060 nm] compared to 10.6 μm [10,600
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`nm].” (Id.) Petitioners have cited no contrary evidence.
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`Energetiq was the first to recognize that, even though short wavelength
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`lasers were supposed to produce lower absorption and larger plasma according to
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`inverse bremsstrahlung, they instead were able to sustain small, bright plasmas in
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`higher pressure gases. (Smith Decl. at ¶ 35 (Ex. 2016).) It was only after
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`Energetiq’s invention that researchers, trying to understand this phenomenon,
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`recognized that short wavelength lasers produced significant additional heating due
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`to absorption by bound-bound electrons which could sustain a plasma even though
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`these lasers produced lower absorption for free electrons under the inverse
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`bremsstrahlung mechanism. (Id.) That is, after Energetiq made its invention, it
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`was discovered that for short wavelength lasers, the plasma heating due to bound-
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`bound electron absorption took dominance over inverse bremsstrahlung. (Id.;
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`Bezel et al, “High Power Laser-Sustained Plasma Light Sources for KLA-Tencor
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`Broadband Inspection Tools” at 17 (undated) (Ex. 2014) (“Bezel”).)
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`Applying the inverse bremsstrahlung principles, energy absorbed by a
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`plasma is approximately proportional to the square of the wavelength (λ2) of the
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`light being absorbed. (Smith Decl. at ¶ 36 (Ex. 2016).) Thus, conventional
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`wisdom understood that as the wavelength is made shorter, the energy absorbed by
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`the plasma decreases. (Id.) Less energy absorbed means lower brightness. (Id. at
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`¶ 36.) By way of example, under the inverse bremsstrahlung Eq. 1 (see fn. 1,
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`above), energy absorption is approximately 100 times stronger for a CO2 laser
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`(λ=10,600 nm) than a NIR laser (λ=1,060 nm). (Id. at 36.)
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`That this was conventional wisdom is clear – numerous references
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`recognized this relationship between laser wavelength and energy absorption and
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`expressly discouraged incorporating shorter wavelength lasers, like that of Beterov,
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`IPR2015-01368
`U.S. Patent N