Trials@uspto.gov
`571-272-7822
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` Paper No. 7
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` Entered: September 6, 2017
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`UNITED STATES PATENT AND TRADEMARK OFFICE
`____________
`
`BEFORE THE PATENT TRIAL AND APPEAL BOARD
`____________
`
`HAMAMATSU CORPORATION,
`Petitioner,
`
`v.
`
`PRESIDENT & FELLOWS OF HARVARD COLLEGE,
`Patent Owner.
`____________
`
`Case IPR2017-00909
`Patent 8,080,467 B2
`____________
`
`
`
`Before JONI Y. CHANG, JENNIFER S. BISK, and
`JACQUELINE T. HARLOW, Administrative Patent Judges.
`
`HARLOW, Administrative Patent Judge.
`
`
`DECISION
`Denying Institution of Inter Partes Review
`37 C.F.R. § 42.108
`
`
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`
`
`571-272-7822
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`
`
`
`
`
`
`
` Paper No. 7
`
`
` Entered: September 6, 2017
`
`
`
`
`
`
`
`
`
`UNITED STATES PATENT AND TRADEMARK OFFICE
`____________
`
`BEFORE THE PATENT TRIAL AND APPEAL BOARD
`____________
`
`HAMAMATSU CORPORATION,
`Petitioner,
`
`v.
`
`PRESIDENT & FELLOWS OF HARVARD COLLEGE,
`Patent Owner.
`____________
`
`Case IPR2017-00909
`Patent 8,080,467 B2
`____________
`
`
`
`Before JONI Y. CHANG, JENNIFER S. BISK, and
`JACQUELINE T. HARLOW, Administrative Patent Judges.
`
`HARLOW, Administrative Patent Judge.
`
`
`DECISION
`Denying Institution of Inter Partes Review
`37 C.F.R. § 42.108
`
`
`
`
`
`
`
`
`
`
`
`
`
`IPR2017-00909
`Patent 8,080,467 B2
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`INTRODUCTION
`I.
`Hamamatsu Corporation (“Petitioner”), filed a Petition requesting an
`inter partes review of claims 1–3 and 6–8 of U.S. Patent No. 8,080,467 B2
`(Ex. 1001, “the ’467 patent”). Paper 2 (“Pet.”). President & Fellows of
`Harvard College (“Patent Owner”) filed a Preliminary Response. Paper 6
`(“Prelim. Resp.”). We have authority to determine whether to institute an
`inter partes review under 35 U.S.C. § 314, which provides that an inter
`partes review may not be instituted unless the information presented in the
`petition “shows that there is a reasonable likelihood that the petitioner would
`prevail with respect to at least 1 of the claims challenged in the petition.”
`For the reasons set forth below, we deny the Petition.
`
`A. Related Matters
`The ’467 patent is asserted against Petitioner in SiOnyx LLC v.
`Hamamatsu Photonics K.K., Case No. MAD-1-15-cv-13488 (D. Mass.)
`Pet. 1; Paper 4, 1.
`
`B. The ’467 Patent
`The ’467 patent is titled “Silicon-Based Visible and Near-Infrared
`Optoelectric Devices.” Ex. 1001, [54]. The ’467 patent issued from
`U.S. Patent Application No. 12/776,694, filed on May 10, 2010. Id. at [21],
`[22]. The ’467 patent is a continuation of U.S. Patent Application
`No. 12/365,492, filed on February 4, 2009, which is a continuation of
`U.S. Patent Application No. 11/445,900, filed on June 2, 2006 (now
`U.S. Pat. No. 7,504,702), which is a continuation of U.S. Patent Application
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`No. 10/950,230, filed on September 24, 2004 (now U.S. Patent
`No. 7,057,256), which is a continuation-in-part of U.S. Patent Application
`No. 10/155,429, filed on May 24, 2002 (now U.S. Patent No. 7,390,689).
`Id. at [63]. The ’467 patent claims priority to U.S. Provisional Patent
`Application No. 60/293,590. Id. at [60].
`The ’467 patent describes methods for fabricating “silicon
`photodetectors that are suitable for detecting electromagnetic radiation over
`a wide wavelength range, e.g., from visible to the infrared, with enhanced
`responsivity.” Ex. 1001, 1:28–31. The ’467 patent explains that although
`silicon is less expensive and more easily oxidized than other
`semiconductors, its utility in photodetectors is limited by the fact that it “is a
`relatively poor light emitter,” and not well-suited “for use in detecting
`radiation having long wavelengths, such as, infrared radiation employed for
`telecommunications.” Id. at 1:32–41.
`The ’467 patent discloses a two-step process for producing
`silicon-based photodetectors that purportedly exhibit superior
`long-wavelength absorption and responsivity relative to silicon-based
`photodetectors fabricated using prior art methods. Id. at 5:58–65, 10:54–65,
`12:4–18, 16:63–17:4. In the first step, the “surface of a silicon substrate is
`irradiated with one or more laser pulses while exposing the surface to a
`substance having an electron-donating constituent so as to generate surface
`inclusions containing a concentration of the electron-donating constituent.”
`Id. at 5:58–65. In the second step, the substrate is annealed at “a sufficiently
`elevated temperature for a selected time duration so as to cause an increase
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`in the charge carrier density in the microstructured layer, e.g., by a factor in
`a range of about 10 percent to about 200 percent.” Id. at 10:54–60. The
`’467 patent teaches that the substrate can preferably be annealed at a
`temperature in a range of about 500 K to about 900 K, for a duration in a
`range of about a few minutes to about a few hours. Id. at 10:60–67.
`With regard to the laser pulse irradiation step, the ’467 patent
`discloses that the resultant, unannealed, surface “exhibits an undulating
`surface morphology (topography) with micron-sized surface height
`variations” (Ex. 1001, 7:42–43), as well as improved photon absorptance for
`longer-wavelength radiation, such as infrared (id. at 12:4–18). Figure 5 of
`the ’467 patent is reproduced below.
`
`Figure 5 shows “wavelength absorptance of prototype microstructured
`silicon wafers as a function of an average number of 100 laser shots
`(8 kJ/m2) per location employed for microstructuring the wafers in the
`presence of SF6.” Id. at 4:9–13. “This exemplary data indicates that the
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`microstructured wafers exhibit an enhanced absorption of incident
`electromagnetic radiation, relative to unstructured silicon, across the entire
`recorded wavelength range, and particularly for wavelengths above about
`1050 nm, which corresponds to the band-gap energy of crystalline silicon
`(1.05 eV).” Id. at 12:4–9.
`The ’467 patent additionally reports that “proper annealing,”
`exemplified as annealing at a temperature of 725 K or 825 K, enhances the
`responsivity of a photodetector employing a wafer irradiated in accordance
`with the first step described above. Ex. 1001, 16:63–17:4. Figure 13 of the
`’467 patent is reproduced below.
`
`Figure 13 “presents graphs depicting responsivity of a plurality of silicon
`wafers microstructured by exposure to femtosecond laser pulses in the
`presence of SF6 (with no annealing and with annealing at different
`temperatures) as a function of wavelength in comparison with that of a
`commercial photodiode.” Id. at 56–61. The ’467 patent explains that
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`Figure 13 “shows that proper annealing of a silicon wafer irradiated by a
`plurality of short laser pulses, as described above, can considerably enhance
`the responsivity of a photodetector that employs that wafer.” Id. at 63–66.
`The ’467 patent further explains, however, that “a photodetector that
`incorporates a microstructure wafer, annealed, subsequent to irradiation by
`laser pulses, at a temperature of 1075 [K] for thirty minutes exhibits a much
`degraded responsivity relative to those annealed at 725 K or 825 K.” Id. at
`17:4–8.
`
`C. Illustrative Claim
`
`Claim 1, reproduced below, is the sole challenged independent claim,
`and is illustrative of the claimed subject matter.
`1.
`A method of fabricating a semiconductor wafer,
`comprising:
`irradiating one or more surface locations of a silicon
`substrate with a plurality of temporally short laser pulses while
`exposing said one or more locations to a substance so as to
`generate a plurality of surface inclusions containing at least a
`constituent of said substance in a surface layer of said substrate,
`and
`
`annealing said substrate at an elevated temperature and for
`a duration selected to enhance a density of charge carriers in said
`surface layer.
`Ex. 1001, 22:39–49.
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`D. Evidence Relied Upon
`Petitioner relies upon the following prior art references (Pet. 12–21):
`Gibbons, Ion Implantation in Semiconductors––Part II: Damage
`Production and Annealing, 60(9) PROC. IEEE, 1062–1096 (1972)
`(“Gibbons”).
`
`Wu, et al., Near-unity below-band-gap absorption by microstructured
`silicon, 78(13) APP. PHYS. LETTERS, 1850–1852 (2001) (Ex. 1008)
`(“Wu Article”).
`
`Wu, Femtosecond laser-gas-solid interactions (2000) (Ph.D. thesis, Harvard
`University) (Ex. 1006) (“Wu Thesis”).
`
`Petitioner also relies upon the Declaration of Shukri J. Souri, Ph.D.
`(“Souri Declaration”) (Ex. 1012) to support its contentions.
`
`E. Asserted Grounds of Unpatentability
`Petitioner asserts the following grounds of unpatentability (Pet. 21–
`
`40):
`
`Claim(s)
`1, 2, 6–8
`1, 2, 6–8
`3
`3
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`Reference(s)
`Basis
`§ 103(a) Wu Thesis and Gibbons
`§ 103(a) Wu Article and Gibbons
`§ 103(a) Wu Thesis, Gibbons, and Carey
`§ 103(a) Wu Article, Gibbons, and Carey
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`II. ANALYSIS
`A. Claim Construction
`In an inter partes review, the Board interprets claim terms in an
`unexpired patent according to the broadest reasonable construction in light
`of the specification of the patent in which they appear. 37 C.F.R.
`§ 42.100(b); Cuozzo Speed Techs., LLC v. Lee, 136 S. Ct. 2131, 2142 (2016)
`(affirming applicability of broadest reasonable construction standard to inter
`partes review proceedings). Under that standard, and absent any special
`definitions, we give claim terms their ordinary and customary meaning, as
`would be understood by one of ordinary skill in the art at the time of the
`invention, in the context of the entire disclosure. In re Translogic Tech.,
`Inc., 504 F.3d 1249, 1257 (Fed. Cir. 2007). Only those terms that are in
`controversy need be construed, and only to the extent necessary to resolve
`the controversy. Vivid Techs., Inc. v. Am. Sci. & Eng’g, Inc., 200 F.3d 795,
`803 (Fed. Cir. 1999).
`Neither Petitioner nor Patent Owner requests construction of any term
`recited in the challenged claims. Pet. 11; Prelim. Resp. 11. We determine,
`therefore, for purposes of this Decision, none of the terms in the challenged
`claims require express construction at this stage of the proceeding.
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`B. Obviousness Grounds of Unpatentability
`Based on Wu Thesis and Gibbons
`
`Petitioner asserts that claims 1, 2, and 6–8 are unpatentable under
`§ 103(a) as obvious in view of the Wu Thesis and Gibbons. Pet. 21–30.
`Patent Owner Disagrees. Prelim. Resp. 11–31.
`The question of obviousness is resolved on the basis of underlying
`factual determinations including (1) the scope and content of the prior art,
`(2) any differences between the claimed subject matter and the prior art,
`(3) the level of skill in the art, and (4) where in evidence, so-called
`secondary considerations. Graham v. John Deere Co. of Kansas City,
`383 U.S. 1, 17–18 (1966). If the differences between the claimed subject
`matter and the prior art are such that the subject matter, as a whole, would
`have been obvious at the time the invention was made to a person having
`ordinary skill in the art to which said subject matter pertains, the claim is
`unpatentable under 35 U.S.C. § 103(a). KSR Int’l Co. v. Teleflex Inc.,
`550 U.S. 398, 406 (2007).
`“[A] patent composed of several elements is not proved obvious
`merely by demonstrating that each of its elements was, independently,
`known in the prior art.” Id. at 418. Rather, “it can be important to identify a
`reason that would have prompted a person of ordinary skill in the relevant
`field to combine the elements in the way the claimed new invention does.”
`Id.; see also Belden Inc. v. Berk–Tek LLC, 805 F.3d 1064, 1073 (Fed. Cir.
`2015) (“[O]bviousness concerns whether a skilled artisan not only could
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`have made but would have been motivated to make the combinations or
`modifications of prior art to arrive at the claimed invention.”).
`
`1. Wu Thesis
`The Wu Thesis describes methods for modifying silicon substrates
`“using femtosecond laser pulses [to] produce[] structures via novel
`mechanisms of surface damage.” Ex. 1006, 1. In particular, the Wu Thesis
`teaches that femtosecond laser-pulse irradiation of an undoped silicon wafer
`in the presence of SF6 gas results in the formation of a plurality of spikes
`having heights of about 10–12 μm on the wafer. Id. at 12–13. The Wu
`Thesis reports that these spikes contain high concentrations of sulfur and
`fluorine, and “are of crystalline nature, but contain many structural defects.”
`Id. at 21.
`The Wu Thesis also discloses that the aforementioned “[s]piked
`silicon has astonishing light absorption properties” (Ex. 1006, 37), including
`that it “absorbs nearly all incident light from the near-UV to the mid-IR” (id.
`at 38). The Wu Thesis observes that, in contrast to ordinary silicon, in
`which photon energies smaller than the bandgap energy are not absorbed,
`“[i]n spiked silicon, there is no difference in the absorption of below or
`above bandgap photon energies.” Id. Figure 3.6 of the Wu Thesis is
`reproduced below.
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`Figure 3.6 depicts the increased absorptance of spiked silicon as compared
`to ordinary silicon for photon energies below the bandgap energy. Id.
`The Wu Thesis employs annealing (Ex. 1006, 51) to investigate the
`“especially puzzling” difference in below-bandgap absorption between
`ordinary and spiked silicon (id. at 38). The Wu Thesis explains:
`In order to test if sulfur is responsible for the below-band
`gap absorption, we performed a vacuum anneal (P = 10-7 Torr)
`at 1210 K for three hours on the sample with the 10–12 μm spike
`height. The anneal does not change the macroscopic morphology
`of the spikes. At this temperature, sulfur is ejected from the
`silicon lattice and can diffuse from the bulk into the surface
`region. Wilson,[1] who introduced sulfur into silicon by ion
`implantation, found that the sulfur remains at its lattice site for
`temperatures below 1000 K. Above 1000 K it starts to form
`complexes with the damages formed during the ion implantation.
`For temperatures exceeding 1200 K, the damages have annealed
`
`
`1 Wilson, Depth distributions of sulfur implanted into silicon as a function of
`ion energy, ion fluence, and anneal temperature, 55 J. APPL. PHYS. 3490
`(1984). Wilson has not been submitted as an Exhibit in this case.
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`out and the sulfur diffuses to the surface. We performed SIMS
`and XPS of the surface before and after the anneal. . . . After
`anneal, the sulfur content is decreased compared to the sample
`before the anneal.
`Id. at 52 (internal citation omitted).
`Figure 3.12 of the Wu Thesis is reproduced below.
`
`Figure 3.12 shows the “[a]bsorptance of spiked silicon before and after
`vacuum anneal for 3 hours at 1210 K.” Ex. 1006, 55. The Wu Thesis
`reports that “[a]fter the anneal, the optical properties of spiked silicon
`changed. The reflectance of below-band gap radiation returned to almost the
`values of that of flat silicon . . . . The below-band gap transmittance
`increased . . . and the absorptance decreased by roughly a factor of 2.” Id.
`The Wu Thesis reasons that the above-described “simultaneous
`decrease in absorptance and the sulfur concentration suggests that the
`subgap absorptance of spiked silicon is associated with the sulfur embedded
`in the silicon.” Ex. 1006, 55. In addition, based on ion channeling
`experiments and SEM studies, the Wu Thesis reports that “the anneal does
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`not produce a significant change in the amount of disorder in the spikes.”
`Id. at 58. The Wu Thesis, therefore, concludes that “[t]he most likely
`explanation for the near-unity absorption [of spiked silicon] is therefore a
`combination of multiple reflections and states within the band gap of silicon.
`These subgap states likely stem mostly from impurities in silicon with some
`contributions from structural defects” (id. at 60).
`The Wu Thesis speculates that “[t]he observed near-unity light
`absorption of spiked silicon surfaces has the potential to greatly enhance the
`efficiency of [photovoltaic devices]” (Ex. 1006, 61), but observes that, in
`view of the “high concentration of chemical and structural defects” present,
`it is “not immediately obvious if the increased light absorption of spiked
`silicon could be used to increase the quantum efficiency of photovoltaic
`devices.” Id. at 62.
`The Wu Thesis examines passivation of dangling bonds via
`hydrogenation as a potential method for reducing the density of defects in
`spiked silicon (Ex. 1006, 69), and reports that hydrogenation “changes the
`photovoltaic characteristics of spiked silicon drastically; the photocurrent
`measurements after hydrogenation of the device show that hydrogenation of
`the spiked surface for several hours causes an increase in the measured
`photocurrent as high as 48% when comparing illuminating the spiked part to
`the flat part” (id. at 79–80). The Wu Thesis additionally notes that
`hydrogenation changes the surface structure of spiked silicon: “the tall
`silicon spikes are transformed into much thinner and sharper spikes.” Id. at
`80.
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`2. Gibbons
`Gibbons reviews prior studies concerning ion implantation and
`annealing, focusing on work addressed to “implantation-produced damage
`and its annealing characteristics, especially in silicon.” Ex. 1007, Abstract.
`Gibbons explains that “[f]or conditions of practical importance in ion
`implantation, the radiation damage produced by the injected ions is severe,
`and the crystal must be carefully annealed if the chemical effects of the
`implanted ions are to dominate the residual damage.” Id.
`Gibbons discusses the phenomenon of “reverse annealing” in the
`context of silicon implanted with either boron, phosphorous, or arsenic. Id.
`at 1091. With particular regard to a study of boron implanted silicon,
`Gibbons reports that for certain implant doses, the substitutional boron
`concentration initially rises as a function of temperature from approximately
`400°C to 500°C, “decreases markedly” from 500°C to 600°C––this
`corresponds to “reverse annealing”––and increases again at temperatures of
`600°C and above. Id. at 1091, Fig. 49.
`Gibbons does not address doping via the application of laser pulse in
`the presence of a background gas, the implantation of sulfur atoms in silicon
`substrate, or whether “negative annealing” is observed upon implantation of
`sulfur atoms into silicon.
`
`3. Obviousness Analysis
`Petitioner contends that an ordinarily skilled artisan would have
`sought to combine the method for fabricating a sulfur-doped spiked silicon
`wafer taught by the Wu Thesis with the annealing techniques disclosed by
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`Gibbons in order to “achieve optimal efficiency in an optoelectronic device.”
`Pet. 22.2
`Petitioner acknowledges, through its expert, Dr. Souri, that the
`annealing step described by the Wu Thesis was performed to “test the effects
`of sulfur incorporation in the silicon lattice on the optical properties of the
`sample related to absorptance in the infrared range.” Ex. 1012 ¶ 62.
`Petitioner additionally recognizes that the annealing protocol employed by
`the Wu Thesis “prove[d] deleterious to the functionality of the silicon
`device, particularly to its infrared wavelength absorptance capabilities.”
`Pet. 21. Petitioner nevertheless asserts that an ordinarily skilled artisan
`would have understood, based on disclosure by the Wu Thesis of the effect
`of different temperatures on the location of sulfur atoms relative to the
`silicon substrate into which they were originally implanted (Ex. 1006, 52),
`“that anneal temperature plays a large role in the location and activation of
`sulfur dopants and resulting electrical optical properties of the doped sample,
`and that optimizing the annealing parameters is a crucial element to
`enhancing the performance of a photovoltaic device” (Pet. 22).
`
`
`2 According to Petitioner, the ’467 patent is only entitled to an effective
`filing date of September 24, 2004. Pet. 6–9. Petitioner additionally asserts
`that the Wu Thesis was publicly available by June 2001, and, therefore,
`qualifies as prior art under 35 U.S.C § 102(b). Id. at 12–14. Because we
`determine that Petitioner has not established a reasonable likelihood of
`prevailing on its assertion that an ordinarily skilled artisan would have had
`reason to combine, and a reasonable expectation of success in combining the
`Wu Thesis and Gibbons, we need not address these contentions.
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`Petitioner further contends that an ordinarily skilled artisan would
`have understood the Wu Thesis to teach that “extreme annealing can have an
`adverse effect on the absorptance” (Pet. 22), and would have turned to
`Gibbons for guidance “on the material effects of less extreme annealing
`procedures” (id. at 22–23). Petitioner acknowledges that Gibbons is
`“primarily directed to the implantation of boron, a p-type dopant in silicon,”
`but asserts, relying on Dr. Souri, that the conclusions drawn by Gibbons “are
`generally applicable for practical application of other dopants, such as
`phosphorous, arsine, antimony, and bismuth, which are n-type dopants.”
`Pet. 17; Ex. 1012 ¶ 49.
`Petitioner, therefore, contends that an ordinarily skilled artisan in
`possession of the Wu Thesis and Gibbons “would have recognized the
`ability to optimize optical properties of silicon based on the surface
`texturing[] and impurity incorporation taught by Wu Thesis, and the ability
`to further optimize the electrical properties of the final photodetector device
`by changing free carrier concentration through appropriate annealing
`procedures.” Pet. 23; see also id. at 26 (“By combining the doping step of
`Wu Thesis with the anneal optimization presented by Gibbons, one of
`ordinary skill in the art can enhance the charge carrier density in an
`optoelectronic device, thereby tuning its electrical properties and overall
`responsivity.”).
`Petitioner additionally asserts that the combination of the Wu Thesis
`and Gibbons is “nothing more than the bringing together of two,
`well-known, conventional semiconductor processing techniques, neither of
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`which is performed any differently from the prior art when combined.”
`Pet. 23. In this regard, Petitioner acknowledges that Gibbons does not study
`the effects of annealing on sulfur-doped silicon, but argues that a relevant
`skilled artisan “would reasonably anticipate that the teachings of Gibbons
`may be applied to other dopant impurities.” Id. at 23–24; see also id. at 26
`(asserting that the proposed combination would not yield a surprising result).
`We do not find Petitioner’s arguments persuasive. Petitioner does not
`adequately explain why an ordinarily skilled artisan would have sought to
`anneal the sulfur-doped spiked silicon disclosed by the Wu Thesis in view of
`that reference’s teachings concerning the characteristics of spiked silicon,
`and the limitations of annealing such devices. As Dr. Souri recognizes, the
`annealing step described by the Wu Thesis was performed to “test the effects
`of sulfur incorporation in the silicon lattice on the optical properties of the
`sample related to absorptance in the infrared range.” Ex. 1012 ¶ 62. The
`Wu Thesis does not posit the use of annealing to improve the performance of
`a photovoltaic device, or suggest any positive effect of annealing on dopant
`activation or on the electrical properties of spiked silicon.
`Moreover, the annealing experiments described in the Wu Thesis
`undisputedly show that the annealing protocol employed is “deleterious to
`the functionality of the silicon device, particularly to its infrared wavelength
`absorptance capabilities.” Pet. 21 (emphasis added). In addition, although
`the Wu Thesis recognizes the “high concentration of chemical and structural
`defects” present in spiked silicon (Ex. 1006, 62), it does not contemplate the
`use of annealing to address those defects. Notably, the Wu Thesis indicates
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`that even “extreme annealing” (Pet. 22) “does not change the macroscopic
`morphology of the spikes” (Ex. 1006, 52), and “does not produce a
`significant change in the amount of disorder in the spikes” (id. at 58).
`The Wu Thesis focuses instead on passivation, and in particular,
`hydrogenation, as a method to address the chemical and structural defects
`observed in spiked silicon. Id. at 69. In contrast to the “deleterious” effects
`of annealing (Pet. 21), and its failure to change the macrostructure (id. at 52)
`or reduce the amount of disorder in the spikes (id. at 58), the Wu Thesis
`reports that hydrogenation improves the photovoltaic characteristics of
`spiked silicon (id. at 79), and alters the surface structure, transforming tall
`spikes into thinner, sharper ones (id. at 80). The Wu Thesis reasons that
`“[t]he defects that cause recombination of electrons and holes, could be
`associated with dangling bonds, because hydrogenation, which ties up
`dangling bonds, changes the photovoltaic characteristics of spiked silicon
`drastically . . . .” Id. at 79.
`Petitioner does not adequately explain why an ordinarily skilled
`artisan would have sought to anneal the spiked silicon disclosed by the Wu
`Thesis in view of the above teachings, which point away from the use of
`annealing to improve spiked silicon devices, and suggest instead the utility
`of hydrogenation to cure the structural defects in, and improve the electrical
`properties of, such devices. Petitioner states that an ordinarily skilled artisan
`would have sought to “achieve optimal efficiency in an optoelectronic
`device” (Pet. 22), but does not adequately address why such an artisan
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`would have turned to annealing in general, and Gibbons in particular, to
`improve spiked silicon in the first place.
`Furthermore, we do not agree that the description in the Wu Thesis of
`work performed by Wilson—which itself has not been submitted as prior art,
`or even as an exhibit in this matter—would have suggested to a relevant
`skilled artisan “that anneal temperature plays a large role in the location and
`activation of sulfur dopants and resulting electrical optical properties of the
`doped sample, and that optimizing the annealing parameters is a crucial
`element to enhancing the performance of a photovoltaic device” (Pet. 22).
`The description of Wilson by the Wu Thesis on which Petitioner relies
`addresses only the location of sulfur atoms, relative to the silicon substrate in
`which they were implanted, as a function of temperature:
`Wilson, who introduced sulfur into silicon by ion implantation,
`found that the sulfur remains at its lattice site for temperatures
`below 1000 K. Above 1000 K it starts to form complexes with
`the damages formed during the ion implantation.
` For
`temperatures exceeding 1200 K, the damages have annealed out
`and the sulfur diffuses to the surface.
`Ex. 1006, 52. The Wu Thesis does not, either in its description of Wilson or
`elsewhere, indicate an annealing time “selected to enhance a density of
`charge carriers in [the] surface layer,” as recited in claim 1, address the
`activation of sulfur dopants or the resultant electrical properties of doped
`substrates, or suggest that optimizing annealing parameters is crucial to
`enhancing the performance of a photovoltaic device. To the contrary, as
`described above, the Wu Thesis presents data showing that, as performed,
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`annealing decreases optical performance, and fails to amend the structural
`defects present in spiked silicon.
`Nor has Petitioner adequately explained why an ordinarily skilled
`artisan would turn to Gibbons for guidance concerning annealing parameters
`for sulfur-doped spiked silicon. As Petitioner acknowledges, Gibbons
`addresses annealing subsequent to ion implantation (Pet. 16–17), which is a
`different method of substrate doping than the application of femtosecond
`laser pulses in the presence of SF6 gas disclosed by the Wu Thesis to
`fabricate spiked silicon (Ex. 1006, 12–13; Pet. 16–17). Petitioner does not
`endeavor to explain why an ordinarily skilled artisan would have turned to
`Gibbons in view of the different doping method employed by the Wu Thesis,
`and in particular, disclosure by the Wu Thesis that annealing impairs optical
`performance (Ex. 1006, 55), and fails to reduce the disorder of spiked silicon
`(id. at 62). Nor does Petitioner adequately address why a relevant skilled
`artisan would have sought guidance from Gibbons for improving a
`sulfur-doped substrate. In this regard, we note the conclusory nature of
`Dr. Souri’s testimony that “Gibbons discusses a wide range of dopants and
`one of ordinary skill in the art would reasonably anticipate that the teachings
`of Gibbons may be applied to other dopant impurities including sulfur”
`(Ex. 1012 ¶ 68). 37 C.F.R. § 42.65(a).
`Similarly, Petitioner has not sufficiently articulated, for purposes of
`this decision, why an ordinarily skilled artisan would have had a reasonable
`expectation of success in making the proposed combination. Gibbons at best
`suggests a high-level relationship between certain annealing parameters, as
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`exemplified by studies of silicon that has been doped with boron through ion
`implantation. As explained above, neither Gibbons nor the Wu Thesis
`indicates that annealing at an elevated temperature and for a selected
`duration would improve sulfur-doped spiked silicon devices, much less
`suggests how annealing might be employed to improve the electrical
`characteristics of such devices, or “enhance a density of charge carriers in”
`the surface layer.
`Thus, although we agree with Petitioner that annealing was
`well-known in the semiconductor art at the time of invention of the
`’467 patent, we cannot agree that the proposed combination is “nothing
`more than the bringing together of two, well-known, conventional
`semiconductor processing techniques, neither of which is performed any
`differently from the prior art when combined.” Pet. 23.
`
`4. Conclusion
`For the foregoing reasons, we conclude that Petitioner has not shown
`a reasonable likelihood of prevailing on its assertion that claims 1, 2, and 6–
`8 are obvious in view of the Wu Thesis and Gibbons.
`
`C. Obviousness Grounds of Unpatentability
`Based on Wu Article and Gibbons
`
`Petitioner asserts that claims 1, 2, and 6–8 are unpatentable under
`§ 103(a) as obvious in view of the Wu Article and Gibbons. Pet. 30–38.
`Patent Owner disagrees. Prelim. Resp. 31–39.
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`1. Wu Article
`The Wu Article describes a method for “increasing the optical
`absorptance of silicon from a few percent to roughly 90% in the
`near-infrared region (1.1–2.5 μm) as well as from roughly 60% to roughly
`90% at shorter wavelengths (0.25–1.1 μm)” using laser-chemical etching.
`Ex. 1008, 1850.3
`The Wu Article discloses “irradiating a Si(111) surface with a train of
`800 nm, 100 fs laser pulses in the presence of SF6” to yield a
`microstructured surface that includes “a quasiordered array of sharp conical
`microstructures up to 50 μm high that are about 0.8 μm wide near the tip and
`up to 10 μm wide near the base.” Id. The Wu Article reports that such
`microstructured silicon surfaces “have visible to near-infrared reflectance of
`a few percent and absorptance of about 90%.” Id.
`The Wu Article assesses the absorptance characteristics of
`microstructured silicon prepared as described above, as compared to
`microstructured silicon that has been subjected to 3 hours of vacuum
`annealing at 1200 K, and crystalline silicon. Figure 3 of the Wu Article is
`reproduced below.
`
`
`3 We note that, as filed, Ex. 1008 includes two instances of the first page of
`the Wu Article. For clarity, we refer to the original pagination of the Wu
`Article, rather than the page numbers added by Petitioner.
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`Figure 3 shows “shows the absorptance for three microstructured surfaces of
`varying spike heights (1–2, 4–7, and 10–12 μm), for an annealed sample
`(spike height 10–12 μm), and for the substrate silicon prior to
`microstructuring [n-Si(111), 260 μm thick, with resistivity ρ=8–12 Ωm].”
`Ex. 1008, 1851. With regard to the annealing protocol, the Wu Article
`explains that “[a]nnealing was performed in vacuum for 3 h at 1200 K.” Id.
`The Wu Article reports that “[t]he absorptance of the annealed sample is
`essentially unchanged above the bandgap (λ ˂ 1.1 μm), but decreases
`significantly below the bandgap (λ ˃
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