WO2014001886A1 - Film de matériau semi-conducteur polycristallin, procédé de fabrication de celui-ci et moules d'orientation/surfusion pour celui-ci, et dispositif électronique - Google Patents

Film de matériau semi-conducteur polycristallin, procédé de fabrication de celui-ci et moules d'orientation/surfusion pour celui-ci, et dispositif électronique Download PDF

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Publication number
WO2014001886A1
WO2014001886A1 PCT/IB2013/001370 IB2013001370W WO2014001886A1 WO 2014001886 A1 WO2014001886 A1 WO 2014001886A1 IB 2013001370 W IB2013001370 W IB 2013001370W WO 2014001886 A1 WO2014001886 A1 WO 2014001886A1
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WIPO (PCT)
Prior art keywords
mold
film
undercooling
orienting
contact points
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PCT/IB2013/001370
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English (en)
Inventor
Patrick Leempoel
Pierre-Yves PICHON
Axel SCHÖNECKER
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Rgs Development B.V.
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Publication of WO2014001886A1 publication Critical patent/WO2014001886A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
    • C30B15/007—Pulling on a substrate
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B28/00—Production of homogeneous polycrystalline material with defined structure
    • C30B28/04—Production of homogeneous polycrystalline material with defined structure from liquids
    • C30B28/10—Production of homogeneous polycrystalline material with defined structure from liquids by pulling from a melt
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/06—Silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic Table
    • H01L31/182—Special manufacturing methods for polycrystalline Si, e.g. Si ribbon, poly Si ingots, thin films of polycrystalline Si
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • inventions described herein include a film of polycrystalline semiconductor material, a method of making the film, orienting/undercooling molds that are useful in the method, and an electronic device comprising or prepared from the film.
  • Sharp is concerned with forming a polycrystalline silicon sheet on a mold while controlling adhesive force of the sheet to the mold to allow easy stripping of the sheet from the mold.
  • Sharp uses a cooling member having a cooling face populated with a plurality of nucleation-promoting sites (sheet adhering portions) that are uniformly spaced apart from each other by nucleation-inhibiting areas (sheet stripping portions). Difference in the adhesive force to the polycrystalline silicon sheet between the sheet adhering and sheet stripping portions is based on their different shapes and/or materials.
  • dots of silicon carbide, silicon nitride, or boron nitride are arrayed as the sheet adhering portions on areas of carbon plate as the sheet stripping portions.
  • the material for the dots was considered to be necessary to be able to provide a starting point for crystallizations suitable for growth of silicon crystals.
  • molten silicon crystallizes beginning at the silicon carbide sites on the cooling face of the carbon cooling member to give the polycrystalline silicon sheet.
  • FIG. 1 Another approach to making a polycrystalline silicon film is mentioned in WO 2010/104838 to 1366 Technologies (1366).
  • 1366 is concerned with using a porous mold that must allow a flow of gas to pass through it.
  • the porous mold is subjected to a differential pressure regime of from 1 kilopascal (kPa) to 100 kPa when it is being contacted with a molten semi-conductor material, and after the contacting the degree of differential pressure regime is reduced to release a formed body of semi-conductor material from the porous mold.
  • the porosity and gas permeability of the mold and differential pressure regime of the method were considered to be necessary to be able to form and release the film.
  • the films of polycrystalline silicon cast thereon are undesirably thick relative to average lateral grain size.
  • crystals in such films have grown in a vertical direction perpendicular to the cooling surface of the mold at a rate about the same as the rate of growth in a lateral direction parallel to the cooling surface. Therefore in the film of Sharp, the grain size, measured in the lateral direction, typically is at most two times the film thickness, measured in the vertical direction. In the film of 1366, the grain size, measured in the lateral direction, typically is at most three to five times the film thickness, measured in the vertical direction.
  • the average lateral grain size becomes too small such that the electrical performance or quality of the film is reduced (e.g., too many grain boundaries form that inhibit conduction of electrons and/or increase the amount of recombination of excess charge carriers).
  • This growth regime makes Sharp's and 1366's molds and films, and others configured like them, unsuitable for electronics applications needing larger average lateral grain sizes but thinner films.
  • these molds may contain too many nucleation sites per unit surface area and lead to growth of mounds or bumps above each nucleation site. An undesirable result is an uneven, bumpy surface on thin silicon films. Until now it seemed that reducing bumpiness of thinner silicon films, and simultaneously controlling average lateral grain size and thickness of films of polycrystalline silicon have been insoluble problems.
  • the orientation of crystals in the prior films may be non-uniform or random, and so the dislocation density of the film may be too high also.
  • porous molds are operated under a differential pressure regime, which restricts types of casting methods that can be used therewith, requires specialized equipment, and restricts the types of materials that can be used for the porous mold.
  • a refractory material is naturally non-porous and cannot be used as a porous mold without cutting holes therethrough.
  • the holes must be large enough to permit flow of a gas through the porous mold under a differential pressure regime for solidifying a semiconductor material thereon and contributing to releasing of the solid therefrom, but not so large that the holes would allow a melt of a semi-conductor material to enter.
  • the porous molds may impart undesirable surface structure to the silicon films.
  • Objective technical problems recognized by the present inventors and solved by this invention include one or more of the following: orient crystals; increase average lateral grain size of a polycrystalline semiconductor material in a film thereof more than thickness of the film; reduce bumpiness of the film; provide an orienting/undercooling mold for manufacturing the film; and provide an improved film of polycrystalline semiconductor material.
  • the invention solves one or more of the problems in an unexpected way.
  • the present invention includes a film of a polycrystalline semiconductor material, a method of making the film and orienting/undercooling mold that is useful in the method, and an electronic device.
  • the orienting/undercooling mold has at least one orienting/undercooling surface consisting essentially of a configuration of monocrystalline semiconductor material and a low nucleation-potency material.
  • An orienting/undercooling mold that is impermeable to gas flow, the orienting/undercooling mold comprising a first orienting/undercooling surface configured with a basal surface consisting essentially of a low nucleation-potency material; a plurality of contact points, at least some of the plurality of contact points consisting essentially of a monocrystalline semiconductor material for orienting crystal growth and controlling positions of nucleation sites on the orienting/undercooling surface, and any remainder of the plurality of contact points consisting essentially of a low nucleation-potency material for controlling heat transfer without functioning as nucleation sites; and wherein crystal lattices of at least 80 percent of the total number of the contact points consisting essentially of a monocrystalline semiconductor material are oriented parallel to each other.
  • An orienting/undercooling mold that is impermeable to gas flow, the orienting/undercooling mold comprising a first orienting/undercooling surface that consists essentially of a basal surface and a plurality of contact points; wherein the contact points are either raised contact points that are disposed above the basal surface and are connected to the basal surface, the contact points are flush contact points that are disposed at the basal surface and are level with the basal surface, or the contact points are lowered contact points that are disposed under the basal surface and are connected to the basal surface, or the contact points are a combination of any two or more of the raised, flush, and lowered contact points; wherein the basal surface consists essentially of a low nucleation-potency material; wherein at least some of the plurality of contact points independently consist essentially of the monocrystalline semiconductor material and are useful for contacting a melt of the semiconductor material and for orienting crystal growth and controlling positions of nucleation sites on the orienting/undercooling surface and any remainder
  • a method of making a film of a polycrystalline semiconductor material on the orienting/undercooling mold that is impermeable to gas flow comprising contacting under effective crystallizing conditions a melt of the semiconductor material at a bulk temperature Ts with the first orienting/undercooling surface of the orienting/undercooling mold at a bulk temperature TM O IJ > wherein Ts > Tiuoia; allowing the film to form thereon; and removing the undercooling mold with the film from contact of any remaining melt; wherein the film comprises a natural-side surface and a mold-side surface, the natural-side surface spaced apart from the mold-side surface by the film thickness; wherein the mold-side surface of the film is in contact with the first orienting/undercooling surface of the orienting/undercooling mold; and wherein the average lateral grain size of the crystals is greater than two times thickness of the film, wherein average lateral grain size is measured according to ASTM El 12-10.
  • An electronic device comprising, or prepared from, the film.
  • the invention method and orienting/undercooling molds may be integrated into any casting process for making films of polycrystalline semiconductor materials, including as a "drop-in" aspect of a known process.
  • the invention film may be used in electronics applications in need of a semiconducting film and may be used in or to prepare the invention electronic device.
  • the electronic device is useful in electronic applications such as computing, photography, lighting, and electricity generation.
  • Figure (Fig.) 1 illustrates an embodiment of the orienting/undercooling mold from a top-down perspective.
  • Fig. la illustrates a perspective view of the embodiment of Fig. 1.
  • Fig. lb illustrates a section view of the embodiment of Fig. 1.
  • FIG. 2 illustrates another embodiment of the orienting/undercooling mold from a top-down perspective.
  • Fig. 2a illustrates a perspective view of the undercooling mold of Fig. 2.
  • FIG. 3 illustrates still another embodiment of the orienting/undercooling mold from a top-down perspective.
  • Fig. 3a illustrates a perspective view of the undercooling mold of Fig. 3.
  • FIG. 4 illustrates still another embodiment of the orienting/undercooling mold from a top-down perspective.
  • Fig. 4a illustrates a perspective view of the undercooling mold of Fig. 4.
  • Fig. 5 is a gray-scale, confocal microscopy image of an example of the orienting/undercooling mold.
  • Figs. 6A to 6D are partial views of "snapshots" at four sequential time points of an embodiment of the method.
  • Fig. 7 is a black-and-white photograph of an example of the film that may be prepared by the method illustrated in Figs. 6A to 6D.
  • Fig. 8 illustrates another embodiment of the undercooling mold from a top- down perspective.
  • Fig. 8a illustrates a perspective view of the undercooling mold of Fig. 8.
  • Figs. 9 and 9A are gray-scale microscopic photographs of examples of the orienting/undercooling molds comprising a plurality of raised contact points in combination with a low nucleation potency material disposed between the raised contact points from top-down perspectives.
  • Fig. 10 is a gray-scale microscopic photograph of an example of the orienting/undercooling mold from a top-down perspective.
  • Fig. 11 is a gray-scale electron back scattering diffraction (EBSD) measurement of a film of a polycrystalline semiconductor material grown on an orienting/undercooling mold similar to that of Fig. 10.
  • EBSD gray-scale electron back scattering diffraction
  • Fig. 12 is a gray-scale electron back scattering diffraction (EBSD) measurement of another film of a polycrystalline semiconductor material grown on an orienting/undercooling mold similar to that of Fig. 10.
  • EBSD gray-scale electron back scattering diffraction
  • orienting/undercooling mold 100 has a first orienting/undercooling surface (the area within the rectangular-shaped O/U mold 100) consisting essentially of basal surface 110 and a plurality of spaced apart raised contact points 120 that are disposed on basal surface 110.
  • the raised contact points 120 may be disposed directly on a mold body (170; see Fig. 6A), which may be of a same or different material as the basal surface 110.
  • the "may” confers a choice, not an imperative.
  • "on” means above the plane of and in fluid communication with.
  • Raised contact points 120 are also shown in Figs. 6A to 6D.
  • Raised contact points 120 have diameter, d, 121, and are spaced apart from nearest neighboring raised contact points 120 by distance, x, 125. Since in this embodiment all raised contact points 120 are substantially spaced apart by a same distance, x, 125, in this embodiment x substantially equals the average distance AR between raised contact points 120.
  • Raised contact points 120 are arranged in an "equilateral triangle-comer array," i.e., a template or arrangement wherein raised contact points 120 are located at hypothetical comers of a plurality of evenly spaced apart (on average) invisible equilateral triangles (not shown) having lengths equal to distance, x, 125.
  • Basal surface 110 consists essentially of the LNP material, alternatively the combination of two or more LNP materials.
  • Some of the plurality of raised contact points 120 consist essentially of the monocrystalline semiconductor (mono-SC) material (e.g., monocrystalline silicon) and a remainder of the plurality of raised contact points 120 consists essentially of the LNP material. Alternatively, all raised contact points 120 consist essentially of the mono-SC material.
  • First O/U surface (not numbered) is disposed on a mold body (not shown; see 170 in Fig. 6A).
  • O/U mold 100 is a planar sheet.
  • a section view IB- I B that bisects a row (not indicated) of raised contact points 120 along the length of O/U mold 100 is shown in Fig. l b.
  • Fig. la is a perspective view of the O/U mold 100 of Fig. 1 to illustrate raised contact points 120 extend like hemispherical mounds up from and to above basal surface 110.
  • Fig. lb illustrates a section view I B- IB of the O/U mold 100.
  • orienting/undercooling mold 200 has a first orienting/undercooling surface (the area within the square-shaped O/U mold 200) consisting essentially of basal surface 210 and a plurality of spaced apart circular flush contact points 220 that are disposed at basal surface 210.
  • “at” means level with the plane of and in fluid communication with, e.g., embedded part way.
  • Flush contact points 220 have diameter, d, 221 and are spaced apart from nearest neighboring flush contact points 220 by horizontal distance, x, 225 and vertical distance, y, 226.
  • Flush contact points 220 are arranged in an "square-corner array," i.e., a template or arrangement wherein flush contact points 220 are located at hypothetical corners of a plurality of evenly spaced apart (on average) invisible squares (not shown) having lengths equal to horizontal distance, x, 125, which equals vertical distance, y, 226.
  • Basal surface 210 consists essentially of the LNP material, alternatively the combination of any two or more LNP materials.
  • At least some of the plurality of flush contact points 220 consist essentially of the mono-SC material and a remainder of the plurality of flush contact points 220 consists essentially of the LNP material.
  • all flush contact points 220 consist essentially of the mono-SC material.
  • O/U mold 200 is a planar sheet.
  • Fig. 2a is a perspective view of the undercooling mold 200 of Fig. 2 to illustrate top surfaces (not indicated) of flush contact points 220 are level with basal surface 210.
  • orienting/undercooling mold 300 has a first orienting/undercooling surface (the area within square-shaped O/U mold 300) consisting essentially of basal surface 310 and a plurality of evenly spaced apart (on average) pyramid-shaped raised contact points 320 that are disposed on basal surface 310.
  • Raised contact points 320 are arranged in the "equilateral triangle-corner array.”
  • Basal surface 310 consists essentially of the LNP material, alternatively the combination of any two or more LNP materials. At least some of the plurality of raised contact points 320 consist essentially of the mono-SC material and a remainder of the plurality of raised contact points 320 consists essentially of the LNP material.
  • all raised contact points 320 consist essentially of the mono-SC material.
  • First OAJ surface (not numbered) is disposed on a mold body (not shown).
  • OAJ mold 300 is a planar sheet.
  • Fig. 3a is a perspective view of the undercooling mold 300 of Fig. 3 to illustrate raised contact points 320 extend like pyramids up from and to above basal surface 310.
  • orienting/undercooling mold 400 has a first orienting/undercooling surface (the area within rectangular-shaped OAJ mold 400) consisting essentially of basal surface 410 and a plurality of spaced apart rectangular lowered contact points 420 that are disposed under, but not covered by, basal surface 410.
  • basal surface 410 consists essentially of the LNP material, alternatively the combination of any two or more LNP materials.
  • At least some of the plurality of lowered contact points 420 consist essentially of the mono-SC material and a remainder of the plurality of lowered contact points 420 consists essentially of the LNP material. Alternatively, all lowered contact points 420 consist essentially of the mono-SC material.
  • First OAJ surface (not numbered) is disposed on a mold body (not shown).
  • OAJ mold 400 is a planar sheet.
  • Fig. 4a is a perspective view of the OAJ mold 400 of Fig. 4 to illustrate lowered contact points 420 extend like rectangular wells below basal surface 410.
  • Fig. 5 is a gray-scale, confocal microscopy image of an example of the orienting/undercooling mold 500 having a first orienting/undercooling surface consisting essentially of a plurality of approximately hemispherical-shaped, raised contact points 520 disposed on basal surface 510 in a "square-corner array.”
  • OAJ mold 500 is an example of the subgenus O/U mold 100 depicted in Fig. 1 and shown in cutaway profile in Figs. 6A to 6D.
  • O/U mold 500 is a planar sheet.
  • Figs. 6A to 6D are partial views of "snapshots" at four sequential time points (i.e., from Fig. 6A to 6B to 6C to 6D) of an embodiment of the O/U mold 100 and the method.
  • the method comprises a process of crystallizing a melt of the semiconductor material (e.g., 20) on O/U mold 100 (see also Fig. 1).
  • first O/U surface (not numbered) is disposed on mold body 170, which is the portion of O/U mold 100 below phantom line 171. The method aspects of Figs. 6A to 6D are also described later.
  • orienting/undercooling mold 800 has a first orienting/undercooling surface (the area within square-shaped O/U mold 800) consisting essentially of basal surface 810 and a plurality of evenly spaced apart (on average) cube-shaped raised contact points 820 that are disposed on basal surface 810. Raised contact points 820 are arranged in a non-uniform array. Basal surface 810 consists essentially of the LNP material, or the combination of any two or more LNP materials. Raised contact points 820 consist essentially of, alternatively consist of, the LNP material, or the combination of any two or more LNP materials.
  • First O/U surface (not numbered) is disposed on a mold body (not shown).
  • O/U mold 800 is a planar sheet.
  • Fig. 8a is a perspective view of the O/U mold 800 of Fig. 8 to illustrate raised contact points 820 extend like cubes up from and to above basal surface 810.
  • Figs. 9 and 9a utilize the same reference numerals (where applicable) as Fig. 1 for purposes of consistency and clarity, but features shown in Figs. 9 and 9a may be different from those of Fig. 1.
  • Figs. 9 and 9a are gray-scale microscopic photographs (from a top-down perspective) of examples of the orienting/undercooling molds 100 comprising a plurality of raised contact points 120 in combination with the LNP material disposed between the raised contact points 120, as described in greater detail in the Examples.
  • the low nucleation potency material of the orienting/undercooling molds 100 of Figs. 9 and 9a constitutes the basal surface 110 of the orienting/undercooling molds 100.
  • Raised contact points 120 are spaced apart from nearest neighboring raised contact points 120 by distance, x, 125. Since in this embodiment all raised contact points 120 are substantially spaced apart by a same distance, x, 125, in this embodiment x substantially equals the average distance AR between raised contact points 120, with x, 125, and AR being about 200 ⁇ .
  • Fig. 10 utilizes the same reference numerals (where applicable) as Figs. 1, 9, and 9a for purposes of consistency and clarity, but features shown in Fig. 10 may be different from those of Figs. 1, 9, and/or 9a.
  • Fig. 10 is a gray-scale microscopic photograph of an example of the orienting/undercooling mold 100 from a top-down perspective.
  • the orienting/undercooling mold 100 of Fig. 10 comprises a plurality of raised contact points 120 formed from laser scribing and surface etching, as described in the Examples. Raised contact points 120 are spaced apart from nearest neighboring raised contact points 120 by distance, x, 125.
  • x substantially equals the average distance AR between raised contact points 120, with x, 125, and AR being about 200 ⁇ .
  • Raised contact points 120 are located in between the laser scribing lines (not numbered).
  • Fig. 11 is a gray-scale electron back scattering diffraction (EBSD) measurement of a Film PSM 90 grown on an orienting/undercooling mold similar to that of Fig. 10.
  • the EBSD measurement illustrates that most of the Film PSM (dark gray area) has the same crystal orientation as the orienting/undercooling mold utilized to prepare the Film PSM of Fig. 11 and that the lateral grain size of most of the Film PSM is actually much larger than the thickness of the Film PSM .
  • Some areas show tilted crystalline orientation (lighter shade of gray). Lines in Fig. 11 indicate small angle grain boundaries (not numbered).
  • Fig. 12 is a gray-scale EBSD measurement of a Film PSM 90 grown on an orienting/undercooling mold similar to that of Fig. 10.
  • the crystal orientation of the orienting/undercooling mold utilized to prepare the Film PSM 90 of Fig. 12 is different from that utilized to prepare the Film PSM 90 of Fig. 11.
  • the EBSD measurement shows that most of the Film PSM (dark gray area) has the same crystal orientation as the orienting/undercooling mold utilized to prepare the Film PSM of Fig. 12 and that the lateral grain size of most of the Film PSM is actually much larger than the thickness of the Film PSM Some areas show tilted crystalline orientation (lighter shade of gray). Lines in Fig. 12 indicate small angle grain boundaries (not numbered).
  • the discussion of the 0/U mold that follows pertains to the illustrated 0/U molds (e.g., 100, 200, 300, 400, 500, and 800) and their relevant features (e.g., 0/U surface (not numbered) consisting essentially of, alternatively consisting of, contact points (e.g., 120, 220, 320, 420, 520, and 820) and basal surfaces (e.g., 110, 210, 310, 410, 500, and 810), respectively).
  • contact points e.g., 120, 220, 320, 420, 520, and 820
  • basal surfaces e.g., 110, 210, 310, 410, 500, and 810
  • the discussion of the Film PSM that follows pertains to the illustrated Film PS (e.g., 90) and its relevant features (e.g., height h, 81; lateral grain size L, 82; crystals 80; grain boundary 85; natural-side surface 91; and bumps 93).
  • the discussion also pertains to the non-illustrated alternative embodiments of the Film PSM and their relevant features.
  • the numbers will not be repeated below except where a particular portion of the description refers to a subset of examples thereof. This paragraph may serve as a basis for amending the specification to parenthetically add the relevant numbers of the illustrated aspects as examples thereof.
  • a "combination" of any two or more materials means an alloy or physical blend of such materials. Unless defined otherwise herein, “consisting essentially of means at least 95% (e.g., > 95 weight percent of a composition or > 95 area percent of a surface), alternatively at least 99%, alternatively at least 99.9%. Unless defined otherwise herein, “consisting of means 100%.
  • the “contacting” comprises effective touching, e.g., as for facilitating crystallization or deposition.
  • the "first” is merely a convenient identifier and does not imply order or quantity (i.e., does not require there to be a "second”).
  • the "impermeable to gas flow” means a mold that has no open-cell porosity, such that no gas (e.g., gas of nitrogen or argon) can flow through the mold body from one O/U surface (e.g., the first O/U surface) to an opposite surface (e.g., an optional second O/U surface) thereof.
  • the mold is not suitable for establishing a differential pressure across thickness of the mold and cannot be used to establish an underpressure between it the Film PSM within the timeframe of a melt solidification process.
  • the O/U mold may prevent movement of a bulk mass of gaseous fluid from one surface (e.g., the first O/U surface) to an opposite surface of a material, or vice versa, thereby prohibiting transmission of the gas flow therethrough.
  • gas flow is the technically distinct diffusion of gas molecules through the material, which may take place depending on the size of the gas molecule (e.g., 3 ⁇ 4 gas) compared to spacing between atoms of the material.
  • the gas may be an inert gas, e.g., nitrogen gas or argon gas, wherein "inert" is in respect to a gas permeability test method.
  • Structurally, impermeable to gas flow typically means essentially lacking open or interconnected pores between the surfaces.
  • the gas permeability may be measured with nitrogen gas at 25 °C according to ASTM C577-07e2 ⁇ Standard Test Method for Permeability of Refractories) for monolithic refractories, and comprises forming a 5.08 centimeter cube of the material to be tested, applying a backpressure of from 21 kilopascals (kPa) to 41 kPa (e.g., 21 kPa), and measuring flow rate of nitrogen through the cube.
  • a 1 millimeter (mm) thick material of the O U mold may have a nitrogen gas permeability of less than or equal to nitrogen gas permeability of a 1 mm thick monolithic sheet of graphite, all when tested according to ASTM C577- 07e2.
  • the "monolithic” means a material that naturally has a closed cell structure and that has not had portions removed to increase its porosity or to generate open cell structures.
  • An example of a gas flow-impermeable O/U mold has a mold body that is a dense monolithic, 1 mm thick sheet (e.g., graphite) with an argon gas permeability of ⁇ 2 10 " ⁇ square meter (m ⁇ ) (i.e., 0.002 Darcy or less).
  • the 1 millimeter thick material of the O/U mold may have an argon gas or nitrogen gas permeability of less than 0.5x10 " ⁇ square meter (mm ⁇ ), alternatively ⁇ 0.2x10 " ⁇ mm ⁇ , alternatively ⁇ 1x10 " ⁇ mm ⁇ , alternatively ⁇ 1x10 " ⁇ mm ⁇ , all when tested with a 1 cubic centimeter per second flow rate of nitrogen gas under a pressure gradient of 101 kPa per centimeter across an area of 1 square centimeter.
  • the 1 mm thick material of the O/U mold may be incapable of supporting across the thickness a differential pressure regime of 1 kilopascal (kPa) or greater, i.e., any differential pressure regime across the thickness may be ⁇ 0.5 kPa, alternatively ⁇ 0.3 kPa, alternatively ⁇ 0.1 kPa, alternatively ⁇ 0.05 kPa.
  • kPa kilopascal
  • the "localized” means at a position limited by an extent of physical touching.
  • the "mold-side” means formed or originated in contact with or adjacent the O/U surface of the O/U mold (e.g., 100, 200, 300, 400, 500, or 800) during the casting step of the method.
  • the "natural-side” means formed or originated in contact with the melt (e.g., 20) of the semiconductor material during the casting step of the method.
  • the "orienting/undercooling” or “O/U” means orienting and undercooling.
  • the “orienting” and “oriented” refer to crystal lattices and generally means positioning crystal lattices in parallel relative to a specified reference point. Crystal lattices of the contact points may be oriented in parallel relative to each other. This may enable crystals or gains (e.g., 80) of the polycrystalline semiconductor material of the Film PS (e.g., 90) to be oriented relative to the contact points (e.g., 120, 220, 320, 420, 520, or 820) of the mono-SC material, which contact points function as nucleation sites for growing the crystals that form the Film PSM .
  • crystals or gains e.g. 80
  • the contact points e.g., 120, 220, 320, 420, 520, or 820
  • the "undercooling” generally means a process comprising producing a degree of "coolness" of a material below a transformation temperature of the material without obtaining the transformation.
  • the undercooling process may comprise cooling a liquid (e.g., 20) on the O/U mold to a temperature below its thermodynamical equilibrium solidification temperature without the liquid solidifying. The lower the temperature falls below the solidification temperature without nucleation of the liquid, the greater the undercooling effect of the O/U mold.
  • the undercooling may be measured experimentally with a test material using Differential Scanning Calorimetry (DSC).
  • DSC Differential Scanning Calorimetry
  • the undercooling expressed in degrees Kelvin (°K) may be measured by a method comprising: embedding a solid sample of the semiconductor material (e.g., solid silicon) into a test refractory material (e.g., fused silica) having a higher melting point than that of the semiconductor material; without melting the test refractory material, heating the solid sample above its equilibrium melting point to give a melt sample of the semiconductor material (e.g., molten silicon); slowly cooling the melt sample under the equilibrium melting point until nucleation thereof occurs as detected by DSC. The purer the test material the more accurate the DSC undercooling value.
  • a solid sample of the semiconductor material e.g., solid silicon
  • a test refractory material e.g., fused silica
  • the "orienting/undercooling mold” or "O/U mold” of the present invention means a new type of casting mold that is impermeable to gas flow and has at least one orienting/cooling surface or "O/U surface” (not numbered).
  • the O/U mold is impermeable to gas flow.
  • the O/U surface is configured in such a way that of the plurality of contact points, at least some contact points consist essentially of a mono- SC material useful for orienting crystal growth and controlling positions of nucleation sites on the O/U surface, and any remainder of the plurality of contact points consist essentially of a low nucleation-potency material, which together with the basal surface is useful for controlling heat transfer without functioning as nucleation sites and for localized cooling of the melt of a semiconductor material to a local temperature at least 17 °K below its thermodynamical equilibrium solidification temperature (essentially, m.p.) without the melt solidifying except solidifying in an oriented manner at the mono-SC material-type contact points so as to produce the Film PSM having oriented, alternatively oriented and aligned crystals according to the method.
  • nucleation potency of the basal surface and the remainder, if any, of the contact points that consist essentially of the LNP material is significantly lower than nucleation potency at the contact points that consist essentially of the mono-SC material
  • the basal surface and any remainder of contact points do not substantially serve, or do not serve, as nucleation sites (e.g., 60) during the contacting step of the method.
  • nucleation sites e.g. 60
  • less than 10%, alternatively ⁇ 5%, alternatively ⁇ 3%, alternatively ⁇ 1%, alternatively ⁇ 0.1%, alternatively 0% of the total number of nucleation sites is found on the basal surface and any remainder of LNP material contact points, combined.
  • the O U surface of the O U mold may also function to inhibit or prevent migration of any impurities from the mold body (e.g., 170) into the melt of the semiconductor material during the method.
  • the O/U surface may be interior in, alternatively exterior on the O/U mold.
  • the interior O/U surface e.g., a concave surface
  • the contact points of the mono-SC material are aligned with each other, which collectively may result in improved orienting of crystals in the Film PSM .
  • the "aligned” and “aligning” refer to the contact points and means axially disposed or disposing axially in or substantially parallel in an x-y-z coordinate relative to a reference point on the basal surface.
  • the contact points may be aligned with each other, i.e., axially disposed in parallel in an x-y-z coordinate vertically relative to a planar basal surface.
  • substantially parallel means at least 80%
  • at least 90% alternatively at least 95%, alternatively at least 98%
  • in parallel means 100% of the plurality of their crystal lattices may be oriented with each other (i.e., rotationally disposed so that the crystal lattices are parallel with each other).
  • crystal growth from the melt may be oriented and positions (i.e., locations) of nucleation sites on the O/U surface, and thus in the Film PSM may be controlled in terms of number of crystals, alignment, and spatial relationships (e.g., size and distance) between them.
  • each, such O/U surface independently is configured with a unique surface structure (e.g., 120/110, 220/210, 320/310, 420/410, 520/510, or 820/810).
  • the configuration consists essentially of the contact points, at least some of which consist of the mono-SC material, and the basal surface (e.g., 110, 210, 310, 410, 510, or 810) consisting essentially of, alternatively consisting of, the LNP material, or the combination of any two or more LNP materials.
  • the mono-SC material-type contact points enable crystal orientation or crystal orientation and alignment of the crystals of the Film PSM .
  • the basal surface enables the localized control of heat transfer from the melt of the semiconductor material without functioning as nucleation sites therefor. Together the configuration enables the method of making the Film PSM .
  • the combination of any two or more LNP materials is, itself, an LNP material.
  • the "consist of a material means at least 99.00 wt%, alternatively at least 99.99 wt%, alternatively at least 99.999 wt%, alternatively 100 wt% of the material.
  • any embodiment of the O/U mold may be characterized by describing the configuration of the material of the O/U surface and the surface structure (e.g., 120/110, 220/210, 320/310, 420/410, 520/510, or 820/810) of those O/U surface.
  • the present invention advantageously may decouple surface structure ("texture") from the materials (e.g., mono-SC material and LNP material) of the O/U surface for orienting crystal growth from the melt and controlling positions (i.e., locations) or numbers of nucleation sites on the O/U surface and the LNP material for controlling heat transfer without functioning as sites of nucleation for the melt.
  • Controlling positions or numbers of nucleation sites on the O/U surface of the O/U mold enables controlling positions and numbers of crystals in the Film PS .
  • the present invention advantageously makes use of a non-porous mono-SC material for a mold that may be used in certain configurations to avoid imparting porosity-related fine surface structure to the Film PSM .
  • the method employing the O/U mold does not require or allow a differential pressure regime through the O U mold via the O/U surface(s).
  • the "monocrystalline” means a unitary crystal of a homogenous solid substance, alternatively a plurality of such single crystals with oriented crystal lattices, each of the plurality functioning as a different one of the contact points that consist essentially of the mono-SC material.
  • the plurality of single crystals function as the unitary crystal.
  • the unitary crystal at its contact points has essentially 100% (not counting rare lattice imperfections) crystal lattice orientation.
  • the plurality of single crystals are distinct from bound crystals of a polycrystalline material in that there are no grain boundaries between the single crystals.
  • the plurality of single crystals in the O/U mold are not directly touching each other and the at least 80%, alternatively at least 90%, alternatively at least 95%, alternatively at least 99%, alternatively 100%, of the number of the crystal orientations are the same.
  • Orientation of crystal lattices of the single crystals may be determined by electron backscatter diffraction pattern analysis (EBSD/EBSP).
  • the "semiconductor material” means a substance that is characterizable by an electrical conductivity at 25 °C between that of an insulator and that of a good electrically conducting metal.
  • the solid substance may exhibit at least one semiconducting property.
  • the semiconductor material may be silicon; alternatively germanium; alternatively alloys and compounds of silicon; alternatively alloys and compounds of germanium; alternatively alloys and compounds of gallium (gallium arsenides (e.g., GaAs or AlGaAs)); alternatively aluminum nitride (A1N); alternatively indium phosphide (InP); alternatively cadmium telluride (CdTe); alternatively copper-indium-selenide alloys (e.g., or copper-indium-gallium or copper-indium-gallium-diselenide (CIGS)).
  • gallium gallium arsenides (e.g., GaAs or AlGaAs)); alternatively aluminum nitride (A1N); alternatively indium phosphide (InP); alternatively cadmium telluride (CdTe); alternatively copper-indium-selenide alloys (e.g., or copper-indium-gallium or copper-in
  • the semiconductor material may be characterizable as being pure silicon, e.g., intrinsic or i-type silicon; alternatively doped silicon, e.g., with carbon atoms (e.g., produced as SiC), oxygen atoms (e.g., produced as in SiO x ), nitrogen atoms (produced as in S13N4), and/or silicon containing at least one n-type or p-type dopant such as boron or phosphorous, respectively.
  • the C, O, or N atoms may be added via in situ reaction of the silicon melt with a reactive atmosphere gas (described later) during the contacting step of the method, and may end up concentrated in a layer at a surface of the Film PSM .
  • the C, O, or N atoms may also end up at a surface of the melt of the semiconductor material, and may modify the surface energy and/or wetting properties of the melt during the method.
  • the dopant may be 1 to 10 parts per million in the material.
  • the "pure silicon” means a substance that is at least 99.99 atomic percent (at%) ("four 9s"), alternatively at least 99.999 at% ("five 9s"), alternatively at least 99.9999 at% ("six 9s”), alternatively at least 99.99999 at% ("seven 9s"), alternatively at least 99.999999 at% ("eight 9s”), alternatively at least 99.9999999 at% ("nine 9s") of the element 14 of the Periodic Table of the Elements. Any reference herein to a Group or Groups of elements or the Periodic Table of the Elements means those of the 201 1 edition of the Periodic Table of the Elements promulgated by IUPAC (International Union of Pure and Applied Chemistry). All "%” and parts are, unless otherwise noted, based on a total of 100% and total number of parts (e.g., 100 at% for atomic percent).
  • the purity of silicon, or other semiconductor material may be determined by any suitable technique.
  • Two such techniques are Inductively Coupled-Plasma Optical Emission Spectrometry (ICP-OES, also referred to as ICP Atomic Emission Spectrometry) and Inductively Coupled-Plasma Mass Spectrometry (ICP-MS).
  • ICP- MS may be performed using any suitable ICP-MS instrument, e.g., an Agilent 7500cs ICP-MS instrument with Octopole Reaction System (ORS) (Agilent Technologies, Inc., Santa Clara, California, USA). These techniques also may be used to characterize purity of other semiconductor materials. The techniques may be performed at 30 °C.
  • Total concentrations of C, O, H, and N in the semiconductor material may be measured by Instrumental Gas Analysis (IGA) after heating a sample of the semiconductor material to generate volatile forms of C, O, H, and/or N; and measuring the volatile forms.
  • IGA Instrumental Gas Analysis
  • a > 2,000 °C oxygen plasma may combust C, and the amount of C may be determined by measuring the quantity of the resulting CO and CO2 gases by infrared spectroscopy.
  • N or O another sample may be placed in a graphite crucible and inserted between electrodes in a furnace. After purging the furnace with an inert gas (gas of He or Ar), an electric current high enough to generate gases is passed through the crucible, creating a temperature increase to > 2,500 °C.
  • Any gases generated in the furnace (CO, CO2, N2 and 3 ⁇ 4) are released into the flowing inert gas stream, which is directed to an appropriate detector: infrared spectroscopy for measuring O as CO and CO2, or thermal conductivity detector for measuring N and H as N2 and respectively.
  • the O U surface alternatively the O/U mold may lack one or more materials such as silver; silver silicide; silver and silver silicide; any one of the foregoing LNP materials, silver, and silver silicide; any one of the foregoing HNP materials other than the mono-SC material, silver, and silver silicide; or silicon carbide, any one of the foregoing LNP materials, silver, and silver silicide.
  • the O/U surface may contain at most a trivial amount (e.g., non- nucleation quantity) of a high nucleation-potency material (HNP material).
  • HNP material high nucleation-potency material
  • the "high nucleation-potency material” or “HNP material” is a refractory substance other than the mono-SC material, the refractory substance being characterized by an insufficient extent of undercooling of ⁇ 15 °K, alternatively ⁇ 13 °K, alternatively ⁇ 10 °K.
  • An example of the HNP material is silicon carbide (SiC; extent of undercooling estimated to be ⁇ 10 °K).
  • the "consisting essentially of a low nucleation-potency material” means the O/U surface may contain at most the trivial amount of the HNP material other than the mono-SC material of the contact points. Any HNP material in the basal surface of the O/U mold would be sequestered so as to not physically touch the melt of the semiconductor material or serve as a site for nucleation of the melt. For example, any HNP material would be coated by the LNP material or spaced or held away from direct physical contact with the melt by the mono-SC material and/or the LNP material.
  • the configuration of the O/U surface O/U mold is such that at the beginning of the contacting step of the method, no part of the O/U surface would have a HNP material other than the mono-SC material in physical contact with the melt.
  • all of the basal surface, alternatively all of the O/U mold, may lack the HNP material other than the mono-SC material.
  • the "low nucleation-potency material” or “LNP material” means a refractory substance characterizable by a high energy barrier to nucleation of the semiconductor material.
  • the nucleation energy barrier may be estimated using the DSC undercooling data and cooling rate, and expressed in Joules. The higher the energy barrier the greater the undercooling.
  • the extent of undercooling is a local temperature of the semiconductor material that is below the solidification temperature (essentially m.p.) of the semiconductor material at which nucleation of the melt of the semiconductor material would begin.
  • Nucleation of melt of the semiconductor material (e.g., molten silicon) on the LNP material is more difficult to start than nucleation on the mono-SC material because the LNP material has a higher energy barrier to nucleation than does the mono-SC material.
  • the extent of undercooling of the melt of the semiconductor material (e.g., molten silicon) required for crystallization of the semiconductor material (e.g., silicon) to begin on the LNP material is significantly greater than the extent of undercooling required for crystallization of the semiconductor material (e.g., silicon) to begin on the HNP material.
  • Undercooling values of the materials herein may be measured or estimated from the DSC measurements using known techniques.
  • the LNP material may be defined as having the sufficient extent of undercooling > 17 ° , alternatively > 20 °K, alternatively > 50 ° , alternatively > 100 °K, alternatively > 125 °K, alternatively > 150 °K.
  • the LNP material may, alternatively may not, have a melting point higher than the melting point of the semiconductor material (e.g., m.p. of silicon is
  • the LNP material when contacting the melt of the semiconductor material, may not melt, soften, or chemically react therewith during the method in a manner that would prevent making of the Film PSM .
  • the LNP material may be silicon nitride, alternatively graphite, alternatively glassy carbon, alternatively a silicon dioxide, alternatively boron nitride, alternatively a combination of any two or more thereof.
  • the silicon dioxide may be quartz, alternatively an amorphous sodium silicate glass, alternatively fused silica (i.e., vitreous silicon dioxide).
  • the fused silica may be a high purity fused silica available from Corning, Inc. (Corning, New York, USA) under the name HPFS® Fused Silica
  • the LNP material may be silicon nitride, alternatively graphite, alternatively glassy carbon, alternatively quartz, alternatively an amorphous sodium silicate glass, alternatively fused silica, alternatively a combination of any two or more thereof.
  • the LNP material may be graphite, alternatively glassy carbon, alternatively quartz, alternatively an amorphous sodium silicate glass, alternatively fused silica, alternatively a combination of any two or more thereof.
  • the LNP material may be any one of the silicon dioxide materials, e.g., fused silica.
  • the low nucleation-potency material is graphite, a silicon dioxide, quartz, fused silica, or a combination of any two or more of graphite, quartz, and fused silica.
  • the LNP material may be monolithic and impermeable to gas flow. These LNP materials may also be employed with melts of other semiconductor materials.
  • the examples of the LNP material may be ranked in order of increasing (i.e., from lower to higher) nucleation-potency (decreasing nucleation energy barrier) as follows: boron nitride ⁇ a silicon dioxide « a carbon ⁇ silicon nitride.
  • the nucleation-potency of the LNP material may vary somewhat from semiconductor material to semiconductor material, but their undercooling values for silicon melt are believed to be representative of an overall trend for all the semiconductor materials. Undercooling values of the LNP material for silicon melt may be measured or estimated from the DSC measurements, or, for boron nitride, from wetting angle (contact angle) data.
  • the °K undercooling values for silicon melt on the LNP materials are: (a) using wetting data we estimate undercooling of boron nitride (BN) is > 130 ° ; (b) measured undercooling of silicon dioxide (SiC ⁇ ) is somewhere from > 100 °K to 130 °K; (c) using wetting data, we estimate undercooling of carbon is from 20 °K to 25 ° ; and (d) measured undercooling of silicon nitride (S13N4) is
  • the undercooling surface consists of either boron nitride (boron nitride by itself) or a combination of boron nitride and either a silicon dioxide, silicon nitride, or silicon dioxide and silicon nitride.
  • Graphite means a crystalline, allotropic form of carbon presenting a surface layer consisting essentially of carbon atoms (i.e., lacking a surface layer of silicon carbide), alternatively consisting of carbon atoms (i.e., a pure surface layer of carbon atoms).
  • the LNP material e.g., graphite
  • the rate of crystallization of semiconductor material on the contact points that consist essentially of the mono-SC material is faster than the rate of any reaction thereof with the basal surface, and with any remainder contact points that may consist essentially of graphite, to form a surface reaction product (e.g., a silicon carbide).
  • the Film PSM e.g., film of polycrystalline silicon
  • the Film PSM forms before, and without its crystallization being influenced by, any in situ generation of a reaction product that would be more than the trivial amount of the HNP material.
  • the combination may consist essentially of: boron nitride and any one of a SiC ⁇ or S13N4; alternatively a SiC*2 and S13N4; alternatively a S1O2 and a carbon; alternatively a carbon and S13N4.
  • the SiC>2/Si3N4 combination may consist essentially of amorphous sodium silicate/Si3N4; quartz/Si3N4; or fused silica/Si3N4.
  • the SiC ⁇ /carbon combination may consist essentially of amorphous sodium silicate/pure graphite; quartz/graphite; or fused silica/pure graphite; alternatively, amorphous sodium silicate/glassy carbon; quartz/glassy carbon; or fused silica glassy carbon.
  • the carbon/Si3N4 combination may consist essentially of pure graphite/Si3N4; alternatively glassy carbon/Si3N4.
  • the contact points of the O/U mold that consist essentially of the mono-SC material independently may consist of a same or different mono-SC material; alternatively all such contact points may consist of the same mono-SC material.
  • the at least 80% of the number of mono-SC material contact points have the same crystal orientation.
  • the remainder, if any, of contact points that consist essentially of the LNP material, alternatively the combination of any two or more LNP materials, independently may consist of a same or different LNP material, alternatively all such contact points may consist of the same LNP material.
  • the at least some of the plurality of the raised contact points may consist of monocrystalline silicon.
  • the contact points of the O U mold e.g., 100, 300, 500, or 800
  • the raised contact points e.g., 120, 320, 520, or 820
  • the LNP material of the basal surface independently may be any LNP material or combination thereof and the raised contact points independently may be a pure silicon.
  • the LNP material of the basal surface e.g., 110, 310, 510, or 810) may respectively be: the SiC ⁇ ; alternatively the S13N4; alternatively the carbon.
  • the energy barrier of the contact points that consist essentially of the mono- SC material to nucleating the melt of the semiconductor material is lower than the nucleation energy barrier of the basal surface or the remainder of the contact points that consist essentially of LNP material. Nucleation of a melt simultaneously in contact with the contact points and the basal surface would be favored at the contact points that consist essentially of the mono-SC material over the basal surface and any remainder contact points that consist essentially of the LNP material.
  • the undercooling °K value of the LNP material of the basal surface and any remainder contact points is greater (e.g., by at least 10 °K, alternatively at least 20 ° , alternatively at least 50 ° , alternatively at least 75 ° , alternatively at least 100 °K) than the undercooling °K value of the mono-SC material-type of the contact points.
  • the contact points may all be part of the unitary crystal of the mono-SC material (e.g., monocrystalline silicon).
  • the unitary crystal suitable for producing the O/U surface thereon may be readily prepared by any suitable method, including known methods such as by the so-called Czochralski process.
  • the O U surface would be produced as described later.
  • all the contact points of the O/U surface would have oriented crystal lattices or oriented unit cells.
  • a melt contact area or the portion of the contact points that would physically contact the melt of the semiconductor material during the method may be readily produced as described above so as to be aligned with each other.
  • melt contact areas at the upper portions of the contact points may be made co- parallel (whether or not co-planar), co-pyramidal, co-cubic, or co-hemi-spherical, such as by polishing or laser etching the O/U surface or the contact points may be produced in substantially identical shapes via laser ablation or other precision shaping method.
  • the crystalline contact points may constitute a plurality of crystals of the same mono-SC material (e.g., a plurality of crystals of monocrystalline silicon), each crystal being a different one of the crystalline contact points.
  • Such crystals may be of the same crystal structure group or class and have the same unit cell (e.g., a diamond cubic structure of monocrystalline silicon).
  • Such crystals may be aligned and their lattices oriented with each other by precision placement of identically sized and shaped crystals on a planar basal surface.
  • the contact points of the O/U mold may be of uniform size, alternatively nonuniform size (e.g., random distribution of exposed surface areas).
  • the "non-uniform" means irregular and includes but is not limited to random.
  • the non-uniformly sized contact points may provide one or more advantages over the uniformly-sized contact points. Such advantages may comprise ease of manufacture of the non-uniformly- sized contact points on the O/U mold.
  • the Film PSM produced with the non-uniformly- sized contact points may advantageously have a random arrangement of grains sizes, grain locations, crystal structures, local thicknesses, or a combination of any two of gain sizes, grain locations, crystal structures, and local thickness. Such a non-uniform arrangement may improve mechanical stability (e.g., resistance to fracture) or separability of the film (from the mold), e.g., as described later.
  • the contact points are disposed geometrically with respect to each other so as to orient or orient and align the crystals of the semiconductor material during growth of the Film PSM . Also, the contact points are spaced apart by a sufficient distance to collectively provide sufficient heat transfer and localized undercooling as described herein so as to preferentially enable the lateral crystal growth and enable the Film PSM to be made thereon.
  • the low nucleation-potential material desirably enables the basal surface and any remainder of contact points to lack nucleation activity, i.e., at least some, alternatively majority of contact points may be the remainder type contact points, which may not serve as and may be prevented from serving as sites of crystallization.
  • the configuration of the surface structure of the O/U surface of the O/U mold comprises a uniform arrangement (e.g., distribution or spacing) of the contact points
  • a non-uniform arrangement of the contact points (e.g., 820) at discrete locations.
  • the non-uniform arrangement of the contact points may result in a broader range of grain sizes in the
  • the non-uniform arrangement (e.g., distribution or spacing) of the contact points may provide one or more advantages over the uniform arrangement of the contact points. Such advantages may comprise ease of manufacture of the contact points on the O/U mold.
  • the Film PSM produced with the non-uniformly arranged contact points e.g., 820
  • Such a non-uniform arrangement may improve mechanical flexibility or separability of the film (from the mold).
  • such a non-uniform arrangement or size or both of the contact points may enable manufacturing a Film PSM having a corner or edge that separates earlier from the O/U mold than other areas of the Film PSM , which would be useful in the separating (detaching) step.
  • such a non-uniform arrangement of contact points may enhance mechanical stability of the Film PSM by enabling the producing of locally thicker areas in the Film PSM such as at a periphery of the Film PSM or at a centroid of the Film PSM .
  • Such thicker areas may reinforce the Film PS against cracking, especially when average film thickness, as described later, is low, e.g., from 40 to 150 ⁇ .
  • the contact points are spaced apart from each other by the average distance AR (e.g., average of all x, 125 of Fig. 1; or average of all x, 225 and/or y, 226 of Fig. 2).
  • the average distance AR between contact points is sufficient for enabling the favoring laterally growing the Film PSM and orienting the growth of the crystals therein. If the average distance AR between the contact points would be too short (e.g., ⁇ 5 microns), then a Film PSM of polycrystalline material having a thickness (e.g., h, 81 of Fig.
  • a Film PSM having an L AVG e.g., average of all L, 82 of Fig. 6D
  • thickness e.g., h, 81
  • nucleation may being on too many contact points. If the average distance AR between the contact points would be too long (e.g., > 800 microns), then the meniscus of the melt may find an additional contact point on the basal surface therebetween. In the O/U mold, the average distance AR is neither too short nor too long.
  • the "average distance AR” generally is the mean spacing of "roughness motifs" expressed in the length unit of the x-axis as determined by test ISO 12085 (1996) (Geometrical Product Specifications (GPS) - Surface Texture: Profile Method - Motif Parameters (roughness and waviness parameters)) using confocal microscopy. If the O/U surface has isotropy, a 2-dimensional profile is extracted in a direction perpendicular to the main direction of the O/U surface texture, if present. This main direction would be parallel to any grooves or ridges, which would be visible with 3D confocal microscopy. If the O/U surface does not have isotropy, the profile may be extracted in any direction.
  • the average distance AR is based on measurements of x (e.g., 125, 225) values made from the axes of all the contact points that consist essentially of the mono-SC material and that are perpendicular to the basal surface, as is shown for x (e.g., 125, 225); and y (e.g., 226).
  • the average distance AR between contact points may be from 5 to 800 ⁇ , alternatively from 5 to 250 ⁇ , alternatively from 450 to 800 ⁇ , alternatively from 50 to 800 ⁇ , alternatively from 5 to 80 ⁇ , alternatively from 10 to 500 ⁇ , alternatively from 100 to 400 ⁇ (e.g., 200 ⁇ ).
  • the arrangement of contact points, and the spacing between contact points may be uniform, alternatively non-uniform.
  • local maximum spacing between any particular neighboring pair of contact points may be within +100%, alternatively ⁇ 70%, alternatively ⁇ 50%, alternatively ⁇ 20%, alternatively ⁇ 10%, alternatively ⁇ 5% of the average distance AR.
  • any particular neighboring pair of contact points may be spaced apart by up to 1 ,600 ⁇ (800 ⁇ + (1.00*800 ⁇ ) for +100% of 800 ⁇ ), e.g., by 960 ⁇ (800 ⁇ + (0.20*800 ⁇ ) for +20% of 800 ⁇ ) or as little as 4 ⁇ (5 ⁇ - (0.20*5 ⁇ ) for -20% of 5 ⁇ ) as long as the average distance AR is as described above.
  • the O/U surface of the O/U mold may be characterizable by a grains contact area (not indicated).
  • the grains contact area is the areal portion of the mono-SC material-type contact points of the O U surface that would be or is chemically bonded or adhered to the Film PSM after the contacting step, and before the optional separating step (described later), of the method.
  • the grains contact area is distinct from the "melt contact area" of the O/U surface that is in physical contact with the melt , and the "non-contact area” that is not in physical contact with the melt, during the contacting step of the method.
  • the number of nucleation sites and the grains contact area may be readily determined by optical microscope imaging of at least a 1 millimeter squared (mm ⁇ )-portion of the O/U surface of the O/U mold after the Film PSM has been separated therefrom.
  • the 1 mm ⁇ -portion contains at least 10 contact points, at least some of which are the mono-SC material-type contact points, which acted as nucleation sites (e.g., 60) during the method.
  • the areal portion of the O/U surface that had been chemically bonded or adhered to the Film PSM i.e., the grains contact area
  • the grains contact area may be from 0.10 to 10%, alternatively from 0.20 to 10.0%, alternatively from 1 to 9%, alternatively from 2 to 9%, alternatively from 0.10 to 8%, alternatively from 0.20 to 8%, alternatively from 0.20 to 6%, alternatively from 0.5 to 5%.
  • the grains contact area may further be defined to be that which is sufficiently low for enabling separation of the Film PSM and the O/U mold from each other without cracking or breaking the Film PSM .
  • the grains contact area of the O/U mold advantageously provides sufficient bonding between the contact points that consist essentially of the mono-SC material and the mold-side surface (e.g., 92) of the Film PSM to control detaching of the Film PSM from the O/U mold. Too little grains contact area (typically ⁇ 0.1%) and the Film PSM may release from the O/U mold too soon, and then bend due to differential temperature gradient in the Film PSM .
  • Too much grains contact area (typically > 10%) and mechanical stress builds up in the Film PSM until the Film PSM does not separate from the O/U mold without either breaking or cracking the Film ; eventually developing dislocations of the crystals, thereby reducing the Film PSM 's electrical conduction functionality; removing portions of the mono-SC material-type contact points with the Film PSM , thereby deteriorating the O/U mold for reuse; or a combination of any two or more of the breaking, developing dislocations, and removing.
  • the configuration of the O/U surface, including the grains contact area may minimize or prevent the bowing, warping, fracturing, deviation from flatness, or dislocation of the Film PSM , as described later.
  • an optional part of the configuration of the O/U surface of the O/U mold having the raised contact points is a maximum depth Rx from the highest one of the raised contact points to the basal surface as determined by ISO 12085 (1996).
  • the "maximum depth Rx” may be determined according to ISO 12085 (1996) as “maximum depth of the roughness motifs.”
  • Maximum depth Rx may be sufficient to space the melt of the semiconductor material away from the basal surface during the contacting step, e.g., via inert gas pockets.
  • Maximum depth Rx may be from 25 to 200 microns (e.g., 200 microns), alternatively from 50 to 150 microns, alternatively from 75 to 125 microns (e.g., 100 microns), alternatively any combination of one of the foregoing lower values (e.g., 50 microns) with one of the foregoing upper values (e.g., 125 microns).
  • the contact points of the O/U mold may consist of (have only) the raised contact points (e.g., 120, 320, 520, or 820), alternatively consist of the flush contact points (e.g., 220), alternatively consist of the lowered contact points (e.g., 420), alternatively consist of a combination of any two or three of raised, flush, and lowered contact points.
  • the combination may be raised and flush contact points; alternatively raised and lowered contact points; alternatively flush and lowered contact points; alternatively raised, flush and lowered contact points.
  • the contact points are localized at discrete locations on, at, or under the basal surface of the O/U mold.
  • the raised contact points rise from the basal surface (e.g., 110, 310, 510, or 810) to a maximum height equal to maximum depth Rx above the basal surface portion of the O/U surface of the O/U mold (e.g., 100, 300, 500, or 800).
  • the raised contact points may be shaped as hemispheres, mesas, pyramids, cylinders, cones, boxes, or any other effective shape.
  • the flush contact points (e.g., 220) are at and even with the basal surface (e.g., 210).
  • the flush contact points (e.g., 220) may be any geometric profile such as (e.g., circular (e.g., 220), square, or rectangular discs).
  • the lowered contact points extend downward from, under and below the basal surface (410) to a maximum depth equal to from 5% to 75%, alternatively at most 50%, alternatively at most 20% of the thickness of the O U mold.
  • the lowered contact points may define any volumetric space or well under the O/U surface, but not covered by the basal surface.
  • Such subsurface volumetric space may define an inverted (e.g., upside-down) hemisphere, mesa, pyramid, cylinder, cone, or box.
  • the O/U mold typically further comprises at least a second major surface (e.g., as in a planar sheet having two major surfaces).
  • the second major surface may, alternatively may not be configured as a second undercooling surface (not shown).
  • the O/U mold may further comprise a second O/U surface (not shown) spaced-apart from the first O/U surface, wherein the second O/U surface independently is defined as the first O/U surface is defined.
  • the first and second O/U surfaces may be opposite each other and spaced apart from each other by the thickness (not indicated) of the sheet and their respective basal surfaces may be approximately parallel to each other
  • the second O/U surface may be adjacent and spaced apart from the first O/U surface by a groove or ridge on the O/U mold as in an embodiment of the segmented O/U mold described below.
  • the O/U mold independently may have 3 or more O/U surfaces (not numbered), e.g., at most 4, alternatively at most 3 O/U surfaces.
  • the O/U mold may be further described by its bulk physical structure and bulk material.
  • the bulk physical structure comprises a mold body comprising, alternatively consisting essentially of, alternatively consisting of, a bulk material.
  • the O/U surface material is disposed on the mold body.
  • the bulk physical structure may give the O/U mold any size and shape.
  • the shape of the O/U mold includes its three dimensional configuration and location of its O/U surface.
  • the shape may be continuous or semicontinuous (e.g., segmented or matrix or laminate), or discontinuous; planar or non-planar; and/or symmetric or asymmetric.
  • the continuous physical structure may be a continuous band or belt, which may be circular (e.g., a loop) or linear (e.g., a linear tape).
  • the semicontinuous physical shape may be a segmented sheet comprising two or more O/U surfaces spaced apart from nearest ones by a groove, alternatively a ridge.
  • the O/U mold may be a planar sheet having two spaced apart major surfaces, at least one major surface being segmented with at least two independently configured O/U surfaces spaced apart from each other by grooves and/or ridges.
  • a different Film PSM may be separately formed on each one of the spaced apart O/U surfaces.
  • the discontinuous physical shape may be a sheet, wedge, cylinder, hemisphere or sphere.
  • the planar physical shape may be a sheet, which may be symmetric or asymmetric.
  • the symmetric planar physical shape may be circular, oval, or rectangular; alternatively rectangular, alternatively square.
  • the non-planar physical shape may be curved, bent, angled, or trough-shaped.
  • the planar sheet may be a monolithic sheet, which means the planar sheet is impermeable to gas flow.
  • the size of the O/U mold and profile of the O/U surface may be larger than the size of the Film PSM that is to be prepared.
  • the size of the O/U mold includes its length, width, and thickness. The width and length may be equal for square- (e.g., 200) and circular-shaped (not shown) O/U molds.
  • the thickness of the O/U mold may be from 0.1 to 100 mm, alternatively from 0.5 to 75 mm, alternatively from 1 to 50 mm, e.g., 0.10, 0.20, 1 , 2, 5, 10 or 25 mm.
  • Each of the length and width, alternatively length and height, alternatively diameter, of the O/U mold independently may be from 1 mm to 100 cm, with dimensions for research purposes generally being smaller and dimensions for manufacturing generally being larger.
  • the research dimensions independently may be from 0.5 to 10 mm, alternatively from 1 to 8 mm, alternatively from 2 to 5 mm.
  • the manufacturing dimensions independently may be from 1 to 100 cm, e.g., from 5 to 75 cm, alternatively from 10 to 50 cm, e.g., from 16 to 25 cm.
  • the bulk material of the mold body typically comprises, alternatively consists essentially of, alternatively consists of, a solid refractory material.
  • the material of the bulk material of the mold body and the O/U surface may be the same or different. Resaid, the bulk material may, alternatively may not, be the LNP material, alternatively the H P material, alternatively the mono-SC material. When the bulk material is the LNP material or mono-SC material, it may be the same as or different from the LNP material or mono-SC material of the 0/U surface.
  • the bulk material may the sequestered HNP material (e.g., silicon carbide), alternatively a combination of at least two such materials, alternatively a combination of at least one high, and at least one low, nucleation-potency material, all so long as the HNP material of the mold body does not constitute or become a part of the O/U surface of the O/U mold.
  • the mold body may lack the HNP material.
  • Any O/U mold described herein and of unspecified shape may be in the shape of a planar sheet.
  • the planar sheet has the first O/U surface on one side (not numbered), alternatively first and second O/U surfaces, one on each major side thereof.
  • the O/U mold may be the planar sheet having one O/U surface, alternatively the planar sheet has two O/U surfaces, wherein each O/U surface independently consists of: raised contact points of a unitary crystal of monocrystalline silicon and a basal surface of fused silica; alternatively raised contact points of a unitary crystal of monocrystalline silicon and a basal surface of graphite; alternatively raised contact points of a plurality of crystals of monocrystalline silicon having oriented crystal lattices and a basal surface of fused silica; alternatively raised contact points of a plurality of crystals of monocrystalline silicon having oriented crystal lattices and a basal surface of graphite.
  • Each of the two O/U surfaces of the planar sheet may be the same, alternatively different.
  • the O/U mold may be the wedge-shape having one, alternatively both major exterior surfaces independently is a different one of the O/U surface, wherein the basal surfaces are angled at from > 0 to 10 degrees with respect to each other.
  • the O/U mold may be cylindrical-shaped (having concave and/or convex O/U surface), hemi-cylindrical-shaped (having concave and/or convex O/U surface), bowl-shaped (having concave and/or convex O/U surface), pyramid shaped, or any other shape suitable for accommodating the at least one O/U surface.
  • the O/U surface may, alternatively may not be formed in situ before the contacting step of the method.
  • the O/U surface may not be removable (e.g., detachable) as such from the mold body to which it may be operatively connected.
  • the O/U surface may be integral with, alternatively integral with and share a material in common with the mold body.
  • the O/U surface of the O/U mold may be prepared such that the contact points may be produced at discrete locations and occupy discrete areas above, at, or under the O/U surface not numbered). Use any suitable preparation method, including methods known in the art, for preparing the O/U surface.
  • General techniques for producing an O/U surface having the flush contact points include selective ablation of a mold body (e.g., 170) of the mono-SC material to give an intermediate surface (not shown) comprising unremoved structures spaced apart by a plurality or continuum of subsurface volumetric spaces (not shown), followed by coating the entire intermediate surface, including filling of the subsurface volumetric spaces, with the LNP material to give a coated surface (not shown), followed by polishing of the entire coated surface to remove enough of the LNP material to a depth so as to expose the unremoved structures of the mono-SC material while maintaining the added LNP material in the subsurface volumetric spaces (not shown) to give the first O/U surface having flush contact points (e.g., 220).
  • General techniques for producing an O/U surface having the raised contact points (e.g., 120, 320, 520, or 820) or lowered contact points (e.g., 420) include blanket deposition followed by patterning, alternatively selective deposition, alternatively patterning.
  • An example of a known preparation method comprises laser- etching away portions of a unitary crystal of the mono-SC material down to a subsurface and around other portions of the mono-SC material that become mono-SC material-type raised contact points, wherein the mono-SC material that has been laser- etched away forms valleys above the subsurface, and depositing LNP material in the valleys to coat the valleys with the basal surface (e.g., 110, 310, 510, or 810) material.
  • a layer of monocrystalline silicon may be deposited or glued with an Si- H resin on a LNP material, then portions of the layer may be selectively etched away.
  • the preparation method may comprise masking a mold body (not shown) of the mono-SC material with a template of masking LNP material that becomes the basal surface (e.g., 410) and that leaves exposed only portions of the mold body that become the mono-SC material-type lowered contact points (e.g., 420).
  • Masks having different templates may be sequentially used in the preparation method so as to obtain an O/U mold having raised contact points consisting essentially of different mono-SC materials.
  • a mask material is graphite, which may be applied to a basal surface consisting essentially of graphite or the LNP material other than graphite such as a silicon dioxide (e.g., fused silica, amorphous silicate glass, or quartz) or the combination thereof; and later removed by reaction (e.g., combustion) when desired.
  • the preparation method may comprise providing a basal surface consisting essentially of a continuous layer of the LNP material deposited over the mono-SC material; laser ablation or photolithography and etching away openings in the continuous layer of LNP material so as to leave behind underneath portions of the mono-SC material that end up as the mono-SC material- type lowered contact points (e.g., 420).
  • the method of making the Film PSM may employ any O U mold. During the method, provided there is heat transfer from the melt of the semiconductor material to the O/U mold, the melt may not physically touch the O U mold, although physical touching may occur at the melt contact area.
  • the basal surface (e.g., 110, 310, 510, or 810) of the O/U surface, not numbered) of the O/U molds e.g., 100, 300, 500, or 800
  • raised contact points e.g., 120, 320, 520, or 820
  • a gas alternatively a plurality of spaced apart gas pockets (e.g., 30).
  • the gas pockets may, alternatively may not be in fluid communication with each other during the cooling or casting.
  • the gas may be an inert gas such as a gas of helium, argon, xenon, or neon; alternatively neon, helium, or argon; alternatively helium or argon; alternatively helium; alternatively argon; alternatively a mixture of any two or more of helium, argon, xenon, and neon gases.
  • the gas atmosphere may further comprise a reactive gas that may react with an exposed surface of a silicon melt during the contacting step of the method, the reactive gas may be hydrogen, nitrogen, CO, CO2, O2, or a mixture of any two or more thereof.
  • the O/U mold with flush contact points (e.g., 220) or lowered contact points (e.g., 420) may be used at a static pressure that facilitates contacting of the melt therewith.
  • the pressure may be lower than (e.g., vacuum), alternatively higher (e.g., pressurized inert gas) than, alternatively same as standard pressure (101 kilopascals).
  • the semiconductor material is initially employed in the method as the melt, which is not semiconducting as such.
  • the "melt” or “molten” means a liquid formed by heating a substance, which would otherwise be a solid at 25 °C, to an initial bulk temperature, Ts.
  • the melt may be formed by any suitable means such as by melting a semiconductor material in a heated vessel such as a crucible (not shown).
  • the vessel (not shown) may be made from a refractory material or from a metal alloy or ceramic containing an interior coating of a refractory material such as fused silica, SiC, graphite, or silicon nitride.
  • the vessel may further have at least one heating element to form the heat to melt the semiconductor material and/or maintain the melt of the semiconductor material at a desired bulk temperature, Ts.
  • suitable heating elements include resistive or inductive heating elements, infrared (IR) heat sources (e.g., IR lamps), flame heat sources.
  • the inductive heating element may be a radio frequency (RF) induction heating element.
  • Initial bulk temperature Ts of the melt of the semiconductor material during the method may be an average temperature with localized small variations (e.g., nearer versus farther from a wall of the vessel).
  • Initial bulk temperature, Ts, of the melt may be at least 1 °C, alternatively at least 5 °C, alternatively at least 10 °C, alternatively at least 20 °C, alternatively at least 50 °C higher than m.p. of the semiconductor material (e.g., ⁇ 100 °C higher than m.p.).
  • the average Ts may be from 1414 to 1550 °C, alternatively from 1430 to 1490 °C, alternatively from 1440 to 1460 °C.
  • the method may, alternatively may not, further comprise a preliminary step before the contacting step, the preliminary step comprising heating a solid, non-film form of the semiconductor material to give the melt of the semiconductor material.
  • This preliminary step may be performed in situ before the contacting step, alternatively the preliminary step may be performed prior to and in a crucible that is separate from the crucible or other container for the melt that is used in the method.
  • the solid, non-film form of the semiconductor material may be monocrystalline, alternatively polycrystalline. Examples of the solid, non-film form of the semiconductor material are chunks, granules, briquettes, and ingots, and combinations of any two or more of chunks, granules, briquettes, and ingots.
  • the semiconductor material of the solid, non-film form may be polycrystalline silicon.
  • the melt of the semiconductor material typically is not completely enclosed in a mold.
  • the melt is in contact with a single undercooling surface of a single undercooling mold and, optionally, side walls of the crucible, alternatively side walls of an open casting frame.
  • the upper surface of the melt is open to the gas atmosphere described later.
  • bulk temperature, T s of the melt of the semiconductor material may be increased or decreased passively, e.g., solely by allowing heat transfer from walls of a heated crucible (not shown) containing the melt; alternatively solely by allowing heat transfer from the melt to the O/U mold, respectively.
  • bulk temperature, Ts, of the melt may be increased or decreased actively, e.g., by increasing temperature of the crucible containing the melt; alternatively by decreasing temperature of the crucible, respectively.
  • At least the O/U surface, alternatively all, of the O/U mold begins at an initial bulk temperature, ⁇ ⁇ ⁇ ⁇ 0 ⁇ is less than the initial bulk temperature, Ts, of the melt and less than the melting point (m.p.) of the material to be solidified.
  • the initial Tiu o i d of the O/U mold during the method may be from -50 °C to ⁇ m.p. of the semiconductor material.
  • the initial ⁇ intend ⁇ may be within 1 ,000 °C, alternatively within 900 °C, alternatively within 800 °C, alternatively within 600 °C, alternatively within 400 °C, alternatively within 200 °C, alternatively within 100 °C, alternatively within 50 °C, alternatively within 30 °C of the initial T s of the melt of the semiconductor material.
  • the initial T ⁇ i d may be from -50 to 1413 °C, alternatively from -30 to 0 °C, alternatively from 0 to 50 °C, alternatively from 50 to 300 °C, alternatively from 300 to 500 °C, alternatively from 500 to 900 °C, alternatively from 900 to 1 ,200 °C, alternatively from 1 ,200 to 1410 °C.
  • heat from the melt may increase TM O W above the initial temperature.
  • bulk temperature, ⁇ ⁇ ⁇ , of the O/U mold may be increased or decreased passively, e.g., solely by allowing heat transfer from the melt of the semiconductor material to the O/U mold; alternatively by allowing heat transfer from the O/U mold to the atmosphere (e.g., argon gas), respectively.
  • bulk temperature, ⁇ 0 ⁇ , of the O/U mold may be increased or decreased actively, e.g., by employing laser heating of the O/U mold; alternatively by employing an O/U mold having a mold body defining tunnels (not shown) for circulating a cooling gas or liquid therethrough, respectively.
  • the tunnels are disposed in the mold body such that the cooling gas or liquid does not form a differential pressure regime thereacross via the undercooling surface(s), and typically does not form any differential pressure regime.
  • the initial bulk temperature, TM O W, of the O/U mold may be adjusted actively before the contacting step, and thereafter the bulk temperature, Tjvfoid, of the O U mold allowed to adjust passively during the contacting step.
  • performance effective parameters of the method may be adjusted if desired, to influence or modulate the number of nucleation sites.
  • the adjustments may be made from run to run or during a single run.
  • the adjustment may comprise any one of (a) to (g): (a) increasing or decreasing bulk temperature, T O W, of the O/U mold; (b) increasing or decreasing bulk temperature, Ts, of the melt of the semiconductor material; (c) decreasing or increasing the average distance AR (e.g., average of x, 125 or 225) between contact points, especially between mono-SC material-type contact points; (d) increasing or decreasing maximum depth Rx of the basal surface (e.g., 110, 310, 510, or 810) below the raised contact points (e.g., 120, 320, 520, or 820), alternatively lowered contact points (e.g., 420); (e) using a LNP material having a greater or lesser undercoolin g ( >K); (f) increasing or decreasing (static) pressure of the melt against the O
  • the combination (g) may comprise (a) and (b); (c) and (a) and (b); (c) and (e); (a) and (f); (c) and (f); (e) and (f); or at least three, alternatively all of (a) to (f).
  • the LNP material may beneficially control heat transfer resistance between the crystallizing semiconductor material and the O/U mold. This may improve crystallization velocity of crystals (e.g., 60, 70, or 75) as they grow during the method such that the rate of lateral crystal growth (e.g., as indicated by arrows 71 and 75) parallel to the O/U surface of the O/U mold unexpectedly exceeds vertical crystal growth (e.g., as indicated by double-headed arrow for h, 79) away from the O/U surface of the O/U mold.
  • crystals e.g. 60, 70, or 75
  • vertical crystal growth e.g., as indicated by double-headed arrow for h, 79
  • the method may produce a Film PSM having thickness h (e.g., 81, wherein thickness 81 may be somewhat greater than thickness 79) and wherein the Film is characterizable by the L /h ratio > 2 as described herein.
  • the h of the L AVG /h ratio is always of the Film PSM (e.g., 81), not growing crystal (e.g., 79) unless noted otherwise.)
  • Such a Film PSM may be expected to " have significantly increased electrical properties compared to electrical properties of a non-invention film wherein L AVG /h ratio ⁇ 2, wherein the electrical properties are beneficial to the application for which the Film PSM is intended or in which the Film PSM is used (e.g., increased electrical conduction or lower electrical resistivity).
  • the method employs the "effective crystallizing conditions," which comprise a combination of environmental circumstances that enable the method to prepare the Film PSM .
  • the environmental circumstances comprise temperature, pressure, and gas atmosphere of the process used to make the Film PSM , as well as a period of time.
  • Temperature comprises the initial Tivi o i d of the O/U mold being lower than the initial Ts or melting point of the semiconductor material so as to reach an extent of undercooling sufficient for starting crystallization of the semiconductor material.
  • Temperature also comprises the Ts of the melt of the semiconductor material being initially above, and then with localized undercooling below the melting point of the semiconductor material.
  • initial bulk temperature, Ts, of the melt of the semiconductor material may start above the melting point thereof, during the method the melt temperature decreases by virtue of the melt being in contact with the O/U mold.
  • the cooling of the melt continues until at the cooling surface the melt becomes or is locally undercooled below m.p. of the semiconductor material to an extent of undercooling that nucleation begins.
  • the cooling of the melt may be via passive contact with the O U mold, alternatively via active cooling of the O/U mold may be passive, alternatively active (e.g., via the optional cooling tunnels).
  • Pressure enables a sufficient amount of atmosphere for performing the method, but does not create a differential pressure regime greater than 0.49 kPa across the thickness of the O/U mold from the first O/U surface to an opposite surface (e.g., the optional second O/U surface).
  • the differential pressure regime, if any, across the thickness may be from 0 kPa to ⁇ 0.49 kPa.
  • the maximum differential pressure regime across the thickness may be ⁇ 0.40 kPa, alternatively ⁇ 0.30 kPa, alternatively ⁇ 0.10 kPa, alternatively ⁇ 0.050 kPa, alternatively ⁇ 0.010 kPa.
  • the gas atmosphere is described previously.
  • the gas atmosphere typically consists essentially of the inert gas, or a mixture of two or more inert gases.
  • the gas atmosphere may further consist essentially of a reducing gas, e.g., 3 ⁇ 4 gas.
  • the gas atmosphere may consist essentially of an inert gas/H2 gas mixture having from 1 to 3 wt% 3 ⁇ 4 gas based on total weight of the mixture (e.g., 99.0 wt% Ar(g)/1.0 wt% 3 ⁇ 4 gas or 97.5 wt% Ar(g)/2.5 wt% H2 gas or a mixture therebetween).
  • the gas atmosphere may further consist essentially of a vapor of the semiconductor material.
  • the gas atmosphere may lack, or contain in immaterial amount, an oxidizer (e.g., gas of ( > or
  • the gas atmosphere of the contacting step of the method may include a trace amount of air that has leaked into the chamber of the casting apparatus containing the gas atmosphere.
  • the gas atmosphere described herein is not limited to use in the contact step of the method.
  • any such gas atmosphere independently may be used in any one or more optional steps of the method such as the preliminary heating step, post-casting cooling step, separating step, or any combination thereof.
  • the method typically may employ the inert gas.
  • the rate of lateral crystal growth e.g., as indicated by arrows 71 and 75 of Fig. 6C
  • vertical crystal growth e.g., as leading to height h, 79 of Fig. 6C
  • effective crystallizing conditions comprising an atmosphere consisting essentially of an inert gas or an inert gas and hydrogen gas, the inert gas having a higher thermal conductivity than the thermal conductivity of another inert gas.
  • the method may employ helium gas, which has a higher thermal conductivity about 2.5 times that of argon gas.
  • helium gas pockets between the melt of the semiconductor material and basal surface of the O/U surface of the O/U mold may advantageously increase heat transfer from the semiconductor material to the O U mold without contributing to nucleation (e.g., 60) of the melt. This may allow the crystals (e.g., 70 and 75 of Fig. 6C) of semiconductor material to grow favoring laterally (e.g., as indicated by arrows 71 and 75 of Fig. 6C) over gas pockets (e.g., 30) of helium at a faster rate than over gas pockets (e.g., 30) of argon.
  • the O U may remain in contact with the melt of the semiconductor material for a period of time (contact period) sufficient to form the Film PSM thereon, and may be long enough to allow some of the Film PSM to remelt, but the contact period is not so long as to allow all of the Film PSM to remelt.
  • a suitable contact period may be from > 0 to 30 seconds, e.g., from 0.1 to 30 seconds.
  • Contact period may vary depending on the initial ⁇ 0 ⁇ ⁇ ) of the undercooling mold and/or the initial Ts of the melt of the semiconductor material. Typically, the contact period may be from 0.5 to 20 seconds, alternatively from 0.75 to 10 seconds, alternatively from 1 to 4 seconds.
  • the method may be carried out as described herein or, if desired, by readily adapting it to any other process that produces a film of polycrystalline semiconductor material on a surface (e.g., not shown) of a casting mold (not shown).
  • Such processes include known methods that use a non-invention mold or substrate (not shown) for casting films (e.g., foils, or sheets (not shown)) of a polycrystalline semiconductor material thereon. Applying the invention method to such a known process comprises replacing the non-invention mold or substrate (not shown) with one of the O U molds of the present invention.
  • the invention method may be readily adapted to any polycrystalline semiconductor film casting method discovered in the future.
  • the invention method may be adapted to any one or more of the methods (i) to (iii).
  • the method may be (i), alternatively (ii) or (iii), alternatively (ii), alternatively (iii).
  • Method (i) comprises inverting the O/U mold so that its O/U surface is disposed downward, and contacting the contact points to an upper surface
  • a planar sheet O/U mold (e.g., 100, 200, 300, 400, 500, or 800) may be disposed horizontally with contact points pointing downward, and the O/U mold moved from left to right while contacting for a suitable contact time a bath of a bulk form of the melt of the semiconductor material. Then upon the O/U mold exiting from the bath a coating of the melt of the semiconductor material, the Film PSM , or a combination thereof may cover the O/U surface of the O/U mold, and ultimately give the Film PSM .
  • Method (ii) comprises moving the O/U mold through the bottom of a casting frame (not shown) containing the melt of the semiconductor material so that a bottom layer of the melt of the semiconductor material is spread over and crystallizes on the O U surface of the O/U mold while remaining melt remains behind in the casting frame (the "draw-down" method, e.g., as described in US 2009/0044925 Al ).
  • a planar sheet O/U mold e.g., 100, 200, 300, 400, 500, or 800
  • the Film PSM may cover the O/U surface of the O/U mold, and ultimately give the Film PSM .
  • Method (iii) comprises disposing the O/U mold (planar or non-planar) in a non-horizontal disposition (e.g., a vertical disposition), and dipping the non- horizontally disposed (e.g., vertical) O/U mold into a bath of a bulk form of the melt of semiconductor material and removing the O/U mold therefrom (the "dipping" method, e.g., as described in any one of US 7,771 ,643 Bl ; US 2010/0290946 Al ; US 201 1/0033643 Al ; US 201 1/0101281 Al ; and US 201 1/0135902 Al).
  • the "dipping" method e.g., as described in any one of US 7,771 ,643 Bl ; US 2010/0290946 Al ; US 201 1/0033643 Al ; US 201 1/0101281 Al ; and US 201 1/0135902 Al).
  • the Film PSM Upon the O/U mold being raised and removed from the bath of the melt of the semiconductor material a coating of the melt, the Film PSM , or a combination thereof may substantially cover the O/U surface of the O/U mold, and ultimately give the Film PSM .
  • Suitable contact times e.g., from 1 to 30 seconds are described herein or in the references or may be readily determined.
  • the draw-down method (ii) may employ a different O/U mold than that used in the dipping method (iii) or kissing method (i).
  • the O/U mold may be exposed to fumes above the melt for a period of time
  • exposure period sufficient to form particles generated by the fumes on its O/U surface prior to initiating the contacting step of the method.
  • the exposure period is at least 10 seconds, e.g., from 10 to 60 seconds, alternatively from 10 to 30 seconds, alternatively from 15 to 25 seconds.
  • the particles may function as a release
  • a minimized exposure period may be ⁇ 5 seconds, alternatively ⁇ 3 seconds, alternatively ⁇ 2 seconds, alternatively ⁇ 1 second.
  • any one of the embodiments of the present method forms the Film PSM over most, if not all, of the undercooling surface of the undercooling mold. Because direction of solidification of the melt typically occurs from the mold-side surface towards the forming natural side surface of the growing Film PSM , there is potential to concentrate impurities at the solidification front until solidification stops at the natural side surface of the Film PSM . If desired, the natural side surface can be etched to remove the impurities concentrated there. During the contacting step, there is even potential to release the impurities from the natural side surface back into a bulk of the melt (not shown). Thus, there is potential to refine the semiconductor material (e.g., silicon) by the method. Therefore, even embodiments of the Film PSM wherein L AVG may be less than ideal L AVG for maximizing efficiency of the electronic device (e.g., solar cell), the Film PSM may have increased purity compared to the bulk melt and be suitable for high performance electronics applications.
  • L AVG may be less than ideal L AVG for maximizing efficiency of the
  • the method may further comprise a step of separating the Film PSM and O/U mold from each other.
  • the O/U mold and Film PSM may be allowed to cool somewhat before the separating.
  • the separating may occur spontaneously, alternatively a motive force may be applied to the Film PSM , wherein the motive force is effective for removing the Film PSM from the undercooling mold without significantly damaging the Film PSM for use in the applications.
  • the method may, alternatively may not, further comprise a step of recrystallizing at least some portion, alternatively all of the Film PSM .
  • the recrystallizing may be performed on the free standing Film PSM , alternatively the supported Film PSM .
  • the method may, alternatively may not, further comprise a preliminary step before the contacting step, the preliminary step comprising preparing the O U surface on the mold body to give the undercooling mold.
  • the preliminary step may be performed in situ before the contacting step, alternatively the preliminary step may be performed prior to and separate from the method.
  • the material of the melt of the semiconductor material may be any of the semiconductor materials described herein.
  • the material of the melt may be the same as the semiconductor material of the mono-SC material.
  • both semiconductor materials may be silicon, alternatively the doped silicon, alternatively the pure silicon.
  • the material of the melt may be the pure silicon, and the material of the Film PSM of silicon may be a purer silicon (e.g., having a higher number of 9s purity), e.g., as a result of the refining aspect described later.
  • the O/U surface may be used in one-time use in the method, alternatively the O/U surface may be configured for multiple-time uses in the method.
  • Figs. 6A to 6D Some beneficial aspects of the method may be further illustrated as shown in Figs. 6A to 6D.
  • the method forms an embodiment of the Film PSM (e.g., 90).
  • Fig. 6A lower surface 21 of melt of the semiconductor material (melt) 20 sits atop a plurality (five shown or partially shown) of raised contact points 120 of O U mold 100.
  • Left, right and top portions of melt 20 are shown as wavy lines indicating cut off or partial views.
  • Vertical height and horizontal length of melt 20 are substantially greater than indicated in Fig. 6A. This is because at this time point melt 20 is a bulk material, which for convenience is not shown in its entirety.
  • Left and right portions of O/U mold 100 are shown as partial views.
  • Horizontal length of O/U mold 100 is substantially greater than indicated in Fig. 6A.
  • Inert gas pockets 30 are disposed between melt of the semiconductor material 20 and basal surface 110 of the O/U mold 100.
  • Raised contact points 120 are spaced apart from each other by distance, x, 125 (see also Fig. 1). Crystallizing of the melt 20 has not yet begun in Fig. 6A. Next see Fig. 6B.
  • Fig. 6B two nucleation crystals 60 have started forming on top of two of the five raised contact points 120 of O/U mold 100 shown.
  • Left, right and top portions of melt 20 are shown as partial views.
  • Vertical height and horizontal length of melt 20 are substantially greater than indicated in Fig. 6B. This is because at this time point melt 20 is the bulk material of Fig. 6A.
  • Left and right portions of O/U mold 100 are shown as partial views.
  • Horizontal length of O/U mold 100 is substantially greater than indicated in Fig. 6B.
  • the two raised contact points 120 having nucleation are of the mono-SC material-type.
  • Nucleation at the remaining raised contact points 120 may be inhibited or prevented, for example if the three contact points 120 lacking nucleation are the remainder raised contact points 120 consisting essentially of the LNP material. Melt of the semiconductor material 20 remains. A next snapshot in time is shown in Fig. 6C.
  • lateral size of each of intermediate crystals 70 and 75 is substantially greater than thickness, h, 79.
  • Some melt 20 (Fig. 6B) remains (not indicated). Melt 20 is no longer the bulk material, and hence height of residual melt 20 is about the same as height of crystals 70 and 75 indicated by double-headed arrow 79.
  • Fig. 6C would show beginning formation of bumps on natural-side surface (see 93 in Fig. 6D). However, for convenience Fig. 6C does not show beginning formation of bumps so as to illustrate the forming of an alternative embodiment of a Film PSM (not shown) wherein bumpiness on the natural-side surface would be reduced such that bumps would not form thereon. A next snapshot in time is shown in Fig. 6D.
  • Fig. 6D to reach two final crystals 80, which abut each other at grain boundary 85 so as to comprise a portion of Film PSM 90 of polycrystalline semiconductor material.
  • Film 90 defines spaced apart natural-side surface 91 and mold-side surface 92.
  • Natural-side surface 91 defines a plurality of bumps 93. Each bump 93 is disposed above a different mono-SC material-type raised contact point 120.
  • Final crystal 82 also abuts another final crystal (not shown) at grain boundary 87.
  • Each of crystals 80 independently have lateral grain size, L, 82, indicated by horizontal single-headed arrow (arrowhead on right side not visible in this partial view); and thickness, h, 81, indicated by vertical double-headed arrow.
  • Average of all lateral grain size, L, 82, is > 4 times thickness, h, 81. Raised contact points 120 are spaced apart from each other by distance, x, 125 (see also Fig. 1). Average of all lateral grain size, L, 82, is > 3 times distance, x, 125. No melt 20 (Fig. 6B) remains. Note regarding previous discussion above for Fig. 6C: the alternative embodiment of a Film PSM (not shown) wherein bumpiness on the natural-side surface would be reduced such that bumps would not form thereon, that alternative Film PSM would be the same as Film PSM 90 except lacking bumps 93.
  • the O U mold and method may be characterizable by the Film PSM it can produce.
  • the Film PS may be a film of a polycrystalline silicon that is formed from a melt of silicon according to Test Method 1 (described later).
  • the "film of a polycrystalline semiconductor material” or “Film PSM” means a substantially solid sheet having a length, width, and thickness and the natural-side surface (e.g., 91) and the mold-side surface (e.g., 92), the natural-side surface spaced apart from the mold-side surface by the Film PSM thickness (e.g., h, 81).
  • the Film PSM may have a length-to-width ratio ranging from 1 to 10, 1 to 6, 1 to 3, from 1 to 2.5, from 1 to 2, from 1 to 1 , or from 1 to 0.5, from 1 to 0.33, from 1 to 0.2, or from 1 to 0.1.
  • the Film PSM may have a length or width ranging from 50 mm to 5 meters, from 50 mm to 1 m, or from 50 mm to 500 mm, or from 100 mm to 300 mm, e.g., a square of 156 mm x 156 mm.
  • the Film PSM may have any shape, including a shape that is continuous, semicontinuous (e.g., segmented), or discontinuous; planar or non-planar; symmetric or asymmetric.
  • the continuous Film PSM may be a tape.
  • the semicontinuous Film PSM may be a segmented sheet comprising two or more sections spaced apart from nearest ones by a groove, alternatively a ridge. Each section may be independently used to manufacture the electronic device.
  • the sections of the Film PSM may be separated from each other, e.g., to give a plurality of wafers.
  • the discontinuous physical shape may be a sheet, cylinder, hemisphere or sphere.
  • the planar Film PSM may be a tape, alternatively a wafer, e.g., a square, rectangular, or circular wafer.
  • the non-planar Film PSM may be curved, bent, angled, or trough-shaped.
  • the Film PSM comprises, or consists essentially of, a plurality of crystals ("grains," 80) of the semiconductor material that touch or abut each other at and along grain boundaries (e.g., 85 and 87).
  • the Film PSM may, alternatively may not define one or more (e.g., up to 30) apertures therethrough (from the mold-side surface through the thickness to the natural-side surface). The apertures may enable use of the Film PS defining same in a metallization wrap-through photovoltaic cell.
  • the Film PSM may further comprise a peripheral edge (not indicated) in operative connection to the natural- and mold-side surfaces so as to form a Film PSM body.
  • the peripheral edge may have a height equal to height, h (e.g., 81).
  • the Film PSM may be characterizable as a layer, coating, sheet, or wafer, e.g., having integral grain boundaries (e.g., 85 and 87) between crystals (e.g., 80) of the semiconductor material.
  • Surfaces (e.g., 91 and 92) of the Film PSM independently may be smooth or textured.
  • the respective textures of the natural- and mold-side surfaces (e.g., 91 and 92) may be different if the O/U surface of the O/U mold imparts a differentiating pattern to the mold-side surface of the Film PS .
  • the Film PSM may be bonded to the nucleation sites (e.g., 60) (i.e., some of the contact points) of the O/U mold.
  • the O U surface may be configured with average distance Ar and aligning and orientation of crystal lattices of contact points that consist essentially of the mono-SC material such that Film PSM may be quasi-monocrystalline, i.e., have relatively few oriented and aligned crystals.
  • the Film PSM may be a free standing Film PSM (e.g., 700), e.g., an unsupported or loose Film PSM , no longer bonded to the O/U mold after the optional separating step.
  • the free standing Film PSM may be a free standing sheet or free-standing wafer.
  • the Film PSM may be a supported Film PSM (e.g., 90) on a support member.
  • the "supported” means integral or covalently bonded to the support member.
  • the support member may be the O/U mold, alternatively another component of the electronic device, e.g., a motherboard or a camera or lamp housing.
  • the "film thickness” or “Film 1 ⁇ thickness” (e.g., h, 81) is measured between corresponding points on the natural-side and the mold-side surface of the Film PSM and means an average, alternatively median, alternatively maximum distance between the mold-side and natural-side surfaces. Thickness is measured within a sampling area (not indicated) on the Film PSM . The sampling area may be defined as the whole or a representative portion of the Film PSM .
  • the thickness, h (e.g., 81), of the Film PSM may be a function of, among other things, the configuration of the material and structure of the undercooling surface of the undercooling mold, and the contact time during which the melt of the semiconductor material is in contact with the undercooling surface.
  • Film PSM thickness may be measured according to ASTM F657 - 92 (1999) ⁇ Standard Test Method for Measuring Warp and Total Thickness Variation on Silicon Wafers by Noncontact Scanning); and expressed in microns.
  • Thickness, h (e.g. 81) of the Film PSM may be controlled by modulating the heat transfer from the melt to the O/U mold. The heat transfer may be influenced by the particular material and size of the O U mold and by the configuration of the O/U surface, as well as the effective crystallizing conditions such as Tivioid and T$ as described before. Using such parameters, thickness, h (e.g.
  • thickness, h (e.g. 81) of the Film PSM may be readily controlled by an artisan so as to produce Film PSM s suitable for use in electronic devices such as photovoltaic cells.
  • thickness, h (e.g. 81) of the Film PSM may be from 25 to 500 microns, alternatively from 50 to 400 microns, alternatively from 100 to 300 microns (e.g., from 100 to 250 microns).
  • the Film PSM may be characterizable by the Film PSM 's average lateral grain size, L AVG , wherein average lateral grain size is measured according to ASTM El 12- 10 (Standard Test Methods for Determining Average Grain Size).
  • the "average lateral grain size" or “L AVG” is measured in the lateral direction, i.e., parallel to the mold- side surface of the Film PSM and means length or longest dimension of a crystal of the polycrystalline semiconductor material as viewed from the Film PSM 's mold-side surface.
  • Average lateral grain size L AV0 may be controlled by modulating the heat transfer from the melt to the O/U mold.
  • the heat transfer may be influenced by the particular material and size of the O/U mold and by the configuration of the O/U surface, as well as the effective crystallizing conditions such as Tivioid and Ts as described before.
  • L AV0 of the Film PSM may be readily controlled by an artisan so as to produce Film PSM s suitable for use in electronic devices such as photovoltaic cells.
  • L AVG may be at least 1 mm, alternatively at least 2 mm, alternatively at least 3 mm (e.g., up to 10 mm, alternatively ⁇ 8 mm, alternatively ⁇ 6 mm).
  • the Film PSM may be characterizable such that the Film PSM 's L AVG /h ratio
  • the L /h ratio may be > 2.
  • the average lateral grain size (L ; e.g., average of all L, 82) of the crystals is greater than 2 times thickness h (e.g., 81) of the Film PSM .
  • the Film PSM 's L AVG /h ratio is greater than 2, alternatively > 4, alternatively > 5, alternatively > 6, alternatively > 10, alternatively > 20, all when measured according to ASTM El 12-10.
  • a maximum L AVG /h ratio may be 30, alternatively 25, alternatively 21 , as determined by ASTM El 12-10.
  • the L AVG /h ratio may be any one of the foregoing values.
  • the L /h ratio may be any one of the foregoing values.
  • thickness, h may be from 50 to 300 microns, alternatively from 75 to 250 microns, alternatively from 100 to 200 microns; and independently L AVG may be at least 1 mm, alternatively at least 2 mm, alternatively at least 3 mm (e.g., up to 10 mm, alternatively ⁇ 8 mm, alternatively ⁇ 6 mm).
  • the Film PSM may have reduced bumpiness on its natural-side surface (e.g., 91). Reduced bumpiness may be achieved by ensuring that the Film PSM is grown to a thickness, h (e.g., 81) that is greater than the average distance AR between contact points of the O/U mold. Therefore, in the method the Film PSM may be grown to thickness, h, on an O/U mold having a particular average distance AR between contact points such that the ratio of h/Ar is > 1.0, alternatively > 1.10, alternatively > 1.5, alternatively > 2, alternatively > 5.
  • reduced bumpiness may be a fewer number of bumps (e.g., 93) per given area of natural-side surface; alternatively a lower height, Rz, of bumps (e.g., 93); alternatively a reduced total thickness variability (TTV).
  • TTV is the normalized difference between the maximum and minimum values of thickness, h (e.g., 81).
  • TTV is equal to wnere l max anc Vnin are tne max i m um and minimum thicknesses within the sampling area and t tar g et is the target thickness.
  • TTV is measured within a sampling area (not indicated) on the Film PSM .
  • the sampling area may be defined as the whole or a representative portion of the Film .
  • TTV may be measured according to ASTM F657 - 92 (1999).
  • the Film PSM may have a TTV of less than 30, alternatively less than 25%, alternatively less than 20%, alternatively less than 15%, alternatively less than 10%, alternatively less than 5%, alternatively less than 4%, alternatively less than 3%, alternatively less than 2%, alternatively less than 1%.
  • the Film PS may have a maximum height Rz of the bumps or mounds.
  • Maximum height Rz of the mounds or bumps (e.g., 93) is determined according to ISO 12085 (1996) as described previously for Rx and wherein the lower the Rz, the lower Film PSM bumpiness.
  • the mono-SC material-type raised contact points (e.g., 120, 320, 520, or 820) of the O/U mold (e.g., 100, 300, 500, or 800) generally induce formation of mounds on the natural-side surface of the Film PS (i.e., Film PSM surface opposite mold-side surface of the Film PSM ), but the configuration of the O/U mold advantageously reduces maximum height Rz of those mounds or bumps when compared to a film of the same semiconductor material grown on non-invention mold having a basal surface of an HNP material.
  • the maximum height Rz of the mounds equals a maximum depth from the highest mound to the natural-side surface.
  • the maximum height Rz (not indicated) of the mounds on natural-side surface of the Film PSM may be less than 50%, alternatively less than 33%, alternatively less than 25%, alternatively less than 20% of the thickness (e.g., h, 81) of the Film PSM .
  • the natural-side surface of the Film PSM having reduced bumpiness may advantageously reduce need for or extent of downstream processing (e.g., mechanical texturization and/or polishing) compared to non-invention films.
  • the Film PSM may have characteristic (a), (b), or (c): (a) the L AVG /h ratio as described herein; (b) a maximum height Rz, determined as for Rx of ISO 12085 (1996), that is less than 50 percent of the thickness of the Film PSM ; or (c) both (a) and (b).
  • the configuration of the O/U surface of the O/U mold may minimize or prevent bowing, warping, fracturing, deviation from flatness, and/or dislocation density of the Film PSM .
  • the "bowing" is the deviation of the center point of the median surface of a free standing Film PSM from the median surface reference plane established by three points equally spaced on a circle with a diameter less than the diameter of the Film PSM . Bowing may be measured according to ASTM F534 -02 (Standard Test Method for Bow of Silicon Wafers), Section 3.1.2.
  • the bowing value may be expressed as a percentage of Film PSM thickness, h (e.g., 81), wherein the lower the percentage the less bowing.
  • the Film PSM may have a bowing of less than 10%, alternatively less than 5%, alternatively less than 4%, alternatively less than 3%, alternatively less than 2%, alternatively less than 1% of thickness, h (e.g., 81).
  • the "warping" is the differences between maximum and minimum distances of the median surface of a free standing Film PSM from a reference plane. Unlike bowing, warping uses the entire median surface of the Film PSM instead of just the surface at the center point. Warping may be measured according to ASTM F 1390 - 97 (Standard Test Method for Measuring Warp on Silicon Wafers by Automated Noncontact Scanning). The warping value may be expressed as a percentage of Film PSM thickness, h (e.g., 81), wherein the lower the percentage the less warping.
  • the Film PSM may have a warping of less than 10%, alternatively less than 5%, alternatively less than 4%, alternatively less than 3%, alternatively less than 2%, alternatively less than 1% of thickness, h (e.g., 81).
  • the "flatness” is the deviation of the front surface of the free standing Film PSM , expressed in total indicator reading (TIR) or maximum focal plane deviation (FPD), relative to a specified reference plane when the back surface of the wafer is ideally flat. Bowing and warping are measured based on the median surface of the Film PSM relative to a reference plane, whereas flatness measurements are based on the top surface (e.g., natural-side surface) of the wafer relative to the reference plane.
  • Flatness may be global flatness, alternatively site flatness. Global flatness and site flatness independently may be a TIR or FPD value.
  • Flatness measurements may be determined according to ASTM F1530 - 94 (Standard Test Method for Measuring Flatness, Thickness, and Thickness Variation on Silicon Wafers by Automated Noncontact Scanning).
  • the flatness values may be expressed as a percentage of Film PSM thickness, h (e.g., 81), wherein the lower the percentage the less deviation from flatness.
  • the Film PSM may have a flatness of less than 10%, alternatively less than 5%, alternatively less than 4%, alternatively less than 3%, alternatively less than 2%, alternatively less than 1% of thickness, h (e.g., 81).
  • the "dislocation density" (DD) of the free standing Film PSM may be measured with a GT-PVSCAN6000 instrument (GTSolar, Nashua, New Hampshire, USA) at a resolution of 50 microns, as described by Sopori B., et al., Wafer and Solar Cell Characterization by GT-PVSCAN6000, 12 th Workshop on Crystalline Silicon Solar Cell Materials and Processes, NREL/BK-520-32717, August 2002.
  • the "dislocation” means a non-ideal packing of the atoms within the Film PSM .
  • the Film PSM may be characterizable as having low thermal stress, low mechanical stress, or both.
  • the low stress Film PSM advantageously inhibits or prevents dislocation formation.
  • the Film PSM may have fewer crystal imperfections than comparative films prepared on other molds. Types of crystal imperfections that may be improved in the Film PSM include voids, dislocations, disruptions at grain boundaries, and precipitations. Dislocation may arise from stress applied to the crystal (e.g., during crystal growth). A comparative film having a greater number of dislocations may have decreased electrical properties compared to the Film PSM .
  • the DD typically is ⁇ 10,000/square centimeter (1 x l O ⁇ /cm ⁇ ).
  • the Film PSM may be characterizable as having DD ⁇ 1 x
  • the Film PSM may be characterizable as having improved orientation or alignment and orientation of the crystals or grains of the polycrystalline semiconductor material thereof.
  • the improved crystal orientation may reduce dislocation density (DD) in the Film PSM .
  • the Film PSM may be characterizable by any one or more of the product-by- process limitations imparted by the method and/or O/U mold described herein; and/or any one or more of the Film PSM limitations described herein.
  • the invention may include a combination of any two, alternatively any three, alternatively any four or more limitations: undercooling (° ), LNP material, grains contact area, DD, AR, Rx, Rz, and L AVG /h ratio.
  • the Film PSM may be used directly to prepare the electronic device, or a base material useful for conducting electrons in a controlled manner in the electronic device.
  • at least a portion, alternatively all of the Film PSM may be recrystallized. Recrystallization comprises at least partially remelting the Film PS , and recrystallizing the resulting at least partial remelt. If desired, the recrystallizing step may be performed with the at least partial remelt in contact with the O/U surface of the O/U mold.
  • a sheet of polycrystalline semiconductor material that has not been prepared by the method may be at least partially remelted and the resulting at least partial remelt may be recrystallized in contact with the 0/U surface of the 0/U mold, which may advantageously produce an alternative embodiment of the Film PSM having an L AVG /h ratio greater than the L AVG /h ratio of the sheet.
  • the recrystallization may comprise providing first and second O/U molds that are planar sheets, which may be the same as, alternatively different than, each other; and performing the recrystallizing step with the at least partial remelt in contact with the O/U surface of the first 0/U mold and with the O/U surface of the second O/U mold.
  • the second O/U mold is spaced apart from the first O/U mold by the at least partial remelt so as to comprise a laminate.
  • the laminate may comprise a bottom layer that is the first O/U mold, an inner layer that is the at least partial remelt, and an upper layer that is the second O/U mold, wherein the undercooling surfaces of the first and second undercooling molds are disposed facing each other.
  • the peripheral edge of the laminate may be placed in contact with a particulate form of LNP material.
  • the entire Film PSM or sheet may be remelted, and the resulting complete remelt may be recrystallized.
  • Examples of the electronic devices are an integrated circuit (not shown); a microprocessor comprising the integrated circuit; a computer machine or digital camera comprising the microprocessor; a light-emitting semiconductor diode (LE D, not shown); a lamp comprising the LED; a lighting appliance comprising the lamp; a photovoltaic cell (not shown); or a photovoltaic module comprising at least one such photovoltaic cell.
  • the Film PSM may have improved performance (e.g., improved electrical efficiency) as L AVG /h ratio increases further above 2 (e.g., sequentially to 4, 5, 6, 7, 8, 10, 15, or 20). E.g., PV cell efficiency of the Film PSM in electronics applications may increase.
  • Test Method 1 used to determine whether any O/U mold favors the laterally growing a film of polycrystalline semiconductor material from a melt of the semiconductor material such that L AVG of the crystals is greater than 2 times thickness (e.g., h, 81) of the Film PS and/or such that maximum height Rz of the mounds of grains of the natural-side surface of the Film PSM of the polycrystalline material is less than 50 percent of the thickness of the Film PSM , wherein Rz is determined as for Rx of ISO 12085 (1996).
  • the experimental conditions are: atmosphere consists of anhydrous argon gas at 15 kilopascals (kPa); starting material is a melt of 99.9999 atomic percent purity silicon; initial bulk temperature, T s , of the Si melt is 1450 °C; initial bulk temperature, ⁇ ⁇ ⁇ , of the O U mold is 1 190 °C; the apparatus is the drawdown apparatus of WO 2005/104244 ( Figure 1 and description from page 3, line 9, to page 4, line 16, of WO 2005/104244 are incorporated here by reference); the O/U mold, with first O/U surface disposed facing up, is moved through bottom of casting frame 2 of figure 1 of WO 2005/104244 at a speed of 0.10 meter per second; average thickness (h, 81) of the resulting film of polycrystalline silicon is 300 microns.
  • atmosphere consists of anhydrous argon gas at 15 kilopascals (kPa); starting material is a melt of 99.9999 atomic percent purity silicon; initial bulk temperature, T s , of
  • FIG. 5 is a gray-scale confocal microscopy image of an example of the O/U mold 500 having a first O/U surface (the area within square- shaped O/U mold 500) consisting essentially of a plurality of hemispherical-shaped raised contact points 520 disposed on basal surface 510 in an "square-corner array.”
  • Basal surface 510 consists essentially of fused silica and raised contact points 520 consist of monocrystalline silicon embedded in or adhered to the fused silica.
  • O/U mold 500 is 130 mm long by 100 mm wide, of which the portion useful for measuring average distance AR is 4 mm long by 3 mm wide.
  • O/U mold 500 contains an 18-by- 13 array of 234 raised contact points 520.
  • the average distance AR between raised contact points 520 is 200 microns by ISO 12085. Removing the material creates "valleys" between raised contact points 520 that are believed to be filled with inert gas during the method to become gas pockets.
  • Raised contact points 520 are disposed above basal surface 510, which is at a maximum depth Rx (not indicated) of 100 microns as determined by ISO 12085 (1996).
  • O/U surface is thus configured with pyramid-shaped raised contact points 520 of the LNP material for localized undercooling.
  • FIG. 7 is a black-and-white photograph of an example of a free standing Film PSM 700 of polycrystalline silicon that is prepared by the method adapted to the general method of US 2009/0044925 Al .
  • a monocrystalline silicon mold body is used that is textured by grinding to give raised contact points (not shown) that on average are spaced apart from each other by average distance AR of from 100 to 300 ⁇ .
  • a mask of graphite is disposed between the raised contact points to give an O/U mold having basal surface of graphite and raised contact points of monocrystalline Si.
  • the O/U mold is at an initial bulk temperature, T Mo
  • Film PSM 700 is obtained by separating Film PSM 90 of Fig. 6D from O/U mold 100.
  • Film PSM 700 is 150 mm long and 100 mm wide and has a plurality of large crystals (not all shown), including crystal 780 having an L AVG of approximately 3 mm and a thickness of about 300 ⁇ .
  • L AVG of the polycrystalline silicon (not indicated) in Film PSM 700 is from 200 to 500 ⁇ .
  • Ex 2 An O/U mold in accordance with the subject invention is prepared.
  • the O/U mold comprises a LNP material in combination with a H P material.
  • the LNP material comprises silicon dioxide (Si0 2 ) and the FINP material comprises silicon carbide (SiC).
  • the O/U mold is prepared from an initial mold comprising SiC.
  • a composition comprising water, polyvinyl alcohol (PVA), and silicon nitride (Si 3 N 4 ) powder/particles having an average particle size of less than 1 ⁇ is sprayed onto a surface of the initial mold to form a layer. The layer uniformly coats the surface of the initial mold.
  • PVA polyvinyl alcohol
  • Si 3 N 4 silicon nitride
  • the layer is dried to evaporate the water and/or IPA therefrom and to harden the layer to form a hardened layer.
  • the hardened layer is oxidized in air for 5 hours at 1200 °C to form a silicon dioxide (Si0 2 ) layer on the silicon nitride (Si 3 N 4 ) particles.
  • the silicon dioxide (Si0 2 ) layer ultimately acts as a binder between the silicon nitride (Si 3 N 4 ) particles and as the LNP material that ultimately contacts a melt of semiconducting material.
  • a geometric structure can be applied to the surface of the O/U mold (i.e., the surface having the silicon dioxide (Si0 2 ) layer on the silicon nitride (Si 3 N 4 ) particles) with locally higher areas, with the silicon dioxide (Si0 2 ) being at least partially removed mechanically and/or chemically.
  • Figs. 9 and 9a which are described in greater detail above, are gray-scaled microscopic images of the O/U surface of the O/U mold formed in Ex 2, with dark areas representing the HNP material and the lighter (i.e., light gray to white) areas representing the LNP material.
  • Ex 3 An 0/U mold in accordance with the subject invention is prepared.
  • Fig. 10 is a gray-scaled microscopic image of the 0/U surface of the 0/U mold of Ex 3.
  • the HNP material of Ex 3 comprises monocrystalline silicon.
  • the O/U mold of Ex 3 allows for not only control of the grain size within the film of semiconductor material, but also for control of the grain orientation within the film of semiconductor material.
  • the O/U surface of the O/U mold is textured using a laser to form a square pattern having lines spaced by 200 ⁇ . The raised contact points of the O/U mold are present in the area between the intersecting textured lines formed by the laser.
  • the monocrystalline silicon mold can be manufactured with different crystal orientations at the surface of the mold, which can be characterized by the Miller indices in a direction vertical of the mold surface.
  • a mono-crystalline silicon orienting mold may optionally be combined with the method as described in Ex 2 to manufacture an O/U surface and O/U mold.
  • Films of polycrystalline semiconductor material are formed on the O/U molds of Ex 3 in accordance with the subject invention.
  • films of polycrystalline silicon are formed on the O/U mold of Ex 3 in accordance with the subject invention.
  • the films of polycrystalline silicon are then subjected to an electron back scatter diffraction (EBSD) analyses so as to characterize the crystal orientation thereof.
  • EBSD electron back scatter diffraction
  • the orientation of the O/U mold is largely replicated in the crystal orientation of the films of polycrystalline silicon, while grain size of the dominant crystal orientation is much greater than the wafer thickness of about 150 ⁇ .
  • Figs. 11 and 12 are gray-scaled EBSD analyses of the films of polycrystalline silicon grown on the O/U molds of Ex 3 while being vertically oriented.
  • Fig. 11 is representative of the EBSD analysis of the film of polycrystalline silicon formed with the O/U mold of Ex 3 (Fig. 10) with a certain crystal orientation
  • Fig. 12 is representative of the EBSD analysis of the film of polycrystalline silicon formed with the O/U mold of Ex. 3 (Fig. 10) with another crystal orientation.
  • Figs. 11 and 12 show the crystal orientation of the respective films of polycrystalline silicon is in most areas identical to the crystal orientation of the O/U mold utilized at the mold-film interface.

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Abstract

La présente invention concerne un film de matériau semi-conducteur polycristallin, un procédé de fabrication du film et des moules d'orientation/surfusion qui sont utiles dans le procédé, et un dispositif électronique comprenant ou préparé à partir du film. Un moule d'orientation/surfusion qui est imperméable à l'écoulement de gaz, le moule d'orientation/surfusion comprenant une première surface d'orientation/surfusion configurée avec une surface basale essentiellement constituée d'un matériau à faible pouvoir de nucléation et avec une pluralité de points de contact, au moins certains de la pluralité de points de contact essentiellement étant constitués d'un matériau semi-conducteur monocristallin pour orienter la croissance de cristal et contrôler les positions de sites de nucléation sur la surface d'orientation/surfusion, et le reste éventuel de la pluralité de points de contact étant essentiellement constitués d'un matériau à faible pouvoir de nucléation pour contrôler le transfert thermique sans fonctionner en tant que sites de nucléation ; et les réseaux cristallins d'au moins 80 pour cent du nombre total des points de contact essentiellement constitués d'un matériau semi-conducteur monocristallin étant orientés parallèlement les uns aux autres.
PCT/IB2013/001370 2012-06-27 2013-06-27 Film de matériau semi-conducteur polycristallin, procédé de fabrication de celui-ci et moules d'orientation/surfusion pour celui-ci, et dispositif électronique WO2014001886A1 (fr)

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