WO2014001888A1 - Film de matériau semi-conducteur polycristallin, procédé de fabrication de celui-ci et moules de surfusion pour celui-ci, et dispositif électronique - Google Patents

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

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Publication number
WO2014001888A1
WO2014001888A1 PCT/IB2013/001372 IB2013001372W WO2014001888A1 WO 2014001888 A1 WO2014001888 A1 WO 2014001888A1 IB 2013001372 W IB2013001372 W IB 2013001372W WO 2014001888 A1 WO2014001888 A1 WO 2014001888A1
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Prior art keywords
undercooling
mold
film
alternatively
contact points
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PCT/IB2013/001372
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English (en)
Inventor
Eelko HOEK
Patrick LEMMPOEL
Pierre-Yves PICHON
Axel SCHÖNECKER
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Rgs Development B.V.
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Publication of WO2014001888A1 publication Critical patent/WO2014001888A1/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, 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: 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 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 polycrystalline semiconductor material, a method of making the film and undercooling molds that are useful in the method, and an electronic device.
  • the undercooling mold has at least one undercooling surface consisting essentially of a low nucleation-potency material.
  • An undercooling mold that is impermeable to gas flow, the undercooling mold comprising a first undercooling surface configured with contact points consisting essentially of a low nucleation-potency material for localized undercooling a melt of a semiconductor material by at least 17 degrees Kelvin.
  • An undercooling mold that is impermeable to gas flow, the undercooling mold comprising a first undercooling surface that is characterizable by 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, or a combination of any two or more low nucleation-potency materials; wherein the contact points independently consist essentially of a low nucleation- potency material, or a combination of any two or more low nucleation-potency materials and are useful for contacting a melt of the semiconductor material; wherein on average
  • a method of making a film of polycrystalline semiconductor material on the undercooling mold comprising contacting under effective crystallizing conditions a melt of the semiconductor material at a bulk temperature Ts with the first undercooling surface of the undercooling mold at a bulk temperature TM O W, wherein s > M O M; allowing the film to form thereon; and removing the undercooling mold with the film from contact with 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 undercooling surface of the 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 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 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 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 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 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 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 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.
  • Fig. 9 is a gray-scale microscopic photograph of an embodiment of the undercooling mold.
  • the undercooling mold of Fig. 9 is coated with a low nucleation potency material.
  • Fig. 10 is a gray- scale microscopic photograph of a cross-section of a film of silicon grown on a mold comprising a low nucleation potency material.
  • Figs. 11a and lib are gray-scale microscopic photographs of a film of silicon grown on a mold comprising a low nucleation potency material and having lateral crystal dimensions greater than a thickness of the film.
  • Fig. lib is an enlarged grayscale microscopic photograph of the cross-section of the film of silicon of Fig. 11a.
  • Fig. 12 is a gray-scale microscopic photograph of a top view of a film of silicon grown on a mold comprising a low nucleation potency material and having grain boundaries visualized via a grain boundary etch.
  • undercooling mold 100 has a first undercooling surface (the area within the rectangular-shaped undercooling 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. 6 A), 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-corner array," i.e., a template or arrangement wherein raised contact points 120 are located at hypothetical corners 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 any two or more LNP materials.
  • Raised contact points 120 consist essentially of, alternatively consist of, the LNP material.
  • First undercooling surface (not numbered) is disposed on a mold body (not shown; see 170 in Fig. 6A).
  • Undercooling mold 100 is a planar sheet.
  • a section view IB-IB that bisects a row (not indicated) of raised contact points 120 along the length of undercooling mold 100 is shown in Fig. lb.
  • Fig. la is a perspective view of the undercooling 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 IB-IB of the undercooling mold 100.
  • undercooling mold 200 has a first undercooling surface (the area within the square-shaped undercooling 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.
  • Flush contact points 220 consist essentially of, alternatively consist of, the LNP material, alternatively the combination of any two or more LNP materials.
  • First undercooling surface (not numbered) is disposed on a mold body (not shown). Undercooling 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.
  • undercooling mold 300 has a first undercooling surface (the area within square-shaped undercooling 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, or the combination of any two or more LNP materials.
  • Raised contact points 320 consist essentially of, alternatively consist of, the LNP material, or the combination of any two or more LNP materials.
  • First undercooling surface (not numbered) is disposed on a mold body (not shown).
  • Undercooling 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.
  • undercooling mold 400 has a first undercooling surface (the area within rectangular-shaped undercooling 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.
  • under means below the plane of and in fluid communication with.
  • Lowered contact points 420 are arranged in the "equilateral triangle-corner array.”
  • Basal surface 410 consists essentially of the LNP material, or the combination of any two or more LNP materials.
  • Lowered contact points 420 consist essentially of, alternatively consist of, the LNP material, or the combination of any two or more LNP materials.
  • Undercooling mold 400 is a planar sheet.
  • Fig. 4a is a perspective view of the undercooling 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 undercooling mold 500 having a first 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.”
  • Undercooling mold 500 is an example of the subgenus undercooling mold 100 depicted in Fig. 1 and shown in cutaway profile in Figs. 6A to 6D.
  • Undercooling 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 undercooling mold 100 and the method.
  • the method comprises a process of crystallizing a melt of the semiconductor material (e.g., 20) on undercooling mold 100 (see also Fig. 1).
  • first undercooling surface (not numbered) is disposed on mold body 170, which is the portion of undercooling mold 100 below phantom line 171. The method aspects of Figs. 6 A to 6D are also described later.
  • undercooling mold 800 has a first undercooling surface (the area within square-shaped undercooling 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 undercooling surface (not numbered) is disposed on a mold body (not shown). Undercooling mold 800 is a planar sheet.
  • Fig. 8a is a perspective view of the undercooling mold 800 of Fig. 8 to illustrate raised contact points 820 extend like cubes up from and to above basal surface 810.
  • Fig. 9 is a gray-scale microscopic photograph of an embodiment of the undercooling mold. More specifically, as described in greater details in the Examples, the undercooling mold of Fig.9 comprises SiC but the first undercooling surface comprises a silicon dioxide (Si0 2 ) layer, which is a LNP material.
  • Si0 2 silicon dioxide
  • Fig.10 is a gray-scale microscopic photograph of a cross-section of a film of silicon 90 grown on an undercooling mold comprising a low nucleation potency material.
  • the LNP material of the undercooling mold comprises graphite.
  • the lateral grain size L is greater than twice the thickness h of the film of silicon 90 of Fig.10.
  • Figs.11a and lib are gray-scale microscopic photographs of a film of silicon 90 having lateral crystal sizes L greater than a thickness h of the film of silicon 90.
  • the film of silicon 90 illustrated in Figs.11a and lib was grown on an undercooling mold comprising graphite as the LNP material.
  • Fig. lib is an enlarged gray-scale microscopic photograph of the cross-section of the film of silicon 90 of Fig.11a.
  • the visible black lines in the film of silicon 90 of Figs. 11a and lib indicates that enhanced lateral crystal growth velocity is based upon a twin assisted growth mechanism.
  • Fig. 12 is a gray-scale microscopic photograph of a top view of a film of silicon 90 grown on a mold comprising a low nucleation potency material and having grain boundaries visualized via a grain boundary etch.
  • the film of silicon 90 of Fig. 12 was grown on an undercooling mold comprising graphite as the LNP material.
  • the large area without grain boundaries in the film of silicon of Fig.12 demonstrates enhanced lateral crystal growth in the film of silicon 90.
  • undercooling mold Unless indicated otherwise, the discussion of the undercooling mold that follows pertains to the illustrated undercooling molds 100, 200, 300, 400, 500, and 800 and their relevant features (e.g., undercooling surface (not numbered) consisting essentially of, alternatively consisting of, contact points 120, 220, 320, 420, 520, and 820 and basal surfaces 110, 210, 310, 410, 500, and 810, respectively) as well as to the non-illustrated alternative embodiments of the undercooling mold and their relevant features.
  • undercooling surface not numbered
  • the discussion of the Film PSM that follows pertains to the illustrated Film PSM 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) as well as 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 their 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 cooling surface (e.g., the first undercooling surface) to an opposite surface (e.g., an optional second undercooling 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 undercooling mold may prevent movement of a bulk mass of gaseous fluid from one surface (e.g., the first undercooling 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.
  • inert e.g., nitrogen gas or argon gas
  • 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.
  • kPa kilopascals
  • 41 kPa e.g., 21 kPa
  • a 1 millimeter (mm) thick material of the undercooling mold may have a nitrogen gas permeability of less than or equal to nitrogen gas permeability of 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 undercooling mold would be a dense monolithic, 1 mm thick sheet (e.g., graphite) with an argon gas permeability of ⁇ 2x10 " ⁇ square meter (m ⁇ ) (i.e., 0.002 Darcy or less).
  • the 1 millimeter thick material of the undercooling mold may have an argon gas or nitrogen gas permeability of less than 0.5x10 " ⁇ m ⁇ , alternatively ⁇ 0.2x10 " ⁇ m ⁇ , alternatively ⁇ 1x10 " ⁇ m ⁇ , alternatively ⁇ 1x10 " ⁇ m ⁇ , 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 undercooling 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 undercooling surface of the undercooling 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 "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 undercooling 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 undercooling 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 "undercooling mold” of the present invention means a new type of casting mold that is impermeable to gas flow and has at least one undercooling surface.
  • the undercooling mold is impermeable to gas flow.
  • the undercooling surface is useful 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 until a sufficient extent of undercooling has been achieved before nucleation begins and for controlling heat transfer and controlling number of nucleation sites on the undercooling surface so as to not produce nucleation at every contact point, and so as to produce the Film PSM (e.g., 90) according to the method.
  • the Film PSM e.g. 90
  • the undercooling surface of the undercooling 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 undercooling surface may be interior in, alternatively exterior on the undercooling mold.
  • the interior undercooling surface e.g., a concave surface
  • each, such undercooling 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 (e.g., 120, 220, 320, 420, 520, or 820) consisting of the LNP material, or the combination of any two or more LNP materials, and the basal surface consisting of the LNP material, or the combination of any two or more LNP materials.
  • the configuration enables nucleation and crystallization to an extent sufficient to form the crystals of the Film and at the same time sufficient extent of the localized undercooling of the melt of the semiconductor material.
  • 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 undercooling surface may consist of the LNP material or the combination thereof.
  • the "consist of a LNP material means at least 99.00 wt%, alternatively 99.99 wt%, alternatively at least 99.999 wt%, alternatively 100 wt% of the LNP material.
  • any embodiment of the undercooling mold may be characterized by describing the configuration of the material of the undercooling surface and the surface structure (e.g., 120/110, 220/210, 320/310, 420/410, 520/510, or 820/810) of those undercooling surface.
  • the present invention advantageously may decouple surface structure ("texture") from the materials (e.g., LNP material) of the undercooling surface for controlling positions (i.e., locations) or numbers of nucleation sites on the undercooling 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 undercooling surface of the undercooling mold enables controlling positions and numbers of crystals in the Film PSM .
  • the present invention advantageously makes use of a non-porous LNP 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 undercooling mold does not require or allow a differential pressure regime through the undercooling mold via the undercooling surface(s).
  • 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 2011 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 3 ⁇ 4, respectively.
  • the undercooling surface alternatively the undercooling 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, silver, and silver silicide; or silicon carbide, any one of the foregoing LNP materials, silver, and silver silicide.
  • the undercooling 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 that may be 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) and silicon.
  • the "consisting essentially of a low nucleation-potency material” means the undercooling surface may contain at most the trivial amount of the HNP material. Any HNP material 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 LNP material.
  • the configuration of the undercooling surface of the undercooling mold is such that at the beginning of the contacting step of the method, no part of the undercooling surface would have a HNP material in physical contact with the melt.
  • all of the undercooling surface, alternatively all of the undercooling mold may lack the HNP material, i.e., would consist of the LNP material or the combination thereof.
  • the "low nucleation-potency material” or “LNP material” means a refractory substance characterizable by a high energy barrier to nucleation of the semiconductor material (e.g., silicon) and yet a capability of nucleating at least one melt of the semiconductor material that is sufficient to form the Film PSM .
  • 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 the melt (e.g., molten silicon) on the LNP material is more difficult to start than nucleation on the HNP material because the LNP material has a higher energy barrier to nucleation than does the HNP material.
  • the extent of undercooling of the melt (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 °K, alternatively > 50 °K, alternatively > 100 °K, alternatively > 125 °K.
  • the localized undercooling at the contact points of the undercooling mold may be > 20 °K, alternatively > 50 °K, 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 1414 degrees Celsius (°C)).
  • 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.
  • 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 Standard Grade, Corning code 7980.
  • 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 °K; (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 °K; 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 is faster than the rate of any reaction thereof with the undercooling surface 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 S1O2 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/Si3N ; 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 undercooling mold independently may consist essentially of, alternatively consist of, a same or different LNP material; alternatively all contact points may consist essentially of, alternatively consist of, the same LNP material.
  • the basal surface e.g., 110, 210, 310, 410, 510, or 810) may consist essentially of a same or different LNP material; alternatively the entire basal surface may consist essentially of, alternatively consist of, the same LNP material.
  • all of the contact points may consist essentially of a same first LNP material, the entire basal surface may consist essentially of a second LNP material, wherein the first and second LNP materials may be the same as, alternatively different than, each other.
  • the raised contact points consist essentially of, alternatively consist of, the low nucleation-potential material.
  • the contact points of the undercooling 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 the combination thereof
  • the LNP material of the raised contact points independently may be any LNP material, or the combination thereof.
  • the LNP material of the raised contact points and the LNP material of the basal surface may respectively be: the SiC ⁇ and the carbon; alternatively the S1O2 and S13N4; alternatively the carbon and S13N4; alternatively the carbon and the SiC ⁇ ; alternatively S13N4 and the SiC ⁇ ; alternatively
  • S13N4 and the carbon alternatively two different S1O2 materials; alternatively two different carbon materials; alternatively the same SiC ⁇ material; alternatively the same carbon material; alternatively both S13N4.
  • the energy barrier of the flush or lowered contact points (e.g., 220 or 420) to nucleating the melt of the semiconductor material is lower than the nucleation energy barrier of the basal surface (e.g., 210 and 410, respectively). Nucleation of a melt simultaneously in contact with a flush or lowered contact point and the basal surface would be favored at the flush or lowered contact point over the basal surface.
  • Each of the LNP material of the flush contact points and LNP material of the lowered contact points is different than the LNP material of the basal surface, respectively. I.e., the first and second LNP materials are different for the flush or lowered contact points and the basal surface, respectively.
  • Flush contact points and lowered contact points consist essentially of a LNP material that has a lesser undercooling than the undercooling of the LNP material of the basal surface.
  • the undercooling °K value of the LNP material of the basal surface is greater (e.g., by at least 10 °K, alternatively at least 20 °K, alternatively at least 50 °K, alternatively at least 75 °K, alternatively at least 100 °K) than the undercooling °K value of the flush or lowered contact points.
  • the basal surface may have a 50 °K undercooling value and the flush or lowered contact points may have a 30 °K undercooling value.
  • the contact points may be amorphous LNP material, alternatively crystalline LNP material, alternatively a combination of amorphous LNP material in some contact points and crystalline LNP material in other contact points.
  • the amorphous contact points may be amorphous sodium silicate glass, alternatively amorphous boron nitride.
  • the glassy carbon also known as vitreous carbon, is not an amorphous carbon because glassy carbon consists essentially of two-dimensional structural elements and does not exhibit "dangling" bonds (IUPAC Gold Book).
  • the crystalline contact points may all be part of a single crystal of the LNP material (e.g., single crystal of a quartz crystalline form of silicon dioxide or a single crystal of a graphite form of carbon or a single crystal of crystalline boron nitride).
  • a single crystal suitable for producing the undercooling surface thereon may be readily prepared by any suitable method, including known methods. The undercooling surface would be produced as described later. By virtue of being prepared from a single crystal, all the contact points of the undercooling surface would have oriented crystal lattices or oriented unit cells. Further, 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.
  • the 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 undercooling 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 or different LNP material (e.g., a plurality of quartz crystals of silicon dioxide), 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.
  • Such crystals may be aligned and their lattices oriented with each other, alternatively such crystals may be aligned with each other but non-uniformly oriented, alternatively such crystals may be non-aligned and non-oriented.
  • Such crystals may be aligned and their lattices oriented with each other during the preparation of the undercooling surface such as by precision placement of identically sized and shaped crystals on a planar basal surface.
  • 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.
  • 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 when the LNP material is crystalline then at least 80%, alternatively at least 90%, alternatively at least 95%, alternatively at least 98%, and "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).
  • the contact points of the undercooling mold may be of uniform size, alternatively non-uniform 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 undercooling 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 spaced apart by a sufficient distance to collectively provide sufficient heat transfer and localized undercooling as described herein so as to preferentially enable a higher rate of lateral crystal growth and enable the Film PSM to be made thereon.
  • their low nucleation-potential material desirably enable a plurality, alternatively a majority, of the contact points to lack nucleation activity, i.e., the plurality, alternatively majority of contact points may not serve as and may be prevented from serving as sites of crystallization.
  • the configuration of the surface structure of the undercooling surface of the undercooling mold comprises a uniform arrangement (e.g., distribution or spacing) of the contact points (e.g., 120, 220, 320, 420, or 520) at discrete locations; alternatively 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 Film PSM than would the uniform arrangement of the contact points.
  • 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 undercooling mold.
  • the Film PSM produced with the non-uniformly arranged 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 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 undercooling mold than other areas of the Film PSM , which would be useful in the separating (detaching) step.
  • such a nonuniform 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 PSM 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 of the LNP material is sufficient for enabling the favoring laterally growing the Film PSM of polycrystalline semiconductor material. If the average distance AR between the contact points would be too short (e.g., ⁇ 5 microns), then a Film PSM 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 melt of the silicon may find an additional contact point on the basal surface therebetween. In the undercooling 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 undercooling surface has isotropy, a 2 -dimensional profile is extracted in a direction perpendicular to the main direction of the undercooling 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 undercooling 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 the contact points 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 5 ⁇ ); or as little as 4 ⁇ (5 ⁇ ⁇ - (0.20*5 ⁇ ⁇ ⁇ ) for -20% of 5 ⁇ ) as long as the average distance AR is as described above.
  • an average distance between contact points that acted as sites of nucleation in the method may be > 2 times, alternatively > 4 times, alternatively > 6 times, alternatively > 10 times the average distance AR of the undercooling surface.
  • the undercooling surface of the undercooling mold may be characterizable by a grains contact area (not indicated).
  • the grains contact area is the areal portion of the contact points of the undercooling 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 undercooling 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 undercooling surface of the undercooling mold after the
  • the 1 mm ⁇ -portion contains at least 10 contact points, at least some of which acted as nucleation sites during the method.
  • the areal portion of the undercooling 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 undercooling mold from each other without cracking or breaking the Film PSM .
  • the grains contact area of the undercooling mold advantageously provides sufficient bonding between the portion of contact points that act during the method as nucleation sites (e.g., 60) on the undercooling surface of the undercooling mold and the mold-side surface (e.g., 92) of the Film PSM to control detaching of the Film PSM from the undercooling mold. Too little grains contact area (typically ⁇ 0.1%) and the Film PSM may release from the undercooling 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 undercooling mold without either breaking or cracking the Film PSM ; eventually developing dislocations of the crystals, thereby reducing the Film PSM 's electrical conduction functionality; removing portions of the contact points with the Film PSM , thereby deteriorating the undercooling mold for reuse; or a combination of any two or more of the breaking, developing dislocations, and removing.
  • the configuration of the undercooling surface, including the grains contact area may minimize or prevent the bowing, warping, fracturing, deviation from flatness, or dislocation density of the Film PSM , as described later.
  • the number of nucleation sites as a proportion of the number of contact points may be ⁇ 90%, alternatively ⁇ 75%, alternatively ⁇ 50%, alternatively ⁇ 40%, alternatively ⁇ 25%.
  • an optional part of the configuration of the undercooling surface of the undercooling 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 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 undercooling 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 undercooling mold.
  • the raised contact points (e.g., 120, 320, 520, or 820) are connected to the basal surface (e.g., 110, 310, 510, or 810) and are at a maximum height equal to maximum depth Rx above the basal surface portion of the undercooling surface of the undercooling 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 are at and even with the basal surface (e.g., 210).
  • the flush contact points 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 undercooling mold.
  • the lowered contact points may define any volumetric space or well under the undercooling 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 undercooling 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 undercooling mold may further comprise a second undercooling surface (not shown) spaced-apart from the first undercooling surface, wherein the second undercooling surface independently is defined as the first undercooling surface is defined.
  • the first and second undercooling 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 undercooling surface may be adjacent and spaced apart from the first undercooling surface by a groove or ridge on the undercooling mold as in an embodiment of the segmented undercooling mold described below.
  • the undercooling mold independently may have 3 or more undercooling surfaces (not numbered), e.g., at most 6, alternatively at most 5, alternatively at most 4, alternatively at most 3 undercooling surfaces.
  • the undercooling mold may be further described by its bulk physical structure and bulk material.
  • the bulk physical structure comprises a mold body comprising a bulk material.
  • the undercooling surface material is disposed on the mold body.
  • the bulk physical structure may give the undercooling mold any size and shape.
  • the shape of the undercooling mold includes its three dimensional configuration and location of its undercooling 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 undercooling surfaces spaced apart from nearest ones by a groove, alternatively a ridge.
  • the undercooling 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 undercooling 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 undercooling 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 monolithic, which means the planar sheet is impermeable to gas flow.
  • the size of the undercooling mold and profile of the undercooling surface may be larger than the size of the Film PSM that is to be prepared.
  • the size of the undercooling mold includes its length, width, and thickness. The width and length may be equal for square- (e.g., 200) and circular-shaped (not shown) undercooling molds.
  • the thickness of the undercooling 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 undercooling 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 bulk material of the mold body and the material of the undercooling surface may be the same or different. Resaid, the bulk material may, alternatively may not, be the LNP material. When the bulk material is the LNP material, it may be the same as or different from the LNP material of the undercooling surface.
  • the bulk material may the sequestered HNP material (e.g., silicon carbide or silicon), 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 undercooling surface of the undercooling mold.
  • the mold body may lack the HNP material.
  • Any undercooling mold as described herein and of unspecified shape may be in the shape of a planar sheet.
  • the planar sheet has the first undercooling surface on one side (not numbered), alternatively first and second undercooling surfaces, one on each major side thereof.
  • the undercooling mold may be the planar sheet having one undercooling surface, alternatively the planar sheet has two undercooling surfaces, wherein each undercooling surface independently consists of: raised contact points of fused silica and a basal surface of fused silica; alternatively raised contact points of fused silica and a basal surface of graphite; alternatively raised contact points of graphite and a basal surface of fused silica; alternatively raised contact points of fused silica and a basal surface of fused silica.
  • Each of the two undercooling surfaces of the planar sheet may be the same, alternatively different.
  • the undercooling mold may be the wedge-shape having one, alternatively both major exterior surfaces independently is a different one of the undercooling surface, wherein the basal surfaces are angled at from > 0 to 10 degrees with respect to each other.
  • the undercooling mold may be cylindrical- shaped (having concave and/or convex undercooling surface), hemi-cylindrical- shaped (having concave and/or convex undercooling surface), bowl-shaped (having concave and/or convex undercooling surface), pyramid shaped, or any other shape suitable for accommodating the at least one undercooling surface.
  • the undercooling surface may, alternatively may not be formed in situ before the contacting step of the method.
  • the undercooling surface may not be removable (e.g., detachable) as such from the mold body to which it may be operatively connected.
  • the undercooling surface may be integral with, alternatively integral with and share a material in common with the mold body.
  • the undercooling surface on the undercooling mold may be prepared such that the contact points may be produced at discrete locations and occupy discrete areas above, at, or under the undercooling surface.
  • General techniques for producing an undercooling surface having the flush contact points include selective ablation of a mold body of a first LNP 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 a different LNP material to give a coated surface (not shown), followed by polishing of the entire coated surface to remove enough of the different LNP material to a depth so as to expose the unremoved structures of the first LNP material while maintaining the added different LNP material in the subsurface volumetric spaces (not shown) to give the first undercooling surface having flush contact points (e.g., 220).
  • General techniques useful for producing an undercooling 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.
  • An example of such a known preparation method comprises masking the basal surface (e.g., 110, 310, 510, or 810) with a template of masking material (not shown) that leaves exposed only portions of the basal surface upon which raised contact points are to be disposed; depositing by a chemical vapor deposition method the LNP material on the exposed portions to form the raised contact points thereon; and removing the masking material to give the undercooling mold (e.g., 100, 300, 500, or 800).
  • the preparation method may comprise masking a mold body (not shown) with a template of masking material that becomes the basal surface (e.g., 410) and that leaves exposed only portions of the mold body that become the lowered contact points (e.g., 420).
  • Masks having different templates may be sequentially used in the preparation method so as to obtain an undercooling mold having raised contact points consisting essentially of different LNP materials.
  • An example of 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); and later removed by reaction (e.g., combustion) when desired.
  • the preparation method may comprise depositing a continuous layer of the LNP material on the basal surface to give even portions that end up as the flush contact points (e.g., 220).
  • the preparation method may comprise providing a basal surface consisting essentially of a continuous layer of the LNP material; laser ablation or photolithography and etching away openings in the continuous layer so as to leave behind underneath portions of the continuous layer that end up as the lowered contact points (e.g., 420).
  • the preparation method may comprise providing a continuous layer of the LNP material; laser-etching away portions of the material down to a basal surface and around other portions of the material that become raised contact points (e.g., 120, 320, 520, or 820, wherein the material that has been laser-etched away forms valleys above basal surface (e.g., 110, 310, 510, or 810).
  • the method of making the Film PSM may employ any undercooling mold. During the method, provided there is heat transfer from the melt of the semiconductor material to the undercooling mold, the melt may not physically touch the undercooling mold, although physical touching may occur at the melt contact area.
  • the basal surface (e.g., 110, 310, 510, or 810) of the undercooling surface, not numbered) of the undercooling molds e.g., 100, 300, 500, or 800
  • raised contact points e.g., 120, 320, 520, or 820
  • a gas atmosphere alternatively a plurality of spaced apart gas pockets (e.g., 30) thereof.
  • the gas pockets may, alternatively may not be in fluid communication with each other during the cooling or casting.
  • the gas atmosphere 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,
  • the undercooling 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 than (e.g., pressurized inert gas), 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 vessel (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.
  • Initial bulk temperature Ts of the melt (e.g., 20) 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 T s 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, Ts, 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 vessel such as a crucible (not shown) containing the melt; alternatively solely by allowing heat transfer from the melt to the undercooling 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.
  • 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.
  • ⁇ 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 T of the undercooling mold during the method may be from -50 °C to ⁇ m.p. of the semiconductor material.
  • the initial Ti i o i d 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 Ts of the melt of the semiconductor material.
  • the initial T 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 T above the initial temperature.
  • bulk temperature, TMoid, °f me undercooling mold may be increased or decreased passively, e.g., solely by allowing heat transfer from the melt of the semiconductor material to the undercooling mold; alternatively by allowing heat transfer from the undercooling mold to the atmosphere (e.g., argon gas), respectively.
  • bulk temperature, TMoid, of the undercooling mold may be increased or decreased actively, e.g., by employing laser heating of the undercooling mold; alternatively by employing an undercooling 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, T Mo id, of the undercooling mold may be adjusted actively before the contacting step, and thereafter the bulk temperature, T oid, of the undercooling 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 of the undercooling 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; (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 undercooling (°K); (f) increasing or decreasing (static) pressure of the melt against the undercooling surface of the undercooling mold; and (g) a combination of any
  • 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
  • the LNP material may beneficially control heat transfer resistance between the crystallizing semiconductor material and the undercooling 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 undercooling surface of the undercooling mold unexpectedly exceeds vertical crystal growth (e.g., as indicated by double-headed arrow for h, 79) away from the undercooling surface of the undercooling 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 PSM is characterizable by the L AVG /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 .
  • Temperature comprises the initial T O W of the undercooling 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. That is, while 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 undercooling mold. The cooling of the melt continues until at the cooling surface the melt becomes or is locally undercooled below m.p.
  • the cooling of the melt may be via passive contact with the undercooling mold, alternatively via active cooling of the undercooling mold (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 undercooling mold from the first undercooling surface to an opposite surface (e.g., the optional second undercooling 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% H2 gas based on total weight of the mixture (e.g., 99.0 wt%
  • 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 O2 or CO2), water vapor, organic vapors, or any combination thereof.
  • an oxidizer e.g., gas of O2 or CO2
  • water vapor e.g., water vapor, organic vapors, or any combination thereof.
  • 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 undercooling surface of the undercooling mold may advantageously increase heat transfer from the semiconductor material to the undercooling 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 undercooling mold 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 TM O C I 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 general 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 undercooling 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 known methods (i) to (iii).
  • the method may be (i), alternatively (ii) or (iii), alternatively (ii), alternatively (iii).
  • Method (i) comprises inverting the undercooling mold so that its undercooling surface is disposed downward, and contacting the contact points to an upper surface (not indicated) of the melt of the semiconductor material (e.g., the "kissing" method, e.g., as in US 6,413,313; WO 2002/020882; WO 2003/029143; WO 2004/003262; WO 2004/003263; WO 2004/003264; WO 2004/005592; WO 2004/025000; JP 2001019595; JP 2001085344; or JP 2001151505).
  • the "kissing" method e.g., as in US 6,413,313; WO 2002/020882; WO 2003/029143; WO 2004/003262; WO 2004/003263; WO 2004/003264; WO 2004/005592; WO 2004/025000; JP 2001019595; JP 2001085344; or JP 2001151505
  • undercooling mold e.g., 100, 200, 300, 400, 500, or 800
  • undercooling mold may be disposed horizontally, but inverted opposite to the horizontally with contact points pointing downward, and the undercooling 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.
  • the Film PSM or a combination thereof may cover the undercooling surface of the undercooling mold, and ultimately give the Film PSM .
  • Method (ii) comprises moving the undercooling 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 undercooling surface of the undercooling 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 undercooling mold e.g., 100, 200, 300, 400, 500, or 800
  • the Film PSM may cover the undercooling surface of the undercooling mold, and ultimately give the Film PSM .
  • Method (iii) comprises disposing the undercooling mold (planar or non- planar) in a non-horizontal disposition (e.g., a vertical disposition), and dipping the non-horizontally disposed (e.g., vertical) undercooling mold into a bath of the bulk form of the melt of the semiconductor material and removing the undercooling mold therefrom (the "dipping" method, e.g., as described in any one of US 7,771,643 Bl ; US 2010/0290946 Al ; US 2011/0033643 Al ; US 2011/0101281 Al ; and US 201 1/0135902 Al).
  • the Film PSM Upon the undercooling 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 undercooling surface of the undercooling 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 undercooling mold than that used in the dipping method (iii) or kissing method (i).
  • the undercooling 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 undercooling 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 "layer” and aid the optional separating step.
  • the exposure period is minimized so that the particles do not affect method or form part of the Film PSM .
  • 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 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).
  • the Film PSM may have increased purity compared to the bulk melt and be suitable for high performance electronics applications.
  • the method may further comprise a step of separating the Film PSM and undercooling mold from each other.
  • the undercooling 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. Therefore, even embodiments of the Film PSM wherein grain size may be less than ideal 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.
  • 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 undercooling 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 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 of a polycrystalline 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 before.
  • the undercooling surface may be used in one-time use in the method, alternatively the undercooling surface may be configured for multiple-time uses in the method.
  • Figs. 6A to 6D Some beneficial aspects of the metho'd may be further illustrated as shown in Figs. 6A to 6D.
  • the method forms an embodiment of the Film PSM (e.g., 90) of the polycrystalline semiconductor material.
  • Fig. 6 A 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 undercooling 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 melt, which for convenience is not shown in its entirety.
  • Left and right portions of undercooling mold 100 are shown as partial views.
  • Horizontal length of undercooling mold 100 is substantially greater than indicated in Fig. 6A.
  • Inert gas pockets 30 are disposed between melt 20 and basal surface 110 of the undercooling 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 undercooling 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 a bulk material.
  • Left and right portions of undercooling mold 100 are shown as partial views.
  • Horizontal length of undercooling mold 100 is substantially greater than indicated in Fig. 6B.
  • Nucleation at the remaining contact points 120 may be inhibited or prevented, for example if the remaining contact points 120 function to locally heat the melt 20. Melt of the semiconductor material 20 remains.
  • a next snapshot in time is shown in Fig. 6C.
  • 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.
  • the two intermediate crystals 70 and 75 of Fig. 6C have grown as shown in Fig. 6D to reach two final crystals 80, which abut each other at grain boundary 85 so as to comprise a portion of Film 90 of polycrystalline semiconductor material.
  • Film PSM 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 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), which in this embodiment substantially equals the average distance AR between raised contact points 120 of undercooling mold 100. 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 undercooling mold and method may be characterizable by the Film PSM it can produce.
  • the Film PSM may be the film of a polycrystalline silicon that is formed from a melt of the 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 PSM 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 undercooling surface of the undercooling mold imparts a differentiating pattern to the mold-side surface (e.g., 92) of the Film PSM .
  • the Film PSM may be bonded to the nucleation sites (e.g., 60) (i.e., some of the contact points) of the undercooling mold.
  • the undercooling surface may be configured with average distance Ar 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 undercooling 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 undercooling mold, alternatively another component of the electronic device, e.g., a motherboard or a camera or lamp housing.
  • the "film thickness” or "Film bM 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 undercooling mold. The heat transfer may be influenced by the particular material and size of the undercooling mold and by the configuration of the undercooling surface, as well as the effective crystallizing conditions such as TM O I ⁇ I and Ts 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) and thickness is measured according to ASTM F657 - 92 (1999).
  • 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 AVG may be controlled by modulating the heat transfer from the melt to the undercooling mold.
  • L AVG 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 AVG /h ratio may be > 2.
  • the average lateral grain size (L AVG ; 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 AVG /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 undercooling mold. Therefore, in the method the Film PSM may be grown to thickness, h, on an undercooling 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 (tmax' nV get' wnere ⁇ max min ⁇ tne maximum and minimum thicknesses within the sampling area and target s the target thickness.
  • TTV is measured within a sampling area (not indicated) on the Film .
  • the sampling area may be defined as the whole or a representative portion of the Film PSM .
  • 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 PSM 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. The lower Rz, the lower Film PSM bumpiness.
  • the raised contact points (e.g., 120, 320, 520, or 820) of the undercooling mold generally induce formation of mounds on the natural-side surface of the Film PSM (i.e., Film PSM surface opposite mold-side surface of the Film PSM ), but the configuration of the undercooling 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 raised contact points and/or 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 undercooling surface of the undercooling mold may minimize or prevent bowing, warping, fracturing, deviation from flatness, or dislocation density of the Film PSM .
  • the "bowing" is the deviation of the center point of the median surface of the 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 . 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 20%, alternatively less than 10%, alternatively less than 5%, alternatively less than 3%, alternatively less than 2%, alternatively less than 1% of thickness, h.
  • the "warping" is the differences between maximum and minimum distances of the median surface of the 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 F1390 - 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 20%, alternatively less than 10%, alternatively less than 5%, alternatively less than 3%, alternatively less than 2%, alternatively less than 1% of thickness, h.
  • 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 20%, alternatively less than 10%), alternatively less than 5%, alternatively less than 3%, alternatively less than 2%, alternatively less than 1% of thickness, h.
  • the "dislocation density" (DD) of the free standing Film 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.
  • 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 PS 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 present Film.
  • the DD typically is ⁇
  • 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.
  • the Film PSM may be characterizable by any one or more of the product-by- process limitations imparted by the method and/or undercooling 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 (°K), 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 PSM , 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 undercooling surface of the undercooling 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 undercooling surface of the undercooling 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 undercooling 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 undercooling surface of the first undercooling mold and with the undercooling surface of the second undercooling mold.
  • the second undercooling mold is spaced apart from the first undercooling mold by the at least partial remelt so as to comprise a laminate.
  • the laminate may comprise a bottom layer that is the first undercooling mold, an inner layer that is the at least partial remelt, and an upper layer that is the second undercooling 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 (LED, 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.
  • Non-limiting examples of the invention follow. They illustrate some specific embodiments and aforementioned advantages. The invention provides additional embodiments that incorporate any one limitation, alternatively any two limitations, of the Examples, which limitations thereby may serve as a basis for amending claims.
  • Test Method 1 used to determine whether any undercooling 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 PSM and/or such that maximum height Rz of the mounds of grains of the natural-side surface of the Film PSM is less than 50 percent of the thickness of the Film PSM , wherein Rz is determined as for Rx of ISO 12085 (1996).
  • thickness e.g., h, 81
  • 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, Ts, of the Si melt is 1450 °C; initial bulk temperature, T of the undercooling mold is 1190 °C; the apparatus is the draw-down 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 undercooling mold, with first undercooling 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 PSM of polycrystalline silicon is 300 microns.
  • Example (Ex) A: Fig. 5 is a gray-scale confocal microscopy image of an example of the undercooling mold 500 having a first undercooling surface (the area within square-shaped undercooling mold 500) consisting essentially of a plurality of hemispherical-shaped raised contact points 520 disposed on basal surface 510 in an "square-corner array.”
  • Undercooling mold 500 consists essentially of graphite (i.e., lacking a surface layer of SiC) and was prepared by laser-etching away portions of a continuous layer of graphite to remove material down to basal surface 510 and leaving behind material that consist essentially of the raised contact points 520.
  • Undercooling mold 500 was 130 mm long by 100 mm wide, of which the portion used to measure average distance AR was 3.5 mm long by 2.8 mm wide.
  • the average distance AR between raised contact points 520 was 200 microns by ISO 12085. Removing the material created "valleys" between raised contact points 520 that were believed to be filled with inert gas during the method to become gas pockets.
  • Raised contact points 520 were disposed above basal surface 510, which is at maximum depth Rx (not indicated) of from 30 to 70 microns as determined by ISO 12085 (1996). Undercooling surface was 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 prepared by the method adapted to the general method of US 2009/0044925 Al.
  • a graphite undercooling mold e.g., a graphite embodiment of 120, 320, 520, or 820 was used that had an undercooling surface (not shown) that had been textured by grinding to give contact points (not shown) that on average were spaced apart from each other by average distance AR of from 100 to 300 ⁇ .
  • Film PSM 700 was obtained by separating Film PSM 90 of Fig. 6D from undercooling mold 100.
  • Film PSM 700 was 130 mm long and 100 mm wide and had a plurality of large crystals (not all shown), including crystal 780 having an L AVG of more than 3 mm and a thickness of about 300 ⁇ .
  • L AVG of the polycrystalline silicon (not indicated) in Film PSM 700 was from 200 to 500 ⁇ .
  • Ex 2 An undercooling mold in accordance with the subject invention is prepared.
  • the undercooling mold comprises a low nucleation potency material in combination with a high nucleation potency material.
  • the low nucleation potency material comprises silicon dioxide (Si0 2 ) and the high nucleation potency material comprises silicon carbide (SiC).
  • the undercooling 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 PVA 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 of the hardened layer.
  • the silicon dioxide (Si0 2 ) layer ultimately acts as a binder between the silicon nitride (Si 3 N 4 ) particles and as the low nucleation potency material that ultimately contacts a melt of semiconducting material.
  • Fig. 9 is a gray-scale microscopic photograph of the undercooling mold prepared in Ex 2. The presence of the silicon dioxide (Si0 2 ) layer on the silicon carbide changes surface properties of the undercooling mold of Ex 2 to low nucleation potency because Si0 2 is a LNP material.
  • the low nucleation potency mold comprises graphite. Although graphite is a relatively poor wetting material for liquid semiconductors, and is a low nucleation potency material, graphite is also reactive with certain liquid semiconductors, e.g. liquid silicon. To this end, graphite generally reacts in the presence of liquid silicon to form silicon carbide (SiC).
  • SiC silicon carbide
  • SiC was characterized as a high nucleation potency material by Beaudhuin et al. (M. Beaudhuin , G. Chichignoud, P. Bertho, T. Duffar, M. Lemiti, K. Zaidat, Carbon reaction with levitated silicon - Experimental and thermodynamic approaches, 2012 Materials Chemistry and Physics 133 (2012) 284- 288).
  • Beaudhuin et al. M. Beaudhuin , G. Chichignoud, P. Bertho, T. Duffar, M. Lemiti, K. Zaidat, Carbon reaction with levitated silicon - Experimental and thermodynamic approaches, 2012 Materials Chemistry and Physics 133 (2012) 284- 288).
  • under-cooling of more than 17 K could not be reached for electromagnetic levitated liquid silicon intentionally contaminated with C, due to SiC formation and silicon nucleation.
  • the kinetics of this reaction are slow relative to the time of contact between a melt of semiconductor material, e.g. liquid silicon, therefore a graphite mold
  • Figs. 11a and lib are gray-scale microscopic photographs of a film of silicon 90 having lateral crystal sizes L greater than a thickness h of the film of silicon 90.
  • the film of silicon 90 illustrated in Figs. 11a and lib was grown on an undercooling mold comprising graphite as the LNP material.
  • Fig. lib is an enlarged gray-scale microscopic photograph of the cross-section of the film of silicon 90 of Fig.11a.
  • the visible black lines in the film of silicon 90 of Figs. 11a and lib indicates that enhanced lateral crystal growth velocity is based upon a twin assisted growth mechanism.
  • the lateral crystal sizes L as compared to thickness h in Figs.11a and lib demonstrate the effectiveness of the undercooling molds of the invention in preparing films of semiconductor materials.
  • Fig. 12 is a gray-scale microscopic photograph of a top view of a film of silicon 90 grown on a mold comprising a low nucleation potency material and having grain boundaries visualized via a grain boundary etch.
  • the film of silicon 90 of Fig. 12 was grown on an undercooling mold comprising graphite as the LNP material.
  • the large area without grain boundaries in the film of silicon of Fig. 12 demonstrates enhanced lateral crystal growth in the film of silicon 90.
  • the large grain boundary free area in comparison to a film thickness of 300 ⁇ also demonstrates the effectiveness of the invention.

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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 de surfusion qui sont utiles dans le procédé, et un dispositif électronique comprenant ou préparé à partir du film. Un moule de surfusion comprenant une première surface de surfusion configurée avec des points de contact essentiellement constitués d'un matériau à faible pouvoir de nucléation pour la surfusion localisée et le moule de surfusion est caractérisable comme étant utile pour favoriser la croissance latérale d'un film de silicium polycristallin à partir d'une matière fondue du silicium selon la méthode d'essai 1 de sorte que la taille de grain latérale moyenne des cristaux soit supérieure à 2 fois l'épaisseur du film, et la taille de grain latérale moyenne est mesurée conformément à l'ASTM E112-10.
PCT/IB2013/001372 2012-06-27 2013-06-27 Film de matériau semi-conducteur polycristallin, procédé de fabrication de celui-ci et moules de surfusion pour celui-ci, et dispositif électronique WO2014001888A1 (fr)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108556088A (zh) * 2017-12-20 2018-09-21 浙江云峰莫干山装饰建材有限公司 一种重组装饰材铁质模具的维修方法
CN111646475A (zh) * 2020-06-03 2020-09-11 洛阳中硅高科技有限公司 一体式石墨底座和电子级多晶硅生产系统
CN115008777A (zh) * 2022-06-10 2022-09-06 安徽省国盛量子科技有限公司 一种温度传感宽场探头的制作方法

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