Classifications

• • 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
• • 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
  • C30B15/20—Controlling or regulating
  • C30B15/22—Stabilisation or shape controlling of the molten zone near the pulled crystal; Controlling the section of the crystal
• • 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
  • C30B15/34—Edge-defined film-fed crystal-growth using dies or slits
• • 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
  • C30B29/08—Germanium
• • 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
  • C30B29/10—Inorganic compounds or compositions
  • C30B29/40—AIIIBV compounds wherein A is B, Al, Ga, In or Tl and B is N, P, As, Sb or Bi
  • C30B29/42—Gallium arsenide
• • 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

Definitions

• the subject of the present invention is a method for drawing semiconductor tapes, in particular polycrystalline silicon, of small thickness from a molten silicon bath.
• the most used semiconductor ribbons are polycrystalline silicon ribbons.
• the following description therefore relates to silicon ribbons, but bearing in mind that the invention also relates to ribbons of other semi-conductive materials, such as for example germanium or gallium arsenide.
• a strip of thin thickness and generally of carbon scrolls vertically, from bottom to top and at a constant speed, in a bath of molten silicon.
• a thin layer of silicon is deposited on each of the two faces of the carbon band.
• the strip emerging from the bath is a composite strip consisting of a carbon core inserted between two layers of silicon.
• the carbon core is subsequently removed by burning in a high temperature oven.
• two silicon strips of small thickness are obtained which are cut into plates.
• the RST process is for example described in patents FR 2,386,359, FR 2,550,965 and FR 2,561,139.
• the other method, the method STR is illustrated schematically in FIG. 1.
• a draft crucible 10 contains a molten silicon bath 12.
• the bottom of the crucible is pierced with two orifices through which penetrate two filaments 14 and 16 parallel, vertical and spaced from each other. These filaments scroll at a constant speed, from bottom to top, in the silicon bath.
• a seed initially allows crystallization of the silicon to begin between the two filaments on the surface of the silicon bath.
• a self-supporting ribbon 18 can then be pulled between the two filaments, which serve to stabilize or anchor the edges of the ribbon.
• the growth of the ribbon 18 is developed by the meniscus 20 which is formed by capillarity over a height of about 7 mm above the surface of the silicon bath between the filaments 14 and 16.
• Patent application WO 2004/035877 describes a form of implementation of the STR method, as well as means for reducing or eliminating the meniscus deformation that sometimes occurs.
• the STR method has other disadvantages. For example, it has low productivity due to its low draw speed, of the order of 1.7 cm / min. Beyond this pulling speed occurs a warpage of the ribbon due to thermal stresses that deform the surface of the silicon ribbon. It was then proposed to perform in parallel several draws in the same building. However, the parallel draw is hampered by the problem of interference between free liquid menisci. Indeed, menisci tend to attract to reduce surface energy, which leads to flatness defects ribbons. This problem is partly solved by the patent application WO 2004/042122 A1, at the cost of a complication of the method, with the establishment around the ribbons of control elements of the shape of the meniscus in the lateral part of the ribbon .
• STR system Another disadvantage of the STR system lies in the fact that in practice the thickness of the ribbon is hardly less than 250 micrometers. Below this thickness, the silicon ribbon becomes left and fragile and is difficult to handle in the steps of manufacturing photovoltaic cells.
• the STR process includes a priming phase, germination, which is critical and delicate at the start of the ribbon draw or restart after accidental breaks in the liquid meniscus.
• the present invention aims to improve the STR method by overcoming one or more of the aforementioned drawbacks.
• the invention relates to a method of drawing at least one ribbon of a semiconductor material in which two parallel filaments spaced from each other pass vertically, from bottom to top and continuously the surface of a bath of said molten semiconductor material, said ribbon being formed from a meniscus located between said filaments and substantially at said surface.
• a support strip is interposed between the filaments and contained in the plane defined by the filaments, the support strip traversing vertically, from bottom to top and continuously, the bath surface of the molten semiconductor material to the same speed of travel as the filaments, the ribbon of semiconductor material forming on one of the two faces of the support strip and being supported by said face.
• the filaments are carbon or silica and their diameter is between 0.3 and 1 mm. They can be covered with a thin layer of pyrolytic graphite.
• the support strip is carbon and its thickness is between 200 and 350 microns.
• the molten semiconductor material is contained in a drawing crucible provided with a substantially horizontal bottom, said bottom comprising a slot through which the support strip and the filaments penetrate.
• the slot preferably has a rectangular horizontal section whose width is slightly greater than the thickness of the support strip and, at each of the two ends of the rectangular section, a circular horizontal section through which the filaments pass.
• the semiconductor material may be based on a semiconductor element such as silicon or germanium or a congruent or quasi-congruent semiconductor compound, such as, for example, gallium arsenide.
• FIG. 1 schematically illustrates the method STR according to the prior art
• FIG. 2 illustrates the method according to the present invention
• FIGS. 3 and 4 show, in horizontal section along horizontal planes at heights respectively indicated by III and IV in FIG. 2, the two filaments and the two semiconductor ribbons, silicon in the example described, surrounding the carbon support band;
• FIG. 5 shows schematically in horizontal section the slot of the draft crucible through which pass the support strip and the filaments.
• a support band preferably made of carbon, is used in the STR method while retaining the two filaments of carbon.
• the support strip has the effect of reinforcing the anchoring of the liquid silicon meniscus on the edges of the strip by wetting effect.
• the drawing crucible made for example of silica or carbon, is filled with silicon made liquid by raising its temperature.
• the support strip is contained in the vertical plane defined by the two longitudinal axes of symmetry of the filaments 24 and 26 (which have a substantially cylindrical shape but not necessarily a revolution, a rectangular section for example being possible).
• This slot 28, also shown in horizontal section in Figure 5, has the shape of an elongated rectangle 30 terminated at each of its two ends by a circular surface 32 or 34.
• the width of the rectangle 30 is slightly greater than the width of the support strip 22 and the diameter of the circular surfaces 32 and 34 is slightly greater than the diameter of the filaments so that the support strip 22 and the two filaments 24 and 26 pass through the slot 28.
• the distance between the edges of the slot 28 of the support strip 22 and filaments 24-26 is such that the molten silicon contained in the crucible does not flow through the slot.
• the width of the section rectangular 30 of the slot may be of the order of 600 micrometers and the diameter of the circular sections 32-34 of the order of 1 mm.
• the support strip 22 and the filaments 24-26 pass through the slot 28 and pass vertically, from bottom to top, the drawing crucible filled with liquid silicon. Unrepresented means pull vertically at a constant speed the assembly formed by the strip 22 and the filaments 24-26, in the direction of the arrow 36.
• the drawing speed can reach values close to 5 cm / min, without appearance of effect of warping of the surfaces of the composite, for silicon strips of about 200 microns thick and 10 cm / min for ribbons of about 80 microns thick.
• the maximum draw speed in the conventional STR process is about 1.7 cm / min, so about 3 to 6 times lower.
• a meniscus is formed at the junction 38 of the surface of the liquid silicon with the support strip 22 and the filaments 24-26.
• FIGS 3 and 4 show in section, in horizontal planes at heights respectively indicated by III and IV relative to the silicon bath, the shapes of the ribbons 40 and 42 adhering to the support strip 22 and 24-26 filaments.
• the silicon has cooled and crystallized to form the silicon ribbons while at the height of the IV plane, at a height of a few millimeters (typically less than 6 mm) relative to the surface of the molten silicon, the silicon 44 is not yet solidified and forms a meniscus.
• the filaments 24 and 26 are identical, made of carbon or silica, optionally coated with pyrolytic graphite, and their diameter is between 0.3 and 1 mm. They are spaced from the edges of the support strip 22 by about 100 microns so as to prevent any contact likely to deform the support strip.
• the thickness of the support strip 22 is between 200 and 350 microns, preferably between 200 and 300 microns.
• This support strip is preferably made of carbon, for example flexible graphite made from expanded natural graphite and then rolled.
• the support strip 22 may be delivered in rolls one meter in width and several hundred meters in length. However, for the embodiment described here, a width, for example between five and twenty centimeters, is preferably used. After drawing, a composite strip is obtained consisting of the support strip 22, the two filaments 24-26 and the two silicon strips 40-42 supported by the support strip and the filaments.
• the next step is firstly, by means of a laser for example, to cut into composite plates, generally rectangular, the composite strip and to cut the edges of the composite strip or composite plates so as to expose the song of carbon ribbons.
• the filaments 24-26 are thus eliminated.
• the support band 22 is destroyed by burning, for example in air, at high temperature (about 1000 ° C) to obtain two polycrystalline silicon plates.
• the faces of the plates, previously free or located opposite the support strip 22, then undergo a light etching to remove the oxide layer, silica, which is formed on the surface.
• This oxidized layer is very thin, of the order of a few tenths of a micrometer. Stripping can be done by various conventional routes.
• the support band thanks to its thermophysical characteristics, brings additional advantages to the conventional two-filament STR process, which avoids or minimizes the formation of a composite strip with left surfaces. Indeed, on the one hand, the participation of the support band in the extraction of the latent heat of crystallization relatively decreases the temperature gradient in the silicon band at the level of the crystallization front, which delays the appearance of the phenomenon.
• the presence of the support strip in the draft crucible divides by two the width of the molten silicon bath, which attenuates the thermal convection currents that tend to develop in the bath and as a consequence the displacement of the isotherm of crystallization that they can induce.
• the presence of the support strip considerably reduces the possibility of displacement of the crystallization meniscus due to the disturbances that it undergoes by the variations of the connection angle of the liquid surface with the walls of the impression crucible and / or by the presence of a neighboring meniscus when several ribbons are drawn simultaneously from the same molten silicon bath.
• the presence of the support band physically maintains the point of attachment of the liquid meniscus in an almost fixed vertical plane, with a possibility of displacement in a direction perpendicular to the support band typically less than ⁇ 100 micrometers.
• the present invention therefore makes it possible, compared with the conventional STR method, to obtain silicon ribbons of smaller thickness, for example less than 150 micrometers, with better flatness and at higher draw speeds (and therefore with higher productivity).
• the invention is therefore particularly well suited to the production of photovoltaic cells by using the silicon ribbons thus produced.
• a single ribbon can be produced, instead of two simultaneously, by preventing the deposition of silicon on one of the two faces of the support strip.
• the support strip and the two filaments do not penetrate into the silicon bath by the bottom of the frame but by the side walls or dive directly into the bath from above and, by a return mechanism, also emerge from the top of the bath.

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• Chemical & Material Sciences (AREA)
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• Power Engineering (AREA)
• Inorganic Chemistry (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Silicon Compounds (AREA)

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• 2005
  • 2005-04-22 FR FR0551032A patent/FR2884834B1/fr not_active Expired - Fee Related
• 2006
  • 2006-03-01 WO PCT/FR2006/050185 patent/WO2006111668A1/fr active Application Filing
  • 2006-03-01 EP EP06726209A patent/EP1871926A1/de not_active Withdrawn
  • 2006-03-01 JP JP2008507134A patent/JP2008536793A/ja active Pending
  • 2006-03-01 US US11/884,242 patent/US20090050051A1/en not_active Abandoned
  • 2006-03-01 AU AU2006238527A patent/AU2006238527A1/en not_active Abandoned
  • 2006-03-01 CN CNA2006800059155A patent/CN101128625A/zh active Pending

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