Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
  • C01B33/021—Preparation
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
  • C01B33/037—Purification
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
  • C23C4/123—Spraying molten metal
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/18—After-treatment

Definitions

• the present invention relates to the field of the preparation of silicon (Si) of high quality / purity, especially photovoltaic quality (PV), from sawing sludge.
• Si silicon
• PV photovoltaic quality
• Si silicon
• PV photovoltaic
• a preferred way to develop the basic silicon elements derives from the purification of metallurgical Si.
• the ingots from the successive phases of purification are then cut into slices. This step leads to a production of purified silicon waste, mixed with cutting agents (from the saw, for example SiC, diamond, ...) and lubricants.
• the estimate of the level of waste can reach 50%.
• the acid treatment process emits liquid effluents that will have to be treated.
• the product formed is a purified silicon powder, more or less coarse.
• the present invention relates to the use of thermal plasma for the purification of silicon from sawing sludge.
• the plasma is an inductive thermal plasma.
• sawing sludge in particular partly purified, is meant silicon particles mainly obtained from purified silicon ingots added contaminants from the tool that was used to saw the ingot, in particular carbon, iron, SiC ...
• Silicon powders (Si) generally have an average grain size of between 0.1 and 10 micrometers.
• Plasma technique allows to deposit a material (“feedstock”), typically a powder, a liquid or a suspension, by introducing it into a plasma jet, emanating from a plasma torch. In the jet, the material is melted and propelled to a substrate. The melted droplets solidify rapidly and form a deposit on the substrate.
• feedstock typically a powder, a liquid or a suspension
• the plasma jet can be generated in two ways:
• DC plasma direct current
• inductive plasma or RF high-frequency inductive coupling or radio frequency
• the sawing sludge is advantageously treated by inductive thermal plasma or RF, which offers the possibility of a larger volume of treatment and a higher level of purity.
• the corresponding plasma device is considered as a high temperature chemical reactor that can be the seat of physical transformations (fusion, evaporation, condensation, purification) and chemical reactions (synthesis, reduction, oxidation, introduction or separation of doping elements).
• fusion, evaporation, condensation, purification physical transformations
• chemical reactions synthesis, reduction, oxidation, introduction or separation of doping elements.
• the control of plasma process parameters makes it possible to determine the purity levels of the silicon obtained.
• the advantage of the use of the inductive thermal plasma is to be able to feed a large quantity (flow) of "feedstock", unlike a thermal plasma generated by direct current.
• the thermal plasma is a method for removing impurities without leaving residues.
• the degree of purity of the silicon deposited depends on the parameters of the applied plasma.
• the purity of the deposited silicon is such that it can be used in photovoltaics or in microelectronics.
• the invention thus provides a relatively simple, effective and fast way to recycle or reuse these sludge, by extracting or purifying the silicon present therein.
• the present invention relates to a method of forming a silicon deposit on a substrate which comprises the following steps:
• the sawing sludge containing silicon does not undergo any prior treatment stage including purification, before being subjected to thermal plasma.
• the method according to the invention allows, simultaneously and concomitantly via the thermal plasma, the purification of sawing sludge containing silicon and the formation of a silicon deposit on a substrate.
• the thermal plasma is preferably inductive and is conventionally generated, known to those skilled in the art and explained above.
• the "feedstock” consists essentially of sawing sludge from the sawing of silicon ingots. In practice, it contains silicon dust, as well as residues of the sawing tool, such as iron, SiC, carbon.
• the plasma is applied to this "feedstock" which can be in the form of a solid or a suspension.
• the sawing sludge is mixed with a solvent, preferably hydrogenated water, before being subjected to plasma.
• a solvent preferably hydrogenated water
• the addition of solvent makes it possible to adjust the viscosity of the "feedstock".
• several methods of introducing the "feedstock" into the plasma are possible.
• the biphasic mixture liquid or solvent + fines derived from the sawing
• the biphasic mixture is atomized with a gas of at least one atom.
• atomization such as, for example, argon, or helium, optionally supplemented with hydrogen at a level of 10% by volume, in an atomization probe, so as to obtain drops formed of the solvent and silicon microparticles.
• the reducing gas mixture employed is particularly useful for reducing SiC.
• it is brought into the plasma center via a propellant of the same nature as before.
• the material in the presence in this case the silicon microparticles, is melted and propelled towards a substrate.
• a solvent In the case where a solvent has been added, it evaporates.
• the melted droplets solidify and form a deposit on the substrate, according to the principle of thermal spraying.
• the substrate may consist of a silicon ingot.
• the substrate may be made of a refractory material, advantageously chosen from the following group: molybdenum (Mo), tantalum (Ta), and tungsten (W) and their alloys.
• Mo molybdenum
• Ta tantalum
• W tungsten
• the silicon deposit obtained is advantageously separated or extracted from the substrate, which then plays the role of support.
• the substrate is cooled for example by being supported by a copper substrate holder traversed by a water cooling circuit.
• the silicon deposition is subjected to the application of a plasma jet, allowing its recrystallization in situ.
• the substrate may be subjected to rotational or lateral movement.
• the plasma jet can be implemented in the same way as previously during the purification step using the same apparatus.
• all the steps of purification and possible recrystallization can be carried out in the same enclosure.
• Preferably, for this recrystallization step use will be made of a mixture of argon and hydrogen H 2 gas.
• the method according to the invention thus makes it possible to enrich said ingots.
• the present invention provides a solution for reinjecting the sludge by-product sludge into the PV cell manufacturing die.
• the method according to the invention makes it possible to manufacture silicon wafers.
• the parameters of the applied plasma allow the control of the characteristics of the deposited deposit.
• the invention allows the manufacture of silicon wafers of thickness between 100 and 300 ⁇ , of controlled thickness.
• Figure 1 illustrates a device and a method for reloading silicon ingots through the passage of sawing sludge in an inductive thermal plasma.
• FIG. 2 illustrates a device and a method allowing the production of silicon wafers by the passage of sawing sludge in an inductive thermal plasma.
• FIG. 3 illustrates a device and a method enabling the crystallization, by in situ heat treatment by plasma, of silicon wafers obtained by the passage of sawing sludge in an inductive thermal plasma.
• the substrate (2) is a silicon ingot
• the silicon ingot is enriched or recharged in silicon.
• the inductive thermal plasma device comprises the following elements:
• a plasma jet 4 for example with argon and with hydrogen (Ar / H 2 ).
• an atomization probe 5 is provided in the case of injection into the center of the plasma by atomization.
• the plasma device thus constituted is fed by the "feedstock" 1, constituted in this case by the recovered sludge.
• a solvent preferably hydrogenated water, is added to adjust the viscosity to the appropriate conditions for atomization.
• the biphasic mixture (liquid and fines from the sawing phase, the liquid corresponding to the residual liquid initially contained in the sawing sludge to which a solvent can be added to control the viscosity) is injected into the center plasma, either by atomization, as described in US 5,609,921, or via a propellant, depending on the viscosity.
• an atomizing gas is added to the mixture which then passes into the atomization probe 5. Droplets comprising solvent and silicon microparticles are thus formed.
• the purpose of the atomizing gas is to split the continuous flow of sludge (possibly with added solvent) into microdroplets. As previously explained, due to having finely divided flavors, the heat treatment in the plasma is more effective.
• the atomization probe is the device that allows the meeting of the gas flow (atomizing gas) and the liquid vein (sludge) to form the droplets.
• the method according to the invention has a second application: as illustrated in FIG. 2, it allows the direct production of Si plates from sawing sludges from Si ingots.
• the sludge is introduced into the inductive plasma by atomization and then the Si melted by the plasma is recovered on a substrate 2 'to form a thin Si plate (6 ), generally between 100 and 300 ⁇ .
• the essential difference with respect to the previous example is the nature of the substrate 2 'which is no longer a silicon ingot but a support / substrate planar or not, preferably of a refractory nature. In this way, the formed Si plate 6 does not adhere to the support / substrate of refractory material chosen for its properties of non reactivity with Si.
• the substrate of refractory nature is itself cooled so that possible chemical reactions with the molten silicon during the deposition on the substrate are avoided.
• a subsequent step is to extract the formed Si plate 6 from its support 2 '.
• This step consists in scanning the Si 6 plate by the plasma jet 4.
• This treatment thermal offers the advantage of recrystallizing the grains of Si that constitute the plate, by adjusting their size as a function of the passage time of the plasma jet on the surface, but also according to the intrinsic parameters of the plasma (power, composition and flow rates of the gases plasmagenes).
• this step it is possible to animate the substrate or support V in a lateral or rotational movement.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Inorganic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Silicon Compounds (AREA)

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• 2010
  • 2010-07-30 FR FR1056299A patent/FR2963337B1/fr not_active Expired - Fee Related
• 2011
  • 2011-06-10 EP EP11735480.3A patent/EP2598439A1/de not_active Withdrawn
  • 2011-06-10 WO PCT/FR2011/051331 patent/WO2012013876A1/fr active Application Filing
• 2013
  • 2013-01-28 US US13/751,497 patent/US20130139550A1/en not_active Abandoned

Non-Patent Citations (1)

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