Silicon granule for preparation of trichlorosilane and associated production method

Abstract

To provide a production method for silicon granules that are brought about by reusing waste generated when cutting silicon ingots and are particularly suitable for preparing trichlorosilane.SOLUTION: The production method comprises: a) a step of supplying silicon waste derived from substrates, wherein the waste comprises silicon particles covered with an insulating or metal surface layer; b) a step of chemically treating the silicon waste to remove the insulating or metal surface layer and drying the silicon particles to form a powder; c) a step of metallurgically treating the powder to melt the silicon particles and form a liquid silicon bath; d) a step of introducing at least one co-catalyst into the liquid silicon bath; and e) a step of solidifying the liquid silicon to form silicon granules, wherein the silicon granules comprise a size of 10 to 500 μm, a dopant comprising phosphorus or boron each having a mass fraction of less than 5 ppm, a co-catalyst having a mass fraction of 1 to 2500 ppm, and metal impurities excluding the co-catalyst and having a mass fraction of less than 50 ppm.SELECTED DRAWING: None

Description

Detailed Description of the Invention

[0001] [Field of the Invention] The present invention relates to silicon production lines for the photovoltaic industry. In particular, the present invention relates to silicon granules produced by recycling waste ("kerf") from sawing silicon ingots and which are particularly suitable for the preparation of trichlorosilane (TCS).

[0002] [Technical Background of the Invention] The production chain for the high purity silicon required for the photovoltaic industry is a series of complex metallurgical and chemical processes.

[0003] The initial material, metallurgical silicon (MG-Si, for "metallurgical grade silicon"), results from the carbo-reduction reaction of quartz mixed with a highly reactive reducing agent such as anthracite or charcoal, always accompanied by wood. The mixture is brought to extremely high temperatures in an electric arc furnace. The mixture undergoes various refinements until solidified metallurgical silicon is obtained, either in the form of ingots that will later be crushed, or in the form of granules with an average diameter of several hundred microns. Metallurgical silicon has many impurities, including: Impurities of metallic type (Fe, Al, C, Ti, etc.) in proportions well above 200 ppm (ppm: parts per million by mass), Doping type impurities, such as phosphorus (P) and boron (B), in proportions higher than 20 ppm; Impurities of organic (C) or oxygen (O) type in proportions higher than 100 ppm.

[0004] Since this concentration of impurities is incompatible with the specifications for photovoltaic silicon, the metallurgical silicon granules or fragments are chemically treated by chlorination or hydrochlorination, and at the end of the chemical process by chlorination or hydrochlorination, the following gaseous compound containing silicon is obtained: trichlorosilane (HSiCl3, also known as TCS).

[0005] The chlorination process is carried out in a fluidized bed reactor, where granular or pulverized MG-Si is contacted with hydrogen chloride gas. The temperature and pressure of the reactor are about 300°C and 4 bar, respectively. At the end of the chlorination process, TCS is formed in the majority, and silicon tetrachloride (STC) and other chlorinated compounds containing silicon or impurities are also formed.

[0006] An alternative hydrochlorination process is also carried out in a fluidized bed reactor at higher temperatures and pressures (450°C, 10-50 bar). Granular or crushed metallurgical silicon is contacted with STC (SiCl) and hydrogen. At the outlet, TCS is formed at a lower rate compared to the chlorination reaction, and other chlorinated compounds containing silicon or impurities are also produced.

[0007] The "impure" TCS from either the chlorination or hydrochlorination process is then purified by a series of distillation steps, which are very long and impose a large burden of investment and operating costs in the silicon production chain. In particular, dopant-type impurities (P, B) are very difficult to remove, and a high reflux ratio (typically higher than 100) in the distillation column is required to achieve the required purity of TCS.

[0008] The purified TCS can then be converted into high purity silicon fragments or grains that constitute the feedstock for pulling photovoltaic quality (PV) ingots, commonly referred to as PCS (polycrystalline silicon).

[0009] The first means for forming PCS consists of decomposing TCS at high temperatures (approximately 1200°C) in a Siemens Bell Reactor ("bell jar reactor"); silicon is gradually deposited on a filament placed inside the reactor, and at the end of the process, a silicon bar is formed with a typical purity of 6N (>99.9999%) to 11N. The high-purity bar is then crushed to obtain large pieces ("chunks") of silicon that will be melted to pull ingots.

[0010] An alternative route involves converting TCS to monosilane (SiH4) and then decomposing the monosilane in a fluidized bed reactor. SiH4, placed in contact with the fine silicon seeds, allows for the formation of high-purity silicon grains. Silicon grains larger than 400 microns can be melted together in chunks to pull photovoltaic-grade ingots. Silicon grains smaller than 400 microns, roughly 10% of production, cannot be used, particularly because their ejection is incompatible with the electrical and mechanical components of the ingot-pulling equipment, as well as because of the high percentage of oxides that reduce the efficiency of the pulling process.

[0011] The PV-grade silicon ingot then undergoes several cutting steps: a first step to cut the ingot blank to define rectangular blocks, and a second step to cut the ingot into slices, which is responsible for a significant loss (kerf) of about 40-50% of the high-purity silicon raw material.

[0012] Traditionally, cutting is carried out by sawing using a SiC-based abrasive and an organic lubricant (PEG, polyethylene glycol). Document WO 2010127669 provides a solution for recycling the kerf from this type of cutting. According to the method described, the solid components of the kerf, including the silicon fraction with the required purity, are compressed and formed into granules with a suitable size; the granules with a suitable size are then introduced into a reactor containing hydrogen chloride to obtain trichlorosilane (TCS) and silicon tetrachloride, the iron components of the kerf being converted into iron chloride, while the SiC fraction present collects in the form of dust at the bottom of the reactor.

[0013] In practice, kerfs containing a high amount of SiC (more than two-thirds) compared to silicon are very difficult to process, complicating the industrial implementation of the proposed solution. The agglomeration of fine particles (called "fines") by binders is ineffective at reaction temperatures, and said fine particles quickly exit the fluidized bed. Finally, the accumulation of SiC slows down the reactor productivity very quickly.

[0014] For several years, the cutting of PV-grade silicon ingots has been carried out using a diamond wire and water or PEG used as a lubricant. The waste product (kerf) consists mainly of silicon, with some impurities associated with the wear of the diamond wire. Therefore, there is growing interest in recovering and reusing these kerfs and reintroducing the silicon they contain into the photovoltaic silicon production chain.

[0015] [Subject of the Invention] The present invention relates to an alternative solution for recycling silicon waste. The present invention particularly relates to silicon granules resulting from the recycling of kerf and particularly suitable for preparing TCS. The present invention also relates to a manufacturing method for the silicon granules.

[0016] [Brief description of the invention] The present invention relates to silicon granules having a size of 10 to 500 microns, in particular silicon granules suitable for preparing trichlorosilane (TCS), a mass fraction of less than 5 ppm of a dopant comprising phosphorus or boron; At least one cocatalyst selected from iron, aluminum, and calcium in a mass fraction of 1 to 2500 ppm; a mass fraction of less than 50 ppm of metal impurities, excluding said at least one cocatalyst; The present invention relates to a silicon granule comprising:

[0017] According to other advantageous and non-limiting features of the present invention, taken alone or in combination: The mass fraction of oxygen is less than 100 ppm.

[0018] The present invention also relates to a powder preparation comprising the silicon granules as described above, wherein the average size of the silicon granules in the powder preparation is between 50 and 400 microns.

[0019] According to a particular embodiment, the size of the silicon granules in the powder preparation is greater than 50 microns.

[0020] The present invention also provides a manufacturing method for the silicon granules as described above, comprising: a) providing silicon waste from cutting photovoltaic quality ingots with diamond wire, said waste comprising silicon particles covered with an oxide layer and mixed with impurities in an aqueous medium, and / or providing silicon waste crushed from downgraded substrates from the microelectronics or photovoltaic industry, said waste comprising silicon particles covered with an oxide layer and mixed with impurities; b) chemically treating the waste material to separate the silicon particles from all or some of the impurities and drying the silicon particles to form a powder; c) metallurgically processing the powder to melt the silicon particles and form a liquid silicon bath; d) introducing at least one co-catalyst into the liquid silicon bath in an amount such that the mass fraction of the co-catalyst in the silicon granules is between 1 and 2500 ppm; e) solidifying the liquid silicone to form silicone granules; The present invention relates to a manufacturing method including:

[0021] According to other advantageous, non-limiting features of the present invention, taken alone or in any technically feasible combination: Step e) comprises granulating the liquid silicon droplets by rapid cooling; Step e) includes pouring the liquid silicon into an ingot mold configured to allow rapid cooling to form a block of solidified silicon; The solidified silicon block is crushed to form silicon granules, The method comprises a step f) of sorting the silicon granules by size by separating them by sieving or flight, In step d), at least one co-catalyst selected from iron, aluminum and calcium is introduced into the liquid silicon bath in the form of a metal or metal alloy, Step a) comprises providing silicon granules with a size of less than 400 microns resulting from a fluidized bed reactor based on the decomposition of monosilane, and mixing the silicon granules with silicon waste; In step c), silicon particles with a size of less than 400 microns resulting from the fluidized bed reactor based on the decomposition of monosilane are melted together with a powder of silicon particles, Step a) comprises providing downgraded substrates from the microelectronics or photovoltaic industry, crushed and mixed with silicon waste resulting from the sawing of photovoltaic quality ingots with diamond wire, In step c), crushed fragments of downgraded substrates from the microelectronics or photovoltaic industry are fused with a powder of silicon particles.

[0022] Finally, the present invention relates to a process for obtaining trichlorosilane (TCS) by chlorination or hydrochlorination, which uses a powdery preparation as described above.

[0023] Table 1 shows the typical composition of state-of-the-art metallurgical silicon as determined by optical emission discharge mass spectrometry; Tables 2a, 2b, and 2c show examples of compositions of silicon granules according to the present invention, as measured by optical emission discharge mass spectrometry. Table 3 shows the typical composition of silicon particles in the powder resulting from the chemical treatment step of the manufacturing method according to the present invention, as determined by optical emission discharge mass spectrometry. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic diagram showing the chemical processing steps of the manufacturing method according to the present invention. [Figure 2] 4 is a graph showing an example of the size distribution of silicon particles in the powder resulting from the chemical treatment step of the manufacturing method according to the present invention.

[0025] [Detailed Description of the Invention] Other features and advantages of the present invention will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.

[0026] The present invention relates to silicon granules specially adapted to optimize the production of trichlorosilane (TCS) in chlorination or hydrochlorination processes.

[0027] The term "granules" in the context of the present invention must be understood in a broad sense, i.e. corresponds to small-sized grains or particles which may have different shapes, in particular spherical, round, rectangular or angular.

[0028] The silicon granules according to the present invention have a size of approximately 10 microns to approximately 500 microns. The so-called granule size here is the "equivalent Sauter diameter" of the silicon granule. The "equivalent Sauter diameter" is the diameter of a sphere that behaves similarly between particle size measurements by a defined technique. In particular, mention may be made by way of example of a measurement technique based on Malvern-type laser diffraction.

[0029] The silicon granules contain small amounts of dopants, in particular phosphorus and boron type dopants, each dopant having a mass fraction of less than 5 ppm. It should be noted that the unit "ppm" (parts per million) is used in the following description to always relate to mass fractions.

[0030] Advantageously, the silicon granules also contain small amounts (less than 5 ppm) of other dopants, such as arsenic, antimony.

[0031] The silicon granules according to the present invention also contain at least one cocatalyst selected from iron, aluminum, and calcium, and the mass fraction of the cocatalyst can be adjusted between 1 and 2500 ppm, preferably between 100 and 2000 ppm. The cocatalyst is an impurity that must be present in the silicon matrix to promote the reaction, particularly the chlorination or hydrochlorination reaction. These cocatalysts generally exist as intermetallic compounds at the grain boundaries of silicon.

[0032] For example, at least one metal impurity other than the cocatalyst, such as titanium, nickel, zinc, chromium, magnesium, manganese, vanadium, etc., is present in the silicon granules in a small amount corresponding to a mass fraction of each impurity of less than 50 ppm, or even less than 30 ppm, or even less than 10 ppm.

[0033] The powder preparations containing silicon granules according to the invention are particularly advantageous for producing TCS by chlorination or hydrochlorination processes, for reasons that will now be explained.

[0034] On the other hand, the low mass fraction of dopants and metal impurities (other than cocatalysts) contained in silicon granules allows for a significant limit on the number of distillation cycles required to purify TCS. It should not be forgotten that distillation of phosphorus and boron compounds is particularly long and complex: granular or crushed metallurgical silicon, commonly used as input material for chlorination or hydrochlorination processes, typically contains 70-100 ppm phosphorus and 50-70 ppm boron (Table 1). Silicon granules according to the present invention contain less than 5 ppm of each of these dopants. Table 2a illustrates an example of the composition of silicon granules according to the present invention, as measured by glow discharge mass spectrometry (GDMS): boron is present at 0.4 ppm and phosphorus at 2 ppm, more than 30 times lower than in metallurgical silicon. Therefore, TCS made from this type of granule is much simpler and faster to purify.

[0035] [Table 1]

[0036] [Table 2]

[0037] On the other hand, the reactivity of the silicon granules in the fluidized bed depends on several parameters other than pressure and temperature during the chlorination and hydrochlorination reactions. In particular: The content of silicon granules in terms of certain "beneficial" impurities that must subsequently be considered as co-catalysts, · In the fluidized bed, the nature and amount of catalyst added to the reaction mass i.e. silicon granules.

[0038] As indicated in the introduction, the following reaction takes place in the chlorination: Si + HCl → TCS + STC + impurities and by-products

[0039] In the hydrochlorination process, the reaction is as follows: Si + 2H2 + 3STC → 4TCS + impurities and by-products.

[0040] The morphology of the intermetallic compounds in the silicon granules and the presence of specific co-catalysts in selected proportions allow for more efficient activation of the chlorination or hydrochlorination chemical reactions.

[0041] In chlorination, the most commonly used catalyst is copper. Furthermore, the aluminum and iron content of the granules of the powder preparation of the present invention is optimized to obtain the maximum reaction rate and highest TCS selectivity.

[0042] Powder preparations suitable for chlorination processes advantageously have a limited iron content, since iron reduces the selectivity of TCS. The granules of the powder preparation may, for example, have the composition of Table 2b.

[0043] [Table 3] In hydrochlorination, the most active cocatalysts are iron and aluminum, and the amount of iron must be significantly higher than in chlorination. Copper is also commonly used to catalyze the reaction.

[0044] For example, a powder preparation suitable for a hydrochlorination process may have the composition of Table 2c. Advantageously, with silicon having a low aluminum content (e.g., 1000 ppm), the copper chloride can be introduced directly into the fluidized bed reactor in the form of microbeads with a d50 of approximately 50 μm to improve the efficiency of the reaction.

[0045] [Table 4]

[0046] The silicon granules according to the invention contain a mass fraction of 1 to 2500 ppm of (at least one) co-catalyst in order to catalyze effectively without unnecessary recontamination of the silicon: therefore, the production process for TCS starting from this type of granules is more efficient and allows a significant increase in energy and production capacity thanks to improved reactivity and faster purification.

[0047] Advantageously, the average size of the silicon granules in the powder preparation is between 50 and 400 microns. The average size, also called d50, means the size larger than and smaller than the size of 50% by volume of the silicon granules.

[0048] The reactivity of silicon granules in a fluidized bed for chlorination or hydrochlorination is also related to the d50 of the silicon granules, depending on the specific surface of the particles. A d50 of 50 to 400 microns is perfectly suitable for the chlorination process.

[0049] For use in hydrochlorination processes, the powder preparation of the present invention contains only silicon granules of a size greater than 50 microns, finer granules being less compatible with hydrochlorination processes for practical reasons, as they clog heat exchangers.

[0050] The silicon granules of the present invention are particularly suitable for the production of TCS by chlorination or hydrochlorination in that the silicon granules have a size and chemical composition that favors the efficiency and reactivity of chlorination and hydrochlorination reactions in a fluidized bed, and also have a low content of "non-reaction useful" dopants and metal impurities (i.e., excluding cocatalysts) that limit subsequent steps for purifying the TCS.

[0051] Suitability therefore results from the size of the silicon granules and their chemical composition, a combination of parameters that can be optimized and adjusted according to the uniqueness of each chlorination or hydrochlorination process.

[0052] According to another advantageous embodiment, the mass fraction of oxygen contained in the silicon granules is less than 100 ppm. The oxygen essentially originates from the oxide layer that normally covers the silicon granules. A thinnest possible oxide layer will promote the reactivity of the chemical reaction in the fluidized bed of the chlorination or hydrochlorination process, since the catalyst will quickly come into contact with the silicon surface and especially the intermetallic compounds (from the cocatalyst).

[0053] In order to maintain a low oxygen content, the powder preparation according to the invention is advantageously packaged under a neutral atmosphere, e.g. nitrogen, thus limiting any contact with oxygen-rich atmospheres that could oxidize the silicon granules.

[0054] The present invention also relates to a manufacturing method for silicon granules.

[0055] The manufacturing method comprises the step a) of providing silicon waste (kerf) resulting from cutting a photovoltaic quality ingot with a diamond wire, said waste comprising silicon particles covered with an oxide layer and mixed in an aqueous medium with impurities, these impurities comprising metal particles and possibly organic additives.

[0056] According to certain embodiments, step a) may also include providing silicon granules from a fluidized bed reactor based on the decomposition of monosilane. Preferably, the silicon granules provided in step a) are granules less than about 400 microns in size, which, as mentioned in the introduction, are less compatible with the process for pulling PV ingots. The silicon granules can be mixed with silicon waste (kerf) in step a) of the process. It should be noted that the silicon granules can alternatively be used alone (without being mixed with kerf) and passed through subsequent stages of the manufacturing method.

[0057] According to another particular method of implementation, step a) can include the supply of degraded substrates from the microelectronics or photovoltaic industry. Degraded substrates refer to silicon-based substrates that have been removed from the production line due to breakage, defects, or other non-conformities, or end-of-life substrates, and can be reused. For example, these degraded substrates can be monocrystalline or polycrystalline silicon wafers, SOI (silicon on insulator) wafers, defective or end-of-life solar panels, etc., containing uniform or patterned insulating or metal layers that form all or part of the components.

[0058] These downgraded substrates can be crushed and continue with subsequent steps of the process according to the invention, or the downgraded substrates can be mixed with silicon waste (kerf) in step a) of the process before continuing with the process steps.

[0059] The manufacturing method then comprises a step b) of chemically treating the material provided in step a) with the aim, on the one hand, to separate the silicon particles from all or some of the impurities and, on the other hand, to dry the silicon particles to form a powder.

[0060] The silicon waste (kerf) is in the form of a roughly 5% suspension of silicon and metal particles in an aqueous liquid supplemented with soluble organic additives, such as PEG. The first operation usually consists of roughly separating the liquid portion, which can potentially be reused in the cutting system. The remaining paste-like mixture then typically contains silicon particles 1 covered with an oxide layer 2 and a layer 3 of organic compounds, as well as metal particles or ions 4 (Fig. 1a). This paste-like mixture then undergoes chemical treatment steps, the order of which is as follows: Dispersing impurities 4, such as particles from the ingot support resulting from cutting with a metal or diamond wire, and organic compounds 3 (Fig. 1b), Filtering the silicon particles 1 from the solid phase to remove liquid and impurities (Fig. 1c), The operation is repeated to obtain an agglomerate of silicon particles that is substantially free of contaminating residues (impurities), treating the agglomerates of silicon particles 1 by "etching" with a chemical solution that minimizes or reduces the oxide layer 2 located on the surface of said particles 1. In particular, a solution based on hydrofluoric acid may be applied to the agglomerates, which may then be subjected to several rinsing cycles with water; The agglomerates are dried under an inert atmosphere to obtain a dry powder, which is advantageously stored under an inert atmosphere.

[0061] These chemical treatment sequences can be carried out in particular according to state-of-the-art chemical processes, such as those described by Lombardi in the publication entitled "High yield recycling process of silicon kerf from diamond wire wafering" (24th European Photovoltaic Solar Energy Conference, September 21-25, 2009, Hamburg, Germany).

[0062] The result of this step b) of the chemical treatment is a fine powder with a substantially Gaussian particle size distribution typically centered on 1 micron (d50 of about 1 micron), as illustrated by way of example in Figure 2. A typical chemical composition of the fine powder is illustrated in Table 3. The purity level of the fine powder is very good: this is because, on the one hand, the silicon particles result from sawing high-purity ingots, and, on the other hand, the chemical treatment makes it possible to separate the silicon particles from most of the impurities present in the sawing waste (metal particles and organic additives).

[0063] [Table 5]

[0064] In a particular embodiment in which degraded substrates are introduced as silicon waste in step a), said degraded substrates may be subjected to a step b) of chemical treatment making it possible to remove all or part of the surface layer to which the substrate is reactive. The chemical treatment step may comprise the known sequence of dry or wet etching of said surface layer, rinsing and drying of the degraded substrate. The substrates will then be crushed and subjected, alone or mixed with a powder of silicon particles obtained from other waste, to the following step c) of the manufacturing method.

[0065] The manufacturing method then includes a step c) of metallurgically treating the fine powder obtained in step b), the purpose of which is to melt the silicon particles of the powder and form a liquid silicon bath.

[0066] The melting of fine silicon particles is complex to carry out industrially. The increase in the specific surface with decreasing d50 and the presence of a highly insulating layer of silicon oxide (SiO2) on the surface of the particles make the operation delicate. Different melting methods have been proposed in the prior art, in particular in documents U.S. Pat. No. 4,354,987 and EP 0,158,563, and may be used in the context of the present invention.

[0067] According to an advantageous embodiment of the invention, the metallurgical processing of the powder is carried out in a melting apparatus equipped with a graphite crucible using induction heating. The temperature of the crucible is raised to approximately 1500°C. Fine powder of silicon particles is introduced into the crucible through the top opening. The silicon forming the particles will melt, flow out of the "shell" formed by the oxide layer, and into a bath of liquid silicon. The oxide remaining in a solid state will agglomerate and float in the liquid silicon bath. At least one orifice provided in the crucible allows a continuous flow of liquid silicon through a channel that achieves this purpose. How the liquid silicon is shaped at the outlet of the channel that achieves this purpose will be explained later.

[0068] According to a particular embodiment, in step c), silicon granules, advantageously of a size less than 400 microns, resulting from the fluidized bed reactor due to the decomposition of monosilane, may be melted together with the silicon particle powder or melted alone, thereby making it possible to effectively reintroduce small silicon granules (10% of the production volume as mentioned in the introduction) into the fluidized bed PV silicon production line.

[0069] The manufacturing method also includes a step d) of introducing into the liquid silicon bath at least one co-catalyst selected from aluminum, iron and calcium, with the aim of optimizing the content of the co-catalyst or co-catalysts in the silicon granules resulting from the manufacturing method.

[0070] The optimization of the co-catalyst content is carried out by controlled addition in the liquid silicon bath, avoiding the addition of dopants (phosphorus and boron) or other metal impurities that are "not beneficial" (especially for the chlorination or hydrochlorination processes) and are not desired in the final PCS silicon. The nature and amount of the co-catalyst(s) introduced depends on the intended use of the silicon granules, especially for chlorination or hydrochlorination, and on the specific conditions for carrying out these processes.

[0071] Step d) makes it possible to use the liquid silicon bath to adjust the nature and amount of the mixed co-catalyst(s) and thus the mass fraction of the co-catalyst(s) in the silicon granules obtained from the production method according to the invention; such adjustment makes it possible to optimize the reaction rate of the chlorination or hydrochlorination process and to increase the selectivity of TCS and the purity of the TCS produced.

[0072] The optimum amount of one or more co-catalysts is advantageously introduced into the liquid silicon bath by addition in the form of metals (Al, Fe) or in the form of alloys (e.g. FeSi, SiCa, etc.).

[0073] At least one cocatalyst is introduced at a concentration of 1 to 2500 ppm by mass of the liquid silicon, i.e., in such an amount that the mass fraction of the cocatalyst in the silicon granules resulting from the production process is 1 to 2500 ppm; advantageously, the mass fraction of the cocatalyst is selected between 100 and 2000 ppm. As previously mentioned, the mass fraction of the cocatalyst in the silicon granules is adjusted according to the specifics of the target chlorination or hydrochlorination process.

[0074] The manufacturing method then comprises a step e) of solidifying the liquid silicon with the aim of forming silicon granules.

[0075] According to a first embodiment, step e) comprises a granulation step by rapid cooling of the liquid silicon droplets leaving the melter channel. The silicon droplets fall onto a cold surface and are subjected to centrifugal force, dispersing them before they re-agglomerate in the powder preparation: solidification (quenching) of the silicon droplets is rapid and ensures a uniform concentration of the co-catalyst(s) as intermetallic compounds in the silicon granules. The size of the silicon granules will essentially depend on the size of the liquid silicon droplets and the speed of centrifugation. The granulation step is carried out under a neutral atmosphere (e.g., argon) to avoid or at least limit oxidation of the silicon granules.

[0076] According to a second embodiment, step e) involves forcing liquid silicon through a melter channel into an ingot mold configured to allow rapid cooling to form a solidified silicon block. In practice, the mold is thick (e.g., 15 cm cast iron A319) while the solidified silicon block is thin (e.g., 5 cm), which ensures rapid cooling and thus a relatively uniform concentration of one or more co-catalysts (in the form of intermetallic compounds) in the solidified silicon block. Step e) then involves crushing the solidified silicon block to form silicon granules under a nitrogen atmosphere.

[0077] The manufacturing method according to the present invention may also include a separation step f) of separating the silicon granules by size by sieving or flight. It is therefore possible to combine powder preparations of silicon granules with an average size (d50) of 50 to 400 microns. For certain uses (in particular for hydrochlorination processes), the separation step of separating the silicon granules by size makes it possible to combine powder preparations that do not contain silicon granules with a size below 50 microns.

[0078] Of course, the present invention is not limited to the described embodiments and examples, and variations are possible without departing from the scope of the invention as defined by the claims.

[0079] invention 1. Silicon granules having a size of 10 to 500 microns for preparing trichlorosilane, a mass fraction of less than 5 ppm of a dopant comprising phosphorus or boron; At least one cocatalyst selected from iron, aluminum, and calcium in a mass fraction of 1 to 2500 ppm; and a mass fraction of metal impurities, excluding the at least one co-catalyst, of less than 50 ppm. 2. Silicon granules according to claim 1, wherein the mass fraction of oxygen is less than 100 ppm. 3. A powder preparation comprising the silicon granules according to invention 1 or 2, wherein the average size of the silicon granules is 50 to 400 microns. 4. A powder preparation according to claim 3, wherein the average size of the silicon granules is greater than 50 microns. 5. A method for producing silicon granules according to invention 1 or 2, a) providing silicon waste from cutting photovoltaic quality ingots with a diamond wire, said silicon waste comprising silicon particles covered with an oxide layer and mixed with impurities in an aqueous medium; b) chemically treating the silicon waste to separate the silicon particles from all or some of the impurities and drying the silicon particles to form a powder; c) metallurgically processing the powder to melt the silicon particles and form a liquid silicon bath; d) introducing at least one co-catalyst into the liquid silicon bath in an amount such that the mass fraction of said co-catalyst in the silicon granules is between 1 and 2500 ppm; e) solidifying the liquid silicon to form the silicon granules. 6. The method according to claim 5, wherein step e) comprises granulating the liquid silicon droplets by rapid cooling. 7. The method of claim 5, wherein step e) comprises pouring the liquid silicon into an ingot mold configured to allow rapid cooling to form a solidified silicon block. 8. The method according to claim 7, wherein the solidified silicon block is crushed to form the silicon granules. 9. The method according to any one of claims 5 to 8, comprising a step f) of sorting the silicon granules by size by separating them by sieving or flying. 10. A method according to any one of claims 5 to 9, wherein in step d) the at least one co-catalyst selected from iron, aluminum and calcium is introduced into the liquid silicon bath in the form of a metal or metal alloy. 11. The method according to any one of claims 5 to 10, wherein step a) comprises providing silicon granules of a size less than 400 microns resulting from a fluidized bed reactor based on the decomposition of monosilane, and the silicon granules are mixed with silicon waste. 12. A method according to any one of claims 5 to 11, wherein in step c) silicon particles of a size less than 400 microns resulting from a fluidized bed reactor based on the decomposition of monosilane are melted together with the powder of said silicon particles. 13. A method according to any one of claims 5 to 12, wherein step a) comprises providing downgraded substrates from the microelectronics or photovoltaic industry which have been crushed and mixed with the silicon waste resulting from the sawing of photovoltaic quality ingots with a diamond wire. 14. A method according to any one of claims 5 to 13, wherein in step c) crushed fragments of downgraded substrates from the microelectronics or photovoltaic industry are fused together with the powder of silicon particles. 15. A method for obtaining trichlorosilane (TCS) by chlorination or hydrochlorination, which uses the powdery preparation according to invention 3 or 4.

Claims

1. A method for producing silicon granules, comprising: a) providing silicon waste from crushed and downgraded substrates from the photovoltaic industry, said waste comprising silicon particles covered with an insulating or metallic surface layer; b) chemically treating the silicon waste to remove all or part of the insulating or metallic surface layer and drying the silicon particles to form a powder; c) metallurgically processing the powder to melt the silicon particles and form a liquid silicon bath; d) introducing at least one co-catalyst selected from iron, aluminum and calcium into the liquid silicon bath in an amount such that the mass fraction of the co-catalyst in the silicon granules is between 1 and 2500 ppm; e) solidifying the liquid silicon to form the silicon granules; the silicon granules have an equivalent Sauter diameter of 10 to 500 microns; The silicon granules are a dopant comprising phosphorus or boron, each at a mass fraction of less than 5 ppm; at least one cocatalyst in a mass fraction of 1 to 2500 ppm; and metal impurities, excluding said at least one co-catalyst, each at a mass fraction of less than 50 ppm.

2. 10. The method of claim 1, wherein step e) comprises granulating by rapidly cooling droplets of liquid silicon.

3. 10. The method of claim 1, wherein step e) comprises pouring the liquid silicon into an ingot mold configured to allow rapid cooling to form a solidified silicon block.

4. The method of claim 3 , wherein the solidified silicon block is crushed to form the silicon granules.

5. 5. The method according to any one of claims 1 to 4, comprising a step f) of sorting the silicon granules by size by separating them by sieving or flying.

6. 2. The method of claim 1, wherein in step d) the at least one co-catalyst is introduced into the liquid silicon bath in the form of a metal or metal alloy.

7. 2. The method of claim 1, wherein in step c), silicon particles with an equivalent Sauter diameter of less than 400 microns resulting from a fluidized bed reactor based on decomposition of monosilane are dissolved together with the powder of silicon particles.

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