CA2355862A1 - Agglomeration of silicon powders - Google Patents
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- CA2355862A1 CA2355862A1 CA002355862A CA2355862A CA2355862A1 CA 2355862 A1 CA2355862 A1 CA 2355862A1 CA 002355862 A CA002355862 A CA 002355862A CA 2355862 A CA2355862 A CA 2355862A CA 2355862 A1 CA2355862 A1 CA 2355862A1
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Abstract
According to a method for agglomerating silicon powders, the silicon powder is heated to a temperature of at least 250 ~C, preferably 1200 to 1500 ~C, using the effect of microwave radiation in the wavelength range 0.5 kHz to 300 GHz.
Fine silicon dust with a particle size of less than 100µm is preferably used as the starting material. Metal-containing and/or boron, phosphorus, arsenic or antimony-containing doping agents can be added to the silicon powder before or after the microwave treatment. The resulting granulate is optionally broken, milled and sifted. The invention also relates to a silicon granulate which can be produced by this method. Said granulate preferably has a porosity of 0 to 80 % and foreign phases or precipitates on the grain boundary of the monocrystals. The inventive silicon granulate can be used for producing silicon monocrystals or multicrystalline silicon blocks or for reacting with hydrogen chloride or halogenated hydrocarbons in fluidised beds or shaft furnaces.
Fine silicon dust with a particle size of less than 100µm is preferably used as the starting material. Metal-containing and/or boron, phosphorus, arsenic or antimony-containing doping agents can be added to the silicon powder before or after the microwave treatment. The resulting granulate is optionally broken, milled and sifted. The invention also relates to a silicon granulate which can be produced by this method. Said granulate preferably has a porosity of 0 to 80 % and foreign phases or precipitates on the grain boundary of the monocrystals. The inventive silicon granulate can be used for producing silicon monocrystals or multicrystalline silicon blocks or for reacting with hydrogen chloride or halogenated hydrocarbons in fluidised beds or shaft furnaces.
Description
Le A 33 170-Foreign Countries Ps/ngb/NT
A>=~lameration of silicon powders The present invention relates to a process for the agglomeration of silicon powders, and to silicon granules which can be prepared by this process, and to the use thereof.
S
The chemical conversion of metallic silicon into silanes or, vice versa, the conversion of silanes into silicon is often carried out in fluidized beds, for example the Miiller-Rochow reaction, the hydrochlorination, the decomposition of SiH4 or the decom-position of HSiCl3 (cf. DE 36 38 931, DE 37 39 895, DE 43 27 308, US
5,382,412, US 4,883,687, US 4,784,840, US 3,963,838). In these processes, the particle size of useful powders are limited to certain particle diameters by the aerodynamic require-ments of the fluidized bed reactors. Only these selected ranges allow optimum realization of the advantages of fluidized bed reactors (cf. Y.G.Yates, "Fundamentals of Fluidized-bed Chemical Processes", Butterworths London 1983; E. Klar, "Copper 1 S Catalysts for the Direct Process", p.174, in Silicon for the Chemical Industry III, Sandefjord Norwegen 1996 - The Norwegian Univ. Sci.A.Tech., Trondheim p. 9-10).
During reaction of Si powders with the reactants, the initially charged particles are continously reduced in size and lose their optimum diameter of > 40 um. On the other hand, another process is based on particle growth during SiH4 decomposition for the preparation of compact Si powders so as to produce particle diameters of more than 600 pm. As this cannot be accomplished in an ideal manner by a gas phase decomposition process, powder fractions below these limits have to be tolerated:
However, these ultrafine powders impede the processing thereof in subsequent melt processes, or it is virtually impossible to process them.
The conversion of metal powders into compact melts is known per se and can be achieved by a suflicicnt supply of thern~al energy by means of heat conduction. As heating of powders becomes more difficult with decreasing heat conductivity, 3U uniform penetration of the nratcrial is not possible. This results in a considerable Le A 33 170-Foreign Countries temperature gradient. Thus, the heating rate which can be achieved is limited by the heat conduction.
Furthermore, a sintering process utilizing microwaves is known for heating large S volumes and porous bodies. This process is disclosed e.g. in DE 195 15 342 in a particular process design. However, this document does not mention the applica~:iort of this process to ultrafine Si powders containing catalytically relevant contaminants, the distribution of which can be crucial for the success of fluidized bed syntheses using these powder mixtures. Nor does this document disclose conditioning of amorphous high-purity micropowders to form sintered bodies for subsequent melt and refining processes while maintaining the purity level in the manner accarding to the invention.
In existing processes, such as crucible pulling in quartz or graphite crucibles (Czochralski crystal pulling process) or various float zone processes, particulate granules of relatively high density are heated by electromagnetic induction to provide a compact melt bath for the zone purification. Suitable processes for such a metallurgical purification (segregation) are in principle any processes which comprise heating the Si metal and controlled cooling in accordance with defined temperature/time conditions (EP 699 625, ERDA/JPL/954559 70/2 Hunt, Dosaj, McCormick, Solar Silicon Via Improved a. Expanded Metallurgical Silicon Technology 1977; Amerlaan, C.A.J. Hrsg., Proc. Symos. Sci. a. Techn. of Defects in Silicon of the E-Mrs Meeting Straf3bourg, May/June 1989; W. Zulehner, Elesevier Sequoia 1989 Mater. Sci. A. Eng. Vol. B4 No. 1-4; Heimann, Huber, Seidensticker, Zulehner, in Silicon Chemical Etching, Ed. J. Grabmeier, Springer Berlin 1982;
Sil-bernagel, Chem. Ing. Tech. 50 (1978) 8, p. 611-617; Dietze, Milh(bauer, Chemiker Zeitung 97 (1973) 3 p. 151-155; Dietl, Helmreich, Sirtl, "Solar Silicon", in Crystals:
Growth Properiics a. Appl. S Springer Verlag Berlin 1981, p. 43fn.
Le A 33 170-Foreign Countries A variant on sintering Si powders is diclosed by C.J. Santana, K.S. Jones in J. Mater.
Sci. 31 (1996) p. 4985-90, which comprises sintering/compacting the Si powder to full density, i.e. to high density to produce a wafer, by hot-pressing.
S In view of this prior art, the object of the present invention is to improve the suitability of fine Si powders which have diameters of 1 to 1000 pm an:i p-.~cr meat transfer characteristics, owing to their low bulk density, for various methods of further processing. It should be possible to vary selectively the particle size, chemical composition, reactivity and/or phase distribution of the contaminants in the Si matrix, using as little energy as possible. Furthermore, the treated silicon should be readily convertible into a fluidizable powder, if desired.
This object is achieved by heating the silicon powder to a temperature of at least 250°C, preferably from 1200 to 1500°C, by exposure to microwave radiation in the wavelength range from 0.5 kHz to 300 GHz, thereby agglomerating the silicon powder. It has been found, surprisingly, that a silicon powder treated in this manner has many improved properties. Depending on the conditions, a sintered body of relatively high density and/or a powder of different reactivity are obtained.
It is possible to vary selectively the particle size, chemical composition, reactivity or phase distribution of the contaminants in the Si matrix. Furthermore, the sintered bodies/powders have a porosity after heating which makes it possible:
a) to convert the Si body into a fluidizable powder with minimum additional effort (crushing instead of grinding), or b) to deplete the contaminants by classifying after crushing/grinding or by chemical purification steps, or c) to provide advantageously the sintered bode, which only contains minor gas 3U inclusions, in Si raclts for further refining steps.
Le A 33 170-Foreign Countries The invention allows the agglomeration of an ultrafme Si metal powder below the melting temperature of the silicon, with minimal energy consumption, or the controlled conduct or preparation of phase separations or refining processes at a temperature no higher than the melting temperature. In the case of powders which are already in the desired particle size range, the process is solely aimed at conditioning at an elevated temperature.
Adhesion to the wall material should be minimal. This form of heating makes it possible to let the sintering process only proceed up to the point at which the majority of the ultrafine powder has multiplied in its particle size by a factor of 2 to 100.
The starting material used for the agglomeration is preferably fine silcion dust having a particle size of less than 600 pm, particluarly preferably of less the 100 Vim.
Powders of this type are widely available industrially as particle size fractions from Si powder grinding for Miiller-Rochow synthesis or hydrochlorination, anti as aunts from ultrafine dust separation (e.g. in a cyclone) in these fluidized bed processes;
such as Muller-Rochow, hydrochlorination, decomposition of silane to form ultrapure Si. These dusts can no longer be used advantageously in a fluidized bed process, in a shaft furnace or in subsequent processes owing to their aerodynamic or chemical properties.
In contrast, the agglomerate obtained preferably has an average particle size of at least 30 pm, rendering it reusable for the abovementioned fluidized bed processes.
The microwave heat treatment according to the invention can be carried out in a stirred moving bed, preferably in a fluidized bed. Any inhomogenities in the heat distribution which might still occur are eliminated in such a stirred bed. The microwaves arc introduced by means of appropriate antennae through the external wall or into the interior of the agglomeration reactors.
Le A 33 170-Foreign Countries -S-The heat treatment is preferably carried out in a reactor made of microwave-transparent and/or microwave-reflecting material, in particular non-oxide ceramic, graphite, oxide ceramic or quartz. Such crucible materials allow efficient heating of the material and ensure low wall adhesion with respect to liquid Si.
Prior to the microwave treatment, the silicon powder can be admixed with dopants containing metals and/or boron, phosphorus, arsenic or antimony (Ag, Al, As, Cd, Cs, Cu, Ce, Co, Cr, Fe, In, Ir, Mo, Mn, Cr, Ni, P, Pt, Pd, Rh, Ru, Se, Sb, Sn, V, Zn).
During subsequent further processing, substances of this type then act as catalysts, e.g. when a reaction with halides RX (R = Me, Et, Phe; X = Cl, Br) is carried out.
Alternatively or additionally, the granules obtained by the microwave treatment can first be admixed with dopants containing metals and/or boron, phosphorus, arsenic or antimony in accordance with e.g. the usual requirements for the Rochow synthesis or the hydrochlorination.
Furthermore, the granules obtained by the microwave treatment can be ground and optionally classified. Grinding of the granules is considerably facilitated owing to their porosity. In addition, the crushing or grinding procedure preferably produces surfaces of different chemical composition which generate a different reactivity with respect to reactants of the type RX and a different product composition compared to untreated Si.
Owing to their increased particle size, the powders which have been agglomerated and then classified are easier to handle in a fluidized bed than the precursor powders.
Occasionally, these powders allow impurity depletion by classifying andlor chemical purification steps.
The invention further comprises silicon granules obtainable by a process according to the invention. The advantageous properties of such granules have been described hcrcinbcforc.
Le A 33 170-Foreign Countries The silicon granules preferably have a porosity of 0 to 80 %. High-porosity granules are particularly suitable for easier grinding (or crushing).
The average crystal size of the individual crystals of the silicon granules is generally less than SO um. Metal-containing and/or nonmetal-containing foreign phases or precipitates are preferably present at the grain boundaries of the individual crystals.
The silicon granules according to the invention can preferably be used for the preparation of silicon single crystals, in particular by the Czochralski metima cx tlm float zone method.
However, it is likewise possible to prepare multicrystalline silicon blocks, preferably by oriented crystallization of melts of the silicon granules. An agglomerated ultrafme Si powder containing few impurities is utilized in a refining process by heating the ultrafine powder by means of electromagnetic waves to temperatures up to the melting point followed by introducing the resulting sintered body into another melt furnace in which multicrystalline Si for semiconductor applications is prepared by a segregation process.
Finally; it is likewise possible to use the silicon granules according to the invention for reaction with hydrogen chloride or halogenated hydrocarbons. In this case, the particle size of the granules which is adapted to fluidized bed processes has a particularly beneficial effect. The silicon granules have preferably been admixed with catalysts suitable for processes such as the Muller-Rochow synthesis or the hydrochlorination, to promote the reaction with halides RX (R = Me, Et, Phe; X
= CI, Br).
The sintered powders which have been crushed in a subsequent step according to tlic 3U invention can furthennore be adrnixcd w ith catalysts from the group of thosr elements which arc used in prior an fluidircd bed synthesis of mcthylchlorosilanes, Le A 33 170-Foreign Countries phenylchlorosilanes, hydridochlorosilanes or chlorosilanes (or hydrogenation thereof in the presence of Si powders), i.e. in particular Ag, Al, As, Cd, Cs, Cu, Ce, Co, Cr, Fe, In, Ir, Mn, Mo, Ni, P, Pt, Pd, Rh, Ru, Se, Sb, Sn, V, Zn.
The silicon granules according to the invention should be admixed with the abovementioned catalysts prior to heating in an amount which allows sufficient activation for the abovementioned syntheses. In this case, heating can then preferably remain limited to temperatures below the melting point of the elements.
In particular, the silicon granules according to the invention can be p~Lru:2d ø"y optionally purifying, agglomerating, crushing, grinding and classifying powders derived from the grinding or dust separation sections of fluidized bed reactors in which RX and Si are reacted (R = Me, Et, Phe; X = Cl, Br). Subsequently, 0 to of fresh metallurgically prepared silicon of the same particle size suitable for 1 S fluidized beds can be added.
The silicon granules according to the invention which are particularly suitable for use in reactions with RX can be prepared in such a manner that all or part of the constituents contaminating the Si are present in separate phases after heating by means of electromagnetic waves, and can be depleted by crushing/grinding/-evaporating and classifying and/or by washing, leaching or extracting.
The examples which follow illustrate the invention.
Le A 33 170-Foreign Countries _g_ 1. Principles The ultrafine Si powders which are widely avaliable industrially are particle size fractions from Si powder grinding for Miiller-Rochow synthesis or hydro-chlorination, and dusts from ultrafme dust separation (e.g. cyclone) in these fluidized bed processes (Miiller-Rochow synthesis, hydrochlorination, decomposition of silane). These dusts can no longer be used advantageously in a fluidized bed process or in subsequent processes owing to their aerodynamic or chemical properties.
General chemical suitability for MCS synthesis can be evaluated e.g. using a laboratory-scale stirred bed which is relatively insensitive to the particle size distribution. The main characterizing physical parameter determining the suitability for use in a fluidized bed is known to be a defined average particle size of more than 30 pm, in addition to the chemical composition. Exemplary details and the desired particle size are given by Rosch, Kalchauer p.7 in "Silicon for the Chemical Industry III", Sandefjord Norwegen 1996 - Ed: Oye, Rong, and by Ceccaroli, Nygaard, Tuset, The Norwegian Univ. Sci. a. Tech., Trondheim 1996 p. 269 ff. , E. Klar ibid.
p. 169, or in DE I95 32 315, p.3 1. 55-64.
2. Agglomeration 2.1. Induction furnace process A vacuum induction melting and casting furnace IS 1 III from LEYL~OLD
HERAEUS was used to prepare sintered bodies in an induction furnace. The features of this furnace are, interalia an operating frequency of 10 kHz, a power of 30 kW and a maximum vacuum of 1.3~ i 0~5 mbar.
The powder samples were mechnicaliv precompacted at a pressure of about 0.5 bar.
About 100-200 g of the precompacted sample were then placed in a quarts, SiC
or corundum crucible, ideally, for reasons of easy dernoulding and high heating talc, in Le A 33 170-Foreign Countries _g_ a graphite crucible which was superficially coated with Si3N4 (BAYER CFI
06051, about 0.3-0.5 mm thick) or was made of Si3N4 only. The furnace was evacuated twice at 0.5 - 8 mbar (using an oiI diffusion pump to reach 1.310-5 mbar) and then repressurized with Ar or He at atmospheric pressure.
Heating to 700-1600°C took 15-40 min (depending on the crucible material and preliminary conventional preheating to about 200°C). .
A specific heating energy of about 28 kJ/g (for 100 g of sample) = 7.8 kWh/kg was found which was inversely proportional to the sample weight. The samples were cooled down to about 300-150°C within about 2 h under He protective gas.
2.2. Microwave furnace process It is likewise possible to use a microwave furnace instead of the induction furnace.
This furnace was characterized by generation of energy by means of a magnetron at 2.45 GHz, 3 kW adjustable from 250 W by means of variable plates to limit the irradiated cavity. Energy supplied: 500-700 W, adjustable up to a maximum of 1700 W, rapid heating between 500 and 1200°C.
Crucible materials used for Si were A1203 and Si3N4 crucibles superficially coated with Si3N4 (BAYER CFI 06051, about 0.3-0.5 mm thick). Sample sizes were 100-200 g. The samples were mechanically precompacted as described above.
The furnace cavity was evacuated twice at O.I mbar and repressurized with He or Ar.
Depending on sample size, crucible insulation and preheating to 200°C, temperatures of 1200-1450°C (surface temperature determined by means of a pyrometer) and thus the melting point of Si ( 1-l?3'C) were obtained after 15-GO nlln.
Le A 33 170-Foreign Countries A specific heating energy of about 19 kJ/g (for 100 g of sample) = S.3 kWh/kg was found which was likewise inversely proportional to the sample weight.
The samples were cooled down to about 300°C within about I-1.S h under He S protective gas.
3. Evaluation 3.1. Evaluation of the sintered Si powder in the reaction with methyl chloride or ~drocarbon The powder was classified or screened, and then 40 g of powder of the reported selected particle size were filled into a quartz tube having a glass frit bottom and a stirrer inserted via a stirrer bearing. The preferred particle size was usually 7I-1S 160 pm, after crushing, grinding and classifying or screening the granules.
3.1.1 In the case of the reaction of Si with methyl chloride, the Si powder was usually admixed with 3.2 g of Cu/CuZO/Cu0 catalyst (86% of Cu) and 0.048 ZnO. The methyl chloride flow was 1.8 I/h and 2 bar abs. The gas space was subsequently filled with nitrogen. The contents of the glass tube were heated to 370°C for a short period of 1 h by means of an electrically-heated tube furnace from HERAEUS, and then a pressure of 2 bar abs was maintained during reaction by means of an inclined tube manometer at 300°C or 330°C, respectively, within 8 hours.
The resulting products which vaporize readily at 300°C were withdrawn through a descending glass condenser having a coolant temperature of 1S°C, and condensed.
The effluent gases which were not condensable under these conditions, consisting of MeCI, HCI etc., were passrd into the exhaust air stream. The liquids of the various mrthvlchlorosilanes or chlorosilanes u~hich were condensable at 1S-20°C
were Le A 33 170-Foreign Countries collected in a receiver underneath the condenser and analyzed in a gas chromato-graph.
(For details, cf. DE 19S 32 31S).
S 3.2.1 In the case of the reaction Si+HCI instead of methyl chloride, the subsequent addition of catalytic additives was omitted. The pressure selected was likewise 1 bar gauge, but in this case the amount of HCl (4.2/9.61/h, via digital flow meters) and the temperature (220-3S0°C) were varied. Preactivation at 370°C was omitted.
3.2. Suitability for MCS synthesis: Examples 3.2.1. Comparative example: Reaction using standard metal-grade Si in a laboratory-scale stirred bed Metal grade silicon granules obtained from LILLEBY were ground in an agate mill using an electromechanical pestle. A fraction having a particle diameter of 7I-160 um was isolated from the laboratory-scale stirred bed by means of screening using ASTM standard screens.
Trace component contents were determined by ICP-AS.
The reaction with methyl chloride as mentioned in 3.1.1 produces the methyl-chlorosilane amounts reported in the first column, "comparison", of Table 1.
3.2.2. Example la (Comparative example: Use of untreated grinding fines) Grinding fines obtained from the silicon granules employed in the Comparative Example during ~:rinding in a hammer mill using ceramic balls under N~
protective 3U gas under industrial conditions wvrc blown from the mill into a filter.
These grinding fines were detcnnincd to have an average particle diameter of 3S ym and a Le A 33 i 70-Foreign Countries distribution of 5-50 pm. The particle size distribution was determined by means of a MALVERN Master Sizer 2000 (measurement of scattered light) in this case and by means of ASTM standard screens in the other cases above 36 um.
The above-described procedure 3.1.1. for reacting methyl chloride in accordance with the Miiller-Rochow method in a laboratory-scale stirred bed reactor produced the methylchlorosilane mixture reported in Table 1 {column 2, heading "1a").
In this procedure, the most important parameters to be optimized are a sufficiently high production rate and a high MeZSiCl2 content, however, it is equally or even more important to have achieved a particle diameter greater than 40 um and thus suitability for the fluidized bed, a property which cannot be evaluated.
For la, the production rate and the Me2SiCI2 concentration are found to be at the lower end of the expected range.
3.2 3. Example lb (Use of grinding fines treated according to the invention) 200 g of the grinding fines collected in the grinding process of Comparative Example 3.2.2. were subjected to microwave agglomeration (microwave furnace of type II) 2.2. under Ar protective gas. Heating time: 30 min. Temperature, sintered density and particle size after grinding and classifyng are reported in Table 1 (column 3, heading "lb"). Energy supplied: 500-1500 watts.
The energy was switched off and the material was cooled down to about 200°C and then discharged. The material was then cooled down to room temperature (25°C) in air and the agglomerate was subjected to grinding and screening. A crushing process using a hammer and an agate mill equipped with an electromechanically movable pestle yielded a powder having the properties reported in Table 1.
A 71-1(0 um fraction havins_: a DSO% value of 120 pm was isolated by screening for the comparative tests in the laboratory-scale reactor.
Le A 33 170-Foreign Countries The high Fe content of the grinding fines from Example la is found to be reduced to a level in the vicinity of the standard material from the Comparative Example in the grinding and classifying process.
The production rate is at the lower end of the expected range, the MezSiCl2 concentration was improved compared to the Comparative Example/Standard.
3.2.4. Example 2 (untreated Si dust from the fluidized bed of the Rochow synthesis) Unsintered fine dust from the fluidized bed of the Rochow synthesis (see also Examples 2b-2d) was evaluated as described above (Table 1, column 4, heading ,~2~~ ).
This Si dust had an average particle diameter of 20 p.m and an Si content of about 76 %. In addition, it contained 11.4 % of Cu, 3 % of Fe, 2.9 % of C, 0.3 % of Zn, 2 % of Cl and other metals prior to sintering.
The properties in the laboratory-scale stirred bed with respect to production rate and MeZSiCl2 concentration are very similar to those of the Si from the Comparative Example.
3.2.5. Examples 2a to 2d (Si fluidized bed dust treated according to the invention) Dust 2 from the fluidized, bed was subjected to stepwise heating by microwave exposure and agglomerated to various degrees.
The microwave furnace was charged with the Si dust described in 2. The temperature was increased to about 800-820°C within 40 min and then maintained at this Icvcl for about 30 min, with Cu salts evaporating in the form of a plasma cloud. The material was hcatcd further ..~ithin 20 min to a preselected level of 4 different final tempera-lures, with a maximum of 1500°C (in each case surface temperatures detemtined by Le A 33 170-Foreign Countries means of a pyrometer). The final temperatures were maintained for about 20 min:
The irradiation source was then switched off and the material was allowed to cool.
The powder separated after crushing, grinding and classifying to obtain a 10-160 p.m fraction (Cu content: 11.4 %) was evaluated in comparison with unsintered fine dust from Example 2 in 3.2.4. (Table 1, columns 4-7, headings "2a" to "2d) The production rate for methylchlorosilanes and the Me2SiC12 concentration were found to drop above 800-900°C and then arnve at a lower intermediate maximum for the main component. The agglomerated Si is less suitable for reaction with methyl chloride when this process sequence is employed.
3.2.6. Examples 3a and b (mixture of fluidized bed dust and ~rindin~ fines from metal grade silicon) 85 parts of metal grade silicon grinding fines from Example la. are admixed with 15 parts of ultrafine dust from the cyclone of a fluidized bed for methylchlorosilane synthesis.
Example 3a illustrates the result for the unsintered product (Table 1, column 8, heading "3a").
In Example 3b, the powder was partially sintered according to the invention.
The production rate is found to drop while the Me2SiClZ content increases (Table l, column 9, heading "3b") 3.2.7. Examples 4a and 4b (activation of metal grade Si powder +
catalyst/promoter mixture A standard metal grade Si powder from 3.2.1.-Comparative Example of particle size 71-170 pm was admixed with the amounts of catalyst (Cu/CuO, Zn, Sn) reported Le A 33 170-Foreign Countries in the Table and subjected to microwave heating under Ar protection in Example 4b.
The reported temperature below the melting point was maintained for about 30 min.
The material was then cooled down to 150°C under protective gas.
Table I {columns 10,1 l, headings "4a", "4b") shows an increase in the production rate of the resulting methylchlorosilane mixture and a small increase in Me2SiC12 concentration for a defined composition. .
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_ Le A 33 170-Foreign Countries 3.2.8. Examples Sa and Sb (Si ~rindin~ fines from Example 1a in hydrochlori-nation Table 2 shows that both the grinding fines in their original state and the grinding fines agglomerated according to the invention have roughly the same reactivity and product composition in the case of hydrochlorination in a laboratory-scale stirred bed (process as described in 3.1.2 except that HCI was used here instead of CH3C1).
3.2.9. Examples 6a and 6b (fluidized bed dust from Example 2 in hydrochlorination When the hydrochlorination is earned out using fine dust discharge from the fluidized bed (cyclone) for methylchlorosilane synthesis, the differences as illustrated in Table 2 are found between the original ultrafine fluidized bed dust and the dust 1 S agglomerated and ground according to the invention.
The agglomerated, ground and screened dust produces more SiCl4 at a production rate which is mostly lower. However, when the amount of available HCl is increased from 4.2 1/h to 9,6 1/h, the production rate increases to reach a level similar to that of the unagglomerated Si from 2 or 6a.
3.3.10. Example 7 (Si microdust from the decompostion of SiH4 to produce ultrapure A powder having an average particle size of 2 ftm and a distribution of 0.05-5 um was separated from the process for the preparation of ultrapure Si by decomposition of SiH., at 700-800°C in accordance with US 47 84 840 or US 48 83 687.
20U g of this powder were then placed in a microwave furnace as described above.
3O The powder was heated to 1450°C within GO min under He to give a melt cake Le A 33 170-Foreign Countries having a density of 1.9 g/cm' which was allowed to cool down to 200°C
under protective gas.
When using an Si3N4 crucible, a compact ingotlregulus was obtained which was S placed in a melt furnace (ULLMANN ENCYCLOPEDIA of Ind Chem., 1993 A 23 p.739, BRIDGEMAN melt furnace (J.C. Brice: Crystal Growth Processes, Blackie Glasgow & London (1986) p. 104).
The sample was melted at 1450°C and then subjected to programmed solidification in defined steps to produce multicrystalline Si having crystallite sizes of usually 5-50 mm. As a result, a multicrystalline Si block was obtained from which the outer regions were cut off to provide a multicrystalline core of the composition and structure desired for solar grade Si. After agglomeration according to the invention and conversion into multicrystalline Si using a BRIGDEMAN furnace, this material had a conductivity of about 2000 Ohm~cm. The core can be sawed into 350 l.~m Si slices which can be used as wafers in a solar module.
Le A 33 170-Foreign Countries Table 2 Composition of sintered Si powders and reaction products with HCI
5a 5b 6a 6b 6b 7 prior to sinteringgrml0.8 0.8 0.8 0.8 0.8 0.3 particle size um 35 35 35 35 35 10 D 90%
Si % 97 97 77 77 77 99.99999 C % 3 3 3 Cu % 11 11 11 Fe % 1 1 3 3 3 AI % 0.38 0.38 0.6 0.6 0.6 Ca % 0.13 0.12 Zn % 0.1 0.1 0.3 0.3 0.3 Sn % 0.0180.0180.018 sintering temp.C - 1050 1300 1300 sintered densityyml0.5 1.6 0.5 1.6 1.6 2.6 particle size Nm 1050 40-16010-5040-16040-160 used 050%
additions after% 0 0 0 0 0 0 sintering resistance of onm~ann.b. n.b. n.b.n.b. n.b. 2000 Si Hydrochlorination ~ after J ~ after 8h afterafterSh~after Hh Sh 16h ~
4.z 1 of Ham H2SiCl2 % 0.7 0.1 HSiCl3 % 87 58 SiCl4 % 12 42 Prod. rate gm 3.5 1.8 @4.21 HCUh )~
s.s I of Ham H2SiCl2 % 0.1 0.5 0.1 0.3 HSiCl3 % 85 96 75 65 SiCl4 % 15 4 25 35 Prod. rate gm 7.2 9 8.5 10.4 @9.61 HCUh )~
4.21 or Ham H2SiC12 % 0.01 0.06 0.3 0.1 HSiCl3 % 90.4 92.2 85 55 SiCl4 % 9.6 7.8 15 45 Prod, rate gm 2.4 3.2 3.7 1.8 @4.21 HCUh )~
s.s I of Ham H2SiCl2 % 0.1 0.1 HSiCl3 % 86 89.5 SiCl4 % 14 10.5 Prod, rate gm 10 10 9.61 HCUh )-4.21 Ot HGm H2SiCl2 % 0.03 0.01 0 0.1 0.04 HSiCl3 % 81.9 79.3 84 50.5 25 SiCl4 % 17.5 20.6 15 49.5 74.9 Prod rate 4.21gm 3.2 3.5 4 3.2 3.8 HCUh )~
gm )~ in g SiCl4IHSiCl3
A>=~lameration of silicon powders The present invention relates to a process for the agglomeration of silicon powders, and to silicon granules which can be prepared by this process, and to the use thereof.
S
The chemical conversion of metallic silicon into silanes or, vice versa, the conversion of silanes into silicon is often carried out in fluidized beds, for example the Miiller-Rochow reaction, the hydrochlorination, the decomposition of SiH4 or the decom-position of HSiCl3 (cf. DE 36 38 931, DE 37 39 895, DE 43 27 308, US
5,382,412, US 4,883,687, US 4,784,840, US 3,963,838). In these processes, the particle size of useful powders are limited to certain particle diameters by the aerodynamic require-ments of the fluidized bed reactors. Only these selected ranges allow optimum realization of the advantages of fluidized bed reactors (cf. Y.G.Yates, "Fundamentals of Fluidized-bed Chemical Processes", Butterworths London 1983; E. Klar, "Copper 1 S Catalysts for the Direct Process", p.174, in Silicon for the Chemical Industry III, Sandefjord Norwegen 1996 - The Norwegian Univ. Sci.A.Tech., Trondheim p. 9-10).
During reaction of Si powders with the reactants, the initially charged particles are continously reduced in size and lose their optimum diameter of > 40 um. On the other hand, another process is based on particle growth during SiH4 decomposition for the preparation of compact Si powders so as to produce particle diameters of more than 600 pm. As this cannot be accomplished in an ideal manner by a gas phase decomposition process, powder fractions below these limits have to be tolerated:
However, these ultrafine powders impede the processing thereof in subsequent melt processes, or it is virtually impossible to process them.
The conversion of metal powders into compact melts is known per se and can be achieved by a suflicicnt supply of thern~al energy by means of heat conduction. As heating of powders becomes more difficult with decreasing heat conductivity, 3U uniform penetration of the nratcrial is not possible. This results in a considerable Le A 33 170-Foreign Countries temperature gradient. Thus, the heating rate which can be achieved is limited by the heat conduction.
Furthermore, a sintering process utilizing microwaves is known for heating large S volumes and porous bodies. This process is disclosed e.g. in DE 195 15 342 in a particular process design. However, this document does not mention the applica~:iort of this process to ultrafine Si powders containing catalytically relevant contaminants, the distribution of which can be crucial for the success of fluidized bed syntheses using these powder mixtures. Nor does this document disclose conditioning of amorphous high-purity micropowders to form sintered bodies for subsequent melt and refining processes while maintaining the purity level in the manner accarding to the invention.
In existing processes, such as crucible pulling in quartz or graphite crucibles (Czochralski crystal pulling process) or various float zone processes, particulate granules of relatively high density are heated by electromagnetic induction to provide a compact melt bath for the zone purification. Suitable processes for such a metallurgical purification (segregation) are in principle any processes which comprise heating the Si metal and controlled cooling in accordance with defined temperature/time conditions (EP 699 625, ERDA/JPL/954559 70/2 Hunt, Dosaj, McCormick, Solar Silicon Via Improved a. Expanded Metallurgical Silicon Technology 1977; Amerlaan, C.A.J. Hrsg., Proc. Symos. Sci. a. Techn. of Defects in Silicon of the E-Mrs Meeting Straf3bourg, May/June 1989; W. Zulehner, Elesevier Sequoia 1989 Mater. Sci. A. Eng. Vol. B4 No. 1-4; Heimann, Huber, Seidensticker, Zulehner, in Silicon Chemical Etching, Ed. J. Grabmeier, Springer Berlin 1982;
Sil-bernagel, Chem. Ing. Tech. 50 (1978) 8, p. 611-617; Dietze, Milh(bauer, Chemiker Zeitung 97 (1973) 3 p. 151-155; Dietl, Helmreich, Sirtl, "Solar Silicon", in Crystals:
Growth Properiics a. Appl. S Springer Verlag Berlin 1981, p. 43fn.
Le A 33 170-Foreign Countries A variant on sintering Si powders is diclosed by C.J. Santana, K.S. Jones in J. Mater.
Sci. 31 (1996) p. 4985-90, which comprises sintering/compacting the Si powder to full density, i.e. to high density to produce a wafer, by hot-pressing.
S In view of this prior art, the object of the present invention is to improve the suitability of fine Si powders which have diameters of 1 to 1000 pm an:i p-.~cr meat transfer characteristics, owing to their low bulk density, for various methods of further processing. It should be possible to vary selectively the particle size, chemical composition, reactivity and/or phase distribution of the contaminants in the Si matrix, using as little energy as possible. Furthermore, the treated silicon should be readily convertible into a fluidizable powder, if desired.
This object is achieved by heating the silicon powder to a temperature of at least 250°C, preferably from 1200 to 1500°C, by exposure to microwave radiation in the wavelength range from 0.5 kHz to 300 GHz, thereby agglomerating the silicon powder. It has been found, surprisingly, that a silicon powder treated in this manner has many improved properties. Depending on the conditions, a sintered body of relatively high density and/or a powder of different reactivity are obtained.
It is possible to vary selectively the particle size, chemical composition, reactivity or phase distribution of the contaminants in the Si matrix. Furthermore, the sintered bodies/powders have a porosity after heating which makes it possible:
a) to convert the Si body into a fluidizable powder with minimum additional effort (crushing instead of grinding), or b) to deplete the contaminants by classifying after crushing/grinding or by chemical purification steps, or c) to provide advantageously the sintered bode, which only contains minor gas 3U inclusions, in Si raclts for further refining steps.
Le A 33 170-Foreign Countries The invention allows the agglomeration of an ultrafme Si metal powder below the melting temperature of the silicon, with minimal energy consumption, or the controlled conduct or preparation of phase separations or refining processes at a temperature no higher than the melting temperature. In the case of powders which are already in the desired particle size range, the process is solely aimed at conditioning at an elevated temperature.
Adhesion to the wall material should be minimal. This form of heating makes it possible to let the sintering process only proceed up to the point at which the majority of the ultrafine powder has multiplied in its particle size by a factor of 2 to 100.
The starting material used for the agglomeration is preferably fine silcion dust having a particle size of less than 600 pm, particluarly preferably of less the 100 Vim.
Powders of this type are widely available industrially as particle size fractions from Si powder grinding for Miiller-Rochow synthesis or hydrochlorination, anti as aunts from ultrafine dust separation (e.g. in a cyclone) in these fluidized bed processes;
such as Muller-Rochow, hydrochlorination, decomposition of silane to form ultrapure Si. These dusts can no longer be used advantageously in a fluidized bed process, in a shaft furnace or in subsequent processes owing to their aerodynamic or chemical properties.
In contrast, the agglomerate obtained preferably has an average particle size of at least 30 pm, rendering it reusable for the abovementioned fluidized bed processes.
The microwave heat treatment according to the invention can be carried out in a stirred moving bed, preferably in a fluidized bed. Any inhomogenities in the heat distribution which might still occur are eliminated in such a stirred bed. The microwaves arc introduced by means of appropriate antennae through the external wall or into the interior of the agglomeration reactors.
Le A 33 170-Foreign Countries -S-The heat treatment is preferably carried out in a reactor made of microwave-transparent and/or microwave-reflecting material, in particular non-oxide ceramic, graphite, oxide ceramic or quartz. Such crucible materials allow efficient heating of the material and ensure low wall adhesion with respect to liquid Si.
Prior to the microwave treatment, the silicon powder can be admixed with dopants containing metals and/or boron, phosphorus, arsenic or antimony (Ag, Al, As, Cd, Cs, Cu, Ce, Co, Cr, Fe, In, Ir, Mo, Mn, Cr, Ni, P, Pt, Pd, Rh, Ru, Se, Sb, Sn, V, Zn).
During subsequent further processing, substances of this type then act as catalysts, e.g. when a reaction with halides RX (R = Me, Et, Phe; X = Cl, Br) is carried out.
Alternatively or additionally, the granules obtained by the microwave treatment can first be admixed with dopants containing metals and/or boron, phosphorus, arsenic or antimony in accordance with e.g. the usual requirements for the Rochow synthesis or the hydrochlorination.
Furthermore, the granules obtained by the microwave treatment can be ground and optionally classified. Grinding of the granules is considerably facilitated owing to their porosity. In addition, the crushing or grinding procedure preferably produces surfaces of different chemical composition which generate a different reactivity with respect to reactants of the type RX and a different product composition compared to untreated Si.
Owing to their increased particle size, the powders which have been agglomerated and then classified are easier to handle in a fluidized bed than the precursor powders.
Occasionally, these powders allow impurity depletion by classifying andlor chemical purification steps.
The invention further comprises silicon granules obtainable by a process according to the invention. The advantageous properties of such granules have been described hcrcinbcforc.
Le A 33 170-Foreign Countries The silicon granules preferably have a porosity of 0 to 80 %. High-porosity granules are particularly suitable for easier grinding (or crushing).
The average crystal size of the individual crystals of the silicon granules is generally less than SO um. Metal-containing and/or nonmetal-containing foreign phases or precipitates are preferably present at the grain boundaries of the individual crystals.
The silicon granules according to the invention can preferably be used for the preparation of silicon single crystals, in particular by the Czochralski metima cx tlm float zone method.
However, it is likewise possible to prepare multicrystalline silicon blocks, preferably by oriented crystallization of melts of the silicon granules. An agglomerated ultrafme Si powder containing few impurities is utilized in a refining process by heating the ultrafine powder by means of electromagnetic waves to temperatures up to the melting point followed by introducing the resulting sintered body into another melt furnace in which multicrystalline Si for semiconductor applications is prepared by a segregation process.
Finally; it is likewise possible to use the silicon granules according to the invention for reaction with hydrogen chloride or halogenated hydrocarbons. In this case, the particle size of the granules which is adapted to fluidized bed processes has a particularly beneficial effect. The silicon granules have preferably been admixed with catalysts suitable for processes such as the Muller-Rochow synthesis or the hydrochlorination, to promote the reaction with halides RX (R = Me, Et, Phe; X
= CI, Br).
The sintered powders which have been crushed in a subsequent step according to tlic 3U invention can furthennore be adrnixcd w ith catalysts from the group of thosr elements which arc used in prior an fluidircd bed synthesis of mcthylchlorosilanes, Le A 33 170-Foreign Countries phenylchlorosilanes, hydridochlorosilanes or chlorosilanes (or hydrogenation thereof in the presence of Si powders), i.e. in particular Ag, Al, As, Cd, Cs, Cu, Ce, Co, Cr, Fe, In, Ir, Mn, Mo, Ni, P, Pt, Pd, Rh, Ru, Se, Sb, Sn, V, Zn.
The silicon granules according to the invention should be admixed with the abovementioned catalysts prior to heating in an amount which allows sufficient activation for the abovementioned syntheses. In this case, heating can then preferably remain limited to temperatures below the melting point of the elements.
In particular, the silicon granules according to the invention can be p~Lru:2d ø"y optionally purifying, agglomerating, crushing, grinding and classifying powders derived from the grinding or dust separation sections of fluidized bed reactors in which RX and Si are reacted (R = Me, Et, Phe; X = Cl, Br). Subsequently, 0 to of fresh metallurgically prepared silicon of the same particle size suitable for 1 S fluidized beds can be added.
The silicon granules according to the invention which are particularly suitable for use in reactions with RX can be prepared in such a manner that all or part of the constituents contaminating the Si are present in separate phases after heating by means of electromagnetic waves, and can be depleted by crushing/grinding/-evaporating and classifying and/or by washing, leaching or extracting.
The examples which follow illustrate the invention.
Le A 33 170-Foreign Countries _g_ 1. Principles The ultrafine Si powders which are widely avaliable industrially are particle size fractions from Si powder grinding for Miiller-Rochow synthesis or hydro-chlorination, and dusts from ultrafme dust separation (e.g. cyclone) in these fluidized bed processes (Miiller-Rochow synthesis, hydrochlorination, decomposition of silane). These dusts can no longer be used advantageously in a fluidized bed process or in subsequent processes owing to their aerodynamic or chemical properties.
General chemical suitability for MCS synthesis can be evaluated e.g. using a laboratory-scale stirred bed which is relatively insensitive to the particle size distribution. The main characterizing physical parameter determining the suitability for use in a fluidized bed is known to be a defined average particle size of more than 30 pm, in addition to the chemical composition. Exemplary details and the desired particle size are given by Rosch, Kalchauer p.7 in "Silicon for the Chemical Industry III", Sandefjord Norwegen 1996 - Ed: Oye, Rong, and by Ceccaroli, Nygaard, Tuset, The Norwegian Univ. Sci. a. Tech., Trondheim 1996 p. 269 ff. , E. Klar ibid.
p. 169, or in DE I95 32 315, p.3 1. 55-64.
2. Agglomeration 2.1. Induction furnace process A vacuum induction melting and casting furnace IS 1 III from LEYL~OLD
HERAEUS was used to prepare sintered bodies in an induction furnace. The features of this furnace are, interalia an operating frequency of 10 kHz, a power of 30 kW and a maximum vacuum of 1.3~ i 0~5 mbar.
The powder samples were mechnicaliv precompacted at a pressure of about 0.5 bar.
About 100-200 g of the precompacted sample were then placed in a quarts, SiC
or corundum crucible, ideally, for reasons of easy dernoulding and high heating talc, in Le A 33 170-Foreign Countries _g_ a graphite crucible which was superficially coated with Si3N4 (BAYER CFI
06051, about 0.3-0.5 mm thick) or was made of Si3N4 only. The furnace was evacuated twice at 0.5 - 8 mbar (using an oiI diffusion pump to reach 1.310-5 mbar) and then repressurized with Ar or He at atmospheric pressure.
Heating to 700-1600°C took 15-40 min (depending on the crucible material and preliminary conventional preheating to about 200°C). .
A specific heating energy of about 28 kJ/g (for 100 g of sample) = 7.8 kWh/kg was found which was inversely proportional to the sample weight. The samples were cooled down to about 300-150°C within about 2 h under He protective gas.
2.2. Microwave furnace process It is likewise possible to use a microwave furnace instead of the induction furnace.
This furnace was characterized by generation of energy by means of a magnetron at 2.45 GHz, 3 kW adjustable from 250 W by means of variable plates to limit the irradiated cavity. Energy supplied: 500-700 W, adjustable up to a maximum of 1700 W, rapid heating between 500 and 1200°C.
Crucible materials used for Si were A1203 and Si3N4 crucibles superficially coated with Si3N4 (BAYER CFI 06051, about 0.3-0.5 mm thick). Sample sizes were 100-200 g. The samples were mechanically precompacted as described above.
The furnace cavity was evacuated twice at O.I mbar and repressurized with He or Ar.
Depending on sample size, crucible insulation and preheating to 200°C, temperatures of 1200-1450°C (surface temperature determined by means of a pyrometer) and thus the melting point of Si ( 1-l?3'C) were obtained after 15-GO nlln.
Le A 33 170-Foreign Countries A specific heating energy of about 19 kJ/g (for 100 g of sample) = S.3 kWh/kg was found which was likewise inversely proportional to the sample weight.
The samples were cooled down to about 300°C within about I-1.S h under He S protective gas.
3. Evaluation 3.1. Evaluation of the sintered Si powder in the reaction with methyl chloride or ~drocarbon The powder was classified or screened, and then 40 g of powder of the reported selected particle size were filled into a quartz tube having a glass frit bottom and a stirrer inserted via a stirrer bearing. The preferred particle size was usually 7I-1S 160 pm, after crushing, grinding and classifying or screening the granules.
3.1.1 In the case of the reaction of Si with methyl chloride, the Si powder was usually admixed with 3.2 g of Cu/CuZO/Cu0 catalyst (86% of Cu) and 0.048 ZnO. The methyl chloride flow was 1.8 I/h and 2 bar abs. The gas space was subsequently filled with nitrogen. The contents of the glass tube were heated to 370°C for a short period of 1 h by means of an electrically-heated tube furnace from HERAEUS, and then a pressure of 2 bar abs was maintained during reaction by means of an inclined tube manometer at 300°C or 330°C, respectively, within 8 hours.
The resulting products which vaporize readily at 300°C were withdrawn through a descending glass condenser having a coolant temperature of 1S°C, and condensed.
The effluent gases which were not condensable under these conditions, consisting of MeCI, HCI etc., were passrd into the exhaust air stream. The liquids of the various mrthvlchlorosilanes or chlorosilanes u~hich were condensable at 1S-20°C
were Le A 33 170-Foreign Countries collected in a receiver underneath the condenser and analyzed in a gas chromato-graph.
(For details, cf. DE 19S 32 31S).
S 3.2.1 In the case of the reaction Si+HCI instead of methyl chloride, the subsequent addition of catalytic additives was omitted. The pressure selected was likewise 1 bar gauge, but in this case the amount of HCl (4.2/9.61/h, via digital flow meters) and the temperature (220-3S0°C) were varied. Preactivation at 370°C was omitted.
3.2. Suitability for MCS synthesis: Examples 3.2.1. Comparative example: Reaction using standard metal-grade Si in a laboratory-scale stirred bed Metal grade silicon granules obtained from LILLEBY were ground in an agate mill using an electromechanical pestle. A fraction having a particle diameter of 7I-160 um was isolated from the laboratory-scale stirred bed by means of screening using ASTM standard screens.
Trace component contents were determined by ICP-AS.
The reaction with methyl chloride as mentioned in 3.1.1 produces the methyl-chlorosilane amounts reported in the first column, "comparison", of Table 1.
3.2.2. Example la (Comparative example: Use of untreated grinding fines) Grinding fines obtained from the silicon granules employed in the Comparative Example during ~:rinding in a hammer mill using ceramic balls under N~
protective 3U gas under industrial conditions wvrc blown from the mill into a filter.
These grinding fines were detcnnincd to have an average particle diameter of 3S ym and a Le A 33 i 70-Foreign Countries distribution of 5-50 pm. The particle size distribution was determined by means of a MALVERN Master Sizer 2000 (measurement of scattered light) in this case and by means of ASTM standard screens in the other cases above 36 um.
The above-described procedure 3.1.1. for reacting methyl chloride in accordance with the Miiller-Rochow method in a laboratory-scale stirred bed reactor produced the methylchlorosilane mixture reported in Table 1 {column 2, heading "1a").
In this procedure, the most important parameters to be optimized are a sufficiently high production rate and a high MeZSiCl2 content, however, it is equally or even more important to have achieved a particle diameter greater than 40 um and thus suitability for the fluidized bed, a property which cannot be evaluated.
For la, the production rate and the Me2SiCI2 concentration are found to be at the lower end of the expected range.
3.2 3. Example lb (Use of grinding fines treated according to the invention) 200 g of the grinding fines collected in the grinding process of Comparative Example 3.2.2. were subjected to microwave agglomeration (microwave furnace of type II) 2.2. under Ar protective gas. Heating time: 30 min. Temperature, sintered density and particle size after grinding and classifyng are reported in Table 1 (column 3, heading "lb"). Energy supplied: 500-1500 watts.
The energy was switched off and the material was cooled down to about 200°C and then discharged. The material was then cooled down to room temperature (25°C) in air and the agglomerate was subjected to grinding and screening. A crushing process using a hammer and an agate mill equipped with an electromechanically movable pestle yielded a powder having the properties reported in Table 1.
A 71-1(0 um fraction havins_: a DSO% value of 120 pm was isolated by screening for the comparative tests in the laboratory-scale reactor.
Le A 33 170-Foreign Countries The high Fe content of the grinding fines from Example la is found to be reduced to a level in the vicinity of the standard material from the Comparative Example in the grinding and classifying process.
The production rate is at the lower end of the expected range, the MezSiCl2 concentration was improved compared to the Comparative Example/Standard.
3.2.4. Example 2 (untreated Si dust from the fluidized bed of the Rochow synthesis) Unsintered fine dust from the fluidized bed of the Rochow synthesis (see also Examples 2b-2d) was evaluated as described above (Table 1, column 4, heading ,~2~~ ).
This Si dust had an average particle diameter of 20 p.m and an Si content of about 76 %. In addition, it contained 11.4 % of Cu, 3 % of Fe, 2.9 % of C, 0.3 % of Zn, 2 % of Cl and other metals prior to sintering.
The properties in the laboratory-scale stirred bed with respect to production rate and MeZSiCl2 concentration are very similar to those of the Si from the Comparative Example.
3.2.5. Examples 2a to 2d (Si fluidized bed dust treated according to the invention) Dust 2 from the fluidized, bed was subjected to stepwise heating by microwave exposure and agglomerated to various degrees.
The microwave furnace was charged with the Si dust described in 2. The temperature was increased to about 800-820°C within 40 min and then maintained at this Icvcl for about 30 min, with Cu salts evaporating in the form of a plasma cloud. The material was hcatcd further ..~ithin 20 min to a preselected level of 4 different final tempera-lures, with a maximum of 1500°C (in each case surface temperatures detemtined by Le A 33 170-Foreign Countries means of a pyrometer). The final temperatures were maintained for about 20 min:
The irradiation source was then switched off and the material was allowed to cool.
The powder separated after crushing, grinding and classifying to obtain a 10-160 p.m fraction (Cu content: 11.4 %) was evaluated in comparison with unsintered fine dust from Example 2 in 3.2.4. (Table 1, columns 4-7, headings "2a" to "2d) The production rate for methylchlorosilanes and the Me2SiC12 concentration were found to drop above 800-900°C and then arnve at a lower intermediate maximum for the main component. The agglomerated Si is less suitable for reaction with methyl chloride when this process sequence is employed.
3.2.6. Examples 3a and b (mixture of fluidized bed dust and ~rindin~ fines from metal grade silicon) 85 parts of metal grade silicon grinding fines from Example la. are admixed with 15 parts of ultrafine dust from the cyclone of a fluidized bed for methylchlorosilane synthesis.
Example 3a illustrates the result for the unsintered product (Table 1, column 8, heading "3a").
In Example 3b, the powder was partially sintered according to the invention.
The production rate is found to drop while the Me2SiClZ content increases (Table l, column 9, heading "3b") 3.2.7. Examples 4a and 4b (activation of metal grade Si powder +
catalyst/promoter mixture A standard metal grade Si powder from 3.2.1.-Comparative Example of particle size 71-170 pm was admixed with the amounts of catalyst (Cu/CuO, Zn, Sn) reported Le A 33 170-Foreign Countries in the Table and subjected to microwave heating under Ar protection in Example 4b.
The reported temperature below the melting point was maintained for about 30 min.
The material was then cooled down to 150°C under protective gas.
Table I {columns 10,1 l, headings "4a", "4b") shows an increase in the production rate of the resulting methylchlorosilane mixture and a small increase in Me2SiC12 concentration for a defined composition. .
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_ Le A 33 170-Foreign Countries 3.2.8. Examples Sa and Sb (Si ~rindin~ fines from Example 1a in hydrochlori-nation Table 2 shows that both the grinding fines in their original state and the grinding fines agglomerated according to the invention have roughly the same reactivity and product composition in the case of hydrochlorination in a laboratory-scale stirred bed (process as described in 3.1.2 except that HCI was used here instead of CH3C1).
3.2.9. Examples 6a and 6b (fluidized bed dust from Example 2 in hydrochlorination When the hydrochlorination is earned out using fine dust discharge from the fluidized bed (cyclone) for methylchlorosilane synthesis, the differences as illustrated in Table 2 are found between the original ultrafine fluidized bed dust and the dust 1 S agglomerated and ground according to the invention.
The agglomerated, ground and screened dust produces more SiCl4 at a production rate which is mostly lower. However, when the amount of available HCl is increased from 4.2 1/h to 9,6 1/h, the production rate increases to reach a level similar to that of the unagglomerated Si from 2 or 6a.
3.3.10. Example 7 (Si microdust from the decompostion of SiH4 to produce ultrapure A powder having an average particle size of 2 ftm and a distribution of 0.05-5 um was separated from the process for the preparation of ultrapure Si by decomposition of SiH., at 700-800°C in accordance with US 47 84 840 or US 48 83 687.
20U g of this powder were then placed in a microwave furnace as described above.
3O The powder was heated to 1450°C within GO min under He to give a melt cake Le A 33 170-Foreign Countries having a density of 1.9 g/cm' which was allowed to cool down to 200°C
under protective gas.
When using an Si3N4 crucible, a compact ingotlregulus was obtained which was S placed in a melt furnace (ULLMANN ENCYCLOPEDIA of Ind Chem., 1993 A 23 p.739, BRIDGEMAN melt furnace (J.C. Brice: Crystal Growth Processes, Blackie Glasgow & London (1986) p. 104).
The sample was melted at 1450°C and then subjected to programmed solidification in defined steps to produce multicrystalline Si having crystallite sizes of usually 5-50 mm. As a result, a multicrystalline Si block was obtained from which the outer regions were cut off to provide a multicrystalline core of the composition and structure desired for solar grade Si. After agglomeration according to the invention and conversion into multicrystalline Si using a BRIGDEMAN furnace, this material had a conductivity of about 2000 Ohm~cm. The core can be sawed into 350 l.~m Si slices which can be used as wafers in a solar module.
Le A 33 170-Foreign Countries Table 2 Composition of sintered Si powders and reaction products with HCI
5a 5b 6a 6b 6b 7 prior to sinteringgrml0.8 0.8 0.8 0.8 0.8 0.3 particle size um 35 35 35 35 35 10 D 90%
Si % 97 97 77 77 77 99.99999 C % 3 3 3 Cu % 11 11 11 Fe % 1 1 3 3 3 AI % 0.38 0.38 0.6 0.6 0.6 Ca % 0.13 0.12 Zn % 0.1 0.1 0.3 0.3 0.3 Sn % 0.0180.0180.018 sintering temp.C - 1050 1300 1300 sintered densityyml0.5 1.6 0.5 1.6 1.6 2.6 particle size Nm 1050 40-16010-5040-16040-160 used 050%
additions after% 0 0 0 0 0 0 sintering resistance of onm~ann.b. n.b. n.b.n.b. n.b. 2000 Si Hydrochlorination ~ after J ~ after 8h afterafterSh~after Hh Sh 16h ~
4.z 1 of Ham H2SiCl2 % 0.7 0.1 HSiCl3 % 87 58 SiCl4 % 12 42 Prod. rate gm 3.5 1.8 @4.21 HCUh )~
s.s I of Ham H2SiCl2 % 0.1 0.5 0.1 0.3 HSiCl3 % 85 96 75 65 SiCl4 % 15 4 25 35 Prod. rate gm 7.2 9 8.5 10.4 @9.61 HCUh )~
4.21 or Ham H2SiC12 % 0.01 0.06 0.3 0.1 HSiCl3 % 90.4 92.2 85 55 SiCl4 % 9.6 7.8 15 45 Prod, rate gm 2.4 3.2 3.7 1.8 @4.21 HCUh )~
s.s I of Ham H2SiCl2 % 0.1 0.1 HSiCl3 % 86 89.5 SiCl4 % 14 10.5 Prod, rate gm 10 10 9.61 HCUh )-4.21 Ot HGm H2SiCl2 % 0.03 0.01 0 0.1 0.04 HSiCl3 % 81.9 79.3 84 50.5 25 SiCl4 % 17.5 20.6 15 49.5 74.9 Prod rate 4.21gm 3.2 3.5 4 3.2 3.8 HCUh )~
gm )~ in g SiCl4IHSiCl3
Claims (14)
1. Process for the agglomeration of silicon powders, characterized in that the silicon powder is heated to a temperature of at least 300°C, preferably from 1200 to 1500°C, by exposure to microwave radiation in the wavelength range from 0.5 kHz to 300 GHz, and compacted to form sintered bodies of variable porosity.
2. Process according to Claim 1, characterized in that the starting material used is fine silicon dust having a particle size of less than 600 µm, preferably less than 100 µm.
3. Process according to Claim 1 or 2, characterized in that the agglomerate has a particle size of at least 30 µm.
4. Process according to any of Claims 1 to 3, characterized in that the heat treatment is carried out in a stirred moving bed, a tumble mixer, a rotary tube or a fluidized bed provided with internal or external means for introducing electromagnetic radiation.
5. Process according to any of Claims 1 to 4, characterized in that the heat treatment is carried out in a reactor made of microwave-transparent and/or microwave-reflecting material, preferably non-oxide ceramic, graphite, oxide ceramic or quartz.
6. Process according to any of Claims 1 to 5, characterized in that the silicon powder has been admixed with dopants containing metals, especially e.g. Cu, Ag, Al, Ca, Sn, Zn and/or boron, phosphorus, arsenic or antimony, prior to the microwave treatment.
7. Process according to any of Claims 1 to 6, characterized in that the agglomerate obtained by the microwave treatment has been admixed with dopants containing metals, e.g. Cu, Ag, Al, Ca, Sn, Zn and/or boron, phosphorus, arsenic oder antimony.
8. Process according to any of Claims 1 to 7, characterized in that the agglomerate obtained by the microwave treatment is ground and optionally classified, and the fine fraction is returned to the agglomeration zone.
9. Silicon granules, characterized in that they are obtainable by a process according to any of Claims 1 to 8.
10. Silicon granules according to Claim 9, characterized in that they have a porosity of 0 to 80 %.
11. Silicon granules according to Claim 9 or 10, characterized in that metal-containing and/or nonmetal-containing foreign phases or precipitates are present at the grain boundaries of the individual crystals.
12. Use of the silicon granules according to any of Claims 9 to 12 for the preparation of silicon single crystals, preferably by the Czochralski method or the float zone method.
13. Use of the silicon,granules according to any of Claims 9 to 10 for the preparation of multicrystalline silicon blocks, preferably by oriented crystallization of melts of the silicon granules to form multicrystalline Si.
14. Use of the silicon granules according to any of Claims 9 to 10, optionally after grinding and classifying, for reaction with hydrogen chloride or halogenated hydrocarbons RX in the temperature range 150-700°C in fluidized beds or shaft furnaces.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19859288A DE19859288A1 (en) | 1998-12-22 | 1998-12-22 | Agglomeration of silicon powders |
| DE19859288.4 | 1998-12-22 | ||
| PCT/EP1999/009694 WO2000037719A1 (en) | 1998-12-22 | 1999-12-09 | Agglomeration of silicon powders |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2355862A1 true CA2355862A1 (en) | 2000-06-29 |
Family
ID=7892132
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002355862A Abandoned CA2355862A1 (en) | 1998-12-22 | 1999-12-09 | Agglomeration of silicon powders |
Country Status (10)
| Country | Link |
|---|---|
| EP (1) | EP1144736B1 (en) |
| JP (1) | JP2002533289A (en) |
| AT (1) | ATE274610T1 (en) |
| AU (1) | AU2095800A (en) |
| BR (1) | BR9916497A (en) |
| CA (1) | CA2355862A1 (en) |
| DE (2) | DE19859288A1 (en) |
| NO (1) | NO20013091D0 (en) |
| WO (1) | WO2000037719A1 (en) |
| ZA (1) | ZA200104768B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7927385B2 (en) | 2007-06-01 | 2011-04-19 | Gt Solar Incorporated | Processing of fine silicon powder to produce bulk silicon |
| US8405183B2 (en) | 2003-04-14 | 2013-03-26 | S'Tile Pole des Eco-Industries | Semiconductor structure |
| US9493358B2 (en) | 2003-04-14 | 2016-11-15 | Stile | Photovoltaic module including integrated photovoltaic cells |
| US9741881B2 (en) | 2003-04-14 | 2017-08-22 | S'tile | Photovoltaic module including integrated photovoltaic cells |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2832253B1 (en) * | 2001-11-12 | 2005-05-27 | Michelis Quiriconi Raymond De | SOLAR CELL BASED ON (SE) (SI) IRIDIUM APPAUVRI |
| US7175685B1 (en) | 2002-04-15 | 2007-02-13 | Gt Solar Incorporated | Dry conversion of high purity ultrafine silicon powder to densified pellet form for silicon melting applications |
| FR2853562B1 (en) * | 2003-04-14 | 2006-08-11 | Centre Nat Rech Scient | PROCESS FOR PRODUCING SEMICONDUCTOR PELLETS |
| US8192648B2 (en) | 2003-04-14 | 2012-06-05 | S'tile | Method for forming a sintered semiconductor material |
| JP4869061B2 (en) | 2003-04-14 | 2012-02-01 | セントレ・ナショナル・デ・ラ・レシェルシェ・サイエンティフィーク | Sintered semiconductor material |
| DE102004027563A1 (en) * | 2004-06-04 | 2005-12-22 | Joint Solar Silicon Gmbh & Co. Kg | Silicon and process for its production |
| AP2959A (en) * | 2007-10-04 | 2014-08-31 | Huntsman Corp Australia Pty Ltd | Compositions and methods for coagulating silica from mineral processing streams |
| DE102007050010A1 (en) * | 2007-10-17 | 2009-06-25 | Jan-Philipp Mai | Method and apparatus for producing silicon |
| DE112009000068T5 (en) | 2008-06-24 | 2011-04-21 | JIANGXI SAI WEI LDK SOLAR HI-TECH Co., Ltd., Xinyu | Method of using silicon powder and silicon ingots as a raw material with good filling performance in single crystal or polycrystalline furnaces |
| DE102008036143A1 (en) | 2008-08-01 | 2010-02-04 | Berlinsolar Gmbh | Process for removing nonmetallic impurities from metallurgical silicon |
| DE102009035041B3 (en) * | 2009-07-28 | 2011-01-05 | Sunicon Ag | System for producing silicon granulates, comprises a device for granulating powdered silicon particles with a device for agglomeration the silicon particles and a device for melting the agglomerated silicon particles, and a cooling device |
| KR101854731B1 (en) * | 2011-07-28 | 2018-05-04 | 엘지이노텍 주식회사 | Method for ingot |
| JP5178939B1 (en) * | 2012-07-11 | 2013-04-10 | 和宏 永田 | Method for producing silicon by microwave and microwave reduction furnace |
| DE102012018548B4 (en) * | 2012-09-20 | 2016-11-17 | Technische Universität Bergakademie Freiberg | Process for recycling used solar modules and solar cells made of silicon and silicon-containing components |
| RU2545272C1 (en) * | 2013-09-25 | 2015-03-27 | Федеральное государственное бюджетное образовательное учреждение высшего профессионального образования "Уфимский государственный нефтяной технический университет" | Production of pellets from dressing tailings |
| DE102016104979A1 (en) * | 2016-03-17 | 2017-09-21 | Jpm Silicon Gmbh | Process for melting and cleaning metals, in particular metal waste |
| NO345463B1 (en) * | 2017-04-06 | 2021-02-15 | Elkem Materials | Silicon powder for use in anodes for lithium-ion batteries and method for production of silicon powder |
| CN112846197A (en) * | 2021-01-05 | 2021-05-28 | 北京科技大学 | Method for improving laser absorption rate of 3D printing metal powder |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL95386C (en) * | 1954-02-24 | |||
| DE3518829A1 (en) * | 1985-05-24 | 1986-11-27 | Heliotronic Forschungs- und Entwicklungsgesellschaft für Solarzellen-Grundstoffe mbH, 8263 Burghausen | METHOD FOR THE PRODUCTION OF MOLDED BODIES FROM SILICON GRANULES FOR THE PRODUCTION OF SILICONE MELTS |
| JP3342898B2 (en) * | 1991-11-26 | 2002-11-11 | 株式会社東芝 | Silicon sintered body and wafer holding board, sputtering target and silicon wafer formed using the same |
| JP2922078B2 (en) * | 1993-03-17 | 1999-07-19 | 株式会社トクヤマ | Silicon rod manufacturing method |
| DE19515342A1 (en) * | 1995-04-26 | 1996-10-31 | Widia Gmbh | Process, device for the thermal treatment of substances in a microwave oven and use of this process and this device |
-
1998
- 1998-12-22 DE DE19859288A patent/DE19859288A1/en not_active Withdrawn
-
1999
- 1999-12-09 WO PCT/EP1999/009694 patent/WO2000037719A1/en active IP Right Grant
- 1999-12-09 DE DE59910364T patent/DE59910364D1/en not_active Expired - Fee Related
- 1999-12-09 JP JP2000589766A patent/JP2002533289A/en active Pending
- 1999-12-09 AU AU20958/00A patent/AU2095800A/en not_active Abandoned
- 1999-12-09 BR BR9916497-3A patent/BR9916497A/en not_active IP Right Cessation
- 1999-12-09 EP EP99965444A patent/EP1144736B1/en not_active Expired - Lifetime
- 1999-12-09 CA CA002355862A patent/CA2355862A1/en not_active Abandoned
- 1999-12-09 AT AT99965444T patent/ATE274610T1/en not_active IP Right Cessation
-
2001
- 2001-06-12 ZA ZA200104768A patent/ZA200104768B/en unknown
- 2001-06-21 NO NO20013091A patent/NO20013091D0/en not_active Application Discontinuation
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8405183B2 (en) | 2003-04-14 | 2013-03-26 | S'Tile Pole des Eco-Industries | Semiconductor structure |
| US9493358B2 (en) | 2003-04-14 | 2016-11-15 | Stile | Photovoltaic module including integrated photovoltaic cells |
| US9741881B2 (en) | 2003-04-14 | 2017-08-22 | S'tile | Photovoltaic module including integrated photovoltaic cells |
| US7927385B2 (en) | 2007-06-01 | 2011-04-19 | Gt Solar Incorporated | Processing of fine silicon powder to produce bulk silicon |
Also Published As
| Publication number | Publication date |
|---|---|
| NO20013091L (en) | 2001-06-21 |
| BR9916497A (en) | 2001-10-09 |
| ATE274610T1 (en) | 2004-09-15 |
| DE19859288A1 (en) | 2000-06-29 |
| WO2000037719A1 (en) | 2000-06-29 |
| NO20013091D0 (en) | 2001-06-21 |
| AU2095800A (en) | 2000-07-12 |
| ZA200104768B (en) | 2002-05-14 |
| EP1144736A1 (en) | 2001-10-17 |
| EP1144736B1 (en) | 2004-08-25 |
| DE59910364D1 (en) | 2004-09-30 |
| JP2002533289A (en) | 2002-10-08 |
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