Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/02—Silicon
  • C01B33/021—Preparation
  • C01B33/023—Preparation by reduction of silica or free silica-containing material
  • C01B33/025—Preparation by reduction of silica or free silica-containing material with carbon or a solid carbonaceous material, i.e. carbo-thermal process

Definitions

• the invention relates to a process for producing silicon by reacting silicon oxide at elevated temperature by adding silicon carbide and optionally a second carbon source to the reaction mixture. Furthermore, the invention discloses a composition which can be used in the method according to the invention.
• the core of the invention is the use of silicon carbide as a reaction initiator and / or reaction accelerator in a kaialytica amount in the production of silicon or in an alternative in approximately equimolar amounts for the production of silicon.
• the silicon for solar applications or in microelectronics are used, such as for the production of high purity silicon by means of epitaxy or silicon nitride (SiN) 1 silicon oxide (SiO), silicon oxynitride (SiON), silicon oxycarbide (SiOC) or silicon carbide (SiC), the produced silicon meet particularly high demands on its purity. This is especially true in the production of thin layers of these materials.
• the silicon is previously converted to halosilanes, which are then converted into high-purity semiconductor silicon or solar silicon.
• DE 30 13 319 discloses a process for producing a silicon of concrete purity starting from silica and a carbonaceous reducing agent such as carbon black. indicating the maximum boron and phosphorus contents.
• the carbonaceous reducing agent was used in the form of tablets with a high purity binder such as starch.
• the object of the invention was to increase the cost-effectiveness of the process for producing silicon by finding a reaction initiator and reaction accelerator for this process which no longer has the stated disadvantages.
• the reaction starter and / or Christsbeschieuniger should be as pure and inexpensive.
• reaction initiators and / or reaction accelerators should not themselves introduce any interfering impurities or, preferably, impurities in very small amounts into the silicon melt for the reasons stated at the outset.
• a silicon oxide, in particular silicon dioxide, reacted at elevated temperature by silicon carbide the silicon oxide or silicon carbide in a Composition containing silicon oxide is added to the process, it is particularly preferred if the silicon oxide, and the Siiiziumcarbid be added in approximately stoichiometric ratio, ie about 1 mol of SiO 2 to 2 mol of SiC to produce silicon, in particular the reaction mixture for producing silicon from silicon oxide and silicon carbide.
• a silicon oxide in particular silicon dioxide
• a silicon oxide is reacted at elevated temperature by adding silicon carbide and a second carbon source to the silicon oxide or silicon carbide and a second carbon source in a composition containing silicon oxide; in this variant, the concentration of Si carbide be lowered so that it acts more as a reaction initiator and / or reaction accelerator and less than reactants.
• about 1 mole of silica may be reacted with about 1 mole of silicon carbide and about 1 mole of a second carbon source.
• the method for producing silicon by reaction of silicon oxide at elevated temperature Siiiziumcarbid the method for producing silicon by reaction of silicon oxide at elevated temperature Siiiziumcarbid
• Silicon oxide added is an electrical energy source
• the core of the invention is a Siiiziumcarbid as
• the Siiiziumcarbid is therefore fed separately to the process.
• silicon carbide is added as a reaction initiator and / or reaction accelerator to the process or composition. Since silicon carbide decomposes itself only at temperatures of about 2700-3070 0 C, it was surprising that it can be added to the process for the production of silicon as a reaction initiator and / or reaction accelerator or as a reactant.
• second carbon sources compounds or materials which do not consist of silicon carbide, have no silicon carbide or contain no silicon carbide.
• the second carbon source is not silicon carbide, has no silicon carbide, or does not contain silicon carbide.
• the function of the second carbon nucleus is more that of a pure reactant. while the silicon carbide is also a reaction initiator and / or reaction accelerator.
• the second carbon source is preferably selected from the compounds mentioned.
• the contamination of the second carbon sources with boron and / or phosphorus or boron and / or phosphorus-containing compounds should be less than 10 ppm for boron, in particular between 10 ppm and 0.001 ppt, and less than 20 ppm for phosphorus are, in particular between 20 ppm and 0.001 ppt, in parts by weight.
• the data ppm, ppb and / or ppt are to be construed as the proportions of the weights in mg / kg, ⁇ g / kg etc.
• the content of boron is preferably between 7 ppm and 1 ppt, preferably between 8 ppm and 1 ppt, more preferably between 5 ppm and 1 ppt or below, for example between 0.001 ppm and 0.001 ppt, preferably in the range of the analytical detection limit.
• the content of phosphorus should preferably be between 18 ppm and 1 ppt, preferably between 15 ppm and 1 ppt, more preferably between 10 ppm and 1 ppt or less.
• the content of phosphorus is preferably in the range of the analytical detection limit. In general, these limits are sought for all reactants or additives of the process to be suitable for the production of solar and / or semiconductor silicon.
• Suitable silicon oxides are generally all compounds containing a silicon oxide and / or minerals, provided that they have a purity suitable for the process and thus for the process product and do not introduce any interfering elements and / or compounds into the process or incinerate without residue. As stated above, pure or high purity silica-containing compounds or materials are used in the process.
• the contamination of the silicon oxide with boron and / or phosphorus or boron and / or phosphorus-containing compounds for boron should be below 10 ppm, in particular between 10 ppm and 0.001 ppt, and for phosphorus below 20 ppm, in particular between 20 ppm and 0.001 ppt.
• the content of boron is preferably between 7 ppm and 1 ppt, preferably between 6 ppm and 1 ppt, more preferably between 5 ppm and 1 ppt or below, or for example between 0.001 ppm and 0.001 ppt, preferably in the range of the analytical detection limit.
• the content of phosphorus of the silicon oxides should preferably be between 18 ppm and 1 ppt, preferably between 15 ppm and 1 more preferably between 10 ppm and 1 ppt or below.
• the content of phosphorus is preferably in the range of the analytical detection limit.
• silicon oxides are quartz, quartzite and / or silicas prepared in a conventional manner. These may be the silicon dioxides occurring in crystalline modifications, such as moganite (chalcedony), ⁇ -quartz (deep quartz), ⁇ -quartz (high quartz). Tridymite, cristobalite, coesite, stishovite or amorphous Si ⁇ 2 be. In addition, preference is given to silicic acids, in particular precipitated silicas or silica gels, to pyrogenic SiO 2. fumed silica or silica in the process and / or composition.
• Conventional pyrogenic silicas are amorphous SiO 2 powders with an average diameter of 5 to 50 nm and a specific surface area of 50 to 600 m 2 / g.
• the above enumeration is not exhaustive, it will be apparent to those skilled in the art that it may also employ other sources of silica suitable in the process and / or composition for the process.
• the silicon oxide in particular SiO.sub.2, can be pulverulent, granular, porous, foamed, as an extrudate, as a pressure and / or as a porous glass body optionally together with other additives, in particular together with the second carbon source and / or silicon carbide and optionally a binder and / or or forming assistant, submitted and / or used.
• Preference is given to using a pulverulent, porous silicon dioxide as a shaped body, in particular in an extrudate or pressing, more preferably together with the second carbon source in an extrudate or pressing, for example in a pellet or briquette.
• all solid reactants should be. how silica, silicon carbide and optionally the second carbon source are used in a form in the process or in the composition which provides the greatest possible surface area for the course of the reaction.
• the information may relate to the starting materials and in particular to the reaction mixture in the process:
• Siiiziummonoxid as Patinai ® can, about 1 of a second source of carbon and silicon carbide are used in small quantities added as a reaction initiator or a reaction accelerator mol.
• Amounts of silicon carbide as the reaction initiator and / or reaction accelerator are about 0.0001% by weight to 25% by weight, preferably 0.0001 to 20% by weight, particularly preferably 0.0001 to 15% by weight, in particular 1 to 10 wt .-% based on the total weight of the reaction mixture, in particular comprising
• reaction initiator about 2 moles of a second carbon source and silicon carbide may be added in small amounts as a reaction initiator or reaction accelerator.
• Typical amounts of silicon carbide as reaction initiator and / or reaction accelerator are about 0.0001 wt .-% to 25 wt .-%, preferably 0.0001 to 20 wt .-%, particularly preferably 0.0001 to 15 wt .-%, in particular 1 to 10 wt .-% based on the total weight of the reaction mixture, in particular comprising silicon oxide, silicon carbide and a second carbon source and optionally further additives.
• about 2 mol of silicon carbide as the reactant can be used in the process for 1 mol of silicon dioxide, and optionally a second carbon source may be present in small amounts.
• Typical amounts of the second carbon source are about 0.0001 wt .-% to 29 wt .-%, Favor! 0.001 to 25 wt .-%, particularly preferred! 0.01 to 20% by weight. most preferably 0.1 to 15 wt .-%, in particular 1 to 10 wt .-% based on the total weight of the reaction mixture, in particular comprising silicon dioxide, silicon carbide and a second carbon source and optionally further additives.
• silicon dioxide can be reacted with silicon carbide and / or a second carbon source according to the following reaction equations:
• Control carbon source Preferably, silicon carbide and the second should be
• Silicon dioxide are used in the process or present in the process.
• Carbon source be composed of 2 mol SIC to 0 mol second
• Carbon source up to 0.00001 mol SiC to 1.99999 moi second carbon source
• the 2 Mo! to SiC and optionally C together from 2 to 0.00001 mo! SiC and 0 to 1, 99999 mo! C, in particular from 0.0001 to 0.5 mol SiC and 1.9999 to 1.5 mol C, preferably 0.001 to 1 mo! SiC and 1, 999 to 1 mol C, particularly preferably 0.01 to 1, 5 mo! SiC and 1, 99 to 0.5 mol C, in particular it is preferably 0.1 to 1, 9 mol SiC and 1, 9 to 0.1 mol C to about 1 mo!
• Suitable silicon carbides for use in the process or composition according to the invention are all poly-phthalic phases, where appropriate the silicon carbide may be coated with a passivating layer of SiC> 2. Individual polytype phases with different stability can preferably be used in the process, because they can be used to control, for example, the course of the reaction or the start of the reaction of the process. High purity silicon carbide is colorless and is preferably used in the process.
• the process or composition may include, as silicon carbide, technical SiC (carborundum), metallurgical SiC, SiC bond matrices, open porous or dense silicon carbide ceramics, such as silicate bonded silicon carbide SiC (RSiC). reaction-bonded, silicon-infused silicon carbide (SiSiC).
• the contamination of the silicon carbide with boron and / or phosphorus or boron and / or phosphorus-containing compounds is preferably less than 10 ppm for boron, in particular between 10 ppm and 0.001 ppt, and for phosphorus less than 20 ppm, in particular between 20 ppm and 0.001 ppt ,
• the content is preferably present
• Siiiziumcarbid between 7 ppm and 1 ppt, preferably between 6 ppm and 1 ppt, more preferably between 5 ppm and 1 ppt or less, or, for example, between 0.001 ppm and 0.001 ppt, preferably in the range of the analytical detection limit.
• the content of phosphorus of a silicon carbide should preferably be between 18 ppm and 1 ppt, preferably between 15 ppm and
• the content of phosphorus is preferably in the range of the analytical detection limit.
• silicon carbides are increasingly being used as a composite material, for example for the production of semiconductors, brake disk material or heat shields and other products
• the method according to the invention and the composition according to the invention offer a possibility for elegant recycling of these products after use or the waste or scrap produced in their manufacture.
• the only requirement for the silicon carbides to be recycled is sufficient purity for the process, preferably silicon carbides are recycled, which meet the above specification with respect to boron and / or phosphorus.
• the silicon carbide may be a) powdery, granular and / or lumpy and / or b) in a porous glass, in particular quartz glass, in an extrudate and / or pressing, such as pellet or briquette, optionally be added together with other additives to the process .
• Other additives may include, but are not limited to, silicon oxides or the second carbon sources such as sugars, graphite, carbon fibers, and processing aids such as binders.
• compositions are added continuously or discontinuously.
• the silicon carbide is added in the amounts and in the course of the process to the extent that a particularly economical process is achieved. Therefore, it may be advantageous if the silicon carbide is added gradually in a continuous manner in order to ensure sustained reaction acceleration
• the reaction takes place in conventional melting furnaces for the production of silicon, such as metallurgical silicon, or other suitable furnaces, such as induction furnaces.
• suitable furnaces such as induction furnaces.
• the design of such furnaces, particularly preferably electric furnaces, which use an electric arc as an energy source, are well known to the skilled person and are not part of this application.
• DC furnaces they have a melting electrode and a bottom electrode or, as an AC furnace, usually three melting electrodes.
• the arc length is controlled by means of an electrode regulator.
• the electric arc furnaces are generally based on a reaction chamber made of refractory materials, in the lower region of which liquid silicon can be tapped or discharged.
• the raw materials are added in the upper area in which the graphite electrodes are arranged to generate the arc.
• These ovens are usually operated at temperatures in the range around 1800 0 C. It is also the expert It is known that the furnace superstructures themselves must not contribute to a contamination of the silicon produced.
• the method can be carried out in such a way that a) the silicon carbide and silicon oxide, in particular silicon dioxide, and optionally the second carbon source are each fed separately to the process, in particular the reaction space, and if appropriate subsequently mixed and / or b) the silicon carbide together with silicon oxide, in particular silicon dioxide, and optionally the second carbon source in a composition and / or c) the silicon oxide, in particular silicon dioxide, together with the second carbon source in a composition, in particular in the form of an extrudate, preferably as a pellet or briquette, and / or d) the silicon carbide in a composition with the second carbon source is added or added to the process.
• This composition may comprise a physical mixture, an extrudate or also a carbon fiber reinforced silicon carbide.
• the silicon carbide and / or silicon oxide and optionally the second carbon source may be supplied to the process as a material to be recycled.
• the only prerequisite for all compounds to be recycled is that they have sufficient purity to form a silicon in the process from which solar grade silicon and / or semiaritic acid can be produced.
• silicon oxides offer quartz glass, for example, cullet. To name just a few, these may be Suprasil, SQ 1, Herasil, Spektrosil A.
• the purity of these quartz glasses can be determined, for example, via the absorption rates at specific wavelengths, such as at 157 nm or 193 nm.
• the second carbon source it is possible, for example, to use approximately spent electrodes which have been brought into a desired shape, for example as powder.
• the silicon produced or obtained by the process according to the invention is preferably suitable a) for further processing in the process for the production of solar silicon or semiconductor silicon or b) as solar silicon or semiaritanium silicon.
• the impurities of the produced silicon with boron and / or phosphorus-containing compounds should be in the range of less than 10 ppm to 0.0001 ppt for boron, more preferably in the range of 5 ppm to 0.0001 ppt, preferably in the range of 3 ppm to 0.0001
• the content of phosphorus should be in the range of below 10 ppm to 0.0001 ppt, in particular in the range of 5 ppm to 0.0001 ppt, preferably, in the range of 1 ppb to 0.0001 ppt, stated in parts by weight in the range of 3 ppm to 0.0001 ppt, or more preferably in the range of 1 ppb to 0.0001 ppt, in parts by weight.
• the range of impurities is generally not limited downwards, but is determined solely by the current detection limits of the analytical methods.
• ICP-MS For the detection of boron and / or phosphorus-containing compounds, ICP-MS or else a spectral analysis or resistance measurements can be offered.
• the invention also relates to a composition which is particularly suitable for use in the above process for the production of silicon and whose quality is preferably suitable as solar silicon or for the production of solar silicon and / or semiconductor silicon, wherein the
• Composition contains silicon oxide and silicon carbide and optionally a second carbon source.
• silica especially silicon dioxide.
• Silicon carbide and optionally second carbon source are in particular the above-mentioned, preferably they meet the purity requirements listed there.
• the silicon carbide may also in the composition, according to the above a) powdered, gromig and / or lumpy and / or b) in a porous glass, in particular quartz glass, in an extrudate and / or pellet optionally present together with other additives.
• the composition may include silicon-infiltrated silicon carbide and / or carbon fiber-containing silicon carbide.
• the silica in particular Si ⁇ > 2, powdery, granular, porous, foamed, as an extrudate, as a pellet and / or as a porous glass body optionally together with other additives, in particular together with the second carbon source and / or silicon carbide, in the Be contained in the composition.
• Preferred is a composition in which the silica is present together with the second carbon source in the form of extrudates. especially preferred as a pellet.
• Another object of the invention is also the use of silicon carbide according to any one of the preceding claims as a reaction initiator and / or reaction accelerator in the production of silicon or the use of silicon carbide in approximately equimolar amounts with respect to the silica or in particular according to an above ratio of silica to SiC and C for the production of silicon, in particular for the production of solar silicon, preferably as a crude product for the production of solar silicon and / or semiconductor silicon.
• Silicon as a base material for solar cells and / or semiconductors or in particular as a starting material for the production of solar grade silicon.
• the invention also provides a kit containing separated formulations, in particular in separate containers, such as containers, bags and / or cans, in particular in the form of an extrudate and / or powder of silicon oxide, in particular silicon dioxide, silicon carbide and / or the second carbon source, in particular for use according to the above.
• silica directly with the second carbon source as an extrudate, in particular as a pellet, in a container in the
• Kit is present and the silicon carbide powder in a second container.
• SiO2 (AEROSIL ® OX 50) and C (graphite) were in a weight ratio of about 75: reacted in the presence of SiC 25th Procedure:
• An electric arc which serves as an energy source, is ignited in a conventional manner. It is a creeping start of the reaction by exiting gaseous compounds between SiO 2 and C to observe. Subsequently, powdered 1 wt .-% SIC is added in. After a very short time, there is a very strong increase in the reaction to the appearance of luminous phenomena. Subsequently, the reaction proceeded even after the addition of SiC further under intensive, heilem orange lighting (approximately 1000 0 C).
• Occurring gases are detected 1% by weight of powdery SiC is added, and after a short time this leads to a strong increase in the reaction, as can be seen from the appearance of luminous phenomena
• the solid obtained after completion of the reaction was identified as silicon by SEM and EDX analysis (energy dispersive X-ray spectroscopy).
• SiO 2 (! EROS L ® OX 50), and C were as a mixture 65: 35 brought at high temperature (> 1700 0 C) in a tube for reaction. The reaction barely started and proceeded without noticeable progress. A bright glow could not be observed.

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