CN1204298A - Method and apparatus for producing polysilicon and method for producing silicon substrate for solar cells - Google Patents

Abstract

A process and an apparatus which enable mass production of polycrystalline silicon and a substrate made therefrom at a low cost from metallic silicon or silicon oxide as a starting material in a flow production line involving a series of continuous steps. The polycrystalline silicon and the silicon substrate for solar cells are prepared from metallic silicon through step A of refining metallic silicon under redudced pressure and solidifying the metallic silicon to remove impurities from the molten metal, thereby preparing an ingot; step B of cutting and removing an impurity-enriched portion of the ingot; step C of remelting the residue and removing boron and carbon by oxidation from the molten metal under an oxidizing atmosphere, followed by blowing of a gaseous mixture of argon with hydrogen to conduct deoxidation, step D of casting the molten metal after the deoxidation into a mold to conduct unidirectional solidification, thereby preparing an ingot;

Description

Method and apparatus for producing polysilicon and method for producing silicon substrate for solar cells

technical field

The present invention relates to the manufacturing method and device of polysilicon and the manufacturing method of silicon substrate for solar cell, especially relate to a kind of using metallic silicon or silicon oxide as starting material, through the assembly line operation of a series of processes to manufacture the solar energy as the final product Production technology of polysilicon substrates for batteries.

Background technique

Research on solar cells has been going on for a long time. Recently, a solar cell with a photoelectric conversion efficiency of about 13-15% under sunlight on the ground has appeared, and has gradually achieved practical application in various uses. . However, as general household electricity or energy sources for automobiles, ships, and working machinery, it cannot be said to be very popular in my country, at least. The reason for this is that the silicon substrate technology necessary for the manufacture of solar cells has not yet been established to enable inexpensive mass production.

Now, in order to manufacture silicon substrates for solar cells, the use of chemical methods has been able to use metal silicon (99.5% by weight of Si) with low raw material purity as a starting material to directly prepare a bulk silicon substrate suitable for use as a semiconductor. of high-purity silicon. Then use metallurgical methods to remelt the bulk high-purity silicon and adjust it to a chemical composition suitable for solar cells, then use the drawing method or directional solidification method to make the obtained melt into silicon ingots, and finally the The silicon ingot is sliced into thin slices. That is to say, as shown in Fig. 5, metal silicon is first reacted with hydrochloric acid, gasified into trichlorosilane, impurities are removed by rectification of the gas, and then reacted with hydrogen, according to the so-called CVD (chemical Vapor phase deposition) makes it possible to precipitate high-purity silicon from gas. Therefore, the obtained high-purity silicon is only an aggregate composed of silicon particles with weak bonding force between crystal particles. In addition, even if the boron contained in the high-purity silicon forming the aggregate is reduced to about 0.001 ppm, it cannot meet the specific resistance specification of 0.5 to 1.5 Ω·cm required as a substrate for a P-type semiconductor. Require. In order to use the above-mentioned high-purity silicon for solar cells, it is necessary to adjust its specific resistance and control its crystallinity so that single crystals or crystals with a grain size of several mm or more are obtained, and the grain boundaries thereof do not adversely affect photoelectric conversion efficiency Therefore, the above-mentioned high-purity silicon cannot be directly made into a substrate in this state. Then, as shown on the right side of Figure 5, one must go through re-melting the block, adjusting the composition of the melt (adding boron), ingotizing (pulling for single crystals, orienting for multi-crystalline) Solidification method) and the process of forming the substrate.

However, the said previous manufacturing method must again adjust the composition (mainly add boron) and refine the high-purity silicon ingots that have reached the level that can be used in semiconductors, so that they can be used in solar cells, which not only complicates the process , the pass rate is low, and remelting equipment and additional energy are required, so the manufacturing cost is high. Therefore, as mentioned above, the solar cells that can be purchased at present are all expensive products, and this becomes an obstacle preventing it from being widely used. In addition, according to the chemical method, in order to achieve high purity of metal silicon, a large amount of substances polluting the environment such as silane and chloride are unavoidably produced, which becomes an obstacle to mass production, so there is also a problem. In addition, due to the impact of the above-mentioned manufacturing methods, the recently disclosed technology research trend is to further subdivide the manufacturing process, such as the high purification and solidification technology of metal silicon.

For example, Japanese Patent Laid-Open No. 5-139713 discloses a method of "obtaining silicon with a low boron content, which is to keep molten silicon in a container containing silicon dioxide or silicon dioxide as the main component. A plasma gas jet of an inert gas is injected onto the surface of the melt while the inert gas is blown from the bottom of the vessel". In addition, Japanese Patent Laid-Open Publication No. 7-17704 discloses a method of "highly efficient removal of boron. When using electron beams to melt metal silicon, on the surface of metal silicon powder, relative to every 1 kg of silicon, 1.5-15 kg of SiO ₂ "is formed. Also, regarding the solidification technique, JP-A-61-141612 proposes "a technique for preventing inclusions from being precipitated in a silicon ingot by rotating the mold when molten silicon is poured into it". In addition, the present applicant himself proposed a "purification method by directional solidification of molten metal silicon" in Japanese Patent Application No. Hei 7-29500 (filing date: February 17, 2017).

On the other hand, there is not no technology to directly manufacture silicon for solar cells from metallic silicon. For example, Japanese Patent Application Laid-Open No. 62-252393 discloses a zone melting method (Zonemelting), which uses waste silicon from the electronics industry that was once used as a semiconductor as a starting material, and uses a mixture of argon, hydrogen, and oxygen. The plasma jet generated by the gas will zone-melt the raw material. However, this method is only a method of utilizing industrial waste and cannot become a mainstream technology requiring mass production of silicon substrates. In addition, although raw material silicon is economical to use, if high purity is required, this method cannot be a substitute for the above-mentioned troublesome production method. In addition, JP-A-63-218506 discloses a method of producing bulk silicon for solar cells or electronic devices from powdery, granular or unground metal silicon by plasma melting. However, the principle of this method is the same as that of the above-mentioned JP-A-62-252393, and it is a zone melting method using plasma, which has the disadvantages of high power consumption and mass production. In addition, the examples in this publication only obtain about 50 g of rod-shaped silicon on a laboratory scale, and there is no description of a silicon substrate for solar cells of a practical size.

disclosure of invention

In view of the foregoing, it is an object of the present invention to provide a polysilicon as a product and a substrate manufactured using the polysilicon, which are produced cheaply and in large quantities by using metal silicon or silicon oxide as a starting material and carrying out flow-line operation through a series of continuous processes. manufacturing methods and devices.

In order to achieve the above object, the present inventors conducted intensive studies focusing on obtaining the maximum economic effect by using only metallurgical methods instead of chemical methods, and thus completed the present invention.

That is to say, the present invention provides a method for producing polysilicon, which is characterized in that polysilicon is produced from metal silicon using the following steps:

A． Metal silicon is melted in a vacuum, the phosphorus in it is gasified and volatilized to remove it, and then solidified to remove impurity components from the melt, thereby obtaining an ingot;

B． Cut off the impurity-concentrated part of the above-mentioned ingot;

C． The remaining part after the impurity-concentrated part is cut off is remelted, and then boron and carbon are oxidized and removed from the melt in an oxidizing atmosphere, and then argon or a mixture of argon and hydrogen is blown into the melt for deoxidation;

D． Casting the above-mentioned deoxidized melt into a mold for directional solidification to obtain an ingot;

E． The impurity-concentrated portion of the ingot obtained by directional solidification is excised.

In addition, the present invention also provides a method for producing polycrystalline silicon, which is characterized in that the above-mentioned metallic silicon is obtained by reducing and refining silicon oxide.

In addition, the present invention also provides a method for producing polysilicon, which is characterized in that, firstly, the molten metal silicon obtained by refining silicon oxide is transferred into a crucible, and the boron and carbon are oxidized and removed in an oxidizing atmosphere, and then solidified , then carry out the B process of claim 1, carry out melting in vacuum, then carry out the C, D and E process of claim 1.

In addition, the present invention also provides a method for producing polysilicon, characterized in that the above-mentioned oxidizing atmosphere is formed by H ₂ O, CO ₂ or O ₂ gas, and the amount used is as small as possible so that the interface between the above-mentioned melt and the gas is not affected. Covered with silicon oxide, the silicon oxide generated on the surface of the above-mentioned melt is removed by local heating with a plasma arc, or H ₂ O, CO ₂ or O ₂ gas is blown into the melt to replace the above-mentioned oxidizing atmosphere.

In addition, the present invention also provides a method for producing polysilicon, which is characterized in that SiO ₂ or Si ₃ N ₄ is used as the above-mentioned release agent, and the moving speed of the solidification interface when solidifying to remove the above-mentioned impurities is 5mm/ Min or less, the moving speed of the solidification interface during directional solidification is less than 2mm/min, or the ingot is cut at a height above 70% from the lower end of the ingot.

In addition, the present invention also provides a method for producing polysilicon, characterized in that the phosphorus concentration in the melt is reduced to below 0.3 ppm, the boron concentration is reduced to below 0.6 ppm or the carbon concentration is reduced to below 10 ppm .

The present invention has also been accomplished in terms of a manufacturing device, that is, a polysilicon manufacturing device, characterized in that the device comprises: a heating device for melting or heating metal silicon; a holding container for holding molten metal silicon; A first mold for casting the melt in the holding vessels; a decompression chamber surrounding these holding vessels and the molds for vaporizing phosphorus from the melt; A remelting device for remelting or heating; a refining vessel for holding the remelted melt; a nozzle for blowing or injecting an oxidizing gas, hydrogen or a mixture of hydrogen and argon into the melt in the refining vessel; The second mold for casting the deoxidized melt into ingots.

In addition, the present invention provides a polycrystalline silicon manufacturing device, characterized in that the vacuum degree in the decompression chamber is higher than 10 ^-3 Torr, and the water-cooled jacketed crucible or graphite crucible made of copper is used as the holding container, and the holding container is made of SiO ₂ Quality crucible, SiO ₂ molded crucible or SiO ₂ lined crucible as the above refining vessel.

In addition, the present invention provides a polysilicon manufacturing device, wherein the heating device is an electron gun, and the remelting device is a plasma arc torch or a DC arc source.

In addition, the present invention provides a polysilicon manufacturing apparatus, characterized in that the side walls of the first and second molds are formed of heat insulating materials, the bottoms thereof are formed of water-cooled jackets, and the above molds are arranged for heating Casting into the heat source of the melt, and making the ratio of the height H of the casting mold to its diameter W be W/H>0.5.

In addition, the main aspect of the present invention is to provide a method for manufacturing a silicon substrate for solar cells, which is characterized in that the polycrystalline silicon ingot obtained by any of the above-mentioned manufacturing methods is cut into thin plates with a thickness of 100-450 μm.

According to the present invention, polysilicon or silicon substrates for solar cells can be manufactured using the above-mentioned method and apparatus without the need for a step of adjusting the composition of high-purity silicon, which was indispensable in the conventional method. In addition, not only can the useless consumption of energy be reduced, but also because only metallurgical methods are used, a large amount of substances that pollute the environment that are unique to the use of chemical methods will not be produced, so that the size of the equipment can be safely realized. As a result, a silicon substrate for solar cells with excellent photoelectric conversion efficiency can be provided at a much lower price than in the past. Furthermore, the polycrystalline silicon obtained by carrying out the present invention can be effectively used as a raw material for making iron and the like without making a substrate.

As described above, according to the present invention, waste of energy can be avoided, and equipment can be enlarged, so that polycrystalline silicon with high purity and polycrystalline silicon substrates for solar cells can be mass-produced. As a result, it is possible to provide a polycrystalline silicon substrate for a solar cell whose photoelectric conversion efficiency on the ground is not different from that obtained by a conventional method at a particularly low price, and thus the widespread use of solar cells can be expected. In addition, the obtained polysilicon can be effectively used as a raw material for iron making, etc. even if it is not used for manufacturing a substrate.

A brief description of the attached drawings

Fig. 1 is a flow chart showing an example of a method for producing polycrystalline silicon and a silicon substrate for a solar cell in the present invention.

Fig. 2 is a flow chart of another scheme showing the manufacturing method of said polysilicon and solar cell silicon substrate in the present invention.

Fig. 3 is a schematic diagram of an apparatus for carrying out the method of manufacturing polysilicon and silicon substrates for solar cells in the present invention.

Fig. 4 is an apparatus for carrying out another embodiment of the polycrystalline silicon and silicon substrate manufacturing method for solar cells mentioned in the present invention.

Fig. 5 is a flow chart showing a conventional method of manufacturing a silicon substrate for a solar cell.

Best way to implement the invention

FIG. 1 shows an example of a method of manufacturing polysilicon and a silicon substrate for a solar cell in the present invention as a flow chart (the part surrounded by a dotted line is the manufacturing of the substrate).

First, metal silicon with a lower purity (99.5% by weight) is put into a graphite or water-cooled copper holding vessel and melted under vacuum. At this time, known gas heating, electric heating, etc. can be used as heating means, but an electron gun is preferable. Here, the molten metal silicon (hereinafter referred to as the melt) is kept in the above-mentioned holding container at a temperature range of 1450 to 1900°C for a predetermined time (for example, 30 to 60 minutes) in order to make the phosphorus contained in the impurities And aluminum gasification removal (vacuum refining). It is preferred to reduce the phosphorus concentration in the melt to below 0.3 ppm. Then, in order to reduce impurities such as Fe, Al, Ti, Ca to 100ppm or less, the melt is cast into the first mold and cooled, so that the melt solidifies from the bottom to the top, and the moving speed of the solidification interface is 5mm/ min. As a result, an ingot in which the above-mentioned impurity element-concentrated melt is finally solidified is obtained.

Next, about 30% of the upper portion of the ingot where the impurity elements were concentrated was cut off. The remaining ingot is then loaded into a melting furnace with a plasma arc to remelt it. In this case, the heating means is not limited to plasma arc. Boron and carbon in the melt are removed in the form of oxides by raising the temperature of the molten melt to a temperature above 1450° C. and reacting with an oxidizing gas at the same time (oxidative refining). Then, argon or argon-hydrogen mixed gas is blown into the melt after oxidation refining for a certain period of time. As a result, the oxygen in the melt is removed to below 10 ppm. The above oxidation refining may be performed in a decompression chamber or may be performed in the atmosphere. Next, the deoxidized melt is poured as a refined product into a second mold coated with a mold release agent, and directionally solidified to obtain an ingot. Impurity elements are concentrated in the upper part of the ingot, so this part (usually accounting for about 20%) is cut off and removed, and the remaining part is used as a polysilicon product.

The polysilicon manufacturing method has been described above, but in the case of making silicon substrates for solar cells, the remainder is cut (flaked) into sheets with a thickness of 100 to 450 µm by a multi-wire saw.

Since the above-mentioned metal silicon as a starting material can usually be obtained by reducing and refining silicon oxide, the use of silicon oxide as a starting material also belongs to the present invention. For the refining method of silicon oxide, any known method may be used in order to obtain a product having the same level of purity as metal silicon originally used in the above-mentioned present invention. For example, a submerged arc melting furnace can be used to melt and reduce silicon oxide using carbon as a reducing agent. In addition, according to the present invention, when producing metal silicon from silicon oxide, it may also be considered to remove components unnecessary as polycrystalline silicon or silicon substrates for solar cells in advance. That is to say, as shown in the flowchart of FIG. 2 , a so-called pre-refining method is carried out by charging silicon oxide obtained from silicon oxide in a molten state with relatively low purity into a refining vessel (such as a crucible). Specifically, oxidizing gas (H ₂ O, CO _{2 ,} etc.) is blown into the melt in the crucible to remove boron and carbon as oxides, and then solidify. Next, the obtained ingot was melted and vacuum refined in the above-mentioned decompression chamber to dephosphorize it, and then directional solidified to obtain an ingot of polycrystalline silicon. In order to obtain the substrate, the ingot can be sliced into thin slices in the same manner as above. The advantage of this method is that the steps of "deboronation, decarburization" and "solidification for removal of impurities" of the present invention described above are not required by changing a part of conventional metal silicon manufacturing operations. As a result, certain equipment can be saved and energy consumption can be significantly reduced, so polysilicon and silicon substrates for solar cells can be obtained at a lower cost with the same level as the products obtained by the above-mentioned method of the present invention. Especially if the deboron and decarburization operations have been completed in advance at the mine site during the manufacturing stage of metal silicon, then for polysilicon or substrate manufacturers, the latter operations are very easy to carry out.

Incidentally, the moving speed of the solidification interface in the present invention is 5 mm/min or less in the first casting mold and 2 mm/min or less in the second casting mold. The concentration of impurity metal elements such as Al and Al on the top of the ingot is insufficient. In addition, the reason why the above-mentioned ingot is cut at a height above 70% from the lower end of the ingot is that the remaining portion below this height can achieve the target composition required as polysilicon. In addition, in the present invention, the vacuum degree in the above-mentioned decompression chamber is required to be higher than 10 ^-3 Torr, in order to make the vapor pressure of phosphorus in metallic silicon suitable for gasification dephosphorization.

In addition, in the present invention, the reason for reducing the phosphorus concentration in the melt to below 0.3ppm is to ensure that the solar cell can work stably; the reason for reducing the boron concentration to below 0.6ppm is to make it suitable as a P Type semiconductor substrates; the reason for reducing the carbon concentration to below 10ppm is to suppress the precipitation of SiC in silicon crystals and prevent the reduction of photoelectric conversion efficiency.

In addition, a water-cooled jacketed crucible made of copper or a graphite crucible is used as the holding vessel when the metal silicon is melted, and a _SiO2- based crucible, _SiO2 die or _SiO2- lined crucible is used as the above-mentioned refining vessel. The reason is that silicon It is easy to react with other substances, so if a container other than the above is used, these component elements will be mixed into silicon. Incidentally, when operations such as deboronization are performed at the production stage of metal silicon, inexpensive Al ₂ O ₃ , MgO, graphite, etc. other than SiO ₂ can be used as the lining of the refractory. The reason is that, for example, even if these impurities are mixed, they can be removed in the subsequent treatment stage. In addition, the reason for using SiO ₂ or Si ₃ N ₄ as a mold release agent used during solidification is the same as above. The reason why a mold release agent is necessary is that when molten silicon expands by 10% in volume as it solidifies, the use of a mold release agent prevents residual stress.

In addition, in the apparatus of the present invention, as shown in FIG. 3, the melt 2 of metal silicon 1 flows into the subsequent steps almost continuously except at the time of solidification. According to this method, the manufacturing operation can be smoothed, the operation time can be shortened, and the manufacturing cost can be lowered. In addition, since the device used in the present invention is only based on a metallurgical method, it can be easily scaled up without producing substances that pollute the environment, and it is expected to reduce production costs through mass production.

In order to remove boron and carbon in the melt 2, the oxidizing gas used should only have weak oxidizing ability, preferably H ₂ O or CO ₂ . If the oxidizing force is too strong, a _SiO2 film will be formed on the surface of the melt, thereby hindering the removal of boron or carbon dioxide. Therefore, in this case, in order to remove the film, it is necessary to use the plasma arc torch 4 or spray an arc from a DC arc source. In addition, the above-mentioned oxidizing gas can also be directly blown into the melt. The material of the nozzle 5 for blowing the oxidizing gas is limited to graphite or SiO ₂ . If materials other than these two are used, it will cause contamination of melt 2. In addition, it is preferable to use a well-known multi-wire saw or multi-blade saw for cutting the ingot 6 taken out from the second mold 9 into thin slices (not shown). The reason for limiting the thickness of the sheet to 100 to 450 μm is that if it is less than 100 μm, its strength will be too low, and if it exceeds 450 μm, its photoelectric conversion efficiency will decrease.

In the device according to the invention, a special concept has been adopted for the structure of the solidified casting mold 9 . As shown in Fig. 3 specifically, its shape is like a so-called basin type, and the ratio of its diameter W to height H is above 0.5. In addition, an insulating material 11 is provided on its side wall, a water-cooled jacket 10 is provided at its bottom, and a heating source 8 is provided above it, so as to be able to adjust the moving speed of the above-mentioned solidification interface.

In addition, in the present invention, in order to increase the purity of silicon, the solidification operations performed in the first and second molds may be repeated (solidification and then melting) multiple times. In addition, a plurality of casting molds can be prepared, and the above-mentioned holding vessel or refining vessel can be enlarged, and the melts in these vessels can be poured into the casting molds. In addition, in the present invention, the order of implementation of the above-mentioned steps A, B, C, D, and E can be different except that D and E are placed last.

Example 1

As shown in Figure 3, there is an electron gun with an output power of 300KW in the upper part of the decompression chamber 18, and metal silicon 1 is fed into a graphite holding container 19 (also called a melting furnace) at a rate of 10kg/hour for melting. At this time, the decompression chamber 18 was brought to a vacuum degree of 10 ^-3 Torr, and a part of phosphorus and aluminum elements were gasified from the melt 2 and removed. Then pour the solution 2 into a water-cooled copper mold 9, irradiate the surface of the melt with an electron beam 3 to keep it in a molten state, and then make it solidify from the bottom upward at a solidification interface moving speed of 1 mm/min to obtain 50 kg Ingot 6. The upper 20% (symbol A) of this ingot 6 was cut off and removed. Table 1 shows the chemical composition of the ingot. Table 1 Unit (ppm) B P Fe Al Ti Ca C o Silicon metal 7 twenty three 980 860 180 950 ~5000 - rough refined ingot 7 <0.1 1 0 8.5 2 10 35 - Substrate 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 3.5 5.7

Then the remaining part of the ingot 6 was placed in a silica crucible (refining vessel) 16, and the ingot was melted by a plasma arc torch 4 with an output power of 100KW arranged above it. Then, the temperature of the melt was kept at 1600 DEG C. while blowing an argon-water vapor mixed gas 21 containing 15% by volume of water vapor to the surface of the melt. At this time, a sample was taken from the melt 2, and the specific resistance of the sample was measured. After about 2 hours, the specific resistance became 1Ω·cm, and at this time, the mixed gas 21 was replaced with pure argon to perform deoxidation for 30 minutes. The melt was then cast into a second graphite mold coated with a release agent Si ₃ N ₄ , cooled and solidified from the bottom in an argon atmosphere, thereby obtaining an ingot. At this time, the surface of the melt was heated by a graphite heater 8 installed above the casting mold 9 . As a result, the moving speed of the solidification interface was 0.7mm/min.

After solidification, the upper 30% of the obtained ingot 6 was cut off, and the remaining part was used as a polysilicon product. Then, the product was cut into a thin sheet with a thickness of 350 μm each using a multi-wire saw to obtain 300 silicon substrates for solar cells with a size of 15 cm×15 cm. The properties of the substrate are as follows: the specific resistance is 1.2Ω·cm; the lifetime of minority carriers is 12 microseconds; the photoelectric conversion efficiency is 13.8%. In addition, its chemical composition is shown in Table 1.

Example 2

Place the lower 70% of the ingot 6 obtained from the first mold in the same manner as Example 1 in a silica crucible (refining container) 16, and use a plasma that is configured above it and has an output of 100KW. The arc torch 4 melts the ingot. Then the temperature of the melt 2 is kept at 1600°C, and argon-water vapor containing 15% by volume of water vapor is blown into the melt 2 at a flow rate of 10 liters/minute through a porous plug 15 arranged at the bottom of the crucible 16. Mixed gas 21 for deboronation and decarburization. Then deoxidation, directional solidification and cutting operations were performed to obtain a polysilicon product, and the product was sliced in the same manner as in Example 1 to obtain a silicon substrate for solar cells.

The size, number and properties of the obtained substrates were almost the same as in Example 1.

Example 3

In the electric arc furnace 12 shown in FIG. 4 , silicon oxide as a starting material was melted and reduced using a carbonaceous reducing agent to obtain molten metal silicon with the chemical composition shown in Table 2. When discharging, 50kg of said metal silicon 1 is poured into a crucible 14 that an inner wall is lined with a silicon dioxide refractory layer and a porous plug 15 is equipped with at its bottom, and blown into the melt by the porous plug 15 Infuse an argon-steam mixture containing 20% by volume of water vapor for 30 minutes. The temperature of melt 2 is raised to 1650° C. due to the heat of oxidation of silicon, causing deboronation and decarburization reactions. This melt 2 was cast into the above-mentioned first mold having a SiC heater above it and a bottom cooling system, and cooled and solidified at a solidification interface moving speed of 1.5 mm/min. Next, the lower 80% of the obtained ingot is put into a holding vessel arranged in the above-mentioned decompression chamber for melting, dephosphorization and deoxidation, and then the melt is cast into the above-mentioned second mold for directional solidification. 30% of the upper portion of the ingot 6 thus obtained was cut off, and the remaining portion was used as a polysilicon product. The product was then cut into thin slices of the above-mentioned size by a multi-blade saw to obtain 300 polycrystalline silicon substrates for solar cells. The specific resistance of the substrate is 0.9Ω·cm, the lifetime of minority carriers is 10 microseconds, and the photoelectric conversion efficiency is 13.5%. In addition, its chemical composition is shown in Table 2. Table 2 Unit (ppm) B P Fe Al Ti Ca C o Silicon metal in crucible 7 25 1010 800 180 950 ~5000 - Ingot refined in crucible 7 twenty three 10 25 3 13 6 40 Substrate 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 4 1

Finally, the advantages of the method and device for manufacturing polysilicon and the method for manufacturing polysilicon substrates for solar cells in the present invention are compared with the prior art, and the comparison results are summarized as follows.

That is to say, the method for producing polycrystalline silicon and the method for producing polycrystalline silicon substrates for solar cells in the present invention have no problem in terms of resources (the problem of shortage of raw materials will not occur), and there is no by-product that pollutes the environment. As a metallurgical The technology can basically accommodate the enlargement of equipment and mass production, so even if the demand for solar cells is hundreds of times that of the current one, the necessary substrates can be supplied stably. In addition, according to the conventional production method, the substrate made of massive high-purity silicon needs to be pulverized and other steps, so about 20% by weight loss or defective products will be produced, but in the present invention, from the production of silicon to Obtaining the substrate is a continuous, integrated process, resulting in low losses and efficient use of power and energy. Therefore, the price of the silicon substrate obtained by implementing the present invention can be reduced to less than half of conventional products, and the solar cell can be economically used as a power generating device.

Possibility of industrial use

According to the present invention, a high-purity polysilicon or silicon substrate for solar cells can be produced using only metallurgical methods and by continuous flow operations. Therefore, it is suitable for enlargement of equipment, and energy waste can be avoided, and it is very suitable for manufacture of the substrate for solar cells.

Claims (21)

1. A method for producing polysilicon, characterized in that polysilicon is produced from metallic silicon using the following steps: A． Metal silicon is melted in a vacuum, the phosphorus in it is gasified to remove it, and then solidified to remove impurity components from the melt, thereby obtaining an ingot; B． Cut off the impurity-concentrated part of the above-mentioned ingot; C． Remelt the remaining part after removing the impurity-concentrated part, then oxidize and remove boron and carbon from the melt in an oxidizing atmosphere, and then blow argon or a mixture of argon and hydrogen into the melt for deoxidation ; D． Casting the above-mentioned deoxidized melt into a mold for directional solidification to obtain an ingot; E． The impurity-concentrated portion of the ingot obtained by directional solidification is excised. 2. The method for producing polysilicon according to claim 1, wherein the metal silicon is obtained by reduction refining of silicon oxide. 3. A method for producing polysilicon, which is characterized in that firstly, molten metal silicon obtained by refining silicon oxide is transferred into a crucible, oxidized to remove boron and carbon in an oxidative atmosphere, and then solidified, and then carry out the process of claim 1. The B process of claim 1 is melted in a vacuum, and then the C, D and E processes of claim 1 are carried out. 4. The method for producing polysilicon according to any one of claims 1-3, characterized in that the above-mentioned oxidative atmosphere is formed by H ₂ O, CO ₂ or O ₂ gas, and its consumption is as small as possible so that the above-mentioned melt and The gas interface is not covered by silicon oxide. 5. The method for producing polysilicon according to claim 4, wherein the silicon oxide formed on the surface of the melt is removed by local heating with a plasma arc. 6. The method for producing polysilicon according to any one of claims 1 to 5, characterized in that H ₂ O, CO ₂ or O ₂ gas is used to blow into the melt instead of being in an oxidizing atmosphere. 7. The method for producing polycrystalline silicon according to any one of claims 1 to 6, wherein SiO ₂ or Si ₃ N ₄ is used as the release agent. 8. The method for producing polycrystalline silicon according to any one of claims 1 to 7, wherein the solidification interface movement speed during solidification for removing the impurities is 5 mm/min or less, and the solidification interface movement speed during directional solidification is 5 mm/min. The moving speed is below 2mm/min. 9. 8. The method for producing polycrystalline silicon according to any one of claims 1 to 8, wherein the ingot is cut at a height of 70% or more from the lower end of the ingot. 10. The method for producing polycrystalline silicon according to any one of claims 1 to 9, wherein the concentration of phosphorus in the melt is reduced to 0.3 ppm or less. 11. The method for producing polysilicon according to any one of claims 1 to 10, wherein the concentration of boron in the melt is reduced to 0.6 ppm or less. 12. The method for producing polycrystalline silicon according to any one of claims 1 to 11, wherein the carbon concentration in the melt is reduced to 10 ppm or less. 13. A polysilicon manufacturing device, characterized in that the device comprises: a heating device for melting or heating metal silicon; a holding container for holding molten metal silicon; a first mold for casting the melt in the holding container ; surrounding these holding vessels and moulds, decompression chambers for vaporizing phosphorus from the melt; remelting means for remelting or heating a portion of the ingot taken from the above moulds; for holding Refining vessel for the remelted melt; nozzles for blowing or spraying oxidizing gas, hydrogen or a mixture of hydrogen and argon into the melt in the refining vessel; for casting deoxidized melt into ingots 2nd mold. 14. The polysilicon manufacturing apparatus according to claim 13, wherein the degree of vacuum in the decompression chamber is higher than 10 ^-3 Torr. 15. The polysilicon manufacturing device according to claim 13 or 14, wherein a water-cooled jacketed crucible made of copper or a graphite crucible is used as the above-mentioned holding container, and a _SiO2 quality crucible, a _SiO2 molded crucible, or a _SiO2 lined crucible is used as the above-mentioned holding vessel. Refining container. 16. 13. The polysilicon manufacturing apparatus according to any one of claims 13 to 15, wherein said heating means is an electron gun. 17. 13. The polysilicon manufacturing apparatus according to any one of claims 13 to 16, wherein the remelting device is a plasma arc torch or a DC arc source. 18. The polysilicon manufacturing apparatus according to any one of claims 13 to 17, wherein the side walls of the first and second casting molds are formed of heat insulating materials, and the bottoms thereof are formed of water-cooled jackets, and above these casting molds A heating source is configured for heating the cast melt. 19. The polycrystalline silicon manufacturing apparatus according to any one of claims 13 to 18, wherein the ratio of the height H of the mold to the diameter W thereof is W/H>0.5. 20. A method for manufacturing a silicon substrate for solar cells, characterized in that the polycrystalline silicon ingot obtained according to any one of claims 1-12 is cut into thin slices. twenty one. The method of manufacturing a silicon substrate for a solar cell according to claim 20, wherein the thickness of said sheet is 100 to 450 [mu]m.

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