JP2006036628A - Method for producing polycrystalline silicon and polycrystalline silicon for photovoltaic power generation produced by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make an external heating means for heating a core material for the precipitation and adhesion of a polycrystalline silicon unnecessary even in the period of an initial heating, to allow enhanced precipitation and adhesion speed from an initial stage of the reaction, and to further allow repeated use of the core material. <P>SOLUTION: In a method for precipitating high purity polycrystalline silicon, comprising supplying a silane gas as a raw material onto a red-hot seed rod at a high temperature in a sealed reaction furnace and subjecting the silane gas to pyrolysis or the reduction by hydrogen, a member made of an alloy having a re-crystallization temperature of ≥1,200°C is used as the seed rod. Preferably, the member made of an alloy having a re-crystallization temperature of ≥1,200°C is made of Re-W, W-Ta, Zr-Nb or a titanium-zirconium-carbon-added molybdenum (TZM) alloy. The member is a wire having a diameter of ≥0.5 mm, a sheet or a square bar having a thickness of ≥1 mm or a tube having a diameter of ≥1 mm, a thickness of ≥0.2 mm and an inner diameter of ≤5 mm. Further, preferably, the sheet, the wire, the square bar or the tube has a taper, and more preferably, the tube is a hollow double tube having a taper. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing high-purity polycrystalline silicon at a low cost and in large quantities, and particularly relates to a stable supply of silicon raw material for photovoltaic power generation.

Siemens method and monosilane method are mainly used as conventional high purity polycrystalline silicon production methods. In these methods, a raw material silane gas is supplied from a nozzle provided at the bottom of a closed reaction furnace into a high-temperature reaction furnace, and a raw material gas is formed on a solid silicon rod surface (silicon seed rod or core material) provided in the furnace. Is deposited or grown by thermal decomposition or hydrogen reduction to produce polycrystalline silicon.
The raw material silane gas used is a highly purified chlorosilane represented by the formula Cl _n SiH _4-n (n = 0 to 4), and monosilane, trichlorosilane, tetrachlorosilane alone or a mixture thereof is used. In the Siemens method, trichlorosilane (n = 3) is mainly used, and in the monosilane method, monosilane (n = 0) is mainly used. Silicon obtained by pyrolysis or hydrogen reduction of these source gases at high temperatures has the same composition as a silicon seed rod (hereinafter referred to as Si seed rod) set in advance in the furnace, so it extends from the center to the outer periphery. Homogeneous and high purity. Since this has a purity essential for the semiconductor industry, it is called semiconductor grade polycrystalline silicon (SEG · Si).

In spite of the pre-war invention, the Siemens method has been able to stably obtain homogeneous and high-purity polycrystalline silicon. The reaction formula in the case of trichlorosilane is shown below.
SiHCl ₃ → (pyrolysis) → Si (polycrystalline silicon)
Quartz was used as the initial reactor (bell jar) material in the Siemens process. However, as the demand for polycrystalline silicon has increased, reactors have become larger in order to increase productivity, and metal bell jars made of corrosion-resistant metals such as carbon steel and high nickel steel are now used. . Further, improvements such as making the inner surface of the furnace mirror surface or silver plating have been made as means for making the temperature control in the furnace uniform and easy and preventing loss of the furnace due to heat radiation (Patent Document 1).

On the other hand, in response to the increase in the size of the reactor, the number of seed rods increased and the length of the rods also increased, so the yield of high-purity products with uniform diameter and good quality deteriorated. In addition, as solutions for improving the uniformity and smoothness of the lot shape, various improvements have been made to date such as improvement of the raw material gas supply nozzle structure, improvement of the exhaust gas outlet position and its structure (Patent Document 2, Patent Document 3), etc. Has been proposed.
The monosilane method uses monosilane (SiH ₄ ) as a raw material. Since the thermal decomposition reaction of monosilane involves the formation of silicon powder, it differs from the thermal decomposition of the Siemens method (pyrolysis temperature 759-950 ° C.). The core material is a Si rod as in the Siemens method. Since the obtained polycrystalline silicon is made of monosilane as a raw material, it is free from chlorine contamination, has a higher purity than the Siemens method, and is mainly used as a raw material for the production of FZ (floating zone) method single crystals.

On the other hand, various proposals have been made regarding methods for producing polycrystalline silicon for photovoltaic power generation, such as a method for purifying metallic silicon and a fluidized bed reaction, but none has been put to practical use for the reasons described later.
The Siemens method is characterized by being able to easily obtain a high-purity product because it is SEG / Si by thermally decomposing or hydrogen reducing the purified silane gas in a sealed container that is not easily contaminated. Since the diameter of the Si seed rod for depositing the silicon crystal after pyrolysis is very thin, around 5 mm, the specific surface area was small at the beginning of the reaction, and the deposition rate was slow.

Furthermore, since the resistivity of Si (Si seed rod) is as large as 1 kilohm or more and it is difficult to conduct electricity at room temperature, it is necessary to heat from the outside to a temperature that can be energized using a preheating device at the start of the reaction. there were. Heating not only requires a special high-voltage power supply but also consumes a lot of power, resulting in an increase in price.
A method using a thin core rod of metal such as Mo, W, Ta, Nb, etc. having a high recrystallization temperature instead of the Si seed rod used in the Siemens method is also known (Patent Document 4). When Mo is used, it becomes flexible when the reaction temperature exceeds 900 ° C. due to thermal expansion or electrical vibration caused by electric heating, and then becomes equiaxed recrystallized particles. As a result of embrittlement and easy deformation with respect to load, the silicon product became curved, sometimes contacting with an adjacent carrier, short circuiting the electrical circuit and causing the reaction to be interrupted.

In addition, Ta alone reacts with hydrogen at high temperature and becomes brittle, and Nb and W alone have a recrystallization temperature of 1,150 ° C. or higher, but have no impact strength, and both have problems in strength. It was.
Furthermore, since SEG / Si obtained using a thin core rod of metal such as Mo, W, Ta, and Nb has to remove the core (material) portion by some method after the reaction is completed, In use, "thin" was recommended. However, since the embrittled core member after the reaction is brittle and easily collapses, it has been difficult to completely remove it from SEG / Si. Furthermore, these metals have a problem that they penetrate into the deposited and grown silicon and deteriorate the product purity. In addition, once used, it cannot be reused, and using these carriers having a high unit price has not been put into practical use because it is not a satisfactory method in terms of price.

On the other hand, the Siemens method is an indispensable technique for producing high-purity polycrystalline silicon, except for the price. Accordingly, it can be understood that high-purity polycrystalline silicon at a low price can be easily obtained if the productivity in the initial reaction state of the Siemens method can be improved as described above.
Polycrystalline silicon obtained by the monosilane method has no chlorine contamination because it uses monosilane as a raw material, has higher purity than the Siemens method, and is mainly used as a raw material for producing FZ method single crystals. The FZ method is required to have a uniform diameter, a large diameter that is as close as possible to the diameter of single crystal silicon, and a product that does not contain impurities such as insoluble powder and is not bent. Various improved techniques have been proposed. For example, the gas flow rate in the furnace is regulated for the purpose of removing the film staying around the heating filament in order to accelerate the deposition of silicon (Patent Document 5), and the reaction gas is entrained in order to avoid admixture of insoluble powder. That is sent to the cooling wall of the powder catcher together with the silicon powder (Patent Document 6), in order to decompose monosilane at an effective rate, a large part of the reaction mixture leaving the decomposer is recycled to the supply flow of the decomposer. There have been proposed ones that circulate (Patent Document 7), and ones that comprise a filament core wire connecting bridge made of tantalum, molybdenum, tungsten, or zirconium (Patent Document 8) having a low electrical resistance so as not to become high temperature when energized.

However, when the member is made of the metal described in Patent Document 8, as described above, there is a problem that it is recrystallized at 1200 ° C. or higher, becomes brittle, and cannot be reused.
In addition, monosilane is ignitable, and not only a lot of safety devices are required for handling it, but also the yield is low because fine powder is by-produced during the reaction, and the production cost is high.
Various methods have been proposed and tried as a method for producing a silicon raw material for solar power generation (high purity). The ultimate goal is low cost and high quality. In particular, for solar power generation, a low-priced and high-purity silicon raw material is desired, but unfortunately no dedicated raw material source has been found.

  The polycrystalline silicon raw material currently used for photovoltaic power generation is “low-grade SEG / Si, bulk scrap (top, tail, etc.) produced as a by-product from the manufacturing process of polycrystalline silicon for semiconductors and silicon wafers for ICs. It depends on the crystal side face residue, crucible residue, or Si wafer scrap. However, the amount of by-product scrap is not only limited, but the amount has been decreasing in recent years, and stable securing of raw materials has become a big problem for the development of photovoltaic power generation.

  In order to achieve low cost, it is necessary that the starting material be cheap, and there have been many attempts so far. The first is to refine metallic silicon (MG · Si) or silicon by-produced from the semiconductor industry. For example, a method for purifying a surface of molten silicon by injecting a plasma jet gas (Patent Document 9, Patent Document 10, Patent Document 1), a method using a DC arc furnace (Patent Document 12), a method using an electron beam ,It has been known. Also, a method of purifying silicon waste discarded from the semiconductor industry by unidirectional solidification (Patent Document 13), a method of purifying by adding an inert gas and a powder of active gas or CaO to molten silicon (Patent Document 13) 14, Patent Document 15), and many methods such as a method of purifying MG / Si under reduced pressure and using a difference in boiling point (Patent Document 16, Patent Document 17) have been proposed. However, a satisfactory purification method using these raw materials has not yet been established.

The reason why it is difficult to purify molten silicon is that silicon atoms easily form a stable compound with other elements, but B (boron), a p-type impurity, is easily removed from silicon. This is because it is difficult to do. Since the solid-liquid distribution (segregation) coefficient of B with respect to Si is close to 0.81 and 1, it cannot be separated or purified by a solid-liquid separation method such as unidirectional solidification. Even if a difference in boiling point, gas blowing, or the like is used, it is difficult to completely treat the entire system.
The only purification method of B is to chemically react “metallic silicon” with “hydrochloric acid” to form silane gas, and then to separate and purify boron chlorination obtained by the reaction of B + HCl by distillation or adsorption. The purified silane gas containing no impurities is then reduced to high purity SEG · Si. The method of the present invention is commonly called a gas purification method, that is, a Siemens method or a monosilane method. Both methods have the disadvantage of being too expensive because they consume a lot of energy in the production process, and have been problematic for use as a raw material for photovoltaic power generation.

Thus, the most reliable method is to gasify B and cut by distillation. By gasification, other impurity elements dissolved in Si are also gasified and can be removed by the difference in boiling points. A fluidized bed reaction is known as a gasification method other than the Siemens method and the monosilane method described above. In an externally heated reactor, the raw material (trichlorosilane + hydrogen) is supplied from the lower part of the reactor, the Si fine particles in the furnace are flowed, the product is deposited and grown on the fluidized particles, and polycrystalline silicon is grown. obtain. After the reaction, the gas is extracted from the upper part of the furnace (Patent Document 18, Patent Document 19). The purity is six nine (99.9999%) or higher, and the grade for photovoltaic power generation is satisfactory.
Although this method can produce high-purity products at low cost, the reaction is externally heated, so that Si deposits and grows on the inner surface of the reaction tube, preventing continuous reaction, and increasing the size of the reaction tube. Unfortunately, it has not been put into practical use until now.

  From the above, it can be understood that the gasification method is excellent if high purity polycrystalline silicon is to be obtained. The difference between raw materials for semiconductor and photovoltaic power generation is the purity level, the former being eleven nine (11N) and the latter being said to be at least six nines (99.9999%) higher than that. . Therefore, it can be understood that a “dedicated raw material source for photovoltaic power generation” can be obtained if a method capable of satisfying the target purity, lowering the price several times from the former, and stably supplying can be developed.

Japanese Examined Patent Publication No. 6-41369 Japanese Patent Laid-Open No. 5-13991 Japanese Patent Laid-Open No. 6-172093 JP 47-22827 A JP-A-63-123806 JP-A-8-169797 JP-A 61-127617 JP-A-3-150298 JP 63-218506 A JP-A-4-338108 JP-A-5-139713 JP-A-4-37602 Japanese Patent Laid-Open No. 5-270814 JP-A-4-16504 JP-A-5-330815 JP-A 64-56311 JP-A-11-116229 JP 57-14520 A Japanese Patent Laid-Open No. 57-145021

  In view of the circumstances as described above, the present invention does not require an external heating means from the initial heating for heating the core material on which the silicon polycrystal is deposited, and the deposition rate can be increased from the initial stage of the reaction, Furthermore, it is an object of the present invention to make it possible to stably obtain a high-purity silicon polycrystal at low cost by making it possible to repeatedly use the core material.

  The present invention was invented as a result of diligently studying a method for producing polycrystalline silicon with greatly increased productivity. The method for producing polycrystalline silicon according to the present invention was carried out in a sealed reactor at high temperature. In a method in which raw material silane gas is supplied onto a heated seed rod and pyrolysis or hydrogen reduction is performed to precipitate high-purity polycrystalline silicon, the seed rod uses an alloy member having a recrystallization temperature of 1200 ° C. or higher. It is characterized by that. The alloy member having a recrystallization temperature of 1200 ° C. or higher is rhenium-tungsten (Re-W), tungsten-tantalum (W-Ta), zirconium-niobium (Zr-Nb), titanium-zirconium-carbon-added molybdenum ( TZM) alloy having a diameter of 0.5 mm or more, a plate or square having a thickness of 1 mm or more, or a diameter of 1 mm or more, a thickness of 0.2 mm or more, and a hollow diameter of 5 mm or less. It is preferably a tube material, particularly a lanthanum-added molybdenum alloy.

The plate, wire, square or tube is preferably tapered, and the tube is preferably a hollow double tube and tapered. The alloy member can be reused.
The polycrystalline silicon for photovoltaic power generation of the present invention is polycrystalline silicon obtained by the production method as defined in claim 1, wherein the raw material silane gas is trichlorosilane, and has a resistivity of n-type 2 to 500 Ωcm. The lifetime is 10 to 500 μsec.

  As described above, the method of the present invention is to use an alloy member having a recrystallization temperature of 1200 ° C. or more, a large diameter, and conductivity even at room temperature, instead of the Si seed rod. Other conditions such as the material and structure of the reactor, mixing ratio and flow rate of silane gas and hydrogen gas, reaction temperature and time are the same as in the conventional method, and no changes are required. In addition, heating at the initial stage of the reaction is easy, and the time for taking out the product silicon after the reaction can be rapidly reduced because the alloy member can be rapidly cooled, thereby achieving cost reduction. In addition, the product purity obtained is very low in contamination by members, and high-quality polycrystalline silicon can be produced at low cost and in large quantities. In addition, the purity of the obtained product is extremely low due to contamination by the alloy members used, and it is possible to produce polycrystalline silicon for semiconductors and solar power generation in large quantities at low cost.

  The alloy member diameter of the present invention used in place of the Si seed rod is preferably thick even in terms of strength in order to increase the silicon deposition area (deposition rate) in the initial reaction. Since the alloy member of the present invention used in place of the Si seed rod is not a ceramic, but a metal, it has strength and can be processed thinly and thinly. Is ignored, a wire with a diameter of 0.5 mm can also be manufactured. The same applies to the thickness and width of the plate material. However, in the case of a plate material having a wire diameter of 0.5 mm or less or a thickness of 1 mm or less, the support is bent or collapsed due to physical forces such as stress and electric vibration generated in the support (core material) due to thermal expansion during energization heating. In addition, during the reaction, these surfaces are hatched (silicide), and the strength becomes brittle and cannot be reused. However, since the surface of the core material is silicided and Mo does not diffuse into silicon, the degree of contamination is very small even if the product is contaminated.

  On the other hand, as the maximum diameter of the wire or the maximum thickness of the plate increases, the larger the value, the greater the electric capacity required for heating, and a larger power supply device is required. Therefore, although the maximum diameter of the wire rod or the maximum thickness of the plate material is limited by the heating device capacity, it is also possible to use the external heating device in combination to heat the members in the reaction furnace, and if the capacity is sufficient 100 mm or more is also possible. In addition, any shape, such as a rod, a plate, or a square shape, can be used, and the shape may be a uniform diameter or may be tapered. The reason for providing the taper is that it is convenient to pull out the product from the core material.

  In addition, the core material is a hollow body structure or double tube structure that allows the inside of the reaction tube to be rapidly cooled so that silicon products deposited and grown after the reaction can be quickly recovered in order to improve productivity. Thus, the shape may be tapered. The thickness of the hollow tube is 0.2 mm or more, preferably 0.5 mm or more. In the case of a double tube having a diameter of 5 mm or more, the diameter is of a thickness that fits in the hollow tube. When the thickness of the hollow tube is less than 0.2 mm, it is not preferable for the same reason as described above. On the other hand, the maximum diameter and thickness are both selected depending on the heating capacity. Considering common sense, a maximum diameter of 15 mm or less and a wall thickness of 3 mm or less are recommended. It is preferable to use the same thickness and material of the double tube set in the hollow tube as the heat-resistant member of the present invention. A heat resistant member may be used.

An image of the hollow double tube member is shown in FIG.
In FIG. 1, reference numeral 1 denotes a reactor base board on which a bell jar (not shown) is provided. 2 is a member support in the bell jar and supports the reaction tube 3. Polycrystalline silicon (not shown) is deposited on the outside of the reaction tube 3 by reaction.
4 is an inner tube, and a cooling medium (gas) is introduced into the inner tube 4 (arrow 5) and flows into the inside of the reaction tube 3 from the upper opening (not shown), and the reaction tube 3 is cooled. Derived (arrow 6).

The surface of the core material (member) is preferably a smooth surface so that the silicon growth rate is uniform, but it is not necessarily limited to a mirror surface (processing). This is because the obtained polycrystalline silicon becomes a lump after the core material must be removed after the reaction. Therefore, it cannot be used for the FZ method which requires a rod-shaped raw material, and becomes a CZ (chocolate ski) method or a cast method raw material. In addition, since the alloy member is intended for reuse, if the surface smoothness is excessively pursued at the time of reuse, a new cost is generated and the original cost reduction of the present invention is hindered.
As a member having a recrystallization temperature of 900 ° C. or more, Re-W (rhenium content: 10% or less. Recrystallization temperature [1500 to 1650 ° C.]), W-Ta (tungsten content: 5% or less. Recrystallization temperature) [1550 to 1650 ° C.]), Zr—Nb (zirconium content 1.5% or less, recrystallization temperature [1200 to 1350 ° C.]), TZM (recrystallization temperature [1250 to 1450 ° C.]), TEM material ( The most popular center composition is Ti: Zr: C = 0.5: 0.07: 0.005% by mass, generally recrystallization temperature [1250 to 1450 ° C.]. However, since it becomes equiaxed recrystallized particles above the crystallization temperature, it becomes brittle and loses high-temperature strength in the same manner as single Ta or W, so that it is necessary to pay maximum attention to the ambient temperature (reaction temperature).

  On the other hand, there is a lanthanum-added molybdenum alloy (recrystallization temperature [1350 ° C.]) material that does not embrittle but recrystallizes at a recrystallization temperature of 900 ° C. or higher. The manufacturing method of the lanthanum-added molybdenum alloy is manufactured by a method known in the art. For example, at least one processing method selected from hydrogen reduction of Mo powder containing several percent lanthanum (La) as a dopant by weight ratio, followed by pressing and hot-forging or rolling the sintered ingot. Then, it is obtained by carrying out a grain coarsening treatment by heating to a temperature above the recrystallization temperature (see, for example, JP-B-2-38659 and JP-B-3-22460). The lanthanum-added molybdenum alloy material obtained by this method has a crystal grain size coarsened by La doping, and then becomes a long and slender fiber by rolling, so that even if heated above the recrystallization temperature, In addition, there is a feature that deformation at high temperature is small, plastic working is possible even when the temperature is returned to room temperature, and impact resistance is not lost.

The method of disposing the alloy member of the present invention in the reaction furnace is set in an inverted U shape (gate shape) on the electrode holder on the base board as in the conventional Siemens method or monosilane method. It is possible to arrange the members in the reaction furnace diagonally (in a mountain shape), and in this method, a horizontal bar becomes unnecessary.
For various items related to the present invention member and electrode holder connection method and in-furnace placement method, power supply circuit connection method, contact prevention method with neighboring members, etc., methods known in the art can be adopted, No additional special measures are required.

The reaction method and conditions may be the same as those for the Si seed rod.
Trichlorosilane is thermally decomposed at a temperature of 1000 to 1200 ° C. The only difference between the Si seed method or monosilane method Si alloy rod and the alloy member of the present invention is that the alloy member can be energized from the beginning of the reaction, and can reach the reaction temperature in a short time. Both energy and power consumption are low (low cost). The thus obtained “polycrystalline silicon” is crushed into a mass of 20 to 100 mm called nugget and becomes a raw material of “single crystal silicon” by the CZ (chocolate ski) method. On the other hand, when using a lanthanum-added molybdenum alloy material among the alloy members, as described above, even after cutting the polycrystalline silicon after the reaction, it is flexible and has strength before the reaction. Can be reused.

The merit of using alloy parts is
I. Since a thick core diameter can be used, productivity in the initial reaction is large.
B. Since electricity can be supplied from the beginning of the reaction, the power consumption rate is low. Alternatively, the power consumption required for energization is very small compared to the Si seed rod.
C. Since the used member can be reused, the cost is reduced.
It is. An inexpensive polycrystalline silicon raw material for semiconductors can be obtained by (i) to (c).
In addition to these a to c, in order to further reduce the price, in addition to using an alloy member,
D. If cheap raw materials (trichlorosilane with low purity) are used and the obtained polycrystalline quality satisfies the polycrystalline silicon purity for photovoltaic power generation, the price will be further reduced.
That is, it can be understood that a polycrystalline silicon raw material that is inexpensive and dedicated to photovoltaic power generation can be obtained.

The price of trichlorosilane raw material is proportional to purity. Purity is determined by the concentration of boron contained in trichlorosilane, and its price is inversely proportional to the boron content. Semiconductor grade boron content is ppb level, chemical grade is ppm to percent (%) level. There is a difference of 3 digits or more at the minimum, and the price of the latter is cheap.
The purity of SEG · Si obtained using ppb level trichlorosilane is eleven nine. At this level, the accuracy depends on the analysis method, but the total of these 6 elements of Fe, Cu, Ni, Cr, Zn, Na is less than 5 ppb (measurement method: ICP method), Al (aluminum) and B The standard quality is 0.1 ppb (measurement method: photoluminescence method) or less, and the resistivity is n-type and 1000 Ω (measurement method: 4-terminal method) or more.

On the other hand, the purity of metal silicon (MG · Si) used for the production of silicone resin is 98 to 99% (1 to 2 nine levels). A method for producing metallic silicon is obtained by reducing silica (SiO ₂ ) with carbon (C). The conductivity type and resistivity are p-type, in the range of 0.05 to 0.6 Ωcm, and the lifetime cannot be measured (0 second level), so it cannot be used as a raw material for photovoltaic power generation.
Polycrystalline silicon for solar cells (SOG.Si) is located between SEG.Si and MG.Si. Until now, there has been no clearly defined standard for the total impurity level of various elements contained in SOG / Si.

However, there are reports on single elements contained in silicon.
According to this, Ni / 5.0 (ppm; the same applies hereinafter), C / 4.2, Al / 0.57, Cu / 0.31, B / 0.3, Sb / 0.06, Fe / 0. 023, P / 0.015, Cr / 0.0092, Ti / 0.0001 or less. However, this value is a value when these metal elements are contained alone as impurities in silicon, and does not suggest a case where these elements are mixed in the entire system. According to our experimental results, it was found impossible to discuss the whole system by specifying the content of individual elements alone. This is because the impurity content in the starting material MG · Si varies depending on the production place (person), and also in the subsequent reaction process, impurity contamination of various elements is caused from the reactor members.

It is expensive and time consuming to measure the quality of polycrystalline silicon raw material produced in large quantities, which element is contaminated for each raw material used. As a result of intensive studies, it has been found that the quality of SOG / Si should be defined by the conductivity type, resistivity, and lifetime. The values are n-type conductivity, 2-500 Ωcm resistivity, and 10-500 μs lifetime.
In order to produce a photovoltaic power generation wafer, SOG · Si is used as a raw material to form single crystal (CZ method) or polycrystalline (cast method) silicon, which is then cut into a wafer of a desired size. The resistivity of silicon wafers currently used for photovoltaic power generation is 0.5 to 8 Ωcm regardless of whether they are n-type or p-type conductors, single crystals, and polycrystals. Therefore, the quality of SOG / Si, which is a starting material before being cut into a wafer, needs to be higher than that.

  Now, if SOG / Si quality is n-type 2Ωcm and polycrystallize without adding dopant, silicon will be contaminated by p-type impurities from the peripheral members used in the machine during the crystallization reaction. As a result, the resulting crystal becomes p-type, and the resistivity also decreases. Therefore, the quality of SOG / Si for photovoltaic power generation is preferably n-type conductivity and 2 Ωcm or more in resistivity. The upper limit is 500 Ωcm, but more than this is for ICs, which is expensive for solar power generation. The quality of commercially available SEG · Si is generally n-type 1000 Ωcm or higher.

  As described above, the silicon raw material for photovoltaic power generation does not require semiconductor-grade purity and shape. In the method of the present invention, it can be understood that the polycrystalline silicon raw material for photovoltaic power generation, which is inexpensive, can be manufactured because of the advantages (i) to (d) described above. There is no quality problem.

[Example 1]
A lanthanum (La) doped lanthanum-added molybdenum alloy material (trade name: TEM material: manufactured by Allied Material Co., Ltd.) was rounded to produce a hollow tube having a diameter of 9 mmφ and a height of 300 mm. This was set in a portal shape on a quartz bell-shaped jar (inner diameter 120 mmφ, height 500 mm), and heated by energization. In the method of setting the portal shape, the upper end of the vertical tube was cut into a V shape, and a horizontal tube was placed thereon. After the temperature of the core surface reaches 1180 ° C. with an optical pyrometer, trichlorosilane and hydrogen gas are supplied at a flow rate ratio of 1:10 at a rate of 0.6 liter / minute of trichlorosilane and 10.8 liter / minute of hydrogen. After 8 hours, the reaction was stopped and the diameter was measured. As a result, it grew to 16.2 mm. The trichlorosilane used was of an electronics grade, and the B (boron) concentration in the trichlorosilane was 1 ppb or less outside the detection limit in the chemical analysis method. In addition, the external heating was not performed.

  The obtained ingot had a slight gap between the ingot and the TEM tube, and both could be easily separated by hitting with a hammer. The ingot before crushing was cut out to a thickness of 2 mm, and the lanthanum-added molybdenum alloy core was extracted with tweezers, and then the conductivity type, resistivity, and lifetime were measured. The measurement method was measured by conductivity type: laser light PN determination machine, resistivity: 4-probe method, lifetime: μ wave attenuation method (manufactured by SEMILAB). The results were n-type, 5 KΩcm or more (outside the detection limit), an average value of 470 μs, and were of semiconductor quality. The lifetime was low in the central portion, 67 μsec, the outer peripheral portion was 870 μsec, and the average value was 470 μsec.

[Example 2]
The same reaction as in Example 1 was performed using a TEM tube having the same dimensions as in Example 1. However, the TEM tube was heated at 1800 ° C. for 10 hours before the reaction (in a hydrogen atmosphere) to carry out embrittlement prevention treatment. When the reaction was stopped after 8 hours and the diameter was measured, it grew to 16.2 mm. In addition, the external heating was not performed.
The obtained ingot was subjected to the same treatment as in Example 1, and then its conductivity type, resistivity and lifetime were measured. The results are shown in Table 1.

[Example 3]
The TEM material used in Example 2 was reused and the same reaction as in Example 1 was performed. When the reaction was stopped after 8 hours and the diameter was measured, it grew to 16.1 mm. In addition, the external heating was not performed.
The obtained ingot was subjected to the same treatment as in Example 1, and then its conductivity type, resistivity and lifetime were measured. The results are shown in Table 1. Furthermore, the amount of Mo and La in the Si ingot after the reaction was measured. Any content was 1 ppb or less.

[Examples 4, 5, 6, and 7]
The reaction for each time shown in Table 1 was carried out in the same manner as in Example 1. However, a TEM material having the same dimensions as in Example 2 and using the same method for heat treatment was used. When the reaction was stopped after each time and the product diameter was measured, the deposition amount shown in Table 1 was obtained. The deposition amount was 85 g after 4 hours, 180 g after 8 hours, and 507 g after 20 hours. Moreover, the external heating was not performed.
The obtained ingot was subjected to the same treatment as in Example 1, and then its conductivity type, resistivity and lifetime were measured. The results are shown in Table 1.

[Example 8]
A TEM material having a plate thickness of 0.3 mm was rounded to produce a hollow taper tube having an upper diameter of 8 mmφ, a lower diameter of 10 mmφ, and a height of 300 mm. This was set in a gate shape on a quartz bell jar and heated by energization. The reaction was carried out for 8 hours under the same conditions as in Example 1. As a result, the upper diameter grew to 16.0 mm and the lower diameter grew to 18.3 mm. After the reaction, the hollow tube was able to be pulled out because it was tapered. The characteristics of this product are shown in Table 1.

[Example 9]
A TEM material having a thickness of 0.2 mm was rounded to produce a hollow double tube having a hollow tube having a thickness of 0.2 mm and a diameter of 2 mm inside a hollow taper tube having a height of 300 mm, an upper diameter of 8 mmφ, and a lower diameter of 10 mmφ. The hollow double tube is for rapidly cooling the reaction system after the reaction, and serves as an inlet for introducing a nonvolatile gas. The gas outlet was integrated with the electrode holder at the bottom. After the reaction, nitrogen gas was used as a non-volatile gas, which was supplied into the double tube to quench the silicon rod. The obtained silicon could be easily separated from the carrier. The reaction conditions were the same as in Example 1, and the reaction was performed for 8 hours. As a result, the upper diameter grew to 16.1 mmφ, and the lower diameter grew to 18.2 mm. After the reaction, the hollow tube was tapered and could be pulled out. The TEM material also retained flexibility and could be reused. The single crystal silicon purity also satisfied the semiconductor grade (see Table 1).

[Example 10]
An embrittlement prevention treated TEM material having a thickness of 1 mm was rounded to produce a hollow tube having an outer diameter of 23 mm and an inner diameter of 21 mm. Using this, the same reaction as in Example 2 was performed. In addition, since the electric capacity of the reactor was insufficient, an external heating apparatus was used and the temperature was raised to the reaction temperature. After 8 hours of reaction, it grew to 28.7 mm.
The obtained silicon was separated from the hollow tube, and its conductivity type, resistivity and lifetime were measured. The results are shown in Table 1. The quality satisfied the semiconductor grade (n-type 5 KΩcm or more).

  From Examples 1 to 10, when the alloy member of the present invention is used instead of the Si seed rod and trichlorosilane having an electronic purity is used, it is easy to obtain the “low-cost polycrystal for semiconductors having the same quality as the“ Siemens method or monosilane method ”. It was confirmed that “silicon” was obtained. Moreover, since the polycrystalline silicon for semiconductors obtained is inexpensive to manufacture, there is another advantage that it can be used not only for ICs but also as “polycrystalline silicon raw material for photovoltaic power generation” (see Examples 14 to 16). ).

[Example 11]
The reaction was carried out for 8 hours in the same manner as in Example 1, using an embrittlement-prevented TEM tube having the same dimensions as in Example 2. However, the B concentration in the used trichlorosilane was a 498 ppb product (chemical grade product). The analysis method of B was a chemical analysis method, and the average value of the values analyzed four times was adopted. After 8 hours, the reaction was stopped and the diameter was measured. As a result, it grew to 16.0 mm. In addition, the external heating was not performed. The conductivity type, resistivity, and lifetime of this were measured. The results are shown in Table 1.

[Example 12]
The reaction was carried out for 8 hours in the same manner as in Example 1, using an embrittlement-prevented TEM tube having the same dimensions as in Example 2. However, the B concentration in the used trichlorosilane was 48 ppb product (chemical grade product). The analysis method of B was the same as the previous method, and the average value of the values measured four times was adopted. When the reaction was stopped after 8 hours and the diameter was measured, it grew to 16.1 mm. In addition, the external heating was not performed. The conductivity type, resistivity, and lifetime of this were measured. The results are shown in Table 1.

[Example 13]
The reaction was carried out for 8 hours in the same manner as in Example 11 using a TEM rod having an outer diameter of 9 mm. Note that the TEM rod was subjected to a brittleness preventing heat treatment in the same manner as in Example 2 before starting the reaction. When the reaction was stopped after 8 hours and the diameter was measured, it grew to 16.0 mm. In addition, heating from the outside was necessary. The conductivity type, resistivity, and lifetime of this were measured. The results are shown in Table 1.

[Example 14]
In Example 2, p-type mother single crystal silicon having a boron content (0.01 Ωcm) was added to polycrystalline silicon (n-type, 5 KΩcm or more) obtained after 24 hours of reaction time, and p-type 1.0 Ωcm was obtained by a casting method. Produced polycrystalline silicon for solar power generation. This was sliced to a thickness of 300 μm (10 mm square × 300 μm), a 10 mm square solar power generation cell was prepared after etching, and the photoelectric conversion efficiency was measured. The result was 18.7%.

[Example 15]
In Example 11, p-type mother single-crystal silicon having a boron content (0.01 Ωcm) was added to polycrystalline silicon (n-type, 5 Ωcm) obtained after 24 hours of reaction time, and p-type 1.0 Ωcm was obtained by a casting method. Polycrystalline silicon for solar power generation was manufactured. Slicing was performed in the same manner as in the previous section, and a 10 mm square photovoltaic power generation cell was prepared after etching, and the photoelectric conversion efficiency was measured. The result was 17.9%.

[Example 16]
In Example 12, polycrystalline silicon obtained after 24 hours of reaction time (n-type, p-type mother single crystal silicon having a boron content (0.01 Ωcm) to 50 Ωcm was added, and a p-type 1.0 Ωcm solar cell was cast. Polycrystalline silicon for photovoltaic power generation was produced, and its photoelectric conversion efficiency was 18.2%.

  From Examples 11 to 16, using the alloy member of the present invention instead of the Si seed rod, and obtained by thermally decomposing chemical grade raw material silane (trichlorosilane), “conductivity type n type, resistivity 2 to 500 Ωcm, life It was confirmed that “polycrystalline silicon having a time of 10 to 500 μs” is useful as a dedicated raw material for polycrystalline silicon for photovoltaic power generation. In addition, mass production can be easily performed without improving the existing facilities.

[Comparative Example 1]
Instead of the TEM tube of Example 1, a pure Mo rod having a diameter of 9 mmφ was used, and polycrystalline silicon was produced under the same conditions as in Example 1. The obtained silicon rod was cut into 1 mm thickness, and an electron micrograph was taken. The photograph is shown in FIG. 2, and the boundary (“B” in FIG. 2) between the surface of Mo (core) (“A” in FIG. 2) and Si (deposited Si) (“D, E” in FIG. 2). In FIG. 2, Mo is silicided, and there is a crack layer (“C” in FIG. 2) between the Si layer deposited on the core material. Also, white lines run radially toward the outside of Si, and the growth of Si grains can be read. Furthermore, the core Mo was recrystallized (lower right photograph in FIG. 2), it had no strength and was brittle, and Mo could not be recovered in the state of a rod. In addition, the external heating was not performed.

[Comparative Example 2]
In Example 2, a reaction was carried out under the same dimensions and conditions as in Example 2 using a TEM tube having a thickness of 0.05 mm. After the start of energization, the TEM tube was bent when the temperature rose to 600 ° C., and the reaction could not be continued.

[Comparative Example 3]
In Example 1, trichlorosilane having a B concentration of 980 ppm was used, and the reaction was performed in the same manner as in Example 1 for 24 hours. The conductivity type, resistivity, and lifetime of the obtained polycrystalline silicon were measured. The results were n-type, 1 Ωcm, and 5 μs, respectively. Using this material, polycrystalline silicon for photovoltaic power generation was produced by a casting method without using a dopant. The conductivity type, resistivity, and lifetime of the resulting cast polycrystalline silicon were p-type, 0.4 Ωcm, and 3 μs, respectively. In addition, the conversion efficiency after cell formation was as low as 9.8%, and could not be used as a polycrystalline wafer for photovoltaic power generation.

[Reference example] (Siemens method)
Instead of the TEM member (seed rod) in Example 1, an 8 mm square rod single crystal silicon rod (a high purity semiconductor polycrystalline silicon obtained by the FZ method was cut into a 9 mm square rod) was used. Polycrystalline silicon was produced under the same conditions as in Example 1. However, since the silicon rod is an insulator at room temperature and cannot be energized and heated, it was heated from the outside. When the reaction was stopped after 8 hours and the diameter was measured, it grew to 15.8 mm. Although the growth rate per reaction time is not different from the result of the present invention, it took 2 hours for the temperature to rise before the start of the reaction.
The conductivity type, resistivity, and lifetime of the obtained ingot were measured. The results were n-type, 5 KΩcm or more (outside the detection limit) and 1200 μs, respectively, and the lifetime was superior to that of the polycrystalline silicon obtained in Example 2 of the present invention. As in the present invention, the purity of polycrystalline silicon for semiconductors was satisfied. However, external heating is required before the start of the reaction, and productivity per hour is lower than that of the present invention.

  According to the present invention, since heating of the alloy member at the start of the deposition reaction of silicon can be performed quickly and easily, a high-purity silicon polycrystal can be produced at a low cost, and for IC and solar power generation. It contributes greatly to the field of silicon material manufacturing.

It is a schematic diagram which shows the image of the double pipe member used by this invention. 2 is a cross-sectional electrophotography of the silicon rod obtained in Comparative Example 1.

Explanation of symbols

1: Base board (of reactor) 2: Member support base 3: Reaction tube 4: Inner tube 5: Gas introduction (arrow)
6: Gas derivation (arrow)
A: Core material (Mo)
B: Mo silicided portion (Mo _x Si _y )
C: Crack zone D: Polycrystalline Si (equal axis grains)
E: Polycrystalline Si (columnar grains)

Claims (7)

  In a method in which a raw material silane gas is supplied onto a heated seed rod in a sealed reactor at a high temperature and pyrolyzed or hydrogen reduced to precipitate high-purity polycrystalline silicon, the seed rod has a recrystallization temperature of 1200. A method for producing polycrystalline silicon, comprising using a member made of an alloy having a temperature of ℃ or higher.   The alloy member having a recrystallization temperature of 1200 ° C. or higher is rhenium-tungsten (Re-W), tungsten-tantalum (W-Ta), zirconium-niobium (Zr-Nb), titanium-zirconium-carbon-added molybdenum ( TZM) alloy having a diameter of 0.5 mm or more, a plate or square having a thickness of 1 mm or more, or a diameter of 1 mm or more, a thickness of 0.2 mm or more, and a hollow diameter of 5 mm or less. The method for producing polycrystalline silicon according to claim 1, which is a tube material.   The method for producing polycrystalline silicon according to claim 2, wherein the alloy member having a recrystallization temperature of 1200 ° C or higher is a lanthanum-added molybdenum alloy.   4. The method for producing polycrystalline silicon according to claim 2, wherein the plate material, the wire material, the square material, or the tube material is tapered.   The method for producing polycrystalline silicon according to claim 4, wherein the tube material is a hollow double tube and is tapered.   The method for producing polycrystalline silicon according to claim 1, wherein the alloy member is a recycled material.   A polycrystalline silicon produced by the production method as defined in claim 1, wherein the raw material silane gas is trichlorosilane, the conductivity type is n-type, the resistivity is 2 to 500 Ωcm, and the lifetime is 10 to 500 μsec. Polycrystalline silicon for photovoltaic power generation characterized by this.

Images