JP2013193931A - Method of producing polycrystalline silicon rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing high purity polycrystalline silicon and a production device for high purity polycrystalline silicon, and specifically, to provide a method of producing a high purity polycrystalline silicon rod and a production device for a high purity polycrystalline silicon rod hardly causing contamination from the surface of a heater installed to heat a silicon core wire.SOLUTION: In a method of producing a polycrystalline silicon rod based on the chemical vapor deposition method, as a means heating a silicon core wire to a temperature at which it can be energized, a heater formed of a silicon capable of being energized at an atmospheric temperature upon startup is arranged along the silicon core wire, and when heating is carried out by energizing the heater, the silicon core wire is energized using radiant heat of the heater.

Description

  The present invention relates to a novel method and apparatus for producing a polycrystalline silicon rod. Specifically, in the reaction chamber, at the time of start-up when silicon is deposited on the heated silicon core wire by chemical vapor deposition, the silicon core wire is heated by the heater, and the silicon is deposited by the heater at the time of silicon deposition. A method of manufacturing a polycrystalline silicon rod capable of effectively preventing silicon contamination is provided.

  Conventionally, there is a method called a Siemens method as one of methods for producing silicon used as a raw material for semiconductors or wafers for photovoltaic power generation. In this method, a silicon core wire is placed inside a reaction chamber formed by covering the bottom wall substrate with a bell jar, and the silicon core wire is heated to a silicon deposition temperature by energizing the silicon core wire, and the In this method, a polycrystalline silicon rod is obtained by depositing silicon on a silicon core wire by supplying a compound and a reducing gas such as hydrogen. This method is characterized in that high-purity silicon can be obtained, and has been industrially implemented as the most common method.

  Incidentally, it is known that the electrical resistance of high-purity silicon suitably used as a semiconductor material is very high, and the electrical resistance tends to decrease as the temperature increases. Therefore, in carrying out the method of energizing the silicon core wire, it is difficult to directly energize the silicon core wire at start-up, and it is necessary to heat to a temperature that allows energization (specifically, 350 ° C. or higher). There is.

  Therefore, conventionally, for the heating of the silicon core wire, an apparatus in which a heater made of a resistive material for preheating the silicon core wire is provided in the reaction chamber. And as a raw material of the heater which consists of this resistive material, refractory metal (refer patent document 1), carbon (refer patent document 2), etc. are used, for example.

  However, in the conventional method using the heater, contamination of the generated polycrystalline silicon becomes a problem at the time of heating by the heater and further at the time of precipitation of silicon.

  That is, while the heater made of the above-mentioned resistive material is energized and the silicon core wire is heated, and while the silicon core wire is energized and chemical vapor deposition proceeds, the reaction chamber becomes very hot. Further, while chemical vapor deposition proceeds, the reaction chamber is exposed to by-product gases (silane compound gas, hydrogen gas, tetrachlorosilane, hydrogen chloride, etc.) generated by reaction with the reactive gas at a high temperature. The Rukoto. As a result, during heating by the heater or when silicon is deposited, the atmospheric temperature in the reaction chamber at the start-up is generally normal temperature, such as metal compounds, carbon, and the like derived from the heater. When heated with a heat medium such as steam, or when heated nitrogen gas or hydrogen gas is circulated in the reaction chamber, the temperature may be higher. Impurities contained in the heater diffuse into the reaction chamber from the heater surface and contaminate the deposited silicon.

JP 2009-536914 A JP 2009-073683 A

  Accordingly, an object of the present invention is to provide a heater for heating on the silicon core wire, energize the heater at the time of start-up, and heat the silicon core wire to a temperature at which the silicon core wire can be energized by the radiant heat of the heater. In the method for producing a polycrystalline silicon rod by depositing and growing silicon on the surface of the silicon core wire, contamination of the silicon deposited on the surface of the silicon core wire by the heater can be suppressed, and a high-purity polycrystalline silicon rod is obtained. An object of the present invention is to provide a manufacturing method capable of achieving the above.

  As a result of intensive research to achieve the above object, the inventors of the present invention are sufficient to make the silicon energizable at the start-up temperature, and it is sufficient to have a very small amount of impurities present, When silicon containing such impurities is used as a heater for the silicon core wire to heat the silicon core wire, and even when exposed to a high temperature environment in which the silicon core wire is deposited, impurities diffusing from the surface of the silicon core wire It has been found that the contamination of the resulting polycrystalline silicon rod can be effectively reduced with a very small amount, and the present invention has been completed.

  That is, in the present invention, a silicon core wire installed in a reaction chamber is heated by energization, a silane compound and a reducing gas are supplied as source gases into the reaction chamber, and the surface of the silicon core wire is formed by chemical vapor deposition. In the method for producing a polycrystalline silicon rod for depositing silicon, a heater made of silicon that can be energized at an ambient temperature at start-up is attached to the silicon core wire, and the heater is energized to generate heat. After heating, the silicon core wire is energized.

  Further, the present invention is an apparatus for carrying out the above production method, wherein a silicon core wire and a heater made of silicon that can be energized at an ambient temperature at start-up are provided in a reaction chamber, and the silicon core wire and silicon There is also provided an apparatus for producing polycrystalline silicon, characterized in that each heater is connected to a power supply facility that can be operated independently.

  According to the present invention, the material of the heater provided to heat the silicon core wire to a temperature at which electricity can be passed is silicon, and the silicon constituting the heater can be energized by containing a very small amount of impurities. Therefore, even if the heater itself is exposed to a very high temperature reactive gas during heating by the heater, or during silicon deposition and growth, diffusion of impurities from the heater surface into the reaction chamber can be remarkably suppressed. There is very little contamination of silicon deposited on the silicon core wire.

  Therefore, according to the manufacturing method of the present invention, it is possible to manufacture polycrystalline silicon having a very high purity as compared with the conventional method, and it is possible to significantly improve the yield of high-purity polycrystalline silicon rods as a semiconductor grade. is there.

  Moreover, as one aspect of the present invention, even after energization of the silicon core wire is started, it is possible to continue energization of the heater made of silicon and deposit silicon on the surface. In this case, since extremely high-purity silicon is deposited on the heater surface, the purity of the entire rod obtained can be increased, and high-purity polycrystalline silicon that can be sufficiently used in solar cell applications is also available. It also has the merit that it can be obtained.

The side sectional view showing the schematic structure of the bell jar type silicon manufacturing device used as one mode of the device for carrying out the method of the present invention.

  The present invention provides a high purity polycrystalline silicon rod by supplying a silane compound and a reducing gas to a silicon core wire heated to a silicon deposition temperature by energization and precipitating silicon on the silicon core wire. It is intended for manufacturing methods. The above method is generally called a chemical vapor deposition method, and a typical one is a Siemens method using a bell jar type silicon manufacturing apparatus.

  In the manufacturing method, the silicon core wire is not particularly limited, but a core wire made of silicon with high purity is preferably used to obtain a high-purity polycrystalline silicon rod. Specifically, a material made of silicon having an electrical resistivity correlated with the amount of impurities of 1000 ohm-cm or more at room temperature is preferable.

  Moreover, since the said silicon | silicone core wire connects both ends with an electrode respectively and supplies with electricity, if the shape is a shape suitable for an apparatus, it will not restrict | limit in particular. For example, in the case of a bell jar type silicon manufacturing apparatus, since it is connected to an electrode provided on the bottom wall substrate of the reaction chamber, generally an inverted U-shaped one is preferably used. The cross-sectional shape of the silicon core wire may be round or quadrangular, and the length of the silicon core wire may be appropriately selected according to the size and performance of the apparatus.

  Next, the silane compounds used in the present invention include silane and chlorosilane gases such as monosilane, trichlorosilane, tetrachlorosilane, monochlorosilane, dichlorosilane, and generally, trichlorosilane gas is preferably used. Is done. As the reducing gas, hydrogen gas is usually preferably used.

  As the supply conditions for the silane compound and the reducing gas, the conditions employed in known methods are employed without any particular limitation.

  In the present invention, a heater made of silicon (hereinafter referred to as a silicon heater) that can be energized at an ambient temperature at start-up is provided as the heater, and the silicon heater can be energized to generate heat and the silicon core wire can be energized by the radiant heat. The biggest feature is heating to a suitable temperature.

  The atmosphere temperature at the time of start-up is the atmosphere temperature in the reaction chamber in which the silicon core wire and the silicon heater are installed when energization of the heater is started. The ambient temperature in the reaction chamber at the start-up is generally room temperature, but when the reaction chamber wall is heated with a heat medium such as hot water or steam, heated nitrogen gas or hydrogen gas is supplied into the reaction chamber. In the case of heating, the temperature may be higher. However, in consideration of the structure and material of the inner wall of the reaction chamber, and also the economy, it is preferably 200 ° C. or lower.

  The silicon heater used in the present invention can be easily energized at the ambient temperature at the start-up, and in order to achieve good heat generation efficiency, the electrical resistivity at the ambient temperature at the start-up is 5 ohm-cm or less. It is preferably made of a silicon material, and the electric resistance as a heater is preferably 750 ohms or less, and particularly preferably 400 ohms or less in order to stably conduct electricity.

  On the other hand, the silicon heater is easier to energize as the material has a lower electrical resistivity. However, when the contamination from the silicon heater to the silicon core wire and deposited silicon is taken into account, the electrical resistivity is correlated with the amount of impurities. Is preferably at least 0.01 ohm-cm at room temperature.

  In addition, as shown in an embodiment described later, in the case of an embodiment in which silicon is deposited on the heater surface and recovered as a polycrystalline silicon rod for solar cells, the silicon heater has a higher purity within a range that satisfies the above conditions. Preferably, the electrical resistivity correlating with purity is preferably 0.1 ohm-cm or more at room temperature, more preferably 0.5 ohm-cm or more at room temperature, more preferably 0.7 ohm-cm or more at room temperature. Used for.

  The electrical resistance of the silicon heater varies depending on the electrical resistivity, the shape and length of the heater, and may be adjusted as appropriate. For example, when the electrical resistance of the silicon heater is 750 ohms, the starting current is 20 amperes and about 15000V By applying the voltage, it is possible to easily energize.

  In general, since the electrical resistance of silicon tends to decrease as the temperature increases, a silicon heater having the same purity can be stably energized as the ambient temperature at start-up increases.

  Next, a method for adjusting the electrical resistivity of the silicon heater will be described. In general, the electrical resistivity of silicon increases as the purity increases, but it has a feature that the electrical resistivity is greatly reduced by adding a very small amount of impurities. Therefore, as one aspect of adjusting the electric conductivity of the silicon heater, for example, the metal silicon having an electric resistivity in the above range can be melted and processed into a heater shape, or the method of the present invention, Alternatively, a high-purity polycrystalline silicon rod obtained by a conventional method can be melted, impurities can be added to adjust the electrical resistivity to the above range, and processed into a heater shape for use.

  The type of impurity added when adjusting the electrical resistivity by adding an impurity is not particularly limited. For example, a group V element such as phosphorus (P) or arsenic (As), or boron (B) or the like III It is preferable to add a group element because the electrical resistivity can be easily adjusted with a small amount. In addition, the amount of addition depends on the purity of the original silicon and the type of impurities to be added, but it cannot be said unconditionally. However, the amount added is adjusted relative to the electrical resistivity so that the desired electrical resistivity can be obtained. do it.

  Also, the shape of the silicon heater is not particularly limited as long as it is suitable for the device, because both ends of the silicon heater are connected to the electrodes in the same manner as the silicon core wire, but for example, in the case of a bell jar type silicon manufacturing device As in the case of the silicon core wire, one having an inverted U-shape or the like is preferably used. The cross-sectional shape may be round or square, and the length of the silicon heater may be appropriately selected according to the size of the apparatus.

  In the present invention, the silicon core wire is heated by using an apparatus in which the silicon heater is attached to the silicon core wire. The silicon heater is energized by heating the silicon heater during start-up, and the silicon core wire is energized by radiant heat from the heater. It is heated to a temperature at which it becomes possible, specifically 350 ° C. or higher, preferably 650 ° C. or higher, more preferably 750 ° C. or higher.

  After reaching the temperature at which the silicon core wire can be sufficiently energized, the silicon core wire is energized to maintain the silicon core wire at the silicon deposition temperature.

  In addition, although the precipitation temperature of the silicon to a silicon core wire is 600 degreeC or more, in order to deposit silicon on the surface of a silicon core wire efficiently, silicon is kept so that a silicon core wire may be hold | maintained at the temperature of about 1000-1100 degreeC. It is preferable to energize the core wire.

  At the same time as starting the energization of the silicon core wire, or when the temperature of the silicon core wire reaches or exceeds the silicon deposition temperature, a silane compound gas and a reducing gas are supplied into the reaction chamber as a reactive gas, Silicon is generated on the surface of the silicon core wire by reaction (reduction reaction) of these reactive gases.

  In the present invention, a plurality of silicon core wires and silicon heaters can be installed according to the size and performance of the apparatus. Regarding the heating of the silicon core wire in an embodiment in which a plurality of silicon core wires are installed, first, the silicon heater attached to the silicon core wire is energized and heated, and by radiant heat from the heater, all of the silicon core wire, or Heat a part above the temperature at which it can be energized. Depending on the arrangement of the heater and the silicon core wire, there may be a case where a part of the silicon core wire can be energized first due to the radiant heat from the heater. A mode in which the remaining silicon core wire is heated to a temperature at which the silicon core wire can be energized stepwise can also be used by utilizing the radiant heat of the silicon core wire.

  As described above, when a polycrystalline silicon rod having a certain thickness is obtained, the supply of the reactive gas and the energization to the silicon core wire are stopped, and the unreacted silane compound gas and reducing gas are supplied from the reaction chamber. Then, after evacuating tetrachlorosilane, hydrogen chloride, and the like by-produced, the reaction chamber is opened and the polycrystalline silicon rod is taken out.

  The polycrystalline silicon rod thus obtained is a highly pure polycrystalline silicon rod in which contamination from the heater is suppressed as compared with a polycrystalline silicon rod manufactured by a method using a conventional heater.

  In the above aspect, after starting energization of the silicon core wire, the silicon heater may stop energization or may be energized as it is and heated to the reaction temperature in the same manner as the silicon core wire.

  In other words, the silicon heater is generally placed in the reaction chamber after the core wire is heated, with the energization stopped as in the case of the conventional heater. If the silicon heater is de-energized after the silicon core wire is energized, silicon is selectively deposited on the surface of the silicon core wire during chemical vapor deposition, so the silicon heater can be energized at the start-up ambient temperature. Can be used repeatedly.

  In this case, even if the silicon heater is de-energized while chemical vapor deposition proceeds in the reaction chamber, some silicon may be deposited on the heater surface depending on the atmosphere in the reaction chamber. Before starting, it is sufficient to confirm that the electrical resistivity can be energized at the ambient temperature at the start-up, and to determine whether or not reuse is possible.

  On the other hand, it is possible to continue energizing the silicon heater even after the energization of the silicon core wire, and to deposit silicon on the surface of the silicon heater. In this case, a polycrystalline silicon rod with silicon grown on the surface of the silicon heater Is obtained. The grown polycrystalline silicon rod has a low silicon purity, but the silicon deposited on the heater surface has a very high purity, so the entire rod can be used as solar power silicon. A high-purity polycrystalline silicon rod.

  Hereinafter, although the manufacturing apparatus suitable for implementing the said manufacturing method is demonstrated based on FIG. 1, this invention is not limited to the aspect shown in FIG.

  FIG. 1 is an example of an apparatus for carrying out the method of the present invention, and is a side sectional view showing a schematic structure of a bell jar type silicon manufacturing apparatus provided with a silicon core wire and a silicon heater.

  In FIG. 1, the silicon manufacturing apparatus 1 of the present invention includes a reaction chamber A formed by covering a bottom wall substrate 3 with a bell jar 5.

  The reaction chamber A has a reactive gas such as a silane compound gas, a reducing gas, a tetrachlorosilane gas, and a hydrogen chloride gas at high temperatures while the silicon core wire is heated and during chemical vapor deposition of silicon. And by-product gas produced by the reaction. For this reason, the material of the inner wall of the bell jar and the upper surface of the bottom wall substrate, which are the inner walls of the reaction chamber A, is preferably chemically inert, such as SUS304, SUS316, Inconel, or the like. By selecting the material, corrosion of the apparatus can be suppressed, and diffusion of impurities from the bell jar inner wall and the bottom wall substrate in the reaction chamber A can be prevented, and contamination of silicon by the impurities can be prevented.

  An inverted U-shaped silicon core wire 7 is erected on the bottom wall substrate 3, and a base portion of the silicon core wire 7 is fitted into an electrode provided on the bottom plate substrate 3, via the electrode. And is configured to be energized. The number of silicon core wires to be installed may be determined relative to the size and performance of the bell jar, and may be one or more.

  Further, on the bottom wall substrate 3, a silicon heater 9 having the same inverted U-shape is erected so as to face the erected silicon core wire 7.

The base portion of the silicon heater is fitted into an electrode provided on the bottom wall substrate 3 like the silicon core wire 7 and is energized through the electrode. Further, at least the electrode in which the silicon heater 9 is fitted and the electrode in which the base of the silicon core wire 7 is fitted are connected to a power supply facility that can be operated independently. Features.
That is, the silicon heater 9 is first energized, and at least the silicon heater 9 and the silicon core wire can be energized so that the silicon core wire 7 can be energized when the silicon core wire 7 reaches a temperature that can be energized by the radiant heat of the silicon heater 9. 7. The electrode in which each base part was inserted is connected to the power supply equipment which can be operated independently.

  Since the silicon heater 9 is provided to heat the high-purity silicon core wire 7 to a temperature at which electricity can be passed, if the required number is installed according to the amount of radiant heat of the silicon heater 9 in the reaction chamber A, Good.

  Further, the installation position of the silicon heater is not particularly limited, but it is preferably installed in consideration of the efficiency of radiant heat.

  In the present invention, in a mode in which a plurality of silicon core wires 7 are installed, since the silicon core wires close to the silicon heater 9 are heated step by step, the silicon core wires are heated and energized in order from the silicon core wires heated to a temperature that allows energization. Further, it is possible to take a form in which the radiant heat of the silicon core wire is also used and the remaining silicon core wire is further heated. In this case, the electrode in which the base of the silicon core wire is fitted is connected to power supply equipment that can be operated independently for each silicon core wire that is energized at the same time.

  That is, the bell jar 5 is closed so as to cover the silicon core wire 7 and the silicon heater 9, and the reaction chamber A is formed.

  In the reaction chamber A formed as described above, a raw material gas supply pipe and a gas discharge pipe are inserted through the bottom wall substrate 3, and a predetermined reactive gas reacts through the raw material gas supply pipe. An unreacted gas or a by-product compound gas is supplied to the chamber A and exhausted from the reaction chamber A through a gas exhaust pipe after the reaction is completed.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples.

Example 1
In a reaction chamber formed by covering the bottom wall substrate with a bell jar, a pair of inverted U-shaped silicon heaters and silicon core wires having independent electrodes were installed. The diameter of the silicon heater is about 8 mm, the electric resistance is 398 ohm at room temperature, the electric resistivity is 0.53 ohm-cm, the carbon concentration is 0.5 ppma, the diameter of the silicon core wire is about 8 mm, and the electric resistivity is 3248 ohm at room temperature. -Cm, carbon concentration was 0.03 ppma. First, the silicon heater was energized at 7966 V via an electrode, and the silicon core wire was heated by the radiant heat of the silicon heater. When the silicon core wire reached 852 ° C., energization of the silicon core wire was started through the electrode. Thereafter, energization of the silicon heater was stopped, the temperature of the silicon core wire was kept at 1050 ° C., supply of trichlorosilane gas and hydrogen gas was started, and polycrystalline silicon was deposited. After completion of the precipitation, the polycrystalline silicon rod (diameter: about 120 mm) obtained from the silicon core wire was collected and the carbon concentration of the polycrystalline silicon rod was measured. The carbon concentration was 0.001 ppma on average.

Example 2
In a reaction chamber formed by covering the bottom wall substrate with a bell jar, a pair of inverted U-shaped silicon heaters and silicon core wires having independent electrodes were installed. The silicon heater has a diameter of about 8 mm, an electrical resistance of 390 ohms at room temperature, an electrical resistivity of 0.52 ohm-cm, a carbon concentration of 0.5 ppma, a diameter of the silicon core wire of about 8 mm, and an electrical resistivity of 3354 ohms at room temperature. -Cm, carbon concentration was 0.03 ppma. First, the silicon heater was energized at 7816 V through an electrode, and the silicon core wire was heated by the radiant heat of the silicon heater. When the silicon core wire reached 856 ° C., energization of the silicon core wire was started through the electrode. The temperature of the silicon core wire and the silicon heater were both maintained at 1050 ° C., the supply of trichlorosilane gas and hydrogen gas was started, and polycrystalline silicon was deposited. After completion of the precipitation, the polycrystalline silicon rod (diameter: about 120 mm) obtained from the silicon core wire was collected and the carbon concentration of the polycrystalline silicon rod was measured. The carbon concentration was 0.002 ppma on average. Further, the polycrystalline silicon rod (diameter: about 120 mm) obtained from the silicon heater was collected, and the carbon concentration of the polycrystalline silicon rod was measured. The carbon concentration was 0.14 ppma on average.

Comparative Example 1
In a reaction chamber formed by covering the bottom wall substrate with a bell jar, a pair of inverted U-shaped carbon heaters and silicon core wires having independent electrodes were installed. The diameter of the silicon core wire was about 8 mm, the electrical resistivity was 3124 ohm-cm at room temperature, and the carbon concentration was 0.03 ppma. First, the carbon heater, which is a resistance material, was energized through an electrode, and the silicon core wire was heated by the radiant heat of the carbon heater. When the silicon core wire reached 848 ° C., energization of the silicon core wire was started through the electrode. Thereafter, energization of the carbon heater was stopped, the temperature of the silicon core wire was maintained at 1050 ° C., supply of trichlorosilane gas and hydrogen gas was started, and polycrystalline silicon was deposited. After completion of the precipitation, the polycrystalline silicon rod (diameter: about 120 mm) obtained from the silicon core wire was collected, and the carbon concentration of the polycrystalline silicon rod was measured. As a result, the carbon concentration was 0.01 ppma on average.

1 Silicon production equipment 3 Bottom wall substrate 5 Bell jar 7 Silicon core wire 9 Silicon heater A Reaction chamber

Claims (3)

A polycrystal in which a silicon core wire installed in a reaction chamber is heated by energization, a silane compound and a reducing gas are supplied as source gases into the reaction chamber, and silicon is deposited on the surface of the silicon core wire by chemical vapor deposition In the method of manufacturing a silicon rod, a heater made of silicon that can be energized at an ambient temperature at start-up is attached to the silicon core wire, and the heater is energized to generate heat, thereby heating the silicon core wire, A method for producing a polycrystalline silicon rod, comprising energizing a silicon core wire. 2. The method for producing a polycrystalline silicon rod according to claim 1, wherein the electrical resistivity of the heater made of silicon is 5.0 ohm-cm or less at an ambient temperature at startup. The reaction chamber has a silicon core wire and a heater made of silicon that can be energized at ambient temperature at startup, and the silicon core wire and the heater made of silicon are connected to power supply equipment that can be operated independently. An apparatus for producing polycrystalline silicon.

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