JP5180947B2 - Cleaning method for a reactor for producing polycrystalline silicon - Google Patents

Description

  The present invention relates to a method for cleaning a reactor for producing polycrystalline silicon, and more particularly to a method for washing a reactor for producing polycrystalline silicon for producing high-purity polycrystalline silicon for solar cells. It is.

With the spread of solar cells in recent years, the demand for polycrystalline silicon is increasing rapidly. Conventionally, the Siemens method (Siemens Method) is mentioned as a method of manufacturing a high purity polycrystalline silicon. The Siemens method is a method of reducing trichlorosilane (SiHCl ₃ ) with hydrogen (H ₂ ). Polycrystalline silicon produced by the Siemens method has a very high purity of eleven-nine (11-N) and is used as silicon for semiconductors. Although the silicon for solar cells has also used a part of the product manufactured as this silicon for semiconductors, it does not require a purity as high as 11-N, and the Siemens method consumes a lot of power. There is a need for an inexpensive manufacturing method suitable for silicon.

Under such circumstances, a method for producing polycrystalline silicon by a zinc reduction method has been proposed as a method for producing silicon for solar cells, and the reaction thereof is represented by the following formula (1):
SiCl ₄ + 2Zn = Si + 2ZnCl ₂ (1)
It is shown by.

  In the method for producing polycrystalline silicon by the zinc reduction method, the purity of the produced polycrystalline silicon is about six-nine (6-N), which is lower than that of silicon for semiconductors, but compared with the Siemens method. It is a production method that is excellent in reaction efficiency and advantageous in production cost as much as about 5 times.

  As a method for producing polycrystalline silicon, for example, liquid or gaseous silicon tetrachloride is reduced with molten zinc in a reaction vessel, and a mixture containing the produced polycrystalline silicon and zinc chloride is taken out of the reaction vessel, A method for producing polycrystalline silicon (Patent Document 1), containing the mixture in a separation vessel, separating zinc chloride in the mixture, and then collecting polycrystalline silicon from the separation vessel; The liquid or gaseous silicon tetrachloride is reduced with molten zinc, and the mixture containing the produced polycrystalline silicon and zinc chloride is taken out of the reaction vessel, and the zinc chloride in the mixture is separated, A method for producing high-purity silicon that recovers crystalline silicon, wherein the separated zinc chloride is electrolyzed to recover metallic zinc and chlorine, and the recovered metallic zinc is again recovered from the silicon tetrachloride. A method for producing high-purity silicon, characterized in that it is used as a base agent and is used for chlorination of metallic silicon to produce silicon tetrachloride by synthesizing recovered chlorine with hydrogen to form hydrogen chloride (Patent Document) 2) has been reported.

  Patent Documents 1 and 2 both reduce liquid or gaseous silicon tetrachloride with molten zinc. However, in the method using molten zinc, there is a problem that polycrystalline silicon becomes powdery and is expensive due to the complexity of post-processing, the difficulty of impurity treatment, and the difficulty of casting.

  Therefore, as a silicon production method for performing a zinc reduction method using silicon tetrachloride vapor and zinc vapor, for example, zinc provided on the side peripheral surface of the reaction tube while heating the reaction tube standing in the vertical direction. While supplying zinc vapor from the vapor supply port, silicon tetrachloride vapor is discharged from below the zinc vapor supply port upward along the central axis of the reaction tube, and the temperature distribution in the reaction tube is changed to the side peripheral surface. There has been reported a method for producing silicon powder such that the center axis side is lower than the side (Patent Document 3).

  There is also a silicon production apparatus that has a silicon compound supply pipe and a zinc supply pipe in a reaction vessel and discharges a reaction product gas containing silicon to the outside of the reaction vessel through a rectifying member in the reaction vessel (Patent Document 4). ).

  Patent Documents 3 and 4 both discharge reaction product gas containing silicon to the outside of the reaction vessel, and the obtained silicon is silicon powder. However, in addition to the problem that powdered silicon is very difficult to melt when it is melted for ingot production, there is a problem that the purity is low and the utility value is poor because the surface area per unit weight is large.

  For this reason, the shape of the obtained silicon is preferably a needle shape or flake shape having a certain size. As a method for producing acicular or flaky silicon, for example, high purity silicon tetrachloride and high purity zinc are vaporized and reacted in a gasified atmosphere, so that most of the silicon taken out as a product is acicular. Or the manufacturing method of the high purity silicon | silicone for solar cells which is flake shape is reported (patent document 5).

  In Patent Document 5, a reactor has a tantalum core or a silicon core that can be energized, and by raising the temperature of the core rod above the reaction temperature, needle-like and flaky silicon is placed on the core rod rather than the reactor. To be deposited.

Japanese Patent Laid-Open No. 11-011925 (Claims) JP-A-11-092130 (Claims) JP 2009-107896 A (Claims) JP 2009-167022 A (Claims) JP 2004-018370 A (Claims)

  However, in Patent Document 5, generated silicon is deposited on a tantalum core or a silicon core, but silicon is also deposited on the furnace wall of the reaction furnace. Silicon is also deposited in the exhaust gas exhaust pipe. In addition, there are places in the reactor where the temperature is locally low, where liquefied or precipitated zinc remains.

  Thus, since silicon and zinc remain in the reaction furnace for producing polycrystalline silicon, they must be removed.

  When silicon is deposited on the furnace wall, the silicon is scraped off from the furnace wall after the polycrystalline silicon manufacturing process is finished, so that there is a problem that labor is required for this scraping and the manufacturing efficiency is lowered. . Further, since a reaction furnace made of quartz is often used as a reaction furnace for producing polycrystalline silicon, there has been a problem that the furnace wall is damaged or broken when silicon is scraped off.

  Further, when zinc is deposited and remains, there is a problem that, like silicon, removal scraping requires labor, and in some cases, the furnace wall is damaged.

  Accordingly, an object of the present invention is to provide a reactor for producing polycrystalline silicon by a zinc reduction method that can remove silicon and zinc remaining in the reactor easily and without damaging the reactor wall. It is in providing a cleaning method.

  As a result of intensive studies to solve the above-described problems in the prior art, the present inventors reacted chlorine gas from a silicon tetrachloride vapor supply pipe while heating the inside of the reactor to 200 to 1,000 ° C. It has been found that silicon and zinc remaining in the reaction furnace can be removed by supplying the gas into the furnace and exhausting it from the exhaust gas exhaust pipe, thereby completing the present invention.

  That is, the present invention (1) is a cleaning method for a reactor in which silicon tetrachloride and zinc are reacted to produce polycrystalline silicon, and the reactor is heated to 200 to 1,000 ° C. with chlorine. Gas is supplied from a silicon tetrachloride vapor supply pipe, exhausted from an exhaust gas discharge pipe, the silicon and zinc remaining in the reaction furnace react with chlorine gas, and the residue is removed. A method for cleaning a reactor for producing polycrystalline silicon is provided.

  According to the present invention, cleaning of a reactor for producing polycrystalline silicon by a zinc reduction method that can remove silicon and zinc remaining in the reactor easily and without damaging the reactor wall of the reactor. A method can be provided.

It is a typical end view showing the example of the form of the reaction furnace for polycrystalline silicon manufacture. It is a figure which shows a mode that the reactor shown in FIG. 1 is wash | cleaned. It is an end elevation which shows the side wall part and silicon carbide stick | rod in FIG. It is a schematic diagram which shows the example of the installation position and shape of a supply pipe of silicon tetrachloride vapor and a supply pipe of zinc vapor. It is a schematic diagram which shows the example of the installation position and shape of a supply pipe of silicon tetrachloride vapor and a supply pipe of zinc vapor. It is a schematic diagram which shows the polycrystalline silicon obtained using the reaction furnace of FIG.

  A method for cleaning a reactor for producing polycrystalline silicon according to the present invention will be described with reference to FIGS. FIG. 1 is a schematic end view showing an example of a reactor for producing polycrystalline silicon. FIG. 2 is a diagram showing a state in which the reactor shown in FIG. 1 is being cleaned.

  In FIG. 1, a reaction furnace 20 includes a side wall part 1 having a vertically long cylindrical shape, a lid part 2 (2a, 2b) that closes the upper and lower sides of the side wall part 1, and a heater 5 for heating the reaction furnace 20; It consists of. A supply pipe 7 for silicon tetrachloride vapor 9 and a supply pipe 8 for zinc vapor 10 are attached to the upper part of the reaction furnace 20, and a discharge for discharging the exhaust gas 11 is provided at the lower part of the reaction furnace 20. A tube 6 is attached. In addition, a silicon carbide rod 3 is installed in the reaction furnace 20 via a silicon carbide rod fixing member 4. Specifically, the fixing member 4 of the silicon carbide rod is hooked on the inner wall collar portion 12 formed on the inner wall of the side wall portion 1, so that the hydrocarbon rod 3 is placed inside the reaction furnace 20. It is installed to protrude downward. The side wall portion 1 and the lid portion 2 are sealed by, for example, sandwiching a sealing material between the respective flange portions and bolting the flange portions together.

  One end of the supply pipe 7 for the silicon tetrachloride vapor is located inside the reaction furnace 20, and the other end is connected to a silicon tetrachloride evaporator. One end of the zinc vapor supply pipe 8 is located inside the reaction furnace 20, and the other end is connected to a zinc evaporator. Further, the exhaust pipe 6 serves as a recovery device for recovering the exhaust gas 11, that is, the zinc chloride gas generated when silicon tetrachloride and zinc react and the silicon tetrachloride vapor and zinc vapor which are unreacted gases. It is connected.

  A method for producing polycrystalline silicon using the reactor 20 will be described. First, silicon tetrachloride and zinc are vaporized by respective evaporators, and silicon tetrachloride vapor 9 is heated from the silicon tetrachloride vapor supply pipe 7 and zinc vapor 10 is heated from the zinc vapor supply pipe 8 by the heater 5. The exhaust gas 11 is discharged from the discharge pipe 6 to the outside of the reaction furnace 20 while being supplied into the reaction furnace 20. At this time, silicon tetrachloride reacts with zinc in the reaction furnace 20 to produce polycrystalline silicon. However, since the silicon carbide rod 3 is installed in the reaction furnace 20, it is produced. Polycrystalline silicon is deposited on the silicon carbide rod 3. Since silicon tetrachloride vapor and zinc vapor are supplied from the upper part of the reaction furnace 20 and the exhaust gas 11 is discharged from the lower part of the reaction furnace 20, the silicon tetrachloride vapor and the zinc vapor are Since the silicon carbide rod 3 is moving downward from the top of 20 and along the flow, a polycrystalline silicon crystal grows so as to cover the silicon carbide rod 3. Further, zinc chloride is also generated by the reaction of silicon tetrachloride and zinc, but the zinc chloride gas is discharged out of the exhaust pipe 6 as an exhaust gas 11 together with unreacted silicon tetrachloride vapor and zinc vapor. .

  In the method for producing polycrystalline silicon using the reaction furnace 20, when the amount of deposited polycrystalline silicon in the reaction furnace 20 increases, the supply of silicon tetrachloride vapor and zinc vapor is stopped, and the reaction furnace 20 is cooled. Then, once the production of polycrystalline silicon is interrupted and the polycrystalline silicon precipitated from the reaction furnace 20 is taken out, the production of polycrystalline silicon in the reaction furnace 20 is resumed. Thus, in the polycrystalline silicon manufacturing method in which polycrystalline silicon is deposited in the reaction furnace, polycrystalline silicon is manufactured by batch processing.

  At this time, if polycrystalline silicon is produced in the reaction furnace 20, silicon is precipitated in the side wall 1 and the discharge pipe 6, and the reaction is considered to lower the temperature locally. Liquefied or precipitated zinc adheres on the lid 2 b on the lower side of the furnace, and a residue is generated in the reaction furnace 20. When batch processing for producing polycrystalline silicon in the reaction furnace 20 is repeated, silicon and zinc are accumulated in the reaction furnace 20 as residues.

  Therefore, the reactor is cleaned by the method for cleaning a reactor for producing polycrystalline silicon according to the present invention. First, the supply of silicon tetrachloride vapor and zinc vapor is stopped, the reaction furnace is cooled, the silicon carbide rod 3 is taken out from the reaction furnace 20, and the batch process is terminated. Next, after removing the silicon carbide rod 3 from the silicon carbide rod fixing member 4, as shown in FIG. 2, the silicon carbide rod fixing member 4 is returned to the reactor 20, and the lid member 2 is Close.

  Next, a chlorine gas transfer pipe is connected to the silicon tetrachloride vapor supply pipe 7. On the other hand, the zinc vapor supply pipe 8 is evaporated from the reaction furnace 20 through the zinc vapor supply pipe 8 by closing a valve attached to the zinc vapor supply pipe 8 or the like. Prevent chlorine gas from flowing back into the zinc vapor supply device such as a vessel.

  Next, the chlorine gas 14 is supplied into the reaction furnace 20 by supplying the chlorine gas 14 from the silicon tetrachloride vapor supply pipe 7 while heating the reaction furnace 20 at 200 to 1,000 ° C. The chlorine gas 14 is discharged from the reaction furnace 20 by supplying and discharging the chlorine gas 14 from the discharge pipe 6. As a result, the silicon and zinc remaining in the reaction furnace 20 react with the chlorine gas 14 to remove these residues. Then, the chlorine gas 14 is supplied and discharged for a predetermined time, and the reaction furnace 20 is cleaned.

  That is, the method for cleaning a reactor for producing polycrystalline silicon according to the present invention is a method for cleaning a reactor in which silicon tetrachloride and zinc are reacted to produce polycrystalline silicon, while heating the inside of the reactor. Then, chlorine gas is supplied from a silicon tetrachloride vapor supply pipe, discharged from an exhaust gas discharge pipe, and the silicon and zinc remaining in the reactor are reacted with chlorine gas to obtain a residue. A method for cleaning a reactor for producing polycrystalline silicon, characterized in that it is removed.

  In the reaction furnace in which the method for cleaning a reactor for producing polycrystalline silicon according to the present invention is performed, silicon tetrachloride vapor and zinc vapor are supplied into the reaction furnace, and silicon tetrachloride vapor and zinc vapor are mixed in the reaction furnace. There is no particular limitation as long as the reaction is performed and polycrystalline silicon is deposited in the reaction furnace.

  Since the inside of the reactor according to the method for cleaning a reactor for producing polycrystalline silicon according to the present invention has a temperature of about 1,000 ° C., the material of the reactor includes quartz such as transparent quartz and opaque quartz, carbonization Silicon, silicon nitride and the like can be mentioned, and silicon carbide and silicon nitride are preferable from the viewpoint of lifetime and removal of deposited polycrystalline silicon, and quartz is preferable from the viewpoint of cost. Further, depending on the structure of the reaction furnace and the like, the material of the reaction furnace is not particularly limited as long as it can withstand the heating temperature during the reaction. Further, the side wall portion and the lid portion of the reactor may be made of different materials.

  And as this reaction furnace, the vertically long reaction furnace as shown in FIG. 1 is preferable. That is, the reactor is a reactor for reacting silicon tetrachloride with zinc to produce polycrystalline silicon, having a silicon tetrachloride vapor supply pipe and a zinc vapor supply pipe in the upper part and in the lower part. A reaction furnace having a discharge pipe for exhaust gas, and a precipitation furnace such as a silicon carbide rod installed in the reaction furnace (hereinafter also referred to as reaction furnace (A)) for producing polycrystalline silicon. It is.

  The shape of the reaction furnace (A) is such that silicon tetrachloride vapor and zinc vapor supplied from the upper part of the reaction furnace react while moving downward from the upper part of the reaction furnace toward the lower part. That is, it is a vertically long shape. In other words, the shape of the reaction furnace is such that the raw material vapor and the exhaust gas flow from the upper part to the lower part of the reaction furnace.

  Although the magnitude | size of this reaction furnace (A) is not specifically limited, It selects suitably by the supply conditions of silicon tetrachloride vapor | steam and zinc vapor | steam. In general, the length of the reaction furnace (A) in the longitudinal direction is preferably 1,000 to 6,000 mm, and in the case of a cylindrical shape, the diameter is 200 to 2,000 mm.

  The precipitation rod is installed in the reaction furnace (A). Examples of the precipitation rod include a silicon carbide rod, a tantalum rod, and a silicon rod, and a silicon carbide rod is preferable. The shape of the precipitation rod is preferably a prismatic shape or a cylindrical shape, and particularly preferably a cylindrical shape. In the case where the shape of the precipitation bar is a columnar shape, the diameter of the precipitation bar is preferably 1 to 20 cm, and particularly preferably 2 to 10 cm from the viewpoint of strength and processing surface. Further, the length of the silicon carbide rod (precipitation rod) existing between the lower side of the fixing member 4 of the silicon carbide rod (precipitation rod) and the upper side of the discharge pipe 6 is preferably 50 to 1,200 mm, 100 to 1,100 mm is particularly preferable, and 200 to 1,000 mm is more preferable.

  Of the precipitation rods, the silicon carbide rod is a molded body of silicon carbide. Usually, the molded body of silicon carbide is a porous body having a large number of pores. The silicon carbide rod is a silicon-impregnated silicon carbide rod in which silicon is impregnated with porous silicon carbide, and the impregnated silicon becomes a seed of polycrystalline silicon crystals produced by the reaction, This is preferable in that the precipitation of polycrystalline silicon on the silicon carbide rod can be promoted. In the silicon-impregnated silicon carbide rod, the mass ratio of silicon carbide: impregnated silicon is preferably 80:20 to 95: 5, and particularly preferably 80:20 to 90:10. The silicon-impregnated silicon carbide rod is obtained by immersing a porous silicon carbide rod in molten silicon and impregnating the silicon carbide holes with the silicon.

  Further, even if a porous silicon carbide rod not impregnated with silicon is installed in the reaction furnace (A) and a reaction between silicon tetrachloride vapor and zinc vapor is performed, the initial stage of the reaction Then, in the porous structure near the outside of the silicon carbide rod, contact between silicon tetrachloride vapor and zinc vapor occurs, and silicon is generated there, so the silicon carbide rod is impregnated with silicon in the vicinity of the outside of the silicon carbide rod. It will be in the same state as it is. Therefore, a porous silicon carbide rod not impregnated with silicon may be used. In particular, when the silicon carbide rod is used repeatedly, a porous silicon carbide rod not impregnated with silicon is used by repeated use. It becomes the state similar to the porous silicon carbide rod impregnated with.

  The number of the deposition rods may be one or two or more. Moreover, the installation position of this precipitation rod is not specifically limited. For example, when the number of the silicon carbide rods (precipitation rods) is 4, as shown in FIG. 3, the silicon carbide rods 3 are equally spaced on an arc centered on the center of the side wall 1 (reactor). It is preferable that it is installed in. The number and position of the silicon carbide rods to be installed are appropriately selected so that the polycrystalline silicon is efficiently precipitated depending on the reaction conditions such as the supply conditions of the raw material vapor and the size of the reaction furnace.

  In FIG. 1, the silicon carbide rod 3 (precipitation rod) is fixed to the silicon carbide rod fixing member 4, and the silicon carbide rod fixing member 4 is connected to the inner wall collar of the furnace. Although it has been described that the silicon carbide rod is installed in the reaction furnace (A) by being hooked on the part 12, it is not limited to this. For example, in FIG. 1, a furnace inner wall collar portion is formed below the attachment position of the discharge pipe 6, and the silicon carbide rod fixing member to which the silicon carbide rod is fixed is hooked on the furnace wall collar portion. A method of installing the silicon carbide rod so as to protrude upward into the reaction furnace from an upper side of the fixing member of the silicon carbide rod, a method of fixing the silicon carbide rod to the lid portion 2b, and the like. The method of installing so that this silicon carbide stick may be stood from the bottom toward the top.

  Further, in order to set the temperature of the precipitation rod to be higher than the temperature in the reaction furnace (A), a heater for heating may be provided inside the precipitation rod. For example, when the temperature in the reactor (A) (side wall temperature of the reactor) is 930 ° C., polycrystalline silicon is selectively deposited on the deposition rod by setting the deposition rod to 1,000 ° C. It becomes possible. In the case of the silicon carbide rod, since silicon carbide is a material that has a high thermal conductivity and receives a lot of radiant heat, the silicon carbide rod receives a lot of radiant heat from the side wall of the reactor, and the silicon carbide rod does not have to be heated. However, it is possible to deposit polycrystalline silicon on the silicon carbide rods selectively to some extent.

  In the reactor (A), the silicon tetrachloride vapor supply pipe and the zinc vapor supply pipe are attached to the upper part of the reaction furnace. The discharge pipe is attached to the lower part of the reactor (A). And in this reaction furnace (A), the downward flow of raw material vapor | steam is formed in this reaction furnace, and the position (in which reaction of silicon tetrachloride and zinc can be caused in reaction furnace (A) ( The silicon tetrachloride vapor supply pipe, the zinc vapor supply pipe, and the discharge pipe are attached to the vertical position.

  The shape and arrangement of the silicon tetrachloride vapor supply pipe and the zinc vapor supply pipe. For example, as shown in FIG. 4 (4-1), the silicon tetrachloride vapor supply pipe and the zinc vapor The horizontal portion of the supply pipe is arranged in a straight line, and as shown in (4-2), the tip of the supply pipe is L-shaped and the outlet of the supply pipe is directed downward. Moreover, as shown in FIG. 5, the example which prevents the horizontal part of the supply pipe | tube of this silicon tetrachloride vapor | steam and the supply pipe | tube of this zinc vapor | steam to line up on a straight line is mentioned. In the embodiment shown in FIG. 5, the silicon tetrachloride vapor and the zinc vapor move so as to swirl in the reactor (A).

  A heater is installed around the side wall of the reactor (A). The heater is preferably an electric heater.

  In the method for cleaning a reactor for producing polycrystalline silicon according to the present invention, the inside of the reactor is heated to 200 to 1,000 ° C., preferably 720 to 900 ° C.

  Then, chlorine gas is supplied into the reaction furnace by supplying chlorine gas from the silicon tetrachloride vapor supply pipe while the inside of the reaction furnace is heated, and chlorine gas is discharged from the exhaust gas discharge pipe. As a result, chlorine gas is discharged from the reactor.

  The supply amount of chlorine gas is 1 to 1,000 volumes / reactor volume / hour, preferably 10 to 1,000 volumes / reactor volume / hour, with respect to the internal volume of the reactor.

  In this way, by reacting chlorine gas with the residual silicon and zinc in the reactor that is being heated, the residue is converted into their chlorides to form compounds with low boiling points. The gas is removed to remove the residue.

  The cleaning time with chlorine gas is appropriately selected depending on the residual amount of the residue in the reactor and the heating temperature of the reactor.

  Since the chlorine gas used for cleaning the reactor contains silicon tetrachloride and zinc chloride, the chlorine gas used for cleaning is separated into chlorine, silicon tetrachloride and zinc chloride by distillation or the like.

  Further, after separating silicon tetrachloride and zinc chloride from the chlorine gas discharged from the exhaust gas discharge pipe, the silicon tetrachloride and zinc chloride separated chlorine gas is again supplied to the silicon tetrachloride vapor supply pipe. The chlorine gas can be circulated by supplying from the above.

  After performing the method for cleaning a reactor for producing polycrystalline silicon according to the present invention, the production of polycrystalline silicon is resumed.

  A method for producing polycrystalline silicon using the reactor (A) is a method for producing polycrystalline silicon by reacting silicon tetrachloride with zinc to produce polycrystalline silicon, wherein silicon tetrachloride vapor and zinc are produced. Steam is supplied from the upper part of the reaction furnace, exhaust gas is discharged from the lower part of the reaction furnace, and the reaction between silicon tetrachloride vapor and zinc vapor is performed in the reaction furnace, and polycrystalline silicon produced is deposited on the precipitation rod. This is a method for producing polycrystalline silicon to be deposited.

  In the production of polycrystalline silicon by the zinc reduction method using silicon tetrachloride vapor and zinc vapor, when the silicon tetrachloride vapor and zinc vapor are vigorously stirred in the reaction furnace, fine polycrystalline particles having a diameter of 3 μm or less Silicon is produced, but such fine-grained polycrystalline silicon has a low packing density and takes time to melt. On the other hand, when silicon tetrachloride vapor and zinc vapor contact gently in the reactor, preferably when they contact at a linear velocity of 5 cm / second or less, dendritic, needle-like or plate-like polycrystalline silicon is produced. However, such dendritic, needle-like or plate-like polycrystalline silicon is easier to melt and has a shorter melting time than fine-grained polycrystalline silicon. Therefore, in the method for producing polycrystalline silicon using the reaction furnace (A), the conditions are such that the silicon tetrachloride vapor and the zinc vapor are not vigorously stirred in the reaction furnace, that is, a fine granular polycrystal having a diameter of 3 μm or less. Silicon tetrachloride vapor and zinc vapor are supplied to the reactor under conditions that do not produce crystalline silicon. That is, in the method for producing polycrystalline silicon using the reactor (A), silicon tetrachloride vapor and zinc vapor are supplied under the supply conditions of the raw material vapor that can easily generate dendritic, needle-like or plate-like polycrystalline silicon, It supplies to this reactor (A). The supply condition of the raw material vapor that easily generates dendritic, needle-like or plate-like polycrystalline silicon is appropriately selected depending on the size of the reactor, the position or number of the silicon carbide rods installed, and the like.

  The supply ratio (molar ratio) of silicon tetrachloride vapor to zinc vapor is silicon tetrachloride vapor: zinc vapor = 0.9: 2 to 1.2: 2, preferably 1: 2 to 1.2: 2. And particularly preferably 1: 2 to 1.1: 2. Further, the silicon tetrachloride vapor and the zinc vapor may be diluted with an inert gas such as nitrogen gas. In that case, the dilution rate of the silicon tetrachloride vapor is a volume ratio ((silicon tetrachloride vapor + inert gas). ) / Silicon tetrachloride vapor), preferably 1.01 to 1.5, particularly preferably 1.05 to 1.3, and the dilution rate of zinc vapor is a volume fraction ((zinc vapor + inert gas) / Zinc vapor), preferably 1.01 to 1.3, particularly preferably 1.03 to 1.2.

  According to “Chemical Handbook” (edited by the Chemical Society of Japan), the boiling point of zinc is 907 ° C., so that the temperature in the reactor (A) is 907 ° C. or more, which is the boiling point of zinc. (A) is heated. The temperature in the reactor (A) is 907 to 1,200 ° C, preferably 930 to 1,100 ° C. The pressure in the reactor (A) is preferably 0 to 700 kPaG, particularly preferably 0 to 500 kPaG. By setting the reaction conditions within the above range, it becomes possible to stably deposit polycrystalline silicon on the silicon carbide rod (precipitation rod).

  In the method for producing polycrystalline silicon using the reaction furnace (A), one or more of the deposition rods with a built-in heater may be used and the deposition rods may be heated. At that time, all of the silicon carbide rods installed in the reaction furnace may be heated, or a part thereof may be heated. Further, the heating start time of the precipitation rod may be before the polycrystalline silicon starts to be deposited on the precipitation rod, that is, before the supply of silicon tetrachloride vapor and zinc vapor, or It may be after some amount of polycrystalline silicon is deposited.

  Then, in the method for producing polycrystalline silicon using the reactor (A), silicon tetrachloride vapor and zinc vapor are moved downward to react silicon tetrachloride with zinc in the reactor (A), While producing polycrystalline silicon, the precipitation rod is made to exist along the flow of silicon tetrachloride vapor and zinc vapor, thereby depositing polycrystalline silicon on the precipitation rod.

  Further, in the method for producing polycrystalline silicon using the reaction furnace (A), a supply pipe for an inert gas such as nitrogen gas is attached to the reaction furnace (A), and the inert gas is supplied to the reaction furnace (A). The reaction furnace (A) can be pressurized with an inert gas.

  In the method for producing polycrystalline silicon using the reactor (A), the production of polycrystalline silicon is completed by stopping the supply of silicon tetrachloride vapor and zinc vapor. Thereafter, the reaction furnace (A) is cooled, and the precipitation rod on which polycrystalline silicon is deposited is taken out of the reaction furnace (A). Then, the deposited polycrystalline silicon is scraped off from the precipitation rod to obtain polycrystalline silicon.

  In the case of the silicon carbide rod, the silicon carbide rod after the polycrystalline silicon is scraped off is used again in the method for producing polycrystalline silicon using the reaction furnace (A). Further, before reuse, the silicon carbide rod may be washed with pure water or an acid such as hydrochloric acid, nitric acid, hydrofluoric acid or the like.

Thus, since the polycrystalline silicon obtained by the manufacturing method of polycrystalline silicon using this reaction furnace (A) is manufactured using zinc as a reducing agent, it contains zinc. The zinc content in the polycrystalline silicon obtained by the method for producing polycrystalline silicon using the reactor (A) is 0.1 to 100 ppm by mass, preferably 0.1 to 10 ppm by mass, particularly preferably 0.00. It is 1-1 mass ppm. When the zinc content in the polycrystalline silicon is within the above range, a high-purity polycrystalline silicon ingot of 6-N or more can be produced. Note that the purity of the polycrystalline silicon is determined by high frequency induction plasma emission spectrometry (ICP-AES). The analysis method is as follows.
To 1.5 g of the obtained polycrystalline silicon, 16 ml of 38% hydrofluoric acid and 30 ml of 55% nitric acid are added and completely dissolved, and then evaporated to dryness. Next, the solution is fixed with 5 ml of 1% nitric acid, and the impurity concentration is measured by ICP-AES (IRIS Advantage / RP type manufactured by Thermo Fisher Scientific Co., Ltd.) to calculate the purity of the polycrystalline silicon.

  Moreover, the shape of the polycrystalline silicon obtained by the polycrystalline silicon manufacturing method using the reactor (A) is a dendritic shape, a needle shape or a plate shape, and is not a fine particle having a diameter of 3 μm or less. In the method for producing polycrystalline silicon using the reactor (A), silicon crystals grow into dendrites or needles, so that they grow into large dendrites or needles. In addition to large dendritic or needle-like ones, there are plate-like ones, small dendritic or needle-like ones, and when scraping from the silicon carbide rod, dendritic or needle-like ones are Some are broken into small dendrites or needles. The size of the dendritic, needle-like or plate-like polycrystalline silicon is preferably 100 μm or more, particularly preferably 500 μm or more, and further preferably 1,000 μm or more. The dendritic, needle-like or plate-like polycrystalline silicon is preferably dendritic, needle-like or plate-like polycrystalline silicon in which 50% by mass or more does not pass through a screen of 100 μm mesh size. Particularly preferred is a dendritic, needle-like or plate-like polycrystalline silicon whose mass% or more does not pass through a screen of 500 μm mesh size. The dendritic shape is a shape comprising a trunk portion 31 and a branch portion 32 extending from the trunk portion 31 as shown in (6-1) of FIG. 6, and the needle shape is a shape shown in FIG. As shown in (6-2), the shape extends in a substantially straight line, and the plate shape is a shape extending in a substantially planar direction such as a scale shape or a flake shape. In addition, there is a shape in which the branches extend further from the dendritic branch 32 and the crystal extends. The size of the dendritic, needle-like or plate-like polycrystalline silicon is the length of the longest part of the crystal in the case of a dendritic shape (the length of 33a in (6-1) in FIG. 6). In the case of a needle shape, it indicates the length of the crystal (the length of 33b in (6-2) in FIG. 6), and in the case of a plate shape, it indicates the longest diameter of the crystal.

  EXAMPLES Next, although an Example is given and this invention is demonstrated more concretely, this is only an illustration and does not restrict | limit this invention.

Example 1
<Manufacture of polycrystalline silicon>
In the following reactor, zinc vapor heated and vaporized from a zinc vapor supply pipe to 930 ° C. was introduced into the reaction furnace together with nitrogen gas, and vaporized by heating to 930 ° C. from a silicon tetrachloride vapor supply pipe. While supplying silicon tetrachloride vapor to the reactor, the inside of the reactor is set to 930 ° C., the heating temperature of the silicon carbide rod is set to 1,000 ° C., silicon tetrachloride is supplied at a rate of 74 g / min, and zinc is supplied at 50 g / min. Feeding at a rate, the reaction between silicon tetrachloride and zinc was carried out.
<Reactor (in the embodiment shown in FIG. 1, the number of silicon carbide rods installed is 3)>
Reaction furnace: A quartz reaction tube having an inner diameter of 300 mm and a length of 2,500 mm is used. Silicon carbide rod: silicon-impregnated silicon carbide rod, outer diameter of 30 mm × length of 1,000 mm, number of three (centering on the center of the reaction furnace) On a circular arc at equal intervals), the silicon carbide: impregnated silicon mass ratio of the silicon-impregnated silicon carbide rod is 85:15
Positional relationship between silicon tetrachloride vapor supply pipe and zinc vapor supply pipe in the vertical direction: the same height Positional relationship between silicon tetrachloride vapor supply pipe and zinc vapor supply pipe in the horizontal direction: Positional relationship shown in Fig. 4 Discharge at reactor outlet Pipe inner diameter: 100mm
Position of the discharge pipe: The lower side of the discharge pipe 6 is 700 mm above the upper surface of the lid 2b on the lower side of the reactor

  And after reacting for 40 hours, it cooled and the silicon carbide rod was taken out of the reaction furnace. It was confirmed that acicular polycrystalline silicon was deposited on the silicon carbide rod. Next, polycrystalline silicon was scraped off from the silicon carbide rod to obtain polycrystalline silicon. The yield of polycrystalline silicon was 62% with respect to the feedstock, and the purity of polycrystalline silicon was 6-N. The silicon carbide rod was not broken when the polycrystalline silicon was scraped off, and was in a reusable state.

  The production of the polycrystalline silicon was repeated 10 batches. After cooling the reaction furnace, the silicon carbide rod was taken out and the residue in the reaction furnace was confirmed. Residue was observed on the side wall and the discharge pipe of the reaction furnace. Residue was also confirmed on the lower lid 2b of the reactor.

Next, the silicon carbide rod is removed from the fixing member of the silicon carbide rod, only the fixing member of the silicon carbide rod is returned into the reactor, the lid member is closed, and a chlorine gas transfer pipe is connected to the silicon tetrachloride vapor supply pipe, The valve attached to the zinc vapor supply pipe was closed. Next, the inside of the reactor was heated to 750 ° C., and chlorine gas was supplied at 38 m ³ / hour to perform cleaning. The pressure in the reaction furnace at this time was 0.1 MPaG or less. After cleaning by supplying chlorine gas for 1 hour, the supply of chlorine gas was stopped and the reactor was cooled. After cooling, the inside of the reactor was checked, and no residue was observed.

  According to the present invention, since the reactor for producing polycrystalline silicon can be easily cleaned, polycrystalline silicon can be produced at low cost.

DESCRIPTION OF SYMBOLS 1 Side wall 2, 2a, 2b of reaction furnace 3 Silicon carbide rod 4 Fixing member 5 of silicon carbide rod 5 Heater 6 Exhaust pipe 7 Silicon tetrachloride vapor supply pipe 8 Zinc vapor supply pipe 9 Silicon tetrachloride vapor 10 Zinc vapor 11 Exhaust Gas 12 Furnace Inner Collar 14 Chlorine Gas 20 Reactor 31 Trunk 32 Branch

Claims (3)

  A method for cleaning a reactor in which silicon tetrachloride and zinc are reacted to produce polycrystalline silicon, wherein chlorine gas is supplied to silicon tetrachloride vapor while heating the reactor to 200 to 1,000 ° C. For the production of polycrystalline silicon, characterized in that it is supplied from a pipe, discharged from an exhaust gas discharge pipe, the silicon and zinc remaining in the reactor react with chlorine gas, and the residue is removed. How to clean the reactor.   After separation of silicon tetrachloride and zinc chloride from chlorine gas discharged from the exhaust gas discharge pipe, chlorine gas from which silicon tetrachloride and zinc chloride have been separated is supplied again from the silicon tetrachloride vapor supply pipe The method for cleaning a reactor for producing polycrystalline silicon according to claim 1, wherein chlorine gas is circulated.   The reactor is a reactor for reacting silicon tetrachloride with zinc to produce polycrystalline silicon, having a silicon tetrachloride vapor supply pipe and a zinc vapor supply pipe in the upper part and an exhaust gas in the lower part. The method for cleaning a reactor for producing silicon according to claim 1, wherein the reactor is a reactor having a discharge pipe.