JP2008285343A - Preparation method of polycrystalline silicon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable the enhancement of recovery efficiency of a polycrystalline silicon. <P>SOLUTION: In a preparation method of the polycrystalline silicon, silicon tetrachloride gas and zinc gas are fed to a reactor R from first and second supply ports 16a and 18a, respectively, and reacted with each other to produce polycrystalline silicon particles in an upper part 14a of the reactor R, provided that the supply ports are formed on a furnace wall part at which the temperature is ≥1,100°C. Then, the produced polycrystalline silicon particles are deposited onto low-temperature parts of the furnace wall 14 in a lower part 14c of the reactor R by providing a temperature gradient along the lower part 14c of the furnace wall 14 inside the reactor R. The deposited polycrystalline silicon particles are melted, subsequently cooled and solidified to obtain the polycrystalline silicon. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing polycrystalline silicon.

A method for producing polycrystalline silicon by reacting silicon tetrachloride gas and zinc gas to produce silicon and cooling and solidifying the produced silicon is known (see Patent Document 1). In this method, the temperature inside the reaction furnace is maintained at 1000 to 1500 ° C.
JP 2004-99421 A

  In the method described in Patent Document 1, the generated polycrystalline silicon particles are easily exhausted from the reaction furnace together with the reaction gas and the carrier gas. Therefore, the recovery efficiency of polycrystalline silicon is poor. Accordingly, an object of the present invention is to improve the recovery efficiency of polycrystalline silicon.

  In the method for producing polycrystalline silicon according to the present invention, silicon tetrachloride gas and zinc gas are respectively introduced into the reactor from the first and second supply ports formed in the furnace wall portion having a temperature of 1100 ° C. or higher in the reactor. The process of producing polycrystalline silicon particles by supplying to the reactor and reacting with the furnace wall in the reactor by forming a temperature gradient along the furnace wall in the reactor. A step of attaching to a low temperature portion, a step of melting the attached polycrystalline silicon particles to obtain a melt, and a step of cooling and solidifying the melt to obtain polycrystalline silicon.

  In the method for producing polycrystalline silicon according to the present invention, a temperature gradient is provided along the furnace wall in the reaction furnace, so that the generated polycrystalline silicon particles are part of the furnace wall in the reaction furnace where the temperature is low due to the thermophoresis effect. To flow and adhere. Thereby, it can suppress that the produced | generated polycrystalline silicon particle is exhausted from a reaction furnace with reaction gas and carrier gas. And since the polycrystalline silicon adhering to the furnace wall is melted and cooled and solidified, the recovery efficiency of polycrystalline silicon can be improved.

  Preferably, the temperature distribution with respect to the furnace wall of the reaction furnace is changed by moving heating means for heating the furnace wall along the reaction furnace. In this case, the adhered polycrystalline silicon particles can be easily melted by moving the heating means to the portion where the polycrystalline silicon particles are adhered on the furnace wall. Further, the polycrystalline silicon particles can be attached along the furnace wall of the reaction furnace. Therefore, the polycrystalline silicon can be efficiently attached and melted, and the recovery efficiency of the polycrystalline silicon can be further improved.

  Preferably, a produced gas containing polycrystalline silicon particles produced by reacting silicon tetrachloride gas and zinc gas between the step of producing polycrystalline silicon particles and the step of attaching polycrystalline silicon particles is preferably used. The method further includes a step of cooling. In this case, polycrystalline silicon grows with the polycrystalline silicon particles contained in the generated gas as nuclei. Since the grown polycrystalline silicon particles are easily dropped by gravity, it is possible to prevent the polycrystalline silicon particles from being exhausted. Therefore, the yield of the produced polycrystalline silicon is improved.

  According to the method for producing polycrystalline silicon of the present invention, the recovery efficiency of polycrystalline silicon can be improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate descriptions are omitted.

  FIG. 1 is a diagram schematically showing a polycrystalline silicon manufacturing apparatus according to the first embodiment. FIG. 1 shows an xyz space coordinate system. The polycrystalline silicon manufacturing apparatus 10 shown in FIG. 1 includes a housing 12 and a reactor R accommodated in the housing 12. The reactor R extends along the z-axis direction parallel to the vertical direction. Thereby, a polycrystalline silicon can be efficiently collect | recovered from the lower end of the reaction furnace R using gravity.

The furnace wall 14 is preferably made of ceramics such as SiO ₂ (quartz), SiC, alumina, or carbon. From the viewpoint of ease of processing and prevention of contamination, SiO ₂ is preferable. The furnace wall 14 may be made of carbon coated with SiC.

  The furnace wall 14 of the reactor R has an upper part 14a (first part), a middle part 14b, and a lower part 14c (second part) arranged in order along the z-axis. The upper part 14a is located upstream of the lower part 14c.

  A supply port 18a for supplying silicon tetrachloride gas G1 into the reaction furnace R and a supply port 16a for supplying zinc gas G2 into the reaction furnace R are formed in the upper portion 14a of the furnace wall 14. The first piping 16 is connected to the supply port 16a, and the second piping 22 is preferably connected to the piping 16 by a stamped joint (connecting portion 20). A zinc supply source 24 is connected to the pipe 22. For example, a zinc melt 26 is accommodated in the zinc supply source 24, and a partition plate 28 is provided on the surface of the zinc melt 26, for example. Zinc gas G <b> 2 is generated from the zinc melt 26. On the other hand, a silicon tetrachloride supply source 30 is connected to the supply port 18a through a pipe 18. In the upper part 14a, the silicon tetrachloride gas G1 and the zinc gas G2 react to generate a product gas G3 containing polycrystalline silicon particles.

  A heater H1 for heating the upper portion 14a is preferably provided around the upper portion 14a. Thereby, the temperature of the upper part 14a can be controlled. The temperature of the upper part 14a is controlled to 1100 ° C. or higher. Thereby, it can suppress that a polycrystalline silicon adheres to the supply port 16a and the supply port 18a. Furthermore, the temperature of the upper part 14a is preferably controlled to 1350 ° C. or lower.

  In the middle part 14b, for example, a supply port 36a for supplying the inert gas G4 into the reaction furnace R is formed. In this case, since the product gas G3 can be cooled by the inert gas G4, the polycrystalline silicon particles contained in the product gas G3 can be crystal-grown. When the particle diameter of the polycrystalline silicon particles is increased, the polycrystalline silicon particles are easily dropped by gravity, so that the polycrystalline silicon particles are easily recovered. The inert gas G4 is a rare gas such as He, Ar, or Xe. From the viewpoint of improving the cooling efficiency of the product gas G3, the temperature of the inert gas G4 is preferably 1000 ° C. or lower. An inert gas supply source 38 is connected to the supply port 36a via a pipe 36. The supply port 36a may be formed in the upper part 14a.

  It is preferable that heaters H2 and H3 for heating the middle part 14b are provided around the middle part 14b. Thereby, the temperature of the middle part 14b can be controlled. The temperature of the middle part 14b is preferably controlled to be lower than that of the upper part 14a in the range of 1100 ° C. or higher and 1350 ° C. or lower by the heaters H2 and H3. However, if it is lowered too much, polycrystalline silicon particles will precipitate on the furnace wall at this portion, so that the temperature is lower than the temperature of the upper portion 14a and is 1100 ° C. or higher in order to promote nuclear growth in the range where it does not precipitate. Have a necessary and sufficient temperature gradient. The temperature difference between the temperature of the heater for heating the upper portion 14a and the temperature of the heater for heating the middle portion 14b is preferably 10 to 100 ° C.

  The lower portion 14c is preferably provided with a funnel 32 for collecting the silicon melt SI1. A heater H4 (heating means) for heating the lower portion 14c is provided around the lower portion 14c. The heater H4 moves along the reaction furnace R in the lower portion 14c. The heater H4 moves up and down along the z-axis direction. For example, the heater H4 is configured to be moved by a motor so that the position can be controlled.

  When the heater H4 is located at the upper position a in the lower portion 14c, a temperature gradient is formed along the lower portion 14c of the furnace wall 14 of the reactor R so that the upper temperature is high and the lower temperature is low. When the heater H4 is located at the central position b in the lower part 14c, a temperature gradient is formed along the lower part 14c of the furnace wall 14 of the reaction furnace R, with the middle temperature being high and the lower temperature being low. Thus, a temperature gradient is formed by the heater H4 along the lower part 14c of the furnace wall 14 of the reaction furnace R, and the temperature distribution changes as the heater H4 moves along the reaction furnace R.

  The polycrystalline silicon particles dropped due to gravity adhere to the funnel 32, and the polycrystalline silicon particles also adhere due to the thermophoresis effect caused by the formation of a temperature gradient. That is, by making the temperature of the funnel 32 lower than the temperature of the upper portion thereof, the silicon particles move toward the funnel and adhere. In the lower part 14c, the attached polycrystalline silicon particles are melted to obtain a silicon melt SI1.

  The silicon melt SI1 is dropped into the container 34 from the tip 32a of the funnel 32. The container 34 is disposed opposite to the tip 32 a of the funnel 32. An example of the container 34 is a crucible. The temperature of the container 34 is controlled to 900 ° C., for example. The silicon melt SI1 is cooled and solidified in the container 34 to obtain polycrystalline silicon SI2. Since the polycrystalline silicon SI2 has high purity, it is used for, for example, a solar cell.

  As described above, the reaction furnace R preferably includes a plurality of heaters H1 to H4 (heating devices) for heating the furnace wall 14. Thereby, a temperature gradient can be given in the vertical direction in the reactor R. As the heating device, a heater that generates heat from the heaters H1 to H4 may be used, or a coil for induction heating the furnace wall 14 may be used. In order to inductively heat the furnace wall 14, the furnace wall 14 is preferably made of carbon or zirconia. Further, the furnace wall 14 may be made of SiC, and a heating element made of carbon or zirconia may be disposed around the furnace wall 14. In the case of induction heating, the temperature responsiveness of the furnace wall 14 is better than when the heaters H1 to H4 themselves generate heat.

  Since the polycrystalline silicon manufacturing apparatus 10 has the heater H1 capable of controlling the temperature of the upper portion 14a to 1100 ° C. or higher, it is possible to prevent the polycrystalline silicon from adhering to the supply port 16a and the supply port 18a. Therefore, the silicon tetrachloride gas G1 and the zinc gas G2 can be stably supplied into the reactor R. Further, the polycrystalline silicon can be continuously taken out of the reaction furnace R, and the yield of the polycrystalline silicon SI2 can be improved.

  FIG. 2 is a view of the reactor R shown in FIG. 1 as viewed from the z-axis direction. The furnace wall 14 of the reactor R surrounds a central axis Ax parallel to the z axis. The supply port 16a is preferably formed at a position symmetrical to the supply port 18a with respect to the central axis Ax when viewed from the z-axis direction. In this case, the silicon tetrachloride gas G1 supplied from the supply port 18a and the zinc gas G2 supplied from the supply port 16a form a vortex around the central axis Ax in the reaction furnace R. For this reason, since the silicon tetrachloride gas G1 and the zinc gas G2 can be sufficiently mixed, the yield of the polycrystalline silicon SI2 can be improved.

  FIG. 3 is a flowchart showing a method for manufacturing polycrystalline silicon according to the first embodiment. It is preferable that the polycrystalline silicon manufacturing method according to the present embodiment is performed using the polycrystalline silicon manufacturing apparatus 10. The following steps S1 to S5 are preferably performed in order. Thereby, polycrystalline silicon SI2 is manufactured. Note that step S2 may not be performed.

(Production of polycrystalline silicon particles)
By making the temperature of the upper part 14a of the furnace wall 14 of the reaction furnace R 1100 ° C. or higher, supplying silicon tetrachloride gas G1 and zinc gas G2 from the supply port 18a and the supply port 16a into the reaction furnace R and reacting them. Then, polycrystalline silicon particles are generated (step S1). In step S1, a large number of polycrystalline silicon particles are generated. At this time, a product gas G3 containing polycrystalline silicon particles is obtained by a reaction between the silicon tetrachloride gas G1 and the zinc gas G2. The product gas G3 includes, for example, silicon gas, silicon droplets, ZnCl ₂ as a reaction byproduct, and the like.

(Cooling of generated gas)
The product gas G3 is cooled (step S2). By cooling, the temperature is lower than the temperature of the upper portion 14a and is a temperature of 1100 ° C. or higher, and a temperature gradient necessary and sufficient to promote nucleus growth is provided in a range where precipitation does not occur. As a result, the polycrystalline silicon grows with the polycrystalline silicon particles contained in the product gas G3 as nuclei, making it easier to collect the polycrystalline silicon particles. As the particle size of the polycrystalline silicon particles increases, they fall by gravity and adhere to the funnel 32. Therefore, the polycrystalline silicon particles are hardly released out of the reaction furnace R, and the yield of the manufactured polycrystalline silicon SI2 is improved. When the product gas G3 is cooled, it is preferable to supply an inert gas G4 to the product gas G3. In this case, a decrease in the temperature of the furnace wall 14 can be suppressed when the product gas G3 is cooled. Thereby, the fall of the yield of polycrystalline silicon SI2 resulting from a polycrystal silicon particle adhering to the furnace wall 14 can be suppressed.

(Adhesion and melting of polycrystalline silicon particles)
By applying a temperature gradient along the lower part 14c of the furnace wall 14 in the reaction furnace R by the heater H4, the generated polycrystalline silicon particles are adhered to the low temperature part of the lower part 14c (step S3). The temperature of the lower part 14c is higher than the boiling point of Zn (907 ° C.). The temperature difference between the temperature of the heater for heating the middle part 14b and the temperature of the heater for heating the lower part 14c is preferably a temperature difference of 100 ° C. or more. Along the lower part 14c of the furnace wall 14 in the reaction furnace R, the temperature close to the heater H4 is high, and the temperature far from the heater H4 is low, so that a temperature gradient is formed in the vertical direction in the lower part 14c. When the temperature gradient is formed, the polycrystalline silicon particles generated in the above-described process flow and adhere to the lower temperature portion of the lower portion 14c of the furnace wall 14 due to the thermophoresis effect.

  Moreover, the temperature distribution with respect to the lower part 14c of the furnace wall 14 changes by moving the heater H4 little by little. Thereby, the polycrystalline silicon particles are adhered along the lower portion 14c. Further, when the temperature of the portion to which the polycrystalline silicon particles are attached becomes high, the attached polycrystalline silicon is melted and a silicon solution SI2 is obtained (step S4).

  The steps S3 and S4 will be described in more detail. First, the heater H4 is moved to the upper position a in the lower part 14c. Then, a temperature gradient is formed along the lower portion 14c of the furnace wall 14 in which the upper temperature is high and the lower temperature is low. At this time, the polycrystalline silicon particles generated above adhere to the constricted portion 32b of the funnel 32 in the lower portion 14c.

  Subsequently, the heater H4 is moved downward little by little. Then, the position where the polycrystalline silicon particles adhere moves little by little.

  When the heater H4 is positioned on the side surface side of the constricted portion 32b of the funnel 32, a temperature gradient is formed along the lower portion 14c of the furnace wall 14 with a high temperature in the middle and a low temperature in the lower side. At this time, polycrystalline silicon particles adhere to the vicinity of the tip 32c of the funnel 32. On the other hand, since the temperature of the constricted portion 32b of the funnel 32 is increased, the polycrystalline silicon adhering to the constricted portion 32b is melted.

  When the polycrystalline silicon adhering to the constricted portion 32b is melted, the silicon melt SI1 flows downward through the inner wall of the funnel 32. The polycrystalline silicon adhering below the funnel 32 is melted by the high-temperature silicon melt SI1 flowing from above, flows downward together with the silicon melt SI1 flowing from above, and drops from the tip of the funnel 32. .

Subsequently, the heater H4 is moved upward little by little to the position a. As a result, the position where the polycrystalline silicon particles adhere gradually moves upward. When the heater H4 is again positioned at the position a, the above-described procedure is repeated, and the deposition of polycrystalline silicon particles and the melting of the deposited polycrystalline silicon can be performed continuously.
(Cooled solidification of melt)

  The silicon melt SI1 is cooled and solidified to obtain polycrystalline silicon SI2 (step S5). It is preferable to take out the silicon melt SI1 from the reaction furnace R using the funnel 32, and to cool and solidify the silicon melt SI1 in the container.

  In the polycrystalline silicon manufacturing method of the present embodiment, a temperature gradient is provided along the lower portion 14c of the furnace wall 14 in the reaction furnace R, so that the generated polycrystalline silicon particles have a temperature at the lower portion 14c due to the thermophoresis effect. It adheres to the lower part. Thereby, it can suppress that the produced | generated polycrystalline silicon particle is exhausted from the reaction furnace R with reaction gas and carrier gas. And since the polycrystalline silicon adhering to the furnace wall 14 is melted and then cooled and solidified, the recovery efficiency of the polycrystalline silicon can be improved.

  Moreover, since the temperature distribution with respect to the lower part 14c is changed by moving the heater H4 which heats the furnace wall 14 along the reaction furnace R, the polycrystalline silicon particles are attached to each position of the lower part 14c, and the attached many Crystalline silicon particles can be easily melted.

  In particular, in this embodiment, since the reactor R is arranged in the vertical direction and the heater H4 is moved up and down, the polycrystalline silicon that melts one after another by the movement of the heater H4 flows downward and can be easily recovered. . Further, in the forward path and the return path of the heater H4, polycrystalline silicon adheres to the furnace wall 14 below the heater H4 one after another due to the thermophoresis effect. Therefore, it is possible to efficiently attach and melt the polycrystalline silicon.

  Moreover, since the temperature of the upper part 14a of the furnace wall 14 is 1100 degreeC or more, compared with the case where the said temperature is less than 1100 degreeC, it is polycrystalline in the supply port 18a of the silicon tetrachloride gas G1, and the supply port 16a of the zinc gas G2. It can suppress that silicon adheres. Therefore, the silicon tetrachloride gas G1 and the zinc gas G2 can be stably supplied into the reactor R. Further, the polycrystalline silicon can be continuously taken out of the reaction furnace R, and the yield of the polycrystalline silicon SI2 can be improved.

  The temperature of the upper portion 14a is preferably 1350 ° C. or lower. When this temperature exceeds 1350 ° C., the yield of the manufactured polycrystalline silicon SI2 tends to decrease. As one of the causes, for example, it is conceivable that the polycrystalline silicon particles contained in the generated gas G3 are minute and are gasified to be exhausted out of the reactor R as exhaust gas.

  Moreover, it is preferable that the distance from the lower end of the supply port 16a to the lower end of the upper part 14a is 10 times or more of the diameter of the supply port 16a. In this case, it is possible to further suppress the adhesion of polycrystalline silicon to the supply port 16a. Moreover, it is preferable that the distance from the lower end of the supply port 18a to the lower end of the upper part 14a is 10 times or more of the diameter of the supply port 18a. In this case, it can further suppress that polycrystalline silicon adheres to the supply port 18a.

It is a figure which shows typically the manufacturing apparatus of the polycrystalline silicon which concerns on 1st Embodiment. It is the figure which looked at the reactor shown by FIG. 1 from the z-axis direction. It is a flowchart which shows the manufacturing method of the polycrystalline silicon which concerns on 1st Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Polycrystalline silicon manufacturing apparatus, 14 ... Furnace wall, 16a ... Supply port (1st supply port), 18a ... Supply port (2nd supply port), 32 ... Funnel, G1 ... Silicon tetrachloride gas, G2 ... Zinc gas, G3 ... Product gas, H4 ... Heater (heating means), R ... Reactor, SI1 ... Silicon melt, SI2 ... Polycrystalline silicon.

Claims (3)

By supplying silicon tetrachloride gas and zinc gas into the reaction furnace from the first and second supply ports formed in the furnace wall portion having a temperature of 1100 ° C. or higher in the reaction furnace, the reaction is performed. Producing crystalline silicon particles;
Attaching the generated polycrystalline silicon particles to a low temperature portion of the furnace wall in the reactor by creating a temperature gradient along the furnace wall in the reactor;
Melting the adhered polycrystalline silicon particles to obtain a melt;
Cooling and solidifying the melt to obtain polycrystalline silicon;
A method for producing polycrystalline silicon.   2. The method for producing polycrystalline silicon according to claim 1, wherein the temperature distribution with respect to the furnace wall of the reaction furnace is changed by moving heating means for heating the furnace wall along the reaction furnace. 3.   Generation including the polycrystalline silicon particles generated by reacting the silicon tetrachloride gas and the zinc gas between the step of generating the polycrystalline silicon particles and the step of attaching the polycrystalline silicon particles. The method for producing polycrystalline silicon according to claim 1, further comprising a step of cooling the gas.

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