JP2010030851A - Method for producing crystalline silicon particle, crucible, method for manufacturing the same, and apparatus for producing crystalline silicone particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: a method for producing crystalline silicon particles, by which crystalline silicon particles having a uniform particle diameter is produced inexpensively in a high productivity; a crucible; and an apparatus for producing the crystalline silicon particles. <P>SOLUTION: The method for producing the crystalline silicon particles includes discharging a silicon melt 6 in the form of droplets from a nozzle part 1c of a crucible 1 and solidifying the silicon melt 6 by cooling it to form the crystalline silicon particles. The crucible 1 is formed of a material containing silicon nitride, and the surface layer portion 1b of the inner surface of the crucible 1 is composed of silicon oxynitride. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing crystalline silicon particles, a crucible, and an apparatus for producing crystalline silicon particles, and in particular, a method for producing crystalline silicon particles suitably used for a photoelectric conversion device, and a crucible used for a method for producing the crystalline silicon particles, The present invention relates to a method for producing the crucible and an apparatus for producing crystalline silicon particles using the crucible.

  Conventionally, a photoelectric conversion device as a solar cell having a high photoelectric conversion efficiency (hereinafter also referred to as conversion efficiency) using a crystalline silicon substrate (crystalline silicon wafer) has been put into practical use. A crystalline silicon substrate used for a solar cell is manufactured by being cut from a large single crystal silicon ingot or polycrystalline silicon ingot having good crystallinity, a small amount of impurities, and no uneven distribution of impurities.

  However, large single crystal silicon ingots or polycrystalline silicon ingots are low in productivity because they take a long time to produce, and as a result, they are cut from large single crystal silicon ingots or polycrystalline silicon ingots. A crystalline silicon substrate is expensive. Therefore, there is a great demand for a photoelectric conversion device with high photoelectric conversion efficiency that can be manufactured at a low cost without manufacturing a large single crystal silicon ingot or a polycrystalline silicon ingot.

  Therefore, as a kind of promising photoelectric conversion device in the future solar cell market, a device using crystalline silicon particles as a photoelectric conversion body has attracted attention. As a raw material for producing crystalline silicon particles, silicon fine particles generated as a result of pulverizing single crystal silicon, high-purity silicon synthesized in a gas phase by a fluidized bed method, or the like is used.

As a method for producing crystalline silicon particles, the above-mentioned raw materials are separated by size or weight, and then melted in a container by infrared irradiation or high-frequency induction heating, and the melt is solidified while freely falling as droplets (for example, , Refer to Patent Document 1), or a method of spheroidizing by high-frequency plasma heating and melting method (for example, refer to Patent Document 2).
International Publication No. WO99 / 22048 pamphlet U.S. Pat. No. 4,188,177

  However, the conventional method for producing crystalline silicon particles has a problem that productivity is low because it is difficult to make the weight of silicon fine particles as a raw material uniform. Since the variation in the weight of the silicon microparticles as the raw material is reflected in the particle size of the crystalline silicon particles produced therefrom, silicon particles having a uniform weight are required. It is difficult to efficiently obtain silicon fine particles by a method such as pulverization or classification so that the dispersion of the particles becomes small.

  Further, when silicon fine particles are produced by pulverization, there is a problem that contamination from the pulverization media is generated, so that impurities cannot be mixed.

  Furthermore, the high-frequency plasma heating and melting apparatus for producing crystalline silicon particles requires a very large power source, and has a problem that the manufacturing cost increases because the apparatus cost is high and the power consumption is large.

  In addition, when crystalline silicon particles are produced by solidifying while dropping the silicon melt as free droplets, there is a problem that the size of the nozzle hole of the nozzle portion of the crucible for discharging the silicon melt varies. That is, although the detailed cause is unknown, when a nozzle portion made of silicon nitride or the like is used, the silicon melt is impregnated into the inner wall surface of the nozzle portion (surface on the silicon melt side) and the surface layer of the inner wall surface of the nozzle hole. As a result, the size of the nozzle hole increases.

  Therefore, the size of the silicon melt droplets can be reduced in a short period of time, from one use of the silicon melt (one use of a predetermined amount of silicon melt in the crucible is used once) to two uses. There is a problem that the crystalline silicon particles having a uniform particle size cannot be produced with high productivity. Moreover, since it becomes necessary to replace a nozzle part frequently, it was very difficult to reduce manufacturing cost.

  Therefore, the present invention has been completed in view of the above-mentioned conventional problems, and the object of the present invention is to provide crystalline silicon particles having a uniform particle size with high productivity and low cost. It is to provide a manufacturing method, a crucible used in the manufacturing method, and an apparatus for manufacturing crystalline silicon particles.

  The method for producing crystalline silicon particles according to the present invention comprises producing crystalline silicon particles by discharging the silicon melt in a droplet form from a nozzle part of a crucible, and cooling and solidifying the silicon melt. In the method, the crucible is made of a material containing silicon nitride, and the surface layer portion of the inner surface is made of silicon oxynitride.

  In the method for producing crystalline silicon particles according to the present invention, preferably, the crucible is formed of silicon oxynitride at the surface layer portion of the inner surface in contact with the silicon melt.

  In the method for producing crystalline silicon particles according to the present invention, preferably, the surface of the surface of the crucible is made of silicon oxynitride.

  In the method for producing crystalline silicon particles of the present invention, preferably, the crucible has a silicon oxide layer on the surface of the surface layer portion made of silicon oxynitride.

  Preferably, in the method for producing crystalline silicon particles of the present invention, the crucible is a crucible body portion made of silicon nitride ceramics, and a surface layer portion made of silicon oxynitride ceramics formed on the inner surface of the crucible body portion; Have

  In the method for producing crystalline silicon particles of the present invention, preferably, the crucible has the surface layer portion formed by oxidizing the crucible body portion.

  In the method for producing crystalline silicon particles according to the present invention, preferably, the crucible is entirely made of silicon oxynitride ceramics.

  In the method for producing crystalline silicon particles according to the present invention, a gas containing oxygen is preferably injected into the crucible.

  In the method for producing crystalline silicon particles of the present invention, preferably, the gas further contains nitrogen.

  In the method for producing crystalline silicon particles of the present invention, preferably, a solid material containing an oxygen element is placed in the crucible.

  In the method for producing crystalline silicon particles of the present invention, preferably, the solid material contains silicon oxide.

  In the method for producing crystalline silicon particles of the present invention, preferably, the solid is quartz.

  In the method for producing crystalline silicon particles of the present invention, preferably, the crucible is arranged in a nitrogen atmosphere.

  In the method for producing crystalline silicon particles according to the present invention, preferably, a step of preparing a crucible body made of a material containing the silicon nitride and the glass material, and a removal of the glass material existing on the inner surface side of the crucible body portion. And a step of oxidizing the inner surface of the crucible body to form the silicon oxynitride.

  The crucible of the present invention is made of a material containing silicon nitride and the inner surface layer portion is made of silicon oxynitride.

  An apparatus for producing crystalline silicon particles according to the present invention comprises a crucible made of a material containing silicon nitride and having an inner surface layer portion made of silicon oxynitride for discharging a silicon melt droplets from a nozzle portion; Cooling solidification means for cooling and solidifying the silicon melt discharged from the nozzle portion.

  In the method for producing crystalline silicon particles of the present invention, since the crucible is made of a material containing silicon nitride and the surface layer portion of the inner surface is made of silicon oxynitride, the silicon repellency melt property of the surface layer portion of the crucible can be improved. Therefore, it is possible to greatly suppress the impregnation of the silicon melt into the surface layer portion on the inner surface of the crucible. That is, silicon oxynitride, which is silicon nitride containing oxygen, has a silicon oxide component that is difficult to wet the silicon melt (easy to repel the silicon melt) and a silicon nitride component that has a high decomposition temperature. It will be a thing. Therefore, the silicon in the silicon melt is largely prevented from reacting with nitrogen, which is a constituent material of the crucible, and the wear on the inner surface of the crucible and the wear on the inner wall surface of the nozzle hole due to the passage of the silicon melt are greatly suppressed. can do.

  As a result, it is possible to effectively suppress the enlargement of the size of the nozzle hole, and it is possible to produce crystalline silicon particles having a uniform particle diameter over a long period of time with high productivity. In addition, since the variation in the particle diameter of the crystalline silicon particles is reduced, the uniformity of crystal growth is increased when the silicon melt is cooled and solidified, and crystalline silicon particles with uniform crystal quality can be manufactured.

  Further, in the method for producing crystalline silicon particles of the present invention, preferably, the crucible has an area of a portion to be subjected to silicon oxynitride treatment of the crucible because the surface layer portion of the portion in contact with the silicon melt on the inner surface is made of silicon oxynitride. The crucible can be efficiently manufactured by reducing the size, and as a result, the crystalline silicon particles can be efficiently manufactured.

  In the method for producing crystalline silicon particles of the present invention, the crucible preferably has a thermal expansion coefficient between the silicon oxynitride portion and the remainder because the surface layer portion of the entire surface is made of silicon oxynitride. Generation of cracks or the like in the crucible due to distortion due to the difference can be suppressed.

  In the method for producing crystalline silicon particles of the present invention, preferably, the crucible has a silicon oxide layer on the surface of the surface layer portion made of silicon oxynitride, so that the silicon repellency of the surface layer portion of the crucible is further enhanced. .

  In addition, the method for producing crystalline silicon particles of the present invention preferably includes a crucible body portion made of silicon nitride ceramics and a surface layer portion made of silicon oxynitride ceramics formed on the inner surface of the crucible body portion. The crucible body can be manufactured with silicon nitride ceramics that is easier to manufacture than a single crystal. More preferably, if the crucible body is oxidized, a surface layer made of silicon oxynitride ceramics can be easily formed. Therefore, an easily manufactured crucible having a surface layer portion with high silicon repellency can be manufactured.

  Moreover, since the crucible body is made of porous silicon nitride ceramics, oxygen can be easily included in the surface layer of the crucible body by oxidation treatment or the like.

  In the method for producing crystalline silicon particles of the present invention, the surface layer portion made of silicon oxynitride ceramics is preferably formed by oxidizing the crucible made of silicon nitride ceramics to form the surface layer portion made of silicon oxynitride ceramics. Can be easily formed.

  In addition, the method for producing crystalline silicon particles of the present invention is preferably a crucible, which is composed entirely of silicon oxynitride ceramics, and thus has a characteristic that the silicon melt is difficult to wet and a characteristic having a high decomposition temperature. It can be. As a result, a crucible having higher chemical stability, wear resistance and other resistance to the silicon melt can be obtained, and crystalline silicon particles having a uniform particle size can be produced with higher productivity.

  Further, in the method for producing crystalline silicon particles of the present invention, if a gas containing oxygen is injected into the crucible, the oxygen concentration in the silicon melt can be brought close to a saturated state. It is possible to reduce the penetration of oxygen in silicon oxynitride into the silicon melt, and to reduce the deterioration of the surface layer portion made of silicon oxynitride.

  Furthermore, if the gas also contains nitrogen, the nitrogen concentration in the silicon melt can be brought close to saturation, so that the dissolution of nitrogen in the silicon oxynitride in the surface layer portion of the crucible into the silicon melt is reduced. And deterioration of the surface layer portion made of silicon oxynitride can be reduced.

  Further, in the method for producing crystalline silicon particles of the present invention, if a solid material containing an oxygen element is disposed in the crucible, the oxygen in the solid material dissolves into the silicon melt of oxygen in silicon oxynitride. And deterioration of the surface layer portion made of silicon oxynitride can be reduced.

  Furthermore, if the solid material contains silicon oxide, it is possible to reduce the mixing of metals that become impurities other than silicon, so that crystalline silicon particles with few impurities can be manufactured.

  In addition, if the solid is quartz, it is possible to further reduce the contamination of impurities into the crystalline silicon particles.

  Further, in the method for producing crystalline silicon particles of the present invention, if the crucible is arranged in a nitrogen atmosphere, even if the temperature rises to near the decomposition temperature of silicon nitride, which is a constituent component of the crucible, Therefore, the heat resistance of the crucible can be improved.

  Since the crucible of the present invention is made of a material containing silicon nitride and the surface layer portion of the inner surface is made of silicon oxynitride, the crucible has both a property that the silicon melt is difficult to wet and a property that has a high decomposition temperature. It has high resistance such as chemical stability and wear resistance. Accordingly, it can be suitably used as a long-life crucible used in direct contact with the silicon melt.

  In the crucible manufacturing method of the present invention, the composition of the surface layer portion can be changed to silicon oxynitride by oxidizing after removing the glass material existing between the silicon nitride particles on the inner surface side of the crucible body. Then, silicon oxynitride can be formed from the inner surface side of the crucible body portion to the depth direction of the crucible body portion. As a result, according to the present manufacturing method, the silicon meltability of the crucible can be further improved.

  An apparatus for producing crystalline silicon particles according to the present invention includes a crucible made of a material containing silicon nitride and having an inner surface layer portion made of silicon oxynitride, and a nozzle of the crucible, for discharging the silicon melt from the nozzle portion in a droplet shape. A cooling and solidifying means that cools and solidifies the silicon melt discharged from the portion, so that the fluctuation of the nozzle hole of the nozzle portion is suppressed and the crystalline silicon particles having a uniform particle size are increased over a long period of time. Can be manufactured with productivity.

  A method for producing crystalline silicon particles, a crucible, a method for producing crucibles, and an apparatus for producing crystalline silicon particles according to the present embodiment will be described in detail below.

  FIG. 1 is a cross-sectional view showing a manufacturing apparatus X used in the method for manufacturing crystalline silicon particles according to the present embodiment. In FIG. 1, 1 is a crucible, 1c is a nozzle hole, 2 is a dropping tube arranged below the crucible 1 so that the longitudinal direction is the vertical direction, 4 is a granular silicon melt, 5 is a crystalline silicon particle, 6 Is a silicon melt in the crucible 1. Moreover, the crucible 1 has the crucible main-body part 1a, the surface layer part 1b, and the nozzle hole 1c.

  The crystalline silicon particles 5 are formed by being discharged as a granular silicon melt from the nozzle hole 1c of the crucible 1 containing the silicon melt 6 and cooled and solidified during the fall.

  The method for producing crystalline silicon particles according to the present embodiment produces crystalline silicon particles 5 by discharging the silicon melt 6 from the nozzle hole 1c of the crucible 1 in a drop shape, and cooling and solidifying the silicon melt 6. The crucible 1 is made of a material containing silicon nitride, and the surface layer portion 1b on the inner surface is made of silicon oxynitride.

  With the above configuration, the silicon repellency of the surface layer portion 1b of the crucible 1 is enhanced, and the surface layer portion of the inner surface of the crucible 1 (the surface on the silicon melt 6 side) is significantly suppressed from being impregnated with the silicon melt 6. be able to. Silicon oxynitride in which a part of nitrogen atoms of silicon nitride is replaced with oxygen has a silicon oxide component in which the silicon melt 6 is difficult to wet (easy to repel the silicon melt) and a silicon nitride component having a high decomposition temperature. Therefore, it has those characteristics together. Accordingly, in such a configuration, the silicon in the silicon melt 6 is largely prevented from reacting with nitrogen, which is a constituent material of the crucible 1, and the inner surface of the crucible 1 is worn due to the passage of the silicon melt 6, and the silicon Abrasion of the inner wall surface of the nozzle hole 1c due to the passage of the melt 6 can be significantly suppressed.

  As a result, in the present embodiment, the enlargement of the size of the nozzle hole 1c can be effectively suppressed, and the crystalline silicon particles 5 having a uniform particle diameter can be manufactured with high productivity over a long period of time. Further, in the present embodiment, since the variation in the particle size of the crystalline silicon particles 5 is reduced, the uniformity of crystal growth is increased when the granular silicon melt 4 is cooled and solidified, so that the crystal with uniform crystal quality is obtained. Silicon particles 5 can be manufactured.

  Moreover, it is preferable that the surface layer part of the part which the crucible 1 touches the silicon melt 6 of an inner surface consists of silicon oxynitride. In this case, the crucible 1 can be efficiently manufactured by reducing the area of the portion where the silicon oxynitride treatment of the crucible 1 is performed. As a result, the crystalline silicon particles 5 can be efficiently manufactured.

  In addition, since the surface portion of the entire surface of the crucible 1 is made of silicon oxynitride, the crucible 1 is cracked due to distortion caused by the difference in thermal expansion coefficient between the silicon oxynitride portion and the remaining portion (silicon nitride). Etc. can be prevented from occurring.

  The crucible 1 is a container for heating and melting a silicon raw material to form a silicon melt 6 and discharging it as a granular silicon melt 4 from a nozzle hole 1c at the bottom. The silicon melt 6 heated and melted in the crucible 1 is discharged into the drop tube 2 from the nozzle hole 1 c and falls into the drop tube 2 as a granular silicon melt 4. The crucible 1 is made of a material having a melting point higher than that of silicon. The crucible 1 is preferably made of a material having low reactivity with the silicon melt 6, and when the reaction with the silicon melt 6 is large, the material of the crucible 1 is mixed in the crystalline silicon particles 5 as impurities in large quantities. Therefore, it is not preferable.

For example, the material of the crucible 1 is preferably silicon nitride, silicon oxynitride, silicon nitride sintered body (silicon nitride ceramics), silicon oxynitride sintered body (silicon oxynitride ceramics), or the like. In particular, from the viewpoint of producing crystalline silicon particles 5 with few impurities, the crucible 1 is preferably composed of high-purity (99.5 wt% to 99.99 wt%) silicon nitride ceramics, single crystal silicon nitride, or the like. It is. As the sintering aid, an oxide containing an alkaline earth metal such as MgO, an oxide of a rare earth metal such as Y ₂ O ₃ , Al ₂ O ₃ or the like is used.

  Further, the liquid surface of the silicon melt 6 is controlled so as to always have a substantially constant height by intermittently supplying the silicon material from the silicon material supply pipe.

As for the crucible 1, it is preferable that the surface layer part of an inner surface consists of silicon oxynitride, and the thickness of the surface layer part is 0.1-20 micrometers. Thus, if it exists in the range of the thickness of the surface layer part mentioned above, the silicon repellency melt property of a surface layer part can be improved more. Silicon oxynitride is obtained by oxidizing some of the nitrogen atoms of silicon nitride inside or from the surface (inner surface) of silicon nitride by oxidizing silicon nitride. FIG. 2 is a schematic diagram schematically showing the chemical composition of the surface layer portion 1b. In FIG. 2, the X axis indicates the crucible depth direction (crucible thickness direction), and the Y axis indicates the content of each element (oxygen, nitrogen, silicon). In the silicon oxynitride layer, silicon, nitrogen, and oxygen atoms are present, and the ratio of nitrogen atoms is from the inside of the crucible body 1a to the surface layer on the inner surface of the crucible body 1a, as shown in the schematic diagram of FIG. The ratio of oxygen atoms increases toward the inside of the crucible body 1a. In FIG. 2, the outermost surface of the surface layer portion 1b is silicon oxide, but in this embodiment, silicon oxynitride may be used. An embodiment in which the outermost surface is silicon oxide will be described in detail below.

  As shown in FIG. 2, the crucible 1 preferably further has a silicon oxide layer on the surface of the surface layer portion. In this case, the silicon repellency of the surface layer on the inner surface of the crucible 1 is further enhanced. The thickness of the silicon oxide layer is preferably about 0.1 μm to 10 μm. By making it within this thickness range, the silicon repellency melt property of the surface layer portion of the inner surface of the crucible 1 is maintained, and the strength of the crucible 1 is reduced due to the difference in thermal expansion coefficient between the silicon oxide layer and other portions. Can be suppressed.

  Moreover, as shown in FIG. 3, the crucible 1 is a cylindrical body such as a cylinder or a rectangular tube, and preferably has a shape in which a nozzle hole (through hole) 1c is formed at the lower end of the cylindrical body. In this case, compared with the case where the nozzle member is manufactured as a separate body, the crucible 1 can be efficiently manufactured integrally with the nozzle portion.

  On the other hand, the crucible 1 may have a separate nozzle member, and the nozzle member may be fixed to the lower end of the crucible body 1a of the cylindrical crucible 1 by a method such as screwing. In this case, the nozzle member can be easily manufactured, and the nozzle member can be easily detached from the crucible body 1a of the crucible 1.

  In FIG. 3, 1b is a surface layer portion made of silicon oxynitride. The surface layer 1b is formed on at least the surface (inner surface) of the crucible 1 on the silicon melt 6 side. This is because the surface of the crucible 1 on the silicon melt 6 side is in direct contact with the silicon melt 6. Moreover, it is preferable that the surface layer part 1b is also formed in the inner wall face of the nozzle hole 1c. This is because the inner wall surface of the nozzle hole 1c is a surface where the flowing silicon melt 6 is in direct contact.

  Further, the surface layer portion 1b may be formed on the entire surface of the crucible 1. In this case, the stress difference due to the difference in thermal expansion coefficient between the surface layer portion 1b and the inside thereof is distributed throughout the crucible 1. It is possible to suppress a decrease in mechanical strength.

  The diameter of the nozzle hole 1c is about 100 μm to 150 μm, whereby the crystalline silicon particles 5 having a particle size of about 300 to 600 μm that are preferably used in the photoelectric conversion device can be easily manufactured. There may be a plurality of nozzle holes 1c.

  The crucible 1 is composed of a crucible body 1a made of silicon nitride and silicon nitride ceramics containing a glass material that can serve as an auxiliary agent, and a surface layer 1b made of silicon oxynitride ceramics around the crucible body 1a. Is preferred. With such a configuration, the crucible body 1a is made of silicon nitride ceramics that are easier to manufacture than a single crystal, and the surface layer of the crucible body 1a is made of silicon oxynitride ceramics by oxidation treatment or the like. It can be a surface layer part. Therefore, a crucible 1 having a surface layer portion having high silicon repellency and easy to manufacture can be manufactured.

  Below, the manufacturing method of the crucible 1 is explained in full detail. After removing the deposits on the inner surface of the crucible body 1a containing silicon nitride and glass material by ultrasonic cleaning, oxidation treatment is performed in an oxygen-nitrogen mixed gas atmosphere. In this case, it is desirable that the processing temperature is 1300 to 1550 ° C. and the processing time is in the range of 1 to 60 hours. As a result, the substitution reaction of nitrogen atoms and oxygen atoms proceeds in the surface layer of the silicon nitride crucible to form silicon oxynitride. When the substitution reaction further proceeds, a silicon oxide layer is formed on the outermost surface. Furthermore, before the oxidation treatment, an acid etching treatment may be performed to remove the glass material contained in the crucible. For example, in this etching treatment, hydrochloric acid is heated to 100 ° C. for 1 to 60 hours. In this way, if the etching treatment is performed, the composition of the surface layer portion can be changed to silicon oxynitride by performing the oxidation treatment after removing the glass material existing between the silicon nitride particles, so that the inner surface of the crucible body portion 1a Silicon oxynitride can be formed from the side to the depth direction of the crucible body 1a. As a result, according to such a crucible manufacturing method, the silicon meltability of the crucible can be further improved.

  The crucible body 1a can be made of either dense silicon nitride ceramics or porous silicon nitride ceramics. However, if the crucible body 1a is made of porous silicon nitride ceramics, the surface layer 1b of the crucible body 1a is oxygenated by oxidation treatment or the like. Can be easily included.

  When the surface layer portion 1b made of silicon oxynitride ceramics is formed by oxidation treatment, the temperature of the oxidation treatment is about 1300 to 1500 ° C., and the treatment time is about 0.5 to 60 hours. Thereby, the surface layer part 1b of suitable thickness (10 micrometers or more) can be formed.

  Further, the surface layer portion 1b made of silicon oxynitride may be formed on the inner surface of the crucible body portion 1a by coating, for example. Specifically, polysilazane may be applied to the inner surface of the crucible body 1a, heated and dried. Application to the inner surface of the crucible body 1a is performed by dipping, brushing or spraying, followed by drying at 40 to 100 ° C. for 2 to 5 hours in order to volatilize the solvent. Next, the surface layer portion of silicon oxynitride and silicon oxide can be formed inside the crucible main body 1a by silicifying polysilazane in a constant temperature and humidity chamber.

  The crucible 1 is preferably made entirely of silicon oxynitride ceramics. In this case, as a whole, the crucible 1 having both the characteristic that the silicon melt 6 is difficult to wet and the characteristic that the decomposition temperature is high can be obtained. As a result, the crucible 1 having higher chemical stability, wear resistance and other resistance to the silicon melt 6 can be obtained, and the crystalline silicon particles 5 having a uniform particle diameter can be manufactured with higher productivity.

  The crucible 1 made entirely of silicon oxynitride ceramics can be manufactured by a method of oxidizing the crucible 1 made of silicon nitride ceramics for a long time.

  In the present embodiment, it is preferable to inject a gas containing oxygen into the crucible 1. That is, in the present embodiment, the inside of the crucible 1 is preferably an oxygen atmosphere. According to such a form, the rate at which oxygen is dissolved from the gas into the silicon melt 6 can be made faster than the rate at which oxygen in silicon oxynitride in the surface layer portion 1b of the crucible is dissolved into the silicon melt 6. Therefore, before the oxygen in silicon oxynitride dissolves in the silicon melt 6, the oxygen concentration in the silicon melt approaches a saturated state. Therefore, in such a form, since the penetration of oxygen in the silicon oxynitride in the surface layer portion 1b of the crucible into the silicon melt 6 can be reduced, the deterioration of the surface layer portion 1b can be reduced.

  Furthermore, it is more preferable that the gas contains nitrogen. According to such a form, the rate at which nitrogen is dissolved from the gas into the silicon melt 6 can be made faster than the rate at which nitrogen in the silicon oxynitride in the surface layer portion 1b of the crucible is dissolved into the silicon melt 6. Therefore, before the nitrogen in the silicon oxynitride dissolves into the silicon melt 6, the nitrogen concentration in the silicon melt approaches a saturated state. Therefore, in such a form, since the penetration of nitrogen in silicon oxynitride in the surface layer portion 1b of the crucible into the silicon melt 6 can be reduced, deterioration of the surface layer portion 1b can be reduced.

  As described above, when the gas is injected into the crucible 1, as shown in FIG. 4, for example, a mixture in which 0.01 to 5% of oxygen is mixed with an inert gas such as argon using a gas mixer is used. The gas 7 is injected into the crucible from the mixed gas inlet 8. With such an oxygen concentration, the inside of the crucible 1 can be in an oxygen atmosphere while reducing the oxidation on the surface of the silicon melt 6.

  Further, in the present embodiment, as shown in FIG. 5, it is preferable to dispose a solid material 9 containing an oxygen element in the crucible 1. According to such a form, oxygen is discharged | emitted from the solid substance 9 arrange | positioned in the crucible 1, and the inside of the crucible 1 can be made into oxygen atmosphere. According to such a form, since the oxygen-containing silicon oxynitride in the surface layer portion 1b of the crucible 1 can be reduced from being dissolved into the silicon melt 6 as in the case where a gas containing oxygen is injected into the crucible 1. Deterioration of the surface layer portion 1b can be reduced. On the other hand, unlike the gas as described above, if a solid material 9 containing a gas is used, the reaction rate with the silicon melt 6 depends on the surface area of the solid material 9, and thus the reaction rate can be controlled gently. . Further, according to such a form using the solid material 9, since the reaction proceeds in the silicon melt 6, the generation of silicon oxide formed by oxidizing the surface of the silicon melt 6 is reduced, and the silicon melt 6 is reduced. The liquid 6 can be discharged efficiently. Furthermore, if this solid substance 9 contains silicon oxide, it is possible to reduce the mixing of metals that become impurities other than silicon, so that the crystalline silicon particles 5 with few impurities can be manufactured. Examples of the solid substance 9 containing silicon oxide include quartz, which is silicon dioxide, quartz, feldspar, which is silicate mineral, mica, olivine, pyroxene, amphibole, and the like. In particular, if this solid material 9 is quartz, since there are few impurities compared with the solid material 9 containing silicon oxide described above, it is possible to further reduce the contamination of the impurities into the crystalline silicon particles 5 as described above. There is an advantage that it is more productive and cheaper than the solid material 9 containing silicon oxide. In addition, the shape of this solid substance 9 includes a plate shape, a rod shape, a granular shape, and a cylindrical shape. Among these, since the plate-like shape tends to relatively increase the specific surface area per unit weight, the reaction rate with the silicon melt 6 can be easily controlled without excessively increasing the weight of the solid.

  Moreover, in this Embodiment, it is preferable to arrange the crucible 1 in a nitrogen atmosphere. That is, in such a form, the inside and outside of the crucible 1 are exposed to nitrogen. According to such formation, since the decomposition of silicon nitride can be reduced by nitrogen even when the temperature of the crucible 1 reaches a temperature close to the decomposition temperature of silicon nitride, which is a constituent component of the crucible 1, the heat resistance of the crucible 1 can be reduced. Can be improved. This is because when the silicon nitride is decomposed by heat, the nitrogen component is desorbed from the silicon nitride, so that the periphery of the crucible 1 is brought close to the saturation state of nitrogen so that the nitrogen component is not easily desorbed. The component reduces detachment.

  The drop tube 2 arranged so that the longitudinal direction is vertical from the nozzle hole 1c of the crucible 1 cools and solidifies the granular silicon melt 4 discharged from the nozzle hole 1c while dropping. It is a container to be made. The inside of the drop tube 2 may be set to a desired pressure with a desired atmospheric gas as necessary. As such an atmospheric gas, an inert gas is preferable, and helium gas or argon gas is particularly preferable. Helium gas or argon gas is an inert gas, and can prevent impurities from being mixed into the granular silicon melt 4 from the atmospheric gas.

  Further, helium gas or argon gas has a small reaction with the granular silicon melt 4, and the reaction layer on the surface of the granular silicon melt 4 is an obstacle to solidification and crystallization of the granular silicon melt 4. Is preferable because the formation of can be suppressed.

  The drop tube 2 is preferably made of a material having a melting point higher than that of silicon (about 1414 ° C.). In that case, even if the granular silicon melt 4 is discharged obliquely and collides with the inner wall of the drop tube 2, the drop tube 2 is not heated above the melting point of the material constituting the drop tube 2. It becomes difficult to mix as impurities into the granular silicon melt 4 with which the two materials collide. When the melting point of the drop tube 2 is lower than the melting point of silicon, when the granular silicon melt 4 is discharged obliquely and collides with the inner wall of the drop tube 2, the drop tube 2 exceeds the melting point of the material. The material of the drop tube 2 may be mixed as impurities into the granular silicon melt 4 that has been heated.

  Therefore, the material of the drop tube 2 is preferably carbon, silicon carbide, silicon oxide, silicon nitride, aluminum oxide or the like having a melting point higher than that of silicon. Further, the drop tube 2 may have a cooling structure such as a water cooling jacket in order to control the temperature profile of the falling granular silicon melt 4. If it is the fall tube 2 which has such a cooling structure, it is preferable that they are stainless steel, aluminum, etc., for example. Further, the drop tube 2 may have a multilayer structure in which a plurality of tubes are concentrically overlapped.

  The crystalline silicon manufacturing apparatus X is provided with a heating device for heating and melting the silicon raw material in the crucible 1. The heating device includes a high-frequency induction heating device such as a high-frequency induction coil, a resistance heating device, and the like. The heating temperature is 1414 ° C. or higher, which is the melting point of silicon, in order to melt silicon. When a resistance heating device is used, for example, it is heated in contact with the crucible 1 in an atmospheric gas composed of the same inert gas as the crucible 1, and a carbon-based heater, for example, graphite, carbon fiber reinforced carbon, SiC coating material A material made of glassy carbon coating material or the like can be used. In addition, when the crucible 1 is indirectly heated from an oxidizing atmosphere outside the furnace core tube (not shown), a resistance heating device having a resistance wire, a resistance plate, or the like containing silicon carbide or molybdenum silicide can be used.

  When using a high-frequency induction heating device as the heating device, for example, by bringing a susceptor made of carbon into contact with the crucible 1 and providing a high-frequency induction coil outside the core tube (not shown) and heating the susceptor with an induced current, There are methods such as heating the crucible 1.

  By introducing an inorganic solid member containing nitrogen into the silicon melt 6 in the crucible 1, a small amount of nitrogen can be mixed in the silicon melt 6 to a saturation concentration. When a small amount of nitrogen is not mixed in the silicon melt 6 at a saturated concentration, the reaction between the silicon of the silicon melt 6 and the nozzle hole 1c is large, and the shape of the nozzle hole 1c is likely to change. As a result, when the nozzle hole 1c becomes large, the size of the granular silicon melt 4 increases with time, and it becomes difficult to obtain crystalline silicon particles 5 having a required particle size. Furthermore, when the nozzle hole 1c becomes large, it becomes difficult to manufacture the crystalline silicon particles 5 by reaching the bottom of the drop tube 2 before the granular silicon melt 4 is solidified.

  Crucible 1 of the present embodiment is made of a material containing silicon nitride, and surface layer portion 1b on the inner surface is made of silicon oxynitride. In this case, the silicon melt 6 has both a characteristic that the silicon melt 6 is difficult to wet and a characteristic that the decomposition temperature is high, and the resistance to the silicon melt 6 such as chemical stability and wear resistance is high. Therefore, the crucible 1 can be suitably used as a long-life crucible 1 used in direct contact with the silicon melt 6.

  An apparatus X for producing crystalline silicon particles 5 according to the present embodiment is a crucible made of a material containing silicon nitride and having an inner surface layer portion 1b made of silicon oxynitride for discharging a silicon melt in a droplet form from a nozzle portion. 1 and a cooling and solidifying means for cooling and solidifying the silicon melt 4 discharged from the nozzle portion of the crucible 1. In this case, it is possible to manufacture the crystalline silicon particles 4 having a uniform particle diameter over a long period of time with high productivity while suppressing fluctuations in the nozzle holes 1c of the nozzle portion.

  The cooling and solidifying means for cooling and solidifying the granular silicon melt 4 is the drop tube 2 or the like for cooling and solidifying the granular silicon melt 4 while dropping it inside, or by natural cooling in the air atmosphere. There may be.

  The embodiments of the method for producing crystalline silicon particles, the crucible, and the apparatus for producing crystalline silicon particles according to the present invention have been described above, but the present invention is not limited to the examples of the above embodiments, Various changes can be made without departing from the gist.

(Example)
Examples of the method for producing crystalline silicon particles of the present embodiment will be described below.

  First, as the crucible 1, a crucible body portion 1a made of silicon nitride ceramics and a surface layer portion 1b made of silicon oxynitride ceramics around the entire crucible body portion 1a were used. The crucible body 1a made of silicon nitride ceramics was produced by hot pressing, and the surface layer 1b made of silicon oxynitride ceramics was formed by oxidation treatment.

  The temperature of the oxidation treatment was about 1480 ° C., and the treatment time was about 1 hour. Thereby, a surface layer portion 1b having a thickness of about 8 μm was formed.

  The shape of the crucible 1 was cylindrical, the outer diameter was 150 mm, the inner diameter (diameter) of the accommodation space for accommodating the silicon raw material was 130 mm, and the diameter of the nozzle hole 1 c was 200 μm.

  An inorganic solid member made of silicon nitride was placed in the crucible 1. The inorganic solid member was a rectangular parallelepiped having a length of 16 mm, a width of 16 mm, and a height of 2 mm, and the corners were rounded to suppress excessive elution of silicon nitride from the corners.

Next, in a crucible 1, as a raw material for crystal silicon grains 5, a p-type dopant B about 1 × 10 ¹⁶ atoms / cm ³ added silicon raw material (boron) was placed 5000 g, the crucible 1 resistance heating By heating.

  Argon gas was used as the atmospheric gas in the crucible 1, and the argon gas was circulated in the crucible 1 to remove exhaust gas such as silicon monoxide generated based on the silicon melt 6 in the crucible 1.

  Next, the crucible 1 is heated to about 1480 ° C. by a resistance heating heater installed so as to surround the crucible 1, and the pressure of the atmospheric gas in the crucible 1 is 0, which is the pressure of the atmospheric gas in the drop tube 2. The pressure is applied to the liquid surface of the silicon melt 6 from 1 MPa to 0.3 MPa, the silicon melt 6 is discharged from the nozzle hole 1 c to the inside of the drop tube 2, and the granular silicon melt 4 is discharged into the drop tube 2. While being dropped inside, it was cooled and solidified to obtain a large number of crystalline silicon particles 5.

The obtained crystalline silicon particles 5 had an average particle diameter of 450 μm, a standard deviation of particle diameter of 70 μm, and a recovery rate of 96%. The recovery rate was obtained by dividing the weight recovered as the crystalline silicon particles 5 within the range of a desired particle size (−300 μm to +300 μm) with respect to the average particle size by the total weight. The obtained crystalline silicon particles 5 contained carbon as a trace component of about 1 × 10 ¹⁸ atoms / cm ³ .

  After the production of the crystalline silicon particles 5 was continuously performed for 20 hours, the crucible 1 was examined. As a result, the surface layer portion 1b on the inner surface of the crucible 1 and the surface layer portion 1b at the nozzle hole 1c were impregnated with the silicon melt 6. It was not recognized, and the diameter of the nozzle hole 1c was almost 200 μm, and hardly changed.

(Comparative example)
As a comparative example, using a crucible 1 made entirely of silicon nitride ceramics, crystalline silicon particles 5 were produced in the same manner as in the above example.

  The obtained crystalline silicon particles 5 had an average particle diameter of 800 μm, a standard deviation of particle diameter of 200 μm, and a recovery rate of 10%.

  After continuously producing the crystalline silicon particles 5 for about 2 hours, the nozzle hole 1c was examined. As a result, the surface layer portion 1b of the nozzle hole 1c was impregnated with the silicon melt 6 in a thickness of 1500 μm, and the diameter of the nozzle hole 1c was Was enlarged from 200 μm to about 1000 μm.

  Therefore, in this example, the continuous production time of the crystalline silicon particles 5 could be 10 times that of the prior art. In addition, the crystalline silicon particles 5 obtained in this example had smaller particle size variations than the crystalline silicon particles 5 obtained in the comparative example, and the recovery rate was increased. This indicates that the method for producing the crystalline silicon particles 5 of the present embodiment can produce the crystalline silicon particles 5 with small particle size variation with high productivity.

It is typical sectional drawing which shows the manufacturing apparatus concerning the manufacturing method of the crystalline silicon particle which concerns on embodiment of this invention. It is a schematic diagram for demonstrating the surface layer part of the crucible which concerns on embodiment of this invention. It is sectional drawing of the crucible which concerns on embodiment of this invention. It is sectional drawing of the crucible concerning the manufacturing method of the crystalline silicon particle which concerns on other embodiment of this invention. It is sectional drawing of the crucible concerning the manufacturing method of the crystalline silicon particle which concerns on other embodiment of this invention.

Explanation of symbols

X: Crystalline silicon particle production apparatus 1: crucible 1a: crucible body 1b: surface layer 1c: nozzle hole 2: drop tube 4: granular silicon melt 5: crystalline silicon particle 6: silicon melt 7: mixed gas 8 : Mixed gas inlet 9: Solid matter

Claims (16)

  A method for producing crystalline silicon particles in which a silicon melt is discharged from a nozzle part of a crucible in a drop shape, and the silicon melt is cooled and solidified to produce crystalline silicon particles, wherein the crucible contains silicon nitride. A method for producing crystalline silicon particles comprising a material containing the same and having an inner surface layer portion comprising silicon oxynitride.   2. The method for producing crystalline silicon particles according to claim 1, wherein a surface layer portion of the inner surface of the crucible made of silicon oxynitride is in contact with the silicon melt.   2. The method for producing crystalline silicon particles according to claim 1, wherein the surface portion of the entire surface of the crucible is made of silicon oxynitride.   The method for producing crystalline silicon particles according to claim 1, wherein the crucible has a silicon oxide layer on a surface of the surface layer portion.   5. The crystalline silicon particle according to claim 1, wherein the crucible has a crucible body portion made of silicon nitride ceramics, and a surface layer portion made of silicon oxynitride ceramics formed on the inner surface of the crucible body portion. Manufacturing method.   6. The method for producing crystalline silicon particles according to claim 5, wherein the crucible is formed by oxidizing the crucible body to form the surface layer.   2. The method for producing crystalline silicon particles according to claim 1, wherein the crucible is entirely made of silicon oxynitride ceramics.   The method for producing crystalline silicon particles according to claim 1, wherein a gas containing oxygen is injected into the crucible.   The method for producing crystalline silicon particles according to claim 8, wherein the gas further contains nitrogen.   The method for producing crystalline silicon particles according to any one of claims 1 to 7, wherein a solid material containing an oxygen element is disposed in the crucible.   The method for producing crystalline silicon particles according to claim 10, wherein the solid material includes silicon oxide.   The method for producing crystalline silicon particles according to claim 11, wherein the solid material is quartz.   The method for producing crystalline silicon particles according to any one of claims 1 to 12, wherein the crucible is arranged in a nitrogen atmosphere.   A crucible made of a material containing silicon nitride and having an inner surface layer portion made of silicon oxynitride. A method for producing a crucible according to claim 14,
Preparing a crucible body made of a material containing the silicon nitride and glass material;
Removing the glass material present on the inner surface side of the crucible body part;
And a step of oxidizing the inner surface of the crucible body and forming the silicon oxynitride on the surface layer of the inner surface of the crucible body.   A crucible made of a material containing silicon nitride and having a surface layer portion made of silicon oxynitride for discharging the silicon melt in a droplet form from the nozzle portion, and the silicon melt discharged from the nozzle portion of the crucible An apparatus for producing crystalline silicon particles, comprising cooling and solidifying means for cooling and solidifying the material.

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