JP2010150106A - Method for producing spherical semiconductor particles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to efficiently produce spherical semiconductor particles in which a p-type or n-type dopant is doped and the dispersion in a mass, size, and shape is small in a method to melt small solid bodies including a semiconductor powder of a prescribed amount to form spherical molten spheres, to cool them to solidify to produce the spherical semiconductor particles. <P>SOLUTION: The method for producing semiconductor particles includes the steps of: forming small solid bodies including predetermined mass of a semiconductor powder and a dopant by a granulation process; heating them to melt and fuse the semiconductor powder included in the small solid bodies to prepare molten spheres; and cooling the molten spheres to solidify them. The small solid bodies preferably contain a binder. The dopant can be contained in the small solid bodies by a method to carry out granulation of a mixture which added the dopant to a semiconductor powder, a method to add during the granulation operation, and a method to contact the granule into a dopant solution or the like. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a spherical semiconductor particle serving as a semiconductor element such as a spherical photoelectric conversion element or a precursor thereof.

  In recent years, it has been studied to use a spherical semiconductor element for a photoelectric conversion element, a diode, an element for hydrogen generation by water decomposition, or the like. In particular, a photoelectric conversion element in which an n-type semiconductor layer is formed along the surface of a spherical p-type semiconductor substrate has attracted attention as a solar cell element that is inexpensive and can be expected to have a high output. As a typical example of a solar cell, a low-concentration type device has been proposed in which a spherical solar cell element is attached in each recess of a support having a large number of recesses, and the inner surface of the recess functions as a reflecting mirror ( For example, Patent Document 1). According to this, the photoelectric conversion part can be thinned, the amount of expensive silicon used can be reduced, and the cost of the solar cell can be reduced. Furthermore, since the light condensing action of the concave reflecting mirror irradiates the element with 4 to 6 times as much light as the direct irradiation light, the irradiation light can be effectively used for photoelectric conversion.

  A melt dripping method has been proposed as one method for producing spherical semiconductor particles. This is because the melt of the semiconductor material placed in the crucible is pressurized with an inert gas and continuously dripped from the nozzle hole provided at the bottom of the crucible, and solidified while the droplet falls in the cooling tower. Is a method of manufacturing spherical semiconductor particles (for example, Patent Documents 1 and 2).

  According to the melt dropping method, semiconductor particles having a diameter of about 0.3 to 2 mm can be mass-produced. However, the resulting particles vary considerably in shape and mass. If there are variations in the resulting particles, in order to use them as a base of a spherical semiconductor element, it is necessary to screen the particles of a predetermined particle size by screening and then finish them into a true sphere by a method such as polishing. . As the shape and size of the semiconductor particles are not uniform, the amount of particles discarded by sieving and the amount of shavings during polishing increase, resulting in significant material loss and yield reduction.

  For this reason, in order to implement industrially, it is necessary to further examine about equipment, manufacturing conditions, etc., and to find optimal conditions about them. Specifically, the material and structure of the crucible, the size and shape of the nozzle holes, the melt drop conditions such as the pressure of the semiconductor melt, and the atmosphere and temperature in the cooling tower.

  On the other hand, a powder melting method has been proposed as a method that makes it easy to automate the manufacturing process of spherical semiconductor particles and that requires less cost (for example, Patent Documents 3, 4, and 5).

  In this method, for example, a template having a large number of through holes is used, and a large number of semiconductor powders having a volume determined by the thickness and the diameter of the through holes are simultaneously weighed to form a mountain or pile shape. Are formed and arranged on a substrate. Then, these small lumps are heated and melted in a heat treatment furnace, and then cooled and solidified. In this method, a raw material doped with a dopant in advance or a raw material not doped with it is used for the semiconductor powder.

  The powder melting method has the advantage of being easier to implement than the melt dropping method. On the other hand, when vibration or impact is applied when transporting or storing a small lump made of semiconductor powder, a part of it collapses to form a mountain shape with an expanded skirt, or even a small lump adjacent to it. There is a risk of overlapping each other at the part where they collapsed. When melted and solidified in a state where such a shape collapses and further a partial overlap has occurred, variations in the shape and mass of the obtained semiconductor particles become extremely large.

When using a doped raw material for the semiconductor powder, it is necessary to dope the semiconductor powder with a dopant in advance. In addition, when an undoped raw material is used, it is necessary to dope a p-type or n-type dopant after producing semiconductor spherical particles. In these methods, a series of steps for producing spherical semiconductor particles must be further added with a dopant doping step for raw materials, or a doping step for spherical particles as a product. Requires equipment and equipment. When spherical semiconductor particles are applied to an element having a pn junction, such as a photoelectric conversion element, the need for such a process, equipment, and apparatus to be added is economical for the powder melting method to be put to practical use. Not right.
U.S. Pat. No. 4,188,177 JP 2000-292265 A US Pat. No. 5,431,127 Japanese National Patent Publication No. 11-502670 US Patent No. 57633201

  The present invention is to manufacture semiconductor particles by such a powder melting method by heating and melting a small amount of a semiconductor powder containing a predetermined amount of semiconductor powder and a p-type or n-type doping agent. An object of the present invention is to provide a method for producing spherical semiconductor particles containing a dopant with a small variation in shape and mass while keeping the advantages as they are, and at a very low cost.

  The method for producing spherical semiconductor particles of the present invention is a first method of preparing a small solid body formed by using a raw material containing a semiconductor powder having a predetermined mass and a doping agent that makes the conductivity type of this semiconductor p-type or n-type. A second step of forming a spherical melt containing the dopant by heating the small solid body to melt and agglomerate the semiconductor powder contained therein, and cooling the spherical melt. And a third step of solidifying.

  In the above production method, it is preferable that the raw material further contains a binder.

  Furthermore, in the manufacturing method described above, it is preferable to adopt one of the following methods in the first step. In the first method, first, a mixture comprising a semiconductor powder and a doping agent, preferably a raw material further containing a binder, is prepared, and then this mixture is made into a small solid body by a granulating operation. This mixture can be prepared, for example, by adding a powdery dopant to the semiconductor powder and mixing them. For mixing in a powder state, a widely used powder mixer can be used. When a small amount of doping agent powder is added to the silicon powder, the mixing uniformity is improved by intermittently injecting compressed air into the mixed powder to cause the powder to flow, or the silicon powder is in a fluidized state. In addition, a uniform mixture can be obtained by spraying a dopant powder from a nozzle and mixing them. Furthermore, in the first method described above, the dopant is attached to the surface of the semiconductor powder in advance by contacting with a solution containing the dopant, and other raw materials such as a binder are used as necessary using this semiconductor powder. The method of granulating together and forming a small solid body can also be taken. In order to attach the doping agent to the surface of the semiconductor powder, the semiconductor powder is mixed or immersed in the semiconductor powder, or wetted by spraying the doping agent solution on the semiconductor powder or the like. It is possible to adopt a method of drying and attaching the doping agent to the semiconductor powder.

  In the second method, during the granulation operation, the above raw materials for producing a small solid are mixed, and a granulated product made of these raw materials is produced, and this is dried as necessary. It is a small solid.

  In the first and second methods described above, it is preferable to include a liquid binder to which a doping agent is added in advance as a raw material.

  In the third method, a granulated product containing a semiconductor powder and preferably a binder is first prepared by a granulating operation, and then this granulated product is brought into contact with a dopant solution. For example, a small solid body can be produced by immersing the granulated material in a doping agent solution for a predetermined time, taking it out, and drying it. Alternatively, the above granulated product may be wetted by spraying a doping agent solution or the like and then dried as necessary.

  According to the present invention, by using a solid containing a semiconductor powder and a doping agent, the possibility that the powder particles fall off or part of the powder collapses in the process from the production to heating and melting, and the mass The variation in size and shape is effectively reduced, and spherical semiconductor particles doped with an n-type or p-type dopant can be obtained efficiently. This is because the agglomeration force between the powder particles by the granulation operation, and when water or a binder is used, the bonding force between the powder particles by these reduces the possibility of the powder particles falling off and collapsing. .

  In the above-described method, in the second step, the small solid is preliminarily heated at a temperature high enough not to melt the semiconductor powder contained therein, and then the fine particles of the semiconductor powder are melted and fused together to form a spherical shape. Heat at a temperature sufficient to form. When silicon is used as a semiconductor, the maximum temperature of preliminary heating is kept in an unmelted state within a range of 1350 to 1412 ° C., and then heated and melted at a temperature within a range of 1413 to 1500 ° C. preferable. Note that if the heating temperature for melting is too high, the heat treatment furnace will deteriorate in a short period of time, so the upper limit of the required heat resistance, durability, and economics such as the cost required for heating. Decide it in consideration. In order to implement industrially, it is desirable to set it as 1500 degrees C or less.

  Furthermore, in the above-described method, the atmosphere in the preliminary heating step is set to an inertness at which the semiconductor powder particles are not substantially oxidized. The atmosphere in the heating step for melting the semiconductor powder is preferably a mixed gas mainly composed of an inert gas and oxygen, and the oxygen concentration in the atmosphere is preferably in the range of about 5 to 20%. As a result, an appropriate oxide film is formed on the surface of the melt to maintain the melt formed by melting and fusing the semiconductor powder in a spherical shape.

  In the method of the present invention, in the heat treatment of the small solid body, the dopant diffuses into the semiconductor powder, and further melts to form a spherical melt uniformly containing the dopant component, which is cooled and solidified to form the spherical semiconductor particles. Is obtained. That is, dopant can be doped in the process of producing spherical semiconductor particles, and high-quality spherical semiconductor particles can be produced at low cost while taking advantage of the powder melting method.

  In the present invention, in order to produce a small solid containing a semiconductor powder as a main component, various methods of granulation can be appropriately selected and used. The small solid is extremely useful for industrially carrying out the method of the present invention because of its ease of handling.

  The method of the present invention can be applied to the production of spherical semiconductor particles made of silicon or germanium. In many cases, the present invention is applied to the production of spherical silicon particles as described in the following embodiments. The silicon powder is preferably a semiconductor grade having a high purity. Even metal grade silicon powder with higher impurity concentration can be used, but the concentration of metal impurities such as iron, nickel, chromium, aluminum, titanium, etc. that adversely affect power generation performance is low. It is desirable to use a powder.

  The small solid can be formed by various granulation operations. In general, the operation of producing granules from the powder itself, a liquid in which the powder is dispersed or dissolved, or a liquid in which the liquid is wetted is called granulation. The produced particles are called a granulated product. In the heating step, the semiconductor powder particles in the small solid are melted and aggregated to form one spherical melt. Therefore, the small solid that is the precursor does not necessarily have to be spherical, but is granular or pellet-shaped. The shape may be any shape such as a flake shape or a square piece shape.

  The granulation method is roughly classified into a dry granulation method and a wet granulation method. The dry granulation method is generally performed by increasing the cohesive force of a material without using a liquid binder or water, and a representative method is a compression granulation method. The compression granulation method includes, for example, a method of filling a predetermined amount of powder in a cylinder and compressing it from above and below with a piston of a press machine, and a method of compressing powder between two rotating rolls.

  The wet granulation method is generally granulated using the adhesive force of water or a binder. Typical methods include rolling granulation, fluidized bed granulation, stirring granulation, and spray granulation. In the rolling granulation method, for example, the core of a mixture of these materials is formed by adding an appropriate amount of a liquid binder while rolling the powder in a bottomed cylindrical container in which only the bottom rotates. This is further grown to obtain a granulated product.

  In the fluidized bed granulation method, for example, hot air is sent from the lower part to form a fluidized bed of powder in the space in the container, and a liquid binder is sprinkled from the upper part or the peripheral wall part for granulation. The stirring granulation method is, for example, a method in which powder and a liquid binder are granulated while being mixed and stirred by rotation of a biaxial screw. As another method included in the wet granulation, there is a method in which a slurry in which a powder is dispersed in a liquid binder is dropped by a predetermined amount from a nozzle hole, and the slurry droplets that are granulated during dropping are solidified. For example, it is possible to solidify the slurry by dropping and collecting the slurry in a liquid that does not dissolve the slurry and drying the slurry.

  As an example of another preferable method for producing a small solid body by a granulation method, there is a method of forming a starting material into a sheet shape or a thin rope shape and cutting it into a predetermined size. Specifically, first, a semiconductor powder or a mixture obtained by adding other raw materials such as a binder to the semiconductor powder is prepared. This semiconductor powder or mixture may be processed into a small granulated material in advance by an appropriate granulating method, if necessary. Next, a semiconductor powder, a mixture, or a small granulated product is compressed between two rotating rollers, or pressed by a press machine, or the like, a sheet shape of a predetermined thickness or a rope shape of a predetermined cross-sectional area To form a green body. The compact is cut into a predetermined dimensional shape such as a square shape or a pellet shape to form a small solid body having a predetermined mass.

  The doping agent can be added to the semiconductor powder at any stage before granulation, during granulation, or after granulation. In addition to the pre-granulation, the semiconductor powder can be mixed with the dopant powder and, if necessary, a binder, or a solution containing the dopant can be sprayed onto the semiconductor powder, or the solution can be wetted with the semiconductor powder. That's fine. Alternatively, granulation may be performed using the semiconductor powder itself in which the doping agent is attached to the surface by contacting the doping agent solution in advance or a mixture with other raw materials such as a binder.

  In the addition during the granulation, the powdery dopant can be added as a powder to the semiconductor powder being granulated, or can be added by spraying the dopant solution. Moreover, the method of spraying the liquid binder which added the doping agent on the semiconductor powder in granulation can also be taken.

  Furthermore, in order to add after granulation, the granulated material may be immersed in a doping agent solution, impregnated, and dried as necessary to form a small solid. Needless to say, in addition to these methods, a semiconductor powder previously doped with a dopant may be used and prepared by the above method so as to be in a predetermined doping state. It is preferable to use a liquid or solid (powder) material as a doping agent at room temperature because it is easier to implement than a gaseous material, and the necessary equipment or apparatus is small and inexpensive. As the doping agent solution, a solution obtained by dissolving a liquid or powdery doping agent in a solvent such as water can be used. Although a liquid doping agent itself can be used instead of the doping agent solution, it is generally preferable to use a solution diluted with a solvent as described above.

  When silicon is used for the semiconductor, a boron compound is preferable as the dopant for the p-type dopant, and a phosphorus compound is preferable for the n-type dopant. Of course, as the doping agent, a raw material that does not contain components that adversely affect the electrical characteristics of the semiconductor device, such as heavy metals, is used. When used by adding to a liquid such as a liquid binder, the solvent is preferably water and the doping agent is preferably water-soluble such as boric acid from the viewpoint of safety and ease of handling.

  As the liquid binder in wet granulation, a solution or emulsion in which a high molecular polymer is dissolved or dispersed in water or an organic solvent is generally used. In dry granulation, a powdery polymer can be used as a binder. In such a binder, it is preferable to use a binder containing at least one polymer selected from the group consisting of polyvinyl alcohol, polyethylene glycol, hydroxypropyl cellulose, paraffin wax, carboxymethyl cellulose, starch, and glucose. These binders may be a polymer solution or emulsion, or the polymer itself. Particularly preferred binders are powders, solutions or emulsions containing at least one selected from the group consisting of polyvinyl alcohol, polyethylene glycol and paraffin wax because they have good binding properties and are easily available in high purity. is there.

  In order to melt the semiconductor powder contained in the above-mentioned small solid body to form a spherical melt and further solidify it by cooling, a continuous heat treatment furnace is used, the inside is maintained in a predetermined atmosphere, and the internal temperature Is set to a desired profile, and the heat treatment is practically carried out continuously by the conveyor. For example, first, in a rare gas or a substantially inert atmosphere mainly composed of the rare gas, the small solid is preliminarily placed at a temperature lower than the melting temperature of the semiconductor powder and high enough not to melt. Next, heat in an atmosphere consisting of a mixed gas of inert gas and oxygen with an oxygen concentration higher than that of the inert atmosphere, and heating at a temperature equal to or higher than the melting temperature to produce a spherical semiconductor melt To do.

  Of course, spherical semiconductor particles can also be produced by batch processing instead of such a continuous processing furnace. For example, using a common heat treatment furnace, perform a preliminary heat treatment in an inert atmosphere at a temperature that does not melt the entire semiconductor powder, then add oxygen to the furnace atmosphere and melt at a higher heating temperature And then solidified by a method such as natural cooling.

  As a gas for forming an inert atmosphere in the preliminary heat treatment, a rare gas such as a gas mainly containing argon can be used. Further, in the next melt formation step, an oxide thin film is formed on the surface of the melt, and a mixed gas containing oxygen in a concentration that does not cause excessive oxidation in the inert gas (hereinafter simply referred to as a mixed gas). ). The oxygen concentration is preferably in the range of 5 to 20% by volume where an oxide thin film having a thickness capable of promoting spheroidization is formed without excessive oxidation when the semiconductor powder melts. .

  The semiconductor powder used as the raw material is preferably a powder composed of particles having an average particle diameter of 10 to 100 μm. When a semiconductor powder having a particle size within this range is used, a small solid with a small variation in mass can be easily produced, and the semiconductor powder can be completely melted in a short time. In addition, when the dopant is a powder, it is preferable to use a powder having an average particle size equal to or smaller than that of the semiconductor powder.

  Next, as a typical embodiment for producing spherical silicon particles by the method of the present invention, an example in which a powder having a conductive type is used as a silicon raw material and a dopant raw material is added during granulation will be described. To do.

(1) About the 1st process In this process, many small solids of predetermined mass containing semiconductor powder are produced. The raw material to be used is classified into any one of a semiconductor powder and a dopant, and a semiconductor powder, a dopant and a binder. In the present embodiment, the case of producing the latter small solid body will be specifically described.

  In this example, it is preferable to use semiconductor grade high-purity silicon powder as a raw material. Here, a semiconductor grade undoped silicon powder is used, a granulated product made of this powder, a doping agent and an organic binder is made, and the granulated product is dried as necessary to obtain a silicon sphere having a diameter of about 1 mm. A small solid body as a precursor.

  First, a granulated material is produced using the rolling granulator shown in FIG. This apparatus includes a cylindrical outer frame 11 having a diameter of about 40 cm, a dish-shaped bottom plate 13 disposed in the outer frame 11 with an air slit 12 between the inner wall and the bottom plate 13 on the back surface thereof. And a support rod 14 supported at the side center. The support bar 14 is driven by a motor (not shown), and the bottom plate 13 rotates. In addition, air is fed into the container composed of the bottom plate 13 and the outer frame 11 from the air slit 12 when the apparatus is used.

About 3000 g of silicon powder is put on the bottom plate 13. Next, the bottom plate 13 is rotated at a speed of 100 to 300 rpm, and the silicon powder 15 is rolled between the outer peripheral portion of the bottom plate 13 and the inner wall of the outer frame 11. About 750 cc of the liquid binder 16 is sprayed toward the silicon powder 15 by the spray gun 17 at an even speed for 30 to 60 minutes. In this liquid binder 16, polyvinyl alcohol as a binder component is dissolved in 10 parts by mass and boric acid as a doping agent is dissolved in a ratio of 1.6 × 10 ⁻⁴ parts by mass with respect to 100 parts by mass of water. Has been. Even after the spraying of the binder 16 is completed, the bottom plate 13 may be rotated for 15 to 30 minutes. Thereby, silicon powder, a binder component, and a doping agent are mixed uniformly, and are granulated while rolling to produce a granulated product.

  During this time, by blowing air from the air slit 12 into a container constituted by the outer frame 11 and the bottom plate 13, the silicon powder 15 or a part of the binder 16 is prevented from dropping from the air slit 12, and the silicon. The rolling of the powder 15 can be promoted.

  The obtained granulated product is sieved into one within a predetermined mass range and one outside the range. For this, a commonly used sieving device can be used. About the small granulated body outside the predetermined mass range which was sieved, the small solid body of the predetermined mass range is produced by further growing it by the above-mentioned procedure using the apparatus of FIG. You can also.

  That is, a small granulated material is supplied into a container composed of the outer frame 11 and the bottom plate 13, and the bottom plate 13 is rotated to roll it. An additional silicon powder 19 is sprayed from a nozzle 18 of a powder supply device (not shown) while spraying the binder 16 toward the small granules during rolling. After spraying a predetermined amount, the bottom plate 13 is continuously rotated for a predetermined time.

  By such an operation, new semiconductor powder particles are mainly bound by the binder component on the surface of the small granulated product, and a large granulated product in which the doping agent is uniformly mixed is obtained. This is sieved and the granulated material in a predetermined mass range is used as a small solid. The additional application amount of the silicon powder 19 and the binder 16 can be easily determined experimentally according to the particle size distribution of the small granules. If necessary, the raw material such as silicon powder can be more effectively utilized by repeating the above-described operation for increasing the particle size.

As the organic binder, the various binders described above can be used. Among them, an aqueous solution of either polyvinyl alcohol or polyethylene glycol is preferable for practical use. By using this binder, it is possible to obtain a small solid body having a substantially spherical shape with good mass uniformity and good binding properties between the silicon powder particles and when the doping agent is a powder. About the compounding ratio of a liquid binder, it is preferable to make polyvinyl alcohol or polyethyleneglycol into the range of 5-20 mass parts with respect to 100 mass parts of water. Furthermore, about mass ratio of a silicon powder and a binder, it is preferable to make solid content of a binder into the range of 2-5 mass parts with respect to 100 mass parts of silicon powder. The content ratio of boric acid as a doping agent with respect to 100 parts by mass of silicon powder in the small solid body is preferably 1 × 10 ⁻⁴ to 1 × 10 ⁻³ parts by mass.

  The mass of the small solid obtained by granulation can be appropriately adjusted depending on the amount and particle size of silicon powder, the composition and amount of binder added, the operating conditions of the granulator, and the like. In this case, a small solid body having a relatively uniform mass can be obtained when silicon powder made of particles having an average particle diameter in the range of 10 to 100 μm is used. Of the semiconductor elements, spherical photoelectric conversion elements or silicon spherical particles as precursors thereof usually have a diameter in the range of 0.5 to 2.0 mm, and their mass is about 0.15 to 9.8 mg. It is in the range. When manufacturing such an element, the mass of the small solid is about 0.16 to 10 mg. In this example, a small solid body of about 1.26 mg was produced to produce silicon particles for solar cells having a diameter of about 1.0 mm.

  In order to increase the strength of the small solid or to facilitate the handling thereof, it is preferable to remove moisture in the binder contained in the small solid by drying, if necessary. This further suppresses contact between the small solid bodies and dropping of the silicon powder particles from the small solid bodies during the transition to the next heat treatment process and during the heat treatment in the next process. As a result, it is possible to obtain silicon spherical particles that have a small variation in mass and are less likely to cause problems such as connection between particles.

  When producing a granulated product containing silicon powder, spraying high-purity water on the rolling powder instead of the binder, and using the resulting binding force, a small solid with a predetermined mass is obtained. You can also get a body.

(2) Second step In this step, the small solid body produced in the first step described above is heated at a temperature equal to or higher than the melting point of silicon to melt and aggregate the semiconductor powder in the small solid body. To form a spherical melt. At this time, the binder contained in the small solid body is substantially removed from the small solid body by being decomposed, vaporized, or burned by the heat treatment in this step, and each small solid body is also removed. In each case, the semiconductor powders in each are melted and integrated into a small spherical silicon melt.

  First, as shown in FIGS. 2 and 3, a large number of small solid bodies 21 each having a substantially spherical shape are arranged on a heat-resistant holding substrate 22 so as not to fuse with each other during melting, and this is subjected to heat treatment. Heat in the furnace. In this heat treatment, boric acid is decomposed, boron is doped into silicon, the binder component is removed, and the silicon powder contained in the small solid body 21 is melted, so that boron is further doped to a predetermined concentration. A spherical melt of silicon is formed. FIG. 3 is a cross-sectional view taken along one-dot chain line III-III in FIG.

  The substrate 22 for holding the small solid body 21 has a low reactivity with silicon and a high heat resistance, such as a quartz glass substrate or a substrate in which a plate-like substrate such as alumina or silicon carbide is coated with silicon nitride. Can be used. In this example, a quartz glass substrate having a thickness of 3 mm, a width of 300 mm, and a length of 300 mm was used as the substrate 22.

  On one main surface side of the substrate 22, a large number of recesses 23 having an opening diameter of about 0.5 mm are formed and arranged at equal intervals. On this substrate 22, the mass produced in the first step is about 1.26 mg and a group of almost spherical small solid bodies 21 is placed, and by applying vibration to the substrate 22, the small solid bodies 21 are shown in FIG. Thus, one piece is held in each recess 23.

  For the heat treatment of the small solid body 21, a heat treatment furnace 41 shown in FIG. 4 is used. As the heat treatment furnace 41, a ceramic firing furnace having a good heat resistance and corrosion resistance on the inner wall of the furnace can be used. In a state where the inside is maintained in a predetermined atmosphere and set to have a predetermined temperature profile, the small solid bodies 21 are continuously carried in, and the silicon powder contained in each is melted and fused so that boron is in a predetermined state. Concentrated dope-like melts are made, cooled and solidified, and carried out as spherical p-type silicon particles.

  The heat treatment furnace 41 includes a carry-in unit 42, a preheating unit 43, a melting unit 44, a solidification unit 45, and a carry-out unit 46, and a transport roller conveyor 47 is disposed so as to penetrate these. Shutters 48 and 49 and shutters 50 and 51 are provided in the carry-in part 42 and the carry-out part 46, respectively. By opening and closing them, the holding substrate 22 is carried into the heat treatment furnace 41 from the carry-in part 42 while maintaining the internal atmosphere of the preheating part 43, the melting part 44 and the solidification part 45 in a predetermined state, and the carry-out part By carrying out from 46, predetermined | prescribed heat processing can be performed to the small solid body arrange | positioned on the board | substrate 22. FIG. The holding substrate 22 is placed on a support plate (not shown) made of, for example, silicon carbide and moves in the heat treatment furnace 41 together with the support plate.

  Between the preheating part 43 and the fusion | melting part 44, the partition body 52 which has an opening of the magnitude | size which can hold | maintain the holding | maintenance board | substrate 22 is arrange | positioned, and the solidification in the terminal part of the heating furnace 41 which is mentioned later Combined with the exhaust of the furnace atmosphere from the part 45, mixing of the oxidizing atmosphere from the melting part 44 into the preheating heating part 43 is prevented, and the inside of the preheating part 43 is maintained in a substantially inert atmosphere. The Further, a plurality of heaters 53 are installed inside the preheating unit 43 and the melting unit 44. As is generally performed, the temperature of each part in the furnace 41 is detected by a platinum temperature sensor or the like, and the supply current to each heater 53 is controlled so that the temperature distribution in the furnace has a predetermined profile. Instead of such a heat treatment furnace using an electric heater, a microwave heat treatment furnace may be used.

  A gas supply pipe 55 for supplying an inert gas from an inert gas supply unit 54 is connected to each of the carry-in unit 42 and the preheating unit 43 of the heat treatment furnace 41. Further, a supply pipe 57 for supplying a low-oxidation mixed gas from a mixed gas supply unit 56 of inert gas and oxygen is connected to the melting unit 44, the solidification unit 45, and the carry-out unit 46. A valve 58 is provided on the branch pipe of the gas supply pipe 55 connected to the carry-in section 42, and a valve 59 is provided on the branch pipe of the gas supply pipe 57 connected to the carry-out section 46. The opening and closing operations of the valves 58 and 59 are performed in conjunction with the opening and closing of the shutters 48 and 49 and the shutters 50 and 51. Exhaust pipes 60, 61, and 62 are connected to the part between the shutters 48, 49 of the carry-in part 42, the end part in the transport direction of the coagulation part 45, and the part between the shutters 50, 51 of the carry-out part 46, respectively. Yes.

  For example, argon or helium is used as the inert gas, and a gas obtained by mixing oxygen with an inert gas is used as the mixed gas. In terms of cost, it is advantageous to use argon as an inert gas.

  First, with the valves 58 and 59 closed and the inner shutters 49 and 50 closed, the inert gas is supplied from the inert gas supply unit 54 to the part of the carry-in unit 42 and the preheating unit 43 through the supply pipe 55. . As a result, air in the main part of the furnace is exhausted from the exhaust pipe 61 through the melting part 44 and the solidification part 45 from the opening of the partition body 52, and the inside of the heat treatment furnace 41 is replaced with an inert gas. Then, an oxidizing gas is supplied from the oxidizing gas supply unit 56 to a part of the melting unit 44, the solidifying unit 45, and the carry-out unit 46 through the supply pipe 57, and the internal atmosphere is replaced with the oxidizing gas. At this time, since the inert gas continues to flow into the melting part 44 from the preheating part 43 through the opening of the partition wall body 52, the partition body 52 oxidizes the melting part 44 side into the inert gas on the preheating part 43 side. Mixing of sex gases is prevented.

  When the replacement of the internal atmosphere of the heat treatment furnace 41 is completed, the shutter 48 of the carry-in unit 42 is opened, and the substrate 22 on which the small solid body is placed is carried between the shutters 48 and 49 of the carry-in unit 42 by the roller conveyor 47. When loaded, the shutter 48 is closed and the valve 58 is opened to introduce an inert gas. As a result, the internal air is discharged from the exhaust pipe 60. When the inert gas is substituted, the shutter 49 is opened, and the substrate 22 is transferred to the preheating unit 43 side. When the first substrate 22 is transferred, the shutter 49 is closed. Then, the valve 58 is closed to stop the supply of the inert gas, the shutter 48 is opened, and the next substrate 22 is carried in. When this substrate 22 is carried in, the atmosphere in the carry-in part 42 is replaced with inert gas from the air in the same procedure as described above. After completion of the replacement, the substrate 22 is transferred to the preheating unit 43 side. Thereafter, the substrate 22 on which the small solid body is placed in the heat treatment furnace 41 is sequentially carried into the heat treatment furnace 41 in the same procedure.

  The temperature in the preheating part 43 of the heat treatment furnace 41 is set to a profile that increases from the side of the carrying-in part 42 toward the vicinity of the partition body 52, and the maximum temperature is maintained within a range of 1350 to 1412 ° C. . In this preheating unit 43, the small solid is heated while being transported in the preheating unit 43, the boric acid contained therein is decomposed, boron diffuses into the silicon powder particles, and the binder in the small solid Decomposes or vaporizes into a small solid mainly composed of silicon doped with boron. Then, the small solid body passes through the partition body 52 and enters the melting portion 44. Since the inside of the melting part 44 has an oxidizing atmosphere, the residual component of the binder is oxidized and substantially disappears. And it heats at about 1450 degreeC, the silicon powder of a small solid body fuse | melts, and the small spherical body melt body in which boron was doped uniformly is formed. At this time, an oxide thin film is formed on the surface, and its spheroidization is promoted.

  Vaporized components generated by the decomposition of boric acid and the binder in the preheating unit 43 and the melting unit 44 or the combustion of the binder are discharged from the exhaust port 61 to the outside of the furnace together with an inert gas.

(3) Third Step In this step, semiconductor particles doped with a dopant that determines the conductivity type are manufactured by cooling and solidifying the melt formed in the second step.

  Boron-doped silicon melt obtained in the melting part 44 is gradually cooled from the melting temperature of silicon to the solidification temperature in the process of being conveyed in the solidification part 45. When the silicon melt is rapidly cooled, molten silicon is confined in the solidified outer shell. As cooling proceeds, the internal silicon solidifies. Since the volume of the internal silicon increases by solidification, stress is generated in the silicon particles. Due to this stress, the outer shell of the particle may be broken to form an abnormal protrusion or a crack may occur. From these things, the relationship between the temperature profile in the solidification part 45 and the conveyance speed by a roller conveyor is set so that a cooling rate may become suitable in the range which does not impair productivity.

  When the substrate 22 on which the p-type silicon particles are placed reaches a position in the vicinity of the shutter 50 of the carry-out unit 46, the shutter 51 is closed, the valve 59 is opened, and the shutter 50 of the carry-out unit 46 from the mixed gas supply unit 56 is opened. , 51 is supplied with a mixed gas. After the air in the region between the shutters in the heating furnace 41 is exhausted from the exhaust port 62 and the inside is replaced with the mixed gas, the shutter 50 is opened, and the substrate 22 is transferred between the shutters 50 and 51. When this transfer is completed, the shutter 50 is closed to prevent outside air from entering the heat treatment furnace 41. Next, the shutter 51 is opened, the substrate 22 is taken out from the carry-out portion 46, and spherical p-type silicon particles having a diameter of about 1 mm that have been placed thereon are collected. Thereafter, the above procedure is repeated to continuously carry out the semiconductor particles to the outside.

  In the above-described embodiment, an example in which boric acid is used as a p-type doping agent has been described. However, boron oxide or the like can be used instead. Since boron oxide has the property of gradually decomposing into boric acid when dissolved in water, the same effect as boric acid can be obtained.

  In order to obtain n-type conductive silicon particles, phosphorus or triphenylphosphine oxide is suitable as the doping agent. It is practical to use phosphorus as a powder, and it is practical to use triphenylphosphine oxide as an aqueous solution.

  Furthermore, even if a p-type or n-type silicon powder containing a high concentration of dopant is prepared in advance and a mixed powder obtained by adding a predetermined ratio to non-doped silicon powder is used, the target p-type or n-type is used. Mold silicon particles can be easily produced.

  The semiconductor particles obtained by the present invention can be used for a base of a spherical semiconductor element used for a diode or an optical sensor or a solar cell. As a representative example, a typical spherical photoelectric conversion element manufactured by processing silicon particles having a diameter of about 1.0 mm obtained by the above-described method, and a photoelectric conversion device (low-concentration type spherical sun) using the same Battery) will be described below.

  First, the p-type silicon particles obtained by the above embodiment are re-melted by heating at a temperature slightly higher than the melting point of silicon in an inert gas atmosphere containing a small amount of oxygen, and then slowly cooled. Thereby, the single crystallization of the p-type silicon particles proceeds, and the effect that the sphericity of the particles is further increased can be obtained. Next, if necessary, the sphericity is increased by polishing small spherical semiconductor particles, and the sphere diameter is adjusted to about 0.9 mm.

For example, phosphorus is diffused into the p-type silicon particles to form an n-type diffusion layer along the surface, thereby obtaining a spherical photoelectric conversion element having a small sphere having a pn junction. This diffusion layer is formed by, for example, spraying a mist of a POCl ₃ solution on p-type silicon particles to uniformly adhere the p-type silicon particles, and then performing a heat treatment at a temperature of about 900 ° C. Next, if necessary, a SnO ₂ film having a thickness of 50 to 100 nm doped with fluorine or antimony to provide conductivity is further formed on the surface as an antireflection film.

  A photoelectric conversion device using this photoelectric conversion element will be described. FIG. 5 is a front view of the power generation unit 101 constituting the photoelectric conversion device, and FIG. 6 is a longitudinal sectional view of the main part of the power generation unit 102.

  A spherical photoelectric conversion element (hereinafter referred to as an element) 103 having a diameter of about 0.9 mm is fixed to each of about 1800 recesses 105 provided on an aluminum support plate 104, and the power generation unit 102. Is formed. By reflecting the light applied to the inner surface of the recess 105 toward the element 103, the photoelectric conversion efficiency of the element 103 can be increased. A part of the element 103 protrudes from the opening provided at the bottom of the recess 105 to the back side of the support plate 104. The n-type diffusion layer 106 on the protruding portion is selectively removed by etching or the like, and the surface of the p-type base portion 107 of the element 103 is exposed. An electrode layer 108 is formed on the exposed portion.

  An electrical insulating layer 110 is bonded to the back surface of the support plate 104, and a through hole is provided in the electrical insulating layer 110 at a portion facing the electrode layer 108. A conductive plate 109 made of aluminum is bonded to the back side of the electrical insulating layer 110, and a through hole is provided in the conductive plate 109 in a portion opposite to the through hole of the electrical insulating layer 110, and a communication hole is formed by these through holes. Is formed. The peripheral edge of the bottom opening of the recess 105 in the support plate 104 and the n-type diffusion layer 106 of the element 103 are electrically connected by a connecting portion 111 made of a conductive adhesive. The portion of the electrode layer 108 located immediately below the p-type base portion 107 of the element 103 and the conductive plate 109 are filled with a slightly larger amount of the conductive paste 113 than filling the communication hole between the electrical insulating layer 110 and the conductive plate 109. Are electrically connected.

  One end of the support plate 104 constitutes one terminal 115 of the power generation unit 101, and one end of the conductive plate 109 protruding from the back side of the end facing the power generation unit 101 constitutes the other terminal 114.

  The output of this power generation unit is about 1 W. A photoelectric generator that outputs power of a desired voltage by electrically connecting a plurality of power generation units or the like and electrically connecting any number of units in series or in parallel. A conversion device can be configured.

  The semiconductor particles produced according to the present invention are particularly useful as a matrix of a spherical photoelectric conversion element used in a photoelectric conversion device for private power generation in a building such as a house.

It is a sketch of the principal part of the rolling granulation apparatus which manufactures a small solid body in embodiment of this invention. It is a front view of the principal part of the board | substrate for a heating which arranged the small solid body in embodiment of this invention. FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 2. It is sectional drawing of an example of the heat processing furnace used in embodiment of this invention. It is a front view of the electric power generation unit of the photoelectric conversion apparatus using the photoelectric conversion element which used the spherical silicon particle manufactured by this invention as a base. It is sectional drawing of the principal part of the electric power generation unit shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Cylindrical outer frame 12 Air slit 13 Dish-shaped bottom plate 14 Rotatable support rod 15 Silicon powder 16 Liquid binder in which doping agent is dissolved 17 Spray gun 18 Nozzle for supplying silicon powder 19 Silicon powder 21 Small solid Body 22 Heat-resistant holding substrate 23 Recessed part 41 Heat treatment furnace 42 Carry-in part 43 Preheating part 44 Melting part 45 Solidification part 46 Carry-out part 47 Roller conveyor 48, 49 Shutter 50, 51 Shutter 52 Partition body 53 Heater 54 Inert gas supply Section 55 Gas supply pipe 56 Mixed gas supply section of inert gas and oxygen 57 Supply pipe 58, 59 Valve 60, 61, 62 Exhaust pipe

Claims (11)

A first step of preparing a small solid body formed by using a raw material containing a semiconductor powder and a doping agent for changing the conductivity type of the semiconductor to either p-type or n-type by a granulation operation. Process,
A second step of forming a spherical melt containing a p-type or n-type dopant by heating the small solid and melting the semiconductor powder in each small solid; and
A third step of cooling and solidifying the spherical melt;
The manufacturing method of the spherical semiconductor particle containing this.   The method for producing spherical semiconductor particles according to claim 1, wherein the small solid body further contains a binder as the raw material. The first step is a step of preparing a mixture of the raw materials, and a step of forming a small solid body made of the mixture by a granulating operation;
The manufacturing method of the spherical semiconductor particle of Claim 1 or 2 containing this. The first step is a step of mixing the raw materials and forming a small solid body made of the raw materials by a granulation operation,
The manufacturing method of the spherical semiconductor particle of Claim 1 or 2 containing this.   The method for producing spherical semiconductor particles according to claim 3 or 4, wherein the binder is a liquid binder, and the doping agent is added to the binder. The first step is to bring the semiconductor powder into contact with a solution containing the doping agent;
And forming a small solid body containing a semiconductor powder brought into contact with a solution containing the doping agent by a granulating operation,
The manufacturing method of the spherical semiconductor particle of Claim 3 containing this. Prior to the step of forming the small solid body, the first step further comprises drying the semiconductor powder brought into contact with the solution,
The manufacturing method of the spherical semiconductor particle of Claim 6 containing this. The first step is a step of forming a granulated product containing the semiconductor powder by a granulating operation, and a step of bringing the granulated product into contact with a solution containing the doping agent;
The manufacturing method of the spherical semiconductor particle of Claim 1 or 2 containing this. The spherical semiconductor according to claim 8, wherein the first step further includes a step of drying the granulated product brought into contact with the solution after the step of bringing the granulated product into contact with the solution containing the doping agent. Particle production method.   The method for producing spherical semiconductor particles according to claim 1, wherein the semiconductor is silicon and the doping agent is a boron compound.   The method for producing spherical semiconductor particles according to claim 1, wherein the semiconductor is silicon and the doping agent is a phosphorus compound.

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