JP2009292652A - Production method of crystalline silicon grain - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing crystalline silicon particles capable of stably producing single crystalline silicon particles at a high efficiency and producing single crystalline crystalline silicon particles at low cost.
Crystal silicon particles 101 are produced by a melt drop method, and then the surface of the crystal silicon particles 101 is polished to form a work-affected layer on the surface layer portion of the crystal silicon particles 101, and then from nitrogen gas The crystalline silicon particles 101 are heated to a temperature not higher than the melting point of silicon in the atmospheric gas or the atmospheric gas containing nitrogen gas as a main component, and a silicon nitride film is formed on the surface of the crystalline silicon particles 101. The crystalline silicon particles 101 are heated in an atmosphere gas or an atmosphere gas composed of oxygen gas and inert gas to melt the silicon inside the silicon nitride film, and the temperature is lowered and solidified to form a single crystal.
[Selection] Figure 1

Description

  The present invention particularly relates to a method for producing crystalline silicon particles suitable for use in a photoelectric conversion device such as a solar cell.

  Photoelectric conversion devices have been developed in view of market needs such as high efficiency in terms of performance such as photoelectric conversion characteristics, consideration of the finite nature of semiconductor resources such as silicon, and low manufacturing costs. As one of promising photoelectric conversion devices in the future market, there is a photoelectric conversion device using crystalline semiconductor particles such as crystalline silicon particles used as a solar cell.

As raw materials for producing crystalline silicon particles which are crystalline semiconductor particles, silicon fine particles generated as a result of pulverizing single crystal silicon, high-purity silicon vapor-phase synthesized by a fluidized bed method, etc. are used. Yes. In order to produce crystalline silicon particles from these raw materials, after separating the raw materials according to size or weight, they are melted in a container using infrared rays or high frequency, and then freely dropped (for example, Patent Document 1, 2), or by a method of melting in a container using high-frequency plasma and then free-falling (for example, see Patent Document 3).
WO99 / 22048 pamphlet U.S. Pat. No. 4,188,177 JP-A-5-78115 U.S. Pat. No. 4,430,150

  However, most of the crystalline silicon particles produced by these methods are polycrystalline (polycrystalline silicon particles). Since polycrystalline silicon particles are aggregates of minute single crystals, grain boundaries exist between the minute single crystals. This grain boundary degrades the electrical characteristics of a photoelectric conversion device using polycrystalline silicon particles. The reason is that the carrier recombination centers are gathered at the grain boundaries, and the recombination of carriers thereby causes the lifetime of minority carriers to be greatly reduced.

  In the case of a semiconductor device whose electrical characteristics are greatly improved with an increase in the life of minority carriers, such as a photoelectric conversion device, the presence of grain boundaries in the crystalline silicon particles used for it deteriorates the electrical characteristics. It becomes a big problem. In other words, if the crystalline silicon particles can be used from a polycrystal to a single crystal (single crystal silicon particles), the electrical characteristics of the photoelectric conversion device can be remarkably improved.

  In addition, since the grain boundary in the polycrystalline silicon particles lowers the mechanical strength of the polycrystalline silicon particles, the polycrystalline silicon particles are affected by the thermal history, thermal strain, mechanical pressure, etc. of each process of manufacturing the photoelectric conversion device. There was also a problem that was easily destroyed.

  Therefore, when producing a photoelectric conversion device using crystalline silicon particles, it is extremely important to produce single crystal silicon particles having no crystal grain boundaries and excellent crystallinity.

  As a method for obtaining such single crystal silicon particles having excellent crystallinity, a silicon compound film such as a silicon oxide film is formed on the surface of polycrystalline silicon particles or amorphous silicon particles, and silicon inside the silicon compound film is formed. A method for producing crystalline silicon particles made of a polycrystal or a single crystal excellent in crystallinity by melting and then solidifying by cooling is known (see, for example, Patent Document 4).

  However, when a polycrystalline silicon particle is heated to melt a silicon compound film formed on the surface thereof, specifically, silicon is melted inside the silicon oxide film and then solidified, it is adjacent when the silicon melts. There was a problem that the polycrystalline silicon particles were united. In this case, since there is no solidification starting point like a seed crystal used in a general method for growing a bulk silicon single crystal such as CZ (Czochralski) method or FZ (floating zone) method, The problem is that solidification does not occur in the direction and polycrystallization occurs due to the generation of a large number of nuclei. In addition, the photoelectric conversion device using the polycrystalline silicon particles has a problem of causing characteristic deterioration.

  In addition, when high-purity polycrystalline silicon synthesized in a gas phase by a fluidized bed method is used as a raw material in the production of crystalline silicon particles, metal impurities such as iron and nickel contained in the starting material contained in the polycrystalline silicon, Further, contamination due to similar metal impurities mixed from the outside during the manufacturing process becomes a problem. Since the metal impurity diffuses between the lattices which do not have a chemical bond in silicon, the impurity atoms are diffused through the gaps in the silicon lattice. This diffused metal impurity forms a deep level in silicon and acts as a carrier recombination center, which causes an increase in leakage current and a decrease in carrier lifetime caused by photoelectric conversion. cause.

  That is, it is difficult to produce desired high-quality single crystal silicon particles by the conventional method for producing crystalline silicon particles, and a photoelectric conversion device having excellent electrical characteristics is produced using the obtained crystalline silicon particles. There is a problem that it is unsuitable as a manufacturing method for this purpose.

  Accordingly, the present invention has been completed in view of the above-mentioned problems in the prior art, and an object of the present invention is to stably and efficiently crystallize crystalline silicon particles such as polycrystalline silicon particles as well as single crystals. Another object of the present invention is to provide a method for producing crystalline silicon particles, which can produce the crystalline silicon particles at low cost.

  According to the method for producing crystalline silicon particles of the present invention, the silicon melt is discharged as particles from the crucible nozzle part containing the silicon melt and dropped, and the granular silicon melt is cooled and solidified while being dropped. Then, a crystalline silicon particle is produced, and then the surface of the crystalline silicon particle is polished to form a work-affected layer on the surface layer portion of the crystalline silicon particle. In an atmospheric gas containing a gas as a main component, the crystalline silicon particles are heated to a temperature below the melting point of silicon to form a silicon nitride film on the surface of the crystalline silicon particles, and then an atmospheric gas or oxygen consisting of oxygen gas The crystalline silicon particles are heated in an atmospheric gas composed of a gas and an inert gas to melt the silicon inside the silicon nitride film and then drop it. Characterized by single crystal solidifying by.

  The method for producing crystalline silicon particles according to the present invention is preferably characterized in that the silicon nitride film contains oxygen.

  In the method for producing crystalline silicon particles according to the present invention, preferably, the crystalline silicon particles are heated in an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and an inert gas so as to form an inner side of the silicon nitride film. When the silicon is melted, cooled and solidified to be single-crystallized, the single-crystallization is performed in a state in which a large number of the crystalline silicon particles are placed in a multilayered manner on the base plate.

  The method for producing crystalline silicon particles according to the present invention is preferably characterized in that the silicon nitride film is removed after the crystalline silicon particles are single-crystallized.

  In the method for producing crystalline silicon particles of the present invention, the silicon melt is discharged as particles from the crucible nozzle part containing the silicon melt and dropped, and the granular silicon melt is cooled and solidified during the dropping. The crystalline silicon particles are prepared by the following steps, and then the surface of the crystalline silicon particles is polished to form a work-affected layer on the surface layer of the crystalline silicon particles, and then the atmosphere gas or nitrogen gas composed of nitrogen gas is the main component. The crystalline silicon particles are heated to a temperature not higher than the melting point of silicon to form a silicon nitride film on the surface of the crystalline silicon particles, and then from the atmospheric gas composed of oxygen gas or oxygen gas and inert gas In the atmosphere gas, the crystalline silicon particles are heated to melt the silicon inside the silicon nitride film, and the temperature is lowered and solidified to form a single crystal. Et al., A silicon nitride film of the mesh structure is formed along a number of microcracks of the work-affected layer. As a result, for example, when a large number of crystalline silicon particles are aligned and single-crystallized, the coalescence of the crystalline silicon particles is effectively suppressed, and the occurrence of crystal cracks and subgrains at the contact surface between the crystalline silicon particles due to the coalescence. Crystalline silicon particles having high quality crystallinity can be produced.

  In addition, since the crystalline silicon particles have a network-structured silicon nitride film on the surface layer, the shape of the crystalline silicon particles is maintained with respect to the volume change when the silicon inside the crystalline silicon particles is melted and solidified during single crystallization. Therefore, sufficient flexibility can be added to the surface layer portion of the crystalline silicon particles.

  In addition, since the silicon nitride film has a higher ability to prevent diffusion of contaminants and impurities into the silicon inside the crystalline silicon particles than the silicon oxide film, the silicon nitride film such as iron (Fe) attached to the surface of the crystalline silicon particles Contamination due to diffusion of heavy metal elements or the like is reduced, and high-quality crystalline silicon particles can be manufactured.

  In the method for producing crystalline silicon particles of the present invention, the silicon nitride film preferably contains oxygen, and in this case, the above-described effects are brought into silicon inside the crystalline silicon particles such as contaminants and impurities. Therefore, the contamination due to diffusion of heavy metal elements such as iron (Fe) adhering to the surface of the crystalline silicon particles is reduced, and high-quality crystalline silicon particles can be produced.

  In addition, since the silicon nitride film contains oxygen, the flexibility of the film is superior to that of a silicon nitride film that does not contain oxygen, and even when the film thickness is large, the silicon inside the crystalline silicon particles is formed during single crystallization. With respect to the volume change at the time of melting and solidifying, a sufficient flexibility to maintain the shape of the crystalline silicon particles can be added to the surface layer portion of the crystalline silicon particles.

  In the method for producing crystalline silicon particles of the present invention, the silicon inside the silicon nitride film is preferably heated by heating the crystalline silicon particles in an atmospheric gas composed of oxygen gas or an atmospheric gas composed of oxygen gas and an inert gas. When a single crystal is formed by melting, cooling and solidifying to form a single crystal, the surface of the crystalline silicon particles is pre-processed by single crystallization in a state in which a large number of crystalline silicon particles are placed on a base plate. In order to effectively prevent coalescence of the crystalline silicon particles formed in the silicon nitride film, a large number of crystalline silicon particles are stacked on the base plate during single crystallization in a heating furnace, By arranging the crystalline silicon particles at a high density, a large number of crystalline silicon particles can be single-crystallized at a time, and it is possible to manufacture the crystalline silicon particles at low cost and with high mass productivity. Therefore, it is possible to efficiently produce crystalline silicon particles used for a photoelectric conversion device or the like.

  In addition, a solidification starting point when a large number of crystalline silicon particles are placed on a base plate in a multilayer manner to melt, solidify and single crystallize is determined by the contact portion between the crystalline silicon particles and the base plate and between the crystalline silicon particles. By setting the contact portion, single crystallization can proceed from the contact portion to above the crystalline silicon particles. Therefore, the crystalline silicon particles can be easily solidified in one direction without using a seed crystal as in the CZ method and the FZ method, and can be easily single-crystallized, and the crystallinity of the crystalline silicon particles can be greatly improved. it can.

  That is, first, the contact point of the crystalline silicon particles with the base plate becomes a solidification starting point, and solidification proceeds in one direction (upward direction) of the crystalline silicon particles. In this case, the contact point of the crystalline silicon particles with the base plate can be set as a solidification starting point without cooling the base plate, but the base plate may be cooled. Next, the solidification of the crystalline silicon particles on the crystalline silicon particles in contact with the solidified crystalline silicon particles proceeds in one direction (upward), starting from the contact point with the solidified crystalline silicon particles. . As a result, the solidification progresses from the lower crystalline silicon particles to the upper crystalline silicon particles as a result.

  In the method for producing crystalline silicon particles of the present invention, preferably, since the silicon nitride film is removed after the crystalline silicon particles are monocrystallized, Fe, Cr, Ni, Mo segregated on the surface layer portion of the crystalline silicon particles. In the case where the crystalline silicon particles obtained by the production method of the present invention are used in a photoelectric conversion device, good photoelectric conversion characteristics can be obtained.

  Hereinafter, a method for producing crystalline silicon particles of the present invention will be described in detail with reference to the accompanying drawings.

  1A to 1D are schematic cross-sectional views showing an embodiment of the method for producing crystalline silicon particles of the present invention. In FIG. 1A, reference numeral 101 denotes crystalline silicon particles, and 201 and 202 denote a lower rotation surface plate and upper rotation having high rigidity as an apparatus for forming a work-affected layer by polishing on the surface of the crystalline silicon particles 101. Reference numeral 203 denotes a free abrasive grain. FIGS. 1B to 1D are cross-sectional views for each process showing a large number of crystalline silicon particles 101 placed in layers on a base plate. In FIGS. 1B to 1D, reference numeral 301 denotes a base plate.

  In the method for producing crystalline silicon particles of the present invention, the silicon melt is discharged as particles from the crucible nozzle part containing the silicon melt and dropped, and the granular silicon melt is cooled and solidified during the dropping. The crystalline silicon particles 101 are produced by the above, and then the surface of the crystalline silicon particles 101 is polished to form a work-affected layer on the surface layer portion of the crystalline silicon particles 101, and then the atmosphere gas or nitrogen gas composed of nitrogen gas In an atmosphere gas containing as a main component, the crystalline silicon particles 101 are heated to a temperature not higher than the melting point of silicon to form a silicon nitride film on the surface of the crystalline silicon particles 101, and then the atmosphere gas or oxygen gas composed of oxygen gas And the crystalline silicon particles 101 are heated in an atmospheric gas composed of an inert gas to melt the silicon inside the silicon nitride film. Cooling to a configuration in which a single crystal solidifying.

  First, as shown in FIG. 3, semiconductor grade crystalline silicon is used as a material for the crystalline silicon particles 101, which is melted in a container using infrared rays or a high frequency induction coil, and then the molten silicon is melted into granular silicon. Polycrystalline crystalline silicon particles 101 are obtained by a melt drop method (jet method) or the like in which the liquid falls freely.

  In the crystal silicon particle production apparatus (jet apparatus) by the melt-drop method of FIG. 3, 1 is a crucible, 1a is a nozzle portion provided at the bottom of the crucible 1, and 2 is a longitudinal direction below the crucible 1 in the vertical direction. 3 is a gas introduction tube made of quartz or the like provided in the crucible 1, 4 is a granular silicon melt, and 5 is a crystalline silicon particle. The crucible 1 is a container for heating and melting silicon particles as a raw material to form a silicon melt and discharging it from the nozzle portion 1a at the bottom as a granular silicon melt 4. The silicon melt heated and melted in the crucible 1 is discharged from the nozzle portion 1 a into the tube 2, and becomes a granular silicon melt 4 that falls inside the tube 2. 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. When the reaction with the silicon melt is large, the material of the crucible 1 is mixed in the crystalline silicon particles 5 as impurities in a large amount. Therefore, it is not preferable.

  For example, the material of the crucible 1 is carbon, silicon carbide sintered body, silicon carbide crystal, boron nitride sintered body, silicon oxynitride sintered body, quartz, quartz crystal, silicon nitride sintered body, oxidation Aluminum sintered bodies, sapphire, magnesium oxide sintered bodies and the like are preferable. Moreover, the composite of these materials, a mixture, or a combination may be sufficient. Further, a silicon carbide film, a silicon nitride film, or a silicon oxide film may be coated on the surface of the base made of the above material. Moreover, as a heating method for heating the raw material to the melting point or more in the crucible 1, electromagnetic induction heating, resistance heating, or the like is suitable.

  The nozzle portion 1a is made of silicon carbide (silicon carbide crystal or silicon carbide sintered body) or silicon nitride (silicon nitride sintered body).

Polycrystalline silicon particles 101 produced by the melt drop method are usually doped with a dopant in order to obtain a desired conductivity type and resistance value. As dopants for silicon, boron, aluminum, gallium, indium, phosphorus, arsenic, and antimony are used. However, boron or phosphorus is used because it has a large segregation coefficient for silicon and a small evaporation coefficient when silicon is melted. desirable. The dopant concentration is about 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ³ added to the silicon crystal material.

  At the time when the crystalline silicon particles 101 are obtained by this melting and dropping method, the crystalline silicon particles 101 have a substantially spherical shape, a teardrop type, a streamline type, or a connected type in which a plurality of particles are connected. It is. When a photoelectric conversion device is manufactured using the polycrystalline silicon particles 101 as it is, good photoelectric conversion characteristics cannot be obtained. The cause is due to metallic impurities such as Fe, Cr, Ni, and Mo normally contained in the polycrystalline crystalline silicon particle 101 and the carrier recombination effect at the crystal grain boundary of the polycrystalline crystalline silicon particle 101. Is.

  In order to improve this, by the method for producing crystalline silicon particles of the present invention, a work-affected layer is formed by polishing on the surface of the crystalline silicon particles 101 obtained by the melt-drop method, and then an atmosphere composed of nitrogen gas Polycrystalline silicon particles 101 are heated to a temperature (500 to 1400 ° C.) below the melting point (1414 ° C.) of silicon in a temperature controlled heating furnace in an atmosphere gas containing gas or nitrogen gas as a main component. A silicon nitride film is formed on the surface of the crystalline silicon particle 101, and then the crystalline silicon particle 101 is heated in an atmospheric gas composed of oxygen gas or an atmospheric gas composed of oxygen gas and an inert gas to form silicon inside the silicon nitride film. Is melted, cooled and solidified to form a single crystal.

  First, the formation of a work-affected layer by polishing will be described. The lower rotary platen 201 and the upper rotary platen 202 shown in FIG. 1 (a) function as a polishing device for the surface of the crystalline silicon particles 101, and at least one of them can rotate. Well, both may rotate. Moreover, when both rotate, you may rotate in a mutually opposite direction, or you may make it rotate in the same direction and each rotation speed differs.

  Further, the rotation axis of the lower rotation platen 201 and the rotation axis of the upper rotation platen 202 may be fixed, or one rotation axis is fixed and the other rotation axis is set to a predetermined locus (circular shape, elliptical shape). Or the like) may be exercised. Alternatively, both the rotational axes may be moved so as to draw a predetermined locus (circular shape, elliptical shape, etc.). Further, at least one of the lower rotating surface plate 201 and the upper rotating surface plate 202 may be structured to be movable in the vertical direction. The material of the lower rotating surface plate 201 and the upper rotating surface plate 202 is SUS (stainless steel) or the like. Further, the shape of the lower rotating surface plate 201 and the upper rotating surface plate 202 in a plan view is a circle, a square, or the like, and may be other shapes.

  Further, one or a plurality of crystalline silicon particles 101 can be arranged between the lower rotating platen 201 and the upper rotating platen 202. If a plurality of crystal silicon particles 101 are arranged, for example, about 100 to 100,000. Deploy. Further, when a plurality of crystalline silicon particles 101 are arranged between the lower rotating surface plate 201 and the upper rotating surface plate 202, all the crystalline silicon particles 101 are considered in consideration of the difference in size of the individual crystalline silicon particles 101. A rubber layer, a rubber film, a rubber sheet, or the like is applied to at least one of the pressing surfaces (contact surfaces with the crystalline silicon particles 101) of the lower rotating surface plate 201 and the upper rotating surface plate 202 so that pressure is applied to the surface of the rotating surface plate 201 substantially uniformly. An elastic layer may be provided.

  Generally, silicon carbide, alumina, diamond or the like is used as the material of the loose abrasive grains 203. When the loose abrasive 203 is not used, a grindstone or a grindstone plate made of silicon carbide, alumina, diamond, or the like can be installed on at least one pressing surface of the lower rotary platen 201 and the upper rotary platen 202. is there.

  In order to form a work-affected layer by polishing in the surface layer portion of the crystalline silicon particles 101, for example, loose abrasive 203 made of SiC having an average particle diameter of about 30 μm is used, the lower rotating platen 201 is fixed, and the upper rotating The platen 202 is rotated at a rotational speed of 5 to 250 rpm, and polishing is performed for 3 to 30 minutes. At this time, the upper rotating surface plate 202 may be moved downward in the axial direction to apply a pressure of about 0.01 MPa to 0.1 MPa to the crystalline silicon particles 101. Thereby, a work-affected layer having a thickness of about 10 μm is formed on the surface layer portion of the crystalline silicon particles 101.

  The work-affected layer generally has a structure in which an amorphous layer, a polycrystalline layer, a mosaic layer, a crack layer, a strain layer, and the like exist from the surface side, and these five layers are collectively referred to as a work-affected layer. . It is assumed that the work-affected layer in the present invention is actually composed of an amorphous layer, a polycrystalline layer, a mosaic layer, and a crack layer. In addition, the work-affected layer is lost by the remelting (remelting) step for single crystallization of the crystalline silicon particles 101.

  The presence of the work-affected layer can be identified by confirming the broadening of the half-value width of the Raman spectrum by Raman spectroscopy or the like.

  Next, the pressure of the atmosphere gas composed of nitrogen gas or the atmosphere gas containing nitrogen gas as a main component in the silicon nitride film forming step (pre-step of single crystallization) is preferably about 0.01 to 0.2 MPa. If the pressure is less than 0.01 MPa, the film thickness of the silicon nitride film is easily reduced or the film quality is deteriorated due to evaporation of nitrogen or oxygen from the silicon nitride film. If the pressure exceeds 0.2 MPa, the film thickness variation of the silicon nitride film is likely to occur. .

  The thickness of the silicon nitride film formed on the surface of the crystalline silicon particles 101 may be about 100 nm to 10 μm. If the thickness is less than 100 nm, the silicon nitride film is easily broken when the silicon inside the crystalline silicon particles 101 is melted. When the thickness exceeds 10 μm, the silicon nitride film tends to be spheroidized by surface tension when silicon inside the crystalline silicon particles 101 is melted, whereas the silicon nitride film is too thick to be easily deformed.

  The pressure of the atmospheric gas composed of oxygen gas or the atmospheric gas composed of oxygen gas and inert gas in the subsequent step (remelting (remelting step for single crystallization)) is preferably about 0.01 to 0.2 MPa. If it is less than 0.01 MPa, the film thickness of the silicon nitride film is reduced and the film quality is liable to deteriorate due to evaporation of nitrogen and oxygen from the silicon nitride film. If it exceeds 0.2 MPa, the shape cannot be kept stable when silicon inside the crystalline silicon particles 101 is melted, and shape control becomes difficult.

  In the case where oxygen gas and inert gas are used in the post-process, the oxygen gas may be contained in an amount of 20% by volume or more, and the inert gas such as argon gas may be contained in an amount of 80% by volume or less.

  In order to fabricate the single crystal crystalline silicon particles 101, as shown in FIG. 1B, a large number (for example, several hundred to several thousand) of polycrystalline silicon particles 101 are formed on the top surface of the base plate 301. Are stacked in two or more layers. The multi-layered placement in the present invention is a state in which the substantially spherical crystalline silicon particles 101 are placed so as to form a plurality of layers in the thickness direction when viewed in the longitudinal sectional view of FIG. , Shows a state of being packed and mounted in close packing.

  Although a large number of crystalline silicon particles 101 may be placed on the base plate 301, they may be placed in a single layer. By placing them in multiple layers, the crystalline silicon particles 101 can be arranged at high density, and a large number of crystalline silicon particles 101 can be single-crystallized at a time, and can be single-crystallized inexpensively and with high productivity. Crystalline silicon particles 101 can be manufactured. Therefore, the crystalline silicon particles 101 used for the photoelectric conversion device and the like can be efficiently manufactured.

  When a large number of crystalline silicon particles 101 are stacked on the base plate 301, the number of layers is not particularly limited, but may be, for example, about 2 to 150 layers.

  The large number of crystalline silicon particles 101 placed on the base plate 301 may be in contact with each other. The base plate 301 is preferably a box-like or plate-like one without an upper lid. In the case of a plate-like shape, the base plate 301 may be stacked and used. Quartz glass, mullite, aluminum oxide, silicon carbide, single crystal sapphire, etc. are suitable for the material of the base plate 301 in order to suppress the reaction with the crystalline silicon particles 101, but it has excellent heat resistance, durability, chemical resistance and cost. Quartz glass is preferred because it is cheap and easy to handle.

  Next, the base plate 301 on which the crystalline silicon particles 101 are placed is introduced into a heating furnace (not shown), and the crystalline silicon particles 101 are heated. Various types of heating furnaces can be used depending on the type of semiconductor material, but since silicon is used as the semiconductor material, a resistance heating type or induction heating type atmosphere firing furnace used for firing ceramics, or a semiconductor element A horizontal oxidation furnace or the like generally used in the manufacturing process is suitable. A resistance heating type atmosphere firing furnace used for firing ceramics is desirable because it is relatively easy to raise a temperature of 1500 ° C. or higher, and a large-sized one capable of mass production of crystalline silicon particles 101 can be obtained at a relatively low cost. .

  Before heating in the atmosphere firing furnace, it is desirable to perform solution cleaning in advance by the RCA method (cleaning method by RCA) in order to remove metal, foreign matter, and the like attached to the surface of the crystalline silicon particles 101. The RCA method is a cleaning method generally used in a semiconductor device manufacturing process as a standard cleaning process for silicon wafers. In the first stage of three stages, ammonium hydroxide and hydrogen peroxide are used. The oxide film and the silicon surface layer on the surface of the silicon wafer are removed with an aqueous solution of, and the oxide film attached in the previous step is removed with a hydrogen fluoride aqueous solution in the second step, and chlorination is performed in the third step. A natural oxide film is formed by removing heavy metals and the like with an aqueous solution of hydrogen and hydrogen peroxide.

  In order to prevent contamination from furnace materials and heating elements in the heating furnace, it is desirable to install a bell jar in the heating furnace that covers the crystalline silicon particles 101 placed on the base plate 301. Quartz glass, mullite, aluminum oxide, silicon carbide, single crystal sapphire, etc. are suitable as the material for the bell jar, but quartz glass is preferred because of its excellent heat resistance, durability, chemical resistance and low cost. is there.

  In the process of heating the crystalline silicon particles 101 in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component in a heating furnace to raise the temperature to a temperature lower than the melting point of silicon (1414 ° C.), A silicon nitride film is formed on the surface of the crystalline silicon particles 101. The formation temperature of the silicon nitride film is preferably 500 ° C. or higher and 1400 ° C. or lower. When the temperature is lower than 500 ° C., the growth rate of the silicon nitride film is slow and it takes time to obtain a sufficient thickness. When the temperature is higher than 1400 ° C., the thickness of the silicon nitride film becomes uneven or the crystalline silicon particles 101 This is not preferable because some melting occurs or the particle shape collapses.

  Since the silicon nitride film formed on the surface of the crystalline silicon particles 101 has a higher coating density and higher strength per unit film thickness than a silicon oxide film or the like, the crystalline silicon particles 101 such as contaminants and impurities are It has the effect that the diffusion preventing power to the inside is large.

  Further, the silicon nitride film preferably contains oxygen. The oxygen content is preferably about 10 mol% or less. If it exceeds 10 mol%, the film quality tends to be deteriorated due to a change in crystal structure or an increase in crystal defects in the silicon nitride film. Further, when the silicon nitride film contains oxygen, the flexibility of the film is further improved. In order to include oxygen in the silicon nitride film, there is a method in which heat treatment is performed in an atmosphere gas in which an appropriate amount of oxygen gas is mixed with nitrogen gas.

  Further, the atmospheric gas in the heating furnace when forming the silicon nitride film on the surface of the crystalline silicon particles 101 preferably has a nitrogen gas partial pressure of 70% or more. When the nitrogen gas partial pressure in the atmospheric gas is less than 70%, the crystalline silicon particles 101 are likely to be coalesced in the subsequent single crystallization step, and the strength of the silicon nitride film is deteriorated. In a state where the two are stacked in layers, the weight of the upper crystalline silicon particles 101 makes it easier for the lower crystalline silicon particles 101 to collapse during melting.

  In addition, each gas partial pressure in the atmospheric gas in a heating furnace can be adjusted with each gas flow rate with respect to the total gas flow rate. Ambient gas is supplied into the bell jar through a gas filter from a gas supply means such as a gas flow meter or a mass flow meter. A mechanism for adjusting a gas pressure and a gas concentration by a device that supplies the gas to the gas supply means Anything that has

  Next, as shown in FIG. 1C, the crystalline silicon particles 101 are heated to a temperature (1414) higher than the melting point (1414 ° C.) of silicon in an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and inert gas. The temperature is raised to over 1480 ° C. The steps shown in FIGS. 1B and 1C may be performed separately or continuously.

  The base plate 301 also functions as a solidification starting point when the crystalline silicon particles 101 are cooled and solidified after being melted. By placing a large number of crystalline silicon particles 101 on the top surface of the base plate 301 in this way, a solidification starting point can be set at a contact portion between each crystalline silicon particle 101 and the base plate 301. The solidification (single crystallization) direction can be set from this one pole toward the upper facing pole. As a result, it is possible to solidify in one direction without using a seed crystal, and the crystallinity of the crystalline silicon particles 101 can be greatly improved by suppressing the generation of subgrains and the like.

  In addition, since a large number of crystal silicon particles 101 are placed in a multi-layered manner, a contact portion with the crystal silicon particles on the base plate 301 that has been crystallized first is set as a solidification starting point and is adjacent thereto. The crystalline silicon particles 101 can be solidified, and the solidification spreads in a chain reaction toward the upper part of the stacked layers, so that the crystallinity of a large number of crystalline silicon particles 101 can be greatly improved. .

  Since the size of the crystalline silicon particles 101 is usually substantially spherical, the average particle diameter is preferably 1500 μm or less, and the shape is preferably closer to a sphere. However, the shape of the crystalline silicon particles 101 is not limited to a spherical shape, and may be a cubic shape, a rectangular parallelepiped shape, or other irregular shapes.

  When the size of the crystalline silicon particle 101 is larger than 1500 μm, the thickness of the silicon nitride film formed on the surface of the crystalline silicon particle 101 becomes relatively thin with respect to the crystalline silicon particle 101 main body. It becomes difficult to keep the shape of the crystalline silicon particles 101 stable when the silicon inside 101 is melted. In addition, it becomes difficult to completely melt the silicon inside the crystalline silicon particles 101, and when the melting is incomplete, subgrains are likely to occur. On the other hand, when the diameter of the crystalline silicon particles 101 is as small as less than 30 μm, it is difficult to stably maintain the shape of the crystalline silicon particles 101 when the silicon inside the crystalline silicon particles 101 is melted.

  Accordingly, the diameter of the crystalline silicon particles 101 is preferably 30 μm to 1500 μm, thereby maintaining the shape of the crystalline silicon particles 101 stably, and the crystalline silicon having a good quality crystallinity with a spherical shape without generation of subgrains. The particles 101 can be manufactured stably.

  The atmospheric gas in the heating furnace in the single crystallization process (post process) in which the crystalline silicon particles 101 are heated to a temperature higher than the melting point of silicon (1414 ° C.) can be an atmospheric gas composed of oxygen gas or oxygen gas and non-crystalline gas. The atmosphere gas is composed of an active gas. Argon gas, nitrogen gas, helium gas, and hydrogen gas are suitable as the inert gas, but argon gas or nitrogen gas is preferred from the viewpoint of low cost and ease of handling. In addition, each gas partial pressure in the atmospheric gas in a heating furnace can be adjusted with each gas flow rate with respect to the total gas flow rate. For example, the atmospheric gas is supplied from the gas supply means into the bell jar through the gas filter. Any device that supplies gas to the gas supply means may have a mechanism capable of adjusting the gas pressure and the gas concentration.

  When the atmospheric gas in the heating furnace in the subsequent process is composed of oxygen gas and inert gas, the oxygen gas partial pressure is preferably 20% or more. When the oxygen gas partial pressure in the atmospheric gas is less than 20%, oxygen evaporation from the silicon nitride film is easily promoted, and the shape cannot be kept stable when silicon inside the crystalline silicon particles 101 is melted, making it difficult to control the shape. Become.

  The crystalline silicon particles 101 are heated to a temperature not lower than the melting point (1414 ° C.) of silicon and preferably not higher than 1480 ° C. During this period, silicon inside the silicon nitride film on the surface is melted in the crystalline silicon particles 101. At this time, the silicon nitride film formed on the surface of the crystalline silicon particles 101 can maintain the shape of the crystalline silicon particles 101 while melting the inner silicon. However, when the temperature of the crystalline silicon particles 101 is difficult to maintain stably, for example, in the case of the crystalline silicon particles 101, the temperature inside the crystalline silicon particles 101 is increased to a temperature exceeding 1480 ° C. When the silicon melts, it becomes difficult to keep the shape of the crystalline silicon particles 101 stable, and the adjacent crystalline silicon particles 101 are likely to coalesce, and the crystalline silicon particles 101 are easily fused to the base plate 301.

  Note that the thickness of the silicon nitride film formed on the surface of the crystalline silicon particles 101 is preferably 100 nm or more in the above average particle diameter range of the crystalline silicon particles 101. When the thickness of the silicon nitride film is less than 100 nm, the silicon nitride film on the surface of the crystalline silicon particles 101 is easily broken when the silicon inside the crystalline silicon particles 101 is melted. Also, if the silicon nitride film has a thickness of 100 nm or more and has the required strength, the silicon inside the crystalline silicon particles 101 tends to be spheroidized by the surface tension when melted, whereas it is nitrided in the above temperature range. Since the silicon film can be sufficiently deformed, the crystalline silicon particles 101 obtained by single-crystallizing the inside can be formed into a shape close to a true sphere.

  On the other hand, when the thickness of the silicon nitride film exceeds 10 μm, the silicon nitride film is not easily deformed in the above temperature range, and the shape of the obtained crystalline silicon particles 101 is not preferably close to a true sphere. .

  Therefore, the thickness of the silicon nitride film on the surface of the crystalline silicon particles 101 is preferably 100 nm to 10 μm with respect to the above average particle diameter range (30 μm to 1500 μm), and thereby, a good value close to a true sphere is obtained. Crystal silicon particles 101 having a shape can be stably obtained. Further, by using the crystalline silicon particles 101 for a photoelectric conversion device, a photoelectric conversion device having excellent conversion efficiency can be obtained.

  Next, as shown in FIG. 1D, in order to solidify the molten silicon inside the silicon nitride film in the crystalline silicon particles 101, the temperature is lowered to a temperature of about 1400 ° C. or lower, which is lower than the melting point of silicon, and is solidified. . At this time, it is solidified while being maintained at a relatively high temperature (about 1360 ° C.) below the melting point of silicon. In this case, the contact portion between the crystalline silicon particles 101 and the base plate 301 is used as a solidification starting point (one pole) and upward. Solidification proceeds in one direction toward the opposite poles of the electrode, so that unidirectional solidification occurs starting from the contact point with the already solidified crystalline silicon particle 101 and is inherited by the entire crystalline silicon particle 101 as it is. Then, the crystal grows, and the obtained crystalline silicon particle 101 becomes a single crystal, so that the crystallinity can be greatly improved.

  Further, if a large number of crystalline silicon particles 101 are placed in a multi-layered manner, the crystal adjacent to the upper side is set with the contact portion with the crystalline silicon particles on the base plate 301 crystallized first as a solidification starting point. Since the silicon particles 101 can be solidified and solidification spreads in a continuous manner toward the upper part of the stacked layers, the crystallinity of a large number of crystalline silicon particles 101 can be greatly improved.

  Moreover, it is preferable to perform a thermal annealing treatment on the crystalline silicon particles 101 during the solidification of the molten crystalline silicon particles 101, for example, a thermal annealing treatment for 30 minutes or more at a constant temperature of 1000 ° C. or higher. By performing this thermal annealing treatment, the strain in the crystal of the crystalline silicon particles 101 generated at the time of solidification, and the interface strain generated at the interface between the silicon nitride film on the surface of the crystalline silicon particles 101 and the inner crystalline silicon are alleviated and removed. Thus, the crystalline silicon particles 101 having good crystallinity can be obtained.

  According to the method for producing crystalline silicon particles of the present invention, crystalline silicon particles having good crystallinity and a reduced amount of unnecessary impurities can be stably produced as described above.

  In the manufacturing method of the present invention, it is preferable that the silicon nitride film is removed after the crystalline silicon particles 101 are monocrystallized. Thereby, metal impurity containing parts such as Fe, Cr, Ni, Mo segregated on the surface layer part of the crystalline silicon particles 101 can be removed, and the crystalline silicon particles 101 obtained by the production method of the present invention are photoelectrically converted. When used in an apparatus, good photoelectric conversion characteristics can be obtained.

  Next, an example of an embodiment of the photoelectric conversion device of the present invention is shown in the cross-sectional view of FIG. In FIG. 2, 406 is a crystalline silicon particle of the first conductivity type (for example, p-type), 407 is a conductive substrate, 408 is a bonding layer between the crystalline silicon particle 406 and the conductive substrate 407, 409 is an insulating material, and 410 is a first material. A two-conductivity type (for example, n-type) semiconductor layer (semiconductor portion), 411 is a translucent conductor layer, and 412 is an electrode.

  In the photoelectric conversion device using the crystalline silicon particles 406 of the present invention, a large number of crystalline silicon particles 406 of the first conductivity type (for example, p-type) are formed on one main surface of the conductive substrate 407, in this example, the upper surface. The lower part is bonded to the conductive substrate 407 by, for example, a bonding layer 408, and an insulating substance 409 is interposed between adjacent ones of the crystalline silicon particles 406 and the upper parts of the crystalline silicon particles 406 are exposed from the insulating substance 409. The second conductive type semiconductor layer 410 and the translucent conductor layer 411 are sequentially provided on the crystalline silicon particles 406.

  In addition, when using this photoelectric conversion apparatus as a solar cell, the electrode 412 is deposited and formed in a predetermined pattern shape on the translucent conductor layer 411, for example, a finger electrode and a bus bar electrode. .

  The crystalline silicon particles 406 in the photoelectric conversion device of the present invention having the above-described configuration are produced by the above-described method for producing crystalline silicon particles of the present invention. Since the crystalline silicon particles 406 are produced by the method for producing crystalline silicon particles of the present invention, the high-quality crystalline silicon particles 406 having an extremely low impurity concentration can be obtained, so that high photoelectric conversion efficiency can be obtained. Minority carrier lifetime, which is an important factor, can be improved. Accordingly, crystalline silicon particles 406 that are preferable as a component of the photoelectric conversion device can be obtained.

The method for producing crystalline silicon particles 406 in the photoelectric conversion device of the present invention is the same as the method for producing crystalline silicon particles described above. The crystalline silicon particle 101 which is a starting material of the crystalline silicon particle 406 is preferably doped with a p-type semiconductor impurity as a first conductivity type dopant so as to have a desired resistance value. As the p-type dopant, boron, aluminum, gallium and the like are preferable, and the addition amount is preferably 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ² . The crystalline silicon particles 406 produced by the above-described method for producing crystalline silicon particles of the present invention are used for producing the photoelectric conversion device of the present invention. The photoelectric conversion device can be used as a power generation unit, and a photovoltaic power generation device configured to supply the generated power from the power generation unit to a load can be obtained.

  The example shown in FIG. 2 is a photoelectric conversion device manufactured using the crystalline silicon particles 406 obtained as described above. In order to obtain this photoelectric conversion device, first, the silicon nitride film formed on the surface of the crystalline silicon particles 406 is removed by etching with hydrofluoric acid. Further, in order to remove the interfacial strain between the silicon nitride film and the crystalline silicon particle 406 and impurities such as p-type dopant, oxygen, carbon, and metal segregated on the surface of the crystalline silicon particle 406, the surface of the crystalline silicon particle 406 is removed. May be removed by etching with hydrofluoric acid or the like. The thickness of the surface layer of the crystalline silicon particles 406 removed at that time is preferably 100 μm or less in the radial direction.

  Next, a large number of crystalline silicon particles 406 are arranged on a conductive substrate 407 made of aluminum or the like. Then, the crystalline silicon particles 406 are bonded to the conductive substrate 407 through the bonding layer 408 generated by heating the whole in a reducing atmosphere. Note that the bonding layer 408 is, for example, an alloy of aluminum and silicon.

  At this time, by using the conductive substrate 407 as an aluminum substrate or a metal substrate including at least aluminum on the surface, the crystalline silicon particles 406 can be bonded at a low temperature, and a light-weight and low-cost photoelectric conversion device. Can be provided. In addition, by making the surface of the conductive substrate 407 rough, reflection of incident light reaching the non-light-receiving region on the surface of the conductive substrate 407 can be made random, and incident light is obliquely inclined in the non-light-receiving region. The light can be reflected and re-reflected toward the surface of the photoelectric conversion device, and incident light can be effectively used by further photoelectrically converting the light at the photoelectric conversion portion of the crystalline silicon particles 406.

  Next, an insulating material 409 is placed on the conductive substrate 407 so that the adjacent crystalline silicon particles 406 are adjacent to each other, and at least the top of these crystalline silicon particles 406 is formed from the insulating material 409. Place it exposed.

  Here, the surface shape of the insulating material 409 between the adjacent crystalline silicon particles 406 is made concave so that the crystalline silicon particle 406 side is high, thereby covering the insulating material 409 and the top thereof. Due to the difference in refractive index with the transparent sealing resin formed in this way, irregular reflection of incident light on the crystalline silicon particles 406 can be promoted in a non-light-receiving region without the crystalline silicon particles 406.

  Next, a second conductive type (for example, n-type) semiconductor layer 410 and a translucent conductor layer 411 are provided on the exposed upper portions of the crystalline silicon particles 406. The semiconductor layer 410 is provided by forming the amorphous or polycrystalline semiconductor layer 410 or by forming the semiconductor layer 410 by a thermal diffusion method or the like. At this time, since the crystalline silicon particles 406 are p-type, the silicon layer which is the semiconductor layer 410 is an n-type semiconductor layer 410. Further, a light-transmitting conductor layer 411 is formed over the semiconductor layer 410. And in order to take out desired electric power as a solar cell, silver paste etc. are apply | coated to a predetermined pattern shape, and the electrodes 412, such as a grid electrode or a finger electrode and a bus-bar electrode, are formed. In this manner, by using the conductive substrate 407 as one electrode and the electrode 412 as the other electrode, a photoelectric conversion device as a solar cell can be obtained.

  In order to form the second conductivity type semiconductor layer 410, the crystal silicon particles 406 are formed on the surface of the crystal silicon particles 406 by a thermal diffusion method with low process costs prior to the bonding of the crystal silicon particles 406 to the conductive substrate 407. May be. In this case, for example, P, As, Sb of group V, B, Al, Ga, etc. of group III are used as the second conductivity type dopant, and the crystalline silicon particles 406 are accommodated in a diffusion furnace made of quartz. The semiconductor layer 410 of the second conductivity type is formed on the surface of the crystalline silicon particles 406 by heating while introducing.

  Next, an example is described along a manufacturing process about the manufacturing method of the crystalline silicon particle of the present invention.

As shown in FIG. 1 (a), first, 1000 pieces of crystalline silicon particles 101 having a boron concentration of 0.6 × 10 ¹⁶ atoms / cm ³ and an average particle diameter of 500 μm were rotated and fixed on the lower side of the lapping apparatus. Arranged on the board 201, the upper rotating surface plate 202 was lowered. Next, the lower rotary platen 201 is rotated at 20 rpm and the upper rotary platen 202 is rotated at 5 rpm so that the upper and lower rotary platens 202 and 201 rotate in directions opposite to each other, thereby releasing SiC having an average particle diameter of 30 μm. Using the abrasive grains 203, the surface of the crystalline silicon particles 101 was polished for 5 minutes.

  It was confirmed by Raman spectroscopy that a work-affected layer having a large number of microcracks and the like was formed on the surface layer portion of the crystal silicon particles 101 whose surface was polished and having a thickness of about 10 μm.

  Next, as shown in FIG. 1B, a large number (1000 pieces) of crystalline silicon particles 101 are placed in a multilayer manner on a quartz glass box-shaped base plate 301, and the atmosphere is fired as a heating furnace. It was housed in a quartz glass bell jar installed inside the furnace. Then, heating is performed while introducing nitrogen gas from a gas supply device, and heating is performed to 1300 ° C. below the melting point of silicon at a nitrogen gas pressure of 0.1 MPa and held for 60 minutes to form a silicon nitride film on the surface of the crystalline silicon particles 101 did. After heating at 1300 ° C. for 60 minutes, the temperature was lowered to room temperature.

  Next, as shown in FIGS. 1C and 1D, an oxygen gas or a mixed gas (oxygen gas and argon gas) (see Table 1) is introduced from the gas supply device while the oxygen gas pressure is 0.02 MPa. The crystalline silicon particles 101 are heated to 1440 ° C. above the melting point of silicon and held for 5 minutes to melt the silicon inside the silicon nitride film on the surface of the crystalline silicon particles 101, and then cooled down at a rate of 2 ° C. per minute. The crystalline silicon particles 101 were solidified. Thereafter, the temperature was further lowered to 1250 ° C., and thermal annealing treatment was performed for 120 minutes while introducing argon gas as an inert gas. After this thermal annealing treatment, the temperature was lowered to around room temperature.

  The silicon nitride film formed on the surface of the recovered crystalline silicon particles 101 was removed with hydrofluoric acid, and the surface of the crystalline silicon particles 101 was etched away with a thickness of 20 μm with hydrofluoric acid.

The crystalline silicon particles 101 are placed on a quartz boat, introduced into a quartz tube controlled at 900 ° C., POCl ₃ gas is bubbled with nitrogen and sent into the quartz tube, and the crystalline silicon is obtained in 30 minutes by a thermal diffusion method. An n-type semiconductor layer 410 having a thickness of about 1 μm was formed on the surface of the particle 101, and then the surface oxynitride film was removed with hydrofluoric acid.

  Next, an aluminum substrate having a size of 50 mm × 50 mm × thickness 0.3 mm was used as the conductive substrate, and 1000 crystalline silicon particles were closely packed on the upper surface. Thereafter, heating is performed in a reducing atmosphere furnace of nitrogen gas containing 5% by volume of hydrogen gas at 600 ° C. exceeding 577 ° C., which is the eutectic temperature of aluminum and silicon, and the lower part of the crystalline silicon particles is used as a conductive substrate. It was made to join. At this time, a bonding layer made of a eutectic of aluminum and silicon was formed in the portion where the crystalline silicon particles were in contact with the conductive substrate, and exhibited strong adhesive strength.

  Furthermore, between the crystalline silicon particles from above, an upper portion of them is exposed, an insulating material made of polyimide resin is applied and dried, and a conductive substrate that becomes the lower electrode, and a translucent conductor that becomes the upper electrode The layers were electrically isolated from each other. A translucent conductor layer as an upper electrode film was formed on the entire surface with a thickness of about 100 nm by sputtering.

  Finally, silver paste was patterned in a grid shape with a dispenser to form an electrode composed of finger electrodes and bus bar electrodes. The silver paste pattern was fired at 500 ° C. in the atmosphere.

  And when manufacturing the photoelectric conversion device of the present invention as described above, the presence or absence of a work-affected layer forming step on the surface of crystalline silicon particles, the presence or absence of a silicon nitride film forming step, a melting step in oxygen gas or a mixed gas In addition, the crystalline silicon particles are single-crystallized in a state where the crystalline silicon particles are placed in a single layer on a quartz glass box-shaped base plate, or in a state of being placed in multiple layers in close packing. The coalescence rate of was examined. The results are shown in Table 1 as Examples 1 to 4 and Comparative Examples 1 and 2.

In addition, for Examples 1 to 4 and Comparative Examples 1 and 2 of the photoelectric conversion device of the present invention obtained by the above-described manufacturing method, photoelectric conversion efficiency (units) showing the electrical characteristics of the photoelectric conversion device with a solar simulator of AM1.5 %) (Expressed as “conversion efficiency” in Table 1). The results are shown in Table 1.

  As shown in Table 1, a silicon oxide film was formed on the surface of the crystalline silicon particles in an atmosphere gas composed of oxygen gas without forming a work-affected layer by polishing on the surface of the crystalline silicon particles, and was prepared by melting and solidifying. Crystalline silicon particles (Comparative Examples 1 and 2) and crystalline silicon produced by forming and melting and solidifying a silicon oxide film on the surface of crystalline silicon particles in an atmospheric gas composed of oxygen gas without forming a silicon nitride film Compared with the particles (Comparative Examples 3 and 4), a work-affected layer is formed by polishing on the surface of the crystalline silicon particles, a silicon nitride film is formed on the surface of the crystalline silicon particles, and an atmospheric gas or mixed gas composed of oxygen gas In the crystalline silicon particles (Examples 1 to 4) produced by melting and solidifying in an atmospheric gas composed of (oxygen gas and inert gas), the coalescence rate is low compared with Comparative Examples 1 to 4 and good It was the result.

  The reason why the coalescence rate of Example 3 is larger than the coalescence rate of Example 1 and the coalescence rate of Example 4 is larger than the coalescence rate of Example 2 is that argon gas is used in the atmospheric gas. Therefore, it is considered that the surface bonding state of the silicon nitride film has changed and the surface tension of the crystalline silicon particles has also changed, making it easier to unite.

  Moreover, in Examples 1-4, the conversion efficiency was high and it was a favorable result with respect to Comparative Examples 1-4.

  The reason why the conversion efficiencies of Examples 1 and 2 are larger than the conversion efficiencies of Examples 3 and 4 is that crystal deterioration due to the occurrence of subgrains at the contact portion between the crystalline silicon particles is reduced. It is done.

  In addition, this invention is not limited to the above embodiment and Example, A various change may be added in the range which does not deviate from the summary of this invention. For example, in order to heat and melt the crystalline silicon particles, a method of melting by irradiating light energy from above the crystalline silicon particles placed on the upper surface of the base plate instead of a heating furnace may be used.

1 shows an example of an embodiment of a method for producing crystalline silicon particles according to the present invention, wherein (a) is a schematic cross-sectional view showing a state in which a work-affected layer is formed by polishing on the surface of crystalline silicon particles; ) To (d) are schematic cross-sectional views for each process showing a state in which crystalline silicon particles are placed in a multilayered manner on a base plate. It is sectional drawing which shows an example of embodiment about the photoelectric conversion apparatus produced using the crystalline silicon particle obtained by the manufacturing method of this invention. It is sectional drawing of the jet apparatus used for the manufacturing method of the crystalline silicon particle of this invention.

Explanation of symbols

101 ... crystalline silicon particle 201 ... lower rotating surface plate 202 ... upper rotating surface plate 203 ... free abrasive grain 301 ... base plate 406 ... crystalline silicon particle 407 ... conductive Substrate 408 ... Bonding layer 409 ... Insulating material 410 ... Semiconductor layer 411 ... Translucent conductor layer 412 ... Electrode

Claims (4)

  The silicon melt is discharged as particles from the nozzle part of the crucible containing the silicon melt and dropped, and the crystalline silicon particles are produced by cooling and solidifying the granular silicon melt while dropping. Forming a work-affected layer on a surface layer portion of the crystalline silicon particles by polishing the surface of the crystalline silicon particles, and then in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component, The crystalline silicon particles are heated to a temperature below the melting point of silicon to form a silicon nitride film on the surface of the crystalline silicon particles, and then in an atmospheric gas composed of oxygen gas or an atmospheric gas composed of oxygen gas and inert gas The crystalline silicon particles are heated to melt the silicon inside the silicon nitride film, and the temperature is lowered and solidified to form a single crystal. Method for producing a crystalline silicon grains.   2. The method for producing crystalline silicon particles according to claim 1, wherein the silicon nitride film contains oxygen.   In an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and an inert gas, the crystalline silicon particles are heated to melt the silicon inside the silicon nitride film, and the temperature is lowered and solidified to form a single crystal. 3. The method for producing crystalline silicon particles according to claim 1, wherein the single crystallizing is performed in a state where a large number of the crystalline silicon particles are stacked on a base plate.   4. The method for producing crystalline silicon particles according to claim 1, wherein the silicon nitride film is removed after the crystalline silicon particles are monocrystallized.

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