WO2008035793A1

WO2008035793A1 - Method for fabricating crystalline silicon grains

Info

Publication number: WO2008035793A1
Application number: PCT/JP2007/068578
Authority: WO
Inventors: Hideyoshi Tanabe; Jun Fukuda; Nobuyuki Kitahara; Hisao Arimune
Original assignee: Kyocera Corporation
Priority date: 2006-09-22
Filing date: 2007-09-25
Publication date: 2008-03-27

Abstract

[PROBLEMS] To provide a method for fabricating crystalline silicon grains, capable of stably single-crystallizing silicon grains at a high efficiency and fabricating single crystal silicon grains at a low cost. [MEANS FOR SOLVING PROBLEMS] In the method for fabricating the crystalline silicon grains, silicon grains (101) are heated to a temperature below or equal to their melting point in an ambient gas consisting of nitrogen gas or in an ambient gas containing nitrogen gas as a main component to form a silicon nitride film on the surfaces of the silicon grains (101). Next, the silicon grains (101) are heated in an ambient gas consisting of oxygen gas or in an ambient gas consisting of oxygen gas and an inert gas to melt silicon on the inner side of the silicon nitride film, and then lowered in temperature to be solidified and single-crystallized.

Description

Specification

Method for producing crystalline silicon particles

Technical field

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

Background art

[0002] Photoelectric conversion devices have been developed based on the needs of the market, such as high efficiency in terms of performance such as photoelectric conversion characteristics, consideration of the finite nature of semiconductor resources such as silicon, low manufacturing costs, and other market needs. It has been advanced. 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 solar cells.

[0003] Raw materials for producing crystalline silicon particles, which are crystalline semiconductor particles, include silicon microparticles generated as a result of pulverizing single crystal silicon, and high-purity silicon vapor-phase synthesized by the fluidized bed method. Etc. are used. In order to produce crystalline silicon particles from these raw materials, the raw materials are separated by size or weight, then melted in a container using infrared rays or high frequency, and then freely dropped (for example, patent documents) 1 or 2), or by a method of melting in a container using high-frequency plasma and then free-falling (for example, see Patent Document 3).

Patent Document 1: Pamphlet of International Publication No. 99/22048

Patent Document 2: US Patent No. 4188177

Patent Document 3: Japanese Patent Laid-Open No. 5-78115

Patent Document 4: US Patent No. 4430150

Patent Document 5: Japanese Patent Laid-Open No. 58-55393

Patent Document 6: Japanese Patent Laid-Open No. 63-79794

Disclosure of the invention

Problems to be solved by the invention

[0004] However, most of the crystalline silicon particles produced by these methods are highly concentrated. It is a crystal (polycrystalline silicon particle). Since polycrystalline silicon particles are aggregates of minute single crystals, there are grain boundaries between these minute single crystals. This grain boundary deteriorates the electrical characteristics of a photoelectric conversion device using polycrystalline silicon particles. The reason for this is that carrier recombination centers are gathered at the grain boundaries, which causes the carrier recombination to significantly reduce the minority carrier lifetime.

[0005] In the case of a semiconductor device such as a photoelectric conversion device in which electrical characteristics are greatly improved with an increase in the lifetime of minority carriers, the presence of grain boundaries in the crystalline silicon particles used therefor deteriorates electrical characteristics. This is a particularly 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.

[0006] In addition, since the grain boundaries in the polycrystalline silicon particles reduce the mechanical strength of the polycrystalline silicon particles, the thermal history, thermal strain, mechanical pressure, etc. of each process of manufacturing the photoelectric conversion device are affected. Therefore, there is a problem that the polycrystalline silicon particles are easily broken.

[0007] Accordingly, 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.

[0008] 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 the silicon compound film There is known 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 the silicon inside (see, for example, Patent Documents 4, 5, and 5). (See 6.)

However, when polycrystalline silicon particles are heated to melt silicon inside a silicon compound film formed on the surface, specifically, a silicon oxide film, and then solidified, There was a problem that adjacent polycrystalline silicon particles coalesced during melting. In this case, since there is no solidification starting point like the seed crystal used in a general method for growing a silicon single crystal of Balta such as the CZ (Chiyoklarsky) method or the FZ (floating zone) method, The problem is that solidification does not occur in the direction and polycrystallization occurs due to the generation of many nuclei. The photoelectric conversion device using the polycrystalline silicon particles has a problem that it causes deterioration of characteristics. [0010] In addition, when high-purity polycrystalline silicon synthesized in a gas phase by a fluidized bed method is used as a raw material for the production of crystalline silicon particles, the starting material contained in the polycrystalline silicon, such as iron or nickel, Contamination due to metal impurities and similar metal impurities introduced from the outside during the manufacturing process becomes a problem. Since metal impurities diffuse between lattices that do not have a chemical bond in silicon, impurity atoms diffuse through the gaps in the silicon lattice. This diffused metal impurity forms a deep level in silicon and acts as a carrier recombination center, causing an increase in leakage current and a decrease in lifetime, causing photodegradation.

That is, in the conventional method for producing crystalline silicon particles, it is difficult to produce a desired high-quality single-crystal silicon particle, and electrical characteristics are obtained using the obtained crystalline silicon particle. It is suitable for making an excellent photoelectric conversion device.

Accordingly, the present invention has been completed in view of the problems in the above-described conventional technology, and an object of the present invention is to stably and efficiently single-crystallize silicon particles such as polycrystalline silicon particles. Another object is to provide a method for producing crystalline silicon particles.

Another object of the present invention is to provide a method for producing crystalline silicon particles, which can produce single crystal silicon particles at low cost. Means for solving the problem

[0013] In the method for producing crystalline silicon particles of the present invention, the silicon particles are heated to a temperature below the melting point of silicon in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component. In an atmosphere gas consisting of oxygen gas or an atmosphere gas consisting of oxygen gas and inert gas, the silicon particles are heated to melt the silicon while maintaining its shape, and then cooled down and solidified to form a single crystal. It is characterized by doing.

[0014] The method for producing crystalline silicon particles of the present invention comprises heating the silicon particles to a temperature not higher than the melting point of silicon in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component. A hard film that is harder than the inside is formed on the surface of the particles, and then the silicon particles are heated in an atmosphere gas composed of an oxygen gas or an atmosphere gas composed of an oxygen gas and an inert gas to form oxygen on the hard film. To melt the silicon inside the hard film, and to cool down and solidify it into a single crystal. It is characterized by.

[0015] The method for producing crystalline silicon particles of the present invention comprises heating the silicon particles to a temperature not higher than the melting point of silicon in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component. A silicon nitride film is formed on the surface of the particles, and then the silicon particles are heated in an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and an inert gas to form silicon inside the silicon nitride film. It is characterized in that it is melted, cooled down and solidified to be a single crystal.

In the method for producing crystalline silicon particles of the present invention, the silicon nitride film preferably contains oxygen.

[0017] In an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and inert gas, the silicon particles are heated to melt the silicon inside the silicon nitride film, and then cooled and solidified. In the crystallization step, it is preferable to perform single crystallization in a state where a large number of the silicon particles are stacked on a base plate.

[0018] Preferably, the silicon nitride film is removed after the silicon particles are monocrystallized.

In this case, the silicon nitride film preferably contains a metal impurity.

[0019] In the method for producing crystalline silicon particles of the present invention, the silicon melt is discharged and dropped in the form of a nozzle part of a crucible containing silicon melt, and the granular silicon melt is being dropped. Next, the crystalline silicon particles are produced by cooling and solidifying them, and then forming a work-affected layer on the surface layer of the crystalline silicon particles by polishing the surface of the crystalline silicon particles. It is preferable to form a silicon nitride film on the surface of the silicon particles by heating the silicon particles to a temperature not higher than the melting point of silicon in an atmospheric gas containing nitrogen gas as a main component. After forming the silicon nitride film, the crystalline silicon particles are heated to melt the silicon inside the silicon nitride film in an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and an inert gas, and the temperature is lowered. To solidify to single crystal

[0020] In another method for producing crystalline silicon particles of the present invention, the silicon particles are heated to a temperature T1 equal to or higher than the melting point Tm of silicon while maintaining the shape thereof, and the silicon inside is melted. The process of supercooling to a temperature T2 that is less than the melting point Tm and above 1383 ° C 1 and step 2 of maintaining at a predetermined temperature within the range of 1383 ° C. or less below the melting point Tm until all the molten silicon particles are next solidified.

[0021] In the step 1, the silicon particles may be supercooled from the temperature T1 to a temperature T2 of 1410 ° C or lower and 1383 ° C or higher.

[0022] Preferably, in the step 1, when the silicon particles are heated to a temperature T1 equal to or higher than the melting point Tm of silicon while maintaining the shape thereof, the silicon particles are placed on the upper surface when the silicon inside is melted. A base plate is installed in a heating device, and the silicon particles are heated to a temperature below its melting point Tm in an atmosphere gas composed of oxygen gas and nitrogen gas to form a silicon oxynitride film on the surface of the silicon particles, The silicon particles are heated to a temperature T1 equal to or higher than their melting point Tm to melt the silicon inside the silicon oxynitride film.

[0023] It is preferable that a single crystal is formed in a state where a large number of the silicon particles are stacked on the base plate. The base plate preferably has a cristobalite crystal layer formed on the surface of a quartz glass substrate.

[0024] After the silicon particles are monocrystallized, the silicon oxynitride film that may contain metal impurities is preferably removed.

The invention's effect

According to the method for producing crystalline silicon particles of the present invention, as pretreatment, silicon particles are heated to a temperature not higher than the melting point of silicon in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component. Thus, a silicon nitride film, which is a hard film harder than the inside, is formed on the surface of the silicon particles. Therefore, when crystallizing a single crystal, the crystalline silicon particles are effectively prevented from coalescing, and there is no generation of crystal cracks or subdarenes at the contact surfaces between the crystalline silicon particles due to coalescence. Silicon particles can be produced.

[0026] Further, since the silicon nitride film has a greater ability to prevent diffusion of contaminants and impurities into the silicon inside the crystalline silicon particles than the silicon oxide film, the iron ( Contamination due to diffusion of heavy metal elements such as Fe) is reduced, and it is possible to produce high-quality crystalline silicon particles.

Further, the silicon nitride film has a higher density and a unit thickness than the silicon oxide film. The silicon nitride film required to stably hold the silicon melt inside the silicon particles when the silicon particles are heated to melt the silicon inside the silicon nitride film and to cool and solidify it. Can be made thinner than the silicon oxide film. As a result, the surface layer of crystalline silicon particles containing many strains and defects to be removed by etching in the subsequent process is reduced, and silicon resources can be used effectively. Further, in the subsequent step, the silicon nitride film can be softened by containing oxygen to melt the silicon inside the silicon nitride film, and the crystalline silicon particles can be made close to spherical by surface tension.

[0028] The silicon nitride film can contain the same effect as described above even if it contains oxygen.

In the method for producing crystalline silicon particles of the present invention, as described above, the silicon nitride film formed on the surface of the silicon particles by the pretreatment effectively prevents coalescence of the silicon particles. During the single crystallization, a large number of silicon particles can be stacked on the base plate, and the silicon particles can be arranged at high density. As a result, a large number of silicon particles can be single-crystallized at a time, and it is possible to manufacture crystalline silicon particles at low cost with high productivity. Therefore, it is possible to efficiently produce crystalline silicon particles used for a photoelectric conversion device or the like.

[0030] Further, when a large number of silicon particles are placed on a base plate in a multilayered manner and melted, solidified, and single-crystallized, the solidification start point is defined as the contact portion between the silicon particles and the base plate and the silicon particles. It is possible to set the contact portion of the substrate and to promote the single crystallization from the contact portion toward the upper part of the silicon particles. Therefore, crystal silicon particles can be easily solidified in one direction without using a seed crystal as in the CZ method and FZ method, and can be easily converted into a single crystal, greatly improving the crystallinity of crystalline silicon particles. Can do.

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) of the crystalline silicon particles. In this case, the contact point of the crystalline silicon particles with the base plate can be set as the solidification start point without cooling the base plate, but the base plate may be cooled. Next, the solidification progresses in one direction (upward) with the solidified crystal silicon particles in contact with the solidified crystal silicon particles and the contact point with the solidified crystal silicon particles as the solidification start point. As a result, solidification proceeds from the lower crystalline silicon particles to the upper crystalline silicon particles as a result. [0032] In addition, the method for producing crystalline silicon particles of the present invention preferably removes the silicon nitride film after single-crystallizing the silicon particles, so that the Fe, Cr, Ni segregated on the surface layer portion of the crystalline silicon particles. , Mo and other metal impurity containing parts can be removed, and when the crystalline silicon particles obtained by the production method of the present invention are used in a photoelectric conversion device, excellent photoelectric conversion can be obtained.

[0033] When a work-affected layer is formed on the surface layer portion of the crystalline silicon particles, a network-structured silicon nitride film is formed along a number of microcracks formed in the work-affected layer. As a result, for example, when a large number of crystalline silicon particles are aligned and single-crystallized, coalescence of the crystalline silicon particles is effectively suppressed, and crystal cracking and subdurale in the contact surface between the crystalline silicon particles due to coalescence are suppressed. It is possible to produce crystalline silicon particles with high quality crystallinity. 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. Sufficient flexibility can be added to the surface layer of the crystalline silicon particles.

[0034] In addition, when the silicon nitride film contains oxygen, the film is more flexible than the V and silicon nitride films containing oxygen, and even when the film thickness is large, crystalline silicon particles are formed during single crystallization. Sufficient flexibility can be added to the surface layer of the crystalline silicon particles to maintain the shape of the crystalline silicon particles against the volume change during melting and solidification of the internal silicon.

[0035] According to another method for producing crystalline silicon particles of the present invention, since the silicon oxynitride film is formed as a pretreatment on the surface of the silicon particles, the crystalline silicon particles are coalesced during single crystallization. It is possible to effectively suppress the occurrence of crystal cracks and subdarenes at the contact surface between the crystalline silicon particles due to coalescence, and to produce crystalline silicon particles having high quality crystallinity.

Further, according to another method for producing crystalline silicon particles of the present invention, silicon particles having a silicon oxynitride film formed on the surface in step 1 are converted from a temperature T1 not lower than the melting point Tm of silicon to a temperature lower than the melting point Tm. By overcooling to a temperature T2 above ° C, the temperature change per second (temperature gradient of temperature decrease) increases, and the steep temperature gradient triggers the solidification of silicon particles (trigger for starting solidification). It becomes. [0036] Further, since solidification occurs at a high temperature of 1383 ° C or higher and the degree of supercooling (Tm-T2) from the melting point Tm of silicon is small, the solidification interface proceeds in one direction. Direction Two-dimensional growth of solidification. As a result, it was possible to produce single crystal silicon particles with high quality crystallinity free from grain boundaries and crystal defects, and crystal defects and disordered crystal orientation occurred in a very small part of the solidification end. Since the shape can be made closer to a true sphere that does not form protrusions, good photoelectric conversion characteristics can be obtained when the crystalline silicon particles are used in a photoelectric conversion device.

[0037] Further, by maintaining a predetermined temperature within a range of 1383 ° C or more below Tm until all the molten silicon particles are solidified, the temperature during solidification can be 1383 ° C or more, It is possible to prevent the formation of protrusions at the end of solidification, the generation of grain boundaries and crystal defects, the generation of uniform nuclei that can be polycrystallized, and the dendrite growth.

[0038] Further, in the case of supercooling from temperature T1 to 1410 ° C or lower and to temperature T2 of 1383 ° C or higher, the degree of supercooling from the melting point Tm is sufficient, so that solidification is likely to occur. It is possible to produce single-crystal silicon particles having high quality crystallinity that do not include grain boundaries or crystal defects formed by the formation of protrusions at the solidification end. On the other hand, at a temperature higher than 1410 ° C, the degree of supercooling (Tm-T2) from the melting point Tm is too small to cause solidification.

[0039] In step 1, when the silicon particles are heated to a temperature T1 equal to or higher than the melting point Tm of silicon while maintaining the shape thereof, the silicon on which the silicon particles are placed on the upper surface is heated when melting the internal silicon. A silicon oxynitride film is formed on the surface of the silicon particles by heating the silicon particles to a temperature below its melting point Tm in an atmospheric gas consisting of oxygen gas and nitrogen gas, and the silicon particles are melted at the melting point Tm. By heating to the above temperature T1, the silicon inside the silicon oxynitride film is melted. That is, since the silicon oxynitride film is formed on the surface of the silicon particles during the single crystallization, the coalescence of the silicon particles is effectively suppressed, and cracks and subdurale in the contact surfaces of the silicon particles due to the coalescence are suppressed. It is possible to produce single-crystal crystalline silicon particles having high quality crystallinity that are free from the occurrence of defects.

[0040] The silicon oxynitride film adheres to the surface of the crystalline silicon particles because it has a greater ability to prevent diffusion of contaminants and impurities into the silicon inside the crystalline silicon particles than the silicon oxide film. Contamination due to diffusion of heavy metal elements such as iron (Fe) is reduced, and high-quality crystalline silicon particles with few impurities can be produced.

[0041] Further, since the silicon oxynitride film has a higher density and higher strength per unit thickness than the silicon oxide film, the silicon particles are heated to melt the silicon inside the silicon oxynitride film. When the temperature is lowered and solidified, the thickness of the silicon oxynitride film necessary for stably holding the silicon melt inside the silicon particles can be made thinner than that of the silicon oxide film. As a result, the surface layer of crystalline silicon particles containing many strains and defects to be removed by etching in the subsequent process is reduced, and silicon resources can be used effectively.

[0042] By single-crystallizing a large number of silicon particles stacked on a base plate, the silicon oxynitride film formed on the surface of the silicon particles effectively combines the silicon particles. In order to prevent this, a large number of silicon particles are placed on a base plate in a single layer during single crystallization in a heating furnace, and a large number of silicon particles are arranged at a high density, so that a large number of silicon particles are placed. The particles can be single crystallized at a time. Accordingly, it is possible to produce crystalline silicon particles at low cost and with high productivity.

[0043] In addition, the solidification starting point when a large number of silicon particles are placed on the base plate in a multilayered manner to melt, solidify, and single crystallize is defined as the contact portion between the silicon particle and the base plate and between the silicon particles. It is possible to set the contact part and to promote single crystallization from the contact part to the upper part of the silicon particles. For this reason, crystal silicon particles can be easily solidified in one direction without using a seed crystal as in the CZ method and FZ method, and single crystal can be easily formed, and the crystallinity of the crystal silicon particles can be greatly improved. Can do.

[0044] Since the cristobalite crystal layer is formed on the surface of the base made of quartz glass in the base plate, the contact point between the silicon particles and the cristobalite crystal layer on the surface of the base plate becomes a solidification start point, thereby causing heterogeneous nucleation. The force S is used to easily crystallize the crystalline silicon particles in one direction to form a single crystal.

[0045] The heterogeneous nucleation means that crystal nuclei are generated in a part of silicon particles, and crystallization spreads from the crystal nuclei to the whole. On the other hand, homogeneous nucleation means that crystal nuclei are formed in the entire silicon particle almost simultaneously and each crystal nuclei grows, which corresponds to the case where polycrystalline crystalline silicon particles are formed. To do. [0046] The cristobalite crystal layer formed on the surface of the quartz glass substrate is stable at a temperature of about 1400 ° C, and functions as a surface structural material (surface reinforcing layer) of the quartz glass substrate. It will have. As a result, the quartz glass substrate acts to prevent the thermal deformation of the substrate, thereby preventing the substrate from being deformed by heat.

[0047] Further, according to the present invention, since the silicon oxynitride film is removed after single-crystallizing the silicon particles, metal impurities such as Fe, Cr, Ni, and Mo segregated on the surface layer portion of the crystalline silicon particles. The containing part can be removed. As a result, when 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.

[0048] FIG. 1 shows an embodiment of the method for producing crystalline silicon particles of the present invention, and (a) to (c) show a state in which silicon particles are placed in a multilayered manner on a base plate. It is sectional drawing for every process

FIG. 2 is a cross-sectional view showing an embodiment of a photoelectric conversion device obtained by the production method of the present invention.

FIG. 3 shows another embodiment of the method for producing crystalline silicon particles of the present invention, and (a) is a schematic cross-sectional view showing a state in which a work-affected layer is formed by polishing on the surface of the crystalline silicon particles. (B) 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.

FIG. 4 is a cross-sectional view of a jet device used in the production method of the present invention.

FIG. 5 shows still another embodiment of the method for producing crystalline silicon particles of the present invention,

(a)-(c) is sectional drawing for every process which shows a mode that the silicon particle was mounted in one layer on the base plate.

FIG. 6 is a cross-sectional photograph showing the results of observation of grain boundaries and pits (crystal defects) on the polished surface of crystalline silicon particles of Example 3-;!

FIG. 7 is a cross-sectional photograph showing the results of observation of grain boundaries and pits (crystal defects) on the polished surface of crystalline silicon particles of Comparative Example 3-;!

FIG. 8 is a graph showing a temperature profile in still another manufacturing method of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

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

[0050] <First embodiment>

FIGS. 1 (a) to 1 (c) each show an embodiment of the method for producing crystalline silicon particles of the present invention. A large number of silicon particles 1 stacked on a base plate 102 are shown in FIG. It is sectional drawing for every process which shows 01.

[0051] First, in order to obtain the silicon particles 101, semiconductor grade crystalline silicon is used as a material of the crystalline silicon particles, and this is melted in a container using an infrared ray or a high frequency coil. After that, polycrystalline silicon particles 101 are obtained by a melt drop method (jet method) or the like in which molten silicon is freely dropped as a granular melt.

[0052] 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. Examples of dopants for silicon include boron, aluminum, gallium, indium, phosphorus, arsenic, and antimony. In particular, it is desirable to use boron or phosphorus because it has a large segregation coefficient for silicon and a small evaporation coefficient when silicon is melted. The dopant concentration is preferably about 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ³ added to the silicon crystal material.

[0053] At the time when the silicon particles 101 were obtained by this melting and dropping method, the shape of the silicon particles 101 was a teardrop type, streamline type, or a plurality of particles connected in addition to a substantially spherical shape. It is a connected type. When a photoelectric conversion device is produced using the polycrystalline silicon particles 101 as it is, good photoelectric conversion characteristics cannot be obtained. The causes include the presence of metal impurities such as Fe, Cr, Ni, and Mo that are usually contained in the polycrystalline silicon particles 101, and the effect of carrier recombination at the crystal grain boundaries. It is.

[0054] In order to improve this, in the present invention, first, as a pre-process, polycrystalline silicon is used in a temperature-controlled heating furnace in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component. The particles 101 are heated to a temperature (500 to; 1400 ° C.) below the melting point of silicon (1414 ° C.) to form a silicon nitride film on the surface of the silicon particles 101. After that, Then, the silicon particles 101 are made into a single crystal by being remelted, cooled and solidified in an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and inert gas.

[0055] The single crystallization of the silicon particles 101 by the production method of the present invention is, for example, a ratio in which about 999 of 1000 silicon particles 101 are completely single-crystallized (99.9% in number ratio). Degree) Power to do S

[0056] Further, after the post-process, it is preferable to remove the silicon nitride film, thereby removing the metal impurity containing portion such as Fe, Cr, Ni, Mo segregated on the surface layer portion of the crystalline silicon particles. Can do. As a result, when 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.

[0057] The pressure of the atmospheric gas composed of nitrogen gas or the atmospheric gas containing nitrogen gas as a main component in the previous step is preferably about 0.01 M to 0.2 MPa. 0. Below OlMPa, 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. On the other hand, when it exceeds 0.2 MPa, the thickness of the silicon nitride film tends to vary.

[0058] The thickness of the silicon nitride film formed on the surface of the silicon particles 101 may be about 100 nm to 10 μm. If it is less than lOOnm, the silicon nitride film is easily broken when the silicon inside the silicon particles melts. If it exceeds 10 m, the silicon nitride film tends to be spheroidized by surface tension when the silicon melts inside the silicon particle, whereas the silicon nitride film is too thick to deform.

[0059] The pressure of the atmospheric gas composed of oxygen gas or oxygen gas and inert gas force in the subsequent process (remelting (remelting) process) is preferably about 0.01 to 0.2 MPa. 0. Below OlMPa, the film thickness of the silicon nitride film is reduced and the film quality is liable to be deteriorated by evaporation of nitrogen and oxygen from the silicon nitride film. If it exceeds 0.2 MPa, the shape cannot be kept stable when the silicon inside the silicon particles is melted, making it difficult to control the shape.

[0060] The oxygen gas is included as an essential gas component in the atmospheric gas in the subsequent process because the diffusion of oxygen into the silicon nitride film increases the flexibility of the silicon nitride film and the shape when the silicon particles 101 melt. This is because it can be maintained more stably. Further, since the oxygen partial pressure in the atmospheric gas is increased, it is possible to reduce oxygen evaporation from the silicon nitride film with a force s. If oxygen is not included in the atmospheric gas, silicon particles 1 This is to prevent 01 from reacting and fixing with quartz on the base plate 102 made of quartz glass or the like during melting.

[0061] When oxygen gas and inert gas are used in the post-process, any gas containing 20% by volume or more of oxygen gas may be used as long as it contains 80% by volume or less of inert gas such as argon gas. When the oxygen gas content is less than 20% by volume, oxygen evaporation from the silicon nitride film is easily promoted, and the shape cannot be kept stable when silicon inside the silicon particles 101 is melted, making shape control difficult.

[0062] In order to produce the single-crystal crystalline silicon particles 101, first, as shown in Fig. 1 (a), a large number (for example, several hundred to several thousand) of polycrystalline silicon particles 101 are placed on the surface. Two or more layers are stacked on the upper surface of the plate 102. The multi-layer placement referred to in the present invention is, when viewed in the longitudinal sectional view of FIG. 1 (a), the substantially spherical silicon particles 101 are placed in a plurality of layers on the upper surface of the base plate 102, It means a state in which it is packed in a close packing and stacked.

[0063] The multiple silicon particles 101 may be placed on the base plate 102 in a single layer, but it is better to place them in multiple layers. By placing them in multiple layers, the silicon particles 101 can be arranged with high density, and a large number of silicon particles 101 can be made into a single crystal at a time. It becomes possible to do. Therefore, it is possible to efficiently produce crystalline silicon particles used in a photoelectric conversion device or the like.

[0064] When a large number of silicon particles 101 are placed on a base plate in a multi-layered manner, the number of layers is not particularly limited! /, For example, 2 to; about 150 layers! /.

[0065] The multiple silicon particles 101 placed on the base plate 102 may be in contact with each other. The base plate 102 is preferably a box or plate having no upper lid. In the case of a plate shape, it may be used by stacking in multiple stages. As the material of the base plate 102, quartz glass, mullite, aluminum oxide, silicon carbide, single crystal sapphire, etc. are suitable for suppressing the reaction with the silicon particles 101. Quartz glass is preferred because it has excellent heat resistance, durability, and chemical resistance, is inexpensive, and is easy to handle.

Next, the base plate 102 on which the silicon particles 101 are placed is introduced into a heating furnace (not shown), and the silicon particles 101 are heated. Various furnaces can be used depending on the type of semiconductor material, but since silicon is used as the semiconductor material, it can be used for firing ceramics. A resistance heating type or induction heating type atmosphere firing furnace used, or a horizontal oxidation furnace generally used in the manufacturing process of a semiconductor element is suitable. Resistance heating type atmosphere firing furnaces used for firing ceramics, etc. are relatively easy to raise the temperature above 1500 ° C, and large-scale ones capable of mass production of crystalline silicon particles are also available at relatively low cost. desirable.

[0067] Prior to heating in the atmospheric firing furnace, the solution may be washed in advance by the RCA method (cleaning method by RCA) in order to remove metal foreign matter adhering to the surface of the silicon particles 101. desirable. The RCA method is a cleaning method generally used in the manufacturing process of semiconductor devices as a standard cleaning process for silicon wafers. Specifically, the oxide film and silicon surface layer on the silicon wafer surface are removed with an aqueous solution of ammonium hydroxide and hydrogen peroxide in the first step of the three steps, and the second step. In step 3, the oxide film attached in the previous step is removed with an aqueous solution of hydrogen fluoride, and in the third step, heavy metal is removed with an aqueous solution of hydrogen chloride and hydrogen peroxide to form a natural oxide film. ,Is Umono.

[0068] In addition, in order to prevent contamination from furnace materials and heating elements in the heating furnace, a bell jar that covers the silicon particles 101 placed on the base plate 102 is installed in the heating furnace. Is desirable. Quartz glass, mullite, aluminum oxide, silicon carbide, single crystal sapphire, etc. are suitable for the material of the bell jar, but it is excellent in heat resistance, durability, chemical resistance and low cost and easy to handle! Glass is preferred.

[0069] In a heating furnace, the silicon particles 101 are heated in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component, and the temperature is raised to a temperature lower than the melting point of silicon (1414 ° C). In the process, a silicon nitride film is formed on the surface of the silicon particle 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, and when the temperature is higher than 1400 ° C, the thickness of the silicon nitride film becomes uneven. Or part of the silicon particles 101 will melt or the shape of the particles will collapse!

[0070] Since the silicon nitride film formed on the surface of the silicon particle 101 has a higher film density and higher strength per unit film thickness than a silicon oxide film or the like, silicon particles such as contaminants and impurities are present. This has the effect that the diffusion blocking power inside the child 101 is large. [0071] Further, the silicon nitride film does not turn even if it contains oxygen. The oxygen content should be about 10 mol% or less. If it exceeds 10 mol%, the film quality tends to deteriorate due to the change in crystal structure and increase in crystal defects in the silicon nitride film.

[0072] The atmosphere gas in the heating furnace when forming the silicon nitride film on the surface of the silicon particle 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 silicon particles 101 are likely to coalesce in the subsequent single crystallization process, and the strength of the silicon nitride film is also deteriorated. That is, when the silicon particles 101 are stacked in layers, the lower silicon particles 101 are easily crushed when melted due to the weight of the upper silicon particles 101.

[0073] Each gas partial pressure in the atmospheric gas in the heating furnace can be adjusted by each gas flow rate with respect to the total gas flow rate. Atmospheric gas is, for example, gas supply means such as a gas flow meter or mass flow meter, force S supplied into the bell jar through a gas filter, and a device for supplying gas to this gas supply means adjusts the gas pressure and concentration. Any device having a possible mechanism may be used.

Next, as shown in FIG. 1 (b), silicon particles 101 are introduced from the melting point of silicon (1414 ° C.) in an atmospheric gas composed of oxygen gas or an atmospheric gas composed of oxygen gas and inert gas. Raise the temperature to a higher temperature. The steps in Fig. 1 (a) and (b) may be performed separately or consecutively.

[0075] Base plate 102 also functions as a starting point for solidification when silicon particles 101 are cooled and solidified after being melted and crystallized. In this way, by placing a large number of silicon particles 101 on the upper surface of the base plate 102, the solidification start point can be set at the contact portion between each silicon particle 101 and the base plate 102. As one of the poles, 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.

[0076] In addition, since a large number of silicon particles 101 are placed in a multi-layered manner, the contact portion with the crystalline silicon particles on the base plate 102 previously crystallized is set as a solidification starting point, and the upper portion thereof. Adjacent silicon particles 101 can be solidified, and the upper part of the multilayered Since solidification spreads in a chain reaction direction, the force S can greatly improve the crystallinity of a large number of silicon particles 101.

[0077] Since the size of the silicon particles 101 is usually almost spherical, the average particle diameter is preferably 1500 in or less, and the shape is preferably closer to the sphere. However, the shape of the silicon particles 101 is not limited to a spherical shape, but may be a cubic shape, a rectangular parallelepiped shape, or other irregular shapes.

[0078] When the size force of the silicon particles 101 is larger than 500 m, the thickness of the silicon nitride film formed on the surface of the silicon particles 101 becomes relatively thin with respect to the silicon particle 101 main body. It becomes difficult to keep the shape of the silicon particles 101 at the time of melting of the silicon inside the silicon particles 101 stable. In addition, it becomes difficult to completely melt the silicon inside the silicon particles 101, and subdurain is likely to occur when the melting is incomplete. On the other hand, when the diameter of the silicon particles 101 is as small as less than 30 m, it is difficult to stably maintain the shape of the silicon particles 101 when the silicon inside the silicon particles 101 is melted.

[0079] Accordingly, it is preferable that the diameter of the silicon particles 101 is 30 m to 1500 m, thereby stably maintaining the shape of the silicon particles 101 and providing a spherical and high-quality crystallinity with no generation of subdarenes. Crystalline silicon particles can be stably produced.

[0080] The temperature of the silicon particle 101 is higher than the melting point of silicon (1414 ° C)! /, The temperature is raised to a temperature! /, And the atmosphere gas in the heating furnace in the subsequent process (post process) is an atmosphere composed of oxygen gas The atmosphere gas consists of gas or oxygen gas and inert 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 the heating furnace can be adjusted by each gas flow rate with respect to the total gas flow rate. For example, if the atmospheric gas is a force supplied from the gas supply means through the gas filter into the bell jar, and the device for supplying the gas to the gas supply means has a mechanism capable of adjusting the gas pressure and the gas concentration. 'Good.

[0081] When the atmospheric gas in the heating furnace in the subsequent step is composed of oxygen gas and inert gas, the oxygen gas partial pressure is preferably 20% or more. Oxygen gas partial pressure in atmospheric gas is not 20% When it is full, oxygen evaporation from the silicon nitride film is easily promoted, and the shape cannot be kept stable when the silicon inside the silicon particles 101 is melted, making it difficult to control the shape.

[0082] The 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 melts in the silicon particles 101. At this time, the silicon nitride film formed on the surface of the silicon particles 101 can maintain the shape of the silicon particles 101 while melting the inner silicon. However, if the temperature of the silicon particle 101 is difficult to maintain stably, for example, in the case of the silicon particle 101, if the temperature is raised to a temperature exceeding 1480 ° C, the inside of the silicon particle 101 When the silicon melts, it becomes difficult to keep the shape of the silicon particles 101 stable, and the adjacent silicon particles 101 tend to coalesce, and the silicon particles 101 are easily fused to the base plate 102.

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

On the other hand, when the thickness of the silicon nitride film exceeds 10 m, the silicon nitride film is deformed in the above temperature region, and the shape of the obtained crystalline silicon particles 101 is a shape close to a true sphere. Desirable because it is hard to become! /.

Therefore, the thickness of the silicon nitride film on the surface of the silicon particles 101 is within the above average particle diameter range.

With respect to (30 am to 1500 μm), it is preferable that lOOnm to 0 μm, so that crystalline silicon particles having a good shape close to a true sphere can be stably obtained. In addition, by using these crystalline silicon particles in a photoelectric conversion device, it is possible to obtain a photoelectric conversion device having excellent conversion efficiency.

Next, as shown in FIG. 1 (c), the molten silicon particles 101 are dissolved in the inner side of the silicon nitride film. In order to solidify the melted silicon, the temperature is lowered to a temperature of about 1400 ° C or less below the melting point and solidified. At this time, when solidifying by maintaining at a relatively high temperature (about 1360 ° C) below the melting point, the contact portion between the silicon particle 101 and the base plate 102 is set as the solidification starting point (one pole) and facing upward. Solidification progresses in one direction toward the pole, so that unidirectional solidification occurs at the point of contact with the already solidified silicon particle 101 and is inherited by the entire silicon particle 101 as it is. Crystals grow and the resulting crystalline silicon particles become single crystals, which can greatly improve crystallinity.

[0087] If a large number of silicon particles 101 are placed in a multilayered manner, the contact portion with the crystalline silicon particles on the base plate 102 that has been crystallized earlier is set as the solidification starting point and is adjacent to the top. Since the solidified silicon particles 101 can be solidified and the solidification spreads in a chained manner toward the upper part of the stacked layers, the crystallinity of a large number of crystalline silicon particles 101 can be greatly improved. I'll do it.

[0088] In addition, during the solidification of the molten silicon particles 101, it is preferable to perform a thermal annealing treatment on the silicon particles 101, for example, a thermal annealing treatment at a constant temperature of 1000 ° C or higher for 30 minutes or longer. By performing this thermal annealing treatment, the distortion in the crystal of the crystalline silicon particles generated at the time of solidification, the interface distortion generated at the interface between the silicon nitride film on the surface of the crystalline silicon particles and the inner crystalline silicon, etc. are alleviated and removed. Therefore, it is necessary to use crystalline silicon particles having good crystallinity.

[0089] According to the method for producing crystalline silicon particles of the present invention, as described above, it is possible to stably produce crystalline silicon particles having good crystallinity and a reduced amount of unnecessary impurities. it can.

Next, an embodiment of the photoelectric conversion device of the present invention will be described with reference to FIG.

[0091] In the photoelectric conversion device using the crystalline silicon particles 406 of the present invention, the first conductive type (for example, p-type) crystalline silicon particles 40 are formed on one main surface of the conductive substrate 407, in this example, the upper surface. A large number of 6 are bonded to the conductive substrate 407 at the lower portion thereof by, for example, a bonding layer 408. An insulating material 409 is interposed between the crystalline silicon particles 406 and 406 adjacent to each other, and an upper portion of the crystalline silicon particles 406 is disposed so as to be exposed from the insulating material 409. Second conductivity type (for example, n-type) semiconductor layer 410 (semiconductor portion) In addition, the translucent conductor layer 41 1 is provided in order.

[0092] The electrode 412 is formed in a predetermined pattern shape on the translucent conductor layer 411 when the photoelectric conversion device is used as a solar cell. For example, the electrode 412 is a finger electrode and a bus bar. Electrode. The electrode 412 may be a conductive plate made of copper, aluminum or the like.

[0093] The crystalline silicon particles 406 in the photoelectric conversion device of the present invention having the above-described configuration are manufactured by the above-described manufacturing method of crystalline silicon particles of the present invention. Since the crystalline silicon particles 406 produced by the method for producing crystalline silicon particles of the present invention have a very low impurity concentration and high quality, the lifetime of minority carriers, which is an important factor for obtaining high photoelectric conversion efficiency, is obtained. Can be improved. Accordingly, crystalline silicon particles 406 that are preferable as a component of the photoelectric conversion device can be obtained.

[0094] 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 silicon particles 101 which are the starting material of the crystalline silicon particles 406 are 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 or the like is 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 apparatus can be used as a power generation means, and a photovoltaic power generation apparatus configured to supply the generated power from the power generation means 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. Furthermore, in order to remove the interfacial strain between the silicon nitride film and the crystalline silicon particles 406 and impurities such as P-type dopant and oxygen, carbon, and metal segregated on the surface of the crystalline silicon particles 406, crystalline silicon particles The surface of 406 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 Hm 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.

[0097] At this time, the conductive substrate 407 is made of an aluminum substrate, or a metal substrate containing at least aluminum on the surface, so that the crystalline silicon particles 406 can be bonded at a low temperature, which is lightweight and inexpensive. A 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 of 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 by the photoelectric conversion portion of the crystalline silicon particles 406.

[0098] Next, an insulating material 409 is placed on the conductive substrate 407 so as to be interposed between adjacent ones of the bonded crystalline silicon particles 406, and at the top of these crystalline silicon particles 406, at least the zenith portion. It is exposed from the insulating material 409.

[0099] Here, the surface shape of the insulating material 409 between the adjacent crystalline silicon particles 406 is assumed to be a concave shape that is higher on the crystalline silicon particle 406 side. Due to the difference in refractive index from the transparent encapsulating resin formed thereon, it is possible to promote the random reflection of incident light on the crystalline silicon particles 406 in the non-light-receiving region without the crystalline silicon particles 406. it can.

Next, a second conductive 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 translucent conductor layer 411 is formed on the semiconductor layer 410. Then, in order to extract desired power as a solar cell, a silver paste or the like is applied in a predetermined pattern shape to form electrodes 412 such as grid electrodes or finger electrodes and bus bar electrodes. In this way, the conductive substrate 407 is By using one electrode and the electrode 412 as the other electrode, a photoelectric conversion device as a solar cell can be obtained.

[0101] Note that in order to form the second conductivity type semiconductor layer 410, a thermal diffusion method with a low process cost is performed on the surface of the crystalline silicon particles 406 prior to the bonding of the crystalline silicon particles 406 to the conductive substrate 407. May be formed. 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.

[0102] <Second Embodiment>

Next, a second embodiment of the present invention will be described. The same steps and constituent members as those in the first embodiment may be denoted by the same reference numerals, and detailed description thereof may be omitted.

3 (a) to 3 (d) are schematic cross-sectional views showing a method for producing crystalline silicon particles that are effective in this embodiment. FIG. 3 (a) shows a method of forming a work-affected layer on the surface of the crystalline silicon particles 101 by polishing using the lower rotating surface plate 201, the upper rotating surface plate 202, and the loose abrasive grains 203 having high rigidity. Show. 3 (b) to 3 (d) are cross-sectional views for each process showing a large number of crystalline silicon particles 101 placed on the base plate 301 in a multilayered manner.

[0103] The method for producing crystalline silicon particles, which is particularly effective for this embodiment, is that the silicon melt is discharged as particles from the nozzle part of the crucible containing the silicon melt and dropped, and the granular silicon melt is being dropped. Then, the crystalline silicon particles 101 are produced by cooling and solidifying, 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. Next, the crystalline silicon particles 101 are heated to a temperature not higher than the melting point of silicon in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component to form a silicon nitride film on the surface of the crystalline silicon particles 101. . Next, in an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and inert gas, the crystalline silicon particles 101 are heated to melt the silicon inside the silicon nitride film, and the temperature is lowered and solidified to form a single crystal. To do.

[0104] First, as shown in FIG. 4, a semiconductor grade crystal is used as the material of the crystalline silicon particles 101. Polycrystalline silicon is melted in a container using silicon and infrared or high-frequency induction coils, and then melted and dropped freely as a granular silicon melt (jet method). Particle 101 is obtained.

[0105] In the crystalline silicon particle manufacturing apparatus (jet apparatus) shown in Fig. 4, the crucible 1 heats and melts the raw silicon particles to form a silicon melt, and the bottom nozzle section la This is a container for discharging the melt 4 of granular silicon. The silicon melt heated and melted in the crucible 1 is discharged into the tube 2 from the nozzle part la, becomes a granular silicon melt 4, falls inside the tube 2, and crystal silicon particles 5 are obtained. The tube 2 is arranged below the crucible 1 so that the longitudinal direction is the vertical direction.

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. This is not preferable. The crucible 1 is provided with a gas introduction pipe 3 made of quartz or the like.

[0106] 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 The body, aluminum oxide sintered body, sapphire, magnesium oxide sintered body and the like are preferable. Further, it may be a composite, mixture or combination of these materials. Further, a silicon carbide film, a silicon nitride film, or a silicon oxide film may be coated on the surface of the substrate made of the above material. Further, as a heating method for heating the raw material to the melting point or higher in the crucible 1, electromagnetic induction heating, resistance heating, or the like is suitable.

[0107] The nozzle portion la is made of silicon carbide (silicon carbide crystal or silicon carbide sintered body) or silicon nitride (silicon nitride sintered body).

[0108] Polycrystalline crystalline 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. Dopants for silicon include boron, aluminum, gallium, indium, phosphorous, arsenic, and antimony. S, boron and phosphorus are used because they have a large segregation coefficient for silicon and a small evaporation coefficient when silicon melts. It is desirable to use it. The dopant concentration is about 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ³ added to the silicon crystal material. [0109] 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 plurality of particles connected to each other. Connected type. When a photoelectric conversion device is produced using the polycrystalline silicon particles 101 as it is, good photoelectric conversion characteristics cannot be obtained. This is because metal impurities such as Fe, Cr, Ni, and Mo that are usually 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 due to.

[0110] In order to improve this, 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 gas composed of nitrogen gas or nitrogen gas is used as a main component. The polycrystalline silicon particles 101 are heated to a temperature (500 to 1400 ° C) below the melting point of silicon (1414 ° C) in a temperature-controlled heating furnace in an atmosphere gas containing the crystalline silicon particles 101 A silicon nitride film is formed on the surface, and then the crystalline silicon particles 101 are heated in an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and an inert gas to melt silicon inside the silicon nitride film, The temperature is lowered 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. 3 (a) function as a polishing device for the surface of the crystalline silicon particles 101, and at least one of them can rotate. Both may be configured to rotate. Also, if both rotate, they may rotate in opposite directions, and some! / May rotate in the same direction so that their rotational speeds are different.

[0112] 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 may be fixed and the other rotation axis set to a predetermined locus. It may be moved so as to draw (a circular or elliptical trajectory). Alternatively, both rotary axes may be moved so as to draw a predetermined locus (circular, elliptical, etc.). Further, at least one of the lower rotating surface plate 201 and the upper rotating surface plate 202 may be configured 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. Also, a plan view of the lower rotating surface plate 201 and the upper rotating surface plate 202 is shown. The shape in is a circle, a quadrangle, etc., and may be other shapes.

[0113] 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. ; Place around 100,000. 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 101 substantially uniformly. An elastic layer may be provided.

[0114] As a material of the loose abrasive 203, silicon carbide, alumina, diamond or the like is generally used. When loose abrasive 203 is not used, a grindstone or grindstone plate made of silicon carbide, alumina, diamond, etc. can be installed on at least one of the pressing surfaces of lower rotating platen 201 and upper rotating platen 202 It is.

[0115] In order to form a work-affected layer on the surface layer portion of the crystalline silicon particles 101 by polishing, for example, loose abrasive 203 made of SiC having an average particle diameter of about 30 m is used, and the lower rotating surface plate 201 is used. Fix and rotate the upper rotating surface plate 202 at a rotation speed of 5 to 250 rpm, and perform polishing for 3 to 30 minutes. At this time, the upper rotating surface plate 202 may be moved downward in the axial direction, and a pressure of about 0.01 MPa to 0.1 IMPa may be applied to the crystalline silicon particles 101. As a result, a work-affected layer having a thickness of about 10 inches is formed on the surface layer of the crystalline silicon particles 101.

[0116] The work-affected layer generally has a structure in which an amorphous layer, a polycrystalline layer, a mosaic layer, a crack layer, a strained layer, etc. exist from the surface side. Call a 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 a remelting (remelting) step for single crystallization of the crystalline silicon particles 101.

[0117] The existence of a work-affected layer can be identified by confirming the broadening of the half-value width of the Raman spectrum by Raman spectroscopy.

[0118] Next, the pressure of the atmosphere gas composed of nitrogen gas or the atmosphere gas containing nitrogen gas as the main component in the silicon nitride film formation step (pre-step of single crystallization) is 0.01 to 0.2 MPa. The degree is good. [0119] The thickness of the silicon nitride film formed on the surface of the crystalline silicon particles 101 may be about lOOnm to about 10 μm.

[0120] The pressure of the atmospheric gas composed of oxygen gas or the atmospheric gas composed of oxygen gas and inert gas in the post-process (remelting step for single crystallization) is 0.01-0.2. About MPa is good.

[0121] When oxygen gas and inert gas are used in the post-process, any gas containing 20% by volume or more of oxygen gas may be used as long as it contains 80% by volume or less of inert gas such as argon gas.

[0122] As shown in Fig. 3 (b), a large number (for example, several hundred to several thousand) of polycrystalline silicon particles 101 are prepared to produce single-crystal crystalline silicon particles 101. Two or more layers are stacked on the upper surface of the plate 301. The multi-layer placement referred to in the present invention means that the substantially spherical crystalline silicon particles 101 are placed so as to form a plurality of layers in the thickness direction as viewed in the longitudinal sectional view of FIG. It shows a state of being filled and stacked and placed.

[0123] 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!

[0124] The crystalline silicon particles 101 are heated in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component in a heating furnace, and the temperature is raised to a temperature lower than the melting point of silicon (1414 ° C). In the process, 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.

[0125] 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 deteriorate due to the change in crystal structure and increase of 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 atmospheric gas in which an appropriate amount of oxygen gas is mixed with nitrogen gas.

Next, as shown in FIG. 3 (c), crystalline silicon particles 101 are melted in silicon at a melting point (1414 ° C.) in an atmospheric gas composed of oxygen gas or an atmospheric gas composed of oxygen gas and inert gas. The temperature is raised to a higher temperature (over 1414 ° C and below 1480 ° C). The processes in Fig. 3 (b) and (c) can be performed separately or consecutively. [0127] Base plate 301 also functions as a starting point for solidification when crystalline silicon particles 101 are cooled and solidified after being melted.

[0128] Further, since a large number of crystalline silicon particles 101 are placed in a multi-layered manner, the contact portion with the crystalline silicon particles on the base plate 301 crystallized first is set as a solidification starting point, It becomes possible for the crystalline silicon particles 101 adjacent to to solidify. As a result, the solidification spreads in a chain reaction toward the upper part of the stacked layers, so that the crystallinity of the large number of crystalline silicon particles 101 can be greatly improved.

Next, as shown in FIG. 3 (d), 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. Let it solidify. At this time, the force to solidify by maintaining at a relatively high temperature (about 1360 ° C) below the melting point of silicon. In this case, the contact portion between the crystalline silicon particle 101 and the base plate 301 is the solidification starting point (one pole). As the solidification progresses in one direction toward the upper facing pole, the unidirectional solidification occurs starting from the contact point with the already solidified crystalline silicon particle 101, and the entire crystalline silicon particle 101 remains as it is. The crystal grows in succession, and the resulting crystalline silicon particle 101 becomes a single crystal.

[0130] If a large number of crystalline silicon particles 101 are placed in a multi-layered manner, the contact portion with the crystalline silicon particles 101 on the base plate 301 that has been crystallized first is set as the solidification starting point. It is possible to solidify the crystalline silicon particles 101 adjacent to each other, and the solidification spreads in a chain toward the upper part rather than the multi-layered structure, so that the crystallinity of a large number of crystalline silicon particles 101 is greatly improved. be able to.

[0131] Further, during the solidification of the crystalline silicon particles 101 whose inside is melted, thermal annealing treatment is performed on the crystalline silicon particles 101, for example, a thermal annealing treatment at a constant temperature of 1000 ° C or more for 30 minutes or more. Is preferred.

[0132] According to the method for producing crystalline silicon particles, which is advantageous for this embodiment, as described above, the crystalline silicon particles having good crystallinity and having a reduced amount of unnecessary impurities can be stabilized. You can power to manufacture. Others are the same as in the previous embodiment, so the description is omitted. <Third embodiment>

[0133] Next, a second embodiment of the present invention will be described. The same steps and components as those in the first and / or second embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. ^{There are s} .

FIG. 5 ω to (c) show an embodiment of the method for producing crystalline silicon particles of the present invention, and shows a cross section for each process showing a large number of silicon particles 101 placed on a base plate 102. FIG.

[0134] In the method for producing crystalline silicon particles of the present invention, the silicon particles 101 are heated to a temperature T1 equal to or higher than the melting point Tm (1412 ° C) of silicon while maintaining the shape thereof, and the silicon inside is melted. The temperature is lower than the melting point Tm, and it is kept at a predetermined temperature in the range of Tm to T2 until the molten silicon particle 101 is completely solidified, and the temperature is lower than the melting point Tm and is 1383 ° C or higher. Step 2 is provided.

[0135] Temperature T1 is 1415-; 1450 ° C strong. Below 1415 ° C, it takes time for silicon particles to melt completely. When it exceeds 1450 ° C, the shape of silicon particles melts. It becomes difficult to keep stable, and the adjacent silicon particles 101 are likely to coalesce, and the silicon particles 101 are easily fused to the base plate 102.

[0136] The temperature T2 in step 1 is less than the melting point Tm of silicon and is 1383 ° C or more. However, when T2 is Tm or more, solidification of the silicon particles 101 is not started and T2 is less than 1383 ° C. In this case, solidification occurs in the temperature range where the degree of supercooling (Tm-T2) is large, so that formation of protrusions at the end of the solidification, generation of grain boundaries and crystal defects can occur, and uniform nucleation that can result in polycrystallization Nya dendritic growth.

[0137] In step 2, the molten silicon particles 101 are kept at a predetermined temperature within 1383 ° C or less below Tm until all the molten silicon particles 101 are solidified, but the predetermined temperature is 1410 or less and 1383 ° C or better. Below 1383 ° C, solidification occurs in the temperature range where the degree of supercooling (Tm-T2) is large, as in step 1.Therefore, formation of protrusions at the end of solidification and generation of grain boundaries and crystal defects occur. Uniform nucleation that can be polycrystallized results in dendrite growth. If the temperature exceeds 1410 ° C, the degree of supercooling (Tm-T2) is too small, and solidification of adjacent silicon particles 101 that are difficult to start coagulation tends to occur. It becomes easy to fuse.

[0138] In addition, the time for holding at a predetermined temperature is about !! ~ 120 minutes is sufficient. If less than 1 minute, solidification of the silicon particles 101 has not yet started, or there is silicon particles 101 being solidified. There is a possibility. If it exceeds 120 minutes, it becomes difficult to keep the shape stable when the silicon particles 101 are melted, and it is easy for the adjacent silicon particles 101 to coalesce, and the silicon particles 101 are easily fused to the base plate 102. Further, the base plate 102 having the quartz glass substrate is thermally deformed due to a high temperature.

[0139] First, semiconductor grade crystalline silicon is used as a material for crystalline silicon particles, which is melted in a container using infrared rays or a high-frequency coil, and then the molten silicon is freely dropped as a granular melt. Polycrystalline silicon particles 101 are obtained by a method (jet method) or the like.

[0140] The 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. The dopants for silicon include boron, aluminum, gallium, indium, phosphorus, arsenic, and antimony, but the segregation coefficient for silicon is large, and the point and the evaporation coefficient when silicon melts are small! / It is preferable to use boron or phosphorus. The dopant concentration is about 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ³ added to the silicon crystal material.

[0141] At the time of obtaining the silicon particles 101 by the melt drop method, the shape of the silicon particles 101 is a teardrop type, a streamline type, a connected type in which a plurality of particles are connected, and a substantially spherical shape, but is solidified and expanded. There are projections formed by the above. When the shape of the silicon particle 101 is a teardrop type, the number of grains is several, and the shape uniformity is superior to other shapes. However, when a photoelectric conversion device is produced using silicon particles 101 such as a teardrop type obtained by the melt-drop method as it is, good photoelectric conversion characteristics cannot be obtained. This is due to metal impurities such as Fe, Cr, Ni, and Mo usually contained in the polycrystalline silicon particles 101 and the carrier recombination effect at the crystal grain boundaries.

[0142] In order to improve the influence of the metal impurities on the polycrystalline silicon particles 101 and the deterioration due to carrier recombination at the grain boundaries, the temperature of the heating furnace or the like is controlled by the method for producing crystalline silicon particles of the present invention. In the device, the polycrystalline silicon particles 101 are heated to By forming a silicon oxynitride film on the surface of the con particle 101, melting the inside of the silicon particle 101, lowering the temperature, and solidifying it, a single crystallized crystalline silicon particle can be manufactured.

[0143] The single crystallization of the silicon particles 101 by the production method of the present invention is, for example, a ratio in which about 999 out of 1000 silicon particles 101 are completely single-crystallized (number ratio is 99.9%). Degree) Power to do S

[0144] In addition, after the silicon particles 101 were monocrystallized, the silicon oxynitride film on the surface was removed, and metal impurity containing portions such as Fe, Cr, Ni, and Mo segregated on the surface layer portion of the crystalline silicon particles Can also be removed. As a result, when 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.

[0145] The atmosphere gas in the heating furnace in the process of raising the temperature of the silicon particles 101 to a temperature higher than the melting point of silicon (1414 ° C) should be an atmosphere gas composed of oxygen gas and inert gas. . As the inert gas, argon gas, nitrogen gas, and helium gas are preferable, and hydrogen gas is also preferable. However, nitrogen gas or argon gas is more preferable because it is low in cost and easy to handle. is there. Further, it may be an atmospheric gas made of oxygen gas. If a silicon oxynitride film is formed on the surface of the silicon particle 101 at a temperature below the melting point Tm! /, If the melting point is above the Tm, there is no problem with oxygen gas alone!

[0146] Each gas partial pressure in the atmospheric gas in the heating furnace can be adjusted by each gas flow rate with respect to the total gas flow rate. The atmospheric gas may be, for example, a force supplied from the gas supply means through the gas filter into the purger as long as the apparatus for supplying the gas to the gas supply means has a mechanism capable of adjusting the gas pressure and the gas concentration.

[0147] When an atmospheric gas composed of an oxygen gas and an inert gas is used as the atmospheric gas for forming the silicon oxynitride film on the surface of the silicon particle 101, the pressure is about 0.01 MPa to 0.2 MPa. Good. If less than OlMPa, evaporation of nitrogen and oxygen from the silicon oxynitride film tends to cause reduction in film thickness and deterioration of the silicon oxynitride film, and if it exceeds 0.2 MPa, variation in film thickness of the silicon oxynitride film occurs. It tends to occur.

[0148] In the case of oxygen gas and inert gas, the oxygen gas partial pressure is preferably 10% or more. Good. When the oxygen gas partial pressure in the atmospheric gas is less than 10%, the oxygen evaporation from the silicon oxynitride film is easily promoted, and the shape cannot be maintained stably when the silicon inside the silicon particles 101 is melted, so that the shape control can be performed. It becomes difficult. Therefore, the partial pressure of inert gas such as nitrogen gas or argon gas should be 90% or less! /.

[0149] In order to produce the single-crystal crystalline silicon particles 101, first, as shown in Fig. 1 (a), a large number (for example, several to several thousand) of polycrystalline silicon particles 101 are placed on the surface. A single layer is placed on the upper surface of the plate 102.

[0150] The multiple silicon particles 101 placed on the base plate 102 may be in contact with each other.

[0151] The multiple silicon particles 101 placed on the base plate 102 may be placed in two or more layers. That is, a large number (for example, several hundred to several thousand) of polycrystalline silicon particles 101 are formed on the upper surface of the base plate 102 in the shape of a substantially spherical silicon particle 101 when viewed in the longitudinal sectional view of FIG. Is a state of being placed so as to form a plurality of layers in the thickness direction, and is a state of being stacked and placed in close packing. By placing them in multiple layers, the silicon particles 101 can be arranged at a high density, and a large number of silicon particles 101 can be single-crystallized at a time, producing crystalline silicon particles at low cost and with high productivity. It becomes possible. Therefore, it is possible to efficiently produce crystalline silicon particles used for a photoelectric conversion device or the like.

[0152] The large number of silicon particles 101 are preferably teardrop-shaped. In this case, the number of grains is on the order of several, and the uniformity of the shape is superior to those of other shapes. However, in addition to the teardrop type, a streamlined type, a connected type in which a plurality of particles are connected, or a substantially spherical shape but a shape in which a protrusion due to solidification expansion is formed does not affect the force.

[0153] The base plate 102 may be stacked and used in a plurality of stages when the box shape without the upper lid or the plate shape is a plate shape. For the material of the base plate 102, quartz glass, mullite, aluminum oxide, silicon carbide, single crystal sapphire, etc. are suitable for suppressing the reaction with the silicon particles 101. Excellent 1S heat resistance, durability, chemical resistance and low cost. From the viewpoint of being easy to handle, Sekiei glass is preferred.

[0154] It is preferable that the base plate 102 has a cristobalite crystal layer formed on the surface of a quartz glass substrate. That is, the silicon particles 101 and the cristobalite crystal layer on the surface of the base plate 102 The contact point becomes a solidification starting point, and non-uniform nucleation occurs, so that the silicon particles 101 are solidified in one direction and can be easily single-crystallized. In addition, the cristobalite crystal layer on the surface of the quartz glass substrate is stable at a temperature of around 1400 ° C and has a function as a surface structure material (surface reinforcing layer) of the quartz glass substrate. Become. As a result, the quartz glass substrate acts to prevent the thermal deformation of the substrate, and the deformation of the substrate due to heat can be prevented.

[0155] The cristobalite crystal layer is formed by repeatedly heat-treating (baking) a quartz glass substrate from room temperature to a temperature exceeding 1200 ° C in an atmosphere containing oxygen, for example, air. That power S. The heat treatment may be repeated one or more times.

[0156] Next, the base plate 102 on which the silicon particles 101 are placed is introduced into a heating furnace (not shown), and the silicon particles 101 are heated. Various furnaces can be used depending on the type of semiconductor material.

[0157] In the process of heating silicon particles 101 in an atmosphere gas consisting of oxygen gas and inert gas in a heating furnace to raise the temperature to a temperature lower than the melting point of silicon (1414 ° C), A silicon oxynitride film is formed on the surface of 101. The formation temperature of the silicon oxynitride film is preferably above room temperature! By introducing and heating an atmospheric gas consisting of oxygen gas and inert gas from room temperature, the force S that forms a silicon oxynitride film with a slow growth rate and a film thickness distribution in a low temperature region of 500 ° C. or lower. By incorporating contaminants and metal impurities adhering to the surface of the silicon particles 101 into the silicon oxynitride film, it becomes a noble layer for preventing contamination inside the silicon. In addition, since the silicon oxynitride film functions as a getter site, contamination by metal impurities from the surrounding environment during heating can be gettered. Further, even at a high temperature near the melting point of silicon, there is an effect of repairing a portion where the silicon oxynitride film is broken due to partial melting.

[0158] Since the silicon oxynitride film formed on the surface of the silicon particle 101 has a higher film density and higher strength per unit film thickness than a silicon oxide film or the like, silicon particles such as contaminants and impurities 101 has an effect of preventing diffusion into the inside of 101.

[0159] The atmosphere in the heating furnace when the silicon oxynitride film is formed on the surface of the silicon particle 101 The gas preferably has an oxygen gas partial pressure of 10% or more. When the partial pressure of oxygen gas in the atmospheric gas is less than 10%, coalescence of silicon particles 101 tends to occur, and the strength of the silicon oxynitride film deteriorates, and the silicon particles 101 are placed in a multilayered state. On the other hand, the weight of the upper silicon particles 101 makes it easier for the lower silicon particles 101 to collapse during melting.

[0160] Next, as shown in FIG. 5 (b), in an atmosphere gas composed of oxygen gas and inert gas or oxygen gas, the silicon particles 101 are higher than the melting point of silicon (1414 ° C)! /, Raise to temperature. Note that the steps in FIGS. 5 (a) and 5 (b) may be performed separately or sequentially.

[0161] The base plate 102 also functions as a starting point for solidification when the silicon particles 101 are melted and supercooled and solidified to be crystallized. In particular, in the case where the base plate 102 has a cristobalite crystal layer formed on the surface of a quartz glass substrate, the contact point between the silicon particles 101 and the cristobalite crystal layer on the surface of the base plate 102 becomes a solidification start point. In addition, non-uniform nucleation is generated, and the silicon particles 101 can be solidified in one direction (for example, upward) and easily single-crystallized. In addition, the cristobalite crystal layer formed on the surface of the quartz glass substrate is stable at a temperature of around 1400 ° C, and functions as a surface structural material (surface reinforcing layer) for the quartz glass substrate. It will have. As a result, the quartz glass substrate acts to prevent the thermal deformation of the substrate, thereby preventing the substrate from being deformed by heat.

[0162] In addition, by placing a large number of silicon particles 101 on the upper surface of the base plate 102, a solidification start point can be set at a contact portion between each silicon particle 101 and the base plate 102. As one pole, 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 generation of subgrains can be suppressed and crystallinity of crystalline silicon particles can be greatly improved.

[0163] Even when a large number of silicon particles 101 are placed on the base plate 102 in a multilayered manner, the contact portion with the crystalline silicon particles on the base plate 102 crystallized first is used as a solidification start point. The adjacent silicon particles 101 can be solidified, and the solidification spreads in a chain reaction toward the upper part rather than the multi-layered structure, greatly improving the crystallinity of a large number of crystalline silicon particles. Can be made. [0164] Since the silicon particles 101 are generally almost spherical in shape, the average particle size is preferably 1500 in or less. When the average particle diameter of the silicon particles 101 exceeds 1500 m, the thickness of the silicon oxynitride film formed on the surface of the silicon particles 101 becomes relatively thin with respect to the silicon particle 101 main body, thereby When silicon is melted, it becomes difficult to keep the shape of the silicon particles 101 stable. Further, it is difficult to completely melt the silicon inside the silicon particles 101, and subgrains are likely to occur when the melting is incomplete. On the other hand, when the average particle size of the silicon particles 101 is less than 30 m, it is difficult to stably maintain the shape of the silicon particles 101 when the silicon inside the silicon particles 101 is melted.

Therefore, it is preferable that the average particle diameter of the silicon particles 101 is 30 m to 1500 m, thereby stably maintaining the shape of the silicon particles 101 and generating a spherical shape with no generation of subdahrain. Crystalline silicon particles having crystallinity can be stably produced.

[0166] The shape of the silicon particles 101 is preferably a teardrop-shaped. The teardrop type has several levels of dullness and is superior in shape uniformity compared to other shapes. However, in addition to the teardrop type, a streamlined type, a connected type in which a plurality of particles are connected, or a substantially spherical shape, but may have a shape in which a protrusion due to solidification expansion is formed. Note that the shape of the silicon particles 101 is not limited to a spherical shape, but may be a cubic shape, a rectangular parallelepiped shape, or other irregular shapes.

[0167] The silicon particles 101 are heated to a temperature T1 not lower than the melting point (1414 ° C) of silicon, preferably not higher than 1450 ° C. During this time, silicon inside the silicon oxynitride film on the surface melts in the silicon particles 101. At this time, the silicon oxynitride film formed on the surface of the silicon particle 101 can maintain the shape of the silicon particle 101 while melting the inner silicon. However, if the temperature of the silicon particle 101 is difficult to maintain stably, for example, in the case of the silicon particle 101, if the temperature is raised to a temperature exceeding 1450 ° C, It becomes difficult to keep the shape of the silicon particles 101 stable when the silicon melts, and the adjacent silicon particles 101 tend to coalesce with each other, and the silicon particles 101 are easily fused to the base plate 102.

Note that the thickness of the silicon oxynitride film formed on the surface of the silicon particles 101 is determined by the silicon particles In the above average particle diameter range of 101, it is preferably lOOnm or more. When the thickness is less than 1 OOnm, the silicon oxynitride film on the surface of the silicon particles 101 is easily broken when the silicon inside the silicon particles 101 is melted.

[0169] In addition, in the case of a silicon oxynitride film having a thickness of lOOnm or more and having a required strength, the silicon inside the silicon particles 101 tends to be spheroidized by surface tension when melted, whereas in the above temperature range, If there is, the silicon oxynitride film can be sufficiently deformed, so that the crystalline silicon particles obtained by single-crystallizing the inside can be made into a shape close to a true sphere.

[0170] On the other hand, when the silicon oxynitride film is thicker than 10, the silicon oxynitride film is hardly deformed in the above temperature range, and the shape of the obtained crystalline silicon particles 101 is close to a true sphere! / , Which is preferable because it is difficult to shape!

[0171] Accordingly, the thickness of the silicon oxynitride film on the surface of the silicon particle 101 is preferably lOOnm to 0 mm with respect to the above average particle diameter range (30 am to 1500 μm). This makes it possible to stably obtain crystalline silicon particles having a good shape close to a true sphere. Further, by using the crystalline silicon particles for a photoelectric conversion device, a photoelectric conversion device having excellent conversion efficiency can be obtained.

Next, as shown in FIG. 5 (c), in order to solidify the molten silicon particles 101 inside the silicon oxynitride film, the temperature is lower than the melting point Tm and is about 1383 ° C. or higher. Decrease the temperature by supercooling to T2 and solidify.

[0173] The temperature gradient of the supercooling is preferably 2 ° C / min or more. If the temperature gradient of subcooling is less than 2 ° C / min, solidification is difficult to start because the temperature change per hour is small. As a result, the temperature is lowered while maintaining the supercooled state, and coalescence of adjacent silicon particles 101 is likely to occur, which is not preferable.

[0174] On the other hand, when the temperature gradient of supercooling exceeds 200 ° C / min, since the temperature change per hour is large, deep supercooling occurs in a short period of time, and the inside of the silicon particles 101 and The temperature difference of the surface becomes large, and grain boundaries are generated by uniform nucleation, protrusions are formed by solidification expansion, and crystal defects are generated.

[0175] Therefore, it is preferable that the temperature gradient of the supercooling is 2 ° C / min to 200 ° C / min. This makes the supercooling from the melting point Tm of silicon at a high temperature of 1383 ° C or higher. Small temperature range It becomes easy to start coagulation. Solidification is a two-dimensional growth of unidirectional solidification in which the solidification interface moves in one direction, and does not include grain boundaries or crystal defects due to the formation of protrusions at the solidification end, and has a high quality crystallinity. Can produce crystalline silicon particles

[0176] The temperature T2 at the time of supercooling is preferably 1410 ° C or lower and 1383 ° C or higher. That is, at a temperature exceeding 1410 ° C., the degree of supercooling (Tm−T2) is too small, so that the solidification of the silicon particles 101 is difficult to start. If the temperature T2 at the time of supercooling is 1410 ° C or less, the solidification of the silicon particles 101 is easy to start, and high-quality crystalline silicon particles that do not contain grain boundaries or crystal defects are produced. can do.

[0177] In addition, when the temperature T2 at the time of supercooling is less than 1383 ° C, solidification occurs in a temperature range where the degree of supercooling (Tm-T2) is large. Therefore, two-dimensional growth of unidirectional solidification is not achieved, and protrusions are formed at the end of solidification, resulting in polycrystalline crystalline silicon particles having grain boundaries and crystal defects.

[0178] Further, until all the molten silicon particles 101 are solidified, they are maintained at a predetermined temperature within a range of T2 and a temperature T2 of 1383 ° C or higher, thereby forming protrusions at the solidification end, It can prevent the generation of crystal defects, the generation of uniform nuclei that can be polycrystallized, and dendrite growth.

[0179] However, even if the temperature T2 at the time of supercooling is lower than 1383 ° C, if the temperature is 1368 ° C or higher, the crystalline silicon particles can be obtained as a single crystal. Protrusions are likely to be formed in the parts. There are crystal defects and crystal orientation disturbances in the protrusions. When a photoelectric conversion device is fabricated using crystalline silicon particles with protrusions, photoelectric conversion due to pn junction deterioration or current leakage at the protrusions It tends to deteriorate characteristics. However, in this case, if the crystalline silicon particles from which the protrusions are removed by a polishing method or the like are used, a photoelectric conversion device in which the photoelectric conversion characteristics are not deteriorated by the protrusions can be manufactured. However, problems such as increased costs due to an increase in the manufacturing process arise. At a temperature of 1383 ° C or higher, there is no formation of protrusions and the shape can be made closer to a true sphere. When used in a device, good photoelectric conversion characteristics can be obtained.

[0180] Therefore, it is subcooled to a temperature T2 of 1410 ° C or lower and 1383 ° C or higher, and until the molten silicon particles 101 are all solidified, it is less than Tm and within a predetermined range of 1383 ° C or higher. Maintaining the temperature results in heterogeneous nucleation and two-dimensional growth of unidirectional solidification, and has high-quality crystallinity that does not include grain boundaries and crystal defects that are not formed by protrusions at the solidification end. Single crystal crystalline silicon particles can be manufactured.

[0181] Also, even when a large number of silicon particles 101 are placed in multiple layers, the molten silicon particles 101 are all solidified by supercooling to a temperature T2 of 1410 ° C or lower and 1383 ° C or higher. By holding at a predetermined temperature until solidification, solidification progresses in one direction from the contact portion between the silicon particle 101 and the base plate 102 to the upper facing pole as the solidification start point (one pole), so that the solidification has already occurred. Unidirectional solidification occurs at the point of contact with the silicon particle 101 as the starting point of solidification. Then, as it is, solidification is inherited in one direction (for example, upward direction) as a whole and the crystal grows, and the resulting crystalline silicon particle becomes a single crystal, which can greatly improve the crystallinity.

[0182] Further, after solidifying the molten silicon particles 101, it is preferable to subject the crystalline silicon particles to a thermal annealing treatment, for example, a thermal annealing treatment at a constant temperature of 1000 ° C or higher for 30 minutes or longer. However, even if it is not held at a constant temperature, the accumulated time in the temperature range of 1000 ° C or higher may be 30 minutes or longer. By carrying out this thermal annealing treatment, the strain in the crystal of the crystalline silicon particles generated during solidification and the interface strain generated at the interface between the silicon oxynitride film on the surface of the crystalline silicon particles and the inner crystalline silicon are alleviated and removed. Further, since gettering of metal impurities is also promoted, crystalline silicon particles having good crystallinity can be obtained.

[0183] In addition, the method for producing crystalline silicon particles of the present invention includes removing the silicon oxynitride film and removing interfacial strain between the silicon oxynitride film and the crystalline silicon particles after the silicon particles are monocrystallized. Is preferred. That is, the silicon oxynitride film, which contains metal impurities such as Fe, Cr, Ni, and Mo, and light element impurities such as oxygen and carbon, segregated on the surface layer of the crystalline silicon particles, is removed. The silicon oxynitride film can be removed by hydrofluoric acid, and the surface of the crystalline silicon particles after removing the silicon oxynitride film can be removed by etching with hydrofluoric acid or the like. it can. The thickness of the surface layer of the crystalline silicon particles removed at that time is preferably 100 m or less in the radial direction.

[0184] The temperature of the silicon particles 101 can be measured by an optical wavelength decomposition measurement method or the like.

That is, the analysis is performed by analyzing the emission spectrum of the silicon particles 101. Specifically, the emission spectrum according to the temperature of silicon is measured in advance as a data table, the emission spectrum of silicon particles 101 in the heating device is measured, and compared with the emission spectrum in the data table. The temperature can be specified without contact with the silicon particles 101. In addition, the temperature of the silicon particles 101 can be specified by thermal analysis from the furnace atmosphere gas temperature, furnace wall temperature, furnace gas pressure, furnace gas type, and the like.

Next, examples of the method for producing crystalline silicon particles of the present invention will be described along the production steps, but the present invention is not limited to the following examples.

Example 1

As shown in FIG. 1 (a), first, 1000 pieces of silicon particles 101 having a boron concentration of 0.6 × 10 ¹⁶ atoms / cm ³ and an average particle size force of S500 m were placed in a quartz glass box. Were placed in layers on a base plate 102 and housed in a quartz glass bell jar installed in an atmosphere firing furnace as a heating furnace. Then, nitrogen gas is heated while being introduced from the gas supply device, heated to 1300 ° C below the melting point of silicon with a nitrogen gas pressure of 0. IMPa, and held for 60 minutes, with a thickness of 200 nm on the surface of the silicon particles 101. A silicon nitride film was formed. After heating at 1300 ° C for 60 minutes, the temperature was lowered to room temperature.

Next, as shown in FIGS. 1 (b) and (c), oxygen gas or a mixed gas (oxygen gas and argon gas) (see Tables 1 and 2) is heated while being introduced from the gas supply device. After heating to 1440 ° C above the melting point of silicon at an oxygen gas pressure of 0.02 MPa and holding for 5 minutes to melt the silicon inside the silicon nitride film on the surface of the silicon particles 101, the rate of temperature decrease is 2 The solution was solidified while being cooled to ° C. Thereafter, the temperature was further lowered to 1250 ° C., and then a thermal annealing treatment was performed for 120 minutes while introducing an argon gas as an inert gas. After this heat annealing treatment, the temperature was lowered to near room temperature.

[0188] The silicon silicon nitride film formed on the surface of the recovered crystalline silicon particles is removed with hydrofluoric acid, and the surface of the crystalline silicon particles is etched in the depth direction with hydrofluoric acid to a predetermined thickness. Removed.

[0189] The crystalline silicon particles are placed on a quartz boat, introduced into a quartz tube controlled at 900 ° C, and POC1 gas is bubbled with nitrogen and sent into the quartz tube, and then by a thermal diffusion method.

Three

In 30 minutes, an n-type semiconductor layer 410 having a thickness of about 1 [I m was formed on the surface of the crystalline silicon particles, and then the surface oxynitride film was removed with hydrofluoric acid.

Next, a 50 mm × 50 mm × 0.3 mm thick aluminum substrate was used as the conductive substrate 407, and 1000 crystalline silicon particles 406 were closely packed on the upper surface. Thereafter, at 600 ° C of greater than 577 ° C which is the eutectic temperature of aluminum and silicon, by heating in a reducing atmosphere furnace a nitrogen gas containing 5 volume ^_0/0 of hydrogen gas, the crystalline silicon particles 406 The lower part was bonded to the conductive substrate 407. At this time, a bonding layer 408 made of a eutectic of aluminum and silicon was formed on the portion where the crystalline silicon particles 406 were in contact with the conductive substrate 407, and exhibited strong adhesive strength.

[0191] Furthermore, between the crystalline silicon particles 406 from above, an upper portion thereof is exposed and an insulating material 409 made of a polyimide resin is applied and dried to form a conductive substrate 407 serving as a lower electrode, and an upper portion. The translucent conductor layer 411 serving as an electrode is electrically insulated and separated. A translucent conductor layer 411 as an upper electrode film was formed on the entire surface with a thickness of about lOOnm by sputtering.

[0192] Finally, a silver paste pattern was formed in a grid using a dispenser to form an electrode 412 composed of a finger electrode and a bus bar electrode. This silver paste pattern was fired at 500 ° C in the atmosphere.

[0193] Then, when manufacturing the photoelectric conversion device of the present invention as described above, the presence or absence of the silicon nitride film forming step, the melting step in oxygen gas or mixed gas, and the silicon particles are further distinguished. We examined the coalescence rate of silicon particles when single-crystallized in a single-layer or close-packed and stacked state on a quartz glass box-like base plate. The results are shown in Table 1 as Examples 1-1 to 4 and Comparative Examples 1-1 and 2.

The coalescence rate was determined from the ratio of the number of coalesced to the total number {(the number of coalesced) X 100 / (the number of the whole)}. For example, if there are 95 non-merged pieces, two mergers and three mergers, the total number is 100 and the coalescence rate is 5%. [0194] Further, regarding the photoelectric conversion devices of Examples 1-;! To 4 and Comparative Examples 1-1 and 2 obtained by the above manufacturing method, the electrical characteristics of the photoelectric conversion devices are shown by the solar simulator of AMI. Photoelectric conversion efficiency (unit:%) (shown as “conversion efficiency” in Table 2) was measured. The results are shown in Table 1.

[table 1]

[0195] As shown in Table 1, a crystalline silicon particle was produced by forming a silicon oxide film on the surface of a silicon particle in an atmospheric gas composed of oxygen gas without forming a silicon nitride film, and melting and solidifying it (Comparison Example: Compared with 1-1, 2), a silicon nitride film is formed on the surface of silicon particles, and it is melted and solidified in an atmospheric gas consisting of oxygen gas force or atmospheric gas consisting of oxygen gas and inert gas. The crystalline silicon particles (Example 1- ;! to 4) produced in this way had good results with a low coalescence rate.

[0196] Note that the coalescence rate of Examples 1-3 and 4 is larger than the coalescence rate of Examples 1-1 and 2, because the surface bonding state of the silicon nitride film is due to the use of argon gas in the atmospheric gas. This is thought to be due to the fact that the surface tension of the silicon particles also changed, making it easier to unite.

[0197] Further, as shown in Table 1, compared with Comparative Examples 1-1 and 2, Examples 1-;! To 4 had high conversion efficiency and good results.

[0198] The conversion efficiencies of Examples 1-1 and 2 are higher than those of Examples 1-3 and 4 because the crystals are due to the generation of subgrains at the contact portions between the crystalline silicon particles. This is thought to be due to the reduction in deterioration.

Example 2

[0199] As shown in Fig. 3 (a), first, 1000 pieces of crystalline silicon particles 101 having a boron concentration of 0.6 X 10 ¹⁶ atoms / cm ³ and an average particle size force of S500 m were added to the lapping apparatus. Lower rotating surface plate 2 It was placed on 01 and the upper rotating platen 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 opposite directions, and the average particle size is 30 m. The surface of the crystalline silicon particles 101 was polished for 5 minutes using SiC free abrasive grains 203.

[0200] It can be confirmed by Raman spectroscopy that a work-affected layer having a large number of microcracks or the like is formed on the surface layer portion of the crystalline silicon particle 101 whose surface is polished by a thickness of about 10 m. It was.

[0201] Next, as shown in FIG. 3 (b), a large number (1000 pieces) of crystalline silicon particles 101 are placed in a multilayer manner on a quartz glass box-like base plate 301, and heated in a heating furnace. It was housed in a quartz glass bell jar installed inside an atmosphere firing furnace. Then, nitrogen gas is heated while being introduced from a gas supply device, heated to 1300 ° C. below the melting point of silicon with a nitrogen gas pressure of 0.1 IMPa, and held for 60 minutes to form a silicon nitride film on the surface of the crystalline silicon particles 101 Formed. After heating at 1300 ° C. for 60 minutes, the temperature was lowered to room temperature.

[0202] Next, as shown in FIGS. 3 (c) and 3 (d), while introducing oxygen gas or a mixed gas (oxygen gas and argon gas) (see Table 1) from the gas supply device, the oxygen gas pressure 0 The crystalline silicon particles 101 were heated to 1440 ° C, which is above the melting point of silicon at 02 MPa, 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 the cooling rate was reduced every minute. The crystalline silicon particles 101 were solidified while cooling at 2 ° C. After that, the temperature was further lowered to 1250 ° C., and a thermal annealing treatment was performed for 120 minutes while introducing an argon gas as an inert gas. After this thermal annealing treatment, the temperature was lowered to near room temperature.

[0203] 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 to a depth of 20 Hm with hydrofluoric acid. did.

[0204] The crystalline silicon particles 101 were placed on a quartz boat, introduced into a quartz tube controlled at 900 ° C, POC1 gas was published with nitrogen and fed into the quartz tube, and the thermal diffusion method was used.

Three

In 30 minutes, a η-type semiconductor layer 410 having a thickness of about 1 μm was formed on the surface of the crystalline silicon particle 101, and then the oxynitride film on the surface was removed with hydrofluoric acid.

[0205] Next, an aluminum substrate of 50 mm X 50 mm X thickness 0.3 mm was used as the conductive substrate. The top surface was arranged with 1000 crystalline silicon particles packed closest. After that, it is heated in a reducing atmosphere furnace of nitrogen gas containing 5% by volume of hydrogen gas at 600 ° C, which exceeds the eutectic temperature of aluminum and silicon of 577 ° C. The lower part was bonded to the conductive substrate. At this time, a bonding layer made of eutectic of aluminum and silicon was formed at the portion where the crystalline silicon particles were in contact with the conductive substrate, and exhibited strong adhesive strength.

[0206] Furthermore, between the crystalline silicon particles from above, an upper portion thereof is exposed and an insulating material made of polyimide resin is applied and dried to form a conductive substrate serving as a lower electrode and an upper electrode. The light-transmitting conductor layer is electrically insulated and separated. A translucent conductor layer as an upper electrode film was formed on the entire surface with a thickness of about lOOnm by sputtering.

[0207] Finally, a silver paste pattern was formed in a grid pattern with a dispenser to form an electrode composed of a finger electrode and a bus bar electrode. The silver paste pattern was fired at 500 ° C in the atmosphere.

[0208] When the photoelectric conversion device of the present invention is manufactured 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, oxygen gas or mixed gas And the crystalline silicon particles are simply placed on a quartz glass box-like base plate in a single layer, or in a state of being placed in layers with close packing. The coalescence rate of the crystalline silicon particles upon crystallization was examined in the same manner as in Example 1. The results are shown in Table 2 as Examples 2-;! To 4 and Comparative Examples 2-1 and 2.

[0209] Further, regarding the photoelectric conversion devices of Examples 2-;! To 4 and Comparative Examples 2-1 and 2 obtained by the above-described manufacturing method, the electrical characteristics of the photoelectric conversion device are shown by a solar simulator of AMI. Photoelectric conversion efficiency (unit:%) (expressed as “conversion efficiency” in Table 1) was measured. The results are shown in Table 2.

[Table 2] About

Work-affected layer Silicon nitride film Mount ratio Conversion efficiency Melting process

Formation process Formation process State (%) () Atmospheric gas

Presence or absence

Example 2-1 Yes Yes Oxygen gas 1 layer 5 9.6 Example 2-2 Yes Yes Oxygen gas Multilayer 1 1 8.5 Mixed gas

Example 2-3 Yes Yes 1 layer 9 7.4

(Oxygen gas + argon gas)

Gas mixture

Example 2-4 Yes Yes Multilayer 16 6.1

(Oxygen gas + argon gas)

Comparative example 2-1 Yes Yes Oxygen gas 1 layer 23 3.9 Comparative example 2-2 No Yes Oxygen gas multilayer 68 4.2 Comparative example 2-3 Yes No Oxygen gas 1 layer 29 4.9 Comparative example 2-4 Yes No Oxygen gas multilayer 71 3.2

[0210] As shown in Table 2, a silicon oxide film was formed on the surface of the crystalline silicon particles in the atmosphere gas composed of oxygen gas without forming a work-affected layer by polishing on the surface of the crystalline silicon particles. Crystal silicon particles produced by solidification (Comparative Examples 2-1 and 2) and a silicon oxide film formed on the surface of the crystalline silicon particles in an atmosphere gas composed of oxygen gas without forming a silicon nitride film and melted Compared with the crystalline silicon particles produced by solidification (Comparative Examples 2-3, 4), a work-affected layer is formed by polishing on the surface of the crystalline silicon particles, and a silicon nitride film is formed on the surface of the crystalline silicon particles. The crystalline silicon particles (Example 2-;! To 4) prepared and melted and solidified in an atmospheric gas composed of oxygen gas or an atmospheric gas composed of mixed gas (oxygen gas and inert gas) Was a good result with a low coalescence rate

[0211] The cause of the coalescence rate of Example 2-3 being greater than the coalescence rate of Example 2-1 and the coalescence rate of Example 2-4 being greater than the coalescence rate of Example 2-2 This is probably because the use of argon gas in the atmosphere gas changed the surface bonding state of the silicon nitride film and the surface tension of the crystalline silicon particles, making it easier to merge.

[0212] In contrast to Comparative Example 2-;! ~ 4, Example 2-;! ~ 4 showed high conversion efficiency and good results.

[0213] The conversion efficiencies of Examples 2-1 and 2 are larger than those of Examples 2-3 and 4 because crystals due to the generation of subgrains at the contact portions between the crystalline silicon particles, etc. This is thought to be due to the reduction in deterioration.

Example 3 [0214] As shown in Fig. 5 (a), first, 20 silicon particles 101 having a boron concentration of 1.0 X 10 ¹⁶ atoms / cm ³ and an average particle size force of 00 m were placed in a quartz glass box. The sample was placed on the base plate 102 in a single layer and housed in a quartz glass tube installed in a carbon heater type heating furnace.

[0215] Next, the box-shaped base plate 102 made of quartz glass was pretreated. That is, heat treatment was repeated 5 times in the air atmosphere from room temperature to around 1430 ° C with a temperature profile of 2 hours for temperature rise and 4 hours for temperature fall. The surface of the base plate 102 after heat treatment has turned white, and when confirmed by X-ray diffraction, a shift from the broad peak of the early quartz glass to the steep peak due to the cristobalite crystal can be confirmed. It was.

Next, as shown in FIGS. 5 (b) and 5 (c), oxygen gas and nitrogen gas are introduced into the heating furnace at a ratio of oxygen gas partial pressure of 20% and nitrogen gas partial pressure of 80%. The silicon particles 101 were heated to form a silicon oxynitride film on the surface of the silicon particles 101. Bow I While continuing to introduce oxygen gas, heat silicon particle 101 to 1430 ° C, which is above the melting point of silicon, and hold it for 5 minutes to remove the silicon inside the silicon oxynitride film on the surface of silicon particle 101. Melted.

[0217] Next, the temperature gradient of the temperature drop was set to 60 ° C / min, and the mixture was supercooled to temperature T2 (four temperatures of 1410 ° C, 1400 ° C, 1390 ° C, and 1383 ° C were set) Subsequently, the silicon particles 101 were coagulated by holding at the respective temperatures T2 (1410 ° C, 1400 ° C, 1390 ° C, 1383.C) for 30 minutes at a constant temperature.

[0218] Thereafter, a heat annealing treatment for 60 minutes was performed in the process of lowering the temperature to 1000 ° C. After this thermal annealing treatment, the temperature was lowered to near room temperature.

[0219] In each of the above steps, a CCD camera as a monitor was installed at the top of the heating furnace to enable in-situ observation of the melting and solidification of the silicon particles 101, and the solidification start temperature and solidification form were monitored. Observed.

[0220] Also, as a comparative example, up to the supercooling temperature T2 (four temperatures of 1380 ° C, 1368 ° C, 1322 ° C, 1250 ° C were set) when melting and supercooling the silicon particles 101 The silicon particles 101 were solidified by supercooling and subsequently holding at the respective temperatures T2 (1380. C, 1368 ° C, 1322 ° C, 1250.C) at a constant temperature for 30 minutes.

[0221] Example 3-1 (T2 = 1410. C), Example 3-2 (T2 = 1400. C), Example 3-3 (T2 = 139) 0 ° C), Example 3-4 (T2 = 1383 ° C), Comparative Example 3-l (T2 = 1380 ° C), Comparative Example 3-2 (T2 = 1368), Comparative Example 3_3 (Ding 2 = 1132) Each of the crystalline silicon particles in Comparative Example 3_4 (Ding 2 = 1250) was examined for crystallinity. The crystallinity was evaluated by performing mirror polishing in which the crystalline silicon particles were embedded in a resin and polished together with the resin. Japan Industry Standard) B liquid (HF: HNO: CH COOH: H 0 = 1: 12. 7: 3: 5. 7)

3 3 2

Using this, selective etching was performed, and grain boundaries and pits (crystal defects) were observed. Figures 6 and 7 show cross-sectional photographs of the resulting crystalline silicon particles.

[0222] As shown in Fig. 6, in Example 3-;! To 4 in which the supercooling temperature T2 is 1410 ° C to 1383 ° C, formation of protrusions at the solidification terminal portion, grain boundaries and crystals Defects and dislocations were not observed, and it was a component that it was a single crystal.

[0223] In Comparative Example 3-1, in which T2 is 1380 ° C, grain boundaries, crystal defects, and dislocations are not observed, and it is a single crystal that has a component force. It was.

[0224] In Comparative Example 3-2 where T2 is 1368 ° C, dislocations and linear defects were observed, but the shape of the linear defects was OSF (oxidation-induced stacking faults), and grain boundaries Instead, it was confirmed to be a single crystal. However, as in Comparative Example 3-1, where T2 was 1380 ° C,! /, A protrusion was formed at the end of solidification! /.

[0225] In Comparative Example 3-3, where T2 is 1322 ° C, and in Comparative Example 3-4, where T2 is 1250 ° C, pits (black) due to crystal defects are observed in the grain boundaries. It turned out to be polycrystalline.

[0226] Therefore, if the supercooling temperature T2 is from 1410 ° C to 1383 ° C, the crystalline silicon particles are single crystals with no protrusions formed at the end of solidification (Example 3-;! To 4). The crystalline silicon particles of Examples 3-1 to 4 are the single crystals of Comparative Example 3-;! To 2, but the crystalline silicon particles in which protrusions were formed at the solidification termination portion, and the comparative Examples 3_3 to 4 Compared to crystalline silicon particles, the shape and crystallinity were excellent.

FIG. 8 shows a temperature profile for the method for producing crystalline silicon particles of the present invention.

Yes

[0228] Regarding the relationship between the crystallinity and the degree of supercooling, it is considered that if unidirectional solidification by heterogeneous nucleation occurs in a state where the degree of supercooling is smaller, a single crystal is more likely to be formed. However, more In order to start solidification in a state where the degree of cooling is small, a larger trigger for the start of solidification is necessary.In the present invention, a larger solidification temperature is obtained by increasing the temperature gradient of the temperature drop by the method of supercooling. Realized the start trigger. In order to generate heterogeneous nucleation, it is considered effective that a cristobalite crystal layer is formed on the surface of a quartz glass substrate.

[0229] When T2 is 1368 ° C or more and 1380 ° C or less, even if the inside of the crystalline silicon particle is a single crystal, protrusions having crystal defects and disorder of crystal orientation are formed in a very small part of the solidification terminal portion. Producing a photoelectric conversion device using crystalline silicon particles having such protrusions easily results in deterioration of the pn junction at the protrusion and deterioration of photoelectric conversion characteristics due to current leakage, which is not preferable. However, in this case, if the crystalline silicon particles from which the protrusions are removed by a polishing method or the like are used, problems such as an increase in cost and the like that can produce a photoelectric conversion device in which the photoelectric conversion characteristics do not deteriorate due to the protrusions occur.

[0230] When T2 is 1383 ° C or higher and 1410 ° C or lower, crystal silicon particles having a shape closer to a true sphere can be produced without formation of protrusions, which is good when the crystal silicon particles are used in a photoelectric conversion device. Photoelectric conversion characteristics can be obtained.

[0231] Polycrystalline crystalline silicon particles with grain boundaries and crystal defects as in Comparative Examples 3-3 and 4 have a high degree of supercooling (Tm-T2), so that solidification is It is thought that uniform nucleation that occurs simultaneously from multiple points on the surface caused dendrite growth.

It should be noted that the present invention is not limited to the above embodiments and examples, and various modifications can be made without departing from the gist of the present invention. For example, in order to heat and melt the crystalline silicon particles, a method may be used in which the crystalline silicon particles are melted by irradiating light energy from above the crystalline silicon particles placed on the upper surface of the base plate.

Claims

The scope of the claims

[1] In an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component, silicon particles are heated to a temperature below the melting point of silicon,

Next, in an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and inert gas, the silicon particles are heated to melt the silicon while maintaining its shape, and then cooled and solidified to form a single crystal. A method for producing crystalline silicon particles.

[2] In an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component, silicon particles are heated to a temperature below the melting point of silicon to form a hard film harder than the inside on the surface of the silicon particles. And

Next, in the atmosphere gas composed of oxygen gas or in the atmosphere gas composed of oxygen gas and inert gas, the silicon particles are heated to be softened by adding oxygen to the hard film, and silicon inside the hard film A method for producing crystalline silicon particles, characterized in that a single crystal is obtained by melting and solidifying by cooling with V.

[3] In an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component, the silicon particles are heated to a temperature below the melting point of silicon to form a silicon nitride film on the surfaces of the silicon particles,

Next, in the atmosphere gas composed of oxygen gas or the atmosphere gas composed of oxygen gas and inert gas, the silicon particles are heated to melt the silicon inside the silicon nitride film, and the temperature is lowered and solidified by using! /. A method for producing crystalline silicon particles, characterized by being single-crystallized.

4. The method for producing crystalline silicon particles according to claim 3, wherein the silicon nitride film contains oxygen.

[5] In an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and inert gas, the silicon particles are heated to melt the silicon inside the silicon nitride film, and then cooled to solidify. 4. The method for producing crystalline silicon particles according to claim 3, wherein the process power for single crystallization is performed in a state where a large number of the silicon particles are placed in a multilayered manner on a base plate.

6. The method for producing crystalline silicon particles according to claim 3, wherein the silicon nitride film is removed after the silicon particles are monocrystallized.

7. The method for producing crystalline silicon particles according to claim 6, wherein the silicon nitride film contains a metal impurity.

8. The method for producing crystalline silicon particles according to claim 3, wherein the pressure of the atmospheric gas composed of nitrogen gas or the atmospheric gas containing nitrogen gas as a main component is 0.01 to 0.2 MPa. .

9. The method for producing crystalline silicon particles according to claim 3, wherein the atmospheric gas composed of nitrogen gas or the atmospheric gas containing nitrogen gas as a main component has a nitrogen gas partial pressure of 70% or more.

10. The method for producing crystalline silicon particles according to claim 3, wherein the silicon nitride film has a thickness of lOOnm to 10 m.

11. The production of crystalline silicon particles according to claim 3, wherein the atmospheric gas comprising oxygen gas or the atmospheric gas comprising oxygen gas and an inert gas has a pressure of 0.01 to 0.2 MPa. Method.

12. The method for producing crystalline silicon particles according to claim 5, wherein the base plate is made of quartz glass, mullite, aluminum oxide, silicon carbide, or sapphire.

13. The method for producing crystalline silicon particles according to claim 4, wherein the content of oxygen contained in the silicon nitride film is 10 mol% or less.

[14] After forming a work-affected layer on the surface portion of the crystalline silicon particles by subjecting the surface of the crystalline silicon particles to polishing, an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component 2. The method for producing crystalline silicon particles according to claim 1, wherein the silicon particles are heated to a temperature below the melting point of silicon to form a silicon nitride film on the surface of the silicon particles.

[15] Crystalline silicon particle force Prepared by discharging and dropping the silicon melt in a granular form from a nozzle part of a crucible containing silicon melt, and cooling and solidifying the granular silicon melt during the fall. 15. The method for producing crystalline silicon particles according to claim 3 or 14, wherein:

[16] A silicon oxynitride film is formed on the surface of the silicon particle by heating the silicon particle to a temperature below its melting point in an atmosphere gas composed of oxygen gas and nitrogen gas, and then on the surface of the silicon particle. With the formed silicon oxynitride film, the silicon particles are heated to a temperature T1 equal to or higher than the melting point Tm of the silicon while maintaining the shape thereof, and the silicon inside is melted, and then the temperature T1 is less than the melting point Tm. Step 1 of supercooling to a temperature T2 above 1383 ° C, and

Next, the step 2 of maintaining the molten silicon particles at a predetermined temperature within the range of 1383 ° C or more below the melting point Tm until all the molten silicon particles are solidified,

13. The method for producing crystalline silicon particles according to claim 12, comprising:

[17] In the step 1, from the temperature T1, the temperature is 1410 ° C or lower and 1383 ° C or higher

17. The method for producing crystalline silicon particles according to claim 16, wherein supercooling is performed to T2.

[18] In step 1, a base plate having silicon particles placed on the upper surface is placed in a heating device, and the silicon particles are heated to a temperature below its melting point Tm in an atmospheric gas composed of oxygen gas and nitrogen gas. 17. The method for producing crystalline silicon particles according to claim 16, wherein a silicon oxynitride film is formed on a surface of the silicon particles.

[19] The method for producing crystalline silicon particles according to [18], wherein a plurality of silicon particles are single-crystallized in a state of being stacked on the base plate.

20. The method for producing crystalline silicon particles according to claim 18, wherein the base plate has a cristobalite crystal layer formed on a surface of a quartz glass substrate.

21. The method for producing crystalline silicon particles according to claim 18, wherein the silicon oxynitride film is removed after the silicon particles are monocrystallized.

22. The method for producing crystalline silicon particles according to claim 21, wherein the silicon oxynitride film contains a metal impurity.

23. The method for producing crystalline silicon particles according to claim 16, wherein the temperature gradient of the supercooling in step 1 is 2 ° C./min to 200 ° C./min.