JP2009292650A - Method for producing crystal silicon particles - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing crystal silicon particles capable of stably single-crystallizing silicon particles at a high efficiency and producing single crystal particles at a low cost. <P>SOLUTION: In the method for producing crystal silicon particles, silicon particles 101 are heated at 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 particles 101. Subsequently, the silicon particles 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 at the inside of the silicon nitride film, and then lowered in temperature to be solidified and single-crystallized. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

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

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

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

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

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

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

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

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

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

  That is, it is difficult to produce desired high-quality single crystal silicon particles by the conventional method for producing crystalline silicon particles, and a photoelectric conversion device having excellent electrical characteristics is produced using the obtained crystalline silicon particles. Therefore, there is a problem that it is not suitable as a manufacturing method.

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

  In the method for producing crystalline silicon particles according to the present invention, a silicon particle is 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 nitride the surface of the silicon particles. A silicon film is formed, 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 melt the silicon inside the silicon nitride film and lower the temperature. It is characterized by solidifying into a single crystal.

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

  In the method for producing crystalline silicon particles of the present invention, preferably, 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 heat silicon inside the silicon nitride film. When the silicon is melted, cooled and solidified to form a single crystal, the single crystal is formed in a state where a large number of the silicon particles are placed on the base plate in a multilayered manner.

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

  In the method for producing crystalline silicon particles according to the present invention, silicon nitride is heated on the surface of silicon particles by 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 film is formed, and then the silicon particles are heated in an atmosphere gas consisting of oxygen gas or an atmosphere gas consisting of oxygen gas and an inert gas to melt the silicon inside the silicon nitride film, and the temperature is lowered and solidified. Since the silicon nitride film is formed as a pretreatment on the surface of the silicon particles during single crystallization because of single crystallization, the combination of the crystalline silicon particles is effectively suppressed, and the crystalline silicon particles by the combination Crystalline silicon particles having high quality crystallinity that do not generate crystal cracks or subgrains at the contact surfaces between them can be produced.

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

  Furthermore, since the silicon nitride film has higher density and higher strength per unit thickness than the silicon oxide film, the silicon nitride film is heated to melt the silicon inside the silicon nitride film and to cool and solidify it. In addition, the film thickness of the silicon nitride 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 a later process is reduced, and silicon resources can be used effectively.

  In the method for producing crystalline silicon particles of the present invention, the silicon nitride film may contain oxygen, and the same effect as described above can be obtained.

  In the method for producing crystalline silicon particles of the present invention, the silicon particles are preferably melted by heating the silicon particles in an atmospheric gas composed of oxygen gas or an atmospheric gas composed of oxygen gas and an inert gas. It is formed on the surface of silicon particles by pretreatment by single crystallizing in a state where a large number of silicon particles are stacked on the base plate when cooling and solidifying to single crystal. In order for the silicon nitride film to effectively prevent coalescence of silicon particles, a large number of silicon particles are placed on the base plate in a single layer in the case of single crystallization in a heating furnace, so that the silicon particles have a high density. By arranging them in a single layer, a large number of silicon particles can be single-crystallized at a time, and it becomes possible to produce crystalline silicon particles at low cost and with high mass productivity. Therefore, it is possible to efficiently produce crystalline silicon particles used for a photoelectric conversion device or the like.

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

  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, and thus segregates on the surface layer portion of the crystalline silicon particles, such as Fe, Cr, Ni, Mo, etc. 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.

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

  1 (a) to 1 (c) each show an example of an embodiment of a method for producing crystalline silicon particles of the present invention, and shows a large number of silicon particles placed on a base plate in a multilayered manner. It is sectional drawing for every process. In FIG. 1, 101 is a silicon particle, 102 is a base plate.

  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 (jet) Method) to obtain polycrystalline silicon particles 101.

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. As dopants for silicon, boron, aluminum, gallium, indium, phosphorus, arsenic, and antimony are used. However, boron or phosphorus is used because it has a large segregation coefficient for silicon and a small evaporation coefficient when silicon is melted. desirable. The dopant concentration is about 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ³ added to the silicon crystal material.

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

  In order to improve this, according to the method for producing crystalline silicon particles of the present invention, first, as a pre-process, in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component, in a temperature-controlled heating furnace The polycrystalline silicon particles 101 are heated to a temperature (500 to 1400 ° C.) below the melting point (1414 ° C.) of silicon to form a silicon nitride film on the surface of the silicon particles 101. The silicon particles 101 are made into a single crystal by remelting in an atmosphere gas or an atmosphere gas composed of an oxygen gas and an inert gas, lowering the temperature, and solidifying.

  The single crystallization of the silicon particles 101 by the manufacturing method of the present invention is performed at a rate (about 99.9% in terms of the number) that, for example, about 999 out of 1000 silicon particles 101 are completely single crystallized. be able to.

  Further, after the post-process, the silicon nitride film may be removed, and the metal impurity containing portion such as Fe, Cr, Ni, Mo, etc. segregated on the surface layer portion of the crystalline silicon particles 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.

  The pressure of the atmospheric gas composed of nitrogen gas in the previous step or the atmospheric gas containing nitrogen gas as a main component is preferably about 0.01 M to 0.2 MPa. If the pressure is less than 0.01 MPa, the film thickness of the silicon nitride film is easily reduced or the film quality is deteriorated due to evaporation of nitrogen or oxygen from the silicon nitride film. If the pressure exceeds 0.2 MPa, the film thickness variation of the silicon nitride film is likely to occur. .

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

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

  The reason why the oxygen gas is included as an essential gas component in the atmospheric gas in the subsequent process is that the diffusion of oxygen into the silicon nitride film increases the flexibility of the silicon nitride film and makes the shape more stable when the silicon particles 101 melt. It is because it is possible to maintain it. Further, since the oxygen partial pressure in the atmospheric gas is increased, oxygen evaporation from the silicon nitride film can be reduced, and when oxygen is not contained in the atmospheric gas, the silicon particles 101 are melted. This is to prevent the base plate 102 made of quartz glass or the like from sometimes reacting and fixing.

  In the case where oxygen gas and inert gas are used in the post-process, the oxygen gas may be contained in an amount of 20% by volume or more, and the inert gas such as argon gas may be contained in an amount of 80% by volume or less. 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 the silicon inside the silicon particles 101 is melted, making it difficult to control the shape.

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

  A large number of silicon particles 101 may be mounted on the base plate 102, but it is preferable that the silicon particles 101 be stacked in layers. By placing in a multi-layered manner, the silicon particles 101 can be arranged at a high density, a large number of silicon particles 101 can be single-crystallized at a time, and crystalline silicon particles are manufactured 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.

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

  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-like or plate-like one without an upper lid. In the case of a plate-like shape, the base plate 102 may be stacked and used. 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, but it has excellent heat resistance, durability, chemical resistance and cost. Quartz glass is preferred because it is cheap and easy to handle.

  Next, the base plate 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 types of heating furnaces can be used depending on the type of semiconductor material, but since silicon is used as the semiconductor material, a resistance heating type or induction heating type atmosphere firing furnace used for firing ceramics, or a semiconductor element A horizontal oxidation furnace or the like generally used in the manufacturing process is suitable. A resistance heating type atmosphere firing furnace used for firing ceramics and the like is desirable because a temperature rise of 1500 ° C. or higher is relatively easy, and a large-sized one capable of mass production of crystalline silicon particles can be obtained relatively inexpensively.

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

  In order to prevent contamination from furnace materials and heating elements in the heating furnace, it is desirable to install a bell jar that covers the silicon particles 101 placed on the base plate 102 in the heating furnace. Quartz glass, mullite, aluminum oxide, silicon carbide, single crystal sapphire, etc. are suitable as the material for the bell jar, but quartz glass is preferred because of its excellent heat resistance, durability, chemical resistance and low cost. is there.

  In the process of heating the silicon particles 101 in an atmosphere gas composed of nitrogen gas or an atmosphere gas containing nitrogen gas as a main component in a heating furnace to raise the temperature to a temperature lower than the melting point (1414 ° C.) of silicon, A silicon nitride film is formed on the surface of the 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. When the temperature is higher than 1400 ° C., the thickness of the silicon nitride film becomes uneven or the silicon particles 101 Partial melting occurs and the particle shape collapses, which is not preferable.

  Since the silicon nitride film formed on the surface of the silicon particles 101 has a higher coating density and higher strength per unit film thickness than a silicon oxide film or the like, the silicon particles 101 such as contaminants and impurities enter the silicon particles 101. Has the effect of having a large diffusion blocking power.

  Further, the silicon nitride film may contain oxygen. The oxygen content is preferably about 10 mol% or less. If it exceeds 10 mol%, the film quality tends to be deteriorated due to a change in crystal structure or an increase in crystal defects in the silicon nitride film.

  Moreover, it is preferable that the atmospheric gas in the heating furnace when forming the silicon nitride film on the surface of the silicon particle 101 has a nitrogen gas partial pressure of 70% or more. When the partial pressure of nitrogen gas in the atmospheric gas is less than 70%, coalescence of the silicon particles 101 is likely to occur in the subsequent single crystallization process, and the strength of the silicon nitride film is deteriorated. Therefore, the lower silicon particles 101 are easily crushed when melted due to the weight of the upper silicon particles 101.

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

  Next, as shown in FIG. 1B, the temperature of the silicon particles 101 is raised to a temperature higher than 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. I will do it. The steps shown in FIGS. 1A and 1B may be performed separately or continuously.

  The base plate 102 also functions as a solidification starting point when the silicon particles 101 are cooled and solidified after being melted to be crystallized. In this way, by placing a large number of silicon particles 101 on the upper surface of the base plate 102, a solidification starting point can be set at a contact portion between each silicon particle 101 and the base plate 102. The solidification (single crystallization) direction can be set from this one pole toward the upper opposing pole. As a result, it is possible to solidify in one direction without using a seed crystal, and the crystallinity of the crystalline silicon particles 101 can be greatly improved by suppressing the generation of subgrains and the like.

  In addition, since a large number of silicon particles 101 are placed in a multi-layered manner, a contact portion with the crystalline silicon particles on the base plate 102 crystallized first is used as a solidification starting point, and silicon adjacent thereto The particles 101 can be solidified, and the solidification spreads in a chain reaction toward the upper part of the stacked layers, so that the crystallinity of a large number of silicon particles 101 can be greatly improved.

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

  When the size of the silicon particle 101 is larger than 1500 μm, the thickness of the silicon nitride film formed on the surface of the silicon particle 101 becomes relatively thin with respect to the silicon particle 101 main body, so It becomes difficult to keep the shape of the silicon particles 101 stable when the silicon melts. In addition, it becomes difficult to completely melt silicon inside the silicon particles 101, and subgrains are 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 μm, it is difficult to stably maintain the shape of the silicon particles 101 when the silicon inside the silicon particles 101 is melted.

  Accordingly, the diameter of the silicon particles 101 is preferably 30 μm to 1500 μm, thereby maintaining the shape of the silicon particles 101 in a stable manner so that crystalline silicon particles having good crystallinity with a spherical shape without generation of subgrains can be obtained. It can be produced stably.

  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.) (post-process) is an atmosphere gas composed of oxygen gas or an oxygen gas and an inert gas. Use atmospheric gas. Argon gas, nitrogen gas, helium gas, and hydrogen gas are suitable as the inert gas, but argon gas or nitrogen gas is preferred from the viewpoint of low cost and ease of handling. In addition, each gas partial pressure in the atmospheric gas in a heating furnace can be adjusted with each gas flow rate with respect to the total gas flow rate. For example, the atmospheric gas is supplied from the gas supply means into the bell jar through the gas filter. Any device that supplies gas to the gas supply means may have a mechanism capable of adjusting the gas pressure and the gas concentration.

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

  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 time, 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 particle 101 can maintain the shape of the silicon particle 101 while melting the inner silicon. However, when the temperature of the silicon particles 101 is difficult to maintain stably, for example, in the case of the silicon particles 101, when the temperature is increased to a temperature exceeding 1480 ° C., It becomes difficult to keep the shape of the silicon particles 101 stable at the time of melting, and it becomes easy for the adjacent silicon particles 101 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 nitride film formed on the surface of the silicon particles 101 is preferably 100 nm 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 100 nm or more, the silicon inside the silicon particles 101 tends to be spheroidized by surface tension at the time of melting, whereas silicon nitride is used in the above temperature range. Since the film is sufficiently deformable, the crystalline silicon particles obtained by single-crystallizing the inside can be made to have a shape close to a true sphere.

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

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

  Next, as shown in FIG. 1C, the molten silicon particles 101 are cooled to a temperature of about 1400 ° C. or lower, which is lower than the melting point, to solidify the molten silicon inside the silicon nitride film. . At this time, when solidifying while maintaining 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 a solidification starting point (one pole) to the upper facing pole. Since solidification proceeds in one direction, solidification occurs in one direction with the contact point with the already solidified silicon particles 101 as a starting point of solidification, and is inherited by the whole silicon particles 101 as it is to grow crystals. The obtained crystalline silicon particles become a single crystal, and crystallinity can be greatly improved.

  In addition, if a large number of silicon particles 101 are placed in a multilayered manner, the silicon particles adjacent to the upper side are set with the contact portion with the crystalline silicon particles on the base plate 102 previously crystallized as the solidification starting point. 101 can be solidified, and solidification spreads in a chained manner toward the upper part of the stacked layers, so that the crystallinity of a large number of crystalline silicon particles 101 can be greatly improved.

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

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

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

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

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

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

The method for producing crystalline silicon particles 406 in the photoelectric conversion device of the present invention is the same as the method for producing crystalline silicon particles described above. The silicon particles 101 that 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 and the like are preferable, and the addition amount is preferably 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ² . The crystalline silicon particles 406 produced by the above-described method for producing crystalline silicon particles of the present invention are used for producing the photoelectric conversion device of the present invention. The photoelectric conversion device can be used as a power generation unit, and a photovoltaic power generation device configured to supply the generated power from the power generation unit to a load can be obtained.

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

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

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

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

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

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

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

  Next, examples of the method for producing crystalline silicon particles of the present invention will be described along the production steps.

As shown in FIG. 1A, first, 1000 pieces of silicon particles 101 having a boron concentration of 0.6 × 10 ¹⁶ atoms / cm ³ and an average particle diameter of 500 μm are converted into a quartz glass box-like base plate. The sample was placed in layers on 102 and accommodated in a quartz glass bell jar installed in an atmosphere firing furnace as a heating furnace. Then, heating is performed while introducing nitrogen gas from the gas supply device, heating is performed to 1300 ° C. below the melting point of silicon at a nitrogen gas pressure of 0.1 MPa, and held for 60 minutes. A film was formed. After heating at 1300 ° C. for 60 minutes, the temperature was lowered to room temperature.

  Next, as shown in FIGS. 1B and 1C, 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, and oxygen gas is supplied. While heating to 1440 ° C. above the melting point of silicon at a 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 temperature is lowered at a rate of 2 ° C. per minute while cooling. Solidified. Thereafter, the temperature was further lowered to 1250 ° C., and thermal annealing treatment was performed for 120 minutes while introducing argon gas as an inert gas. After this thermal annealing treatment, the temperature was lowered to around room temperature.

  The silicon silicon nitride film formed on the surface of the recovered crystalline silicon particles was removed with hydrofluoric acid, and the surface of the crystalline silicon particles was etched away in the depth direction with hydrofluoric acid to a predetermined thickness.

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

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

  Further, an insulating material 409 made of a polyimide resin is applied between the crystalline silicon particles 406 from above so that the upper portions thereof are exposed and dried, and a conductive substrate 407 serving as a lower electrode and a transparent substrate serving as an upper electrode are dried. The optical conductor layer 411 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 100 nm by sputtering.

  Finally, silver paste was patterned in a grid shape with a dispenser to form an electrode 412 composed of finger electrodes and bus bar electrodes. The silver paste pattern was fired at 500 ° C. in the atmosphere.

  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 are distinguished, and the silicon particles are made of quartz glass. The coalescence rate of silicon particles when single-crystallized in a state of being placed in a single layer on a box-shaped base plate or in a state of being placed in a multi-layered manner by close packing was examined. The results are shown in Table 1 as Examples 1 to 4 and Comparative Examples 1 and 2.

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

  As shown in Table 1, crystalline silicon particles produced by forming a silicon oxide film on the surface of silicon particles in an atmosphere gas composed of oxygen gas without forming a silicon nitride film and melting and solidifying them (Comparative Examples 1 and 2) The crystalline silicon particles produced by forming a silicon nitride film on the surface of the silicon particles and melting and solidifying them in an atmosphere gas composed of oxygen gas or an atmosphere gas composed of oxygen gas and inert gas (Example) In 1 to 4), the coalescence rate was low compared to Comparative Examples 1 and 2, and good results were obtained.

  In addition, the coalescence rate of Examples 3 and 4 is larger than the coalescence rate of Examples 1 and 2 because the surface bonding state of the silicon nitride film changes due to the use of argon gas in the atmosphere gas, and the surface tension of the silicon particles It is thought that it changed and became easier to unite.

  Moreover, as shown in Table 2, the conversion efficiency was high in Examples 1 to 4 of the present invention compared to Comparative Examples 1 and 2, and good results were obtained.

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

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

An example of embodiment about the manufacturing method of the crystalline silicon particle | grains of this invention is shown, (a)-(c) is sectional drawing for every process which shows a mode that the silicon particle was mounted in multiple layers on the baseplate. is there. It is sectional drawing which shows an example of embodiment about the photoelectric conversion apparatus obtained by the manufacturing method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Silicon particle 102 ... Base plate 406 ... Crystalline silicon particle 407 ... Conductive substrate 408 ... Bonding layer 409 ... Insulating substance 410 ... Semiconductor layer 411 ... Translucent Conductive layer 412... Electrode

Claims (4)

  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 surface of the silicon particles, and then from the oxygen gas Characterized in that the silicon particles are heated to melt the silicon inside the silicon nitride film, and the temperature is lowered and solidified to form a single crystal in an atmospheric gas comprising oxygen gas or an inert gas. A method for producing crystalline silicon particles.   2. The method for producing crystalline silicon particles according to claim 1, wherein the silicon nitride film contains oxygen.   In the atmosphere gas composed of oxygen gas or the atmosphere gas composed of oxygen gas and inert gas, when the silicon particles are heated, the silicon inside the silicon nitride film is melted and cooled to be solidified to be single-crystallized. 3. The method for producing crystalline silicon particles according to claim 1 or 2, wherein a plurality of silicon particles are single-crystallized in a state of being stacked on a base plate.   4. The method for producing crystalline silicon particles according to claim 1, wherein the silicon nitride film is removed after the silicon particles are monocrystallized.

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