JP2009167052A - Method for manufacturing single crystal silicon particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing single crystal silicon particles by which many single crystal silicon particles each having a shape approximate to a sphere and containing impurities in a drastically reduced content can be manufactured collectively. <P>SOLUTION: The method for manufacturing the single crystal silicon particles 3 comprises removing a projected part 12 of each single crystal silicon particle 3 having the projected part 12 in which impurities are segregated and an oxynitride film 11 formed on its surface, by polishing without substantially deteriorating the surface of each single crystal silicon particle 3. The polishing is carried out by barrel polishing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing single crystal silicon particles suitably used for a photoelectric conversion device such as a solar cell.

  Photoelectric conversion devices are being developed in line with market needs such as improvement in performance such as photoelectric conversion efficiency, consideration of the finite nature of semiconductor resources such as silicon, and reduction in 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 a raw material for producing crystalline silicon particles, silicon fine particles generated as a result of pulverizing single crystal silicon, high-purity silicon synthesized in a gas phase by a fluidized bed method, or the like is used. 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 Document 1, 2), or a method of melting in a container using high-frequency plasma and then free-falling (see, for example, 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 the conventional method are polycrystalline silicon particles. Since polycrystalline silicon particles are aggregates of minute single crystals, there are grain boundaries between the minute single crystals. This grain boundary deteriorates electrical characteristics such as photoelectric conversion efficiency of a photoelectric conversion device using polycrystalline silicon particles. The reason is that the recombination centers of carriers 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 where the electrical characteristics are greatly improved with the increase of the minority carrier lifetime as in the photoelectric conversion device, the presence of the grain boundary in the crystalline silicon particles used for them deteriorates the electrical characteristics. Therefore, if the crystalline silicon particles can be used as single crystal silicon particles, the electrical characteristics of the photoelectric conversion device can be greatly improved.

  In addition, since the grain boundaries in the polycrystalline silicon particles lower 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 manufacturing a photoelectric conversion device using crystalline silicon particles, it is extremely important to manufacture single crystal silicon particles having no crystal grain boundaries and excellent crystallinity.

  As a method for obtaining single crystal silicon particles, 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 inside the silicon compound film is melted and then cooled and solidified. Thus, a method for producing crystalline silicon particles composed of a polycrystal or a single crystal having excellent crystallinity is known (see, for example, Patent Document 4).

  However, when the polycrystalline silicon particles are heated to melt the silicon compound film formed on the surface, specifically, the silicon inside the silicon oxide film and then solidified, the silicon particles are adjacent to each other 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 method for producing a general bulk silicon single crystal such as the Czochralski method (CZ method) or the floating zone method (FZ method), There is a problem that solidification does not occur in one direction and polycrystallization occurs due to the generation of a large number of nuclei. In addition, a photoelectric conversion device using polycrystalline silicon particles has a problem of causing characteristic deterioration.

  In addition, when producing crystalline silicon particles, if high-purity polycrystalline silicon particles synthesized in a gas phase by a fluidized bed method are used as raw materials, metals such as iron and nickel contained in the starting raw material of polycrystalline silicon particles Contamination due to impurities and similar metal impurities mixed from the outside during the manufacturing process becomes a problem. Since the metal impurity diffuses between the lattices having no chemical bond in silicon, the impurity atoms are diffused by sewing the gaps in the silicon lattice. The diffused metal impurity forms a deep level in silicon and acts as a carrier recombination center, resulting in an increase in leakage current and a decrease in carrier lifetime caused by photoelectric conversion. cause.

  That is, it is difficult to produce desired high-quality single-crystal silicon particles by the conventional method for producing crystalline silicon particles, and the photoelectric conversion device having excellent electrical characteristics using the obtained crystalline silicon particles It was difficult to manufacture.

  Therefore, the present invention has been completed in view of the above-mentioned conventional problems, and the object thereof is to collect a large number of single crystal silicon particles having a shape approximating a sphere with a significantly reduced impurity content. As a result, it is possible to provide a method for producing single crystal silicon particles that can be produced simply and at low cost.

  In the method for producing single crystal silicon particles of the present invention, the protrusions of the single crystal silicon particles having protrusions with segregated impurities and having an oxynitride film formed on the surface thereof are not substantially altered by processing. It is removed by polishing.

  In the method for producing single crystal silicon particles of the present invention, preferably, the polishing process is a barrel polishing process.

  In the method for producing single crystal silicon particles of the present invention, preferably, the barrel polishing process uses an abrasive having a spherical shape having a diameter three to thirty times that of the single crystal silicon particles.

  In the method for producing single crystal silicon particles according to the present invention, preferably, the abrasive material includes at least one of alumina, silicon nitride, silicon carbide, mullite, silica and zirconia.

  In the method for producing single crystal silicon particles of the present invention, preferably, the barrel polishing process has a barrel rotation speed of 50 to 500 rpm.

  Further, the method for producing single crystal silicon particles of the present invention is a method in which the silicon melt is discharged in a granular form from the nozzle portion of the crucible, and the granular silicon melt is cooled and solidified to thereby cause impurities to segregate. Manufacturing the quasi-single-crystallized crystalline silicon particles having: removing the cusps of the crystalline silicon particles; forming an oxynitride film on the surface of the crystalline silicon particles; Heating the silicon particles to remelt and solidify the inside of the oxynitride film to produce single crystal silicon particles having protrusions with segregated impurities and having an oxynitride film formed on the surface; Removing the protrusions of the crystalline silicon particles by polishing without substantially altering the surface.

  In the method for producing single crystal silicon particles of the present invention, preferably, the polishing process is a barrel polishing process.

  In the method for producing single crystal silicon particles of the present invention, preferably, the barrel polishing process uses an abrasive having a spherical shape having a diameter three to thirty times that of the single crystal silicon particles.

  In the method for producing single crystal silicon particles according to the present invention, preferably, the abrasive material includes at least one of alumina, silicon nitride, silicon carbide, mullite, silica and zirconia.

  In the method for producing single crystal silicon particles of the present invention, preferably, the barrel polishing process has a barrel rotation speed of 50 to 500 rpm.

  In the method for producing single crystal silicon particles of the present invention, the protrusions of the single crystal silicon particles having protrusions with segregated impurities and having an oxynitride film formed on the surface thereof are not substantially altered by processing. In addition, the metal impurities such as iron and nickel contained in the raw material and the impurities such as carbon introduced in the manufacturing process can be removed by removing the protrusions and oxynitriding. The protrusions can be removed from the single crystal silicon particles whose surface is protected by the film without substantially modifying the surface. As a result, when the oxynitride film is later removed by etching or the like, fine irregularities having convex portions with rounded tips can be formed on the surface of the single crystal silicon particles. Therefore, when producing a photoelectric conversion device using single crystal silicon particles, single crystal silicon particles generated by contacting the jig used for pressing when the single crystal silicon particles are pressed and joined to the conductive substrate. The occurrence of abrasion of the second conductivity type semiconductor portion of the surface layer portion can be reduced, and a photoelectric conversion device having excellent photoelectric conversion efficiency can be obtained.

  Further, by removing the protrusions, the single crystal silicon particles have a nearly spherical shape, and a large number of single crystal silicon particles can be arranged on the conductive substrate with high positional accuracy when manufacturing a photoelectric conversion device. . As a result, electrical characteristics such as photoelectric conversion efficiency of the photoelectric conversion device are improved.

  In the method for producing single crystal silicon particles of the present invention, preferably, the polishing process is a barrel polishing process. Therefore, by efficiently rubbing a large number of single crystal silicon particles with each other in a rotating barrel, protrusions can be efficiently performed. Part can be removed.

  In the method for producing single crystal silicon particles of the present invention, preferably, the barrel polishing process uses an abrasive having a spherical shape whose diameter is 3 to 30 times that of the single crystal silicon particles. In addition, the work-affected layer generated by rubbing can be substantially prevented from being formed. In other words, a spherical abrasive having a diameter larger than that of single crystal silicon particles, compared with a spherical abrasive having a diameter smaller than that of single crystal silicon particles, does not cause the surface of single crystal silicon particles to be affected by rubbing with single crystal silicon particles. It can suppress effectively that a process-affected layer is formed by scratching. Further, by using an abrasive having a spherical shape that is 3 to 30 times the diameter of the single crystal silicon particles, even if the abrasive is rubbed with the single crystal silicon particles, the surface of the single crystal silicon particles is damaged and a work-affected layer is formed. Can be suppressed more effectively.

  In the method for producing single crystal silicon particles according to the present invention, preferably, the abrasive is made of at least one of alumina, silicon nitride, silicon carbide, mullite, silica, and zirconia. The resulting abrasive has a lower hardness than the single crystal silicon particles, and the protrusions can be removed without forming a work-affected layer on the surface of the single crystal silicon particles.

  In the method for producing single crystal silicon particles of the present invention, preferably, the barrel polishing process has a barrel rotation speed of 50 to 500 rpm, so that the protrusions can be efficiently removed from the surface of the single crystal silicon particles. The formation of a work-affected layer on the surface of single crystal silicon particles can be effectively suppressed.

  Further, the method for producing single crystal silicon particles of the present invention is a method in which the silicon melt is discharged in a granular form from the nozzle portion of the crucible, and the granular silicon melt is cooled and solidified to thereby cause impurities to segregate. A step of manufacturing quasi-single-crystallized crystalline silicon particles having a shape, a step of removing the tip of the crystalline silicon particles, a step of forming an oxynitride film on the surface of the crystalline silicon particles, and heating the crystalline silicon particles And re-melting and solidifying the inside of the oxynitride film to produce single crystal silicon particles having protrusions with segregated impurities and having an oxynitride film formed on the surface, and protrusions of the single crystal silicon particles And a step of removing the portion by polishing without substantially modifying the surface, so that a quasi-single-crystallized crystalline silicon having a pointed head where impurities are segregated is provided. In order to remove the protrusions from the single crystal silicon particles having protrusions with segregated impurities, the single crystal silicon particles having good crystallinity with greatly reduced impurity concentration are obtained. can get.

  Further, when the oxynitride film is later removed by etching or the like, fine irregularities having convex portions with rounded tips can be formed on the surface of the single crystal silicon particles. Therefore, when producing a photoelectric conversion device using single crystal silicon particles, single crystal silicon particles generated by contacting the jig used for pressing when the single crystal silicon particles are pressed and joined to the conductive substrate. The occurrence of abrasion of the second conductivity type semiconductor portion of the surface layer portion can be reduced, and a photoelectric conversion device having excellent photoelectric conversion efficiency can be obtained.

  In the method for producing single crystal silicon particles of the present invention, preferably, the polishing process is a barrel polishing process. Therefore, by efficiently rubbing a large number of single crystal silicon particles with each other in a rotating barrel, protrusions can be efficiently performed. Part can be removed.

  In the method for producing single crystal silicon particles of the present invention, preferably, the barrel polishing process uses an abrasive having a spherical shape whose diameter is 3 to 30 times that of the single crystal silicon particles. In addition, the work-affected layer generated by rubbing can be substantially prevented from being formed. In other words, a spherical abrasive having a diameter larger than that of single crystal silicon particles, compared with a spherical abrasive having a diameter smaller than that of single crystal silicon particles, does not cause the surface of single crystal silicon particles to be affected by rubbing with single crystal silicon particles. It can suppress effectively that a process-affected layer is formed by scratching. Therefore, by using an abrasive having a spherical shape that is 3 to 30 times the diameter of the single crystal silicon particles, the surface of the single crystal silicon particles is scratched even if they are rubbed with the single crystal silicon particles, thereby forming a work-affected layer. Can be effectively suppressed.

  In the method for producing single crystal silicon particles according to the present invention, preferably, the abrasive is made of at least one of alumina, silicon nitride, silicon carbide, mullite, silica, and zirconia. The resulting abrasive has a lower hardness than the single crystal silicon particles, and the protrusions can be removed without forming a work-affected layer on the surface of the single crystal silicon particles.

  In the method for producing single crystal silicon particles of the present invention, preferably, the barrel polishing process has a barrel rotation speed of 50 to 500 rpm, so that the protrusions can be efficiently removed from the surface of the single crystal silicon particles. The formation of a work-affected layer on the surface of single crystal silicon particles can be effectively suppressed.

  Hereinafter, the manufacturing method of the single crystal silicon particle of this Embodiment is demonstrated in detail.

  FIG. 1 shows an example of a method for producing single crystal silicon particles according to the present embodiment, and is a cross-sectional view of a barrel polishing apparatus used in the method for producing single crystal silicon particles. FIG. 2 is a cross-sectional view of the single crystal silicon particle 3.

  The method for producing single crystal silicon particles according to the present embodiment (first embodiment) has a protrusion 12 having impurities segregated and a protrusion of single crystal silicon particle 3 having an oxynitride film 11 formed on the surface thereof. 12 is removed by polishing without substantially altering the surface of the single crystal silicon particles 3.

  With the above configuration, metal impurities such as iron and nickel contained in the raw material and impurities such as carbon introduced in the manufacturing process can be removed by removing the protrusions 12, and the oxynitride film 11 The protrusion 12 can be removed from the single crystal silicon particles 3 whose surface is protected without substantially modifying the surface. As a result, when the oxynitride film 11 is later removed by etching or the like, fine irregularities having convex portions with rounded tips can be formed on the surface of the single crystal silicon particles 3. Therefore, when producing a photoelectric conversion device using the single crystal silicon particles 3, the single crystal produced by contacting the jig used for pressing when the single crystal silicon particles 3 are pressed and bonded to the conductive substrate. The occurrence of abrasion of the second conductivity type semiconductor portion of the surface layer portion of the silicon particles 3 can be reduced, and a photoelectric conversion device having excellent photoelectric conversion efficiency can be obtained. Further, by removing the protrusions 12, the single crystal silicon particles 3 have a nearly spherical shape, and when the photoelectric conversion device is manufactured, a large number of single crystal silicon particles 3 are increased on the conductive substrate. Can be arranged. As a result, electrical characteristics such as photoelectric conversion efficiency of the photoelectric conversion device are improved.

  The etching treatment solution used for the etching treatment for removing the oxynitride film 11 by etching contains sodium hydroxide and at least one selected from the group consisting of isopropyl alcohol, lauric acid and n-octanoic acid. Is preferred. Thereby, since the anisotropy of etching of the etching treatment solution is lowered, the tip of the obtained convex portion can be controlled to have a gently curved shape.

  Furthermore, in the method for producing single crystal silicon particles of the present embodiment (second embodiment), the silicon melt is discharged in a granular form from the nozzle portion of the crucible, and the granular silicon melt is cooled and solidified. Thus, a step of manufacturing the quasi-single-crystallized crystalline silicon particles having a cusp with segregated impurities, a step of removing the cusp of the crystalline silicon particle, and the oxynitride film 11 on the surface of the crystalline silicon particle And a step of heating the crystalline silicon particles to remelt and solidify the inside of the oxynitride film 11 to thereby have a projection 12 having segregated impurities and a single crystal having the oxynitride film 11 formed on the surface thereof A step of manufacturing the silicon particles 3 and a step of removing the protrusions 12 of the single crystal silicon particles 3 by polishing without substantially modifying the surface of the processing.

  In this case, in the step of forming the oxynitride film 11 on the surface of the crystalline silicon particles, the crystalline silicon particles are below the melting point of silicon in an atmospheric gas composed of nitrogen gas and oxygen gas or an atmospheric gas containing nitrogen gas as a main component. By heating to a temperature, an oxynitride film 11 is formed on the surface of the crystalline silicon particles. Next, the crystalline silicon particles are heated in an atmosphere gas composed of nitrogen gas and oxygen gas or in an atmosphere gas composed of oxygen gas and inert gas to melt the silicon inside the oxynitride film 11 and to cool and solidify. Then, the single crystallization is performed, and then the protrusions 12 of the single crystal silicon particles 3 are removed by polishing.

  The protrusions 12 of the single crystal silicon particles 3 cause the silicon inside the oxynitride film 11 to undergo volume expansion when the crystal silicon particles are heated to melt and cool the silicon inside the oxynitride film 11 to cool. Formed by waking up.

  First, as the material of the crystalline silicon particles, semiconductor grade, which is the quality of semiconductors used in semiconductor integrated circuits, or solar grade crystalline silicon is used, and this is melted in a container by infrared rays, high frequency induction coils or resistance heating. Thereafter, polycrystalline crystalline silicon particles are obtained by a melt dropping method (jet method) or the like in which the molten silicon is freely dropped as a granular silicon melt.

  In a crystal silicon particle manufacturing apparatus (jet apparatus) used in the melt-drop method, a crucible containing molten silicon is made of a material having a melting point higher than that of silicon. The crucible is preferably made of a material having low reactivity with the silicon melt. When the reaction with the silicon melt is large, the crucible material is preferably mixed in the crystalline silicon particles in a large amount as an impurity. Absent.

  For example, the material of the crucible includes carbon, silicon carbide sintered body, silicon carbide crystal, boron nitride sintered body, silicon oxynitride sintered body, quartz, quartz crystal, silicon nitride sintered body, aluminum oxide Sintered sapphire, sapphire, magnesium oxide sintered body and the like are preferable. Moreover, the composite of these materials, a mixture, or a compound body may be sufficient. Further, the surface of the substrate made of the above material may be coated with a silicon carbide film, a silicon nitride film, or a silicon oxide film. As a heating method for heating the raw material to the melting point or higher in the crucible, an electromagnetic induction heating method, a resistance heating method, or the like is preferable because it can be rapidly heated without directly contacting the raw material.

  The nozzle portion is made of silicon carbide (silicon carbide crystal or silicon carbide sintered body), silicon nitride (silicon nitride sintered body), or the like.

Polycrystalline silicon particles produced by the melt drop method are usually doped with impurities (dopants) 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. However, boron or phosphorus should be used because it has a large segregation coefficient for silicon and a low evaporation coefficient when silicon is melted. Is preferred. The dopant concentration is about 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ³ added to the silicon crystal material.

  At the time when the crystalline silicon particles are obtained by this melting and dropping method, the crystalline silicon particles have a substantially spherical shape, a teardrop type, a streamline type, or a connected type in which a plurality of particles are connected. When a photoelectric conversion device is manufactured using polycrystalline crystalline silicon particles as obtained by the melt drop method, it is difficult to obtain good photoelectric conversion characteristics. The cause is due to metallic impurities such as Fe, Cr, Ni, and Mo usually contained in the polycrystalline crystalline silicon particles, and the carrier recombination effect at the crystal grain boundaries of the polycrystalline crystalline silicon particles. .

  In order to improve this, polycrystalline crystalline silicon particles are melted at a melting point of silicon (1414 ° C.) in a temperature-controlled heating furnace in an atmosphere gas composed of nitrogen gas and oxygen gas or an atmosphere gas containing nitrogen gas as a main component. ) The following temperature (500 to 1400 ° C.) is heated to form the oxynitride film 11 on the surface of the crystalline silicon particles, and then the atmosphere gas composed of nitrogen gas and oxygen gas or the atmosphere composed of oxygen gas and inert gas In the gas, the crystalline silicon particles are heated, and the silicon inside the oxynitride film 11 is melted, cooled, and solidified to form a single crystal. In order to improve crystallinity, this process is repeated several times.

  At this point, there are still a number of single crystal silicon particles 3 having large and small protrusions, and it is very difficult to handle as it is, so whether the single crystal silicon particles 3 having the protrusions 12 are selected and removed. The protrusion 12 needs to be removed by polishing or the like.

  Now, in the second embodiment, before the step of forming the oxynitride film 11 on the surface of the crystalline silicon particles, the step of manufacturing the quasi-single-crystallized crystalline silicon particles having a pointed head where impurities are segregated. And a step of removing the cusps of the crystalline silicon particles. The quasi-single-crystallized crystalline silicon particles are teardrop-shaped and have a crystal quality close to that of a single crystal having only a few grain boundaries.

  Crystal silicon particles that are pseudo-single-crystallized in a teardrop shape can be manufactured with a high manufacturing yield as follows.

  Conventionally, the granular silicon melt discharged from the nozzle part of the crucible located at the upper part of the melting and dropping device (jet device) is in a supercooled state (temperature state of 1214 ° C. or lower) in which the surface temperature rapidly decreases, and thereafter Under the influence of the internal temperature of the granular silicon melt, the surface temperature once rises to near the melting point (1414 ° C.) of silicon, and then the temperature gradually decreases and solidifies. At this time, since the degree of supercooling in the supercooled state (melting point of silicon (1414 ° C.) − Supercooling temperature) is as large as about 300 ° C. or more, a large number of crystal nuclei are generated on the surface of the granular silicon melt. Crystalline crystalline silicon particles. In addition, protrusions are formed on the surface of most crystalline silicon particles due to internal volume expansion during solidification.

  In the second embodiment, by forming the supercooling degree as small as about 40 ° C. to 200 ° C., the formation of protrusions is suppressed, and teardrop-type crystalline silicon particles having a pointed head are manufactured. In the teardrop-type crystalline silicon particles, a pointed head (pointed portion) is formed in the final solidified portion. The teardrop-type crystalline silicon particles are pseudo single crystal particles having a crystal quality close to that of a single crystal having only a few grain boundaries.

  As a means for reducing the degree of supercooling, a heater for controlling the degree of supercooling is provided in the dropping path where the granular silicon melt falls, and silicon oxide is added to the dropping granular silicon melt immediately after being discharged from the crucible. There is a method of colliding crystal nuclei composed of fine particles such as.

  Further, the cusp is a region including the tip of the cusp of the crystalline silicon particles, and is a region of about 0.01 to 16% by volume of the volume of the crystalline silicon particles.

  The concentration of carbon and nitrogen impurities contained in the apex or protrusion can be confirmed by performing a cross-sectional analysis of the crystalline silicon particles by SIMS (Secondary Ion Mass Spectroscopy).

Metal impurities such as Fe, Ni, and Cu cannot be analyzed by SIMS because the concentration is below the detection limit of SIMS. However, since the segregation coefficient is two orders of magnitude smaller than that of carbon and nitrogen, the SIMS analysis of carbon and nitrogen Prediction is possible from the results. As for the segregation state of these impurities, the polished cross-section of the crystalline silicon particles was changed to a JIS standard B etching solution (HF: HNO ₃ : CH ₃ COOH: H ₂ O = 1: 12.7: 3: 5.7 (volume ratio). It can be confirmed by observing etch pits on the surface.

  Further, when removing the cusp of the crystalline silicon particles, it is preferable to remove a part having a depth of 20 μm or more from the surface of the cusp. When a portion having a depth of less than 20 μm is removed from the surface of the pointed head, the segregated portion of impurities tends to remain. When a portion having a depth of 50 μm or more is removed from the surface of the cusp, damage tends to occur on the surface of the crystalline silicon particles other than the cusp. Accordingly, it is preferable to remove a portion having a depth of 20 μm to 50 μm from the surface of the pointed head. In this case, impurities can be removed and the occurrence of crystal defects and contamination of metal impurities can be effectively reduced.

  As a method for removing the pointed head, there are a method of removing by a mechanical polishing method, a method of removing by an etching method using an etching solution, a dry etching method and the like.

  In the first and second embodiments, preferably, the protrusions of the single crystal silicon particles 3 having the oxynitride film 11 formed on the surface thereof are not substantially processed and altered by the surface of the single crystal silicon particles 3. The polishing process for removing by polishing is barrel polishing. Thus, the protrusions can be efficiently removed by rubbing a large number of single crystal silicon particles 3 with each other in the rotating barrel.

  The removal of the protrusion 12 by barrel polishing will be described below. FIG. 1 is a cross-sectional view of a barrel polishing apparatus used in the method for producing crystalline silicon particles of the present embodiment. In FIG. 1, 1 is a barrel pot, 2 is an abrasive, 3 is single crystal silicon particles, 4 is a central axis (rotation axis) of rotation of the barrel pot, and 5 is a lid of the barrel pot. Crystal silicon particles 3, abrasive 2 and water are put into the barrel pot 1, and the barrel pot 1 rotates around the central axis 4.

  In addition, the barrel pot 1 rotates about the central axis 4, reciprocating linear motion in the horizontal direction, reciprocating linear motion in the vertical direction, reciprocating linear motion in directions other than the horizontal and vertical directions, and around the revolution axis. Other motions such as rotational motion may be involved. The barrel pot 1 is preferably made of an elastic material such as hard rubber in order to prevent chipping, cracking, and alteration of the single crystal silicon particles 3 and the abrasive 2, and the temperature rises due to friction caused by polishing. A heat resistant material having a melting point of 100 ° C. or higher is preferable. The barrel pot 1 may have a cylindrical shape or a rectangular tube shape, and a lid 5 may be provided so that the contents of the barrel pot 1 do not leak outside. The lid 5 is made of the same material as the barrel pot 1, but a hard protective layer (protective plate) made of stainless steel or the like may be provided on the upper surface and side surface of the lid 5 to prevent deformation.

  Further, in order to remove the protrusions 12 of the single crystal silicon particles 3 by polishing, for example, the abrasive material 2 made of silicon nitride having an average particle diameter of about 3 mm is accommodated in the barrel pot 1 by about half the volume, and the single crystal The silicon particles 3 are charged at a volume ratio of about 1/10 to 1/100 of the abrasive 2 and the barrel pot 1 with the lid 5 set is rotated at a suitable rotation speed of 50 to 500 rpm for 10 to 60 minutes. Processing. Thereby, the protrusion 12 of the single crystal silicon particle 3 is removed without substantially modifying the surface of the single crystal silicon particle 3.

  The fact that the surface of the single crystal silicon particles 3 is not substantially altered by processing means that the surface of the single crystal silicon particles 3 may have slight scratches having a depth of about 1 μm or less. In addition, 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, and the like exist from the surface side. Call it. In the present embodiment, the surface of the single crystal silicon particles 3 is prevented from being altered by the oxynitride film, and polishing is performed to the extent that only the outermost amorphous layer is formed. Therefore, if the surface of the single crystal silicon particles 3 is not substantially altered by processing, the surface of the single crystal silicon particles 3 may have a slight scratch having a depth of about 1 μm or less. As a result, the single crystal silicon particles 3 3 is a state in which only an amorphous layer is formed on the surface. Of course, this includes the case where no scratches are formed on the surface of the single crystal silicon particles 3 and no amorphous layer is formed.

  The work-affected layer generally has a structure in which an amorphous layer, a polycrystalline layer, a mosaic layer, a crack layer, a strain layer, and the like exist from the surface side, and these five layers are collectively referred to as a work-affected layer. . In the barrel polishing process according to the present embodiment, the surface of the single crystal silicon particles 3 is prevented from being altered by the oxynitride film, and the polishing process is performed to the extent that only the outermost amorphous layer is formed. Finally, the amorphous layer is removed by removing the oxynitride film 11 by chemical etching, and single crystal silicon particles 3 with high crystal quality are obtained. The presence of the work-affected layer can be identified by confirming the broadening of the half-value width of the Raman spectrum by Raman spectroscopy or the like.

  Next, the pressure of the atmospheric gas composed of nitrogen gas and oxygen gas or the atmospheric gas containing nitrogen gas as a main component in the step of forming the oxynitride film 11 (the pre-crystallization step) is about 0.01 to 0.2 MPa. Is good. By setting the pressure to about 0.01 to 0.2 MPa, the thickness of the oxynitride film 11 is not reduced and the film quality is hardly deteriorated due to evaporation of nitrogen and oxygen from the oxynitride film 11, and the thickness of the oxynitride film 11 is reduced. Variation is less likely to occur.

  The thickness of the oxynitride film 11 formed on the surface of the single crystal silicon particles 3 may be about 100 nm to 10 μm. By setting the thickness to about 100 nm to 10 μm, the oxynitride film is melted when silicon inside the single crystal silicon particles 3 is melted. 11 is prevented from breaking, and it becomes easy to spheroidize with surface tension when silicon inside the single crystal silicon particles 3 is melted.

  The pressure of the atmospheric gas composed of nitrogen gas and oxygen gas or the atmospheric gas composed of oxygen gas and inert gas in the subsequent process (remelting (remelting process for single crystallization)) is about 0.01 to 0.2 MPa. Good. By setting the pressure to about 0.01 to 0.2 MPa, evaporation of nitrogen and oxygen from the oxynitride film 11 makes it difficult for the film thickness of the oxynitride film 11 to be reduced and the film quality to be deteriorated. It becomes easy to keep the shape stable when the silicon melts.

  When oxygen gas and inert gas are used in the post-process, the oxygen gas and the inert gas may be contained as long as they contain 20% by volume or more and the inert gas such as argon gas contains 80% by volume or less.

  In order to produce the single crystal silicon particles 3 by the remelting (remelt) method, first, a large number (for example, several hundred to several thousand) of polycrystalline crystal silicon particles are placed on the upper surface of the base plate. A large number of crystalline silicon particles may be placed on the base plate, but may be placed in a single layer, but it is better to place them in multiple layers. By placing in multiple layers, the crystalline silicon particles can be arranged at a high density, and a large number of crystalline silicon particles can be single-crystallized at a time. It can be manufactured. Therefore, the single crystal silicon particle 3 used for a photoelectric conversion apparatus etc. can be manufactured efficiently.

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

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

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

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

  The process of heating crystalline silicon particles in an atmosphere gas composed of nitrogen gas and oxygen gas or an atmosphere gas containing nitrogen gas as a main component in a heating furnace to raise the temperature to a temperature lower than the melting point of silicon (1414 ° C.). Thus, an oxynitride film is formed on the surface of the crystalline silicon particles. The formation temperature of the oxynitride film is preferably 500 ° C. to 1400 ° C. By setting the temperature to 500 ° C. to 1400 ° C., the growth rate of the oxynitride film can be increased so that it does not take time to obtain the desired thickness, and the thickness of the oxynitride film is made uniform. It is possible to suppress partial melting and shape collapse.

  Since the oxynitride film 11 formed on the surface of the crystalline silicon particles has a higher coating density and higher strength per unit film thickness than an oxide film or the like, contaminants, impurities, and the like are present in the single crystal silicon particles 3. It has the effect that the diffusion preventing power that prevents the diffusion to the inside is great.

  Further, the oxygen content of the oxynitride film 11 is preferably about 10 mol% or less. By setting it to 10 mol% or less, it is possible to suppress deterioration of the film quality due to a change in crystal structure and an increase in crystal defects in the oxynitride film 11. Further, since the oxynitride film 11 contains oxygen, the flexibility of the film is improved.

  In addition, the atmospheric gas in the heating furnace when forming the oxynitride film 11 on the surface of the crystalline silicon particles preferably has a nitrogen gas partial pressure of 70% or more. When the nitrogen gas partial pressure is 70% or more, the occurrence of coalescence of crystalline silicon particles is suppressed in the subsequent single crystallization step, and the strength of the oxynitride film 11 is improved, thereby increasing the number of crystals. It is possible to prevent the lower crystalline silicon particles from being crushed when melted due to the weight of the upper crystalline silicon particles in a state where the silicon particles are stacked in layers.

  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, in an atmosphere gas composed of nitrogen gas and oxygen gas or an atmosphere gas composed of oxygen gas and inert gas, the crystalline silicon particles are heated to a temperature higher than the melting point (1414 ° C.) of silicon (above 1414 ° C. and less than 1480 ° C.). The temperature rises. This step may be performed separately or continuously.

  The base plate also functions as a solidification starting point when the crystalline silicon particles are cooled and solidified after being melted to form a single crystal. By placing a large number of crystalline silicon particles on the top surface of the base plate in this way, a solidification starting point can be set at the contact portion between each crystalline silicon particle and the base plate. 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 and the like can be suppressed, and the crystallinity of the single crystal silicon particles 3 can be greatly improved.

  In addition, since a large number of crystalline silicon particles are placed in a multi-layered manner, a contact portion with the single crystal silicon particles 3 on the base plate that has been previously crystallized is set as a solidification starting point, and is adjacent thereto. The crystal silicon particles to be solidified can be solidified, and solidification spreads in a chain reaction toward the upper part by being placed in multiple layers, so that the crystallinity of a large number of single crystal silicon particles 3 is greatly improved. be able to.

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

  Since the average particle diameter of the crystalline silicon particles is 1500 μm or less, the thickness of the oxynitride film 11 formed on the surface of the crystalline silicon particles does not become relatively thin with respect to the crystalline silicon particle body, and the crystalline silicon particles It is possible to keep the shape of the crystalline silicon particles stable when the silicon inside the silicon melts. Moreover, the silicon inside the crystalline silicon particles can be completely melted, and the occurrence of subgrains can be effectively suppressed.

  The average particle size of the crystalline silicon particles is preferably 30 μm or more. In this case, the shape of the crystalline silicon particles can be stably maintained when the silicon inside the crystalline silicon particles is melted.

  Therefore, the average particle diameter (average diameter) of the single crystal silicon particles 3 is preferably 30 μm to 1500 μm, thereby maintaining the shape of the crystal silicon particles stably and having a good spherical shape with no subgrains. The single crystal silicon particles 3 having crystallinity can be stably produced.

  The atmosphere gas in the heating furnace in the single crystallization process (post process) in which the crystalline silicon particles are heated to a temperature higher than the melting point of silicon (1414 ° C.) is an atmosphere gas composed of oxygen gas or oxygen gas and inert. The atmosphere gas is a gas. As the inert gas, argon gas, nitrogen gas, helium gas, and hydrogen gas are suitable, but argon gas or nitrogen gas is preferred from the viewpoint of low cost and easy handling. 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, 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. In this case, the evaporation of oxygen from the oxynitride film 11 is suppressed, and the shape can be kept stable when the silicon inside the crystalline silicon particles is melted.

  The crystalline silicon particles 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 surface oxynitride film 11 is melted in the crystalline silicon particles. At this time, the oxynitride film 11 formed on the surface of the crystalline silicon particles can maintain the shape of the crystalline silicon particles while melting the inner silicon. However, when the temperature is raised to a temperature at which it is difficult to stably maintain the shape of the crystalline silicon particles, for example, a temperature exceeding 1480 ° C., the shape of the crystalline silicon particles is changed when the silicon inside the crystalline silicon particles is melted. It becomes difficult to keep stable, and it becomes easy for the adjacent crystalline silicon particles to coalesce, and the crystalline silicon particles are easily fused to the base plate.

  The thickness of the oxynitride film 11 formed on the surface of the crystalline silicon particles is preferably 100 nm or more in the above average particle diameter range of the crystalline silicon particles. In this case, when the silicon inside the crystalline silicon particles is melted, the oxynitride film 11 on the surface of the crystalline silicon particles is not easily broken. In addition, while silicon inside the crystalline silicon particles tends to be spheroidized by surface tension when it is melted, the oxynitride film 11 can be sufficiently deformed in the above temperature range. The obtained single crystal silicon particles 3 can have a shape close to a true sphere.

  On the other hand, the thickness of the oxynitride film 11 is preferably 10 μm or less. In this case, the oxynitride film 11 is easily deformed in the above temperature range, and the resulting single crystal silicon particle 3 has a shape close to a true sphere.

  Therefore, the thickness of the oxynitride film 11 on the surface of the crystalline silicon particles is preferably 100 nm to 10 μm with respect to the above average particle diameter range (30 μm to 1500 μm). Thereby, the single crystal silicon particle 3 having a good shape close to a true sphere can be stably obtained. Moreover, the photoelectric conversion apparatus excellent in photoelectric conversion efficiency can be obtained by using this single crystal silicon particle 3 for a photoelectric conversion apparatus.

  Next, in order to solidify the molten silicon inside the oxynitride film 11 in the crystalline silicon particles, the temperature is lowered to a temperature of about 1400 ° C. or lower, which is lower than the melting point of silicon, and is solidified. At this time, it is solidified while being maintained at a relatively high temperature (about 1360 ° C.) below the melting point of silicon. In this case, the contact portion between the crystalline silicon particles and the base plate is set as a solidification starting point (one pole) and facing upward. Since solidification proceeds in one direction toward the pole to be solidified, unidirectional solidification occurs with the point of contact with the already solidified single crystal silicon particles 3 as a solidification starting point. Then, the unidirectional solidification is inherited to the whole of the large number of crystalline silicon particles as it is, and the large number of single crystalline silicon particles 3 are collectively obtained.

  Moreover, it is preferable to perform a thermal annealing treatment on the single crystal silicon particles 3 in the course of solidifying the crystalline silicon particles whose inside is melted, for example, a thermal annealing treatment at a constant temperature of 1000 ° C. or more for 30 minutes or more. By performing this thermal annealing treatment, the strain in the crystal of the single crystal silicon particles 3 generated at the time of solidification, and the interface strain generated at the interface between the oxynitride film 11 on the surface of the single crystal silicon particles 3 and the inner single crystal silicon are obtained. Etc. can be relaxed and removed to obtain a single crystal silicon particle 3 having good crystallinity.

  However, the single crystal silicon particles 3 obtained as described above have various large and small protrusions 12 on which carbon and metal impurities are segregated. Next, these protrusions 12 are removed by polishing. In this case, it is preferable that the abrasive 2 has an average particle size (average diameter) that is 3 to 30 times the average particle size (average diameter) of the single crystal silicon particles 3. In this case, the work-affected layer generated by rubbing against the surface of the single crystal silicon particles 3 can be substantially not formed. That is, the spherical abrasive having a diameter larger than that of the single crystal silicon particles 3 is compared with the spherical abrasive having a diameter smaller than that of the single crystal silicon particles 3 even when the single crystal silicon particles 3 are rubbed with each other. It is possible to effectively inhibit the work-affected layer from being formed by damaging the surface of 3. Therefore, by using an abrasive having a spherical shape that is 3 to 30 times the diameter of the single crystal silicon particles, the surface of the single crystal silicon particles 3 is scratched even if they are rubbed with the single crystal silicon particles 3 to form a work-affected layer. Can be effectively suppressed. If it is smaller than 3 times, it is difficult to remove the protrusions 12 and the surface of the single crystal silicon particles 3 is easily scratched. Even if it is larger than 30 times, a work-affected layer and scratches are formed on the surface of the single crystal silicon particles 3. It becomes easy to form.

  The rotation speed of the barrel pot 1 is preferably 50 rpm to 500 rpm. By setting the speed to 50 rpm to 500 rpm, the abrasive 2 and the single crystal silicon particles 3 can efficiently collide without being separated in the barrel pot 1 to remove the protrusions 12, and the kinetic energy of the abrasive 2 is extremely high. It is possible to suppress the damage to the surface of the single crystal silicon particles 3 and the formation of a work-affected layer.

  In the method for manufacturing single crystal silicon particles 3 according to the present embodiment, it is preferable to remove oxynitride film 11 after removing protrusions 12 from single crystal silicon particles 3. Thereby, the metal impurity containing part such as Fe, Cr, Ni, and Mo segregated on the surface layer part of the single crystal silicon particle 3 can be removed, and the single crystal silicon particle 3 obtained by the manufacturing method of the present invention is removed. When used in a photoelectric conversion device, good photoelectric conversion characteristics can be obtained.

  Next, FIG. 3 illustrates an example of the photoelectric conversion device of this embodiment. In FIG. 3, 16 is a first conductivity type (for example, p-type) single crystal silicon particles, 17 is a conductive substrate, 18 is a bonding layer between the single crystal silicon particles 16 and the conductive substrate 17, 19 is an insulating material, 20 Is a second conductivity type (for example, n-type) semiconductor layer (semiconductor portion), 21 is a translucent conductor layer, and 22 is an electrode.

  In the photoelectric conversion device using the single crystal silicon particles 16 of the present embodiment, the first conductivity type (for example, p-type) single crystal silicon particles 16 are formed on one main surface of the conductive substrate 17, in this example, the upper surface. The lower part is bonded to the conductive substrate 17 by the bonding layer 18, for example, and an insulating material 19 is interposed between adjacent ones of the single crystal silicon particles 16 and the upper parts of the single crystal silicon particles 16 are insulated. The single-crystal silicon particles 16 are arranged so as to be exposed from the substance 19, and a second conductive type semiconductor layer 20 and a translucent conductor layer 21 are sequentially provided.

  In addition, when using this photoelectric conversion apparatus as a solar cell, the electrode 22 is deposited on the translucent conductor layer 21 in a predetermined pattern shape, and is, for example, a finger electrode or a bus bar electrode. .

  And the single-crystal silicon particle 16 in the photoelectric conversion apparatus of the said structure is manufactured by the manufacturing method of the single-crystal silicon particle of said this Embodiment. Since the single crystal silicon particles 16 are manufactured by the method for manufacturing single crystal silicon particles of the present embodiment, high quality single crystal silicon particles 16 having an extremely low impurity concentration can be obtained. The lifetime of minority carriers, which is an important factor for obtaining conversion efficiency, can be improved. Therefore, single crystal silicon particles 16 preferable as a component of the photoelectric conversion device can be obtained.

The method for producing single crystal silicon particles 16 in the photoelectric conversion device of the present embodiment is the same as the method for producing single crystal silicon particles described above. The single crystal silicon particles that are the starting material of the single crystal silicon particles 16 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 single crystal silicon particles 16 produced by the above-described method for producing single crystal silicon particles of the present invention are used for producing a photoelectric conversion device. 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. 3 is a photoelectric conversion device manufactured using the single crystal silicon particles 16 obtained as described above. In order to obtain this photoelectric conversion device, first, the silicon nitride film formed on the surface of the single crystal silicon particles 16 is removed by etching with hydrofluoric acid. Further, in order to remove the interfacial strain between the silicon nitride film and the single crystal silicon particles 16 and the impurities such as p-type dopant and oxygen, carbon, and metal segregated on the surface of the single crystal silicon particles 16, the single crystal silicon particles The surface of 16 may be removed by etching with hydrofluoric acid or the like. The thickness of the surface layer of the single crystal silicon particles 16 removed at that time is preferably 100 μm or less in the radial direction.

  Next, a large number of single crystal silicon particles 16 are arranged on a conductive substrate 17 made of aluminum or the like. Then, the single crystal silicon particles 16 are bonded to the conductive substrate 17 through the bonding layer 18 generated by heating the whole in a reducing atmosphere. Note that the bonding layer 18 is, for example, an alloy of aluminum and silicon.

  At this time, the conductive substrate 17 is an aluminum substrate or a metal substrate containing at least aluminum on the surface, so that the single crystal silicon particles 16 can be bonded at a low temperature, and the photoelectric conversion is lightweight and inexpensive. An apparatus can be provided. Further, by making the surface of the conductive substrate 17 rough, the reflection of incident light reaching the non-light receiving region on the surface of the conductive substrate 17 can be made random, and the incident light is slanted in the non-light receiving region. It can be reflected and re-reflected to the surface side of the photoelectric conversion device, and incident light can be used effectively by further photoelectrically converting it by the photoelectric conversion part of the single crystal silicon particles 16.

  Next, an insulating material 19 is placed on the conductive substrate 17 so that it is interposed between adjacent ones of the bonded single crystal silicon particles 16, and at least the top portion of these single crystal silicon particles 16 is an insulating material. 19 to be exposed.

  Here, the surface shape of the insulating material 19 between the adjacent single crystal silicon particles 16 is a concave shape in which the single crystal silicon particle 16 side is high, so that the insulating material 19 and the upper surface of the insulating material 19 are Due to the difference in refractive index with the transparent sealing resin formed by covering the surface, irregular reflection of incident light on the single crystal silicon particles 16 can be promoted in the non-light-receiving region without the single crystal silicon particles 16.

  Next, a second conductive type (for example, n-type) semiconductor layer 20 and a translucent conductor layer 21 are provided on the exposed upper portions of the single crystal silicon particles 16. The semiconductor layer 20 is provided by forming an amorphous or polycrystalline semiconductor layer 20 or by forming the semiconductor layer 20 by a thermal diffusion method or the like. At this time, since the single crystal silicon particles 16 are p-type, the silicon layer which is the semiconductor layer 20 is an n-type semiconductor layer 20. Further, a translucent conductor layer 21 is formed on the semiconductor layer 20. 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 electrodes 22, such as a grid electrode or a finger electrode and a bus-bar electrode, are formed. In this way, by using the conductive substrate 17 as one electrode and the electrode 22 as the other electrode, a photoelectric conversion device as a solar cell can be obtained.

  In order to form the semiconductor layer 20 of the second conductivity type, prior to the bonding of the single crystal silicon particles 16 to the conductive substrate 17, the surface of the single crystal silicon particles 16 is formed on the surface of the single crystal silicon particles 16 by a thermal diffusion method with low process cost. It may be formed. In this case, for example, the group V P, As, Sb or the group III B, Al, Ga or the like is used as the second conductivity type dopant, and the single crystal silicon particles 16 are accommodated in a diffusion furnace made of quartz. The semiconductor layer 20 of the second conductivity type is formed on the surface of the single crystal silicon particles 16 by heating while introducing the dopant.

  Examples of the method for producing single crystal silicon particles will be described below.

[Production process of teardrop-shaped crystalline silicon particles]
A method of solidifying a melt of silicon melted by filling a crucible with a silicon raw material in an inert atmosphere gas composed of Ar gas from a nozzle hole of a nozzle portion formed at the lower end of the crucible Then, p-type crystalline silicon particles composed of teardrop-type pseudo single crystals were produced by a so-called melt-drop method (jet method). Note that boron was included in the crystalline silicon particles as a p-type dopant. The average particle size of the crystalline silicon particles was about 500 μm.

  In order to form crystalline silicon particles composed of teardrop-type pseudo single crystals, a resistance heating heater is provided in the middle of a quartz drop tube in which granular silicon melt falls, immediately after being discharged from the crucible. The degree of supercooling of the granular silicon melt was controlled to be about 64 ° C. (the temperature of the granular silicon melt was about 1350 ° C.). Thereby, only a few crystal nuclei were generated in the granular silicon melt, and pseudo single crystal particles having only a few grain boundaries were obtained.

[Point head removal process]
Next, tear-drop-type pseudo-single-crystallized crystalline silicon particles having a cusp with segregated impurities, polishing stones and pure water as mullite media are accommodated in a cylindrical container, and the number of rotations By rotating at 200 rpm for 60 minutes, a portion from the surface of the tip of the crystalline silicon particles to a depth of 20 μm was removed by polishing.

  Thereafter, the surface of the crystalline silicon particles is removed with hydrofluoric acid and hydrofluoric acid in order to remove foreign matters, metal ions, and minute cracks, oxide films, etc. formed on the surface of the crystalline silicon particles. Then, it was washed and etched. The removal by the etching treatment was performed from the surface of the crystalline silicon particles up to a depth of about 5 μm.

[Formation process of oxynitride film]
Next, a remelting step (remelting step) was performed in order to crystallize the crystalline silicon particles. First, a large number (1000 particles) of crystalline silicon particles having a boron concentration of 0.6 × 10 ¹⁶ atoms / cm ³ and an average particle diameter of 500 μm are stacked on a quartz glass box-shaped base plate. And placed in a quartz glass bell jar installed inside an atmosphere firing furnace as a heating furnace. Then, heating is performed while introducing nitrogen gas and oxygen gas from a gas supply apparatus, and the gas pressure is 0.1 MPa and heated to 1300 ° C. below the melting point of silicon and held for 60 minutes. An oxynitride film was formed. After heating at 1300 ° C. for 60 minutes, the temperature was lowered to room temperature.

[Single crystallization process and protrusion formation process]
Next, while introducing nitrogen gas and oxygen gas or mixed gas (nitrogen gas, oxygen gas and argon gas) from the gas supply device, the single crystal silicon particles are heated to 1440 ° C. above the melting point of silicon at a gas pressure of 0.02 MPa. This was held for 5 minutes to melt the silicon inside the oxynitride film on the surface of the single crystal silicon particles, and then the single crystal silicon particles were solidified while cooling at a rate of 2 ° C. per minute. Thereafter, the temperature was further lowered to 1250 ° C., and then a thermal annealing treatment was performed for 120 minutes. After this thermal annealing treatment, the temperature was lowered to around room temperature. At this time, protrusions having a length of about 10 μm were formed on the single crystal silicon particles at a ratio of the number of about 1/4 (Table 1).

[Projection removal process]
Next, 1000 pieces of single crystal silicon particles having an average particle diameter of 500 μm and 2000 abrasives made of mullite having an average particle diameter of 10 mm are placed inside a barrel pot made of cylindrical hard rubber having a length of 200 mm and a diameter of 200 mm. Housed in. Water was placed in the barrel pot so that the single crystal silicon particles and the abrasive were all immersed, and the lid 5 made of hard rubber was closed.

  Next, the barrel pot was rotated at 200 rpm around the rotation axis (the central axis of the cylinder), and the barrel pot was linearly reciprocated in the horizontal direction (lateral direction) to polish the single crystal silicon particles for 10 minutes. It was confirmed by Raman spectroscopy that the protrusions were removed from the polished single crystal silicon particles, and that a work-affected layer was not formed.

  Further, the oxynitride film formed on the surface of the collected single crystal silicon particles was removed with hydrofluoric acid, and the surface of the single crystal silicon particles was etched away by 20 μm in the depth direction with hydrofluoric acid.

[Manufacturing process of photoelectric conversion device]
Next, 1000 single crystal silicon particles are placed on a quartz boat, introduced into a quartz tube controlled at 900 ° C., POCl ₃ gas is bubbled with nitrogen and fed into the quartz tube, and a thermal diffusion method is performed. In 30 minutes, an n-type semiconductor layer (semiconductor portion) having a thickness of about 1 μm was formed on the surface layer of the single crystal silicon particles. Thereafter, the oxynitride film on the surface of the single crystal silicon particles was removed with hydrofluoric acid.

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

  Furthermore, between the single crystal silicon particles from above, an upper portion thereof is exposed and an insulating material made of polyimide resin is applied and dried, so that a conductive substrate serving as a lower electrode and a light transmitting material serving as an upper electrode The conductor layer is electrically insulated and separated. A translucent conductor layer made of ITO as an upper electrode was formed on the entire surface with a thickness of about 100 nm by sputtering.

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

  And when manufacturing the photoelectric conversion device as described above, when the single crystal silicon particles are subjected to barrel polishing to remove the protrusions and when the barrel polishing is not performed, the remaining ratio of the protrusions and The results of measuring the photoelectric conversion efficiency are shown in Table 1. The photoelectric conversion efficiency of the photoelectric conversion device was measured with an AM1.5 solar simulator.

表１に示す通り、全ての単結晶シリコン粒子の突起部は、バレル研磨加工により除去された。また、光電変換効率もバレル研磨加工をしたものが高く良好な結果であった。これは、１）シリコン原料に含まれていた鉄，ニッケル等の金属不純物及び製造工程で入り込んだ炭素等の不純物を、突起部を除去することによって除去することができたこと、２）酸窒化膜によって表面が保護された単結晶シリコン粒子から表面を実質的に加工変質させずに突起部を除去することができたこと、３）突起部が除去されることによって、単結晶シリコン粒子は真球状に近い形状となり、光電変換装置を製造する際に導電性基板上に多数の単結晶シリコン粒子を位置精度を高めて配列できたこと、が原因していると考えられる。

As shown in Table 1, all the protrusions of the single crystal silicon particles were removed by barrel polishing. Also, the photoelectric conversion efficiency was high when barrel polishing was performed, which was a good result. This was because 1) metal impurities such as iron and nickel contained in the silicon raw material and carbon and other impurities contained in the manufacturing process could be removed by removing the protrusions, and 2) oxynitriding The protrusions could be removed from the single crystal silicon particles whose surfaces were protected by the film without substantially modifying the surface. 3) By removing the protrusions, the single crystal silicon particles were true. The shape is almost spherical, and it is considered that a large number of single crystal silicon particles can be arranged with high positional accuracy on the conductive substrate when manufacturing the photoelectric conversion device.

  In addition, this invention is not limited to the above embodiment and Example, A various change may be added in the range which does not deviate from the summary of this invention. For example, in the remelt process, single crystal silicon particles are heated and melted by using a method of melting by irradiating light energy from above the single crystal silicon particles placed on the upper surface of the base plate, not a heating furnace. May be.

It is a schematic sectional drawing which shows an example about the manufacturing method of the single crystal silicon particle of this Embodiment, and shows a mode that the single crystal silicon particle and the abrasive | polishing material were accommodated in the barrel pot. It is sectional drawing of the single crystal silicon particle which has a projection part in the manufacturing method of the single crystal silicon particle of this Embodiment. It is sectional drawing which shows an example of the photoelectric conversion apparatus produced using the single crystal silicon particle obtained by the manufacturing method of the single crystal silicon particle of this Embodiment.

Explanation of symbols

1: Barrel pot 2: Abrasive material 3: Single crystal silicon particles 4: Center axis (rotation axis) of rotation of barrel pot
5: Barrel pot lid 11: Oxynitride film 12: Projection

Claims (10)

  Manufacture of single crystal silicon particles in which the protrusions of single crystal silicon particles having protrusions with segregated impurities and having an oxynitride film formed on the surface are removed by polishing without substantially modifying the surface. Method.   The method for producing single crystal silicon particles according to claim 1, wherein the polishing is barrel polishing.   3. The method for producing single crystal silicon particles according to claim 2, wherein the barrel polishing process uses an abrasive having a spherical shape whose diameter is 3 to 30 times that of the single crystal silicon particles.   The method for producing single crystal silicon particles according to claim 3, wherein the abrasive includes at least one of alumina, silicon nitride, silicon carbide, mullite, silica, and zirconia.   The method for producing single crystal silicon particles according to any one of claims 2 to 4, wherein in the barrel polishing process, a rotation speed of the barrel is 50 to 500 rpm.   By discharging the silicon melt in a granular form from the nozzle part of the crucible and cooling and solidifying the granular silicon melt, quasi-single crystallized crystalline silicon particles having a pointed head where impurities are segregated are produced. A step of removing the peak of the crystalline silicon particles, a step of forming an oxynitride film on the surface of the crystalline silicon particles, and heating the crystalline silicon particles to remelt the inside of the oxynitride film Solidifying and solidifying, the step of producing single crystal silicon particles having protrusions with segregated impurities and having an oxynitride film formed on the surface; and the protrusions of the single crystal silicon particles substantially including the surface And a step of removing the material by polishing without changing the quality of the material.   The method for producing single crystal silicon particles according to claim 6, wherein the polishing is barrel polishing.   The method for producing single crystal silicon particles according to claim 7, wherein the barrel polishing process uses an abrasive having a spherical shape whose diameter is 3 to 30 times that of the single crystal silicon particles.   The method for producing single crystal silicon particles according to claim 8, wherein the abrasive includes at least one of alumina, silicon nitride, silicon carbide, mullite, silica, and zirconia.   The method for producing single-crystal silicon particles according to any one of claims 7 to 9, wherein the barrel polishing process has a barrel rotation speed of 50 to 500 rpm.

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