JP2003165800A - Particulate metal crystal and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably produce particulate silicon having high crystallinity, and also produce a silicon particle having high crystallinity at a lower cost, when the particulate silicon is produced. <P>SOLUTION: Liquid drops of metal melt are discharged and dropped from the nozzle 2 of a crucible 1, and these liquid drops are solidified while being dropped, so as to produce a particulate metal crystal. Particles to be crystal nucleus are added to the metal melt and liquid drops containing the metal melt having the crystal nucleus are discharged from a nozzle member. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for producing granular metal crystals, and more particularly to a granular metal crystal used for producing silicon particles used in a photoelectric conversion device and a method for producing the same.

[0002]

2. Description of the Related Art In the development of solar cells, market needs such as efficiency in terms of performance, finiteness of resources, or manufacturing cost are taken into consideration. As one of the promising solar cells, a photoelectric conversion element using spherical silicon has been actively developed.

At present, as raw materials for producing granular silicon, fine particles of silicon generated as a result of pulverizing a single crystal silicon material or high-purity silicon vapor-phase-synthesized by a fluidized bed method are used. A method in which the raw materials are separated according to size or weight, and then the raw materials are melted again in a container using an infrared ray or a high-frequency coil, and then free-falled to be spheroidized (for example, WO99 / 2).
No. 2048, U.S. Pat. No. 4,188,177, etc.), or a method of spheroidizing by high-frequency plasma heating and melting (JP-A-5-78115) is also used. Further, as in US Pat. No. 4,188,177, among the spheres produced by dropping, the tear-shaped particles have high crystallinity in which the crystal particles constituting the tear-shaped particles are about 3 to 5 or less. It is said to have.

However, these methods have problems in that the weight of the raw material is made uniform and the amount of impurities is controlled. That is, since the variation in weight is directly reflected on the size of the sphere to be made, a raw material having a uniform weight is desired. Therefore, it is difficult for a metal material such as silicon to efficiently obtain a raw material having a weight corresponding to an effective size for a ball solar solar cell by a method such as crushing or classification.

Further, in order to add a certain amount of impurities as a semiconductor material to the pulverized or classified raw material, it is necessary to mix it into the raw material from the beginning or add it later. Therefore, for example, a method of adding an impurity at the time of producing the raw material at the time of producing a single crystal, a method of adding an impurity in a gas phase after pulverization and diffusing, and the like are used.
However, in the crushing process, contamination is generated from the crushing media, which complicates the process and requires expensive equipment, which inevitably increases costs.

As a method for solving this problem, a method is used in which a trace amount of impurities to be added to the raw material so as to have a certain purity is preliminarily blended, melted once in the crucible, discharged, and at the same time made into particles. (US Pat. No. 607447)
(See No. 6). However, the silicon particles produced are particles having a size of more than 1 mm, and in order to increase the crystallinity, such measures as melting, for example, synthesizing an oxide film on the surface of the spherical particles once produced, and at the same time, in the cooling step, Is a process that requires sufficient control of the cooling temperature profile, and it is difficult to maintain that condition stably. Moreover, the spheres are produced one by one, and the productivity is extremely low. That is, it is unsuitable as a particle production process for forming a solar cell element that requires a large amount of particles.

In addition to these methods, as in US Pat. No. 4,430,150 and Japanese Patent Application Laid-Open No. 11-12091, spherical metal particles are used to maintain their shape in a spherical shape, so that an oxide film is formed around them. It has been proposed that a single crystal be produced by covering the substrate with a heat treatment and then recrystallizing it by heat treatment.

However, even with this method, it is necessary to temporarily produce a certain weight of spherical silicon or silicon powder, so it is necessary to incorporate steps such as granulation or pulverization and classification in the manufacturing process. ,
The manufacturing process is complicated and long, and the productivity is low.

In the present invention, when spherical silicon used for solar cells is manufactured, the spherical silicon can be stably and efficiently manufactured, and at the same time, silicon particles having high crystallinity can be manufactured at low cost. An object is to provide a metal crystal and a method for producing the same.

[0010]

In order to achieve the above object, in the method for producing granular metal crystals according to the first aspect of the present invention, the metal melt is discharged from the nozzle portion of the crucible in the form of drops and dropped. In a method for producing a granular metal crystal by cooling and solidifying a metal melt while falling, a method for producing a granular metal crystal is characterized in that particles serving as crystal nuclei are added to the metal melt and discharged in a drop shape. And

In the above-mentioned method for producing a granular metal crystal, silicon can be used as the metal.

In the above-mentioned method for producing a granular metal crystal, it is desirable that the particles are made of any one or more of silicon carbide, aluminum oxide, silicon oxide, diamond and graphite.

In the above-mentioned method for producing a granular metal crystal, it is desirable that pressure be applied to the metal melt and that the metal melt be discharged in a droplet form from the nozzle portion.

In the granular metal crystal according to claim 5,
Particles made of any one or more of silicon carbide, aluminum oxide, silicon oxide, diamond and graphite are present in a granular metal crystal made of silicon.

[0015]

In the present invention, as to the supply of the granular silicon crystal used for the solar cell, the high productivity and the quality of the crystal have been earnestly studied and studied, and the following has been considered.

That is, the metal melt is discharged from the nozzle portion of the crucible in the form of drops and dropped, and the metal melt is cooled and solidified during the drop to produce granular metal crystals. In the method, particles of high crystallinity as described above can be confirmed with high frequency in a nozzle material having a large abradability, whereas in a nozzle material aiming to suppress the abrasivity and prolong the life of the nozzle, the crystallinity of particles is It originates in the careful observation of the phenomenon of decrease. As a result of analyzing this phenomenon, we found that the particles of the nozzle material are crystal-grown by the particles of the minute nozzle material mixed in the discharge melt due to the wear of the nozzle material, and the particles with high crystallinity are obtained. Thus, the present invention has been achieved.

As described above, in the case of the granular silicon crystal used for the solar cell element, the metal melt is discharged from the nozzle of the crucible in the form of drops and dropped, and the metal melt is cooled and solidified during the fall. In, after the seeds which will be the crystal nuclei are mixed in the metal melt in advance, by discharging the metal melt in a drop shape,
By reducing the particle size, it is possible to efficiently use the silicon material and at the same time improve the crystallinity thereof.

In the solar cell element, the required size of the crystal particles is sufficient if the thickness of the bulk polycrystal is about 300 μm from the viewpoint of optical absorption efficiency.

As a result, a large amount of crystal particles for a solar cell element can be easily produced without a complicated process of granulation and crystallization, and the production cost can be suppressed.

[0020]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a view showing an embodiment of a crucible for forming a granular metal according to the present invention, in which 1 is a crucible as a whole, 2 is a main body member, and 3 is a nozzle member.

The crucible 1 is composed of a cylindrical main body member 2 and a disc-shaped nozzle member 3 attached to the bottom of the main body member 2.

The main body member 2 of the crucible is composed of an inner wall member 2a for suppressing reaction with, for example, silicon and an outer wall member 2b arranged outside the inner wall member 2a. The outer wall member 2b is provided to ensure strength. The inner wall member 2a and the outer wall member 2b are made of a sintered body that has been densified by a casting method, a hot pressing method, or the like. Aluminum oxide, silicon carbide, graphite, etc. are suitable for suppressing the reaction with silicon, but graphite etc. sintered by hot pressing are suitable in terms of workability. In the case of forming with graphite, in order to raise its purity after processing, it is used after being washed with acid, then washed with water and dried. These are, for example, the inner wall member 2
Screws 4 are provided on the outer side of a and the inner side of the outer wall member 2b for assembly.

A nozzle member 3 having a nozzle hole 3a is provided on the tip side of the crucible 1. That is, the nozzle member 3 having the nozzle hole 3a for discharging the metal melt is provided separately from the outer wall member 2b of the crucible 1 having the small diameter portion 2c at the tip, and the nozzle member 3 is used as the main body member 2 of the crucible 1. It is arranged inside the tip small diameter portion 2c. The nozzle member 3 is made of silicon carbide, diamond, aluminum oxide, cubic boron nitride, or the like. A single crystal or a polycrystal is used for each material.

Nozzle holes 3 provided in this nozzle member 3
Plural a may be provided. As a result, productivity can be improved by the number of holes, which is a great advantage in manufacturing.
The nozzle holes 3a are processed by mechanical processing, laser processing, or ultrasonic processing.

As described above, by forming the main body member 2 of the crucible 1 and the nozzle member 3 as separate members so that they can be assembled, only the nozzle member 3 can be replaced, which is expensive. The main body member 2 of the na crucible 1 can be repeatedly used.

A silicon raw material is put into such a crucible 1 and the whole silicon raw material is melted by an induction heating or a resistance heater (not shown). At this time, particles serving as crystal seeds are added to the silicon raw material. It is desirable that the particles that become the crystal nuclei are those that do not easily react even in the melt of silicon, and that various kinds of materials can be used except those whose shape changes and those which diffuse as impurities and cause deterioration of semiconductor characteristics. It is possible to use one.
For example, aluminum oxide, silicon oxide, diamond or graphite can be preferably used. The upper portion of the melted silicon melt is filled with, for example, argon gas at 0.5.
By pressurizing at a pressure of MPa or less and extruding from the nozzle hole 3a of the nozzle member 3, the silicon melt is sprayed to form a large number of drops. A large number of droplets of the melted silicon melt are solidified during free fall and become single crystal silicon or crystalline silicon composed of a small number of crystal grains and are accommodated in a container.

Such silicon particles are used to form solar cells. Therefore, it is desirable that the silicon to be dissolved contains a desired semiconductor impurity.

[0028]

[Example] Inner diameter 19.0 mmφ, outer diameter 25.0 mmφ,
A crucible having a nozzle member 3 processed into a dimension of 143 mm in length and composed of graphite (graphite DFP-2 manufactured by Poco Co., Ltd.) and laser processing the nozzle hole 3a is
The whole temperature was set to 1470 ° C. by setting it in a furnace capable of maintaining an inert gas atmosphere such as r or He. The raw material was supplied to the crucible through a route also kept in an inert atmosphere and completely melted. The silicon raw material was melted and particles were prepared, and the particle size and crystallinity were evaluated. The test was conducted as follows.

Core particles were weighed and added to the silicon raw material, and both were uniformly dispersed in a plastic bag container.
18 g of this silicon raw material was placed at 1450 in an inert atmosphere.
The mixture was charged into a crucible maintained at a temperature of ° C and melted. A gas pressure of 0.15 MPa was applied to the sufficiently dissolved raw material, and the entire amount was sprayed from the nozzle hole at once and discharged.

The particle size distribution of the spheres produced by this ejection was determined, and the crystallization rate in the distribution was determined. In addition,
The particle size distribution here is calculated from the ratio of the number distribution after classification with a sieve.

[0031]

Example 1 0.02 g of silicon carbide (2 to 3 μm) as a core particle was weighed and added to raw silicon.
After both were uniformly dispersed in a container such as a plastic bag, the silicon was sprayed under the above-mentioned conditions. As a result of classifying the shape of the obtained particles, the shape of the particles is a tear shape,
It was classified into a diamond shape and a spherical shape, and the composition ratio was 2: 7: 1.

The results of SEM observation of the cross section of each particle shape are shown in FIGS. In SEM observation, after embedding each particle in a resin and mirror-polishing the cross section, etching treatment with a mixed acid of hydrofluoric acid, nitric acid, and acetic acid was sufficiently performed to observe the grain boundary. FIG. 2 is an SEM image of tear-shaped particles, FIG. 3 is an SEM image of diamond-shaped particles, and FIG. 4 is an SEM image of spherical particles. As shown in the SEM images of FIGS. 2 to 4, in addition to the deeply visible etch pits, the relationship between the shape and the crystal grains constituting the grains was classified as follows.

Although many etch pits are seen,
The number of crystal grains constituting it is about 3 to 5, a single grain (twin crystal) having a high crystallinity with a large number of etch pits similarly, a columnar crystal in the peripheral portion, and a granular crystal in the central portion. It was found to be a polycrystalline body composed of Further, in the diamond-like particles, a particle-like specific etching shape (nucleus) was observed on the twin line.

[0034]

Comparative Example 1 Particles obtained by spraying silicon were classified in the same manner as in Example 1 except that core particles were not added.

As a result, the shape was classified into a tear shape and a spherical shape, the composition ratio thereof was 1: 9, and the diamond shape was hardly observed.

[0036]

Example 2 Addition was performed in the same manner as in Example 1 except that each core particle shown in Table 1 was used, and silicon was sprayed to perform morphological classification under a microscope. Further, as a comparative example, the morphological classification was similarly performed on the spray particles obtained when the silicon carbide shown in Example 1 was not added.

[0037]

[Table 1]

As a result, when particles are added as nuclei,
The composition ratio of the sprayed particles was obviously different from that in the case where no addition was made, and the composition ratio of the diamond-like particles, which had a shape with high crystallinity in Example 1, was the highest.

[0039]

INDUSTRIAL APPLICABILITY As described above, in the method for producing a granular metal crystal according to the present invention, when the metal melt is discharged from the nozzle portion of the crucible in a drop shape and dropped, crystals are formed in the metal melt in the crucible. After adding the particles to be the core, the particles are discharged in a droplet form from the nozzle part, which makes it possible to make the metal melt into a droplet form and easily promote crystallization, which is extremely high in industrial value. .

[Brief description of drawings]

FIG. 1 is a view showing an embodiment of a crucible for forming a granular metal of the present invention.

FIG. 2 is a cross-sectional SEM image of tear-shaped particles.

FIG. 3 is a cross-sectional SEM image of diamond-like particles.

FIG. 4 is a cross-sectional SEM image of spherical particles.

[Explanation of symbols]

1 crucible 2 Body member 2a Inner wall member 2b outer wall member 3 nozzle members 3a nozzle hole 4 kinds

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shin Sugawara             6 at 1166 Haseno, Jamizo-cho, Yokaichi-shi, Shiga               Kyocera Corporation Shiga Yokaichi Factory (72) Inventor Hisao Arimune             6 at 1166 Haseno, Jamizo-cho, Yokaichi-shi, Shiga               Kyocera Corporation Shiga Yokaichi Factory F term (reference) 4G072 AA01 BB06 BB07 BB20 GG03                       HH01 HH33 JJ02 JJ26                 4G077 AA01 BA04 CD10 ED01 HA20                 5F051 AA02 CB02 DA01

Claims (5)

[Claims] 1. A granular metal crystal for producing a granular metal crystal by discharging the metallic melt in a droplet form from a crucible nozzle and dropping it, and cooling and solidifying the metallic melt during the fall. In the method, particles for forming crystal nuclei are added to the metal melt and discharged in the form of drops, which is a method for producing granular metal crystals. 2. The method for producing a granular metal crystal according to claim 1, wherein the metal is silicon. 3. The production of granular metal crystals according to claim 1, wherein the particles are made of any one or more of silicon carbide, aluminum oxide, silicon oxide, diamond and graphite. Method. 4. The method for producing granular metal crystals according to claim 1, wherein a pressure is applied to the metal melt and the metal melt is discharged in a droplet form from the nozzle portion. 5. A granular metal crystal in which particles of silicon carbide, aluminum oxide, silicon oxide, diamond, or graphite are present in the granular metal crystal of silicon.