JP2003073112A - Crucible for forming inorganic particles - Google Patents

Abstract

(57) [Summary] [Problem] Even in the case of manufacturing granular silicon having high reactivity at high temperatures, heat resistance and corrosion resistance (stability resistance) capable of stably maintaining its shape under severe conditions It is an object of the present invention to provide a low-cost crucible having abrasion resistance. SOLUTION: A cylindrical crucible body having a small-diameter portion at one end is provided, and a nozzle portion having a discharge hole of an inorganic melt is provided separately from the crucible body, and the nozzle portion is made of silicon carbide, aluminum oxide. , Cubic boron nitride, or diamond and disposed inside the small diameter portion of the crucible body.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a crucible for forming inorganic particles, and more particularly to a crucible for forming inorganic particles used for producing silicon particles used in a photoelectric conversion device.

[0002]

2. Description of the Related Art In the development of solar cells for supplying the next-generation energy supply, market needs such as efficiency in performance, limited 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 crushing a single crystal silicon material or high-purity silicon vapor-phase-synthesized by a fluidized bed method are used. After separating the raw materials, the raw material is melted again in the container by using an infrared ray or a high frequency coil, and then free-falled to be spheroidized (for example, WO99 / 22048, USP4188177). Etc.).

However, these methods have problems in that the weight of the raw material is made uniform and the amount of impurities is controlled.

As a method for solving this problem, a method has been adopted in which silicon prepared so as to have a certain purity is once melted in a crucible, and is discharged at the same time as particles (see US Pat. No. 6,074,476). ). As the crucible used at this time, quartz and graphite are generally used because heat resistance and strength are required.

As its application, for example, Japanese Patent Laid-Open No. 8-183
According to Japanese Patent No. 694, the graphite forming the crucible is made small in particle diameter and the surface roughness is made small, and the graphite is sintered. As a result, a denser sintered body is obtained and the reaction is suppressed. In addition, the quartz crucible for melting and pulling,
In order to secure its strength, the outside is reinforced with graphite to keep its shape.

On the other hand, as disclosed in JP-A-8-150467 and JP-A-9-52759, in order to improve the corrosion resistance and strength of the structural material, carbide or oxide particles are added to the structural material. In addition, attempts have been made to create composites.

[0008]

However, in any of the materials, when graphite is used at a high temperature such that silicon particles melt, it will inevitably react with silicon. Even if quartz is used, it is difficult to maintain a shape capable of stably discharging the melt at the melting temperature.

That is, in a portion of the hole formed in the crucible for forming silicon particles, which is in contact with the silicon melt, when a reaction with silicon occurs on the surface,
The bond between the particles of the crucible constituent material is weakened, and as a result,
From the weakened part to the corrosion of particles of the crucible constituent material (Er
osin) occurs. In particular, in the case of producing silicon particles at a high speed in order to improve productivity, high dynamic friction generated at the melt spouting portion causes further corrosion, and a stable particle shape cannot be obtained.

Further, in a crucible used in steps such as pulling a single crystal, quartz softens at the melting temperature of silicon, so in order to maintain its shape, the outside is reinforced with graphite to maintain the shape. ing. Therefore, when attempting to discharge molten silicon from under the crucible, it is obvious that the hole formed in the crucible will deform due to its own deformation, and it is difficult to stably spray silicon. is there.

Further, since the crucible as described above is used in a high temperature state, when it is formed by using each material alone, the molding method and the sintering method are extremely complicated and costly such as cast molding and hot pressing. It is not practical because it becomes a costly method.

Therefore, according to the present invention, even when spherical silicon is manufactured using silicon having high reactivity at high temperatures, the shape and heat resistance can be stably maintained under severe conditions. Corrosion (wear resistance)
It is an object of the present invention to provide a crucible that can be manufactured at low cost and that has both of the following.

[0013]

In order to achieve the above object, a crucible for forming inorganic particles according to claim 1 is provided with a nozzle portion for discharging a melt of an inorganic material containing silicon as a main component to make it into particles. In the crucible for forming inorganic particles, the nozzle portion is made of any one of silicon carbide, aluminum oxide, cubic boron nitride, and diamond.

In the above crucible for forming inorganic particles, the nozzle portion is made of silicon carbide having a true specific gravity of 3.0 g / cc or more and 3.3.
Aluminum oxide of 0 g / cc or more, 3.15 g / cc
It is desirable to be made of any one of the above cubic boron nitride and diamond with a weight of 3.35 g / cc or more.

Further, in the above crucible for forming inorganic particles, it is preferable that the nozzle portion is made of any one of single crystal silicon carbide, single crystal aluminum oxide, single crystal cubic boron nitride and single crystal diamond.

Further, in the above crucible for forming inorganic particles, the region other than the nozzle portion is preferably made of any one of a graphite sintered body, an aluminum oxide sintered body and a silicon carbide sintered body.

Further, in the crucible for forming inorganic particles according to claim 6, a cylindrical crucible body having a small diameter portion is provided at one end, and a nozzle having a discharge hole for the melt of the inorganic substance is provided separately from the crucible body. And a nozzle portion is provided inside the small diameter portion of the crucible body.

[0018]

[Function] As a result of intensive experiments conducted on the corrosion of the crucible for forming granular silicon, the mechanism of its occurrence has been considered as follows.

That is, strength deterioration occurs at the boundary between the compound produced by the reaction and the existing particles. The bond strength between particles is originally weak, and the bond between particles is broken by dynamic friction with molten silicon. Any one of the above or a complex phenomenon thereof occurs and corrosion progresses.

In the present invention, the mechanism is suppressed by selecting a material that does not easily form a compound with silicon. Also, in order to increase the bonding strength between particles of the material that constitutes the crucible, the use of a single crystal or a material that has been sintered to a density similar to that of a single crystal solves the problem of the bond strength between particles in the mechanism. Is intended.

Therefore, in the present invention, by taking the above two measures, the progress of the corrosion reaction shown in (3) can be stopped. In particular, in the nozzle portion of the crucible that is most frequently contacted with the silicon melt, the desired function of the crucible can be obtained by selecting a material that does not react with silicon.

As a result, the life of the crucible can be extended and the manufacturing cost can be suppressed.

[0023]

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 inorganic particles according to the present invention, in which 1 is a crucible and 2 is a nozzle portion.

The crucible 1 has an inner wall member 1 for suppressing reaction with, for example, silicon and an outer wall member 2 for ensuring strength.
Composed of and. The inner wall member 1 and the outer wall member 2 are made of a sintered compact densified by casting or hot pressing. Aluminum oxide, silicon carbide, graphite, etc. are suitable for suppressing the reaction with silicon,
From the viewpoint of ease of processing, graphite etc. sintered by hot pressing are suitable. 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. Inner wall member 1
Screws 6 are provided on the outer side of the inner wall member 2 and the inner wall member 2 for assembly.

A nozzle 2 is provided on the tip side of the crucible 1. That is, the nozzle portion 2 having the discharge hole 2a for the melt of the inorganic substance is provided separately from the cylindrical crucible body 1 having the small diameter portion at one end, and the nozzle portion 2 is provided inside the tip small diameter portion of the crucible body 1. It is arranged in. This nozzle 2
It is made of silicon carbide, diamond, aluminum oxide, cubic boron nitride, or the like. Each of these materials is formed by processing a single crystal or is formed by setting its density according to sintering conditions.

The nozzle portion 2 has a true specific gravity of 3. to prevent abrasion of the nozzle hole diameter and form stable inorganic particles.
Desirably, it is made of any one of 0 g / cc or more of silicon carbide, 3.30 g / cc or more of aluminum oxide, 3.15 g / cc or more of cubic boron nitride, and 3.35 g / cc or more of diamond. In addition, this nozzle unit 2
Is formed from any one of single crystal silicon carbide, single crystal aluminum oxide (sapphire), single crystal cubic boron nitride, and single crystal diamond, it further prevents wear of the nozzle hole diameter and stabilizes the inorganic particles. Can be formed.

The nozzle 2 is provided with holes 2a for discharging silicon into particles. A plurality of holes 2a may be provided. The holes 2a are machined or laser-machined so that the holes have the same diameter. The thickness of the nozzle is adjusted so that the thickness of the nozzle is constant with respect to the diameter of the hole.

As described above, by forming the crucible body 1 and the nozzle portion 2 by separate members and assembling them, it is possible to replace only the nozzle portion 2 and the expensive crucible body. 1 can be used repeatedly.

A silicon raw material is put into such a crucible 1 and the whole is melted by an induction heating or a resistance heating heater (not shown). The upper portion of the melted silicon melt is pressurized with argon gas or the like and extruded from the hole 2a of the nozzle portion 2 to be sprayed. When the silicon melt ejected in a mist state is allowed to fall freely, it is solidified during the fall and becomes single crystal silicon or polycrystalline silicon having a diameter of 1 mm or less, and is 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.

Further, the present invention is not limited to the case of forming silicon particles, but can be suitably used in the case of forming other various semiconductor particles and the case of forming metal particles.

[0032]

EXAMPLE The crucible assembled as described above is set in a furnace capable of maintaining an inert atmosphere, and the entire temperature is set. The raw material was supplied to the crucible through a route also kept in an inert atmosphere and completely melted. In this test, the silicon raw material was melted and particles were prepared, and the change rate of the nozzle hole diameter corresponding to the number of times of execution was measured. A specific durability test was conducted as follows.

18 g of a silicon raw material was charged and melted in a crucible maintained at a temperature of 1450 ° C. in an inert atmosphere. A constant gas pressure was applied to the raw material in a sufficiently dissolved state, and the entire amount was sprayed at once from the nozzle hole and discharged. This melting-discharging operation was repeated, and at each of the third, tenth, and twentieth repetitions, the nozzle was taken out and the hole diameter was measured, the change from the initial hole diameter was examined, and the ratio was determined. In addition, in order to investigate the characteristics of the materials manufactured by the same method, test pieces were manufactured and the elastic modulus and bending strength of each material were measured. The results are shown in Table 1.

[0034]

[Table 1]

According to the first embodiment, when the material of the nozzle portion is SiC, the density thereof is 3.0 g / cc or more, and it can be repeatedly used. On the other hand, as shown in the first comparative example, the sintered graphite and the hBN sintered body can be used. In No. 2, the nozzle hole diameter changed significantly significantly as the number of sprays increased. For this reason, it was not possible to continue spraying under constant conditions, and the nozzle portion was not practical.

Further, as shown in Example 1, 3.0 g / c
When the density was less than c, the nozzle hole diameter was significantly changed, and it was still unusable.

On the other hand, as shown in Examples 2 to 4, diamond, aluminum oxide (Al ₂ O ₃ ), c
When using a dense sintered body of BN, a single crystal, or the like, no change in the pore diameter was observed, which was good. On the other hand, the sintered graphite and the hBN sintered body shown in Comparative Example 1 and the use in which the nozzle hole diameter is changed and the spraying is continued in a constant amount when the compactness is lowered as shown in each Example Was not something that could withstand.

The elastic modulus of SiC is 3.2.
× 10^FiveMPa or more, preferably 3.4 × 10^FiveMPa or higher
Above, 9.3 × 10 for diamonds^FiveMore than MPa is desired
Kuha 9.8 × 10^FiveMPa or higher, Al₂O₃Then 2.8x
10^FiveMPa or more, preferably 3.0 × 10^FiveMPa, cB
6.5 × 10 for N^FiveMPa or more, preferably 8.5 × 1
0 ^FiveIt is suitable that it is MPa or more.

Further, the bending strength of SiC is 5
50 MPa or more, preferably 600 MPa or more, and diamond, 1000 MPa or more, preferably 1100 MPa
As described above, 300 MPa or more for Al ₂ O _{3 and} desirably 340
850 MPa or more for MPa and cBN, preferably 970
It is suitable that it is MPa or more.

[0040]

As described above, in the crucible for forming inorganic particles according to the first aspect, in the crucible for forming inorganic particles, the crucible for forming inorganic particles is provided with the nozzle part for discharging the melt of the inorganic substance and granulating the melt. Since it is made of any one of silicon, aluminum oxide, cubic boron nitride, and diamond, the wear property of the hole portion formed in the nozzle is improved,
This nozzle part can be used repeatedly.

Further, in the crucible for forming inorganic particles according to claim 6, a cylindrical crucible body having a small diameter portion at one end is provided, and a nozzle having a discharge hole for the melt of the inorganic substance is provided separately from the crucible body. Since the nozzle part is provided inside the small diameter part of the crucible body, it is possible to replace it with a machined part of the nozzle part only.Therefore, it is possible to repeatedly use expensive materials for the crucible body. It becomes possible and the industrial value is extremely high.

[Brief description of drawings]

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

[Explanation of symbols]

1 crucible 2 nozzles

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hisao Arimune             6 at 1166 Haseno, Jamizo-cho, Yokaichi-shi, Shiga               Kyocera Corporation Shiga Yokaichi Factory F term (reference) 4G072 AA01 BB05 BB11 BB12 GG01                       GG03 GG04 GG05 HH01 QQ01                       UU02

Claims (6)

[Claims] 1. A crucible for forming inorganic particles, comprising a nozzle part for discharging a melt of an inorganic material into particles, wherein the nozzle part is one of silicon carbide, aluminum oxide, cubic boron nitride, and diamond. A crucible for forming inorganic particles, comprising: 2. The crucible for forming inorganic particles according to claim 1, wherein the inorganic material is silicon. 3. The true specific gravity of the nozzle portion is 3.0 g / cc.
2. Silicon carbide described above, 3.30 g / cc or more aluminum oxide, 3.15 g / cc or more cubic boron nitride, 3.
The crucible for forming inorganic particles according to claim 1 or 2, wherein the crucible comprises at least 35 g / cc of diamond. 4. The method according to claim 1, wherein the nozzle portion is made of any one of single crystal silicon carbide, single crystal aluminum oxide, single crystal cubic boron nitride, and single crystal diamond. A crucible for forming inorganic particles as described above. 5. The crucible body other than the nozzle portion is made of any one of a graphite sintered body, an aluminum oxide sintered body, and a silicon carbide sintered body.
A crucible for forming inorganic particles according to claim 4. 6. A cylindrical crucible body having a small diameter portion at one end is provided, and a nozzle portion having a discharge hole for a melt of an inorganic substance is provided separately from the crucible body, and the nozzle portion is provided in the crucible body. A crucible for forming inorganic particles, which is arranged inside the small diameter portion.