JP2006151717A - Method for manufacturing granular crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably manufacture granular silicon having a low impurity concentration and at the same time, to manufacture grains having high crystallinity at a low cost when granular crystalline silicon is manufactured. <P>SOLUTION: The reaction between a melt 5 of a crystal material and a constitutive member of a crucible 1 can be suppressed by making the crystal material into a melt 5 by heating it in a short time by heating the crucible 1 for discharging the melt 5 of the crystal material by high frequency. Thereby, the impurity concentration in the obtained granular crystal can be reduced and the crystal quality of the granular crystal can be improved. Further, the crystal quality of the granular crystal can be also improved by heating falling granular melt by heating a gas used as an atmosphere when the granular melt falls and cooling the falling granular melt. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing granular crystals, and more particularly to a method for producing granular crystals suitable for obtaining granular silicon crystals used in a photoelectric conversion device.

  Photoelectric conversion devices such as solar cells are being developed in response to market needs such as high efficiency in terms of performance, consideration of resource finiteness, or low manufacturing costs. As one of the promising solar cells in the future, a solar cell using granular silicon crystals as a constituent element of photoelectric conversion means has attracted attention. As a method for producing this granular silicon crystal, a technique is known in which a silicon raw material is melted in a container using infrared rays or high frequency, and this molten material is freely dropped as droplets to obtain a granular silicon crystal.

  The granular silicon crystal manufactured by such a method is like single crystal silicon grown by CZ (Czochralski) method or polycrystalline silicon produced by casting method using an expensive semiconductor grade silicon material. Because there is no need to grind to make a thin substrate of about 300 μm after columnar crystals are produced, expensive silicon materials are not wasted in the dicing process and grinding process, and the use efficiency of silicon materials is excellent There is a feature that.

As raw materials for producing granular silicon crystals, for example, silicon fine particles generated as a result of pulverizing a polycrystalline silicon material, high-purity silicon vapor-phase synthesized by a fluidized bed method, or the like is used. In order to produce granular silicon crystals from these raw materials, the raw materials are separated according to size or weight, then melted in a container using infrared rays or high frequency, and this melt can be freely used as droplets (granular melt). There is a method of making particles by dropping (see, for example, Patent Document 1, Patent Document 2, and Patent Document 4). In addition, there is a method (see Patent Document 3) in which molten silicon is scattered to form a particulate crystal.
International Publication No.99 / 22048 Pamphlet U.S. Pat.No. 4,188,177 JP-A-5-78115 US Pat. No. 6,432,330 U.S. Pat.No. 6074476

  However, the above-described method for producing a granular crystal has problems in terms of uniformizing the weight of the raw material and controlling the amount of impurities in the crystal. In particular, since the variation in the weight of the raw material is directly reflected in the size of the granular crystal to be produced, the weight corresponding to the effective size of the granular silicon crystal for solar cells is determined from the raw material having a non-uniform weight. There is a problem that it is difficult to efficiently obtain the silicon raw material particles by a method such as pulverization or classification.

  In addition, in order to add a certain impurity so as to obtain a semiconductor material having desired characteristics in the pulverized and classified raw material, for example, a method of adding the impurity in the stage of preparing the raw material before pulverization, There is a method of diffusing and adding impurities in the gas phase later. However, in any case, the process becomes complicated due to contamination (contamination) in which unnecessary impurities from the grinding media are mixed in the grinding process, and it is necessary to use complicated and expensive equipment. However, there is a problem that an increase in cost is inevitable.

  As a method for producing granular crystals to solve these problems, a small amount of impurities to be added to the raw material so as to be a constant addition amount is prepared in advance and once melted in a crucible, and the melt is converted into droplets from the container. There is a method of discharging and solidifying the particles during the fall to form particles (see Patent Document 5). However, the silicon particles produced in this way become particles having a diameter exceeding 1 mm, and in order to increase the crystallinity, a process of remelting the obtained silicon particles is necessary. The process involves, for example, the formation of an oxide film on the surface of spherical silicon particles once produced, and at the same time, the inside is melted and the cooling temperature profile sufficient to obtain good crystallinity in the subsequent cooling step. Since the process requires control, there is a problem that it is difficult to stably maintain and manage the process conditions to obtain a granular silicon crystal with good crystallinity. Moreover, there is a problem that the silicon particles are produced one by one over time, and the productivity is extremely low. That is, there is a problem that it is not suitable as a method for producing granular silicon crystals for forming a solar cell that requires a large amount of granular silicon crystals.

  The present invention has been devised in view of the problems in the prior art as described above, and its purpose is to produce a granular silicon crystal suitable for producing a granular silicon crystal used for solar cells. An object of the present invention is to provide a method for producing a granular crystal that can be stably and highly efficiently produced, and at the same time, can produce a granular silicon crystal having high crystallinity at a low cost.

As a result of intensive experiments and considerations regarding the productivity in the production of granular silicon crystals used for photoelectric conversion devices such as solar cells, the present inventors have come to consider as follows. That is, in the method for producing a granular crystal, the crystal material melt is discharged and dropped from the nozzle portion of the crucible in a granular form, and the granular melt is heated and cooled to solidify by dropping. Is
(1) As the time for melting the melt of the crystal material is shorter, the contamination due to the mixing of impurities can be reduced.
(2) In indirect heating of the crystal material by heating from the outside, most of the applied heat is consumed by heating the heat insulating material in the periphery of the crucible. To shorten the heating time It is necessary to increase the heating temperature, and the energy consumption for heating increases as the heating temperature is increased.
(3) When discharging the melt of the crystal material from the nozzle part of the crucible, it is important to observe the state at the tip part of the nozzle part, but when a heating method from the outside is adopted for the crucible, Since the heating source covers around the nozzle and the nozzle is hidden, a sufficient observation state cannot be secured.
That's what it means.

  In contrast, the present inventor employs high-frequency heating of the crucible, whereby the crucible is directly heated, and there is no need to arrange a heat insulating material or a susceptor around the crucible. It was noted that heat loss due to heating of the susceptor can be eliminated, and the amount of heat necessary for melting the crystal material can be supplied in a short time. As a result, the time required for melting the crystal material can be shortened, so that it is possible to reduce the mixing of impurities into the melt of the crystal material by shortening the contact time between the melted crystal material and the crucible component. Become. Also, the graphite heating area that forms the side wall of the crucible is cylindrical, and the nozzle part that forms the nozzle hole is formed into a flat plate shape so that the heating area is close to the nozzle and the melt is discharged from the nozzle hole. It is easy to observe the tip of the crucible nozzle part, which is an important observation target, directly with an observation device such as a camera, and the granular melt discharged from the nozzle hole is devised. By oscillating the crucible while observing the diameter and speed of the liquid, the excitation frequency and amplitude are adjusted to obtain the desired particle size, and the reproducibility of the solidification rate is increased to stabilize the impurity distribution, thereby enabling the granularity. Control of crystal quality is facilitated. The inventor has devised the present invention from the above viewpoint.

  The production method of the granular crystal of the present invention is as follows: 1) The crystal material melt is discharged in a granular form from the crucible nozzle part and dropped, and the granular melt is heated and cooled to solidify by dropping. In the method for producing granular crystals for producing granular crystals, the crucible is made of a conductive material, and the crucible is heated at a high frequency to melt the crystalline material into the melt.

  In addition, in the method for producing granular crystals of the present invention, 2) in the configuration of 1) above, the crucible is made of a sintered body of silicon carbide or carbon.

  In addition, the method for producing granular crystals of the present invention is characterized in that 3) In the configuration of 1) above, heating during the dropping of the granular melt is performed using a heated gas.

  The method for producing granular crystals according to the present invention is characterized in that, 4) in the configuration of 3), the gas is heated by resistance heating.

  In addition, the method for producing granular crystals of the present invention is characterized in that 5) In the configuration of 3) or 4) above, argon gas is used as the gas.

  The method for producing granular crystals according to the present invention is characterized in that 6) in the configuration of 3) above, the heated gas is introduced at an angle with respect to the dropping direction of the granular melt. To do.

  According to the method for producing a granular crystal of the present invention, 1) the crystal material melt is discharged in a granular form from the nozzle portion of the crucible and dropped, and the granular melt is heated and cooled during solidification to solidify. In the method for producing granular crystals, the crucible is made of a conductive material, and the crucible is heated at high frequency since the crucible is heated at high frequency to melt the crystalline material into the melt. Since there is no need to use a heat insulating material in the periphery of the crucible, heat loss due to heating of the heat insulating material in the periphery of the crucible can be eliminated, and the amount of heat required for melting the crystal material can be reduced. Can be supplied in time. In addition, since the time required for melting the crystal material can be shortened, the mixing of impurities into the melt of the crystal material can be reduced by shortening the contact time between the melted crystal material and the constituent members of the crucible. Furthermore, since the granular melt discharged from the nozzle hole can be directly observed from the side, the observation can be performed by vibrating the crucible while observing the diameter and speed of the granular melt from the nozzle hole. The quality of the granular crystals can be easily controlled by adjusting the vibration frequency and amplitude to a desired particle size, or by improving the reproducibility of the solidification rate and stabilizing the impurity distribution.

  According to the method for producing granular crystals of the present invention, 2) when the crucible is made of a sintered body of silicon carbide or carbon, it can efficiently absorb high-frequency power and convert it into heat, and can be made of a highly conductive material. Therefore, heat conduction is good and the entire crucible can be heated to a uniform temperature. Moreover, since high-purity materials are easily available and there is little reaction with granular crystals, impurity contamination such as metals in the granular crystals can be suppressed.

  In addition, according to the method for producing granular crystals of the present invention, 3) when the dropping of the granular melt is performed using a heated gas, the temperature profile at which the particles solidify is determined according to the gas supply amount and By controlling the position as a parameter, the heating or cooling process can be set relatively freely. Therefore, the crystallinity of the granular crystals can be improved by adjusting the solidification rate of the particles.

  According to the method for producing granular crystals of the present invention, 4) when the gas is heated by resistance heating, for example, the gas is passed through a long gap of a resistance heating source configured in a complicated shape. Since a sufficient amount of heat can be applied, a large amount of gas necessary for spraying the falling granular melt can be heated.

  In addition, according to the method for producing granular crystals of the present invention, 5) when argon gas is used as the gas, a film such as an oxide or a nitride is not formed on the surface of the granular crystals; Since it does not react with graphite or silicon carbide used as the constituent material, granular crystals can be obtained while the surface of the granular crystals remains clean, and consumption of surrounding members can be reduced.

  In addition, according to the method for producing granular crystals of the present invention, 6) when the heated gas is introduced at an angle with respect to the falling direction of the granular melt, Since the falling direction can be tilted from the discharging direction, the granular melt falling is scattered, and coalescence of the granular crystals due to the collision during the falling can be effectively avoided.

  As described above, according to the method for producing a granular crystal of the present invention, the crucible for discharging the silicon melt is heated at a high frequency, thereby heating the raw material of the crystal material in a short time, and By suppressing the reaction, it is possible to reduce the concentration of impurities mixed into the crystal material, and it is possible to reduce the recombination probability of minority carriers by reducing the level that comes from defects formed by the impurities. By extending the lifetime, the quality of the granular crystals can be improved so that the conversion efficiency can be improved.

  In addition, when the granular melt of the crystalline material is solidified by heating and cooling during the dropping, the heating during the dropping is performed by heating the gas that becomes the atmosphere, for example, the gas is circulated many times. When used, the amount of consumables can be reduced and the amount of heat adjustment for heating and cooling can be reduced, so that the crystal quality can be improved and the cost can be reduced.

  In addition, the method for producing granular crystals of the present invention uses a large-capacity high-frequency power source and directly heats the crucible by high-frequency heating, so that the production by shortening the melting time is repeated when the melting and discharging of the crystal material are repeated many times High quality granular crystals can be produced in a short time compared to other methods due to a significant improvement in properties and a reduction in impurity contamination due to a shortening of the melting time, which is extremely high in productivity.

  From the above, it becomes a suitable production method in the production of granular silicon crystals used in photoelectric conversion devices such as solar cells, and it is possible to simultaneously ensure improvement in crystal quality and productivity of the obtained granular silicon crystals. It will be. Thereby, a large amount of granular silicon crystals for a highly efficient photoelectric conversion device can be easily produced, and the production cost of the granular silicon crystal and thus the photoelectric conversion device can be suppressed.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing an example of a crucible in an example of an embodiment of a method for producing granular crystals of the present invention. In FIG. 1, 1 is a crucible as a whole, 2 is a body member, 3 is a nozzle member, 4 is Nozzle holes 5 are melts of crystal material.

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

  The main body member 2 of the crucible 1 includes, for example, an inner wall member 2a for suppressing reaction with silicon and outer wall members 2b and 2c disposed outside the inner wall member 2a. The outer members 2b and 2c are provided to ensure strength. The inner wall member 2a and the outer wall members 2b and 2c are each formed of a sintered body densified by a casting method, a hot press method, or the like. In order to suppress the reaction with silicon, aluminum oxide, silicon carbide, graphite or the like is suitable, but graphite or the like sintered by hot pressing is suitable in terms of ease of processing.

  The outer wall members 2b and 2c need to be designed in consideration of heat balance and expansion at the melting point of the inorganic substance. As will be described later, the crucible 1 is disposed, for example, inside a quartz tube, and a high-frequency coil is disposed outside the quartz tube, and the outer wall member 2c is mainly heated by high-frequency heating by the high-frequency coil. The temperature of the melt 5 of the crystal material in 1 is controlled. The above materials are suitable for the outer wall members 2b and 2c in order to maintain the outer shape in consideration of the distance to these heat sources and the heat dissipation to the atmospheric gas. The thickness of the outer wall member 2b is usually preferably 3 mm to 15 mm. Further, in this example, the outer wall members 2b and 2c have a structure in which the nozzle member 3 is sandwiched between the two by the screw portion 6 and assembled.

  Since the inner wall member 2 a holds the melt 5 of the crystal material together with the nozzle portion 3, the inner wall member 2 a needs to be made of a material having a melting temperature higher than the melting point of the crystal material, for example, silicon. Furthermore, since the inner wall member 2a is in direct contact with the melt 5 such as silicon that is melted and active, it is most likely as a contamination source of impurities mixed into the granular crystals. It is preferable to use a material that is less reactive with the melt 5 such as silicon than the outer wall member 2b. If silicon (silicon) is used as the crystal material, quartz is suitable as a material having low reactivity with silicon used for the inner wall member 2a.

  Further, a nozzle member 3 having a nozzle hole 4 is provided on the front end side of the crucible 1. That is, a nozzle member 3 having a nozzle hole 4 for discharging the metal melt is provided separately from the outer wall member 2 a of the crucible 1 having a small diameter portion at one end, and the nozzle member 3 is provided as a main body member 2 of the crucible 1. It is arrange | positioned inside the front-end | tip small diameter part. The nozzle member 3 is preferably a sintered body of silicon carbide, carbon, silicon nitride, aluminum oxide, cubic boron nitride, quartz or diamond, and among these, a sintered body of silicon carbide or carbon is preferable.

  As described above, the crucible 1 for producing granular crystals used in the method for producing granular crystals of the present invention has a structure in which the main body member 2 and the nozzle member 3 of the crucible 1 are formed as separate members and can be assembled. By doing so, it becomes possible to replace only the nozzle member 3 that is severely damaged such as wear, and the main body member 2 of the expensive crucible 1 can be used repeatedly. And since the main body member 2 is composed of the inner wall member 2a and the outer wall members 2b and 2c, the main body member 2 can be less deformed, so that the main body member 2 is damaged. However, the member can be easily replaced.

  FIG. 2 is a cross-sectional view showing a configuration example around the crucible 1 in an example of the embodiment of the method for producing granular crystals of the present invention. In FIG. 2, 1 is a crucible, 7 is a high-frequency coil, 8 is a quartz tube, Is an atmosphere (gas), and 10 is a surveillance camera. The structure of the crucible 1 is the same as the example shown in FIG. 1, but the illustration is omitted in FIG.

  In the method for producing granular crystals according to the present invention, it is not necessary to control the precise temperature distribution in the crucible 1 as in a normal single crystal pulling production apparatus, and therefore a method of directly heating the crucible 1 with high frequency can be employed. is there.

  The high-frequency energy generated from the high-frequency coil 7 provided at a position corresponding to the outer crucible 1 of the quartz tube 8 that houses the crucible 1 in the inner upper part is consumed on the surface of the outer wall member 2c of the crucible 1 and becomes thermal energy. Converted. The crystal material in the crucible 1 is melted by this heat to obtain a melt 5. In the example of Patent Document 2, the heating source is a graphite susceptor surrounding the crucible. However, in the present invention, the crucible 1 is directly heated by high-frequency heating, and the graphite susceptor or the like is not used. The heat loss due to can be eliminated, and the amount of heat necessary for melting the crystal material can be supplied in a short time. In addition, since the time required for melting the crystal material can be shortened, the contact time between the melt 5 of the crystal material melted and the constituent members of the crucible 1 (the inner wall member 2a and the nozzle member 3) can be shortened. Thus, contamination of impurities into the melt 5 of the crystal material can be reduced.

  For example, if the crystal material is silicon, elution of elements such as Fe, Al, Mo, and Va contained in a minute amount in the quartz of the inner wall member 2a and the nozzle member 3, the dissolution of silicon monoxide due to the reaction with quartz, Oxygen and carbon impurities can be prevented from being mixed due to the dissolution of carbon monoxide and carbon dioxide generated in the graphite of the outer wall members 2b and 2c and oxygen in the atmospheric gas into the melt 5.

  A raw material of the crystal material, for example, silicon raw material charged in the crucible 1 is melted by heating such as high-frequency heating, and the upper part of the melted silicon melt 5 is pressurized with argon gas or the like at 0.5 MPa or less, for example, to form a nozzle member. The silicon melt 5 is discharged by extruding from the three nozzle holes 4 to form a large number of granular melts 11. When a large number of granular silicon melts 11 freely fall in the atmosphere 9 in the quartz tube 8, they solidify during the dropping and become granular silicon crystals of single crystal silicon or polycrystalline silicon, and below the quartz tube 8. It is accommodated in an arranged container (not shown).

  In the conventional high-frequency heating method for heating the resistance heating device and the susceptor, it was impossible to directly observe how the melt 5 was discharged because the members necessary for the heating concealed the nozzle hole of the crucible. In the method for producing granular crystals, since the crucible 1 is directly heated by high-frequency heating, there is no need to arrange a heating member around the nozzle hole 4, so the shape and distribution of the granular crystals are determined. A liquid column (not shown) immediately below the nozzle hole 4 formed by the melt 5 discharged from the nozzle hole 4 as a main factor can be directly observed from the horizontal direction by the monitoring camera 10 and observed. Furthermore, when obtaining a granular crystal in a monodisperse sphere state by applying vibration to the melt 5, while observing the diameter and speed of the melt poured from the nozzle hole 4 and the granular melt 11, The desired particle size can be obtained by adjusting the excitation frequency and amplitude, and the reproducibility of the solidification rate of the granular melt 11 can be improved to facilitate the control of the quality of the granular crystals by stabilizing the impurity distribution. be able to.

  Next, reference numeral 13 in FIG. 2 denotes a resistance heater for heating the atmosphere (gas) 9, and reference numeral 14 denotes the scattering direction of the granular melt 11 by the gas heated thereby. An example of this gas heating unit is shown in FIG. FIG. 3 is a cross-sectional view showing an example of a heated gas portion in an example of an embodiment of the method for producing granular crystals of the present invention. In FIG. 3, 8 is a quartz tube, 9 is an atmosphere (gas), and 11 is granular. The melt, 12 is a heated gas, 13 is a resistance heater, and 14 is the scattering direction of the granular melt 11.

  The granular melt 11 discharged from the nozzle hole 4 of the crucible 1 is cooled and solidified in the atmosphere (gas) 9 in the quartz tube 8 while dropping into a granular crystal. It is well known that the crystallinity of granular crystals is improved by heating. In the method for producing a granular crystal of the present invention, not only heating but also cooling of the falling granular melt 11 is performed by heating gas 12 higher than the solidification temperature of the crystalline material or heating lower than the solidification temperature. It is preferable to adjust using the gas 12.

  The granular melt 11 discharged from the nozzle hole 4 of the crucible 1 dissipates heat while falling in the quartz tube 8 and is cooled and solidified to solidify. The position where the granular melt 11 solidifies is usually 0.5 m to 1.5 m below the nozzle hole 4, and the position depends on the particle diameter of the granular melt 11. Therefore, the temperature profile at which the granular melt 11 is solidified by spraying the heating gas 12 near the solidified melt 11 having a desired particle size is determined as the solidification temperature of the crystalline material (for example, 1414 ° C. for silicon). ) It can be set freely by heating with the heating gas 12 at the above temperature or cooling with the heating gas 12 at a temperature lower than the solidification temperature (1414 ° C. in the case of silicon). It is possible to easily adjust the solidification rate.

  As shown in FIG. 3, the resistance heater 13 made of graphite for heating the atmosphere (gas) 9 has a long zigzag path for the atmosphere (gas) 9 passing through the resistance heater 13. By narrowing the gap, a large amount of atmosphere (gas) 9 is easily heated and ejected from the lower nozzle as the heated gas 12.

  When oxygen or nitrogen is used as the atmosphere (gas) 9 and the heating gas 12 in the quartz tube 8, a film such as oxide or nitride is formed on the surface of the obtained granular crystal, or the crucible 1 is formed. This is not preferable because it reacts with the constituent graphite, silicon carbide, etc., and consumes them or forms nitrides. In the method for producing granular crystals of the present invention, an inert gas such as argon gas or helium gas or a mixed gas thereof is suitable. If it is an inert gas, while the surface is clean, a granular crystal can be obtained from the granular melt 11, and consumption of the components of the crucible 1 can be suppressed. Further, by using these inert gases as the atmospheric gas, a gas having a temperature above a certain level can be circulated in the quartz tube 8 and the amount of heat applied can be reduced, so that the cost can be reduced.

  When the heated gas 12 heated by the resistance heater 13 is introduced at an angle as shown in FIGS. 2 and 3 with respect to the dropping direction of the granular melt 11, each granular melt is introduced. 11 can be tilted from the falling direction to the ejection direction of the heated gas 12, and can be scattered in the scattering direction 14, so that the falling granular melt 11 is scattered and coalesced between the granular melts 11 by collision Can be avoided. In setting the scattering direction 14 as described above, an angle is set in the ejection direction of the heating gas 12 with respect to the falling direction, and not only the spraying in a fixed direction but also the heating gas 12 is ejected so as to form a vortex. This also allows the granular melt 11 to be effectively scattered.

  As described above, according to the method for producing granular crystals of the present invention, the crucible 1 for discharging the granular crystal melt 5 is heated at a high frequency, thereby heating the raw material of the crystal material in a short time. By suppressing the reaction between the melt 5 and the constituent members of the crucible 1, it is possible to reduce the concentration of impurities mixed into the crystal material, and to reduce the level caused by defects formed by impurities. By reducing it, the recombination probability of minority carriers is reduced and the lifetime is increased, so that the crystal quality of the granular crystals can be improved so that the conversion efficiency can be improved.

  Further, when the granular melt 5 of the crystalline material is heated and cooled during solidification by being dropped, the gas 9 is heated several times by heating the gas 9 serving as the atmosphere. However, it is possible to reduce the amount of consumables and reduce the amount of heat for heating and cooling by using them in a circulating manner, so that stable production can be performed and cost can be reduced. Become.

  The granular silicon crystal, which is a granular crystal thus produced, is used to form a photoelectric conversion element used in a photoelectric conversion device such as a solar cell. Since these granular silicon crystals are produced by the method for producing granular crystals of the present invention, the crucible 1 can be used many times and high-quality silicon with few impurities can be obtained. Thus, a photoelectric conversion device with high conversion efficiency can be obtained.

  In the example of the embodiment described above, an example in which silicon is mainly used as the crystal material has been described. However, as the crystal material used in the method for producing a granular crystal according to the present invention, germanium, tin, or the like can be used in addition to silicon. These granular crystals are suitably used for the formation of semiconductor parts with high purity.

  The crucible configured as described above is set in a furnace that can be maintained in an Ar inert gas atmosphere, and the overall temperature is set. The raw material was supplied to the crucible through a path maintained in an inert atmosphere and completely melted. A nozzle member having an opened nozzle hole was manufactured, and the silicon raw material as a crystal material was melted and the granular melt was discharged, thereby preparing the granular crystal, and the purity of the granular crystal was evaluated. The test was conducted as follows.

A crucible maintained at a temperature of 1450 ° C. in an inert atmosphere was filled with a silicon raw material and dissolved. The crucible is made of graphite processed into dimensions of an inner diameter of 19 mmφ, an outer diameter of 25 mmφ, and a length of 143 mm. A gas pressure was applied to the raw material in a sufficiently dissolved state, and the entire amount was discharged from the nozzle hole and discharged. At this time, the melting method, the melting time, and the impurity concentrations of aluminum and iron contained in the recovered granular silicon crystal were measured and compared. The results are shown in Table 1.

  As a result, the impurity concentration in the silicon material produced by high-frequency heating was clearly lower than that of resistance heating as a comparative example, and the quality as a material was good.

In the above example, the crucible was heated by high-frequency heating, and the granular silicon crystal was produced by changing only the heating method during dropping of the granular melt produced by discharging from the nozzle hole and the gas type used for the heating. After the produced granular silicon crystal was polished to obtain a cross section, the crystallinity was evaluated by etching. Table 2 shows the results.

  As shown in Table 2, the ratio of polycrystalline particles having grain boundaries is clearly higher in the case of non-heating than in the case of heating the atmospheric gas at the time of dropping. The crystal quality was improved.

It is sectional drawing which shows the example of the crucible in an example of embodiment of the manufacturing method of the granular crystal of this invention. It is sectional drawing which shows the structural example of the crucible periphery in an example of embodiment of the manufacturing method of the granular crystal of this invention. It is sectional drawing which shows the example of the gas heating part in the manufacturing method of the granular crystal of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Crucible 2 ... Main body member 2a ... Inner wall member 2b, 2c ... Outer wall member 3 ... Nozzle member 4 ... Nozzle hole 5 ... Crystalline melt 6 ... Screw part of outer wall member 7 ... High frequency coil 8 ... Quartz tube 9 ... Atmosphere (gas)
11 ... Granular melt
12 ... Heating gas
13 ... resistance heater

Claims (6)

In the method for producing granular crystals, the crystalline material melt is discharged from the nozzle part of the crucible in a granular form and dropped, and the granular melt is heated and cooled to solidify by dropping and dropping. A method for producing a granular crystal, wherein the crucible is made of a conductive material, and the crucible is melted to form the melt by heating the crucible at high frequency. The method for producing granular crystals according to claim 1, wherein the crystal material is silicon, and the crucible is made of a sintered body of silicon carbide or carbon. 2. The method for producing granular crystals according to claim 1, wherein the heating during the dropping of the granular melt is performed using a heated gas. The method for producing a granular metal according to claim 3, wherein the gas is heated by resistance heating. The method for producing granular crystals according to claim 3 or 4, wherein argon gas is used as the gas. The method for producing a granular crystal according to claim 3, wherein the heated gas is introduced at an angle with respect to a falling direction of the granular melt.

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