JP2006036583A - Apparatus and method for manufacturing granular crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for manufacturing a high purity granular crystal with high productivity and at a low cost. <P>SOLUTION: A molten liquid being a crystal material is discharged and dropped in a granular state from a nozzle 1a at a crucible 1 in a tube 2 placed to a vertical direction. The granular molten liquid 4 is coagulated by cooling during dropping and then the granular crystal 5 is manufactured in the apparatus. An atmosphere in the tube 2 is controlled by using a specified gas and the tube is connected on the route with a buffer vessel 3 where the specified gas from the tube 2 is stored when its inside pressure is increased and where the stored gas is returned to the tube 2 when the pressure is reduced. As the mixing of an unnecessary gas such as atmospheric air and the like can be prevented by making pressure variation in the tube 2 small, the stable discharge of the molten liquid, the stable coagulation of the crystal material and the prevention of impurity mixing into the granular crystal 5 can be performed and then the high quality and high purity granular crystal can be manufactured with high productivity and at a low cost. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a granular crystal manufacturing apparatus and manufacturing method, and more particularly to a granular crystal manufacturing apparatus and manufacturing method suitable for obtaining a granular silicon crystal used in a photoelectric conversion apparatus.

  Conventionally, solar cells with high conversion efficiency using crystalline silicon wafers have been put into practical use. This crystalline silicon wafer is manufactured by cutting from a large single crystal silicon ingot having good crystallinity, low impurities, and no uneven distribution. However, large single crystal silicon ingots take a long time to produce, so the productivity is poor and this makes it expensive, so there is no need for large single crystal silicon ingots and the emergence of highly efficient next-generation solar cells Is strongly desired.

  Thus, as one of promising photoelectric conversion devices in the future market, solar cells using granular silicon crystals as constituent elements of photoelectric conversion means are attracting attention.

At present, the raw material for producing granular silicon crystals uses fine silicon particles generated as a result of pulverizing a single crystal silicon material or high-purity silicon synthesized in a gas phase by a fluidized bed method. After separating the raw materials by size or weight, a method of melting the raw materials again in a container using infrared rays or a high-frequency coil, and then spheronizing by free-falling (for example, Patent Documents 1 and 2) Or a method of spheroidizing by high-frequency plasma heating and melting (for example, see Patent Document 2).
International Publication No. 99/22048 U.S. Pat.No. 4,188,827 JP-A-5-78115 U.S. Pat.No. 6074476

  However, these methods have a problem that it is difficult to make the weight of the raw material uniform and the productivity is low. Since the variation in the weight of the raw material is reflected in the size of the spheres of the granular crystals that are made, a uniform weight of the raw material is required, but the raw material with the weight corresponding to the effective size is pulverized or classified. It is difficult to obtain efficiently with a metal material. Further, in the pulverizing step, contamination (contamination) from the pulverizing media occurs, so that there is a problem that impurities cannot be avoided. Furthermore, the high-frequency plasma heating and melting apparatus requires a very large power source and the like, and there is a problem that the apparatus cost is high and the production power is high due to the large power consumption.

  As a method for solving these problems, a method is disclosed in which a crystalline material is once melted in a crucible, discharged and simultaneously granulated to obtain granular crystals (see, for example, Patent Document 4).

  However, Patent Document 4 does not have a specific description of a method for controlling the pressure fluctuation of the falling solidification container, which is indispensable for the production of stable granular crystals. In addition, there is no specific description of an atmosphere control method that is indispensable for producing high-quality and high-purity granular crystals. In particular, the control of the inert atmosphere is indispensable for the production of granular crystals made of a crystalline material that easily reacts at a high temperature, such as silicon. When the atmosphere control is insufficient, the surface of the granular silicon crystal is contaminated with impurities such as oxygen and nitrogen, which is not preferable because the crystal quality and purity are lowered.

  Therefore, the conventional techniques as described above have the problems that the productivity of the granular crystal production apparatus and method is low, the purity of the produced granular crystals is low, and the cost is high.

  The present invention has been made in view of the above-described problems in the conventional technology, and has been made to solve these problems. The object of the present invention is to produce granular particles that can produce high-productivity and high-purity granular crystals at low cost. An object is to provide a crystal manufacturing apparatus and a manufacturing method.

  The apparatus for producing granular crystals of the present invention discharges the crystal material melt in a granular manner from a crucible nozzle portion to the inside of a pipe arranged in the vertical direction, and cools the granular melt while dropping. In the granular crystal manufacturing apparatus for manufacturing the granular crystal by solidifying by the solidification, the internal atmosphere of the tube is controlled using a predetermined gas, and the predetermined pressure is removed from the tube when the internal pressure rises in the middle. A buffer container is connected to return the gas stored when the pressure decreases to the pipe.

  The granular crystal production apparatus of the present invention is characterized in that, in the above configuration, the buffer container is provided with a check valve that discharges the gas from the buffer container when a predetermined pressure or higher is reached. Is.

  The method for producing a granular crystal according to the present invention discharges the crystal material melt in a granular manner from the nozzle portion of the crucible to the inside of the pipe and drops it, and cools the granular melt while dropping. In the method for producing granular crystals by solidifying by solidification, the atmosphere inside the tube is controlled using a predetermined gas, and a buffer container is connected in the middle of the tube, The pressure in the pipe is controlled by storing the gas from the pipe in the buffer container when the internal pressure increases and returning the gas stored in the buffer container to the pipe when the pressure decreases. is there.

  Further, the method for producing granular crystals of the present invention is characterized in that, in the above configuration, at least one of argon and helium is used as the gas.

  According to the granular crystal manufacturing apparatus of the present invention, the melt of the crystal material is discharged in a granular form from the nozzle portion of the crucible to the inside of the pipe arranged in the vertical direction, and the granular melt is being dropped. In the granular crystal production apparatus for producing granular crystals by solidifying by cooling to the inside, the tube has an internal atmosphere controlled using a predetermined gas, and when the internal pressure rises in the middle of the tube, A buffer container that stores the predetermined gas and returns the gas stored when the pressure is reduced to the pipe is connected, so that fluctuations in pressure inside the pipe are reduced, and unnecessary gas such as the atmosphere inside the pipe is reduced. Mixing can be prevented, so stable discharge of the melt, stable solidification of the crystal material, and prevention of impurities from mixing into the granular crystals, so that high quality and high purity granular crystals can be produced with high productivity. It is possible to elephants.

  Further, according to the granular crystal manufacturing apparatus of the present invention, when the buffer container is provided with a check valve for discharging the gas from the buffer container when the pressure exceeds a predetermined pressure, the pressure inside the pipe Fluctuations in the pressure and the pressure inside the tube and the pressure inside the buffer container can be prevented from rising above a predetermined pressure, so that stable discharge of the melt can be performed and Damage prevention can be realized.

  Further, according to the method for producing a granular crystal of the present invention, the crystal material melt is discharged in a granular form from the crucible nozzle portion into the pipe arranged in the vertical direction, and dropped. In the method for producing granular crystals, wherein the granular crystals are produced by cooling and solidifying during dropping, the atmosphere inside the tube is controlled using a predetermined gas, and a buffer container is connected in the middle of the tube. By controlling the pressure in the pipe by storing the gas from the pipe in the buffer container when the pressure inside the pipe rises, and returning the gas stored in the buffer container to the pipe when the pressure decreases, Since fluctuations in the pressure inside the tube can be reduced and unnecessary gas such as air can be prevented from entering the inside of the tube, stable discharge of the melt and stable solidification of the crystal material and Because it can be prevent contamination of impurities into Jo crystal, it is possible to produce a granular crystal of a high quality and high purity with high productivity.

  In addition, according to the method for producing granular crystals of the present invention, when at least one of argon and helium is used as the gas, a reaction layer is hardly formed on the surface of the granular crystals. It is possible to effectively improve the sex.

  Hereinafter, an example of an embodiment of a manufacturing apparatus and a manufacturing method of a granular crystal of the present invention is explained in detail based on an accompanying drawing.

  FIG. 1 is a side view showing a schematic configuration of an example of an embodiment of an apparatus for producing granular crystals according to the present invention. In FIG. 1, 1 is a crucible, 1 a is a nozzle part provided at the bottom of the crucible 1, 2 is a pipe disposed vertically below the crucible 1, and 3 is a buffer connected in the middle of the pipe 2. Reference numeral 3a denotes a branch pipe connecting the pipe 2 and the buffer container 3, 3b denotes a check valve, 4 denotes a granular melt, and 5 denotes a granular crystal.

  The crucible 1 is a container for heating and melting a desired crystal material to obtain a melt of the crystal material and discharging it as a granular melt 4 from the nozzle portion 1a at the bottom. The melt of the desired crystal material heated and melted in the crucible 1 is discharged into the tube 2 from the nozzle portion 1 a and becomes a granular melt 4 and falls inside the tube 2. The crucible 1 is made of a material having a melting point higher than that of the desired crystal material. Moreover, it is preferable that the reaction with the melt of the crystal material is small, and when the reaction with the melt of the crystal material is large, the material of the crucible 1 is mixed in the granular crystal 5 in a large amount as an impurity. Therefore, it is not preferable. For example, when the crystal material of the granular crystal 5 is silicon, the material of the crucible 1 is preferably carbon, silicon carbide, silicon oxide, silicon nitride, aluminum oxide or the like. In addition, induction heating, resistance heating, or the like is appropriate as a heating method for heating the crystal material to the melting point or more in the crucible 1.

  The tube 2 arranged vertically from the nozzle part 1a of the crucible 1 is a container that cools and solidifies the granular melt 4 discharged from the nozzle part 1a during the fall. The inside of the tube 2 is controlled to a desired pressure in a desired atmosphere. As this desired atmosphere, helium or argon is preferable. Helium or argon is an inert gas and can prevent impurities from entering the granular melt 4 from the atmosphere. Furthermore, the reaction with the granular melt 4 is small, and the formation of a reaction layer on the surface of the molten material that hinders the solid melt 4 from solidifying and crystallizing is preferable. Further, the pressure is controlled by adjusting the gas inflow amount and the gas discharge amount. Thereby, the internal atmosphere of the pipe 2 is controlled using a predetermined gas.

  The tube 2 is preferably made of a material having a melting point higher than that of the crystal material, or preferably has a cooling structure (not shown) for cooling the tube 2 itself. When the material of the tube 2 has a melting point higher than the melting point of the crystal material, even if the granular melt 4 is discharged in an oblique direction and collides with the inner wall of the tube 3, the tube 2 is heated above the melting point of the material. In other words, the material of the tube 2 is not mixed as impurities into the granular melt 4 collided with. When the melting point of the material of the tube 2 is lower than the melting point of the crystal material, when the granular melt 4 is discharged obliquely and collides with the inner wall of the tube 2, the tube 2 is heated to the melting point of the material or higher. This is not preferable because the material of the pipe 2 may be mixed as impurities into the collided granular melt 4, but it is not preferable to add a cooling structure for cooling the pipe 2 to the pipe 2 to form a granular shape. By preventing the tube 2 from being heated above the melting point of the material due to the collision of the melt 4, it is possible to avoid contamination with impurities. For example, when the material of the granular crystal 5 is silicon, the material of the tube 2 is preferably carbon, silicon carbide, silicon oxide, silicon nitride, aluminum oxide or the like having a melting point higher than that of silicon. Alternatively, for example, in the case of the pipe 2 that is water-cooled with a double pipe structure or a water-cooling jacket, the material of the pipe 2 is preferably stainless steel, aluminum, or the like.

  In the granular crystal production apparatus of the present invention, the buffer container 3 is connected to the middle of the pipe 2 by a branch pipe 3a. When the atmospheric pressure inside the tube 2 is suddenly heated and expanded by discharging the granular melt 4 to the inside of the tube 2 by the buffer container 3, when the pressure rises from the tube 2, a predetermined inside of the tube 2 is provided. The atmosphere inside the tube 2 is quickly restored to a desired pressure by introducing and storing the atmospheric gas in the buffer container 3. On the other hand, when the discharge of the granular melt 4 ends or is interrupted, and the atmospheric gas inside the tube 2 rapidly cools and contracts and the pressure is reduced, the stored atmospheric gas is transferred from the buffer container 3 to the tube 2. By returning it, the atmosphere inside the pipe 2 is quickly restored to a desired pressure, and at the same time, unnecessary gas such as the atmosphere is prevented from flowing into the pipe 2 from the outside. Thereby, the fluctuation of the pressure inside the tube can be reduced, and unnecessary gas such as the atmosphere can be prevented from entering the inside of the tube, so that stable discharge of the melt and stable solidification of the crystal material and the granular crystal 5 can be achieved. It is possible to prevent contamination of impurities.

  The buffer container 3 has a function of storing a predetermined gas, which is an atmospheric gas therein, from the pipe 2 when the pressure inside the pipe 2 is increased, and returning the stored gas to the pipe 2 when the pressure is reduced. The volume of 3 is preferably variable. For example, it is assumed that the gas storage portion has a bellows portion, thereby increasing the volume of the buffer container 3 when storing the gas, and decreasing the volume of the buffer container 3 when returning the stored gas to the pipe 2. To push out the gas. As described above, when the volume of the buffer container 3 is variable, the maximum volume of the buffer container 3 is determined in accordance with the volume in which the gas inside the tube 2 is heated and expanded by discharging the granular melt 4. . For example, when the temperature of the gas inside the tube 2 rises from 50 ° C. to 100 ° C. due to the discharge of the granular melt 4, the volume of the gas inside the tube 2 is estimated to expand by about 15%. It is appropriate that the maximum volume of the buffer container 3 is about 15% of the volume of the tube 2.

  The buffer container 3 selects the amount of gas to be stored according to the volume of the tube 2 and the temperature change inside the tube 2, and the material is a metal material such as stainless steel or aluminum, or a resin such as vinyl chloride, PET, PC, PMMA, or epoxy. Materials, glass materials such as silicate glass, quartz, lead glass, and inorganic materials such as alumina ceramics, cordierite ceramics, silicon carbide ceramics, etc., are combined as appropriate so that the internal volume can be changed, or the internal volume is unchanged. The internal pressure is changed to store the gas.

  However, when selecting a structure in which the internal pressure changes, it is preferable to add a mechanism for making the gas pressure returned to the pipe 2 constant by providing a separate regulator or the like. If the gas pressure returned to the pipe 2 changes, the pressure fluctuation inside the pipe 2 increases, which is not preferable. In addition, examples of the structure that can change the internal volume include a cylinder type, a bellows type, and a balloon type, and examples of the structure that changes the internal pressure include a cylinder type and a liquefaction type.

  The buffer container 3 may be connected to the tube 2 at any of the upper, middle, and lower portions of the tube 2 as long as it does not overlap with other members such as a heating unit disposed around the tube 2. Good.

  The buffer container 3 is preferably connected to the pipe 2 arranged in the vertical direction by a branch pipe 3a arranged in the horizontal direction. As a result, when the granular melt 4 discharged from the nozzle portion 1 a of the crucible 1 falls inside the pipe 2, the granular melt 4 enters the buffer container 3 as the pressure inside the pipe 2 rises. Since it can prevent effectively mixing in, it is preferable. Furthermore, it is more preferable to install the branch pipe 3a obliquely upward in the left-right direction from the pipe 2 because the effect of preventing the granular melt 4 from being mixed further increases. As such a branch pipe 3a, for example, a pipe having an inner diameter of 10 mmφ or more and a length of 2 m or less may be used. When the inner diameter is too thin and the length is too long, the resistance increases when the atmosphere gas flows into the buffer container 3 and when the atmosphere gas is returned from the buffer container 3 to the pipe 2, which is not preferable.

  Further, the buffer container 3 is preferably provided with a check valve 3b that discharges the gas stored in the buffer container 3 from the buffer container 3 when the pressure inside the buffer container 3 is equal to or higher than a predetermined pressure. . By providing such a check valve 3b in the buffer container 3, gas can be discharged to the outside at a predetermined pressure or higher, and there is no gas inflow from the outside. Therefore, excess gas stored in the buffer container 3 Can be discharged to the outside, and when the pressure in the buffer container 3 falls below the predetermined pressure, it is possible to prevent unnecessary gases such as the outside air from flowing into the buffer container 3. Thereby, the inside of the buffer container 3 and the pipe 2 can be maintained at a predetermined pressure, which is further preferable.

  The check valve 3b can be of a spring adjustment type, a lift type or the like, and when the atmospheric gas is heavier than the atmosphere, the check valve 3b is provided above the buffer container 3, When the gas is lighter than the atmosphere, it is preferable to provide a check valve 3b at the bottom of the buffer container 3. In consideration of the case where the atmosphere is mixed in the buffer container 3, the atmosphere gas and the atmosphere are usually separated vertically in the buffer container 3. If the atmosphere is heavier, the buffer container 3 By providing the check valve 3b on the lower side, the atmosphere can be preferentially discharged to the outside, and the atmospheric gas is preferentially returned to the inside of the pipe 2, which is more preferable.

  Further, the predetermined pressure for operating the check valve 3b is set lower than the pressure at which the manufacturing apparatus including the pipe 2 and the buffer container 3 are damaged.

  In the granular crystal manufacturing apparatus of the present invention, an atmosphere gas supply port (not shown) for supplying a predetermined atmosphere gas to the tube 2 in order to control the atmosphere inside the tube 2 using a predetermined gas. ) Is provided. By providing the atmosphere gas supply port in the tube 2, for example, when the inside of the tube 2 once opened to the atmosphere by the maintenance of the apparatus is filled with the atmosphere gas again, a predetermined gas is supplied from the atmosphere gas supply port as the atmosphere gas. Thus, the replacement with the atmospheric gas inside the tube 2 can be performed quickly. Further, even before and after discharging the granular melt 4, the atmospheric gas is constantly supplied from the atmospheric gas supply port little by little and discharged little by little from the check valve 3 b of the buffer container 3 to enter the inside of the pipe 2. If the flow of the atmospheric gas is maintained, the atmosphere inside the tube 2 can be easily controlled in a more stable state, which is further preferable.

  As mentioned above, although embodiment was illustrated about the manufacturing apparatus and manufacturing method of the granular crystal | crystallization of this invention, this invention is not limited to the example of the above embodiment, As long as it does not deviate from the summary of this invention, it is various. You can make any changes.

  Next, specific examples of the granular crystal production apparatus and production method of the present invention will be described based on the example shown in FIG.

First, silicon added with 1 × 10 ¹⁶ atoms / cm ³ of B as a p-type dopant as a crystal material was put into a crucible 1 made of graphite, and the crucible 1 was heated to 1414 ° C. or higher, which is the melting point of silicon. At this time, the inside of the tube 2 made of quartz disposed vertically from the nozzle portion 1a of the crucible 1 is maintained in an inert atmosphere using helium gas, and a branch tube 3a made of quartz is held below the tube 2. A buffer container 3 adjustable between 0-20% of the internal volume of the tube 2 was connected via

  Next, after the silicon melts to form a melt, pressure is applied to the melt in the crucible 1, the silicon melt is discharged from the nozzle portion 1 a into the tube 2, and the silicon melt 4 is obtained. The inside of the tube 2 was dropped, cooled and solidified to obtain a silicon crystal 5. At this time, the helium gas inside the tube 2 is heated from the average temperature of 40 ° C. to 80 ° C. by the granular silicon melt 4, and this heating expands the helium gas, and the expanded helium gas is buffered through the branch tube 3 a. Introduced into container 3 and stored. As a result, the pressure inside the tube 2 before and after the discharge of the granular melt 4 was kept substantially constant.

  Next, when all of the silicon melt in the crucible 1 is completely discharged, the tube 2 is cooled from the surroundings, the internal helium gas is cooled and contracted, and the pressure inside the tube 2 is reduced. The helium gas stored in 3 was returned to the inside of the pipe 2 through the branch pipe 3a. As a result, the pressure inside the tube 2 was kept substantially constant before and after the discharge of the granular melt 4 was completed.

  On the other hand, as a comparative example, the granular crystal 5 was obtained by discharging the silicon granular melt 4 into the tube 2 in the same manner without connecting the buffer container 3 to the tube 2.

About the granular silicon crystal obtained by the Example of the present invention described above and the granular silicon crystal obtained by the comparative example, their mixed oxygen concentration (unit: ppm) was examined, and the pressure inside the tube 2 during production The results are summarized in Table 1 together with the fluctuation (unit: MPa) and the amount of helium gas used (unit: L / min).

  From the results shown in Table 1, in the granular silicon crystal 5 obtained by the example of the present invention, the concentration of mixed oxygen is about 1/100 compared to the granular silicon crystal obtained by the comparative example, and the pressure fluctuation is About 1/10, the amount of helium gas used was about 1/20. As a result, according to the granular crystal manufacturing apparatus and manufacturing method of the present invention, the atmosphere inside the tube 2 can be maintained in a substantially constant state with a small amount of helium gas. 5 can reduce impurities such as oxygen concentration and obtain a crystalline crystal 5 with good crystallinity, and since the buffer container 3 is connected to the tube 2, the pressure fluctuation inside the tube 2 during production This means that productivity is high and reproducibility is good, and that the amount of helium gas used in manufacturing can be reduced, and manufacturing costs can be reduced. It was.

It is a side view which shows schematic structure of an example of embodiment of the manufacturing apparatus of the granular crystal of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Crucible 1a ... Nozzle part 2 ... Pipe 3 ... Buffer container 3a ... Branch pipe 3b ... Check valve 4 ... Granular melt 5 ... Granular crystal

Claims (4)

A granular crystal is produced by discharging and dropping the crystal material melt into a tube arranged vertically from the crucible nozzle portion, and cooling and solidifying the granular melt during the fall. In the granular crystal manufacturing apparatus, the internal atmosphere of the tube is controlled using a predetermined gas, and the predetermined gas is stored from the tube when the internal pressure rises, and is stored when the pressure decreases. An apparatus for producing granular crystals, wherein a buffer container for returning gas to the tube is connected. 2. The apparatus for producing granular crystals according to claim 1, wherein the buffer container is provided with a check valve for discharging the gas from the buffer container when a predetermined pressure or more is reached. A granular crystal is produced by discharging and dropping the crystal material melt into a tube arranged vertically from the crucible nozzle portion, and cooling and solidifying the granular melt during the fall. In the method for producing granular crystals, the atmosphere inside the tube is controlled using a predetermined gas, and a buffer container is connected in the middle of the tube, and the gas is discharged from the tube when the pressure inside the tube rises. Is stored in the buffer container, and the pressure in the pipe is controlled by returning the gas stored in the buffer container to the pipe when the pressure is reduced. 4. The method for producing granular crystals according to claim 3, wherein at least one of argon and helium is used as the gas.

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