JP4817329B2 - Method and apparatus for producing spherical crystals - Google Patents

Description

  The present invention relates to a method and apparatus for producing a spherical crystal such as spherical crystal silicon.

  Spherical crystals are used in various fields. For example, spherical solder for use in the electronics industry, spherical copper, and the like are produced in large quantities. When the material system is focused on silicon, spherical silicon is expected to be applied to photoelectric conversion devices, photonic crystals, spherical IC chips, acceleration sensors, etc., and research and development are actively conducted.

  Solar cells as photoelectric conversion devices are being developed in response to market needs such as effective use of natural energy or low manufacturing costs. The mainstream of solar cells is crystalline silicon, and the manufacturing method is to use a substrate by cutting a large bulk of single crystal or polycrystalline silicon. However, this method has a problem in terms of resource saving and low cost in that raw material loss due to cutting is large. Therefore, as one of promising photoelectric conversion devices in the future market, there is a photoelectric conversion device using spherical crystal silicon.

  Spherical crystals are usually produced by the drop method. In this method, the raw material is heated and melted at a temperature equal to or higher than the melting point in the melting crucible, and the molten raw material melt is continuously applied from the nozzle hole provided at the bottom of the crucible while applying pressure on the upper surface of the melt in the melting crucible. It is discharged by the gravity and surface tension of the molten liquid, aggregated into a spherical shape, cooled and solidified while dropping the drop tube, and collected by a collecting device installed at the bottom of the drop tube (patent Literature 1, Patent Literature 2).

  In the production of the spherical crystal by the dropping method, the size of the spherical crystal is determined by the diameter and length of the nozzle and the pressure applied to the upper surface of the melt. However, the molten liquid is discharged in the vertical direction and follows substantially the same trajectory. In particular, when the pressure is applied to the upper surface of the molten liquid, the discharged molten liquid has a constant initial speed and is randomly shredded. Since there is a speed difference depending on the size of the molten droplet, the molten droplet may coalesce in the middle of dropping, and there is a problem that the size of the obtained granular crystal is not fixed. The melts with different speeds may come into contact with each other during the fall, and a solid type with a plurality of molten droplets in close contact, such as a sandstone or bead shape, may be generated, and a single crystal can be stably formed. It is difficult to obtain.

  In order to produce a spherical crystal with a uniform size distribution, a vibration is applied to the nozzle by a vibration device, or vibration of the vibrator gives a vertical wave to the melt on the upper surface of the nozzle with a vibration plate through a transmission rod, Methods for producing spherical crystals having a single size distribution by chopping the discharged melt beam with the same size are already known (Patent Document 3, Patent Document 4, Patent Document 5, and Patent Document 6).

  However, when the nozzle is vibrated, since the entire crucible including the crucible and the fixture for supporting the crucible and the fixture for supporting the nozzle is vibrated at the same time, the load on the vibrator increases and the cost of the apparatus increases. The other is that the amount of the melt in the crucible decreases as the melt is discharged, so the frequency of the vibration mechanism is precisely set to keep the discharge speed of the melt and the size of the melt droplets constant. It is necessary to control.

On the other hand, in the method in which the vibration of the vibrator is applied to the melt on the upper surface of the nozzle by the transmission rod, the transmission rod and the vibration plate are placed in the melt. Since the melt has extremely high reactivity with other materials, there is a problem that the quality of silicon is deteriorated due to contamination of impurities from the transmission rod and the diaphragm.
US Pat. No. 6,432,330 U.S. Pat. No. 4,188,177 JP 2002-292265 A JP 2006-137622 A JP-A-2005-163103 Japanese Patent Laid-Open No. 1-274859

  An object of the present invention is to improve the above-mentioned conventional defects and to produce a spherical crystal having high crystallinity at the same time as efficiently producing a single size spherical crystal in a spherical crystal production method and production apparatus.

  In order to solve the above-described problems, the present invention provides a spherical crystal manufacturing method and apparatus for manufacturing a predetermined location under a nozzle with respect to a continuous flow of a crystal material melt discharged from a nozzle at the bottom of a crucible. Inert gas is intermittently ejected from the lateral direction at regular intervals, and the discharged melt flow is uniformly shredded to a predetermined size, and at the same time, the falling path of the falling melt is changed obliquely. The main points are to reduce the coalescence due to the contact of the molten droplets and to produce a single size spherical crystal.

Means for solving the problems are as follows.
(1) A raw material for producing a spherical crystal is heated and melted in a melting crucible, and a melt liquid flow of the raw material is provided at the bottom of the crucible while applying a predetermined pressure to the upper surface of the melt in the melting crucible. In the method for producing a spherical crystal that is discharged from the nozzle hole, cooled and solidified while dropping in the drop tube, an inert gas is intermittently ejected in a constant cycle in the drop tube below the nozzle hole, A method for producing a spherical crystal, wherein the discharged melt flow is chopped into single-sized spherical crystals.
(2) The inert gas ejection is performed while changing the direction uniformly toward the melt flow on the circumference centered on the falling melt flow, and the fall path of the falling melt flow is vertical. The method for producing a spherical crystal as set forth in (1), wherein the direction is changed to an oblique orbit.
(3) The method for producing a spherical crystal according to (1) or (2), wherein a raw material for producing the spherical crystal is silicon.
(4) One or a mixture of two or more fine powders of seed crystal silicon, silicon oxide, silicon nitride, boron nitride, and silicon carbide are mixed in the inert gas and adhered to the falling molten liquid stream. The method for producing a spherical crystal according to any one of (1) to (3), wherein:

Further, in the present invention, the above-described problems are solved by the following manufacturing apparatus.
(5) A melting furnace including a melting crucible having a nozzle hole at the bottom, a raw material for melting, a dropping tube for dropping the melt discharged from the melting crucible bottom, and a spherical crystal solidified while dropping the dropping tube And a recovery device, and a gas jet for shredding the melt flow discharged by intermittently jetting an inert gas at a constant cycle in a drop tube below the nozzle hole A spherical crystal production apparatus comprising a mechanism.
(6) The gas ejection mechanism includes a base plate, a rotating plate, and a nozzle plate arranged on a concentric shaft. An annular gas introduction groove is provided in the base plate, and the annular gas introduction is provided in the rotating plate. One or more gas through holes are installed on the circumference corresponding to the groove, and a plurality of gas ejection nozzles are installed on the nozzle plate on the circumference corresponding to the annular gas introduction groove and the gas through hole. The spherical shape according to (5), wherein the inlet of the jet nozzle is on the same concentric circumference as the gas through hole of the rotating plate, and the gas jet outlet is installed toward the central axis of the molten liquid flow falling. Crystal manufacturing equipment.
(7) The gas ejection mechanism includes a plurality of gas ejection nozzles, a gas introduction pipe, and an electromagnetic valve, and the gas ejection nozzles are installed toward the central axis on a concentric circumference centering on the falling melt flow. In addition, the high-speed electromagnetic valves are installed in the gas introduction pipes connected to the respective gas ejection nozzles, and the ejection time of the inert gas is switched by controlling the opening / closing time, the opening / closing sequence, and the opening / closing cycle of each electromagnetic valve. The apparatus for producing a spherical crystal according to (5), wherein the spherical crystal is ejected intermittently at a constant period.

According to the present invention, there is no need to apply vibration to the crucible nozzle or the melt, and the inert gas at a predetermined position below the nozzle with respect to the vertical flow of the continuously melted crystal material melt. Are intermittently ejected from the lateral direction at regular intervals, and the discharged melt flow is equally shredded, and at the same time, the dropping path of the falling melt is changed obliquely, so that the coalescence by contact of the molten droplets Thus, a single size spherical crystal can be produced efficiently.
Also, by mixing the fine powder for seed crystal in the jet gas and adhering it to the chopped melt, the molten droplets start to solidify and grow from a low degree of supercooling. Crystals can be made.

Embodiments of the present invention will be described below in detail with reference to the drawings.
In the example of this embodiment, the crystal material is silicon, and a case where spherical crystal silicon is produced using the dropping apparatus shown in FIG. 1 will be described. The dropping device is composed of a crucible 1 for containing a crystal raw material, a melting furnace 2 for melting the raw material by heating, a gas jetting device 3, a seed crystal fine powder supply device 4, a drop tube 5 and a collecting device 6.

  The silicon raw material 8 is melted by the heater 21 of the melting furnace 2 in the melting crucible 1, the inert gas for extrusion is introduced from the introduction port 11, and the molten silicon melt 8 is applied to the upper surface of the silicon melt in the crucible while It discharges from the nozzle hole 12 provided in this.

  In order to obtain a desired conductivity type and doping concentration, an impurity for doping is usually simultaneously added to a silicon raw material and melted. Doping impurities of p-type silicon include boron, aluminum, and gallium, and n-type doping impurities include phosphorus, arsenic, and antimony. From the viewpoint of the segregation coefficient in silicon and the vapor pressure at the time of melting, boron is usually used for p-type and phosphorus for n-type.

  The discharged silicon melt becomes a continuous flow (beam), and when it falls a little, it is shredded by gravity and surface tension. The beam thickness and the size of the molten droplet to be shredded are determined by the nozzle diameter, length and extrusion pressure. When extruded, the molten liquid has an initial velocity, and randomly chopped molten droplets have a difference in velocity, so the molten droplets coalesce or the enlarged molten droplets are affected by surface tension. It may be shredded again. For this reason, the molten droplet has a wide size distribution, and as a result, the spherical crystal silicon also has a wide size distribution, and it is difficult to obtain a spherical crystal of the same shape.

Therefore, a gas ejection device, which is the elemental technology of the present invention, is installed in the drop tube below the nozzle. FIG. 2 shows an enlarged schematic diagram and a part structure diagram of an example of the gas ejection device.
The gas ejection device includes a base plate 33, a rotating plate 32, and a nozzle plate 31. A gas introduction groove 38 is formed in the base plate 33 in an annular shape. The rotating plate 32 has two or more gas passage holes on the same circumference as the groove of the base plate. The nozzle plate 31 has a plurality of gas ejection nozzles 35, the nozzle inlets are uniformly processed on the same circumference as the base plate introduction grooves and the rotation plate through holes, and the outlets melt in a horizontal direction. Install evenly on the circumference around the liquid beam. The nozzle outlet is processed so that it is narrow in the vertical direction and wide in the horizontal direction. In particular, a shape that converges so as to narrow toward the outlet in the vertical direction is desirable. In this way, the ejected gas gives a force that crosses like a cutter against the vertically falling melt beam.

Next, the operation principle of this gas ejection device will be described.
An inert gas is supplied from a gas source to the introduction groove of the base plate, and the gas is filled at a predetermined pressure. The inert gas is supplied to the nozzle inlet of the nozzle plate that matches the position of the through hole through the through hole of the rotating plate, and is ejected from the nozzle outlet. Next, since the rotating plate is continuously rotated, when the nozzle inlet which has been matched up to now is closed, the nozzle inlet on the opposite side similarly matches the through hole and gas is supplied and ejected. Accordingly, the gas supplied to the groove of the base plate is intermittently ejected by switching the nozzle according to the rotation of the rotating plate.

  The order of gas ejection can be adjusted by the position design of the through hole of the rotating plate. In the case of a clock face with twelve ejection nozzles, the gas injection switches from the nozzle located at 12:00 to the injection from the 7 o'clock position, and then changes to the 1 o'clock position. The timing at which the ejection is switched, that is, the gas ejection cycle, can be adjusted by changing the rotational speed of the rotating plate.

  By the gas injection, the silicon melt beam that continuously falls is shredded evenly by receiving the force from the lateral direction of the gas. At the same time, the falling direction of the silicon melt beam is changed from the vertical direction to the oblique direction, the dropping trajectory of each of the chopped molten droplets is changed, and the interval between the droplets is widened. Accordingly, the coalescence of silicon molten droplets is reduced, and a stable and uniform size distribution can be obtained.

  By changing the number of through holes in the rotating plate, the timing of gas ejection and the dropping trajectory of the molten droplet to be shredded can be changed. For example, when the through hole of the rotating plate is made one, the ejection nozzles are sequentially switched in the rotation direction, the timing (cycle) becomes equal to the rotational speed of the rotating plate, and the dropping trajectory of the shredded molten droplet Becomes spiral.

  By designing the dripping conditions, i.e. crucible nozzle diameter and length, extrusion pressure, and gas ejection device conditions, i.e. the number of ejection nozzles, the number of through holes in the rotating plate and the rotational speed as described above. The size of the spherical crystal silicon to be manufactured can be controlled.

  An apparatus for a similar purpose does not need to be provided directly under the nozzle of the crucible, and only the ejection nozzle can be installed under the nozzle of the crucible, and the base plate and the rotating plate can be installed remotely and connected by piping. An example of the structure is shown in FIG. The operating principle is exactly the same as described above, and a detailed description is omitted here.

  A gas injection device having a similar purpose can also be realized by opening and closing an electromagnetic valve. In this case, a plurality of injection nozzles are arranged concentrically toward the falling melt beam as in the case of the above-described injection device, connected from a gas supply source by piping, and an electronically controlled electromagnetic valve is installed on the way. By controlling the opening / closing time, opening / closing sequence, and opening / closing cycle, gas injection similar to that of the above-described apparatus can be easily realized.

  However, in order to shred the melt flow discharged at high speed, high-speed opening / closing of the electromagnetic valve or a large number of installations is required. For example, when the melt flow is shredded at a speed of 600 balls / second, if the opening / closing speed of the electromagnetic valve is 30 Hz / second, the number of installations is at least 20. Electromagnetic valves that can be opened and closed at high speed are expensive. As the number increases, the cost increases and the installation space also increases. From these situations, it can be seen that the apparatus shown in FIG.

The seed crystal fine powder supply device 4 is connected in the middle of the gas supply line 36, and the seed crystal fine powder is simultaneously injected into the inert gas to be injected. In the case of a silicon raw material, powder of silicon, silicon oxide (SiO ₂ or SiO), silicon nitride, boron nitride, alumina, or a mixture of two or more is used as fine powder for seed crystals. The size of the fine powder is preferably in the range of 1 to 100 μm. The fine powder for seed crystal is put into the supply device 4 and a small amount of inert gas is introduced from the inlet 41 under the device, and a fluidized bed phase of fine powder is generated in the upper space of the container, and the inert gas is discharged from the upper outlet 42. It is ejected and merged with the inert gas in the gas supply line 36 and simultaneously ejected.

  The sprayed fine powder is joined to the chopped molten droplets, acts as a seed, solidifies the molten droplets in a low supercooled state, and starts crystal growth. By doing so, the crystallinity of the produced spherical crystalline silicon is high, and the crystal grain boundaries, crystal defects, and dislocation density are low.

  The solidified spherical crystalline silicon is cooled by an inert gas while freely falling in the dropping tube, and is collected by a collecting device installed at the end of the dropping tube. In order to absorb the impact at the time of landing of the spherical crystalline silicon, a silicone oil having a high heat resistance temperature is used for the collecting device.

  The inert gas used for extruding the silicon melt, supplying the injection device and the fine powder for the seed crystal may be either argon or helium, but generally uses high-purity argon gas which is inexpensive in terms of cost. .

  With the above method, the continuously discharged silicon melt beam is shredded by gas injection, the dropping trajectory is changed obliquely from the vertical direction, and simultaneously joined with the fine powder for seed crystal, and solidification and crystal growth occur. Start with low supercooling. Shredded molten droplets have less contact with each other and coalescence due to contact, resulting in a single size distribution.

  For reference, FIG. 4 shows a high-speed camera photograph when water is dropped in the spray device of the present invention. It can be seen that the continuous water flow is uniformly chopped by the gas injection, and the fall trajectory is inclined from the vertical direction. In this case, since the gas passage hole of the rotating plate is one, the dropping trajectory is spiral.

Next, the manufacturing method of the spherical crystal according to the present invention will be described in detail by taking as an example the case of manufacturing the spherical crystal silicon using the dropping apparatus shown in FIG.
120 g of silicon raw material was placed in the quartz crucible 1 and melted by raising the temperature to 1500 ° C., which is higher than the melting point of silicon, in the melting furnace 2. The silicon raw material is obtained by pulverizing the top and bottom of a single crystal silicon ingot produced by the Czochralski method (CZ method) left over when the electronic device is produced. Boron impurities were added so that the resistivity was 1 Ωcm. After completely dissolving the silicon raw material, an argon inert gas was introduced into the upper space of the crucible, a pressure of 20 kg / cm ² was applied, and the silicon melt was discharged from a nozzle installed at the bottom of the crucible. The nozzle diameter was 0.3 mm and the length was 5 mm.

  The gas injection device was installed in the drop tube under the nozzle of the crucible. The vertical distance between the gas ejection nozzle and the crucible nozzle was 20 mm. Install a water cooling mechanism and heat insulating material between the melting furnace and the fall tube so that the gas to be ejected does not cool the crucible nozzle that has become hot, and at the same time, the heat of the melting furnace does not escape from the opening under the nozzle. Then, an opening with a diameter of 30 mm was installed immediately below the nozzle.

  A gas injection groove having a width of 10 mm and a depth of 5 mm was formed in the base plate of the gas injection device, and two gas through holes having a diameter of 10 mm were processed in the rotating plate. Twelve nozzles were installed on the nozzle plate. The nozzle inlet was circular with a diameter of 10 mm, the outlet was a rectangle with a width of 5 mm and a length of 1 mm, and was processed so as to become narrower at an angle of 5 ° toward the tip of the outlet in the vertical direction. The flow rate of argon gas was 10 L / min. As the fine powder of the seed crystal, quartz fine powder having a size distribution of 1 to 63 μm was used, and the argon gas flow rate for supplying the fine powder was 0.1 L / min.

The spherical crystalline silicon produced by supplying fine powder for seed crystals was in the form of teardrops. When the rotation speed of the motor was changed, the size of the produced spherical crystal silicon changed clearly. When the rotation speed was adjusted to 25 rpm, the average size of the spherical crystalline silicon was 1.0 mm, and the size distribution range was ± 0.1 mm.
When the above gas injection device was not used, the size distribution of the spherical crystalline silicon had a wide range of 0.5 to 1.7 mm even under the same experimental conditions, and the center of the size distribution was about 1.0 mm. It can be seen that the weight of spherical crystalline silicon having a size in the range of 0.8 mm to 1.2 mm represents about 50% of the total, and the productivity is very low.

It is a schematic diagram of the manufacturing apparatus of the spherical crystalline silicon which concerns on this invention. It is a structure schematic diagram of an example of the gas injection device concerning the present invention. It is a structure schematic diagram of an example of the gas injection device concerning the present invention. It is a photograph which shows the mode of a water droplet when using a gas injection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crucible 11 Extrusion pressurized gas inlet 12 Nozzle 2 Melting furnace 21 Heating heater 22 Melting furnace core tube 3 Gas injection apparatus 31 Nozzle plate
32 rotating plate 33 base plate 35 gas ejection nozzle 36 gas supply line 37 gas through hole 38 gas introduction groove 4 seed crystal fine powder supply device 41 gas introduction port 42 fine powder outlet 5 drop tube 6 collection device 61 silicone oil 7 fine powder for seed crystal 8 Melt of crystal raw material 81 Discharged melt flow (beam)
82 Shredded molten droplet 9 Spherical crystalline silicon

Claims (7)

  A nozzle hole in which a raw material for producing a spherical crystal is heated and melted in a melting crucible, and a predetermined pressure is applied to the upper surface of the melt in the melting crucible, and a melt flow of the raw material is provided at the bottom of the crucible. In the method for producing a spherical crystal, which is further discharged and cooled and solidified while dropping in the drop tube, an inert gas is intermittently ejected at a constant period in the drop tube below the nozzle hole, and the discharge is performed. A method for producing a spherical crystal, wherein the melt flow is chopped into single size spherical crystals.   The inert gas ejection is performed while changing the direction uniformly toward the melt flow on the circumference centering on the falling melt flow, and the falling path of the falling melt flow is inclined from the vertical direction. The method for producing a spherical crystal according to claim 1, wherein the orbit is changed to the orbit.   The method for producing a spherical crystal according to claim 1 or 2, wherein a raw material for producing the spherical crystal is silicon.   One or a mixture of two or more fine powders of silicon for seed crystal, silicon oxide, silicon nitride, boron nitride, silicon carbide are mixed in the inert gas and adhered to the falling molten liquid stream The manufacturing method of the spherical crystal of any one of Claim 1 thru | or 3.   A melting furnace that includes a melting crucible having a nozzle hole at the bottom, melts the raw material, a dropping tube that drops the melt discharged from the bottom of the melting crucible, and a recovery device that collects spherical crystals that solidify while dropping the dropping tube And a gas jetting mechanism for shredding the discharged melt flow by intermittently jetting an inert gas at regular intervals in a drop tube below the nozzle hole. An apparatus for producing a spherical crystal.   The gas ejection mechanism includes a base plate, a rotating plate, and a nozzle plate arranged on a concentric shaft. An annular gas introducing groove is installed in the base plate, and the rotating plate corresponds to the annular gas introducing groove. One or more gas through holes are installed on the circumference of the gas, and a plurality of gas ejection nozzles are installed on the circumference corresponding to the annular gas introduction groove and the gas through holes on the nozzle plate. 6. The spherical crystal production according to claim 5, wherein the inlet is on the same concentric circumference as the gas through hole of the rotating plate, and the gas outlet is installed toward the central axis of the falling melt flow. apparatus.   The gas ejection mechanism is composed of a plurality of gas ejection nozzles, a gas introduction pipe, and an electromagnetic valve, and the gas ejection nozzles are installed toward the central axis on a concentric circumference centering on the falling melt flow, A high-speed solenoid valve is installed in the gas inlet pipe connected to the gas ejection nozzle, and the opening / closing sequence, opening / closing cycle and switching cycle of each solenoid valve are controlled to change the ejection direction of the inert gas, 6. The apparatus for producing spherical crystals according to claim 5, wherein the spherical crystals are ejected intermittently at periodic intervals.