JP2006275426A - Manufacturing method for crucible and semiconductor ingot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a crucible and a semiconductor ingot for solving a problem wherein silicon melted liquid in the crucible is supplied into a mold while temperature of the silicon melted liquid is raised beyond necessity. <P>SOLUTION: This crucible has a liquid drain port for draining semiconductor melted liquid, and the liquid drain port is closed by a plug body made of the same component as the semiconductor melted liquid and is opened by destroying the plug body by a destruction means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a crucible and a method for manufacturing a semiconductor ingot using the crucible.

  Solar cells are expected to be put to practical use in a wide range of fields, from small households to large-scale power generation systems, as a clean petroleum alternative energy source. These are classified into crystalline, amorphous, and compound types depending on the type of raw materials used, and most of them currently on the market are crystalline silicon solar cells. This crystalline silicon solar cell is further classified into a single crystal type and a polycrystalline type. Single crystal silicon solar cells have the advantage that the conversion efficiency is easy to increase because the quality of the substrate is good, but the disadvantage is that the manufacturing cost of the substrate is high. On the other hand, polycrystalline silicon solar cells have been distributed in the market for a long time, but in recent years, the demand is increasing as interest in environmental issues is increasing, and higher conversion efficiency is required at lower cost. . In order to cope with such a demand, it is necessary to reduce the cost and quality of the polycrystalline silicon substrate, and it is required to produce a high-purity silicon ingot with a high yield.

  By the way, the polycrystalline silicon substrate used for the above-mentioned polycrystalline silicon solar cell is generally manufactured by a method called a casting method. In this casting method, a silicon melt melted by heating at a high temperature is supplied into a mold made of graphite or the like coated with a release material and solidified unidirectionally from the bottom of the mold, or a silicon raw material is placed in the mold and once melted. This is a method of forming a silicon ingot by unidirectionally solidifying from the bottom again. The ends of the silicon ingot are removed, cut into a desired size, and the cut silicon ingot is sliced to a desired thickness to obtain a polycrystalline silicon substrate for forming a solar cell.

  A conventional silicon ingot (semiconductor ingot) manufacturing apparatus for producing such a polycrystalline silicon ingot is shown in FIG. At the top, a melting crucible 1a for melting the silicon raw material 3 is disposed and held by a holding crucible 1b, and at the bottom of the melting crucible 1a and the holding crucible 1b, a drain outlet for supplying silicon melt into the mold 4 is provided. Further, an upper heating means 6 and a side heating means 7 are arranged on the upper and side portions of the melting crucible 1a and holding crucible 1b, respectively, and a mold in which the silicon melt 10 is poured below the melting crucible 1a and holding crucible 1b. 8 is arranged. As such a mold 8, one in which a mold release material 9 is coated on the inner surface of a mold made of graphite or quartz is used. In general, the release material 9 is provided with silicon nitride which is silicon nitride, silicon carbide which is silicon carbide, silicon oxide which is silicon oxide, or the like.

For example, the drain port 4 provided at the bottom of the melting crucible 1a made of high-purity quartz or the like is closed with the silicon raw material 5, and then the silicon raw material 3 is charged into the melting crucible 1a. The silicon raw material 3 put in the melting crucible 1a is gradually heated and melted by the upper and side upper heating means 6 and the side heating means 7 which are composed of a resistance heating type heater, an induction heating type coil or the like. The raw material close to the drainage port 4 is kept at a low temperature to prevent the silicon melt melted in the melting crucible 1a from being discharged. Thereafter, after all the silicon raw material 3 in the melting crucible 1a is melted, the silicon raw material 5 that closes the drainage port is finally melted, so that the silicon raw material in the melting crucible 1a is completely melted at the moment. Since the supply of the silicon melt is started, the silicon material can be efficiently discharged from the crucible after melting. Further, by providing a nozzle (not shown) so as to hang from the bottom of the melting crucible 1a, the silicon melt discharged from the crucible can be prevented from scattering. The silicon melt supplied into the mold 8 is cooled and solidified to obtain a polycrystalline silicon ingot. (For example, refer to Patent Document 1). These are all arranged in a vacuum vessel (not shown).
Japanese Patent Laid-Open No. 2003-247783

  However, in the conventional semiconductor ingot manufacturing apparatus described above, in the method shown in FIG. 4, the silicon raw material 5 that closes the drainage port is melted and the silicon melt is supplied to the mold. Since it is necessary to apply heat more than necessary to melt the silicon raw material 5, the melt temperature rises until the silicon melt is supplied, and it is particularly difficult to supply at the desired melt temperature. In particular, when the melt temperature of the silicon melt is high, productivity is reduced by the solidification time being exceeded in the solidification process after being supplied into the mold, and the inner surface of the mold 8 is coated by the solidification time being exceeded. There arises a problem that impurities such as Fe diffuse from the released release material 9 into the silicon melt 10 to deteriorate the crystal quality of the silicon ingot.

  The present invention has been made in view of such problems, and due to the structure of the semiconductor ingot manufacturing apparatus and its mechanism, the silicon melt in the crucible is heated more than necessary. It is an object of the present invention to provide a crucible and a method for manufacturing a semiconductor ingot that solve the problem of supplying a liquid into a mold.

  In order to achieve the above object, the crucible of the present invention has a drainage port for discharging the semiconductor melt at the bottom, and the drainage port is closed with a plug of the same component as the semiconductor melt. In the above, the drainage port is opened by destroying the plug with a breaking means.

  Further, the plug body is connected to the drainage port by a plugging means that pressurizes in at least two directions and is plugged.

  Furthermore, the plug body is broken by increasing the pressure of the plug closing means.

  And the said plug is hold | maintained at the solid using the cooling means, It is characterized by the above-mentioned.

  The method for producing a semiconductor ingot according to the present invention comprises a step of supplying a semiconductor raw material to the crucible of the present invention, heating and melting to form a semiconductor melt, a step of placing a mold below the crucible, and the plug body. Supplying the semiconductor melt from the drainage port to the mold by breaking and opening the drainage port.

  The crucible of the present invention has a drain port for discharging the semiconductor melt at the bottom, and the crucible formed by closing the drain port with a plug body having the same component as the semiconductor melt, the drain port is Since the semiconductor melt can be supplied into the mold in a timely manner by opening the plug by destroying the plug with a breaking means, without increasing the melt temperature of the semiconductor melt more than necessary, It becomes possible to supply at a desired melt temperature. Moreover, since the plug is melted into the semiconductor melt in a pulverized state, it can be melted quickly in the mold.

  Further, since the plug is joined to the drainage port by a plugging means that pressurizes in at least two directions, the drainage port can be easily plugged from the outside.

  Furthermore, since the plug body is broken by increasing the pressure applied by the plug closing means, it is not necessary to provide a separate break means, and the production cost of the semiconductor ingot can be reduced.

  The plug is held in a solid state using a cooling means, so that the plug melts and the semiconductor melt leaks even if the melt temperature of the semiconductor melt is increased. Can be suppressed.

  The method for producing a semiconductor ingot according to the present invention comprises a step of supplying a semiconductor raw material to the crucible of the present invention, heating and melting to form a semiconductor melt, a step of placing a mold below the crucible, and the plug body. Supplying the semiconductor melt to the mold from the drainage port by breaking and opening the drainage port, so that the melt of the semiconductor melt melted in the crucible The temperature can be supplied into the mold without increasing the temperature more than necessary. Therefore, since the melt temperature of the semiconductor melt can be lowered and supplied into the mold as compared with the conventional case, the solidification time can be shortened in the solidification step, and the mold release material 9 coated on the inner surface of the mold 8 can be used. Impurities such as Fe can be prevented from diffusing into the silicon melt, and the productivity and the crystal quality of the semiconductor ingot can be prevented from being lowered.

  Hereinafter, the invention according to each claim will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic cross-sectional view of a semiconductor ingot manufacturing apparatus using a crucible of the present invention, wherein 1 is a crucible, 1a is a melting crucible, 1b is a holding crucible, 2 is a plug, 3 is a silicon raw material (semiconductor raw material) Reference numeral 4 denotes a drain port, 6 denotes an upper heating means, 7 denotes a side heating means, 8 denotes a mold, 9 denotes a mold release material, 10 denotes a silicon melt (semiconductor melt), and 11 denotes a closing means.

  As shown in FIG. 1, the crucible 1 is composed of a melting crucible 1a and a holding crucible 1b, and the melting crucible 1a heats and melts the silicon raw material 3 contained therein by heating means (upper heating means 6 and side heating means 7). A silicon melt is formed, and a drainage port 4 for discharging the formed silicon melt is provided at the bottom of the melting crucible 1a, and the silicon melt is supplied to a mold 8 provided below. Then, it is cooled and solidified to obtain a polycrystalline silicon ingot. The obtained silicon ingot is used for, for example, a polycrystalline silicon substrate material for solar cells.

  The melting crucible 1a melts the charged silicon raw material 3, and high-purity quartz or the like is usually used in consideration of the heat resistance strength and the fact that impurities do not diffuse into the semiconductor material. There is no particular limitation as long as the purity is such that melting, evaporation, softening, deformation, decomposition, and the like do not easily occur at a temperature higher than the temperature and do not deteriorate the solar cell characteristics. The size of the melting crucible 1a needs to be a size that can contain the silicon raw material 3 according to the melting amount to be melted at one time. The melting amount of the silicon raw material 3 is, for example, in the range of 1 kg to 250 kg. Further, since the melting crucible 1a is softened at a high temperature and cannot keep its shape, it is held by a holding crucible 1b made of graphite or the like.

  A drain port 4 is provided at the bottom of the crucible 1 so that the molten silicon raw material 3 can be supplied into the mold 8 installed below. Further, a nozzle (not shown) may be provided in the drain port 4 so as to hang down. The nozzle is made of, for example, quartz, and is formed integrally with the melting crucible 1a in a cylindrical shape as a whole. The melting crucible 1a may be formed separately and attached to the bottom of the melting crucible 1a. This nozzle is for suppressing scattering of the discharged silicon melt, and is thick in order not to change the shape of the nozzle due to heat within a range where it does not hit the holding crucible 1b. It is desirable to do. Further, it is desirable that the opening at the tip of the nozzle has such a size that the silicon melt can be smoothly discharged and does not obstruct the direction of dropping of the silicon melt discharged from the drain port 4. In the case where a nozzle is provided, the nozzle is regarded as the drain port 4.

  In the initial stage of discharging the silicon melt, the melt passing through the drainage port 4 is pushed out by the pressure depending on the water level. It begins to flow out of the mouth 4. Therefore, in order to discharge without waste, the bottom of the crucible 1 needs to have a certain inclination or more. Moreover, the shape of the main body of the crucible 1 is not specifically limited.

  The drainage port 4 is closed by a plug 2 having the same component as the semiconductor melt. The plug 2 is composed of the same component as the semiconductor melt in the crucible, that is, if it is a silicon melt, it is made of silicon having the same degree of purity, so that it can be melted as a silicon raw material even if it falls into the mold. Because it can, there is no worry of becoming an impurity of the silicon ingot. Further, the plug body 2 may be provided inside the crucible to close the drainage port 4, or may be provided outside to close the drainage port 4.

  The shape of the plug 2 is not particularly limited as long as the drainage port 4 can be sealed. For example, the plug 2 may be a hexahedron, a cylindrical plate, or a sphere.

  An upper heating means 6 and a side heating means 7, which are heating means, are respectively arranged on the upper part and the side part of the crucible 1. For example, a resistance heating type heater or an induction heating type coil can be used. By these heating means, the silicon raw material 3 housed in the melting crucible 1a can be heated and melted to form a silicon melt.

  The mold 8 provided below the crucible 1 has an opening in the upper part, and the silicon melt 10 can be held and solidified therein. The mold 8 is made of graphite, quartz or the like.

  A mold release material 9 is provided on the inner surface of the mold 8. With such a release material 9, after the silicon melt 10 inside the mold 8 is solidified, the inner wall of the mold 8 and the silicon ingot can be taken out without being fused. As a material of such a release material 9, for example, silicon carbide, silicon oxide, silicon nitride or the like is used.

  The crucible according to the present invention has a drainage port for discharging the semiconductor melt at the bottom, and the crucible is formed by closing the drainage port with a plug of the same component as the semiconductor melt. The plug is opened by destroying it with a breaking means. Thus, since the semiconductor melt can be supplied into the mold in a timely manner by opening the plug 2 by destroying the plug body 2 with the destruction means 12, the melt temperature of the semiconductor melt is increased more than necessary. It is possible to supply at a desired melt temperature without increasing. Further, since the plug body is melted into the semiconductor melt in a pulverized state, when the plug body falls into the mold, the impact applied to the mold can be mitigated. It melts faster inside.

  The breaking means 12 is not a problem as long as it is a mechanism that gives an impact to the plug body 2 and breaks it. For example, when the plug body 2 is provided inside the crucible as shown in FIG. A rod having the same component as the liquid is prepared, inserted into the semiconductor melt from above the crucible, and the plug is hit. In addition, when the semiconductor melt is a silicon melt, a silicon compound such as silicon or silica may be used for the rod having the same component as the semiconductor melt. Moreover, as long as it does not become an impurity of a semiconductor melt, it does not need to be the same component as a semiconductor melt.

  In the case where the plug body 2 is provided outside the crucible, it is preferable that the plug body 2 is joined and closed to the drainage port 4 by the plugging means 11 that pressurizes from at least two directions, as shown in FIG. By allowing the closing means 11 to be driven in the vertical direction, the drainage port 4 and the plug body 2 can be joined and the drainage port can be easily closed. By closing the plug 2 from the outside, the silicon raw material 3 in the crucible 1 leaks into the mold slightly before the silicon raw material 3 completely becomes a silicon melt, and is cooled and solidified. The problem of reducing the yield of ingots can be suppressed. Moreover, by providing the plug body 2 outside the crucible 1, the side heating means 7 can be controlled more easily than in the prior art. Hydraulic power or air can be used as the power of the closing means 11. The material used for the closing means 11 may be any heat-resistant member such as graphite or SUS, for example.

  When the plug body 2 is provided outside the crucible 1, the end face region of the plug body 2 may be hit using a hammer made of a rigid member as shown in FIG. It is preferable to break the plug body 2 by increasing the pressure of 11. Since the plug body 2 can be easily broken by increasing the horizontal pressure applied to hold the plug body 2, it is not necessary to provide a separate breaking means, and the production cost of the silicon ingot is reduced. Since the plug body 2 is crushed and dropped into the mold, it is melted faster in the silicon melt.

  Furthermore, it is preferable that the plug body 2 be held in a solid state using a cooling means. When it is desired to increase the melt temperature of the semiconductor melt and supply it into the mold, it is possible to suppress the problem that the plug 2 is melted and the semiconductor melt leaks. When the plug body 2 is provided inside the crucible, the cooling means can cool the plug body by blowing an inert gas toward the vicinity of the drainage port, and the plug body can be provided outside. If it is provided, the plug body 2 is cooled by providing a structure such as circulating water or gas inside the plug-closing means 11, so that it is not necessary to provide a separate cooling means, and the production cost of the silicon ingot is reduced. Can be reduced.

  Supplying a semiconductor raw material to the crucible of the present invention, heating and melting to form a semiconductor melt, disposing a mold below the crucible, breaking the plug and opening the drainage port As a result, the step of supplying the semiconductor melt from the drain port to the mold makes it possible to supply the silicon melt into the mold in a timely manner, and supply the silicon melt into the mold as in the past. In this case, since it is not necessary to apply heat more than necessary, it can be supplied into the mold at a desired melt temperature. Therefore, since the melt temperature of the silicon melt can be lowered and supplied into the mold as compared with the conventional case, the productivity is reduced because the solidification time is exceeded in the solidification process after being supplied into the mold. Further, it is possible to prevent a problem that impurities such as Fe are diffused into the silicon melt 10 from the release material 9 coated on the inner surface of the mold 8 due to the excessive solidification time and the crystal quality of the silicon ingot is deteriorated.

  It should be noted that the embodiment of the present invention is not limited to the above-described example, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  For example, silicon dioxide may be used for the plug 2. When silicon dioxide is used, the oxygen concentration in the silicon melt increases, but oxygen escapes from the melt as SiO gas from the melt, so there is no concern of becoming an impurity of the silicon ingot. Since the melting point is higher than that, it is very effective for maintaining a high temperature of the silicon melt in the melting crucible. Moreover, it is also possible to suppress the oxygen concentration in the silicon melt by using silicon for the plug 2 and providing an oxide film on the silicon drain port side.

  Further, by providing a temperature measuring means such as a thermocouple in the vicinity of the drainage port, the temperature in the vicinity of the drainage port may be monitored to detect that the silicon raw material has completely melted, and the plug body may be destroyed.

It is a cross-sectional schematic diagram which shows the apparatus used for the manufacturing method of the semiconductor ingot of this invention. It is a cross-sectional schematic diagram which shows the apparatus used for the manufacturing method of the semiconductor ingot of this invention. It is a figure which shows an example of the destruction means of this invention. It is a cross-sectional schematic diagram which shows the manufacturing apparatus of the conventional semiconductor ingot.

Explanation of symbols

1: crucible 1a: melting crucible 1b: holding crucible 2: plug body 3: semiconductor raw material (silicon raw material)
4: Drain port 5: Silicon raw material that closes the drain port 6: Upper heating means 7: Side heating means 8: Mold 9: Release material 10: Semiconductor melt (silicon melt)
11: Closing means 12: Destruction means

Claims (5)

In the crucible having a drainage port for discharging the semiconductor melt at the bottom, and closing the drainage port with a plug of the same component as the semiconductor melt,
The crucible characterized in that the drainage port is opened by destroying the plug with a breaking means. 2. The crucible according to claim 1, wherein the plug body is joined to the drainage port by a plugging means that pressurizes in at least two directions. The crucible according to claim 2, wherein the plug is broken by increasing the pressure applied by the plug-closing means. The crucible according to any one of claims 1 to 3, wherein the plug is held in a solid state using a cooling means. Supplying a semiconductor raw material to the crucible according to any one of claims 1 to 4 and heating and melting it to form a semiconductor melt;
Placing a mold below the crucible;
Supplying the semiconductor melt from the drainage port to the mold by breaking the plug and opening the drainage port.

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