JP2013116844A - Polycrystalline silicon ingot production device, polycrystalline silicon ingot, polycrystalline silicon block, polycrystalline silicon wafer, polycrystalline silicon solar cell, and polycrystalline solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce high-quality polycrystalline silicon ingot at low cost while preventing cracking of ingot and generation of a crystal defect in a polycrystalline silicon ingot production device having a heater on a crucible side.SOLUTION: The polycrystalline silicon ingot production device includes: a crucible 20; a heater positioned on the crucible 20 side; a placing base 40 positioned in contact with a bottom face of the crucible 20; and a heat insulating material 50 positioned between the side face 41 of the placing base 40 and the heater 30 to block heat.

Description

  The present invention relates to a polycrystalline silicon ingot manufacturing apparatus, a polycrystalline silicon ingot, a polycrystalline silicon block, a polycrystalline silicon wafer, a polycrystalline silicon solar cell, and a polycrystalline solar cell module.

  Due to environmental issues, the use of natural energy is attracting attention as an alternative to fossil fuel energy such as oil. Solar cells that generate power using natural energy are actively introduced in Japan and Europe because they do not require large facilities and do not generate noise during operation.

  In solar cells, new solar cells made of compound semiconductors such as cadmium tellurium are being developed. However, solar cells using crystalline silicon as a substrate currently occupy a large share in terms of the safety of the substance itself, past use results and price. Among them, the proportion of polycrystalline silicon solar cells manufactured from a polycrystalline silicon wafer (hereinafter also simply referred to as a wafer) is large.

  Wafers widely used in applications for polycrystalline silicon solar cells are generally manufactured by a method called a casting method. In the wafer manufacturing method by the casting method, a molten silicon is unidirectionally solidified in a crucible to grow a polycrystalline silicon ingot (hereinafter also simply referred to as an ingot), and then cut into blocks from the ingot and further sliced. Thus, a wafer is manufactured.

  Wafers manufactured by the casting method have variations in characteristics when solar cells are manufactured, depending on which height in the ingot is taken out.

  FIG. 10 is a graph showing a general relationship between the position in the height direction of the ingot from which the wafer has been taken out and the output of the solar cell formed from the wafer. In FIG. 10, the vertical axis represents the solar cell output, and the horizontal axis represents the position in the ingot from which the wafer was taken out.

  The cause of the variation in the solar cell output as shown in FIG. 10 is generally explained as follows. In the region I under the ingot solidified in the initial stage when the molten silicon is solidified in one direction, many impurities are diffused from the crucible into the silicon crystal. Due to the influence of the impurities, the output characteristics of the solar cell formed from the wafer taken out from the region I deteriorate.

  In the region II located above the region I, the amount of impurities taken into the crystal due to segregation is small, and the crystal defects are small. Therefore, the output characteristic of the solar cell formed from the wafer taken out from the region II is the best in the ingot or the block.

  In the region III located above the region II, the amount of impurities taken into the crystal gradually increases and crystal defects increase. Therefore, the output characteristics of the solar cell formed from the wafer taken out from the region III are lower than the output characteristics of the solar cell formed from the wafer taken out from the region II.

  In the region IV located above the region III, the amount of impurities taken into the crystal is increased and the crystal defects are further increased as compared with the region III. In addition, after the ingot is completely solidified, impurities are back-diffused from the high-concentration portion of the impurity appearing on the uppermost surface portion of the ingot, thereby further increasing the amount of impurities taken into the crystal.

  Therefore, the output characteristics of the solar cell formed from the wafer taken out from the region IV are remarkably lowered as compared with the output characteristics of the solar cell formed from the wafer taken out from the region III.

  In the above description, the influence of impurities in the raw material and the influence of impurities dissolved out of the crucible are taken into account, but even if these influences are not present, in the regions III and IV, minority carrier traps move upward. The number of crystal defects gradually increases. Therefore, the output characteristics of the solar cell formed from the wafer to be taken out tend to deteriorate as it goes to the upper part of the ingot.

  The cause of the crystal defects is considered to be the stress due to the temperature distribution in the ingot. If the stress is particularly large, the ingot may crack. Therefore, it is important to control the temperature distribution in the ingot, and it is particularly desirable to flatten the solid-liquid interface during crystal growth.

  As prior literatures that disclose a silicon casting apparatus that suppresses ingot cracking and crystal defects, there are Patent Document 1 (Japanese Patent Laid-Open No. 2005-152985) and Patent Document 2 (International Publication No. 2005/092791).

  In the silicon casting apparatus described in Patent Document 1, the heat flux passing through the mold holder from the center of the bottom of the mold is configured to be larger than the heat flux passing through the mold holder from directly below the side of the mold. Yes.

  In the silicon casting apparatus described in Patent Document 2, the bottom surface cooling member is moved relative to the mold or the base in order to change the heat exchange area between the heat radiating surface and the heat receiving surface.

JP 2005-152985 A International Publication No. 2005/092791

  The silicon casting apparatus described in Patent Document 1 is applicable only when the mold heating means is provided on the upper part of the mold, and the case where the mold heating means is provided on the side of the mold is considered. It has not been. In addition, the mold holder has a complicated structure.

  In the silicon casting apparatus described in Patent Document 2, there are many movable members and the apparatus configuration is complicated. In such a silicon casting apparatus, failure of the movable member due to exposure of the inside of the apparatus to a high temperature is likely to occur, and the stability of the apparatus is lowered. In addition, the apparatus cost increases due to the complicated apparatus configuration.

  The present invention has been made in view of the above problems, and in a polycrystalline silicon ingot manufacturing apparatus having a heater on the side of a crucible, the occurrence of ingot cracking and crystal defects can be suppressed, and it is inexpensive and stable. It is an object of the present invention to provide a polycrystalline silicon ingot manufacturing apparatus, a polycrystalline silicon ingot, a polycrystalline silicon block, a polycrystalline silicon wafer, a polycrystalline silicon solar cell, and a polycrystalline solar cell module that can be manufactured.

  The polycrystalline silicon ingot producing apparatus according to the present invention is a polycrystalline silicon ingot producing apparatus that grows a polycrystalline silicon ingot by unidirectionally solidifying molten silicon from below to above. The polycrystalline silicon ingot manufacturing apparatus includes a crucible, a heater positioned on the side of the crucible, a crucible support member positioned in contact with the bottom surface of the crucible, a side surface of the crucible support member and the heater. And a shield that shields heat.

  In one form of this invention, the shield is movable relative to the side surface. The shield in a state where silicon is melted in the crucible is positioned so as to hide the side surface from the heater.

  In one form of this invention, the shield in the state in which silicon is unidirectionally solidified in the crucible is positioned so as to open the side surface.

In one embodiment of the present invention, the shield can cover 50% or more of the side surface.
In one form of this invention, a shield consists of heat insulating materials.

In one embodiment of the present invention, the heat insulating material is a carbon-based felt or an oxide-based felt.
The polycrystalline silicon ingot based on the present invention is manufactured by the polycrystalline silicon ingot manufacturing apparatus described above.

  The polycrystalline silicon block based on this invention is obtained by processing the polycrystalline silicon ingot described above.

  The polycrystalline silicon wafer based on this invention is obtained by processing the above-mentioned polycrystalline silicon ingot.

  The polycrystalline silicon solar cell according to the present invention is formed using the polycrystalline silicon wafer described above.

  A polycrystalline solar cell module according to the present invention is configured by connecting a plurality of the polycrystalline silicon solar cells described above.

  According to the present invention, it is possible to suppress the occurrence of ingot cracking and crystal defects in a polycrystalline silicon ingot manufacturing apparatus in which a heater is disposed on the side, and not only a high-quality polycrystalline silicon ingot can be manufactured at low cost, but also By producing solar cells from ingots, it is possible to supply high-power solar cells to the market at a low price.

It is a partial sectional view showing the state where silicon is melted in the polycrystalline silicon ingot manufacturing device concerning Embodiment 1 of the present invention. It is a partial cross section figure which shows the state in the middle of solidifying silicon unidirectionally in the polycrystalline silicon ingot manufacturing apparatus concerning the embodiment. It is a partial cross section figure which shows the state which has melt | dissolved the silicon in the polycrystalline silicon ingot manufacturing apparatus which concerns on Embodiment 2 of this invention. It is a partial cross section figure which shows the state in the middle of solidifying silicon unidirectionally in the polycrystalline silicon ingot manufacturing apparatus concerning the embodiment. It is a partial cross section figure which shows the state which has melt | dissolved the silicon in the polycrystalline-silicon ingot manufacturing apparatus which concerns on Embodiment 3 of this invention. It is a partial cross section figure which shows the state in the middle of solidifying silicon unidirectionally in the polycrystalline silicon ingot manufacturing apparatus concerning the embodiment. It is a partial cross section figure which shows the state which has melt | dissolved the silicon in the polycrystalline silicon ingot manufacturing apparatus which concerns on Embodiment 4 of this invention. It is a partial cross section figure which shows the state in the middle of solidifying silicon unidirectionally in the polycrystalline silicon ingot manufacturing apparatus concerning the embodiment. It is a histogram which shows the output distribution of the solar cell of an Example and a comparative example. It is a graph which shows the general relationship between the position of the height direction in the ingot from which the wafer was taken out, and the output of the solar cell formed from the wafer.

  Hereinafter, the polycrystalline silicon ingot manufacturing apparatus according to Embodiment 1 of the present invention will be described. In the following description of the embodiments, the same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated.

  Moreover, in the following Embodiments 1-4, although the example which has mounted the crucible 20 directly on the mounting base 40 is given, for example, the crucible 20 is installed in an unillustrated outer crucible made of graphite or the like, and the outer crucible is mounted. You may make it mount on the mounting base 40. FIG. Moreover, although the example which solidifies silicon unidirectionally by lowering the crucible 20 is given, by having a mechanism for raising the heater 30 or a mechanism for partially changing the heating intensity of the heater 30 in the height direction, Silicon may be unidirectionally solidified.

(Embodiment 1)
FIG. 1 is a partial cross-sectional view showing a state in which silicon is melted in the polycrystalline silicon ingot manufacturing apparatus according to Embodiment 1 of the present invention. FIG. 2 is a partial cross-sectional view showing a state where silicon is unidirectionally solidified in the polycrystalline silicon ingot manufacturing apparatus according to the present embodiment.

  As shown in FIGS. 1 and 2, a polycrystalline silicon ingot manufacturing apparatus 1 according to Embodiment 1 of the present invention includes a substantially rectangular parallelepiped casing 10 made of stainless steel. An opening 11 for introducing one end of a gas supply pipe 13 to be described later into the interior of the housing 10 is provided in the upper portion of the housing 10. An exhaust port 12 for exhausting the inside of the housing 10 is provided in the lower portion of the housing 10.

  A crucible 20 is disposed inside the housing 10. The crucible 20 is mounted on a mounting table 40 that is a crucible support member. That is, the mounting table 40 is positioned in contact with the bottom surface of the crucible 20.

  The crucible 20 is made of silica. However, the material of the crucible 20 is not limited to silica but may be graphite. Silicon nitride powder is applied to the inner surface of the crucible 20 in order to prevent reaction with molten silicon. The silicon nitride powder is dried and then sintered.

  The mounting table 40 is formed of a material having higher thermal conductivity and heat resistance than the crucible 20. The mounting table 40 is made of, for example, graphite. The mounting table 40 is connected to the support part 71 at the lower part. The support portion 71 is connected to a drive portion 70 disposed outside the housing 10 so as to be movable up and down as indicated by an arrow 72. The drive unit 70 has a motor.

  The drive unit 70 is connected to a cooling unit 90 disposed outside the housing 10. The cooling unit 90 cools the drive unit 70 and the support unit 71 by circulating a cooling medium inside the drive unit 70 and the support unit 71. The cooling unit 90 includes a pump and a heat exchanger. The bottom part of the crucible 20 can be cooled via the mounting table 40 by cooling the support part 71 by the cooling part 90.

  A heater 30 is disposed around the side of the crucible 20. The heater 30 is disposed so as to surround the crucible 20 at a distance from the crucible 20. The heater 30 is connected to a power source (not shown) disposed outside the housing 10. A shield that shields heat is disposed between the heater 30 and the side surface 41 of the mounting table 40 as described later.

  An inner lid 60 made of a heat insulating material is disposed above the mounting table 40. The inner lid 60 includes a ceiling part 60a facing the mounting table 40, a side wall part 60b surrounding the heater 30 and a bottom part 60c facing the ceiling part 60a. The ceiling 60 a is provided with a hole for introducing one end of the gas supply pipe 13 into the inner lid 60. The inside of the inner lid 60 surrounded by the ceiling portion 60a, the side wall portion 60b, and the bottom portion 60c is a heating region 61.

  A thermocouple (not shown) is arranged in the heating region 61. The thermocouple is connected to a power source. The voltage applied to the heater 30 is controlled by feeding back the temperature measured by the thermocouple to the power source.

  One end of the gas supply pipe 13 is positioned above the crucible 20 in the heating region 61, and the other end is connected to a gas supply unit (not shown) disposed outside the housing 10. An inert gas such as Ar sent from the gas supply unit passes through the inside of the gas supply pipe 13 and is supplied into the heating region 61. The gas supply unit includes a plurality of gas cylinders storing various gases and a mass flow controller.

  The exhaust port 12 is connected to an exhaust unit (not shown) disposed outside the housing 10. The exhaust part includes various vacuum pumps. The inert gas supplied into the heating region 61 passes through the exhaust port 12 and is discharged to the outside of the housing 10.

  Hereinafter, the manufacturing method of the polycrystalline silicon ingot by the polycrystalline silicon ingot manufacturing apparatus 1 according to the present embodiment will be described.

  First, about 400 kg of granular or lump silicon is put into the crucible 20. Thereafter, with the crucible 20 raised to the height shown in FIG. 1, the vacuum pump in the exhaust section is operated to depressurize the inside of the housing 10, and the silicon raw material is heated to about 800 ° C. by the heater 30. Thereafter, while supplying Ar gas into the heating region 61 from the gas supply pipe 13 at a rate of about 40 liters / minute, it is heated to 1550 ° C. to melt all the silicon raw material.

  Next, the temperature is controlled at a temperature of the melting point of silicon + 15 ° C. for 30 minutes, temperature control is performed according to predetermined growth conditions, and the support portion 71 is gradually lowered. Due to the lowering of the support part 71, the bottom part of the crucible 20 comes to be located outside the heating region 61, and radiation from the bottom part of the crucible 20 increases. Therefore, the temperature at the lower part of the crucible 20 is lowered, and the solidification of silicon starts from the bottom of the crucible 20 and the solidified silicon 81 appears.

  Further, by lowering the support portion 71, all the molten silicon 80 is solidified in one direction from the bottom toward the top. After confirming that the silicon has completely solidified to the top, the crucible 20 is raised to the initial position, and is annealed at a temperature of 1200 ° C. for about 2 hours. Thereafter, the set temperature of the heater 30 is lowered at about 50 ° C./hour to cool the polycrystalline silicon ingot.

  When the temperature of the polycrystalline silicon ingot falls to around 900 ° C., the gas sent from the gas supply unit is changed from Ar to He. Thereafter, the polycrystalline silicon ingot is cooled to room temperature.

  End portions containing a large amount of impurities and crystal defects are removed from the polycrystalline silicon ingot, and the polycrystalline silicon block is cut into a predetermined size. Further, a plurality of wafers can be obtained by cutting the polycrystalline silicon block to a predetermined thickness with a wire saw.

  As a result of diligent research, the present inventors have found that in the conventional polycrystalline silicon manufacturing apparatus in which the heater 30 is disposed on the side of the crucible 20, the temperature is set in the mounting table 40 when the molten silicon 80 is unidirectionally solidified. It confirmed that the tendency for the circumference side part side of the mounting base 40 to become higher than the center part side appeared.

  This tendency is due to the influence of heat input from the side surface 41 of the mounting table 40. By this heat input, the temperature of the mounting table 40 becomes higher on the peripheral side than on the central side. As a result, heat removal from the peripheral side portion of the mounting table 40 is suppressed, and the solid-liquid interface of silicon becomes convex upward. Under such a temperature distribution, residual stress is generated in the ingot after the molten silicon 80 is solidified. As a result, ingot cracks and crystal defects are likely to occur.

  In order to prevent cracking of the polycrystalline silicon ingot and suppress crystal defects, it is preferable to flatten the solid-liquid interface shape and linearize the temperature distribution in the vertical direction in the crucible 20. The temperature distribution in the vertical direction in the crucible 20 can be controlled by the descending speed of the crucible 20 when the crucible is cooled, the temperature setting of the heater 30, and the like.

  In order to flatten the solid-liquid interface shape when the molten silicon 80 is solidified in one direction, it is desired to make the temperature distribution in the horizontal plane in the crucible 20 uniform. Therefore, the present inventors have found that it is effective to control heat input and heat dissipation on the side surface 41 of the mounting table 40.

  As shown in FIGS. 1 and 2, in the present embodiment, a shield that shields heat is interposed between the side surface 41 of the mounting table 40 and the heater 30. As the shield, a heat insulating material having heat insulating properties and flexibility is preferable. In the present embodiment, the carbon felt 50 is used as a heat insulating material.

  However, the shield is not limited to carbon felt, and oxide felts such as silica, alumina and zirconia can be used. In addition, a plate, block, or sheet made of a heat insulating material can be used as the shield.

  The upper end portion of the carbon felt 50 is attached to the upper end portion of the side surface 41 of the mounting table 40. The lower end of the carbon felt 50 is attached on the bottom 60 c of the inner lid 60. Therefore, the carbon felt 50 is deformed following the vertical movement of the crucible 20. As a result, the carbon felt 50 is movable relative to the side surface 41 of the mounting table 40.

  The length of the carbon felt 50 is longer than the distance between the upper end portion of the side surface 41 of the mounting table 40 and the bottom portion 60c of the inner lid 60 when the crucible 20 is located at the uppermost position, and the crucible 20 is the most. It is determined to be longer than the distance between the upper end portion of the side surface 41 of the mounting table 40 and the bottom portion 60c of the inner lid 60 when positioned below.

  As shown in FIG. 1, the carbon felt 50 in a state where silicon is melted in the crucible 20 is positioned so as to hide the side surface 41 of the mounting table 40 from the heater 30. Therefore, heat input from the heater 30 on the side surface 41 of the mounting table 40 is reduced by the carbon felt 50. As a result, the in-plane uniformity of the temperature distribution in the mounting table 40 can be improved.

  As shown in FIG. 2, the carbon felt 50 in a state where silicon is unidirectionally solidified in the crucible 20 is deformed so as to be folded on the bottom 60 c of the inner lid 60 and remains in the heating region 61. ing.

  That is, the carbon felt 50 is positioned so as to open the side surface 41 of the mounting table 40 while being interposed between the side surface 41 of the mounting table 40 and the heater 30. Therefore, heat from the heater 30 can be shielded by the carbon felt 50 and heat can be efficiently radiated from the side surface 41 of the mounting table 40 while suppressing heat input to the side surface 41 of the mounting table 40.

  By using the carbon felt 50 according to this embodiment, the temperature distribution in the horizontal plane in the crucible 20 can be made uniform when the molten silicon 80 is solidified. Thereby, the solid-liquid interface shape when the molten silicon 80 is solidified in one direction can be flattened.

  With the polycrystalline silicon ingot manufacturing apparatus 1 using the carbon felt 50 according to the present embodiment, it is possible to suppress the generation of ingot cracks and crystal defects and to manufacture a high-quality polycrystalline silicon ingot at a low cost.

  Hereinafter, a polycrystalline silicon ingot manufacturing apparatus according to Embodiment 2 of the present invention will be described. Note that the polycrystalline silicon ingot manufacturing apparatus 2 according to the present embodiment is different from the polycrystalline silicon ingot manufacturing apparatus 1 according to the first embodiment only in the configuration of the shield, and therefore description of other configurations will not be repeated.

(Embodiment 2)
FIG. 3 is a partial cross-sectional view showing a state where silicon is melted in the polycrystalline silicon ingot manufacturing apparatus according to Embodiment 2 of the present invention. FIG. 4 is a partial cross-sectional view showing a state in the middle of unidirectional solidification of silicon in the polycrystalline silicon ingot manufacturing apparatus according to the present embodiment.

  As shown in FIGS. 3 and 4, in the present embodiment, a heat insulating plate 51 is interposed as a shield between the side surface 41 of the mounting table 40 and the heater 30. In this embodiment, the heat insulation board 51 which made the high silicate glass fiber the plate shape is used. However, the material of the heat insulating plate 51 is not limited to the high silicate glass fiber, and for example, a plate formed by laminating ceramic fibers or a graphite molded heat insulating material may be used.

  The heat insulating plate 51 is rotatably attached to the upper end portion of the side surface 41 of the mounting table 40. The lower end portion of the heat insulating plate 51 is placed so as to be movable on the bottom portion 60 c of the inner lid 60. Therefore, following the vertical movement of the crucible 20, the heat insulating plate 51 rises. As a result, the heat insulating plate 51 is movable relative to the side surface 41 of the mounting table 40.

  The length of the heat insulating plate 51 is longer than the interval between the upper end portion of the side surface 41 of the mounting table 40 and the bottom portion 60c of the inner lid 60 when the crucible 20 is positioned at the uppermost position, and the crucible 20 is the most. It is determined to be longer than the distance between the upper end portion of the side surface 41 of the mounting table 40 and the bottom portion 60c of the inner lid 60 when positioned below.

  As shown in FIG. 3, the heat insulating plate 51 in a state where silicon is melted in the crucible 20 is positioned so as to hide the side surface 41 of the mounting table 40 from the heater 30. Therefore, heat input from the heater 30 on the side surface 41 of the mounting table 40 is reduced by the heat insulating plate 51. As a result, the in-plane uniformity of the temperature distribution in the mounting table 40 can be improved.

  As shown in FIG. 4, the heat insulating plate 51 in the state where the silicon is unidirectionally solidified in the crucible 20 is lifted in contact with the corners of the bottom 60 c of the inner lid 60. Stay on. The heat insulating plate 51 is lifted so as not to cover the side surface of the crucible 20.

  That is, the heat insulating plate 51 is located so as to open the side surface 41 of the mounting table 40 while being interposed between the side surface 41 of the mounting table 40 and the heater 30. Therefore, heat from the heater 30 is shielded by the heat insulating plate 51, and heat can be efficiently radiated from the side surface 41 of the mounting table 40 while suppressing heat input to the side surface 41 of the mounting table 40.

  By using the heat insulating plate 51 according to the present embodiment, the temperature distribution in the horizontal plane in the crucible 20 can be made uniform when the molten silicon 80 is solidified. Thereby, the solid-liquid interface shape when the molten silicon 80 is solidified in one direction can be flattened.

  The polycrystalline silicon ingot manufacturing apparatus 2 using the heat insulating plate 51 according to the present embodiment can suppress the generation of ingot cracks and crystal defects, and can manufacture a high-quality polycrystalline silicon ingot at a low cost.

  Hereinafter, a polycrystalline silicon ingot manufacturing apparatus according to Embodiment 3 of the present invention will be described. Note that the polycrystalline silicon ingot manufacturing apparatus 3 according to the present embodiment is different from the polycrystalline silicon ingot manufacturing apparatus 1 according to the first embodiment only in the configuration of the shield, and therefore description of other configurations will not be repeated.

(Embodiment 3)
FIG. 5 is a partial cross-sectional view showing a state where silicon is melted in the polycrystalline silicon ingot manufacturing apparatus according to Embodiment 3 of the present invention. FIG. 6 is a partial cross-sectional view showing a state in the middle of unidirectional solidification of silicon in the polycrystalline silicon ingot manufacturing apparatus according to the present embodiment.

  As shown in FIGS. 5 and 6, in this embodiment, a heat insulating block 52 is interposed as a shield between the side surface 41 of the mounting table 40 and the heater 30. In this embodiment, the heat insulation block 52 which made the high silicate glass fiber the block shape is used. However, the material of the heat insulating block 52 is not limited to the high silicate glass fiber, and for example, a block formed by stacking ceramic fibers or a carbon-based molded heat insulating material may be used.

  The heat insulating block 52 is placed on the bottom 60 c of the inner lid 60. Therefore, when the crucible 20 moves up and down, the relative positional relationship between the heat insulation block 52 and the mounting table 40 changes. That is, the heat insulating block 52 is movable relative to the side surface 41 of the mounting table 40.

  The size of the heat insulating block 52 is determined so as to cover the entire side surface 41 of the mounting table 40 when the crucible 20 is located at the uppermost position. However, the size of the heat insulating block 52 only needs to cover 50% or more of the side surface of the mounting table 40.

  As shown in FIG. 5, the heat insulating block 52 in a state where silicon is melted in the crucible 20 is positioned so as to hide the side surface 41 of the mounting table 40 from the heater 30. Therefore, heat input from the heater 30 on the side surface 41 of the mounting table 40 is reduced by the heat insulating block 52. As a result, the in-plane uniformity of the temperature distribution in the mounting table 40 can be improved.

  As shown in FIG. 6, the heat insulating block 52 in a state in which silicon is unidirectionally solidified in the crucible 20 is located on the bottom 60 c of the inner lid 60 and remains in the heating region 61.

  That is, the heat insulation block 52 is positioned so as to open the side surface 41 of the mounting table 40 while being interposed between the side surface 41 of the mounting table 40 and the heater 30. Therefore, heat from the heater 30 can be shielded by the heat insulating block 52, and heat can be efficiently radiated from the side surface 41 of the mounting table 40 while suppressing heat input to the side surface 41 of the mounting table 40.

  As a result, the mounting table 40 can be cooled from the state in which the in-plane uniformity of the temperature distribution is improved, and therefore, the bottom surface portion of the crucible 20 can also be cooled in the state in which the in-plane uniformity of the temperature distribution is improved. .

  By using the heat insulation block 52 according to the present embodiment, the temperature distribution in the horizontal plane in the crucible 20 can be made uniform when the molten silicon 80 is solidified. As a result, it is possible to flatten the solid-liquid interface shape when the molten silicon 80 is solidified in one direction.

  With the polycrystalline silicon ingot manufacturing apparatus 3 using the heat insulation block 52 according to the present embodiment, it is possible to suppress the generation of ingot cracks and crystal defects and to manufacture a high-quality polycrystalline silicon ingot at a low cost.

  Hereinafter, a polycrystalline silicon ingot manufacturing apparatus according to Embodiment 4 of the present invention will be described. Note that the polycrystalline silicon ingot manufacturing apparatus 4 according to the present embodiment is different from the polycrystalline silicon ingot manufacturing apparatus 1 according to the first embodiment only in the configuration of the shield, and therefore the description of other configurations will not be repeated.

(Embodiment 4)
FIG. 7 is a partial cross-sectional view showing a state in which silicon is melted in the polycrystalline silicon ingot manufacturing apparatus according to Embodiment 4 of the present invention. FIG. 8 is a partial cross-sectional view showing a state in the middle of unidirectional solidification of silicon in the polycrystalline silicon ingot manufacturing apparatus according to the present embodiment.

  As shown in FIGS. 7 and 8, in the present embodiment, a heat insulating plate 53 is interposed as a shield between the side surface 41 of the mounting table 40 and the heater 30. In this embodiment, the heat insulation board 53 which made the high silicate glass fiber the plate shape is used. However, the material of the heat insulating plate 53 is not limited to the high silicate glass fiber, and for example, a plate formed by laminating ceramic fibers or a carbon-based molded heat insulating material may be used.

  The heat insulating plate 53 is affixed to the side surface 41 of the mounting table 40. Therefore, even if the crucible 20 moves up and down, the relative positional relationship between the heat insulating plate 53 and the mounting table 40 does not change. That is, the heat insulating plate 53 is not movable relative to the side surface 41 of the mounting table 40.

  The size of the heat insulating plate 53 is determined so as to cover the entire side surface 41 of the mounting table 40. However, the size of the heat insulating plate 53 only needs to cover 50% or more of the side surface of the mounting table 40.

  As shown in FIG. 7, the heat insulating plate 53 in a state where silicon is melted in the crucible 20 is positioned so as to cover the side surface 41 of the mounting table 40. Therefore, heat input from the heater 30 on the side surface 41 of the mounting table 40 is reduced by the heat insulating plate 53. As a result, the in-plane uniformity of the temperature distribution in the mounting table 40 can be improved.

  As shown in FIG. 8, the heat insulating plate 53 in a state where silicon is unidirectionally solidified in the crucible 20 is positioned below the bottom portion 60 c of the inner lid 60 and outside the heating region 61.

  That is, the heat insulating plate 53 is located so as to cover the side surface 41 of the mounting table 40 while being interposed between the side surface 41 of the mounting table 40 and the heater 30. Therefore, although heat from the heater 30 is shielded by the heat insulating plate 53 and heat input to the side surface 41 of the mounting table 40 is suppressed, heat radiation from the side surface 41 of the mounting table 40 is also suppressed.

  As a result, the polycrystalline silicon ingot manufacturing apparatus 4 has a slightly lower cooling efficiency than the polycrystalline silicon ingot manufacturing apparatuses 1 to 3 of the first to third embodiments, but the mounting table 40 has an in-plane uniformity of temperature distribution. Therefore, the bottom surface of the crucible 20 can also be cooled with improved in-plane uniformity of the temperature distribution.

  By using the heat insulating plate 53 according to the present embodiment, the temperature distribution in the horizontal plane in the crucible 20 can be made uniform when the molten silicon 80 is solidified. As a result, it is possible to flatten the solid-liquid interface shape when the molten silicon 80 is solidified in one direction.

  By using the heat insulating plate 53 according to the present embodiment, a complicated movable member is not required, so that the polycrystalline silicon ingot manufacturing apparatus 4 that can be manufactured inexpensively and stably can be configured. In addition, it is possible to suppress the occurrence of ingot cracking and crystal defects, and to manufacture a high-quality polycrystalline silicon ingot at a low cost.

  Hereinafter, the output of the polycrystalline silicon solar cell formed from the wafer obtained by processing the polycrystalline silicon ingot manufactured by the polycrystalline silicon ingot manufacturing apparatus 1 according to the first embodiment, and a shield as a comparative example are provided. An experimental example in which the output of a polycrystalline silicon solar cell formed from a wafer obtained by processing a polycrystalline silicon ingot manufactured by a polycrystalline silicon ingot manufacturing apparatus that has not been manufactured will be described.

(Experimental example)
In both the examples and the comparative examples, as a crucible 20 according to the present embodiment, a silica crucible having an inner dimension of 830 mm × 830 mm × 420 mm, a bottom surface thickness of 20 mm, and a side surface thickness of 15 mm It was used. A graphite plate was used as the mounting table.

  In the example, a carbon felt 50 having a thickness of 10 mm and having flexibility was used as the shield. The upper end of the carbon felt 50 was attached to the upper end of the side surface 41 of the mounting table 40, and the lower end was attached to the bottom 60 c of the inner lid 60.

  In both the examples and comparative examples, the method for producing a polycrystalline silicon ingot was the same as in the above embodiment. The silicon raw material was doped with boron so that the specific resistance of the polycrystalline silicon ingot was about 1.5 Ωcm to 2.0 Ωcm.

  In the examples, no abnormality was observed in the appearance of the grown polycrystalline silicon ingot, and no ingot cracking occurred. In the comparative example, a crack having a size of about 15 mm × 25 mm × 6 mm was confirmed in a part of the uppermost corner of the ingot.

  Next, these polycrystalline silicon ingots were blocked with a band saw and then sliced with a wire saw to produce a polycrystalline silicon wafer. These wafers were put into a normal solar cell manufacturing process and their output characteristics were confirmed.

  FIG. 9 is a histogram showing the output distribution of the solar cells of the example and the comparative example. In FIG. 9, the vertical axis indicates the ratio, and the horizontal axis indicates the output of the solar cell.

  As shown in FIG. 9, the polycrystalline silicon solar cell formed from the polycrystalline silicon wafer of the example is a solar cell compared to the polycrystalline silicon solar cell formed from the polycrystalline silicon wafer of the comparative example. The output distribution of is shifted to the higher one.

  A low output solar cell is a solar cell formed from a wafer taken from the top of the ingot. As described above, the cause of the decrease in output is a crystal defect caused by stress inside the ingot.

  Therefore, it was confirmed from this experimental example that the occurrence of ingot cracking and crystal defects can be suppressed by growing a polycrystalline silicon ingot using the shield according to the present embodiment.

  Further, in the examples, since the output of the polycrystalline silicon solar cell could be improved as compared with the comparative example, the characteristics of the polycrystalline solar cell module configured by connecting a plurality of the polycrystalline silicon solar cells were compared with the comparative example. Naturally, this is an improvement over the polycrystalline solar cell module constructed by connecting a plurality of polycrystalline silicon solar cells.

  In the present experimental example, a shield that can cover the entire side surface 41 of the mounting table 40 is provided. However, the entire surface does not necessarily have to be covered, and 50% or more of the side surface 41 of the mounting table 40 can be covered. A high effect can be obtained by providing the shield.

  The embodiments and experimental examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1, 2, 3, 4 Polycrystalline silicon ingot manufacturing apparatus, 10 housing, 11 opening, 12 exhaust port, 13 gas supply pipe, 20 crucible, 30 heater, 40 mounting table, 41 side surface, 50 carbon felt, 51, 53 Insulating plate, 52 Insulating block, 60 Inner lid, 60a Ceiling part, 60b Side wall part, 60c Bottom part, 61 Heating area, 70 Driving part, 71 Support part, 80 Molten silicon, 81 Solidified silicon, 90 Cooling part.

Claims (11)

A polycrystalline silicon ingot manufacturing apparatus for growing a polycrystalline silicon ingot by unidirectionally solidifying molten silicon from below to above,
Crucible,
A heater located on the side of the crucible;
A crucible support member positioned in contact with the bottom surface of the crucible;
An apparatus for producing a polycrystalline silicon ingot, comprising: a shield that is interposed between a side surface of the crucible support member and the heater and shields heat. The shield is movable relative to the side surface;
The polycrystalline silicon ingot manufacturing apparatus according to claim 1, wherein the shield in a state where silicon is melted in the crucible is positioned so as to hide the side surface from the heater.   The polycrystalline silicon ingot manufacturing apparatus according to claim 2, wherein the shield in a state where the silicon is unidirectionally solidified in the crucible is positioned so as to open the side surface.   The polycrystalline silicon ingot manufacturing apparatus according to claim 1, wherein the shielding body can cover 50% or more of the side surface.   The polycrystalline silicon ingot manufacturing apparatus according to claim 1, wherein the shield is made of a heat insulating material.   The polycrystalline silicon ingot manufacturing apparatus according to claim 5, wherein the heat insulating material is a carbon-based felt or an oxide-based felt.   A polycrystalline silicon ingot produced by the polycrystalline silicon ingot producing apparatus according to claim 1.   A polycrystalline silicon block formed by cutting the polycrystalline silicon ingot according to claim 7.   A polycrystalline silicon wafer formed by cutting the polycrystalline silicon ingot according to claim 7.   A polycrystalline silicon solar cell formed from the polycrystalline silicon wafer according to claim 9.   A polycrystalline solar cell module configured by connecting a plurality of polycrystalline silicon solar cells according to claim 10.

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