Silicon ingot and method for producing silicon ingot

Abstract

This silicon ingot 10 is composed of a unidirectional solidified structure. A cross-section orthogonal to the solidification direction of the silicon ingot 10 is circular. The number density of foreign inclusions having an equivalent circle diameter of 3 μm or greater is less than 0.01 / cm2. The silicon ingot 10 has a single-crystal part 11 composed of a single crystal and a poly-crystal part 12 composed of a plurality of crystal grains formed around the single crystal part 11 in the cross-section orthogonal to the solidification direction. The area ratio of the single-crystal part 11 is 25% or higher.

Description

Silicon ingot and method for manufacturing silicon ingot

[0001] This invention relates to a silicon ingot having a unidirectionally solidified structure and a method for manufacturing the silicon ingot. This application claims priority to Japanese Patent Application No. 2023-139153, filed on August 29, 2023, the contents of which are incorporated herein by reference.

[0002] Conventionally, in various apparatuses, such as plasma etching apparatuses and plasma CVD apparatuses, used in the process of manufacturing silicon semiconductor devices, silicon members made of the same material as silicon wafers have been widely used to prevent contamination within the apparatus. The silicon members are manufactured from, for example, silicon ingots with a unidirectional solidification structure. As shown in Patent Document 1, for example, silicon ingots with a unidirectional solidification structure are widely used as materials for components used in semiconductor manufacturing apparatuses, such as liquid crystal sputtering apparatuses, plasma etching apparatuses, and CVD apparatuses.

[0003] Furthermore, as shown in Patent Document 2, suppressing abnormal discharge and particle generation is an issue in plasma processing apparatuses. Inclusions contained in silicon members can cause abnormal discharge when the members are worn out and exposed to the surface during the dry etching process, and can also cause particle generation when the members are further worn out and detached from the members.

[0004] Furthermore, when components are consumed during the dry etching process, differences in etching rates occur between different crystals, and grain boundaries are more selectively consumed, which may cause cracks and particles in the components. For this reason, it is preferable to produce various components from single-crystal silicon ingots that do not have grain boundaries. However, it has been difficult to produce large-sized single-crystal silicon ingots.

[0005] Therefore, Patent Document 3 proposes a columnar crystal silicon ingot obtained by placing seed crystals made of single crystal silicon plates at the bottom of a crucible and unidirectionally solidifying the silicon melt in the crucible to grow single crystals from each of the seed crystals.

[0006] Japanese Patent No. 4531435 Japanese Patent Application Laid-Open No. 2015-106652 Japanese Patent No. 6233114

[0007] In the production of silicon ingots, cracks may occur in the silicon ingot when it is removed from the crucible after casting. For this reason, in the past, a release agent was sometimes applied to the inner wall of the crucible to release the silicon ingot from the crucible. Typically, silicon nitride (silicon nitride film) is used as the release agent, which fails to sufficiently reduce the nitrogen concentration in the silicon ingot, making it impossible to prevent the inclusion of foreign inclusions such as silicon nitride. Furthermore, when a carbon component is installed inside the manufacturing equipment, there is a risk of foreign inclusions such as silicon carbide being mixed into the silicon ingot. If foreign inclusions are present in the silicon melt during unidirectional solidification, these foreign inclusions may act as starting points for crystal growth, potentially preventing sufficient growth of a single crystal.

[0008] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a silicon ingot in which the inclusion of different inclusions is sufficiently suppressed, which has a high proportion of single crystal portions, and which can be used as a raw material for large components, and a method for manufacturing the silicon ingot.

[0009] In order to solve the above problems, the present inventors conducted extensive research and found that by using a crucible with a specific structure for the crucible used in producing a silicon ingot, it is possible to satisfactorily remove the silicon ingot without using a release agent such as silicon nitride, and to sufficiently suppress the inclusion of inclusions. It is also possible to produce a silicon ingot with a high proportion of single crystal portions by placing a seed crystal plate at the bottom of the crucible and performing unidirectional solidification.

[0010] The present invention has been made based on the above findings, and a silicon ingot according to a first aspect of the present invention is a silicon ingot having a unidirectional solidification structure and a circular cross section perpendicular to the solidification direction, in which the number density of different inclusions having a circle equivalent diameter of 3 μm or more is 0.01 pieces / cm ２The silicon ingot has a diameter of less than 1 / 2 mm, and in a cross section perpendicular to the solidification direction, it has a single crystal portion consisting of a single crystal and a polycrystalline portion consisting of a plurality of crystal grains formed around the single crystal portion, and the area ratio of the single crystal portion is 25% or more. The area ratio of the single crystal portion may be a value measured on a cross section at a position 15 mm below the top end of a silicon ingot that has been directionally solidified from the bottom end. The number density of foreign inclusions may be a value calculated by mirror-polishing the cross section at a position 15 mm below the top end and observing the observation surface with a micrometer under an environment with a luminous intensity of 1000 to 2000 lx to calculate the number density of foreign inclusions having a circle equivalent diameter of 3 μm or more.

[0011] According to the silicon ingot of the first aspect of the present invention, the number density of different inclusions having a circle equivalent diameter of 3 μm or more is 0.01 pieces / cm ２ Since the density is less than 3 μm, the inclusion of foreign inclusions is suppressed, and the silicon is particularly suitable as a material for silicon components that can suppress contamination, abnormal discharge, and particle generation. The number density of foreign inclusions with a circle equivalent diameter of 3 μm or more is not limited, but should be 0.001 pieces / cm ２ There is no restriction on the lower limit of the number density, but in consideration of the technical effect and the manufacturing cost, it is industrially preferable that the number density is less than 0.0008 particles / cm. ２ The area ratio of the single crystal portion consisting of a single crystal in the cross section perpendicular to the solidification direction is set to 25% or more, which makes it possible to produce a silicon component using a single crystal portion without grain boundaries. There is no upper limit to the area ratio of the single crystal portion, but considering the technical effect and manufacturing costs, it may be industrially set to about 60%. The number density of the different inclusions is measured by observing the cross section of the silicon ingot.

[0012] A silicon ingot according to a second aspect of the present invention is characterized in that, in the silicon ingot according to the first aspect of the present invention, the diameter of the inscribed circle of the single crystal portion is 300 mm or more in a cross section perpendicular to the solidification direction. According to the silicon ingot according to the second aspect of the present invention, since the diameter of the inscribed circle of the single crystal portion is 300 mm or more, a silicon member having a diameter of 300 mm or more can be produced using the single crystal portion having no grain boundaries.

[0013] The silicon ingot of aspect 3 of the present invention is the silicon ingot of aspect 1 or aspect 2 of the present invention, wherein the nitrogen concentration is 1.0 × 10 １４ atoms / cc (atoms / cm ３ According to the silicon ingot of the third aspect of the present invention, the nitrogen concentration is less than 1.0×10 １４ Since the nitrogen concentration is limited to less than 5.0 × 10 atoms / cc, the inclusion of different inclusions made of nitrides such as silicon nitride is suppressed, making it particularly suitable as a material for silicon components that can suppress contamination, abnormal discharge, and particle generation. Furthermore, during unidirectional solidification, crystal growth originating from different inclusions made of nitrides can be suppressed, and a silicon ingot with a sufficiently high single crystal area ratio can be obtained. The nitrogen concentration is not limited, but is preferably 5.0 × 10 １３ Although there is no restriction on the lower limit of the nitrogen concentration, in consideration of the technical effect and the manufacturing cost, it is industrially preferable that the nitrogen concentration is less than 1.0 × 10 １３ It may be about atoms / cc.

[0014] The silicon ingot of aspect 4 of the present invention is a silicon ingot of any one of aspects 1 to 3 of the present invention, wherein the carbon concentration is 3.5 × 10 １７ atoms / cc (atoms / cm ３ According to the silicon ingot of the fourth aspect of the present invention, the carbon concentration is less than 3.5×10 １７Since the carbon concentration is limited to less than 2.0 × 10 atoms / cc, the inclusion of different inclusions made of carbides such as silicon carbide is suppressed, making the silicon ingot particularly suitable for use as a material for silicon components that can suppress contamination, abnormal discharge, and particle generation. Furthermore, during unidirectional solidification, crystal growth originating from different inclusions made of carbide can be suppressed, resulting in a silicon ingot with a sufficiently high single crystal area ratio. The carbon concentration is not limited, but should be less than 2.0 × 10 １７ Although there is no lower limit for the carbon concentration, in consideration of the technical effect and production costs, it is industrially preferable that the carbon concentration is less than 1.0 × 10 １７ It may be about atoms / cc.

[0015] A silicon ingot manufacturing method according to a fifth aspect of the present invention is a silicon ingot manufacturing method for manufacturing the silicon ingot according to any one of the first to fourth aspects of the present invention, the method comprising: a seed crystal plate placing step of placing a seed crystal plate at the bottom of a crucible; a raw material charging step of charging a silicon raw material into the crucible in which the seed crystal plate is placed; a silicon raw material melting step of melting the silicon raw material to obtain a silicon melt under conditions in which the seed crystal plate does not completely melt; and a unidirectional solidification step of unidirectionally solidifying the silicon melt from the bottom of the crucible in which the seed crystal plate is placed upward; the crucible having a mold, on an inner surface of which are alternately stacked in a thickness direction, slurry layers made of fine silica powder and colloidal silica having an average particle size of 1 μm to 200 μm and stucco layers made of coarse silica powder having an average particle size of 100 μm to 1000 μm, the slurry layers and stucco layers being stacked in total number of layers being 6 or more. The shape of the crucible is not limited, but may be a cylindrical shape with a bottom, such as a cylindrical shape with a bottom or a square cylindrical shape with a bottom.

[0016] According to the method for producing a silicon ingot of aspect 5 of the present invention, a crucible has a mold, and on the inner surface of the mold, slurry layers made of fine silica powder and colloidal silica having an average particle size of 1 μm or more and 200 μm or less and stucco layers made of coarse silica powder having an average particle size of 100 μm or more and 1000 μm or less are alternately stacked in the thickness direction, and the total number of stacked slurry layers and stucco layers is 6 or more. Therefore, when the silicon ingot is removed, stress applied to the silicon ingot is reduced and cracks in the silicon ingot can be suppressed. In addition, since there is no need to use a mold release agent such as silicon nitride, the generation of foreign inclusions such as silicon nitride and silicon carbide in the molten silicon during casting can be suppressed, and a silicon ingot with sufficiently reduced foreign inclusions can be produced.

[0017] The method for producing a silicon ingot includes a seed crystal plate placement step of placing a seed crystal plate at the bottom of a crucible, a raw material charging step of charging a silicon raw material into the crucible in which the seed crystal plate is placed, a silicon raw material melting step of melting the silicon raw material under conditions in which the seed crystal plate does not completely melt to obtain a silicon melt, and a unidirectional solidification step of unidirectionally solidifying the silicon melt from the bottom of the crucible in which the seed crystal plate is placed upward, thereby making it possible to suppress crystal growth starting from heterogeneous inclusions and produce a silicon ingot with a high area ratio of single crystal portions.

[0018] Unless otherwise specified, the average particle size in this specification refers to the median diameter (D50). The average particle sizes of the fine silica powder and the coarse silica powder remain almost unchanged before and after deposition, making it possible to measure the average particle size even after deposition. The slurry layer is formed by applying or spraying a mixture of fine silica powder and colloidal silica onto the inner surface of the mold or the inner surface of the stucco layer, drying, and then firing, resulting in a structure in which the fine silica powder is bonded while retaining its particle shape. The colloidal silica is an aqueous dispersion containing a high concentration of colloidal silica particles with a particle size of 100 nm or less. The stucco layer is formed by spraying coarse silica powder onto the inner surface of the mold or the inner surface of the slurry layer, followed by firing, resulting in a structure in which the coarse silica powder is bonded while retaining its particle shape.

[0019] According to the present invention, it is possible to provide a silicon ingot in which the inclusion of different types of inclusions is sufficiently suppressed, which has a high proportion of single crystal portions, and which can be used as a material for large components, and a method for manufacturing the silicon ingot.

[0020] Fig. 1 is a longitudinal sectional view taken along the casting direction of a silicon ingot according to an embodiment of the present invention; Fig. 2 is a transverse sectional view taken along the direction perpendicular to the casting direction of the silicon ingot according to an embodiment of the present invention; Fig. 3 is a longitudinal sectional view showing an example of a silicon ingot manufacturing apparatus used when manufacturing a silicon ingot according to an embodiment of the present invention; Fig. 4 is a longitudinal sectional view of a crucible used when manufacturing a silicon ingot according to an embodiment of the present invention;

[0021] Hereinafter, a silicon ingot and a method for manufacturing the silicon ingot according to embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments shown below are specifically described to provide a better understanding of the gist of the invention, and unless otherwise specified, do not limit the present invention.

[0022] 1A and 1B, a silicon ingot 10 according to an embodiment of the present invention has a unidirectionally solidified structure that is sequentially solidified from the bottom to the top in FIG. 1A, and has a circular cross section perpendicular to the solidification direction. The diameter of the silicon ingot 10 according to this embodiment is substantially constant from the bottom to the top. As shown in FIG. 1B, the cross section perpendicular to the solidification direction has a single crystal portion 11 made of a single crystal and a polycrystalline portion 12 made of a plurality of crystal grains that is formed in an annular shape around the single crystal portion 11, and the area ratio of the single crystal portion 11 to the cross section is 25% or more.

[0023] As shown in FIG. 1A , the area ratio of the single crystal portions 11 in the cross section of the silicon ingot 10 decreases from the bottom to the top. Since it is practically difficult to measure the area ratio of the single crystal portions 11 in the cross section over the entire length of the silicon ingot 10 from the bottom to the top, in this embodiment, the area ratio of the single crystal portions 11 is measured in a cross section at a position 15 mm below the top of the directionally solidified silicon ingot 10. It is empirically predicted that if the area ratio of the single crystal portions 11 in the cross section at a position 15 mm below the top of the silicon ingot 10 is 25% or more, the area ratio will be 25% or more in all cross sections of the silicon ingot 10 from the bottom to the top. It is more preferable that the area ratio of the single crystal portions 11 is 30% or more.

[0024] In the silicon ingot 10 of this embodiment, the number density of different inclusions having a circle equivalent diameter of 3 μm or more is 0.01 pieces / cm ２ It is said that the diameter is less than 1 / 2 of the diameter of a circle having an area equal to the projected area of ​​the heterogeneous inclusion particle. The equivalent circle diameter is the diameter of a circle having an area equal to the projected area of ​​the heterogeneous inclusion particle, and can be measured by observing the cross section of the silicon ingot using an optical microscope equipped with a micrometer. The equivalent circle diameter and number density of the heterogeneous inclusion particle may also be measured by computer image processing of the optical microscope photograph. The heterogeneous inclusion is a granular substance other than silicon mixed into the silicon ingot, and is mainly composed of, but not limited to, silicon nitride or silicon carbide.

[0025] The number density of dissimilar inclusions is confirmed by collecting an observation sample from the silicon ingot 10, mirror-polishing the observation sample, and observing it. The size of the observation sample depends on the measuring device, but it may be the same diameter as the silicon ingot 10 (for example, a circular sample with a diameter of 600 mm). In this embodiment, the observation sample is collected from the top of the directionally solidified silicon ingot 10, and the number density of dissimilar inclusions is measured. The position from which the observation sample is collected may be the entire cross section at a position 15 mm from the top end of the silicon ingot 10, and observation may be performed. The dissimilar inclusions are considered to include silicon nitride and silicon carbide. The number density of dissimilar inclusions with a circle equivalent diameter of 3 μm or more is 0.001 pieces / cm ２ It is more preferable that the density of the different inclusions is less than or equal to 1 / 2. The number density of the different inclusions is generally measured by cutting the ingot at a position 15 mm from the top end and measuring the circular piece produced as an observation sample. Therefore, in the present application, a circular sample having the diameter of the ingot (Φ600 mm) was used as the sample. For the measurement of the nitrogen concentration and the carbon concentration, cubic samples measuring 5 mm × 5 mm × 5 mm were taken from one location near the center and one location near the periphery of the circular sample and used for the measurement.

[0026] Furthermore, in the silicon ingot 10 of this embodiment, the diameter of the inscribed circle of the single crystal portion 11 in a cross section perpendicular to the solidification direction may be 200 mm or more, and more preferably 300 mm or more. In this embodiment, the diameter of the inscribed circle of the single crystal portion 11 in a cross section at a position 15 mm from the top of the directionally solidified silicon ingot 10 is specified.

[0027] In the silicon ingot 10 of this embodiment, the nitrogen concentration is 1.0×10 １４ atoms / cc, and preferably less than 5.0 × 10 １３It is more preferable that the nitrogen concentration is less than atoms / cc. In this embodiment, the nitrogen concentration of the silicon ingot 10 is measured by SIMS (secondary ion mass spectrometry). The positions for measuring the nitrogen concentration may be near the center of the cross section of the silicon ingot 10 at a position 15 mm below the top end and near a position 5 mm inward from the outer periphery toward the center. If the measured value at these positions falls within the above range, it can be assumed that the nitrogen concentration throughout the silicon ingot 10 falls within the above range.

[0028] Furthermore, in the silicon ingot 10 of this embodiment, the carbon concentration is 3.5×10 １７ atoms / cc, and preferably less than 2.0×10 １７ It is more preferable that the carbon concentration is less than atoms / cc. In this embodiment, the carbon concentration of the silicon ingot 10 is measured by FT-IR (Fourier transform infrared spectroscopy). The position at which the carbon concentration is measured may be the same as the position at which the nitrogen concentration is measured. If the measured value at this position falls within the above range, it can be assumed that the carbon concentration in all parts of the silicon ingot 10 falls within the above range.

[0029] Next, a silicon ingot manufacturing apparatus 20 used to manufacture a silicon ingot according to this embodiment will be described with reference to Fig. 2. The silicon ingot manufacturing apparatus 20 includes a bottomed cylindrical crucible 30 for storing silicon melt L, a chill plate 22 on which the crucible 30 is placed, a lower heater 23 that supports the chill plate 22 from below and is capable of being raised and lowered, and an upper heater 24 that is disposed above the crucible 30 and is also capable of being raised and lowered. A heat insulator 25 having a container-like shape that can be opened and closed is provided around the crucible 30 so as to surround the crucible 30. The chill plate 22 has a hollow structure, and Ar gas is supplied into the chill plate 22 via a supply pipe 26.

[0030] A crucible 30 used in the method for producing a silicon ingot according to this embodiment will be described with reference to Fig. 3. The crucible 30 shown in Fig. 3 has a mold 31 and a silica layer 32 formed to a substantially constant thickness on the inner surface of the mold 31. The mold 31 has a bottomed cylindrical shape such as a rectangular cylinder (e.g., a box shape with an open top) or a cylindrical cylinder, and is made of, for example, quartz or graphite.

[0031] As shown in FIG. 3 , the silica layer 32 is provided inside the mold 31 and has a structure in which a slurry layer 33 made of fine silica powder and colloidal silica with an average particle size of 1 μm to 200 μm and a stucco layer 34 made of coarse silica powder with an average particle size of 100 μm to 1000 μm are alternately layered in the thickness direction. The innermost layer in contact with the silicon ingot is preferably the slurry layer 33, and the total number of the layered slurry layers 33 and stucco layers 34 is six or more. Colloidal silica is an aqueous dispersion containing a high concentration of colloidal silica particles with a particle size of 100 nm or less. The slurry layer 33 is formed by applying or spraying a slurry containing a mixture of fine silica powder and colloidal silica to the inner surface of the mold 31 or the inner surface of the stucco layer 34, drying, and then firing, resulting in a structure in which the fine silica powder is bonded while retaining its particle shape. Colloidal silica is an aqueous dispersion containing a high concentration of colloidal silica particles with a particle size of 100 nm or less, which becomes a slurry when mixed with fine silica powder. The stucco layer 34 is formed by spraying coarse silica powder onto the inner surface of an unfired slurry layer 33 and firing it, with the coarse silica powder retaining its particle shape and bonding to adjacent slurry layers 33, forming a mutually bonded structure. In this embodiment, as shown in Figure 3, the slurry layer 33 is formed at the location in contact with the inner surface of the mold 31, and the total number of stacked slurry layers 33 and stucco layers 34 is six.

[0032] If the total number of layers of the stacked slurry layers 33 and stucco layers 34 is less than six, the stress generated when removing the silicon ingot may not be fully relieved, resulting in cracking of the silicon ingot. For this reason, in this embodiment, the total number of layers of the stacked slurry layers 33 and stucco layers 34 is set to six or more. While there is no upper limit on the total number of layers, industrially, the total number may be 10 or less, considering the balance between technical effect and manufacturing costs. Furthermore, by setting the average particle size of the fine silica powder to between 1 μm and 200 μm, it can be mixed with colloidal silica to form a slurry, thereby enabling the formation of a satisfactory slurry layer 33. Furthermore, by setting the average particle size of the coarse silica powder to between 100 μm and 1000 μm, the surface roughness is not excessively large, facilitating separation from the mold 31.

[0033] In this embodiment, the thickness of the silica layer 32 (total thickness of the laminated slurry layer 33 and stucco layer 34) is preferably 1 mm or more, and more preferably 2 mm or more. On the other hand, the thickness of the silica layer 32 (total thickness of the laminated slurry layer 33 and stucco layer 34) is preferably 30 mm or less, and more preferably 25 mm or less.

[0034] Furthermore, the thickness of the slurry layer 33 is preferably 0.1 mm or more, and more preferably 0.2 mm or more. On the other hand, the thickness of the slurry layer 33 is preferably 5 mm or less, and more preferably 4 mm or less. On the other hand, the thickness of the stucco layer 34 is preferably 0.1 mm or more, and more preferably 0.2 mm or more. On the other hand, the thickness of the stucco layer 34 is preferably 5 mm or less, and more preferably 4 mm or less.

[0035] Next, a method for manufacturing the silicon ingot 10 according to this embodiment using the silicon ingot manufacturing apparatus 20 shown in FIG. 2 will be described.

[0036] First, a seed crystal plate is placed at the bottom of the crucible 30 shown in Fig. 3 (seed crystal plate placement step). The seed crystal plate may be composed of a single crystal, and may be taken from a single crystal silicon ingot or from the single crystal portion 11 of a silicon ingot 10 according to this embodiment that has been previously manufactured. The crystal grows according to the crystal plane orientation of the surface of the seed crystal plate, but there are no particular limitations on the crystal plane orientation of the surface of the seed crystal plate.

[0037] Next, silicon raw material is charged into the crucible 30 in which the seed crystal plate is placed (raw material charging step). The silicon raw material is a mass called a "chunk" obtained by crushing high-purity silicon of 11N (purity 99.999999999). The particle size of this mass silicon raw material is, for example, 30 mm to 100 mm in the major axis direction.

[0038] Next, the silicon raw material charged in the crucible 30 is heated by energizing the upper heater 24 and the lower heater 23. At this time, the output of the lower heater 23 is adjusted so that the seed crystal plate placed at the bottom of the crucible 30 does not completely melt, and the upper chunk of the seed crystal plate is mainly melted from above (silicon raw material melting process). This causes the silicon melt to accumulate in the crucible 30. If the seed crystal plate completely melts, liquid phase epitaxial growth will not occur, and many crystal nuclei will form on the bottom of the crucible, becoming polycrystalline, and a single crystal will not grow well. For this reason, it is necessary to control the temperature so that the seed crystal plate does not completely melt.

[0039] Next, the amount of current supplied to the lower heater 23 is further reduced, and Ar gas is supplied into the chill plate 22 via the supply pipe 26. This cools the bottom of the crucible 30. Furthermore, by gradually reducing the current supplied to the upper heater 24, the silicon melt in the crucible 30 undergoes upward crystal growth while retaining the crystal orientation of the seed crystal plate placed at the bottom of the crucible 30, thereby obtaining a silicon ingot 10 having a unidirectionally solidified structure and a single crystal portion (unidirectional solidification step). As for the casting conditions, it is preferable to adjust the solidification rate to be within the range of 5 mm / h to 20 mm / h.

[0040] After solidification is complete, the silicon ingot 10 formed inside the crucible 30 is removed. In this manner, the silicon ingot 10 of this embodiment is manufactured.

[0041] According to the silicon ingot 10 of this embodiment configured as described above, the number density of different inclusions having a circle equivalent diameter of 3 μm or more is 0.01 pieces / cm ２ Since the thickness is less than 100 μm, the inclusion of different inclusions is suppressed, making the material particularly suitable as a material for silicon components that can suppress contamination, abnormal discharge, and particle generation. In addition, in a cross section perpendicular to the solidification direction, the material has a single crystal portion 11 made of a single crystal and a polycrystalline portion 12 made of multiple crystal grains formed around this single crystal portion 11, and since the area ratio of the single crystal portion 11 is 25% or more, it is possible to manufacture silicon components using a single crystal portion without crystal grain boundaries.

[0042] In the silicon ingot 10 of this embodiment, if the diameter of the inscribed circle of the single crystal portion 11 in a cross section perpendicular to the solidification direction is 300 mm or more, a silicon component having a diameter of 300 mm or more can be produced using the single crystal portion 11 without grain boundaries.

[0043] In the silicon ingot 10 of this embodiment, the nitrogen concentration is 1.0×10 １４ When the concentration is limited to less than atoms / cc, the inclusion of other inclusions such as silicon nitride is suppressed, making it particularly suitable as a material for silicon components that can suppress contamination, abnormal discharge, and particle generation.

[0044] In the silicon ingot 10 of this embodiment, the carbon concentration is 3.5×10 １７ When the concentration is limited to less than atoms / cc, the inclusion of other inclusions such as silicon carbide is suppressed, making it particularly suitable as a material for silicon components that can suppress contamination, abnormal discharge, and particle generation.

[0045] According to the method for manufacturing a silicon ingot of this embodiment, the crucible 30 has a mold 31, and on the inner surface of this mold 31, slurry layers 33 made of fine silica powder and colloidal silica having an average particle size of 1 μm or more and 200 μm or less and stucco layers 34 made of coarse silica powder having an average particle size of 100 μm or more and 1000 μm or less are alternately stacked in the thickness direction, and a structure is used in which the total number of stacked slurry layers 33 and stucco layers 34 is 6 or more. Therefore, when the silicon ingot 10 is removed from the crucible 30, cracks in the silicon ingot 10 can be suppressed, and the generation of foreign inclusions such as silicon nitride and silicon carbide during casting can be suppressed, and a silicon ingot 10 in which these foreign inclusions are sufficiently reduced can be manufactured.

[0046] The method includes a seed crystal plate placement step of placing a seed crystal plate at the bottom of the crucible 30, a raw material charging step of loading a silicon raw material into the crucible in which the seed crystal plate is placed, a silicon raw material melting step of melting the silicon raw material under conditions in which the seed crystal plate does not completely melt to obtain a silicon melt, and a unidirectional solidification step of unidirectionally solidifying the silicon melt from the bottom of the crucible 30 in which the seed crystal plate is placed upward, thereby making it possible to suppress crystal growth starting from heterogeneous inclusions and produce a silicon ingot 10 having a high area ratio of the single crystal portion 11.

[0047] While one embodiment of the present invention has been described above, the present invention is not limited to this embodiment and can be modified as appropriate without departing from the technical spirit of the invention. In this embodiment, as shown in Figure 2, the total number of layers of the stacked slurry layers 33 and stucco layers 34 is six, but the present invention is not limited to this and the total number of layers may be seven or more.

[0048] The outermost layer of silica layer 32 on the mold 31 side may be either a slurry layer 33 or a stucco layer 34, but is preferably slurry layer 33. The innermost layer of silica layer 32 on the silicon melt L side may be either a slurry layer 33 or a stucco layer 34, but is preferably slurry layer 33. Therefore, the total number of slurry layers 33 and stucco layers 34 in silica layer 32 is not limited, but is preferably an odd number.

[0049] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0050] (Example of the Invention) A cylindrical quartz mold with a bottom was prepared, measuring 600 mm in inner diameter, 650 mm in outer diameter, and 550 mm in depth. The thicknesses of the sidewall and bottomwall were both 25 mm, and the boundaries between the sidewall and bottomwall were curved on both the inner and outer peripheries. A slurry layer was formed by applying a slurry containing a fine silica powder with an average particle size of 1 μm to 200 μm and colloidal silica in a 1:1 weight ratio. This slurry layer was then formed four times. A stucco layer was then formed three times by scattering a coarse silica powder with an average particle size of 100 μm to 1,000 μm on the pre-fired slurry layer. This process was repeated alternately until the total number of slurry and stucco layers reached 7. The mold was then heated in a N atmosphere. ２ The crucible was fired under the conditions of a heating temperature of 800°C and a holding time of 8 hours to produce a crucible with a silica layer formed on the inner surface of the mold. The total thickness of the slurry layer and the stucco layer (thickness of the silica layer) was 3 mm.

[0051] A seed crystal plate was placed on the bottom surface of the crucible. Then, a silicon raw material was loaded into the crucible with the seed crystal plate placed therein. Then, a silicon ingot was produced using the silicon ingot production apparatus shown in Figure 2. The silicon raw material was heated by passing electricity through the upper heater and the lower heater of the silicon ingot production apparatus, and the silicon raw material was melted. At this time, the output of the lower heater was adjusted so that the seed crystal plate placed at the bottom of the crucible would not completely melt.

[0052] Next, the amount of current supplied to the lower heater was further reduced, and Ar gas was supplied to the inside of the chill plate through a supply pipe to cool the bottom of the crucible. Furthermore, by gradually reducing the current supplied to the upper heater, the silicon melt in the crucible grew crystals while retaining the crystal orientation of the seed crystal plate placed at the bottom of the crucible, producing a silicon ingot 10 having a unidirectional solidification structure and a single crystal portion.

[0053] (Comparative Example) A quartz mold identical to the mold used in the Example, with dimensions of inner diameter: 600 mm, outer diameter: 650 mm, and depth: 550 mm, was prepared. A 1 mm-thick silicon nitride film was then formed on the inner surface of the mold as a release agent, and a crucible used in the Comparative Example was manufactured. For the film formation, a silicon nitride slurry was applied in the same manner as the silica slurry and then fired. Only one silicon nitride layer was formed.

[0054] A seed crystal plate was placed on the bottom surface of the crucible. Then, similar to the present invention, a silicon raw material was loaded into the crucible with the seed crystal plate placed therein. Then, similar to the present invention, a silicon ingot was produced using the silicon ingot production apparatus shown in FIG.

[0055] The silicon ingot was cut at a height of 15 mm from its top surface, and cubic measurement samples measuring 5 mm × 5 mm × 5 mm were taken from each of the resulting circular samples, each having a diameter of 600 mm, at one location near the center and one location 5 mm inward from the periphery toward the center, and the number density, nitrogen concentration, and carbon concentration of heterogeneous inclusions with a circle-equivalent diameter of 3 μm or more were measured. The measurement results are shown in Table 1.

[0056] The number density of foreign inclusions was determined by mirror-polishing the observation surface of the measurement sample and visually observing the observation surface with a micrometer under an environment of 1000 to 2000 lx luminous intensity, thereby calculating the number density of foreign inclusions with an equivalent circle diameter of 3 μm or more. The nitrogen concentration was measured by SIMS (secondary ion mass spectrometry). The carbon concentration was measured by FT-IR (Fourier transform infrared spectroscopy). Samples taken from the same height position of the same silicon ingot were used to calculate the number density of foreign inclusions, measure the nitrogen concentration, and measure the carbon concentration.

[0057] The area ratio of the single crystal portion and the diameter of the inscribed circle of the single crystal portion were evaluated in a cross section perpendicular to the casting direction at a height of 15 mm from the top surface of the obtained silicon ingot. The evaluation results are shown in Table 1.

[0058]

[0059] In the comparative example, a crucible with a nitride film formed on the inner surface of the mold as a mold release agent was used, and the nitrogen concentration and carbon concentration in the produced silicon ingot were high, and the number density of foreign inclusions was 5.3 pieces / cm ２ Furthermore, a seed crystal plate was placed at the bottom of the crucible and unidirectional solidification was performed, but in the cross section at a height of 15 mm from the top surface of the silicon ingot, the area ratio of the single crystal portion was as small as 5%, and the diameter of the inscribed circle of the single crystal portion was 50 mm, making it difficult to produce a large silicon product using the single crystal portion.

[0060] In contrast, in the present invention example, a crucible was used in which slurry layers and stucco layers were alternately laminated on the inner surface of the mold, with the innermost layer being a slurry layer, and the total number of laminated slurry layers and stucco layers was six. In the produced silicon ingot, the nitrogen concentration and carbon concentration were sufficiently low, and the number density of foreign inclusions was 0.001 pieces / cm ２ A seed crystal plate was placed at the bottom of the crucible and unidirectional solidification was performed, and in the cross section at a height of 15 mm from the top surface of the silicon ingot, the area ratio of the single crystal portion was 30%, which was sufficiently large, and the diameter of the inscribed circle of the single crystal portion was 300 mm, making it possible to produce a large silicon product using the single crystal portion.

[0061] As described above, it has been confirmed that the present invention can provide a silicon ingot in which the inclusion of different types of inclusions is sufficiently suppressed, which has a high proportion of single crystal portions, and which can be used as a material for large components, as well as a method for manufacturing such a silicon ingot.

[0062] The present invention can provide a silicon ingot in which the inclusion of different inclusions is sufficiently suppressed, which has a high proportion of single crystal portions, and which can be used as a material for large components, and a method for manufacturing a silicon ingot, and therefore can be used industrially.

[0063] REFERENCE SIGNS LIST 10 silicon ingot 11 single crystal portion 12 polycrystalline portion 30 crucible 31 mold 33 slurry layer 34 stucco layer

Claims

1. A silicon ingot made of unidirectional solidification structure, with a circular cross section perpendicular to the solidification direction, in which the number density of heterogeneous inclusions with a circle equivalent diameter of 3 μm or more is 0.01 pieces / cm ２ a silicon ingot having a cross section perpendicular to the solidification direction, the cross section having a single crystal portion consisting of a single crystal and a polycrystalline portion consisting of a plurality of crystal grains formed around the single crystal portion, the area ratio of the single crystal portion being 25% or more.

2. The silicon ingot according to claim 1, characterized in that in a cross section perpendicular to the solidification direction, the diameter of the inscribed circle of the single crystal portion is 300 mm or more.

3. Nitrogen concentration is 1.0 x 10 １４ 2. The silicon ingot of claim 1, wherein the SiO 2 content is less than 10000000 atoms / cc.

4. Carbon concentration is 3.5 x 10 １７ 2. The silicon ingot of claim 1, wherein the SiO 2 content is less than 10000000 atoms / cc.

5. A method for producing a silicon ingot according to any one of claims 1 to 4, comprising: a seed crystal plate arrangement step of arranging a seed crystal plate at the bottom of a crucible; a raw material charging step of charging a silicon raw material into the crucible in which the seed crystal plate is arranged; a silicon raw material melting step of melting the silicon raw material under conditions in which the seed crystal plate does not completely melt to obtain a silicon melt; and a unidirectional solidification step of unidirectionally solidifying the silicon melt from the bottom of the crucible in which the seed crystal plate is arranged upward; wherein the crucible has a mold, and on the inner surface of the mold, a slurry layer made of fine silica powder and colloidal silica having an average particle size of 1 μm to 200 μm and a stucco layer made of coarse silica powder having an average particle size of 100 μm to 1000 μm are alternately stacked in the thickness direction, and the total number of the stacked slurry layers and stucco layers is 6 or more.

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