Silicon ingot and method for manufacturing silicon ingot

Abstract

To provide a silicon ingot capable of sufficiently preventing foreign inclusions from mixing, having a high proportion of a single crystal part and used as the raw material of a large-sized member.SOLUTION: A silicon ingot 10 consisting of a unidirectional solidification structure has a cross section orthogonal to the solidification direction and having a round shape. The number density of foreign inclusions having a circle equivalent diameter of 3 μm or more is less than 0.01 pieces / cm2; the cross section orthogonal to the solidification direction includes a single crystal part 11 consisting of a single crystal and a poly-crystal part 12 consisting of a plurality of crystal grains formed around the single crystal part 11; and the area rate of the single crystal part 11 is 25% or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a silicon ingot having a unidirectional solidification structure and a method for producing the silicon ingot. [Background technology]

[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 in order to suppress the occurrence of contamination within the apparatus. Here, the above-mentioned silicon members are manufactured from silicon ingots having a unidirectional solidification structure, for example. Silicon ingots having a unidirectional solidification structure are widely used as materials for parts used in semiconductor manufacturing equipment such as sputtering equipment for liquid crystal, plasma etching equipment, and CVD equipment, as disclosed in Patent Document 1, for example.

[0003] Furthermore, as shown in Patent Document 2, suppressing abnormal discharge and particle generation is an issue in plasma processing apparatuses. Here, inclusions contained in silicon members can cause abnormal discharge if the members are consumed and exposed on the surface during the dry etching process, and can cause particle generation if the members are consumed and detached from the members.

[0004] Furthermore, when components are consumed during a dry etching process, etching rates differ between different crystals, and the grain boundaries are more selectively consumed, which may cause cracks in the components or particles. For this reason, it is preferable to manufacture 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 growing single crystals from each of the seed crystals by unidirectionally solidifying the silicon melt in the crucible. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4531435 [Patent Document 2] JP 2015-106652 A [Patent Document 3] Patent No. 6233114 Summary of the Invention [Problem to be solved by the invention]

[0007] In the production of silicon ingots, there is a risk of cracks occurring when removing the silicon ingot from the crucible after casting. For this reason, in the past, a release agent was sometimes applied to the inner wall of the crucible in order to separate the silicon ingot from the crucible. Normally, silicon nitride (silicon nitride film) is used as the release agent, so the nitrogen concentration in the ingot cannot be sufficiently reduced, and it was not possible to prevent the inclusion of different types of inclusions such as silicon nitride from being mixed in. In addition, when a carbon member is disposed inside the manufacturing device, there was a risk of the inclusion of different types of inclusions such as silicon carbide being mixed in. Here, if dissimilar inclusions are present in the silicon melt during unidirectional solidification, the crystal will grow from these dissimilar inclusions, which may prevent the single crystal from growing sufficiently.

[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 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. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors conducted intensive research and discovered that by giving a crucible used in producing a silicon ingot a specific structure, it is possible to satisfactorily remove the silicon ingot without using a release agent such as silicon nitride, while sufficiently suppressing 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 unidirectionally solidifying it.

[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, and the number density of dissimilar inclusions having a circle equivalent diameter of 3 μm or more is 0.01 pieces / cm 2 The alloy is characterized in that, 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.

[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 content is less than 100%, the inclusion of different types of inclusions is suppressed, making it particularly suitable as a material for silicon components that can suppress contamination, abnormal discharge, and particle generation. Furthermore, since the area ratio of the single crystal portion consisting of a single crystal is set to 25% or more in a cross section perpendicular to the solidification direction, it is possible to manufacture a silicon component using a single crystal portion without grain boundaries. The number density of different inclusions is measured by observing a cross section of a silicon ingot.

[0012] A silicon ingot according to a second aspect of the present invention is the silicon ingot according to the first aspect of the present invention, characterized in that the diameter of the inscribed circle of the single crystal portion in a cross section perpendicular to the solidification direction is 300 mm or more. According to the silicon ingot of aspect 2 of the present invention, the diameter of the inscribed circle of the single crystal portion is 300 mm or more, so that 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 the third aspect of the present invention is the silicon ingot of the first or second aspect of the present invention, wherein the nitrogen concentration is 1.0×10 14 It is characterized by being less than atoms / cc. According to the silicon ingot of the third aspect of the present invention, the nitrogen concentration is 1.0×10 14 Since the concentration is limited to less than atoms / cc, the inclusion of different types 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 heterogeneous inclusions made of nitrides can be suppressed, and a silicon ingot having a sufficiently high area ratio of single crystal portions can be obtained.

[0014] The silicon ingot of the fourth aspect of the present invention is a silicon ingot of any one of the first to third aspects of the present invention, wherein the carbon concentration is 3.5×10 17 It is characterized by being less than atoms / cc. According to the silicon ingot of the fourth aspect of the present invention, the carbon concentration is 3.5×10 17 Since the concentration is limited to less than atoms / cc, the inclusion of different inclusions made of carbides 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. Furthermore, during unidirectional solidification, crystal growth originating from heterogeneous inclusions made of carbides can be suppressed, and a silicon ingot having a sufficiently high area ratio of single crystal portions can be obtained.

[0015] A method for producing a silicon ingot according to a fifth aspect of the present invention is a method for producing a silicon ingot according to any one of the first to fourth aspects of the present invention, 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; the crucible has a mold, and on an 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 laminated in the thickness direction, and the total number of the laminated slurry layers and stucco layers is 6 or more.

[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. This makes it possible to suppress the occurrence of cracks in the silicon ingot when the silicon ingot is removed, and also makes it possible to suppress the occurrence of foreign inclusions such as silicon nitride and silicon carbide during casting, making it possible to produce a silicon ingot in which these foreign inclusions are sufficiently reduced.

[0017] The method includes a seed crystal plate positioning step of positioning a seed crystal plate at the bottom of the crucible, a raw material loading 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 in which the seed crystal plate is placed upward. This makes it possible to suppress crystal growth starting from heterogeneous inclusions, and to produce a silicon ingot with a high area ratio of single crystal portions. Effect of the Invention

[0018] 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 can be used as a material for large components, and a method for manufacturing the silicon ingot. [Brief description of the drawings]

[0019] [Figure 1] 1A and 1B are schematic explanatory diagrams of a silicon ingot according to an embodiment of the present invention, in which (a) is a cross-sectional view taken along the casting direction, and (b) is a cross-sectional view taken along a direction perpendicular to the casting direction. [Diagram 2] FIG. 1 is a schematic explanatory diagram showing an example of a silicon ingot manufacturing apparatus used when manufacturing a silicon ingot according to an embodiment of the present invention. [Diagram 3] FIG. 1 is a schematic explanatory diagram of a crucible used in producing a silicon ingot according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, a silicon ingot and a method for manufacturing a silicon ingot according to an embodiment of the present invention will be described with reference to the attached drawings. Note that the following embodiments are specifically described to better understand the gist of the invention, and do not limit the present invention unless otherwise specified.

[0021] A silicon ingot 10 according to an embodiment of the present invention is made of a directionally solidified structure, and has a circular cross section perpendicular to the solidification direction, as shown in FIG. In a cross section perpendicular to the solidification direction, it has a single crystal portion 11 consisting of a single crystal and a polycrystalline portion 12 consisting of a plurality of crystal grains formed around this single crystal portion 11, and the area ratio of the single crystal portion 11 is 25% or more.

[0022] As shown in FIG. 1(a), the proportion of the single crystal portion 11 decreases toward the top of the silicon ingot 10. In this embodiment, the area ratio of the single crystal portion 11 was measured in a cross section 15 mm from the top of the directionally solidified silicon ingot 10. The area ratio of the single crystal portion 11 is preferably 25% or more, and more preferably 30% or more.

[0023] In the silicon ingot 10 according to the present 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 to be less than this. Here, the number density of the dissimilar inclusions is confirmed by taking an observation sample from the silicon ingot 10, mirror-polishing the observation sample, and observing it. In this embodiment, the observation sample is taken from the upper part of the directionally solidified silicon ingot 10, and the number density of the dissimilar inclusions is measured. The dissimilar inclusions are considered to include silicon nitride and silicon carbide. The number density of heterogeneous inclusions with a circle equivalent diameter of 3 μm or more is 0.001 pieces / cm 2 It is more preferable that:

[0024] 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 is preferably 300 mm or more. In this embodiment, the diameter of the inscribed circle of the single crystal portion 11 in the cross section at a position 15 mm from the top of the directionally solidified silicon ingot 10 is specified. The diameter of the inscribed circle of the single crystal portion 11 is preferably 200 mm or more, and more preferably 300 mm or more.

[0025] In the silicon ingot 10 of this embodiment, the nitrogen concentration is 1.0×10 14 It is preferable that the concentration is less than 5.0×10 atoms / cc. 13 More preferably, it is less than atoms / cc. In this embodiment, the nitrogen concentration of the silicon ingot 10 is measured by SIMS (Secondary Ion Mass Spectrometry).

[0026] Furthermore, in the silicon ingot 10 of this embodiment, the carbon concentration is 3.5×10 17 It is preferable that the concentration is less than 2.0×10 atoms / cc. 17 More preferably, it 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).

[0027] Next, a silicon ingot manufacturing apparatus 20 used in manufacturing a silicon ingot according to the present embodiment will be described with reference to FIG. This silicon ingot manufacturing apparatus 20 includes a crucible 30 in which silicon melt L is stored, a chill plate 22 on which this crucible 30 is placed, a lower heater 23 that supports this chill plate 22 from below, and an upper heater 24 disposed above the crucible 30. Also, a heat insulating material 25 is provided around the crucible 30. The chill plate 22 has a hollow structure, and is configured so that Ar gas is supplied to the inside through a supply pipe 26 .

[0028] Here, the crucible 30 used in the method for producing a silicon ingot of this embodiment will be described with reference to FIG. 3 includes a mold 31 and a silica layer 32 formed on the inner surface of the mold 31. The mold 31 is made of, for example, quartz or graphite.

[0029] As shown in FIG. 3, the silica layer 32 is provided inside the mold 31, and has a structure in which 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 laminated in the thickness direction, with the slurry layer 33 being the innermost layer that comes into contact with the silicon ingot, and the total number of laminated slurry layers 33 and stucco layers 34 being 6 or more. In this embodiment, as shown in FIG. 3, a slurry layer 33 is formed at a location in contact with the inner surface of the mold 31, and the total number of layers of the stacked slurry layers 33 and stucco layers 34 is six.

[0030] Here, if the total number of the stacked slurry layers 33 and stucco layers 34 is less than six, the stress applied when removing the silicon ingot may not be fully relieved, and the silicon ingot may crack. For this reason, in this embodiment, the total number of the stacked slurry layers 33 and stucco layers 34 is set to six or more. Furthermore, by setting the average particle size of the fine silica powder within the range of 1 μm to 200 μm, it can be mixed with colloidal silica to form a slurry, and the above-mentioned slurry layer 33 can be formed satisfactorily. Furthermore, by setting the average particle size of the coarse silica powder to 100 μm or more and 1000 μm or less, the surface roughness does not become larger than necessary, and separation from the mold 31 becomes easy.

[0031] 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.

[0032] Furthermore, the thickness of the slurry layer 33 is preferably 0.1 mm or more, and more preferably 0.2 mm or more, while the thickness of the slurry layer 33 is preferably 5 mm or less, and more preferably 4 mm or less. The thickness of the stucco layer 34 is preferably 0.1 mm or more, and more preferably 0.2 mm or more, while the thickness of the stucco layer 34 is preferably 5 mm or less, and more preferably 4 mm or less.

[0033] Next, a method for producing a silicon ingot 10 according to this embodiment using a silicon ingot production apparatus 20 shown in FIG. 2 will be described.

[0034] 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 may be taken from the single crystal portion 11 of the silicon ingot 10 of this embodiment. Although the crystal grows according to the crystal plane orientation of the plate surface of the seed crystal plate, there is no particular limitation on the crystal plane orientation of the plate surface of the seed crystal plate.

[0035] Next, silicon raw material is charged into the crucible 30 in which the seed crystal plate is placed (raw material charging step). Here, as the silicon raw material, a lump-like material called a "chunk" obtained by crushing high-purity silicon of 11N (purity 99.999999999) is used. The grain size of this lump-like silicon raw material is, for example, 30 mm to 100 mm.

[0036] Next, the silicon raw material charged in the crucible 30 is heated by passing electricity through 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 melt completely, and the upper chunk of the seed crystal plate is mainly melted from above (silicon raw material melting process). As a result, silicon melt is stored in the crucible 30. If the seed crystal plate melts completely, liquid phase epitaxial growth is not possible, and many crystal nuclei are generated on the bottom surface of the crucible, resulting in polycrystals and poor growth of single crystals. For this reason, it is necessary to control the temperature so that the seed crystal plate does not melt completely.

[0037] Next, the amount of electricity supplied to the lower heater 23 is further reduced, and Ar gas is supplied into the inside of the chill plate 22 via the supply pipe 26. This cools the bottom of the crucible 30. Furthermore, by gradually reducing the electricity supplied to the upper heater 24, the silicon melt in the crucible 30 grows into a crystal that inherits the crystal orientation of the seed crystal plate placed at the bottom of the crucible 30, and a silicon ingot 10 having a unidirectional solidification structure and a single crystal portion is obtained (unidirectional solidification process). Here, the casting conditions are preferably adjusted so that the solidification rate is within the range of 5 mm / h to 20 mm / h.

[0038] 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.

[0039] According to the silicon ingot 10 of this embodiment having the above-mentioned configuration, the number density of different inclusions having a circle equivalent diameter of 3 μm or more is 0.01 pieces / cm 2 Since the content is less than 100%, the inclusion of different types of inclusions is suppressed, making it 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, it has a single crystal portion 11 consisting of a single crystal, and a polycrystalline portion 12 consisting of a plurality of crystal grains formed around this single crystal portion 11, and the area ratio of the single crystal portion 11 is 25% or more, so it is possible to manufacture a silicon member using a single crystal portion without crystal grain boundaries.

[0040] In the silicon ingot 10 of this embodiment, when 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.

[0041] In the silicon ingot 10 of this embodiment, the nitrogen concentration is 1.0×10 14 When it is limited to less than atoms / cc, the inclusion of different 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.

[0042] In the silicon ingot 10 of this embodiment, the carbon concentration is 3.5×10 17 When the content is limited to less than atoms / cc, the inclusion of different types of 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.

[0043] According to the silicon ingot manufacturing method 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.

[0044] 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 loading 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. This makes it possible to suppress crystal growth starting from heterogeneous inclusions, and to produce a silicon ingot 10 having a high area ratio of the single crystal portion 11.

[0045] Although 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 concept of the invention. In this embodiment, as shown in FIG. 2, the total number of stacked slurry layers 33 and stucco layers 34 is described as six, but this is not limited thereto, and the total number of layers may be seven or more.

[0046] The outermost layer on the mold 31 side may be a slurry layer 33 or a stucco layer 34, but is preferably a slurry layer 33. Furthermore, the innermost layer on the silicon melt L side may be a slurry layer 33 or a stucco layer 34, but is preferably the slurry layer 33. EXAMPLES

[0047] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0048] (Example of the present invention) A quartz mold having dimensions of inner diameter: 600 mm, outer diameter: 650 mm, and depth: 550 mm was prepared. Then, the slurry layer forming step of forming a slurry layer by applying or spraying a slurry consisting of fine silica powder and colloidal silica having an average particle size of 1 μm to 200 μm was repeated four times, and the stucco layer forming step of forming a stucco layer by scattering coarse silica powder having an average particle size of 100 μm to 1000 μm was repeated three times, so that the total number of the slurry layers and stucco layers was 7. After that, a firing step was performed under the conditions of atmosphere: N2, heating temperature: 800°C, and holding time: 8 hours, to manufacture a crucible with a silica layer formed on the inner surface of the mold. The total thickness of the slurry layers and stucco layers (silica layer thickness) was 3 mm.

[0049] A seed crystal plate was placed on the bottom surface of the crucible, and the silicon raw material was then 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 Fig. 2. The silicon raw material was melted by applying electricity to the upper heater and the lower heater of the silicon ingot production apparatus. 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 melt completely.

[0050] Next, the amount of current flowing through the lower heater is further reduced, and Ar gas is supplied through a supply pipe into the inside of the chill plate to cool the bottom of the crucible. By gradually reducing the current flowing through the upper heater, the silicon melt in the crucible grows crystals while inheriting the crystal orientation of the seed crystal plate placed at the bottom of the crucible, and a silicon ingot 10 having a unidirectional solidification structure and a single crystal portion is produced.

[0051] (Comparative Example) A quartz mold having dimensions of inner diameter: 600 mm, outer diameter: 650 mm, and depth: 550 mm was prepared. A silicon nitride film having a thickness of 1 mm was then formed as a mold release agent on the inner surface of the mold to produce a crucible for use in the comparative example.

[0052] A seed crystal plate was placed on the bottom surface of the crucible, and the silicon raw material was then loaded into the crucible with the seed crystal plate placed therein. Then, similarly to the present invention, a silicon ingot was produced using the silicon ingot production apparatus shown in FIG.

[0053] Measurement samples were taken from each of the silicon ingots at a height of 15 mm from the top surface, and the number density, nitrogen concentration, and carbon concentration of foreign inclusions with a circle equivalent diameter of 3 μm or more were measured. The measurement results are shown in Table 1.

[0054] The number density of foreign inclusions was calculated by mirror-polishing the observation surface of the measurement sample and visually observing the observation surface under an environment with a luminous intensity of 1000 to 2000 lx to calculate the number density of foreign inclusions with a circle equivalent diameter of 3 μm or more. The nitrogen concentration was measured by SIMS (Secondary Ion Mass Spectroscopy), and the carbon concentration was measured by FT-IR (Fourier Transform Infrared Spectroscopy). The calculation of the number density of different inclusions, the measurement of the nitrogen concentration, and the measurement of the carbon concentration were performed using samples taken from the same height position of the same silicon ingot.

[0055] 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.

[0056] [Table 1]

[0057] 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 and carbon concentrations in the produced silicon ingot were high, and the number density of foreign inclusions was 5.3 pieces / cm 2 and contained a large amount of foreign inclusions. In addition, 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 small at 5%, and the diameter of the inscribed circle of the single crystal portion was 50 mm, making it difficult to produce large silicon components using the single crystal portion.

[0058] In contrast, in the present invention, a crucible was used in which slurry layers and stucco layers were alternately laminated on the inner surface of the mold, the innermost layer was a slurry layer, and the total number of the laminated slurry layers and stucco layers was 6. 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 The grain size was less than 1 mm and almost no foreign inclusions were present. A seed crystal plate was placed at the bottom of the crucible and unidirectional solidification was performed. In a 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 large silicon components using the single crystal portion.

[0059] 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 and which has a high proportion of single crystal portions and can be used as a material for large components, as well as a method for manufacturing a silicon ingot. [Explanation of symbols]

[0060] 10 Silicon Ingot 11 Single crystal section 12 Polycrystalline part 30 Crucible 31 Mold 33 Slurry layer 34 Stucco Layer

Claims

1. A silicon ingot having a unidirectional solidification structure and a circular cross section perpendicular to the solidification direction, The number density of foreign inclusions with a circle equivalent diameter of 3 μm or more is 0.01 pieces / cm ２ is less than 1. A silicon ingot, characterized in that, 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.

2. 2. The silicon ingot according to claim 1, wherein the diameter of an inscribed circle of the single crystal portion in a cross section perpendicular to the solidification direction 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 the steps of: The method includes 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, 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 or more and 200 μm or less and a stucco layer made of coarse silica powder having an average particle size of 100 μm or more and 1000 μm or less are alternately laminated in the thickness direction, and the total number of the laminated slurry layers and stucco layers is 6 or more.

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