Silicon ingot

Abstract

To provide a silicon ingot capable of using as a material of a silicon member capable of achieving a long life by suppressing a generation of a local corrosion even in a case of using under a corrosion environment.SOLUTION: A silicon ingot 10 composed of a unidirectional solidification structure has a single crystal region 11 in a center part on a cross-sectional plane orthogonal to a solidification direction. In an outer peripheral side of the single crystal region 11, a corresponding grain boundary region 12 which is constituted with multiple crystal grains and of which a corresponding grain boundary length ratio to a total crystal grain length is 80% or more is formed. In a cross-sectional plane orthogonal to a solidification direction, an area ratio of the single crystal region 11 preferably is 25% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a silicon ingot having a unidirectionally solidified structure. [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 to prevent contamination within the apparatus. Here, the silicon members are manufactured from, for example, silicon ingots with a unidirectional solidification structure. Silicon ingots having a unidirectionally solidified structure are widely used as materials for parts used in semiconductor manufacturing equipment such as sputtering equipment for liquid crystal displays, plasma etching equipment, and CVD equipment, as shown 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 worn out and exposed to the surface during the dry etching process, and can also cause particle generation if 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 in the components or particles. For this reason, it is preferable to fabricate 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, it is necessary to use polycrystalline silicon ingots as the material for large-sized silicon members. Furthermore, Patent Document 3 proposes a columnar crystal silicon ingot (so-called mono-like silicon) 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] Japanese Patent Application Laid-Open No. 2015-106652 [Patent Document 3] Patent No. 6233114 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in polycrystalline silicon and mono-like silicon, grain boundaries exist, and there is a risk that the grain boundaries will corrode preferentially in a corrosive environment (plasma and corrosive chemicals). If the grain boundaries corrode preferentially and form depressions, there is a risk that corrosion will progress in these depressions. This could result in cracks in the silicon member or the generation of particles.

[0008] The present invention has been made in view of the above-mentioned circumstances, and aims to provide a silicon ingot that can be used as a material for silicon members that can suppress the occurrence of localized corrosion and achieve a long life even when used in a corrosive environment. [Means for solving the problem]

[0009] In order to solve the above problems, the inventors conducted extensive research and discovered that at coincidence boundaries, atoms are partially bonded to each other, the bonding strength of the grain boundaries is stronger than that of random grain boundaries, and preferential corrosion of the grain boundaries can be suppressed.

[0010] The present invention has been made based on the above-mentioned findings, and a silicon ingot according to a first aspect of the present invention is a silicon ingot made of a unidirectionally solidified structure, characterized in that, in a cross section perpendicular to the solidification direction, it has a single crystal region at the center, and on the outer periphery of the single crystal region, a CSU region is formed which is made up of a plurality of crystal grains and in which the ratio of the CSU length to the total crystal grain boundary length is 80% or more.

[0011] According to the silicon ingot of the first aspect of the present invention, in a cross section perpendicular to the solidification direction, a single crystal region is formed in the center, and a coincidence grain boundary region consisting of a plurality of crystal grains is formed on the outer periphery of this single crystal region, and the ratio of the coincidence grain boundary length to the total crystal grain boundary length is 80% or more. Therefore, the length of the crystal grain boundaries present in a silicon member manufactured using this silicon ingot as a material can be kept short, and preferential corrosion of the crystal grain boundaries can be suppressed even in a corrosive environment. Therefore, the progress of localized corrosion can be suppressed, and the service life can be extended.

[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 area ratio of the single crystal region in a cross section perpendicular to the solidification direction is 25% or more. According to the silicon ingot of aspect 2 of the present invention, the area ratio occupied by the single crystal region is 25% or more, so that the proportion of single crystal region without grain boundaries is increased, and the length of grain boundaries present in a silicon component manufactured using this silicon ingot as a material can be further reduced.

[0013] A silicon ingot according to a third aspect of the present invention is the silicon ingot according to the first or second aspect of the present invention, characterized in that the diameter of the inscribed circle of the single crystal region in a cross section perpendicular to the solidification direction is 300 mm or more. According to the silicon ingot of the third aspect of the present invention, the diameter of the inscribed circle of the single crystal region is set to 300 mm or more, so that the proportion of single crystal regions without grain boundaries increases, and the length of grain boundaries present in a silicon component manufactured using this silicon ingot as a material can be further reduced.

[0014] A silicon ingot according to a fourth aspect of the present invention is a silicon ingot according to any one of the first to third aspects of the present invention, characterized in that the diameter of the inscribed circle of the corresponding grain boundary region in a cross section perpendicular to the solidification direction is 400 mm or more. According to the silicon ingot of aspect 4 of the present invention, the diameter of the inscribed circle of the corresponding grain boundary region is 400 mm or more. Therefore, a large silicon component having a diameter of 400 mm or more manufactured using this silicon ingot as a material will be composed of a single crystal region and a corresponding grain boundary region, and it will be possible to reliably suppress preferential corrosion of the grain boundary even in a corrosive environment.

[0015] A silicon ingot according to a fifth aspect of the present invention is the silicon ingot according to any one of the first to fourth aspects of the present invention, characterized in that the proportion of Σ3 grain boundaries in the coincidence grain boundary region is 80% or more. According to the silicon ingot of aspect 5 of the present invention, the proportion of Σ3 grain boundaries in the coincidence grain boundaries is 80% or more, and among the coincidence grain boundaries, there are many Σ3 grain boundaries which have a large number of atomic bonds and a high grain boundary bonding strength, which further prevents preferential corrosion of the grain boundaries even in a corrosive environment.

[0016] A silicon ingot according to a sixth aspect of the present invention is the silicon ingot according to any one of the first to fifth aspects of the present invention, characterized in that the average crystal grain size in the coincidence grain boundary region is 10 mm or more. According to the silicon ingot of the sixth aspect of the present invention, the average crystal grain size in the coincidence grain boundary region is set to 10 mm or more, so that there are few grain boundaries, and the progress of localized corrosion can be suppressed. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a silicon ingot that can be used as a material for silicon members that can suppress the occurrence of localized corrosion and achieve a long life even when used in a corrosive environment. [Brief explanation of the drawings]

[0018] [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. [Figure 2] 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. FIG. [Figure 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 INVENTION

[0019] The present invention will be described below with reference to the accompanying drawings, in which: a silicon ingot according to an embodiment of the present invention is described in detail to facilitate a better understanding of the gist of the invention; however, unless otherwise specified, the present invention is not limited to the embodiments.

[0020] A silicon ingot 10 according to an embodiment of the present invention is made of a unidirectionally solidified structure, and has a circular cross section perpendicular to the solidification direction, as shown in FIG. A silicon ingot 10 according to an embodiment of the present invention has a single crystal region 11 consisting of a single crystal at the center of a cross section perpendicular to the solidification direction, and a coincidence grain boundary region 12 consisting of a plurality of crystal grains is formed on the outer periphery of this single crystal region 11, in which the ratio of the coincidence grain boundary length to the total crystal grain boundary length is 80% or more.

[0021] In the silicon ingot 10 of this embodiment, the area ratio of the single crystal region 11 in a cross section perpendicular to the solidification direction is preferably 25% or more. As shown in FIG. 1(a), the proportion of the single crystal region 11 in the silicon ingot 10 decreases toward the top. In this embodiment, the area ratio of the single crystal region 11 was measured in a cross section 15 mm from the top of the directionally solidified silicon ingot 10.

[0022] In the silicon ingot 10 of this embodiment, the diameter of the inscribed circle of the single crystal region 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 region 11 in the cross section at a position 15 mm from the top of the directionally solidified silicon ingot 10 is specified.

[0023] In the silicon ingot 10 of this embodiment, the diameter of the inscribed circle of the CCS boundary region 12 in a cross section perpendicular to the solidification direction is preferably 400 mm or more. As shown in FIG. 1 , the inscribed circle of the CCS boundary region 12 in this embodiment is the inscribed circle in the region from the center of the cross section perpendicular to the solidification direction to the outer periphery of the CCS boundary region 12 (i.e., the region including both the single crystal region 11 and the CCS boundary region 12). In this embodiment, the diameter of the inscribed circle of the coincidence grain boundary region 12 in the cross section at a position 15 mm from the top of the directionally solidified silicon ingot 10 is specified.

[0024] Furthermore, in the silicon ingot 10 of this embodiment, the proportion of Σ3 grain boundaries in the coincidence grain boundary region 12 is preferably 80% or more. In the silicon ingot 10 of this embodiment, the average crystal grain size in the coincidence grain boundary region 12 is preferably 10 mm or more.

[0025] The reason why the crystal structure of the silicon ingot 10 according to this embodiment is defined as described above will be explained below.

[0026] (single crystal region and coincidence grain boundary region) At coincidence boundaries, atoms are partially bonded to each other, and therefore the bonding strength of the grain boundaries is stronger than that of random grain boundaries, making it possible to suppress preferential corrosion at the grain boundaries. Therefore, in the silicon ingot 10 of this embodiment, a single crystal region 11 is present in the center of a cross section perpendicular to the solidification direction, and a coincidence grain boundary region 12, in which the ratio of the coincidence grain boundary length to the total grain boundary length is 80% or more, is present on the outer periphery of this single crystal region 11. As a result, when a silicon member made from this silicon ingot 10 is used in a corrosive environment, preferential corrosion of the grain boundaries can be suppressed, and the lifespan can be extended.

[0027] (Area ratio occupied by single crystal region 11: 25% or more) In the silicon ingot 10 of this embodiment, if the area ratio of the single crystal region 11 in a cross section perpendicular to the solidification direction is as large as 25% or more, the length of the grain boundaries present in a silicon member made from this silicon ingot 10 becomes shorter, making it possible to further suppress preferential corrosion of the grain boundaries when used in a corrosive environment. The area ratio of the single crystal region 11 in the cross section perpendicular to the solidification direction is more preferably 30% or more, and even more preferably 40% or more.

[0028] (Diameter of the inscribed circle of the single crystal region 11: 300 mm or more) In the silicon ingot 10 of this embodiment, when the diameter of the inscribed circle of the single crystal region 11 in the cross section perpendicular to the solidification direction is 300 mm or more, even if a silicon component having a diameter of 300 mm or more is produced, the length of the grain boundaries present in the silicon component becomes short, making it possible to further suppress preferential corrosion of the grain boundaries when used in a corrosive environment. In this embodiment, the diameter of the inscribed circle of the single crystal region 11 in the cross section perpendicular to the solidification direction is more preferably 350 mm or more, and even more preferably 400 mm or more.

[0029] (Diameter of the inscribed circle of the corresponding grain boundary region 12: 400 mm or more) In the silicon ingot 10 of this embodiment, when the diameter of the inscribed circle of the corresponding grain boundary region 12 located on the outer periphery of the single crystal region 11 in a cross section perpendicular to the solidification direction is 400 mm or more, even if a silicon member having a diameter of 400 mm or more is produced, the length of the grain boundaries present in the silicon member becomes short, making it possible to further suppress preferential corrosion of the grain boundaries when used in a corrosive environment. In this embodiment, the diameter of the inscribed circle of the correspondence grain boundary region 12 in the cross section perpendicular to the solidification direction is more preferably 450 mm or more, and even more preferably 500 mm or more.

[0030] (Proportion of Σ3 grain boundaries in the coincidence grain boundary region 12: 80% or more) At the Σ3 grain boundary, one in three atoms are bonded to each other, and since the number of atomic bonds is greater than that of other coincidence grain boundaries and the grain boundary bonding strength is strong, preferential corrosion of the grain boundary is further suppressed even in corrosive environments. Therefore, in this embodiment, it is preferable that the proportion of Σ3 grain boundaries in the coincidence grain boundary region 12 is 80% or more. In this embodiment, the proportion of Σ3 grain boundaries in the coincidence grain boundary region 12 is more preferably 85% or more, and further preferably 90% or more.

[0031] (Average grain size in the coincidence grain boundary region 12: 10 mm or more) In the silicon ingot 10 of this embodiment, when the average crystal grain size in the coincidence grain boundary region 12 is large, such as 10 mm or more, the length of the crystal grain boundary becomes short, and the progression of localized corrosion in a corrosive environment can be further suppressed. In this embodiment, the average crystal grain size in the coincidence grain boundary region 12 is more preferably 15 mm or more, and further preferably 20 mm or more.

[0032] Next, a silicon ingot manufacturing apparatus 20 used to manufacture the silicon ingot 10 according to this 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. In addition, 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 .

[0033] Here, the crucible 30 used in the method for producing a silicon ingot according to this embodiment will be described with reference to FIG. 3 has 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.

[0034] As shown in Figure 3, silica layer 32 is provided inside mold 31, and has a structure in which slurry layers 33 made of fine silica powder and colloidal silica with an average particle size of 1 μm or more and 200 μm or less, and stucco layers 34 made of coarse silica powder with an average particle size of 100 μm or more and 1000 μm or less are alternately stacked in the thickness direction, with slurry layer 33 being the innermost layer that comes into contact with the silicon ingot, and the total number of stacked 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 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.

[0035] If the total number of 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, which may result in cracking of the silicon ingot. For this reason, in this embodiment, the total number of 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.

[0036] In this embodiment, the thickness of silica layer 32 (total thickness of 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 silica layer 32 (total thickness of laminated slurry layer 33 and stucco layer 34) is preferably 30 mm or less, and more preferably 25 mm or less.

[0037] 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.

[0038] Next, a method for manufacturing a silicon ingot 10 according to this embodiment using a silicon ingot manufacturing apparatus 20 shown in FIG. 2 will be described.

[0039] 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 region 11 of the silicon ingot 10 of this embodiment. Although the crystal grows depending on the crystal plane orientation of the surface of the seed crystal plate, there are no particular limitations on the crystal plane orientation of the surface of the seed crystal plate.

[0040] Next, silicon raw material is charged into the crucible 30 in which the seed crystal plate is placed (raw material charging process). Here, the silicon raw material is a lump called a "chunk" obtained by crushing high-purity silicon of 11N (purity 99.999999999). The particle size of this lump silicon raw material is, for example, 30 mm to 100 mm.

[0041] Next, the silicon raw material charged in the crucible 30 is heated by passing current 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 will not occur, and many crystal nuclei will form on the bottom 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.

[0042] 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 crystal growth while inheriting 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 region 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.

[0043] In the unidirectional solidification process, since the temperature gradient of the silicon melt becomes stronger in the vertical direction, which increases the proportion of coincidence grain boundaries in the polycrystalline region, in this embodiment, it is preferable to control the outputs of the upper heater 24 and the lower heater 23 so that the temperature difference between the upper part (top of the ingot) and the lower part (bottom of the ingot) in the furnace is 70° C. or more. In this embodiment, the temperature measurement positions in the furnace at this temperature difference are near the top and near the bottom of the silicon ingot. The temperature difference between the top and bottom of the furnace is more preferably 80° C. or more, and even more preferably 100° C. or more. There is no particular upper limit to the temperature difference between the top and bottom of the furnace, but it may be 250° C. or less, and is preferably 150° C. or less.

[0044] 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.

[0045] The silicon ingot 10 of this embodiment configured as described above has a single crystal region 11 in the center in a cross section perpendicular to the solidification direction, and a coincidence grain boundary region 12 consisting of multiple crystal grains is formed on the outer periphery of this single crystal region 11, and the ratio of the coincidence grain boundary length to the total crystal grain boundary length is 80% or more. This makes it possible to shorten the crystal grain boundary length in a silicon member manufactured using this silicon ingot 10 as a material, and to prevent preferential corrosion of the crystal grain boundaries even in a corrosive environment. This makes it possible to suppress the progression of localized corrosion and extend the service life.

[0046] In the silicon ingot 10 of this embodiment, when the area ratio occupied by the single crystal region 11 in a cross section perpendicular to the solidification direction is 25% or more, the proportion of single crystal regions without grain boundaries increases, and the length of the grain boundaries present in a silicon component made from this silicon ingot 10 can be further reduced, thereby suppressing the progression of localized corrosion when used in a corrosive environment and achieving a longer service life.

[0047] In the silicon ingot 10 of this embodiment, when the diameter of the inscribed circle of the single crystal region 11 in a cross section perpendicular to the solidification direction is 300 mm or more, even if a large silicon component having a diameter of 300 mm or more is manufactured using this silicon ingot 10 as a material, the proportion of single crystal regions without grain boundaries in the silicon component will be high, and the length of the grain boundaries present in the silicon component can be further reduced. This makes it possible to suppress the progression of localized corrosion when used in a corrosive environment and achieve a longer service life.

[0048] In the silicon ingot 10 of this embodiment, if the diameter of the inscribed circle of the CBC region 12 in a cross section perpendicular to the solidification direction is 400 mm or more, even if a large silicon component having a diameter of 400 mm or more is manufactured using this silicon ingot 10 as a material, the silicon component can be composed of the single crystal region 11 and the CBC region 12, and the length of the crystal grain boundaries present in the silicon component can be further reduced. This makes it possible to suppress the progression of localized corrosion when used in a corrosive environment, thereby achieving a longer service life.

[0049] In the silicon ingot 10 of this embodiment, when the proportion of Σ3 grain boundaries in the coincidence grain boundary region 12 is 80% or more, there are many Σ3 grain boundaries among the coincidence grain boundaries, which have a large number of atomic bonds and strong grain boundary bonding strength.Even when a silicon component made from this silicon ingot 10 is used in a corrosive environment, preferential corrosion of the grain boundaries can be further suppressed, thereby achieving a longer lifespan.

[0050] In the silicon ingot 10 of this embodiment, when the average crystal grain size in the corresponding grain boundary region 12 is 10 mm or more, there are few grain boundaries, and even when a silicon component made from this silicon ingot 10 is used in a corrosive environment, the progression of localized corrosion can be further suppressed, thereby achieving a longer service life.

[0051] Although one embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention. In this embodiment, it has been described that only a corresponding grain boundary region is formed on the outer periphery of the single crystal region, but this is not limited to this, and a polycrystalline grain boundary region (where the proportion of corresponding grain boundaries in the crystal grain boundaries is less than 80%) may be formed on the outer periphery of the corresponding grain boundary region.

[0052] 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. The innermost layer on the silicon melt L side may be either a slurry layer 33 or a stucco layer 34, but is preferably the slurry layer 33. [Example]

[0053] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0054] (Examples of the present invention and comparative examples) A quartz mold having dimensions of an inner diameter of 600 mm, an outer diameter of 650 mm, and a depth of 500 mm was prepared. Then, a slurry layer formation process was performed four times by applying or spraying a slurry composed of fine silica powder and colloidal silica with an average particle size of 1 μm to 200 μm to form a slurry layer, and a stucco layer formation process was performed three times by scattering coarse silica powder with an average particle size of 100 μm to 1000 μm to form a stucco layer, alternating until a total of seven slurry and stucco layers were formed. A firing process was then performed under the conditions of an N2 atmosphere, 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 and stucco layers (silica layer thickness) was 3 mm.

[0055] A seed crystal plate was placed on the bottom of the crucible, and 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 Figure 2. The silicon raw material was heated by passing electricity through the upper and lower heaters of the silicon ingot production apparatus, and 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.

[0056] Next, the current 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 to the upper heater, the silicon melt in the crucible grew crystals that inherited the crystal orientation of the seed crystal plate placed at the bottom of the crucible, producing a silicon ingot with a unidirectional solidification structure and a single crystal region. At this time, the temperature difference between the top and bottom of the furnace was adjusted to the value shown in Table 1 by controlling the outputs of the upper and lower heaters.

[0057] A disk material was taken from the obtained silicon ingot at a height of 15 mm from the top surface and evaluated as follows. The measurement results are shown in Table 1.

[0058] An observation sample was taken from the obtained disk material having a diameter of 600 mm at a position of 175 mm radius (correspondence grain boundary region). The crystal structure was then observed using an EBSD device with a measurement area of ​​10 mm x 20 mm. Using the IPF map display, random grain boundaries and special grain boundaries (Σ3 grain boundaries, etc.) were identified from the grain boundary angles, and the length of each grain boundary was measured. The evaluation results are shown in Table 1.

[0059] The area ratio of the single crystal region, the diameter of the inscribed circle of the single crystal region, and the diameter of the inscribed circle of the coincidence grain boundary region were evaluated for the obtained disk material having a diameter of 600 mm. The evaluation results are shown in Table 1.

[0060] [Table 1]

[0061] In Comparative Example 1, no corresponding grain boundaries were present in the polycrystalline region of the cross section at a height of 15 mm from the upper surface of the silicon ingot.

[0062] In contrast, in Examples 1-3 of the present invention, in a cross section at a height of 15 mm from the top surface of the silicon ingot, a CSU region consisting of multiple crystal grains was formed on the outer periphery of the single crystal region, and the ratio of the CSU length to the total crystal grain boundary length was 80% or more.

[0063] As described above, it has been confirmed that the present invention can provide a silicon ingot that can be used as a material for silicon components that can suppress the occurrence of localized corrosion and achieve a long service life even when used in a corrosive environment. [Explanation of symbols]

[0064] 10 Silicon ingots 11 Single crystal region 12 Corresponding grain boundary region

Claims

1. A silicon ingot having a unidirectional solidification structure, In a cross section perpendicular to the solidification direction, a single crystal region is present in the center, A silicon ingot characterized in that a coincidence grain boundary region consisting of a plurality of crystal grains is formed on the outer periphery of the single crystal region, and the ratio of the coincidence grain boundary length to the total crystal grain boundary length is 80% or more.

2. 2. The silicon ingot according to claim 1, wherein the area ratio of the single crystal region in a cross section perpendicular to the solidification direction is 25% or more.

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

4. 3. The silicon ingot according to claim 1, wherein the diameter of an inscribed circle of the corresponding grain boundary region in a cross section perpendicular to the solidification direction is 400 mm or more.

5. 3. The silicon ingot according to claim 1, wherein the proportion of Σ3 grain boundaries in the coincidence grain boundary region is 80% or more.

6. 3. The silicon ingot according to claim 1, wherein the average crystal grain size in the coincidence grain boundary region is 10 mm or more.

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