Silicon ingot

Abstract

This silicon ingot 10 has a unidirectionally solidified structure. The silicon ingot is characterized in that, in a cross-section that is orthogonal to the solidification direction, a single crystal region 11 is formed at a center part, and a coincidence boundary region 12 that comprises a plurality of crystal grains and has a ratio of coincidence boundary length to total grain boundary length of at least 80% is formed on the outer circumferential side of the single crystal region 11. The area fraction of the single crystal region 11 in a cross-section that is orthogonal to the solidification direction is preferably at least 25%.

Description

Silicon ingot

[0001] This invention relates to a silicon ingot having a unidirectionally solidified structure. This application claims priority to Japanese Patent Application No. 2024-060427, filed on April 3, 2024, 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. Here, the silicon members are manufactured from, for example, silicon ingots with a unidirectional solidification structure. Note that, 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. 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 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, it is necessary to use a polycrystalline silicon ingot as a material for large-sized silicon components. Patent Document 3 also 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.

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

[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 the depressions. This could cause cracks in the silicon member or 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 components that can suppress the occurrence of localized corrosion and achieve a long life even when used in a corrosive environment.

[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 aspect 1 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 in the center, and a CSU region made of a plurality of crystal grains is formed on the outer periphery of the single crystal region, the CSU region having a ratio of the CSU length to the total crystal grain boundary length of 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 the area ratio of the single crystal regions in a cross section perpendicular to the solidification direction in the silicon ingot according to the first aspect of the present invention is 25% or more. According to the silicon ingot according to the second aspect of the present invention, the area ratio of the single crystal regions is 25% or more, so that the proportion of single crystal regions without grain boundaries is increased, and the length of grain boundaries present in a silicon member 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 characterized in that, in the silicon ingot according to the first or second aspect of the present invention, the diameter of the inscribed circle of the single crystal region is 300 mm or more in a cross section perpendicular to the solidification direction. According to the silicon ingot according to the third aspect of the present invention, the diameter of the inscribed circle of the single crystal region is 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 member produced 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 characterized in that, in the silicon ingot according to any one of the first to third aspects of the present invention, the diameter of the inscribed circle of the CBC region is 400 mm or more in a cross section perpendicular to the solidification direction. According to the silicon ingot according to the fourth aspect of the present invention, since the diameter of the inscribed circle of the CBC region is 400 mm or more, a large silicon member 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 CBC region, and it will be possible to reliably suppress preferential corrosion of the grain boundaries even in a corrosive environment.

[0015] A silicon ingot according to Aspect 5 of the present invention is characterized in that the proportion (area ratio) of Σ3 grain boundaries in the coincidence grain boundary region is 80% or more in the silicon ingot according to any one of Aspects 1 to 4 of the present invention. According to the silicon ingot according to Aspect 5 of the present invention, the proportion of Σ3 grain boundaries in the coincidence grain boundaries is 80% or more, and there are many Σ3 grain boundaries among the coincidence grain boundaries, which have a large number of atomic bonds and a high grain boundary bonding strength, and this further suppresses 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 CCU boundary region is 10 mm or more. According to the silicon ingot according to the sixth aspect of the present invention, since the average crystal grain size in the CCU boundary region is 10 mm or more, there are few grain boundaries, and the progress of localized corrosion can be suppressed.

[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.

[0018] Fig. 1 is a cross-sectional view along the casting direction of a silicon ingot according to an embodiment of the present invention. Fig. 2 is a cross-sectional view in a direction perpendicular to the casting direction of a silicon ingot according to an embodiment of the present invention. Fig. 3 is a schematic explanatory 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 schematic explanatory view of a crucible used when manufacturing a silicon ingot according to an embodiment of the present 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] 1A and 1B, a silicon ingot 10 according to an embodiment of the present invention has a unidirectionally solidified structure and a circular cross section perpendicular to the solidification direction. In the silicon ingot 10 according to an embodiment of the present invention, a single crystal region 11 consisting of a single crystal is present in the center of the cross section perpendicular to the solidification direction, and a CSI region 12 consisting of a plurality of crystal grains is formed on the outer periphery of the single crystal region 11, and the CSI region 12 has a ratio of the CSI boundary length to the total grain boundary length of 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. 1A, the area ratio of the single crystal region 11 decreases toward the top of the silicon ingot 10, but in this embodiment, the area ratio of the single crystal region 11 was measured in a cross section located 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 a 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 CCB region 12 in a cross section perpendicular to the solidification direction is preferably 400 mm or more. As shown in FIGS. 1A and 1B , the inscribed circle of the CCB 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 CCB region 12 (i.e., the region including both the single crystal region 11 and the CCB region 12). In this embodiment, the diameter of the inscribed circle of the CCB region 12 in a cross section located 15 mm from the top of the directionally solidified silicon ingot 10 is specified. The top of the silicon ingot 10 here refers to the leading end in the direction of solidification, i.e., the last part to solidify.

[0024] Furthermore, in the silicon ingot 10 of this embodiment, the proportion of Σ3 grain boundaries in the CCL region 12 is preferably 80% or more. Furthermore, in the silicon ingot 10 of this embodiment, the average crystal grain size in the CCL 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 Corresponding Grain Boundary Region) Since atoms in a corresponding grain boundary are partially bonded to each other, the bonding strength of the grain boundary is stronger than that of a random grain boundary, and preferential corrosion of the grain boundary can be suppressed. 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 corresponding grain boundary region 12 is present on the outer periphery of this single crystal region 11, in which the ratio of the corresponding grain boundary length to the total grain boundary length is 80% or more. As a result, when a silicon member made from this silicon ingot 10 is used in a corrosive environment, preferential corrosion of the grain boundary can be suppressed, and the lifespan can be extended.

[0027] (Area proportion occupied by single crystal regions 11: 25% or more) In the silicon ingot 10 of this embodiment, if the area proportion occupied by the single crystal regions 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 fabricated from this silicon ingot 10 will be shortened, making it possible to further suppress preferential corrosion of the grain boundaries when used in a corrosive environment. The area proportion occupied by the single crystal regions 11 in a cross section perpendicular to the solidification direction is more preferably 30% or more, even more preferably 40% or more, and may be, for example, 70%.

[0028] (Diameter of inscribed circle of single crystal region 11: 300 mm or more) In the silicon ingot 10 of this embodiment, if 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 will be short, making it possible to further suppress preferential corrosion of the grain boundaries when used in a corrosive environment. Note that, 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, even more preferably 400 mm or more, and may be, for example, 500 mm.

[0029] (Diameter of inscribed circle of correspondence grain boundary region 12: 400 mm or more) In the silicon ingot 10 of this embodiment, if the diameter of the inscribed circle of the correspondence 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 will be short, making it possible to further suppress preferential corrosion of the grain boundaries when used in a corrosive environment. Note that in this embodiment, the diameter of the inscribed circle of the correspondence grain boundary region 12 in a cross section perpendicular to the solidification direction is more preferably 450 mm or more, even more preferably 500 mm or more, and may be, for example, 600 mm.

[0030] (Proportion of Σ3 grain boundaries in the corresponding grain boundary region 12: 80% or more) In the Σ3 grain boundary, atoms are bonded to one another at a rate of three, and since the number of atomic bonds is large and the bonding strength of the grain boundary is strong among the corresponding grain boundaries, preferential corrosion of the grain boundary is further suppressed even in a corrosive environment. For this reason, in this embodiment, the proportion of Σ3 grain boundaries in the corresponding grain boundary region 12 is preferably 80% or more. Note that in this embodiment, the proportion of Σ3 grain boundaries in the corresponding grain boundary region 12 is more preferably 85% or more, and even more preferably 90% or more, and may be, for example, 95%.

[0031] (Average grain size in CCS boundary region 12: 10 mm or more) In the silicon ingot 10 of this embodiment, when the average grain size in the CCS boundary region 12 is as large as 10 mm or more, the length of the grain boundaries is shortened, and the progression of localized corrosion in a corrosive environment can be further suppressed. In this embodiment, the average grain size in the CCS boundary region 12 is more preferably 15 mm or more, and even more preferably 20 mm or more, and may be, for example, 40 mm.

[0032] Next, a silicon ingot manufacturing apparatus 20 used to manufacture the silicon ingot 10 of this embodiment will be described with reference to Figure 2. This silicon ingot manufacturing apparatus 20 includes a crucible 30 in which a silicon melt L is stored, a chill plate 22 on which the crucible 30 is placed, a lower heater 23 that supports the chill plate 22 from below, and an upper heater 24 disposed above the crucible 30. A heat insulating material 25 is provided around the crucible 30. The chill plate 22 has a hollow structure, and Ar gas is supplied to the interior via a supply pipe 26.

[0033] Here, a crucible 30 used in the silicon ingot manufacturing method of 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 on the inner surface of the mold 31. The mold 31 is made of, for example, quartz or graphite.

[0034] 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 to 200 μm and stucco layers 34 made of coarse silica powder having an average particle size of 100 μm to 1000 μm are alternately stacked 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 the stacked slurry layers 33 and stucco layers 34 being 6 or more. In this embodiment, as shown in FIG. 3, the slurry layer 33 is formed at a location that comes into contact with the inner surface of the mold 31, and the total number of the stacked slurry layers 33 and stucco layers 34 is 6.

[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, resulting in cracks in 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 to be in the range of 1 μm to 200 μm, the fine silica powder can be mixed with colloidal silica to form a slurry, thereby successfully forming the above-mentioned slurry layer 33. Furthermore, by setting the average particle size of the coarse silica powder to be in the range of 100 μm to 1000 μm, the surface roughness is not increased more than necessary, making it easier to separate the silicon ingot from the mold 31.

[0036] 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.

[0037] 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.

[0038] 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.

[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. Note that, although the crystal grows according to the crystal plane orientation of the plate surface of the seed crystal plate, there are no particular limitations on the crystal plane orientation of the plate 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 step). Here, 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.

[0041] 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 cannot occur, and many crystal nuclei are generated at the bottom of the crucible, becoming polycrystalline, and a single crystal does not grow well. For this reason, it is necessary to control the temperature so that the seed crystal plate does not completely melt.

[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 retaining 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 step). 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] Here, in the unidirectional solidification process, 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. Therefore, 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 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 limit to the upper limit of the temperature difference between the top and bottom of the furnace, but it may be 250°C or less, and 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 a plurality of 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. Therefore, the length of the crystal grain boundaries present in a silicon member manufactured using this silicon ingot 10 can be kept short, and preferential corrosion of the crystal grain boundaries can be suppressed even in a corrosive environment. Therefore, the progression of localized corrosion can be suppressed, and the service life can be extended.

[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, which can suppress the progression of localized corrosion when used in a corrosive environment and extend the 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 member 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 thereto and can be modified as appropriate within the scope of the technical concept of the invention. In this embodiment, only a CGB region is formed on the outer periphery of the single crystal region, but the present invention is not limited thereto and a polycrystalline grain boundary region (where the proportion of CGBs in the crystal grain boundaries is less than 80%) may be formed on the outer periphery of the CGB region.

[0052] The outermost layer on the mold 31 side may be either the slurry layer 33 or the stucco layer 34, but is preferably the slurry layer 33. The innermost layer on the silicon melt L side may be either the slurry layer 33 or the stucco layer 34, but is preferably the slurry layer 33.

[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 an inner diameter of 600 mm, an outer diameter of 650 mm, and a depth of 500 mm was prepared. A slurry layer forming step of forming a slurry layer by coating or spraying a slurry composed of fine silica powder and colloidal silica having an average particle size of 1 μm to 200 μm was performed four times, and a 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 performed three times, alternately, until the total number of slurry layers and stucco layers was 7. Then, the mold was heated in a nitrogen atmosphere of N ２ The firing process was carried out 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.

[0055] 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.

[0056] Next, the power supply 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 power supply 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 with a unidirectional solidification structure and a single crystal region. At this time, the output of the upper and lower heaters was controlled to adjust the temperature difference between the top and bottom of the furnace to the value shown in Table 1.

[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 600 mm diameter disk material at a position of 175 mm radius (corresponding grain boundary region). Then, the crystal structure was observed using an EBSD device. The measurement range was 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]

[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 top surface of the silicon ingot. This is thought to be because the temperature difference between the top and bottom of the furnace was set to less than 70°C in the unidirectional solidification process.

[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 correspondence grain boundary region consisting of a plurality of crystal grains was formed on the outer periphery of the single crystal region, and the ratio of the correspondence grain boundary 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.

[0064] 10 silicon ingot 11 single crystal region 12 coincidence grain boundary region

Claims

1. 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 in the center, and on the outer periphery of the single crystal region, a coincidence grain boundary region is formed, which is made up of a plurality of crystal grains and has a coincidence grain boundary length that accounts for 80% or more of the total crystal grain boundary length.

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

4. A silicon ingot according to claim 1 or 2, 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.

5. A silicon ingot according to claim 1 or 2, characterized in that the proportion of Σ3 grain boundaries in the coincidence grain boundary region is 80% or more.

6. A silicon ingot according to claim 1 or 2, characterized in that the average crystal grain size in the coincidence grain boundary region is 10 mm or more.

Images