Quartz glass crucible, method for manufacturing the same, and method for manufacturing single crystal silicon

Abstract

To provide: a quartz glass crucible capable of reducing the carbon contamination and pinhole incidences of a silicon single crystal; a method for manufacturing the same; and a method for manufacturing a silicon single crystal.SOLUTION: A quartz glass crucible 1 includes: a crucible base 10 consisting of silica glass; and a coating film 13 formed on the inner surface 10i of the crucible base 10 and including a crystallization accelerator. The average carbon concentration within a depth of 0 μm or more and 300 μm or less from the inner surface 10i of the coating film 13 and the crucible base 10 is 1.0×1012 atoms / cc or more and 3.0×1019 atoms / cc or less.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a quartz glass crucible and a method for manufacturing the same, and more particularly to a quartz glass crucible used for pulling silicon single crystals by the Czochralski method (CZ method). The present invention also relates to a method for manufacturing silicon single crystals using such a quartz glass crucible. [Background technology]

[0002] Most silicon single crystals are manufactured by the CZ method. In the CZ method, polycrystalline silicon raw material is melted in a quartz glass crucible to produce silicon melt, a seed crystal is immersed in the silicon melt, and a large single crystal is grown at the bottom end of the seed crystal by gradually pulling the seed crystal up while rotating the quartz glass crucible and the seed crystal. The CZ method makes it possible to increase the yield of large-diameter silicon single crystals.

[0003] A quartz glass crucible is a container made of silica glass that holds silicon melt during the process of pulling silicon single crystals. Therefore, quartz glass crucibles are required to be highly durable so that they do not deform even at high temperatures above the melting point of silicon and can withstand long-term use. They are also required to be highly pure to prevent impurity contamination of silicon single crystals.

[0004] It is known that brown ring-shaped cristobalite crystals, called brown rings, grow on the inner surface of a quartz glass crucible that comes into contact with the silicon melt when pulling up a silicon single crystal. If the brown rings peel off from the surface of the crucible and get mixed into the silicon melt, they may be carried by the melt convection to the solid-liquid interface and be incorporated into the single crystal, and the peeling of cristobalite can cause dislocations in the silicon single crystal. For this reason, a crystallization promoter is used to actively crystallize the inner surface of the crucible to prevent the peeling of crystal pieces.

[0005] Carbon, an impurity in single-crystalline silicon, is known to promote oxygen precipitation and have an adverse effect on device characteristics such as current leakage. Therefore, it is desirable that the carbon concentration in single-crystalline silicon be as low as possible. Since the carbon element present near the inner surface of the quartz glass crucible is directly incorporated into the silicon melt during the melting of the polycrystalline silicon raw material, it is important to reduce the carbon concentration near the inner surface of the crucible.

[0006] Regarding the carbon concentration of the quartz glass crucible, for example, Patent Document 1 describes a quartz glass crucible in which the nitrogen content of the inner surface layer is 100 to 4000 ppm and the carbon content is 30 to 1000 ppm. This quartz glass crucible is intended to actively supply nitrogen and carbon to the silicon melt from the crucible side, and therefore the crucible contains high concentrations of nitrogen and carbon.

[0007] Patent Document 2 describes a method for manufacturing a silica container including a step of introducing a raw material powder for a substrate (silica particles) onto the inner wall of an outer mold while rotating an outer mold having a hole for decompression and temporarily molding it into a predetermined shape, and a step of supplying a mixed gas containing O2 gas and an inert gas, which has been made to a predetermined dew point temperature or lower by dehumidification, from the inside of the temporarily molded body, ventilating the gas inside the outer mold, adjusting the humidity inside the outer mold, and heating the inside of the temporarily molded body from the outside by discharge heating melting using a carbon electrode while decompressing the temporarily molded body from the outer peripheral side, so that the outer peripheral portion of the temporarily molded body becomes a sintered body and the inner portion becomes a molten glass body to form a silica substrate. With this manufacturing method, carbon particles scattered from the carbon electrode can be oxidized and gasified, and the amount of carbon (C) contained in the silica substrate to be manufactured can be made extremely small.

[0008] Patent Document 3 describes that, in order to produce amorphous synthetic quartz powder with a low residual carbon content and a synthetic quartz crucible using the same, silica gel powder produced by a wet method is preferably fired at a temperature equal to or higher than the dehydration hydroxyl group temperature and lower than the powder sintering temperature in the atmosphere to obtain synthetic quartz powder. Then, this synthetic quartz powder is fired at a temperature equal to or higher than the decarburization temperature and lower than the powder sintering temperature under a vacuum of 100 Pa or less, preferably 50 Pa or less. By manufacturing a quartz crucible using the synthetic quartz powder with a low residual carbon content thus obtained, the carbon concentration in the quartz crucible can be reduced.

[0009] Patent Document 4 describes a cristobalite layer-forming silica glass crucible and a method for manufacturing the same, which can obtain high-quality crystals with at least a low carbon impurity concentration and an expected relatively long lifetime, and are less likely to crack. This silica glass crucible has a bubble-free silica glass layer with a predetermined thickness formed on its inner surface in advance. In the manufacture of such a crucible, the surface of the bubble-free silica glass layer is coated with a hydroxide of an alkaline earth metal element selected from barium (Ba) or the like, and the outer surface of the silica glass crucible is coated with the same substance as the inner surface. Then, heat treatment is carried out in an inert gas atmosphere or the like to form a cristobalite layer on the surface coated with the hydroxide. When Ri (Å) is the ionic radius of the alkaline earth metal, the concentration Ci (ppma) of the alkaline earth metal in any part of the cristobalite layer after heat treatment satisfies the relational expression of Ci ≧ 5.4E4 / |1 - (Ri / 0.42)3|.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0011] However, even when pulling a silicon single crystal using a conventional quartz glass crucible with a reduced carbon concentration, the carbon concentration of the silicon single crystal may increase, and improvement is required. In so-called multi-pulling, where multiple silicon single crystals are pulled from the same crucible by adding a polycrystalline silicon raw material charge, the carbon concentration tends to increase due to the effect of segregation as the number of pulled crystals increases. Therefore, the problem of the carbon concentration in the silicon single crystal is prominent.

[0012] Therefore, an object of the present invention is to provide a quartz glass crucible and a method for manufacturing the same that can reduce the carbon contamination and pinhole generation rate of a silicon single crystal. Another object of the present invention is to provide a method for manufacturing a silicon single crystal using such a quartz glass crucible.

Means for Solving the Problems

[0013] As a result of intensive research to reduce the carbon concentration in a silicon single crystal grown by the CZ method, the inventors of the present application have found that when applying a crystallization accelerator to the inner surface of a quartz glass crucible, it is not sufficient to only reduce the carbon concentration in the crucible substrate made of silica glass. It is necessary to reduce the carbon concentration in the coating film containing the crystallization accelerator, and thereby the carbon concentration in the silicon single crystal can be reduced.

[0014] The present invention is based on such technical knowledge. The quartz glass crucible according to the present invention includes a crucible substrate made of silica glass and a coating film containing a crystallization accelerator formed on the inner surface of the crucible substrate, and the average carbon concentration in the range from a depth of 0 μm or more to 300 μm or less from the coating film and the inner surface of the crucible substrate is 1.0×10 12 atoms / cc or more and 3.0×10 19 atoms / cc or less.

[0015] The quartz glass crucible according to the present invention can reduce the carbon concentration in the silicon single crystal grown by the CZ method because the carbon concentration is reduced not only in the vicinity of the inner surface of the crucible substrate but also in the coating film containing the crystallization accelerator.

[0016] In the present invention, the weight ratio of carbonate in the coating film is preferably 20.0 w% or less. If the weight ratio of carbonate in the coating film is 20.0 w% or less, the average carbon concentration in the coating film can be made 3.0×10 19 atoms / cc or less. The weight ratio of carbonate can be measured by the XPS method or the Raman measurement method.

[0017] In the present invention, the average carbon concentration in the coating film is preferably 3.0×10 18 atoms / cc or less, and the average carbon concentration in the range of 0 μm or more and 300 μm or less from the inner surface of the coating film and the crucible substrate is 1.3×10 16 atoms / cc or less is more preferable. Further, the average carbon concentration in the range of 300 μm or more and 2000 μm or less from the inner surface of the crucible substrate is preferably 1.1×10 19 atoms / cc or less. Thereby, the carbon concentration in the silicon single crystal can be further reduced.

[0018] In the present invention, it is preferable that the coefficient of variation (σ / AVERAGE) of the carbon concentration in the coating film at five points on the bottom of the crucible substrate is 1.1 or less. Here, the five points are a first measurement point that is the center of the bottom, a second measurement point that is a position shifted 0.08 to 0.7 times the radius of the crucible substrate in the radial direction from the first measurement point, a third measurement point that is a position rotated 90° clockwise in the circumferential direction from the second measurement point, a fourth measurement point that is a position rotated 90° clockwise in the circumferential direction from the third measurement point, and a fifth measurement point that is a position rotated 90° clockwise in the circumferential direction from the fourth measurement point. The deviation of the carbon concentration on the inner surface of the crucible causes pinholes to occur in the silicon single crystal. However, by reducing the in-plane variation of the carbon concentration in the coating film formed in the central region of the bottom of the crucible, the generation of pinholes can be prevented.

[0019] It is preferable that the peeling strength of the coating film is 0.3 kN / m or more. If the peeling strength of the coating film is 0.3 kN / m or more, roughening of the inner surface of the crucible and peeling of the brown ring can be suppressed, and dislocation generation in the silicon single crystal can be prevented.

[0020] The nitrogen concentration in the range of 0 μm or more and 300 μm or less from the inner surface of the coating film and the crucible substrate is preferably 4.7×10 17 atoms / cc or less. By reducing the nitrogen concentration in the vicinity of the inner surface of the crucible substrate and in the coating film, the nitrogen incorporated into the silicon single crystal can be reduced. Therefore, the generation of unintentional oxygen precipitation-induced defects in the silicon single crystal can be prevented.

[0021] In addition, the method for manufacturing a quartz glass crucible according to the present invention includes a step of producing a crucible substrate made of silica glass, and a step of applying a coating liquid containing a crystallization accelerator to form a coating film of the crystallization accelerator on the inner surface of the crucible substrate. In the step of producing the crucible substrate, silica powder having a carbon content of less than 6 ppm is used as a raw material for the inner surface of the crucible substrate, and arc melting of the silica powder is performed using a carbon electrode having a bulk specific gravity of 1.50 g / cc or more and 1.75 g / cc or less and a specific resistance of 330 μΩcm or more and 600 μΩcm or less. The crystallization accelerator is a compound having no carbon atom in the molecule of a Group 2a element (Mg, Ca, Sr, Ba).

[0022] When the carbon electrode is oxidized and consumed from the surface during arc melting, CO2 gas is generated. If the specific gravity and specific resistance of the electrode are large, carbon particles may scatter from the surface and be taken into the crucible before burning out by the arc heat. However, in the method for manufacturing a quartz glass crucible according to the present invention, since a carbon electrode having a relatively small specific gravity and specific resistance is used, such problems can be solved, and the carbon concentration in the vicinity of the inner surface of the crucible substrate can be reduced.

[0023] In the method for manufacturing a quartz glass crucible according to the present invention, it is preferable to wash the crucible substrate with hydrofluoric acid of semiconductor grade or higher and pure water before forming the coating film of the crystallization accelerator. Thereby, impurities containing carbon attached to the surface of the crucible substrate can be efficiently removed.

[0024] The crystallization accelerator is preferably a water-soluble compound. Thereby, since the solubility in water is high and the handling of the aqueous solution is easy, uniform application of the crystallization accelerator to the crucible surface can be easily realized.

[0025] The step of forming the coating film preferably involves applying the coating solution while heating the crucible substrate at a temperature of 60°C or higher and 500°C or lower, and particularly preferably at a temperature of 100°C or higher and 180°C or lower. In this case, it is preferable to apply the coating solution while heating the crucible substrate so that the temperature difference between the boiling point of the solvent in the coating solution and the temperature of the crucible substrate is -40.0°C or higher and 100°C or lower, and it is more preferable that the heating temperature of the crucible substrate is equal to or higher than the boiling point of the solvent and 80°C or lower. Thereby, the generation of carbonate can be suppressed and the carbon concentration in the coating film can be reduced.

[0026] The step of applying the coating solution preferably involves spraying the coating solution using a two-fluid nozzle that mixes a gas and a liquid at the spray tip, and preferably spraying the coating solution under a low vacuum of 1×10 2 Pa or higher and 1×10 5 Pa or lower. By applying the coating solution to the heated crucible substrate under a low vacuum in this way, the solvent can be instantaneously evaporated to uniformly fix the crystallization accelerator, and variations in the coating film due to dripping of the coating solution on the crucible surface can be prevented. Also, since the solvent can be evaporated in a short time, the heating time can be shortened, so it is possible to suppress the generation of carbonate.

[0027] In the step of forming the coating film, it is preferable that the maximum thickness of the coating film formed by a single application is 0.5 μm or less, and the coating film is multi-layered by alternately repeating drying and re-application of the coating film. Thereby, a dense and uniform coating film can be formed, and the peeling strength of the coating film can be increased.

[0028] The spraying amount of the coating solution is preferably 300 mL / min or less. By suppressing the spraying amount of the coating solution to 300 mL / min or less in this way, a dense coating film can be uniformly formed.

[0029] Furthermore, the method for producing a silicon single crystal according to the present invention is characterized in that a silicon single crystal is pulled up using the quartz glass crucible according to the present invention having the above characteristics. According to the present invention, a silicon crystal with reduced carbon contamination and pinhole generation rate can be produced.

Advantages of the Invention

[0030] According to the present invention, it is possible to provide a quartz glass crucible and a method for producing the same that can reduce carbon contamination and pinhole generation rate of a silicon single crystal. Further, according to the present invention, it is possible to provide a method for producing a silicon single crystal using such a quartz glass crucible.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0032] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0033] FIG. 1 is a schematic perspective view showing the configuration of a quartz glass crucible according to an embodiment of the present invention. FIG. 2 is a schematic side sectional view and a partially enlarged view of the quartz glass crucible shown in FIG. 1.

[0034] As shown in FIGS. 1 and 2, the quartz glass crucible 1 is a container made of silica glass for holding a silicon melt, and has a cylindrical side wall portion 10a, a bottom portion 10b provided below the side wall portion 10a, and a corner portion 10c provided between the side wall portion 10a and the bottom portion 10b. The bottom portion 10b is preferably a so-called round bottom that is gently curved, but a so-called flat bottom may also be used. The corner portion 10c is a portion having a larger curvature than the bottom portion 10b.

[0035] The diameter (aperture) of the quartz glass crucible 1 varies depending on the diameter of the silicon single crystal ingot pulled up from the silicon melt, but is 18 inches (about 450 mm) or more, preferably 22 inches (about 560 mm), and particularly preferably 32 inches (about 800 mm) or more. Such a large crucible is used for pulling up a large silicon single crystal ingot with a diameter of 300 mm or more, and it is required that the quality of the single crystal is not affected even after long-term use.

[0036] The wall thickness of the crucible varies slightly depending on the part, but the wall thickness of the side wall portion 10a of a crucible of 18 inches or more is preferably 6 mm or more, the wall thickness of the side wall portion 10a of a crucible of 22 inches or more is preferably 7 mm or more, and the wall thickness of the side wall portion 10a of a crucible of 32 inches or more is preferably 10 mm or more. Thereby, a large amount of silicon melt can be stably held at a high temperature.

[0037] As shown in FIG. 2, the quartz glass crucible 1 includes a crucible base body 10 made of silica glass and a coating film 13 of a crystallization accelerator formed on the inner surface 10i of the crucible base body 10. The crucible base body 10 mainly has a two-layer structure, and has a transparent layer 11 (bubble-free layer) that does not contain bubbles and a bubble layer 12 (opaque layer) that contains a large number of minute bubbles, and the coating film 13 is provided inside the transparent layer 11.

[0038] The transparent layer 11 is a layer that constitutes the inner surface 10i of the crucible substrate 10 in contact with the silicon melt, and is provided to prevent the yield of the silicon single crystal from decreasing due to bubbles in the silica glass. Since the inner surface 10i of the crucible reacts with the silicon melt and is eroded, bubbles near the inner surface of the crucible cannot be trapped in the silica glass, and there is a risk that the bubbles burst due to thermal expansion and crucible fragments (silica fragments) peel off. If the crucible fragments released into the silicon melt ride on the melt convection and are carried to the growth interface of the silicon single crystal and incorporated into the silicon single crystal, it causes dislocation of the single crystal. Also, if the bubbles released into the silicon melt float up to reach the solid-liquid interface and are incorporated into the single crystal, it causes the generation of pinholes in the silicon single crystal.

[0039] That the transparent layer 11 does not contain bubbles means that it has a bubble content rate and bubble size such that the single crystal formation rate does not decrease due to bubbles. Such a bubble content rate is, for example, 0.1 vol% or less, and the diameter of the bubbles is, for example, 100 μm or less.

[0040] The thickness of the transparent layer 11 is preferably 0.5 to 10 mm, and is set to an appropriate thickness for each part of the crucible so that it does not completely disappear due to erosion during the crystal pulling process and the bubble layer 12 is not exposed. The transparent layer 11 is preferably provided over the entire crucible from the side wall portion 10a to the bottom portion 10b of the crucible, but it is also possible to omit the transparent layer 11 at the upper end portion of the crucible that does not come into contact with the silicon melt.

[0041] The bubble layer 12 is a main layer of the crucible substrate 10 located outside the transparent layer 11, and is provided to enhance the heat retention of the silicon melt in the crucible and to disperse the radiant heat from the heater of the single crystal pulling apparatus to heat the silicon melt in the crucible as uniformly as possible. Therefore, the bubble layer 12 is provided over the entire crucible from the side wall portion 10a to the bottom portion 10b.

[0042] The bubble content of the bubble layer 12 is preferably higher than that of the transparent layer 11, greater than 0.1 vol% and not more than 5 vol%. This is because if the bubble content of the bubble layer 12 is 0.1 vol% or less, the heat insulation function required for the bubble layer 12 cannot be exerted. Also, when the bubble content of the bubble layer 12 exceeds 5 vol%, the crucible may be deformed due to the thermal expansion of the bubbles, resulting in a possible decrease in the single crystal yield, and furthermore, the heat transfer property becomes insufficient. From the perspective of the balance between heat insulation and heat transfer, the bubble content of the bubble layer 12 is particularly preferably 1 to 4 vol%. The above-mentioned bubble content is the value measured for the crucible at room temperature environment before use.

[0043] In order to prevent contamination of the silicon melt, it is desirable that the silica glass constituting the transparent layer 11 is of high purity. Therefore, the crucible substrate 10 preferably has a two-layer structure of a synthetic silica glass layer (synthetic layer) formed from synthetic quartz powder and a natural silica glass layer (natural layer) formed from natural quartz powder. Synthetic quartz powder can be produced by gas-phase oxidation of silicon tetrachloride (SiCl4) (dry synthesis method) or hydrolysis of silicon alkoxide (sol-gel method). Also, natural quartz powder is produced by pulverizing a natural mineral mainly composed of α-quartz into a granular form.

[0044] The two-layer structure of the synthetic silica glass layer and the natural silica glass layer can be produced by depositing natural quartz powder along the inner surface of the crucible manufacturing mold, depositing synthetic quartz powder thereon, and melting these raw material quartz powders by Joule heat due to arc discharge. In the arc melting process, the transparent layer 11 is formed by removing bubbles by strongly evacuating from the outside of the deposited layer of the raw material quartz powder, and the bubble layer 12 is formed by stopping or weakening the evacuation. Therefore, the interface between the synthetic silica glass layer and the natural silica glass layer does not necessarily coincide with the interface between the transparent layer 11 and the bubble layer 12, but the synthetic silica glass layer preferably has a thickness such that it does not completely disappear due to the erosion of the inner surface of the crucible during the single crystal pulling process, similar to the transparent layer 11.

[0045] The quartz glass crucible 1 according to this embodiment has a structure in which the inner surface 10i of the crucible substrate 10 is covered with a coating film 13 of a crystallization accelerator. The crystallization accelerator is a compound of a Group 2a element (Mg, Ca, Sr, Ba), and plays a role of promoting the crystallization of the inner surface 10i of the crucible substrate 10 during the single crystal pulling process. In this embodiment, the crystallization accelerator preferably has a hydroxide or oxide that does not have a carbon atom in the molecule, and a hydroxide that has a high solubility in water and is easy to handle is particularly preferred. As the Group 2a element as the crystallization accelerator, barium (Ba) is particularly preferred. This is because barium has a smaller segregation coefficient than silicon, is stable at room temperature, and is easy to handle. In addition, barium has advantages such as that the crystallization rate does not decay with crystallization and causes stronger orientation growth than other elements.

[0046] The coating film 13 of the crystallization accelerator is formed in the range of 0.25 times or more and 1 time or less of the crucible outer diameter. In this embodiment, the coating film 13 of the crystallization accelerator is preferably formed on the entire inner surface 10i of the crucible substrate 10 except in the vicinity of the upper end of the rim. The reason for excluding the vicinity of the upper end of the rim is that the vicinity of the upper end of the rim does not contact the silicon melt and does not necessarily need to be crystallized, and also because the vicinity of the upper end of the rim is likely to peel off when crystallized, and the crystal pieces mixed into the silicon melt may cause dislocations in the silicon single crystal.

[0047] The thickness of the coating film 13 is not particularly limited, but is preferably 0.1 to 50 μm, and particularly preferably 1 to 20 μm. If the thickness of the coating film 13 is too thin, the peeling strength of the coating film is weak, and crystallization becomes non-uniform due to the peeling of the coating film 13. Even if the coating film 13 is too thick, the peeling strength decreases and crystallization becomes non-uniform.

[0048] The coating film 13 is preferably non-peeling, and for this purpose, a peeling strength of 0.3 kN / m or more is required. The coating film 13 needs to satisfy such a peeling strength in at least the central region of the bottom of the crucible substrate 10, and it is preferable that such a peeling strength is satisfied throughout the entire formation region of the coating film 13. Here, the central region of the bottom of the crucible substrate 10 refers to the region within a range of 0.5r (r is the outer diameter (radius) of the crucible) from the center of the bottom of the crucible substrate 10.

[0049] Figure 3 is a schematic diagram showing a method for measuring the peeling strength of the coating film 13.

[0050] As shown in Figure 3, the peeling strength of the coating film 13 can be measured using a SAICAS (Surface And Interfacial Cutting Analysis System). The SAICAS 30 can obtain the apparent shear strength from the vertical load F Z (vertical force) and the horizontal load F Y (horizontal force) when the diamond blade 31 is obliquely cutting the coating film, and the peeling strength can be obtained from the horizontal load F Y (horizontal force) when the diamond blade 31 is parallel cutting the interface between the coating film and the substrate. The peeling strength of the coating film 13 can be obtained from the horizontal load F Y when a sample 1s of the crucible piece on which the coating film 13 is formed is placed on the stage and the interface (inner surface 10i of the crucible substrate 10) between the coating film 13 and the crucible substrate 10 is cut with the diamond blade 31.

[0051] The concentration of the crystallization accelerator contained in the coating film 13 is preferably 2.5×10 15 atoms / cm 2 or more. Thus, when the concentration of the crystallization accelerator is relatively high, even if a part of the crystallization accelerator peels off, crystallization can be promoted in the surface direction to achieve uniform crystallization of the inner surface 10i of the crucible substrate 10.

[0052] On the one hand, when the concentration of the crystallization accelerator on the crucible surface is high, the crystallization rate on the crucible surface is fast, and crystallization proceeds in the lateral direction (surface direction) as well. Therefore, the requirement for the peeling strength is more relaxed than in the case of low concentration. Thus, when the concentration of the crystallization accelerator on the crucible surface is higher than 2.6×10 15 atoms / cm 2 , the peeling strength of the crystallization accelerator may be 0.3 kN / m or more.

[0053] The concentration of the crystallization accelerator may be 2.5×10 15 atoms / cm 2 or less. In that case, the peeling strength of the coating film 13 is preferably 0.6 kN / m or more. When the peeling strength of the coating film is high, the inner surface 10i of the crucible substrate 10 can be surely crystallized without using a high-concentration crystallization accelerator.

[0054] When the concentration of the crystallization accelerator on the crucible surface is 2.6×10 15 atoms / cm 2 or less and in the case of low concentration, when the crystallization accelerator peels off, crystal nuclei of brown rings cannot be uniformly formed. Therefore, the peeling strength of the crystallization accelerator is required to be 0.6 kN / m or more.

[0055] In the central region at the bottom of the crucible substrate 10, the peeling strength of the coating film 13 is particularly preferably 0.9 kN / m or more. As described above, a large amount of polycrystalline silicon raw material is filled in the quartz glass crucible 1, and a very large load is applied to the bottom of the crucible. Therefore, the coating film 13 is likely to peel off. However, if the peeling strength of the coating film 13 at the bottom of the crucible substrate 10 is 0.9 kN / m or more, peeling can be prevented even when such a large load is applied.

[0056] The surface roughness (Ra) of the coating film 13 is preferably 0.1 μm or more and 0.25 μm or less. When the surface roughness (Ra) of the coating film is larger than 0.25 μm, the coating film is likely to peel off, and it is difficult to manufacture the coating film with a surface roughness (Ra) smaller than 0.1 μm.

[0057] The carbon concentration in the silicon single crystal grown by the CZ method is desirably as low as possible. For this purpose, it is necessary to minimize the amount of carbon supplied from the quartz glass crucible 1, and it is particularly necessary to pay attention to the carbon concentration not only in the crucible substrate 10 but also in the coating film 13. Therefore, the quartz glass crucible 1 according to the present embodiment has an average carbon concentration in the range of 0 μm to 300 μm from the coating film 13 and the inner surface 10i of the crucible substrate 10 (that is, the surface layer portion of the crucible substrate 10) of 1.0×10 12 atoms / cc or more and 3.0×10 19 atoms / cc or less. Thereby, the amount of carbon dissolved from the quartz glass crucible 1 into the silicon melt can be reduced, and it becomes possible to manufacture a silicon single crystal having a low carbon concentration.

[0058] The average carbon concentration in the coating film 13 is preferably 3.0×10 18 atoms / cc or less. If the average oxygen concentration in the coating film is 3.0×10 18 atoms / cc or less, the amount of carbon supplied from the coating film into the silicon melt can be reduced.

[0059] The average carbon concentration in the coating film 13 and the average carbon concentration in the range of 0 μm to 300 μm from the inner surface of the crucible substrate 10 are both preferably 1.3×10 16 atoms / cc or less. Further, the average carbon concentration in the range of 300 μm or more and 2000 μm or less from the inner surface of the crucible substrate 10 is preferably 1.1×10 19 atoms / cc or less. Thereby, it becomes possible to manufacture a silicon single crystal having a sufficiently low carbon concentration.

[0060] The average carbon density in the range of 300 μm to 2000 μm from the inner surface of the crucible substrate 10 may be higher than the average carbon density of the surface layer portion in the range of 0 μm to 300 μm, but is preferably 1.1×10 19 atoms / cc or less.

[0061] Variations in the in-plane distribution of carbon concentration on the inner surface of the crucible result in variations in the in-plane thickness of the cristobalite layer formed on the inner surface of the crucible, which causes the exfoliation of cristobalite crystals. In particular, if the crystal layer is non-uniform at the bottom of the crucible, it causes pinholes in the single crystal silicon. Therefore, it is desirable that the variation in the in-plane distribution of carbon concentration is small at the bottom of the crucible.

[0062] Specifically, it is preferable that the coefficient of variation when measuring the carbon concentrations at five points P1 to P5 at the bottom of the crucible is 1.1 or less. Here, as shown in FIG. 4, the five points at the bottom of the crucible are the center P1 of the bottom and four points P2 to P5 that are the same distance away from the center P1 in four directions. The other four points P2 to P5 other than the center P1 of the bottom are preferably set at positions 0.08r to 0.7r away from the center P1 (the first measurement point) of the bottom of the crucible substrate 10 in the radial direction (r is the radius of the outer diameter of the crucible substrate 10). The third to fifth measurement points P3 to P5 are positions obtained by rotating the second to fourth measurement points P2 to P4 90° clockwise in the circumferential direction, respectively.

[0063] The quartz glass crucible 1 according to the present embodiment can be manufactured by applying a crystallization accelerator to the inner surface of the crucible substrate 10 after manufacturing the crucible substrate 10 by a so-called rotary mold. method after manufacturing the crucible substrate 10 by a so-called rotary mold.

[0064] FIG. 5 is a schematic diagram showing a method for manufacturing a quartz glass crucible by the rotary mold method.

[0065] As shown in FIG. 5, in the rotary mold method, a mold 14 having a cavity conforming to the outer shape of the crucible is prepared, and natural quartz powder 16a and synthetic quartz powder 16b are sequentially filled along the inner surface 14i of the rotating mold 14 to form a deposited layer 16 of raw material quartz powder. The raw material quartz powder remains attached to the inner surface 14i of the mold 14 by centrifugal force and stays in a fixed position, maintaining the crucible shape.

[0066] In the production of the quartz glass crucible 1, crystalline or amorphous silica powder with a carbon content of less than 6 ppm is prepared, and this silica powder is used as a raw material near the inner surface to produce the quartz glass crucible 1. By using silica powder with a very low carbon content as the raw material near the inner surface of the quartz glass crucible, the carbon concentration near the inner surface of the crucible can be reduced.

[0067] Next, an arc electrode 15 is installed in the mold 14, and the deposited layer 16 of raw material quartz powder is arc-melted from the inside of the mold 14. Specific conditions such as the heating time and heating temperature are appropriately determined in consideration of conditions such as the characteristics of the raw material quartz powder and the size of the crucible.

[0068] In order to reduce the carbon concentration of the inner surface 10i of the crucible substrate 10, it is preferable to use a carbon electrode with a bulk specific gravity of 1.50 g / cc to 1.75 g / cc and a specific resistance of 330 μΩcm to 600 μΩcm as the arc electrode 15. During arc melting, CO2 gas is generated due to the oxidative consumption of the carbon electrode from the surface. Here, when the specific gravity and specific resistance of the electrode are below the above range, not only will a large amount of CO2 gas be generated due to the intense consumption of the electrode, but it will also have an adverse effect on the shape of the crucible. On the other hand, when the specific gravity and specific resistance of the carbon electrode exceed the above range, carbon particles may scatter from the electrode surface and be taken into the crucible before burning out by the arc heat. However, in this embodiment, since a carbon electrode with a specific gravity and specific resistance within the above range is used, an increase in CO2 gas and the scattering of carbon particles can be suppressed. Therefore, the carbon concentration near the inner surface of the crucible substrate 10 can be reduced.

[0069] During arc melting, the amount of bubbles in the molten silica glass is controlled by evacuating the deposited layer 16 of raw material quartz powder through a large number of ventilation holes 14a provided on the inner surface 14i of the mold 14. Specifically, the raw material quartz powder is evacuated at the start of arc melting to form the transparent layer 11, and after the formation of the transparent layer 11, the evacuation of the raw material quartz powder is stopped to form the bubble layer 12.

[0070] Since the arc heat gradually spreads from the inside to the outside of the deposited layer 16 of raw material quartz powder and melts the raw material quartz powder, by changing the reduced pressure conditions at the timing when the raw material quartz powder begins to melt, the transparent layer 11 and the bubble layer 12 can be separately formed. That is, if reduced pressure melting is performed to increase the reduced pressure at the timing when the raw material quartz powder melts, the arc atmosphere gas cannot be trapped in the glass, so the fused quartz becomes silica glass without bubbles. Also, if normal melting (atmospheric pressure melting) is performed to weaken the reduced pressure at the timing when the raw material quartz powder melts, the arc atmosphere gas is trapped in the glass, so the fused silica becomes silica glass containing a large number of bubbles.

[0071] Thereafter, the arc melting is terminated, and the crucible is cooled. Thus, the crucible substrate 10 with the transparent layer 11 and the bubble layer 12 provided in order from the inside to the outside of the crucible wall is completed.

[0072] Next, after shaping the crucible substrate 10 after molding by cutting the rim portion or the like into a predetermined shape, it is washed with a cleaning liquid and further rinsed with pure water. The cleaning liquid is preferably prepared by diluting hydrofluoric acid of semiconductor grade or higher with pure water having TOC ≤ 2 ppb to 10 - 40 w%.

[0073] Next, a crystallization accelerator is applied to the inner surface of the crucible substrate 10. In order to uniformly disperse the crystallization accelerator on the inner surface 10i, a coating liquid in which the crystallization accelerator is dissolved in pure water (15°C to 25°C, 17.2 MΩ or more, TOC ≤ 2 ppb) is prepared. At that time, stirring is performed with a stirrer to increase the solubility of the particles of the crystallization accelerator and make the concentration of the solution uniform.

[0074] Next, the crucible substrate 10 is heated at a temperature of 60°C or higher and 500°C or lower in a halogen heater or a clean oven installed in a clean room, and then the coating liquid is sprayed by a spray nozzle. The solvent of the coating liquid evaporates instantaneously when it comes into contact with the high-temperature crucible, and the components of the crystallization accelerator are fixed to the crucible. As described above, the crystallization accelerator is a compound of Group 2a elements (Mg, Ca, Sr, Ba), and in particular, a hydroxide with high hydrophilicity is optimal for enhancing the fixing property to the crucible.

[0075] The hydroxides of Group 2a elements react with carbon dioxide in the atmosphere to form carbonates (for example, in the case of barium hydroxide, 2.5% becomes barium carbonate). The carbon on the inner surface of the quartz glass crucible is directly incorporated into the silicon melt during the melting of polysilicon. Furthermore, the carbon element incorporated into the silicon single crystal promotes oxygen precipitation and affects device performance such as current leakage. Therefore, in order to reduce the formation of carbonates, it is important to keep the surface temperature of the crucible at 500 °C or lower, preferably 200 °C or lower. In order to accelerate the evaporation of the solvent, it is preferable to heat the crucible substrate 10 so that the temperature difference between the boiling point of the solvent and the crucible is -40.0 °C to 100 °C.

[0076] In order to evaporate the solvent in a short time and reduce the formation of carbonates, it is more preferable to set the heating temperature of the crucible substrate 10 to be 80 °C or lower above the boiling point of the solvent. If the temperature of the crucible substrate 10 is lower than the boiling point of the solvent, the evaporation time of the solvent becomes long, the thickness of the coating film and the concentration distribution of the crystallization accelerator become non-uniform, and thus the peeling strength of the coating film decreases. Also, if the evaporation time of the solvent becomes long, condensation of the coating liquid may occur on the surface of the crucible, which may result in a high and non-uniform carbon concentration. If the temperature of the crucible substrate 10 is 80 °C or lower, the generation of carbonates can be sufficiently suppressed and the carbon concentration in the coating film can be reduced.

[0077] In the spraying of the coating liquid, it is preferable to use a two-fluid nozzle that mixes gas and liquid at the spray tip and sprays them, and it is preferable to adjust the average droplet diameter to 5 μm to 1000 μm. This is because if the droplet diameter is too large, the fixing of the coating liquid becomes non-uniform, the uniformity of the coating film decreases, and the peeling strength decreases. Also, if the droplet diameter is too small, it is difficult to spray the coating liquid. It is particularly preferable that the average droplet diameter is 200 μm or less.

[0078] The spraying amount of the coating liquid is preferably 300 mL / min or less. This is because if the spraying amount of the coating liquid is greater than 300 mL / min, liquid dripping is likely to occur on the coating surface, making it difficult to uniformly fix the crystallization accelerator.

[0079] The spraying of the coating liquid is preferably carried out under a low vacuum of 1×10 2 Pa to 1×10 5 Pa. Under a lower pressure (vacuum), the evaporation of the solvent is accelerated, so that the crystallization accelerator can be uniformly fixed, and a coating film with high peel strength can be formed. In addition, by evaporating the solvent in a short time, the heating time can be shortened, so that the generation of carbonate can be suppressed.

[0080] In the formation of the coating film, the thickness of the crystallization accelerator formed by one-time coating is preferably about 0.5 μm at most, and it is preferably applied in multiple times until the target concentration is reached. Thereby, the strength of the coating film can be made stronger.

[0081] If the crucible is simply heated when spraying the coating liquid, the coating film is likely to be mottled, and it is difficult to form a dense and uniform coating film. However, by controlling the coating conditions as described above, a dense and uniform coating film can be formed, and the peel strength of the coating film can be improved.

[0082] FIG. 6 is a schematic diagram showing a method of applying a crystallization accelerator to the inner surface 10i of the crucible substrate 10.

[0083] As shown in FIG. 6, in the application of the crystallization accelerator, the crucible substrate 10 is placed on the rotary support 17A with the opening facing upward, and the coating liquid 6 is sprayed from the spray nozzle 19 attached to the tip of the robot arm 18 installed inside the crucible substrate 10. At this time, in order to prevent dripping of the coating liquid 6, it is preferable to install a heater 17B outside the crucible substrate 10 and apply the coating while heating the crucible substrate 10 to 60°C to 500°C, and particularly preferably 100°C to 180°C. If the surface temperature of the crucible substrate 10 is 60°C or higher, the solvent evaporates instantaneously on the surface of the crucible substrate 10, so that the crystallization accelerator can be uniformly fixed on the inner surface 10i of the crucible substrate 10.

[0084] When the crystallization accelerator is a metal hydroxide, it reacts with carbon dioxide gas in the atmosphere to form a carbonate. For example, in an air and normal pressure atmosphere, 2.5% of barium hydroxide becomes barium carbonate. The carbonate in the coating film 13 causes an increase in the carbon concentration of the silicon single crystal. In order to suppress the formation of such a carbonate, it is preferable that the surface temperature of the crucible when applying the crystallization accelerator is 500 °C or lower, and particularly preferably 80 °C or higher and lower than the boiling point of the solvent. Thereby, the weight ratio of the carbonate in the total weight of the coating film can be suppressed to 20.0 w% or lower.

[0085] FIG. 7 is a diagram for explaining a single crystal pulling process using the quartz glass crucible 1 according to the present embodiment, and is a schematic cross-sectional view showing the configuration of a single crystal pulling apparatus.

[0086] As shown in FIG. 7, a single crystal pulling apparatus 20 is used in the process of pulling a silicon single crystal by the CZ method. The single crystal pulling apparatus 20 includes a water-cooled chamber 21, a quartz glass crucible 1 that holds a silicon melt in the chamber 21, a carbon susceptor 22 that holds the quartz glass crucible 1, a rotating shaft 23 that rotatably and vertically supports the carbon susceptor 22, a shaft drive mechanism 24 that drives the rotating shaft 23 to rotate and move up and down, a heater 25 disposed around the carbon susceptor 22, a single crystal pulling wire 28 disposed above the quartz glass crucible 1 of the heater 25 and coaxial with the rotating shaft 23, and a wire winding mechanism 29 disposed above the chamber 21.

[0087] The chamber 21 is composed of a main chamber 21a and an elongated cylindrical pull chamber 21b connected to the upper opening of the main chamber 21a. The quartz glass crucible 1, the carbon susceptor 22, and the heater 25 are provided in the main chamber 21a. A gas inlet 21c for introducing an inert gas (purge gas) such as argon gas or a dopant gas into the main chamber 21a is provided at the upper part of the pull chamber 21b, and a gas outlet 21d for discharging the atmospheric gas in the main chamber 21a is provided at the lower part of the main chamber 21a.

[0088] The carbon susceptor 22 is used to maintain the shape of the quartz glass crucible 1 softened at high temperature and holds it so as to surround the quartz glass crucible 1. The quartz glass crucible 1 and the carbon susceptor 22 constitute a double-structured crucible for supporting the silicon melt in the chamber 21.

[0089] The carbon susceptor 22 is fixed to the upper end of the rotating shaft 23, and the lower end of the rotating shaft 23 passes through the bottom of the chamber 21 and is connected to a shaft drive mechanism 24 provided outside the chamber 21.

[0090] The heater 25 is used to melt the polycrystalline silicon raw material filled in the quartz glass crucible 1 to generate the silicon melt 3 and to maintain the molten state of the silicon melt 3. The heater 25 is a resistance heating type carbon heater and is provided so as to surround the quartz glass crucible 1 in the carbon susceptor 22.

[0091] As the single crystal silicon 2 grows, the amount of the silicon melt in the quartz glass crucible 1 decreases, but the quartz glass crucible 1 is raised so that the height of the melt surface becomes constant.

[0092] The wire winding mechanism 29 is disposed above the pull chamber 21b, the wire 28 extends downward from the wire winding mechanism 29 through the inside of the pull chamber 21b, and the tip of the wire 28 reaches the internal space of the main chamber 21a. This figure shows a state where the silicon single crystal 2 during growth is suspended from the wire 28. When pulling up the silicon single crystal 2, the quartz glass crucible 1 and the silicon single crystal 2 are rotated respectively while gradually pulling up the wire 28 to grow the silicon single crystal 2.

[0093] During the single crystal pulling process, the inner surface of the crucible crystallizes, but due to the action of the crystallization accelerator, the crystallization of the inner surface of the crucible proceeds uniformly, so it is possible to prevent the dislocation of the silicon single crystal due to the peeling of the brown ring. In addition, the quartz glass crucible 1 softens, but since the crystallization of the inner surface of the crucible proceeds uniformly, the strength of the crucible can be ensured and deformation can be suppressed. Therefore, it is possible to prevent the crucible from deforming and contacting the furnace internal members, or the volume inside the crucible from changing and the liquid level position of the silicon melt 3 from fluctuating.

[0094] As described above, the quartz glass crucible 1 according to the present embodiment includes a crucible substrate 10 made of silica glass and a coating film 13 of a crystallization accelerator formed on the inner surface 10i of the crucible substrate 10. The average carbon concentration in the coating film 13 and the average carbon concentration in the range of 0 μm to 300 μm from the inner surface of the crucible substrate 10 are both 1.0×10 12 atoms / cc or more and 3.0×10 19 atoms / cc or less. Therefore, carbon contamination of the silicon single crystal caused by the quartz glass crucible can be prevented, and a high-quality silicon single crystal can be manufactured.

[0095] In addition, in the method for manufacturing a quartz glass crucible according to the present embodiment, when preparing silica powder having a carbon content of less than 6 ppm in the raw material near the inner surface of the crucible substrate 10 and arc-melting this silica powder to manufacture a quartz glass crucible, a carbon electrode having a bulk density of 1.50 g / cc to 1.75 g / cc and a specific resistance of 330 μΩcm to 600 μΩcm is used. Therefore, the average carbon concentration within the range of 0 μm to 300 μm from the inner surface of the crucible substrate 10 can be suppressed to 3.0×10 19 atoms / cc or less. Therefore, carbon contamination of the silicon single crystal derived from the quartz glass crucible can be prevented.

[0096] Furthermore, in the method for manufacturing a quartz glass crucible according to the present embodiment, when spraying a coating liquid containing a crystallization accelerator onto the inner surface of the crucible substrate 10, the coating liquid is sprayed using a two-fluid nozzle so that the average droplet diameter is 5 μm or more and 1000 μm or less. Further, the maximum thickness of the coating film formed by a single coating is set to 0.5 μm or less, and drying and recoating of the coating film are alternately repeated until the target carbon concentration is reached to laminate the coating film 13. Therefore, a coating film having a low carbon concentration can be formed.

[0097] As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention, and it goes without saying that those are also included in the scope of the present invention.

[0098] For example, in the above embodiment, the inner surface 10i of the crucible substrate 10 is covered with the coating film 13 of the crystallization accelerator, and the outer surface 10o is not covered with the coating film. However, both the inner surface 10i and the outer surface 10o may be covered with the coating film of the crystallization accelerator. That is, the coating film of the crystallization accelerator only needs to cover at least the inner surface 10i of the crucible substrate 10. Further, the coating film 13 does not necessarily need to be formed over the entire inner surface excluding the vicinity of the upper end of the rim of the crucible substrate, and the coating film on the inner surface of the side wall portion 10a may be omitted. That is, the coating film 13 only needs to be provided on the inner surface of at least the bottom central region (within the range of 0.5r from the bottom center) of the crucible substrate 10.

[0099] Also, in the above embodiment, when spraying the coating liquid onto the inner surface of the crucible substrate 10, the crucible substrate 10 was in an upward state. However, for example, it is also possible to apply the coating liquid in a downward state with the crucible substrate 10 turned upside down. Further, the crucible substrate 10 may be heated while applying the crystallization accelerator, or the coating may be performed after pre-heating the crucible substrate 10. Furthermore, when applying the crystallization accelerator after pre-heating the crucible substrate 10, in order to prevent a rapid decrease in the temperature of the crucible substrate 10 during the coating process, it is also possible to continue heating the crucible while applying the crystallization accelerator using a heating means different from that during pre-heating.

Example

[0100] <Evaluation of Carbon Concentration Near the Inner Surface of the Crucible> A crucible substrate constituting a 32-inch quartz glass crucible was produced by the rotational molding method. In the production of the quartz glass crucibles according to Examples 1 to 5, quartz powder with a carbon content of less than 6 ppm was used as the raw material for the inner surface of the crucible. On the other hand, in the production of the quartz glass crucibles according to Comparative Examples 1 to 4, quartz powder with a carbon content of 6 ppm or more was used as the raw material for the inner surface of the crucible. The carbon content of the quartz powder was measured by the "high-frequency combustion-infrared absorption method".

[0101] During the arc melting of the quartz powder, carbon electrodes with a bulk density of 1.50 g / cc to 1.75 g / cc and a specific resistance of 330 μΩcm to 600 μΩcm were used. The crucible substrate formed a transparent layer by evacuating the raw material powder from the outside of the rotational mold that supports the raw material powder during melting on the inner surface side, and then stopped evacuating or weakened the suction force to form a bubble layer.

[0102] Next, the rim portion of the crucible substrate was cut, washed with a cleaning solution, rinsed with pure water, and then a crystallization accelerator was applied to the inner surface of the crucible. As the cleaning solution, a semiconductor-grade hydrofluoric acid diluted with pure water (TOC ≤ 2 ppb, 17.2 MΩ or more, 15 - 25 °C) to 10 - 40 w% was used. As the crystallization accelerator, an aqueous barium hydroxide solution was used and uniformly applied by the spray method. When applying the crystallization accelerator, the crucible substrate was heated with a halogen heater, and the application was carried out while measuring the surface temperature of the crucible.

[0103] For spraying the crystallization accelerator, a two-fluid nozzle was used, and the thickness of the coating film of the crystallization accelerator formed in one application was set to about 0.5 μm, and the application was repeated until the target concentration (film thickness of about 10 μm) was reached. Thus, as shown in Table 1, a quartz glass crucible with a coating film of the crystallization accelerator formed on the inner surface of the crucible substrate was completed.

[0104] Next, the average carbon concentration and average nitrogen concentration on the inner surface of the quartz glass crucibles according to Comparative Examples 1 - 4 and Examples 1 - 5 were measured, and further the coefficient of variation (σ / AVERAGE) of the carbon concentration was determined. The carbon concentration and nitrogen concentration were measured by D-SIMS (Dynamic-Secondary Ion Mass Spectrometry). For the D-SIMS measurement, a crucible sample with a size of 10 mm × 10 mm × 5 mm cut from the inner surface of the quartz glass crucible was used. The coefficient of variation of the carbon concentration was determined from the carbon concentrations of five points consisting of one point at the center of the bottom of the crucible and four points 0.2r (r is the radius of the outer diameter of the crucible) away from the center in four directions (XY direction).

[0105] Thereafter, using another crucible sample having the same characteristics manufactured under the same conditions as the quartz glass crucibles according to Comparative Examples 1 - 4 and Examples 1 - 5, multi-pulling of silicon single crystals by the CZ method was carried out. The number of multi-pulled crystals was three, and the same crystal pulling conditions were used. Thus, the carbon concentration (relative value) of the third silicon single crystal pulled up, the number of pinholes generated in the silicon single crystal, and the yield (dislocation-free rate) of the silicon single crystal were determined respectively. Note that the yield of the single crystal is the weight ratio of the single crystal to the polycrystalline raw material. The results are shown in Table 1.

[0106] The evaluation of the carbon concentration of the silicon single crystal was performed on the third silicon single crystal in the multi-pulling process where the increase in carbon concentration due to segregation was significant. For the evaluation of pinholes and the yield of the silicon single crystal, all three silicon single crystals were targeted. The evaluation of the inner surface roughness was to evaluate the area occupancy rate of the portion where the brown ring peeled off, the silica glass was exposed, and it became uneven. "Large" indicates 50% or more, "medium" indicates 20% or more and less than 50%, and "small" indicates less than 20%. In the evaluation of pinholes, the total number of wafers obtained by processing the three silicon single crystals obtained by multi-pulling was used as the population, and the ratio of the number of wafers in which pinholes were found was determined as the pinhole occurrence rate. A pinhole occurrence rate of less than 0.1% was defined as "small", and 0.1% or more was defined as "large".

[0107]

Table 1

[0108] As shown in Table 1, the average carbon concentration on the inner surface of the quartz glass crucible according to Comparative Example 1 was 1.2×10 20 atoms / cc, the coefficient of variation of the carbon concentration was 2.2, and the average nitrogen concentration was 4.7×10 16 atoms / cc. The surface temperature of the crucible during the application of the crystallization accelerator was 50°C. When pulling a silicon single crystal using another crucible sample of the same characteristics manufactured under the same conditions as this crucible sample, the surface roughness of the inner surface of the used crucible was medium. The carbon concentration of the silicon single crystal pulled using the quartz glass crucible was determined and used as the reference value for the carbon concentration of subsequent silicon single crystals. Many pinholes were observed in this silicon single crystal. The yield of the silicon single crystal was 72.1%, resulting in a value below 80%.

[0109] The average carbon concentration on the inner surface of the quartz glass crucible according to Comparative Example 2 was 5.8×10 19 atoms / cc, the coefficient of variation of the carbon concentration was 1.8, and the average nitrogen concentration was 7.1×10 16It was atoms / cc. The surface temperature of the crucible during the application of the crystallization accelerator was 22°C. When pulling up a silicon single crystal using another crucible sample of the same characteristics manufactured under the same conditions as this crucible sample, the inner surface of the used crucible had a lot of roughness. The carbon concentration (relative value) of the silicon single crystal pulled up using the quartz glass crucible was 94. Many pinholes were observed in this silicon single crystal. The yield of the silicon single crystal was 60.2%, resulting in a value less than 80%.

[0110] The average carbon concentration on the inner surface of the quartz glass crucible according to Comparative Example 3 was 5.3×10 19 atoms / cc, the coefficient of variation of the carbon concentration was 1.2, and the average nitrogen concentration was 4.1×10 17 atoms / cc. The surface temperature of the crucible during the application of the crystallization accelerator was 265°C. When pulling up a silicon single crystal using another crucible sample of the same characteristics manufactured under the same conditions as this crucible sample, the inner surface of the used crucible had a medium level of roughness. The carbon concentration (relative value) of the silicon single crystal pulled up using the quartz glass crucible was 98. Many pinholes were observed in this silicon single crystal. The yield of the silicon single crystal was 75.0%, resulting in a value less than 80%.

[0111] The average carbon concentration on the inner surface of the quartz glass crucible according to Comparative Example 4 was 5.7×10 20 atoms / cc, the coefficient of variation of the carbon concentration was 1.5, and the average nitrogen concentration was 3.5×10 17 atoms / cc. The surface temperature of the crucible during the application of the crystallization accelerator was 300°C. When pulling up a silicon single crystal using another crucible sample of the same characteristics manufactured under the same conditions as this crucible sample, the inner surface of the used crucible had a lot of roughness. The carbon concentration (relative value) of the silicon single crystal pulled up using the quartz glass crucible was 96. Many pinholes were observed in this silicon single crystal. The yield of the silicon single crystal was 70.6%, resulting in a value less than 80%.

[0112] The quartz glass crucible according to Example 1 has no crystallization accelerator applied to its inner surface. The average carbon concentration on the inner surface of this quartz glass crucible is less than 1.0×10 12 atoms / cc, and the average nitrogen concentration is 4.7×10 16 atoms / cc. When pulling up a silicon single crystal using another crucible sample of the same characteristics manufactured under the same conditions as this crucible sample, the roughness of the inner surface of the used crucible was small. The carbon concentration (relative value) of the silicon single crystal pulled up using the quartz glass crucible was 82. Also, the number of pinholes in the silicon single crystal was small. The yield of the silicon single crystal was 85%, resulting in a good result exceeding 80%.

[0113] The average carbon concentration on the inner surface of the quartz glass crucible according to Example 2 is less than 1.3×10 16 atoms / cc, the coefficient of variation of the carbon concentration is 0.2, and the average nitrogen concentration is 3.1×10 17 atoms / cc. The surface temperature of the crucible during the application of the crystallization accelerator was 250°C. When pulling up a silicon single crystal using another crucible sample of the same characteristics manufactured under the same conditions as this crucible sample, the roughness of the inner surface of the used crucible was small. The carbon concentration (relative value) of the silicon single crystal pulled up using the quartz glass crucible was 82. Also, the number of pinholes in the silicon single crystal was small. The yield of the silicon single crystal was 81.2%, resulting in a good result exceeding 80%.

[0114] The average carbon concentration on the inner surface of the quartz glass crucible according to Example 3 is less than 3.0×10 19 atoms / cc, the coefficient of variation of the carbon concentration is 0.6, and the average nitrogen concentration is 4.7×10 17It was [X] atoms / cc. The surface temperature of the crucible during the application of the crystallization accelerator was 250 °C. When pulling up a silicon single crystal using another crucible sample of the same characteristics manufactured under the same conditions as this crucible sample, the roughness of the inner surface of the used crucible was small. The carbon concentration (relative value) of the silicon single crystal pulled up using the quartz glass crucible was 86. Also, the number of pinholes in the silicon single crystal was small. The yield of the silicon single crystal was 83.5%, achieving a good result exceeding 80%.

[0115] The average carbon concentration on the inner surface of the quartz glass crucible according to Example 4 was less than 5.2×10 14 atoms / cc, the coefficient of variation of the carbon concentration was 0.4, and the average nitrogen concentration was 1.7×10 17 atoms / cc. The surface temperature of the crucible during the application of the crystallization accelerator was 242 °C. When pulling up a silicon single crystal using another crucible sample of the same characteristics manufactured under the same conditions as this crucible sample, the roughness of the inner surface of the used crucible was small. The carbon concentration (relative value) of the silicon single crystal pulled up using the quartz glass crucible was 80. Also, the number of pinholes in the silicon single crystal was small. The yield of the silicon single crystal was 87.0%, achieving a good result exceeding 80%.

[0116] The average carbon concentration on the inner surface of the quartz glass crucible according to Example 5 was less than 1.4×10 12 atoms / cc, the coefficient of variation of the carbon concentration was 1.1, and the average nitrogen concentration was 6.6×10 16 atoms / cc. The surface temperature of the crucible during the application of the crystallization accelerator was 170 °C. When pulling up a silicon single crystal using another crucible sample of the same characteristics manufactured under the same conditions as this crucible sample, the roughness of the inner surface of the used crucible was small. The carbon concentration (relative value) of the silicon single crystal pulled up using the quartz glass crucible was 79. Also, the number of pinholes in the silicon single crystal was small. The yield of the silicon single crystal was 88.5%, achieving a good result exceeding 80%.

[0117] <Evaluation of the Heating Temperature of the Crucible> After preheating the crucible substrate with a halogen heater, a crystallization accelerator was applied to the inner surface of the crucible substrate. When applying the crystallization accelerator, the inner surface temperature of the crucible at the application position was measured non - contact by a radiation thermometer. The weight ratio of the carbonate contained in the coating film of the crystallization accelerator on the quartz glass crucible thus obtained was measured by the XPS method and the Raman measurement method. The results are shown in Table 2.

[0118]

Table 2

[0119] As shown in Table 2, when the surface temperature of the crucible was 20 °C, liquid dripping of the coating liquid occurred on the coating surface. On the other hand, when the surface temperature of the crucible was 60 °C or higher, no liquid dripping occurred and the solvent could be instantaneously evaporated.

[0120] Also, as can be seen from Table 2, when the surface temperature of the crucible was 250 °C or lower, the weight ratio of the carbonate was 2.5 w% or less, while when the surface temperature of the crucible was 500 °C, the weight ratio of the carbonate was 20%, and the weight ratio of the carbonate increased significantly. In order to reduce the carbon concentration in the coating film, it was found that the inner surface temperature of the crucible substrate should be 500 °C or lower when applying the crystallization accelerator.

Explanation of Symbols

[0121] 1 Quartz glass crucible 1s Crucible sample 2 Single - crystal silicon 3 Silicon melt 6 Coating liquid 10 Crucible substrate 10a Side wall part 10b Bottom part 10c Corner part 10i Inner surface of the crucible substrate 10o Outer surface of the crucible substrate 11 Transparent layer 12 Bubble layer 13 Coating film of crystallization accelerator 14 Mold 14a Vent hole 14i Inner surface of the mold 15 Arc electrode 16 Deposition layer of quartz powder 16a Natural quartz powder 16b Synthetic quartz powder 17A Rotating support 17B Heater 18 Robot arm 19 Spray nozzle 20 Single crystal pulling device 21 Chamber 21a Main chamber 21b Pull chamber 21c Gas inlet 21d Gas outlet 22 Carbon susceptor 23 Rotating shaft 24 Shaft drive mechanism 25 Heater 28 Single crystal pulling wire 29 Wire winding mechanism 30 SAICAS 31 Diamond blade

Claims

1. A crucible substrate made of silica glass, and a coating film containing a crystallization accelerator formed on the inner surface of the crucible substrate, wherein both the average carbon concentration in the coating film and the average carbon concentration within a range of 0 μm or more and 300 μm or less from the inner surface of the crucible substrate are 1.0×10 １２ atoms / cc or more and 1.3×10 １６ atoms / cc or less. A quartz glass crucible characterized by the above.

2. The quartz glass crucible according to claim 1, wherein the weight ratio of carbonate in the coating film is 20.0 w% or less.

3. The coefficient of variation (σ / AVERAGE) of the carbon concentration in the coating film at five points on the bottom of the crucible substrate is 1.1 or less, and the five points are a first measurement point that is the center of the bottom, a second measurement point that is a position moved 0.08 times to 0.7 times the radius of the crucible substrate in the radial direction from the first measurement point, a third measurement point that is a position rotated 90° clockwise in the circumferential direction from the second measurement point, a fourth measurement point that is a position rotated 90° clockwise in the circumferential direction from the third measurement point, and a fifth measurement point that is a position rotated 90° clockwise in the circumferential direction from the fourth measurement point. The quartz glass crucible according to claim 1 or 2.

4. The quartz glass crucible according to any one of claims 1 to 3, wherein the peeling strength of the coating film is 0.3 kN / m or more.

5. A step of manufacturing a crucible substrate made of silica glass, and a step of applying a coating liquid containing a crystallization accelerator to form a coating film of the crystallization accelerator on the inner surface of the crucible substrate, In the step of manufacturing the crucible substrate, silica powder having a carbon content of less than 6 ppm is used as a raw material for the inner surface of the crucible substrate, and arc melting of the silica powder is performed using a carbon electrode having a bulk specific gravity of 1.50 g / cc or more and 1.75 g / cc or less and a specific resistance of 330 μΩcm or more and 600 μΩcm or less. The crystallization accelerator is a compound that does not have a carbon atom in the molecule of a Group 2a element (Mg, Ca, Sr, Ba), The step of forming the coating film of the crystallization accelerator is a method for manufacturing a quartz glass crucible, characterized in that the coating liquid is applied while heating the crucible substrate at a temperature of 60°C or higher and 180°C or lower.

6. Before forming the coating film of the crystallization accelerator, the crucible substrate is washed with hydrofluoric acid of semiconductor grade or higher and pure water. The method for manufacturing a quartz glass crucible according to claim 5.

7. The crystallization accelerator is a water-soluble compound. The method for manufacturing a quartz glass crucible according to claim 5 or 6.

8. The coating liquid is applied while heating the crucible substrate so that the temperature difference between the boiling point of the solvent in the coating liquid and the temperature of the crucible substrate is -40.0°C or higher and 100°C or lower. The method for manufacturing a quartz glass crucible according to any one of claims 5 to 7.

9. The coating liquid is applied while heating the crucible substrate at a temperature of 100°C or higher and 180°C or lower. The method for manufacturing a quartz glass crucible according to any one of claims 5 to 8.

10. The step of applying the coating liquid is to spray the coating liquid using a two-fluid nozzle that mixes and sprays a gas and a liquid at the spray destination while heating the crucible substrate under a low vacuum of 1×10 ２ Pa or higher and 1×10 ５ Pa or lower. The method for manufacturing a quartz glass crucible according to any one of claims 5 to 9.

11. The step of applying the coating liquid is to spray the coating liquid using a two-fluid nozzle that mixes and sprays a gas and a liquid at the spray destination. The method for manufacturing a quartz glass crucible according to any one of claims 5 to 10.

12. The step of applying the coating liquid is to set the maximum thickness of the coating film formed by a single application to 0.5 μm or less, and to laminate the coating film by alternately repeating drying and re-application of the coating film. The method for manufacturing a quartz glass crucible according to claim 11.

13. The method for manufacturing a quartz glass crucible according to claim 11 or 12, wherein the spraying amount of the coating liquid is 300 mL / min or less.

14. A method for manufacturing a single crystal silicon, characterized by pulling up a single crystal silicon using the quartz glass crucible according to any one of claims 1 to 4.

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