Quartz glass crucible and method for producing single crystal silicon using same

Abstract

The present invention addresses the problem of providing a quartz glass crucible in which a thick crystal layer can be formed on the outer surface of the crucible at a suitable crystallization rate to improve the strength during crystal pulling. A quartz glass crucible (1) is provided with: a crucible base (10) comprising silica glass; and a coating film (13) that is formed on the outer surface (10o) of the crucible base (10) and contains a crystallization accelerator. The thickness of an outer surface crystal layer formed on the outer surface (10o) of the crucible base body (10) is 0.21-0.5 mm and the crystallization rate is 21-50 [mu] m / hr after 10 hours of the start of heat treatment performed in an Ar atmosphere at a furnace temperature of 1580 DEG C and a furnace pressure of 20 Torr. The crystallization rate of the outer surface (10o) after 20 hours from the start of the heat treatment is 10 [mu] m / hr or less.

Description

Technical Field

[0001] The present invention relates to a quartz glass crucible used when pulling a silicon single crystal by the Czochralski method (CZ method), and also to a method for producing a silicon single crystal using such a quartz glass crucible. Background Art

[0002] Single crystal silicon, the substrate material for semiconductor devices, is mostly produced using the CZ method. The CZ method involves melting polycrystalline silicon raw material in a quartz glass crucible to create a silicon melt. A seed crystal is immersed in the molten silicon. The crucible and seed crystal are rotated while the seed crystal is slowly pulled up, causing a larger single crystal to grow from the lower end of the seed crystal. The CZ method can improve the yield of large-diameter single crystal silicon.

[0003] A quartz glass crucible (silica glass crucible) is a silica glass container used to hold molten silicon during the single crystal silicon pulling process. The inner portion (inner layer) of the quartz glass crucible, which contacts the molten silicon, is essentially composed of a transparent glass layer free of bubbles. The outer portion (outer layer) is composed of a bubble-containing layer containing a large number of bubbles to disperse radiant heat from the outside and uniformly heat the crucible.

[0004] Regarding a quartz glass crucible in which deformation and cracking of the crucible can be suppressed by appropriately crystallizing the quartz glass, for example, Patent Document 1 describes an opaque quartz glass crucible with low devitrification. The quartz glass crucible has an Al concentration of 55 to 100 wtppm, a Ca concentration of 1.2 to 9.5 wtppm, and a molar concentration ratio (Al / Ca) of 15 or more.

[0005] Patent Document 2 describes a quartz glass crucible comprising: a high-aluminum-containing layer composed of quartz glass having a relatively high average aluminum concentration and disposed as the outer surface of the quartz glass crucible; and a low-aluminum-containing layer composed of quartz glass having a lower average aluminum concentration than the high-aluminum-containing layer and disposed inside the high-aluminum-containing layer. The low-aluminum-containing layer includes an opaque layer composed of quartz glass containing a large number of fine bubbles, and the high-aluminum-containing layer is composed of transparent or translucent quartz glass with a lower bubble content than the opaque layer. The average aluminum concentration in the high-aluminum-containing layer is 20 ppm or higher. This quartz glass crucible prevents bubbles from agglomerating or expanding even when the high-aluminum-containing layer crystallizes, and this crystallization progresses toward the interior of the crucible, thereby preventing deformation of the crucible.

[0006] Patent Document 3 describes a quartz glass crucible comprising: a crucible base made of silica glass; and a crystallization promoter-containing layer provided on the outer surface of the crucible base. The concentration of the crystallization promoter contained in the crystallization promoter-containing layer is 1.0×10 13atoms / cm 2 Above and 4.8×10 15 atoms / cm 2 The crucible's outer surface crystallizes neither too quickly nor too slowly, maintaining an appropriate strength development time. This allows it to withstand the long single crystal pulling process while minimizing the gap between it and the carbon susceptor, thereby stably controlling the oxygen concentration and crystal diameter of the single crystal silicon. When heated at a temperature between 1550°C and 1600°C for 25 hours, the crystal layer formed on the outer surface has a thickness of 200 to 500 μm.

[0007] The viscosity of the quartz glass crucible depends on the thermal history of the arc melting temperature, cooling rate, etc. If the thermal history changes, the fictive temperature of the glass will also change. The fictive temperature is related to the glass structure. The glass structure, such as the content ratio of the polycyclic rings in the glass, can be estimated by Raman spectroscopy. In Raman spectroscopy, the content ratio of the polycyclic rings in the glass can be measured, and the fictive temperature can be determined from the result (see non-patent document 1). There is also a known method for estimating the fictive temperature of the glass by FT-IR (Fourier Transform Infrared Spectroscopy) method (see non-patent document 2).

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-105062

[0011] Patent Document 2: Japanese Patent Application No. 2018 / 051714

[0012] Patent Document 3: International Publication No. 2021 / 140729

[0013] Non-patent literature

[0014] Non-patent document 1: AE Geissberger and FL Galeener, “Raman studies of vitreous SiO2 versus fictive temperature”, Phys. Rev. B, Vol. 28, pp. 3266-3271 (1983).

[0015] Non-patent document 2: A. Agarwal, KMDavis, and M. Tomozawa, "A simple IRspectroscopic method for determining fictive temperature of silica glasses", J. Non-Cryst. Solids, Vol. 185, pp. 191-198 (1995). Summary of the Invention

[0016] Technical problem to be solved by the invention

[0017] As described above, when the outer surface of the crucible is coated with a crystallization promoter, the outer surface of the crucible can be crystallized and the strength of the crucible can be improved. In particular, by increasing the coating concentration of the crystallization promoter to promote crystallization, a thicker crystal layer can be formed.

[0018] However, increasing the coating concentration of the crystallization accelerator accelerates the crystallization rate of the crucible's outer surface. If the crystallization rate is too fast, the outer crystal layer of the crucible may foam and peel, causing deformation and a decrease in crucible strength. If the crystallization rate of the crucible's outer surface is too slow, the outer crystal layer may become too thin to maintain the required strength, leading to problems such as crucible buckling and inward collapse.

[0019] Therefore, an object of the present invention is to provide a quartz glass crucible and a method for producing single crystal silicon using the same, which can form a thick crystal layer on the outer surface of the crucible at an appropriate crystallization rate to improve the strength during the crystal pulling process.

[0020] Solutions for solving technical problems

[0021] To solve the above-mentioned problems, a quartz glass crucible according to the present invention is characterized by comprising: a crucible base formed of silica glass; and a coating film containing a crystallization accelerator, formed on the outer surface of the crucible base, wherein the outer surface crystal layer formed on the outer surface of the crucible base has a thickness of 0.21 to 0.5 mm 10 hours after the start of heat treatment at a furnace temperature of 1580° C., a furnace pressure of 20 Torr, and an Ar atmosphere, and a crystallization rate of 21 to 50 μm / hr. The crystallization rate of the outer surface is 10 μm / hr or less 20 hours after the start of the heat treatment.

[0022] According to the present invention, not only can an outer surface crystal layer of sufficient thickness of more than 200 μm be formed on the outer surface of the crucible at high temperature during the pulling process of single crystal silicon, but the outer surface can also be crystallized at an appropriate speed that is neither too fast nor too slow. Therefore, it is possible to prevent the outer surface crystal layer from foaming and peeling while forming an outer surface crystal layer of sufficient thickness to give the crucible the required strength.

[0023] In the present invention, the fictive temperature of the outer surface of the crucible base is preferably at least 50°C lower than the fictive temperature of the base interior at a depth of 5 mm from the outer surface. If the fictive temperature of the outer surface of the crucible base is equal to or slightly lower than the fictive temperature of the base interior, diffusion of the crystallization accelerator and replacement of Si-O bonds become difficult to occur, and a crystal layer having a sufficient thickness to achieve the desired crucible strength in the initial heating phase cannot be obtained. However, if the fictive temperature of the outer surface of the crucible base is at least 50°C lower than the fictive temperature of the base interior, Si-O bonds on the outer surface are more easily broken than those inside the crucible, and diffusion of the crystallization accelerator and replacement of Si-O bonds are more likely to occur, effectively promoting crystallization.

[0024] In the present invention, the Al concentration in a first depth region within 10 mm from the outer surface of the crucible base is preferably higher than the Fe concentration in the first depth region. Furthermore, the Al concentration in a first depth region within 10 mm from the outer surface of the crucible base is preferably higher than the Ca concentration in the first depth region. Since the Al concentration within 10 mm from the outer surface of the quartz glass crucible is higher than the Ca and Fe concentrations, crystallization in the thickness direction is relatively accelerated compared to the in-plane direction of the crucible, and the outer surface of the crucible can be crystallized at an appropriate crystallization rate to a thickness sufficient to achieve a strength development effect.

[0025] The crystallization promoter is preferably Ba, and the Ba concentration in the outer surface crystal layer formed on the outer surface of the crucible base after the heat treatment is less than 10 ppm. If the Ba concentration in the outer surface crystal layer exceeds 10 ppm, the concentration of the crystallization promoter applied to the outer surface of the crucible base is high, which may cause excessive crystallization during the single crystal silicon pulling process, resulting in foaming and delamination of the outer surface crystal layer. However, if the Ba concentration in the outer surface crystal layer is less than 10 ppm, crystallization of the outer surface can be promoted while suppressing foaming and delamination of the outer surface crystal layer.

[0026] It is preferred that the coating film containing the crystallization accelerator comprises barium carbonate and a thickener, and the Ba concentration in the coating film containing the crystallization accelerator is 1.0×10 15 ~1.0×10 18atoms / cm 2 If the Ba concentration is too low, the thickness and range of the crystal layer will be uneven, and the crystal layer that can be expected to have sufficient strength improvement will not be formed. In addition, if the Ba concentration is too high, due to excessive crystallization, there is a risk of the crystal layer cracking during the single crystal silicon pulling process. However, as long as the Ba concentration is within 1.0×10 15 ~1.0×10 18 atoms / cm 2 If the temperature is within the range of , this problem can be avoided and the crystallization of the outer surface can be promoted while suppressing the foaming and peeling of the outer surface crystal layer.

[0027] In a second depth region within two-thirds of the crucible base wall thickness from the outer surface of the crucible base, the boron concentration is preferably 0.02 to 0.05 ppm, the magnesium concentration is 0.02 to 0.4 ppm, and the chromium concentration is 0.02 to 0.08 ppm. If boron, magnesium, and chromium are present in silica glass, the microstructure surrounding these atoms forms a regularly arranged crystalline structure. If these impurities are present to a certain depth from the outer surface of the crucible base, the crystallization rate in the depth direction from the outer surface to the inner surface increases, thereby thickening the outer surface crystal layer to a certain extent, thereby improving the strength of the crucible.

[0028] Preferably, the concentrations of B, Mg, and Cr in a second depth region within 2 / 3 of the wall thickness of the crucible base from the outer surface of the crucible base are higher than the concentrations of B, Mg, and Cr in a third depth region within 2 mm from the inner surface of the crucible base.

[0029] While slowing the crystallization rate of the crucible base's outer surface prevents foaming and delamination of the outer surface crystal layer, due to excessive contact between the crucible and the carbon susceptor, softened silica glass can become embedded in the gaps between the carbon susceptor components. This can cause wrinkles on the crucible's outer surface to extend to the inner surface, creating irregularities on the crucible's inner surface. However, reducing the concentrations of B, Mg, and Cr on the inner surface of the crucible base prevents a decrease in silica glass viscosity and suppresses deformation of the crucible's inner surface.

[0030] Furthermore, the method for producing single crystal silicon according to the present invention is characterized in that the single crystal silicon is pulled by the CZ method using the quartz glass crucible according to the present invention having the above-mentioned characteristics. According to the present invention, the production yield of single crystal silicon can be improved.

[0031] The method for manufacturing a quartz glass crucible according to the present invention is characterized by comprising: a step of manufacturing a crucible base made of silica glass; and a step of forming a coating film containing a crystallization promoter on the outer surface of the crucible base. The crucible base manufacturing step comprises: a step of sequentially adding natural quartz powder and synthetic quartz powder to the inner surface of a rotating mold to form a layer of raw material powders; a step of arc-melting the layer of raw material powders from the inside of the mold; and a step of terminating the arc melting and cooling the molten silica glass. The cooling step heats the mold and maintains a high temperature. This allows a fictive temperature difference of 50°C or greater between the outer surface of the crucible base and the interior of the base at a depth of 5 mm from the outer surface. Consequently, a sufficiently thick outer surface crystal layer can be formed to impart the desired strength to the crucible while preventing foaming and delamination of the outer surface crystal layer.

[0032] Effects of the Invention

[0033] According to the present invention, a quartz glass crucible and a method for manufacturing the same can be provided, which can form a thick crystal layer on the outer surface of the crucible at an appropriate crystallization rate to improve the strength during crystal pulling. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic perspective view showing the structure of a quartz glass crucible according to an embodiment of the present invention.

[0035] Figure 2 yes Figure 1 A schematic side cross-sectional view of a quartz glass crucible is shown.

[0036] Figure 3 Schematic diagram illustrating the impurity concentration distribution from the outer surface of the crucible base toward the depth direction.

[0037] Figure 4 Schematic diagram showing a method for manufacturing a quartz glass crucible by rotational molding.

[0038] Figure 5 1 is a diagram for explaining a single crystal pulling step using the quartz glass crucible according to the present embodiment, and is a schematic cross-sectional view showing the structure of a single crystal pulling apparatus.

[0039] Figure 6 This is a schematic side cross-sectional view showing the crystallization state of a quartz glass crucible caused by heating. DETAILED DESCRIPTION

[0040] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0041] Figure 1: is a schematic perspective view showing the structure of a quartz glass crucible according to an embodiment of the present invention. Figure 2 yes Figure 1 A schematic side cross-sectional view of a quartz glass crucible is shown.

[0042] like Figure 1 and Figure 2 As shown, the quartz glass crucible 1 is a silica glass container for holding silicon melt. It has a cylindrical sidewall 10a, a bottom 10b disposed below the sidewall 10a, and a corner 10c disposed between the sidewall 10a and the bottom 10b. The bottom 10b is preferably a gently curved, so-called round bottom, but may also be a flat bottom. The corner 10c has a greater curvature than the bottom 10b. The boundary between the sidewall 10a and the corner 10c, and the boundary between the bottom 10b and the corner 10c, are locations where the curvature changes from a small curvature to a large curvature.

[0043] The caliber (diameter) of the quartz glass crucible 1 varies depending on the diameter of the single crystal silicon ingot pulled from the silicon melt, but is preferably 18 inches (approximately 450 mm) or larger, preferably 22 inches (approximately 560 mm) or larger, and particularly preferably 32 inches (approximately 800 mm) or larger. This is because such large crucibles are used to pull large single crystal silicon ingots with diameters of 300 mm or larger, and are required to maintain the quality of the single crystal even after prolonged use.

[0044] The crucible wall thickness varies slightly depending on the location, but is preferably between 6 and 20 mm. In particular, the sidewall 10a of a crucible 18 inches or larger is preferably 6 mm or thicker, the sidewall 10a of a crucible 22 inches or larger is preferably 7 mm or thicker, and the sidewall 10a of a crucible 32 inches or larger is preferably 10 mm or thicker. This allows for stable storage of large amounts of silicon melt at high temperatures. The crucible wall thickness is preferably thickest at the corners 10c, with the sidewalls 10a and bottom 10b being thinner than the corners 10c.

[0045] like Figure 2 As shown, a quartz glass crucible 1 includes a crucible base 10 made of silica glass and a coating film 13 containing a crystallization promoter formed on the outer surface 10o of the crucible base 10. The crucible base 10 mainly has a two-layer structure, comprising a transparent layer 11 (bubble-free layer) containing no bubbles and a bubble layer 12 (opaque layer) containing a plurality of fine bubbles. The coating film 13 containing a crystallization promoter is provided on the outer side of the bubble layer 12.

[0046] The transparent layer 11 is a glass layer that constitutes the inner surface 10i of the crucible base 10 that contacts the silicon melt, and is provided to prevent the yield of single crystal silicon from decreasing due to bubbles in the silica glass. The inner surface 10i of the crucible base 10 is melted due to reaction with the silicon melt, so the bubbles near the inner surface cannot be sealed in the silica glass. There is a possibility that the bubbles will burst due to thermal expansion, resulting in the peeling of crucible fragments (silicon dioxide fragments). When the crucible fragments released into the silicon melt are transported to the growth interface of the single crystal silicon by the convection of the melt and are incorporated into the single crystal silicon, they become the cause of dislocation of the single crystal silicon. In addition, when the bubbles released into the silicon melt float up and reach the solid-liquid interface and are incorporated into the single crystal, they become the cause of pinholes in the single crystal silicon.

[0047] The transparent layer 11 does not contain bubbles, which means that the bubble content and bubble size are such that the single crystallization rate is not reduced due to bubbles. The bubble content is, for example, 0.1 vol% or less, and the bubble diameter is, for example, 100 μm or less.

[0048] The thickness of the transparent layer 11 is preferably 0.5 to 10 mm. The thickness is appropriately set at each location in the crucible so that it does not completely disappear due to melting loss during the crystal pulling process, thereby exposing the bubble layer 12. The transparent layer 11 is preferably provided throughout the entire crucible, from the sidewall 10 a to the bottom 10 b. However, the transparent layer 11 may be omitted at the upper end of the crucible, which does not come into contact with the silicon melt.

[0049] The bubble content and bubble diameter of the transparent layer 11 can be measured non-destructively using an optical detection mechanism. The optical detection mechanism includes a light receiving device that receives transmitted light or reflected light irradiated to the crucible. A digital camera including an optical lens and an imaging element can be used as the light receiving device. In addition to visible light, ultraviolet light, and infrared light, X-rays or lasers can also be used as irradiation light. The measurement results obtained by the optical detection mechanism are input into an image processing device to calculate the bubble diameter and bubble content per unit volume.

[0050] The bubble layer 12 is a primary glass layer within the crucible base 10, located outside the transparent layer 11. It is provided to improve the thermal insulation of the silicon melt within the crucible and to disperse radiant heat from the heater of the single crystal pulling apparatus, thereby heating the silicon melt within the crucible as evenly as possible. Therefore, the bubble layer 12 extends across the entire crucible, from the sidewall 10a to the bottom 10b. The thickness of the bubble layer 12 is approximately equal to the value obtained by subtracting the thickness of the transparent layer 11 from the thickness of the crucible base 10, but varies depending on the location within the crucible.

[0051] The bubble content of the bubble layer 12 is higher than that of the transparent layer 11, and is preferably greater than 0.1 vol% and less than 5 vol%. The reason is that if the bubble content of the bubble layer 12 is less than 0.1 vol%, the heat-insulating function required of the bubble layer 12 cannot be exerted. Furthermore, the reason is that when the bubble content of the bubble layer 12 exceeds 5 vol%, there is a possibility that the crucible will be deformed due to the thermal expansion of the bubbles, resulting in a decrease in the single crystal yield, and the heat conductivity becomes insufficient. From the perspective of the balance between heat insulation and heat conductivity, the bubble content of the bubble layer 12 is particularly preferably 1 to 4 vol%. In addition, the bubble content is a value obtained by measuring an unused crucible under room temperature. The bubble content of the bubble layer 12 can be obtained, for example, by measuring the specific gravity of an opaque silica glass piece cut from the crucible (Archimedes method).

[0052] Figure 3 Schematic diagram illustrating the impurity concentration distribution from the outer surface 10 o of the crucible base 10 toward the depth direction.

[0053] like Figure 3 As shown, the Al concentration in the first depth region D1 within at least 10 mm from the outer surface 10° of the crucible base 10 is preferably higher than the Fe and Ca concentrations in this first depth region D1. If the Al concentration in the outer surface layer within 10 mm from the outer surface 10° of the crucible base 10 is lower than the Ca and Fe concentrations, the crystallization promoter applied to the outer surface 10° of the crucible base 10 is less likely to be captured by the Al, thus promoting crystallization in the in-plane direction rather than in the depth direction. To promote crystallization in the depth direction to a thickness that effectively enhances the crucible's strength, it is desirable to increase the Al concentration in the wall to a level that serves as an impurity that acts as a starting point for crystallization.

[0054] The B concentration in the second depth region D2 within two-thirds of the crucible base 10's wall thickness from the outer surface 10o of the crucible base 10 is preferably 0.02-0.05 ppm, the Mg concentration is preferably 0.02-0.4 ppm, and the Cr concentration is preferably 0.02-0.08 ppm. If B, Mg, and Cr are present in silica glass, the microstructure surrounding these atoms will form a regularly arranged crystalline structure. If these impurities are present in a sufficiently deep region from the outer surface 10o of the crucible base 10, crystallization from the outer surface 10o toward the depth will accelerate, thereby forming a relatively thick crystal layer on the outer surface 10o of the crucible base 10 and improving the strength of the crucible.

[0055] The concentrations of B, Mg, and Cr in the second depth region D2 within 2 / 3 of the wall thickness W of the crucible base 10 from the outer surface 10o of the crucible base 10 are preferably higher than the concentrations of B, Mg, and Cr in the third depth region D3 within 2 mm from the inner surface 10i of the crucible base 10. The wall thickness of the crucible base 10 referred to herein refers to the wall thickness at the location where B, Mg, and Cr are measured. The carbon base that supports the quartz glass crucible during the crystal pulling process is composed of multiple components. Joints (grooves) between the components exist on the inner surface of the split carbon base. Therefore, the outer surface 10o of the crucible base 10 may soften before crystallization at high temperatures and become embedded in the gaps in the joints of the split carbon base. When this embedding occurs, the outer surface 10o of the crucible base 10 deforms along the joints, simultaneously inducing deformation of the inner surface 10i of the crucible base 10. However, by reducing the concentrations of B, Mg, and Cr on the inner surface 10 i of the crucible base 10 , it is possible to prevent a decrease in the viscosity of silica glass and suppress deformation of the inner surface of the crucible.

[0056] The fictive temperature T1 (°C) of the outer surface 10° of the crucible base 10 is preferably at least 50°C lower than the fictive temperature T2 (°C) of the base interior at a depth of 5 mm from the outer surface 10°C (T1 < T2 - 50). If the fictive temperature T1 of the outer surface 10° of the crucible base 10 is equal to or slightly lower than the fictive temperature T2 of the interior, diffusion of the crystallization accelerator and substitution of Si-O bonds become difficult to occur, and an outer surface crystal layer having a sufficient thickness to achieve the desired crucible strength in the initial heating phase cannot be obtained. However, if the fictive temperature T1 of the outer surface 10° of the crucible base 10 is at least 50°C lower than the fictive temperature T2 of the interior, Si-O bonds on the outer surface 10° are more easily broken than those inside the crucible base 10, and diffusion of the crystallization accelerator and substitution of Si-O bonds are more likely to occur, effectively promoting crystallization.

[0057] The fictive temperature of the silica glass that constitutes the crucible base 10 can be measured using Raman spectroscopy or FT-IR. In Raman spectroscopy, the area intensity ratio of the peak derived from the three-membered ring structure of Si to the peak derived from the four-membered ring structure is determined from the Raman (scattering) spectrum obtained when laser light is irradiated onto the surface of the sample being measured. By plotting this result on a calibration curve obtained from measurements of a sample with a known fictive temperature, the fictive temperature of the sample can be calculated.

[0058] When measuring fictive temperature using FT-IR, the peak wavelength originating from the structure of quartz glass is detected from the transmission spectrum obtained when a laser is irradiated onto a sample made by thinning the glass being measured. By plotting the obtained results on a calibration curve obtained from measurements of a sample with a known fictive temperature, the fictive temperature of the sample can be calculated.

[0059] A coating film 13 containing a crystallization accelerator is provided on the outer surface 10o of the crucible base 10. The crystallization accelerator contained in the coating film 13 promotes crystallization of the crucible's outer surface at the high temperatures during the single crystal pulling process, thereby improving the crucible's strength. The reasons for providing the coating film 13 containing a crystallization accelerator on the crucible's outer surface are as follows. First, while providing the coating film 13 containing a crystallization accelerator on the crucible's inner surface increases the risk of pinholes forming in the silicon single crystal and the risk of separation between the inner and outer layers of the crucible, providing the coating film 13 on the crucible's outer surface reduces these risks. Furthermore, while providing the coating film 13 containing a crystallization accelerator on the crucible's inner surface carries the risk of contamination of the single crystal due to impurities on the crucible's inner surface, impurity contamination on the crucible's outer surface is tolerated to a certain extent. Therefore, providing the coating film 13 containing a crystallization accelerator on the crucible's outer surface reduces the risk of contamination of the single crystal.

[0060] In this embodiment, although the coating film 13 containing a crystallization accelerator is provided on the entire crucible from the side wall portion 10a to the bottom 10b, it is sufficient to be provided on the side wall portion 10a. The reason is that the side wall portion 10a is more easily deformed than the corner portion 10c and the bottom 10b, and the effect of suppressing the deformation of the crucible by crystallization of the outer surface is also greater. It is preferred that the coating film 13 containing a crystallization accelerator is provided not only on the side wall portion 10a, but also on the corner portion 10c. The coating film 13 containing a crystallization accelerator may also be provided on the bottom 10b of the crucible, or it may not be provided on the bottom 10b of the crucible. The reason is that the bottom 10b of the crucible bears the weight of a large amount of silicon melt and is easily adhered to the carbon base, so it is difficult to generate a gap between the bottom 10b and the carbon base.

[0061] The area from the upper edge of the rim of the outer surface of the crucible sidewall 10a to the lower edge 1 to 3 cm can also be a non-formed region for the coating film 13 containing a crystallization promoter. This can suppress crystallization at the upper edge and prevent dislocation of the single crystal silicon caused by crystal flakes peeled from the upper edge surface mixing into the silicon melt.

[0062] The crystallization promoter contained in the coating film 13 containing a crystallization promoter is preferably Ba (barium) or Sr (strontium), with Ba being particularly preferred. This is because Ba has a smaller segregation coefficient than silicon, is stable at room temperature, and is easy to handle. Furthermore, Ba has the following advantages: the crystallization rate does not decrease with crystallization, and it promotes orientation growth more strongly than other elements.

[0063] The coating film 13 containing a crystallization accelerator contains barium carbonate and a thickener. The concentration of Ba contained in the coating film 13 containing a crystallization accelerator is preferably 1.0×10 15 ~1.0×10 18 atoms / cm 2 , particularly preferably 1.0×10 16 ~1.0×10 17 atoms / cm 2 When the Ba concentration is lower than 1.0×10 15 atoms / cm 2 In the case of Ba concentration higher than 1.0×10 18 atoms / cm 2 In the case of excessive crystallization of the outer surface, the probability of cracks in the outer surface crystal layer increases. However, as long as the Ba concentration is within the above range, this problem can be avoided, and the crystallization of the outer surface can be promoted while suppressing the foaming and delamination of the outer surface crystal layer.

[0064] The thickness of the coating film 13 containing a crystallization accelerator is not particularly limited, but is preferably 0.1 to 50 μm, particularly preferably 1 to 20 μm. This is because if the coating film 13 containing a crystallization accelerator is too thin, the peel strength of the coating film 13 containing a crystallization accelerator is weak, resulting in uneven crystallization due to peeling of the coating film. If the coating film is too thick, the peel strength also decreases, resulting in uneven crystallization.

[0065] When the quartz glass crucible 1 according to this embodiment is heat-treated in a furnace at 1580°C, 20 Torr, and an Ar atmosphere, the length of crystal growth (crystallized length) in the depth direction from the outer surface 10o of the crucible base 10 from the start of the heat treatment until 10 hours later is 0.21 to 0.5 mm. In other words, the thickness of the outer surface crystal layer formed on the outer surface 10o of the crucible base 10 after 10 hours is 210 to 500 μm. Furthermore, while the crystallization rate is 21 to 50 μm / hr 10 hours after the start of the heat treatment, the crystallization rate drops below 10 μm / hr 20 hours after the start of the heat treatment. If the outer surface crystallization rate is faster than 50 μm / hr in the initial crystallization stage, there is a risk of foaming and delamination of the outer surface crystal layer. Furthermore, if the crystallization rate is slower than 21 μm / hr, the outer surface crystallization becomes insufficient, and the required crucible strength cannot be achieved. However, according to the present invention, it is possible to form an outer surface crystal layer having a sufficient thickness to develop the required strength of the crucible without causing foaming and separation of the outer surface crystal layer.

[0066] Here, "10 hours after the start of the heat treatment" refers to the moment when all the polysilicon raw materials in the crucible are melted and stress begins to be applied to the crucible wall. The reason is that if the moment when the outer surface crystal layer becomes of sufficient thickness is later than this, the probability of crucible deformation will become higher. In addition, the crystallization rate 10 hours after the start of the heat treatment is the value obtained by dividing the thickness of the outer surface crystal layer after 10 hours by the heat treatment time (10 hours), and is calculated as the average value of the crystallization rate for 10 hours. In addition, the crystallization rate 20 hours after the start of the heat treatment is the difference between the thickness of the outer surface crystal layer after 20 hours and the thickness of the outer surface crystal layer after 30 hours divided by the heat treatment time (10 hours), and is calculated as the average value of the crystallization rate for 10 hours.

[0067] As mentioned above, the crystallization rate preferably decreases after 15 hours from the start of heat treatment, and is preferably 10 μm / hr or less after 20 hours from the start of heat treatment. If the crystallization rate exceeds 10 μm / hr after 20 hours from the start of heat treatment, the thickness of the outer surface crystal layer will become too thick, and there is a risk of cracking the crystal layer during crystal pulling. By slowing the crystallization rate after melting the polycrystalline raw material, not only can the strength of the crucible be developed earlier, but the strength can also be maintained.

[0068] The thickness of the outer surface crystal layer formed on the outer surface 10o of the crucible base 10 25 hours after the start of the aforementioned 1580°C heat treatment is preferably approximately 210 to 600 μm, particularly preferably 210 to 500 μm. If the thickness of the outer surface crystal layer is less than 210 μm 25 hours after the start of the single crystal pulling process, the probability of deformation of the crucible due to insufficient strength increases. Furthermore, if the thickness of the outer surface crystal layer is thicker than 500 μm, the adhesion between the crucible and the carbon susceptor will deteriorate, and the thermal conductivity between the carbon susceptor and the quartz glass crucible will fluctuate during the crystal pulling process, adversely affecting the control of the oxygen concentration and crystal diameter of the single crystal silicon. Furthermore, if the outer surface crystal layer becomes too thick, it may foam and delaminate, adversely affecting the pulling of the single crystal. However, if the thickness of the crystal layer is within the above range, strength is maintained after the crucible and carbon susceptor are bonded together, and the oxygen concentration and crystal diameter of the single crystal silicon can be stably controlled.

[0069] In a quartz glass crucible coated with a crystallization accelerator on the outer surface, the final thickness of the outer surface crystal layer is believed to be determined by the crystallization accelerator concentration. Increasing the crystallization accelerator concentration can form a thicker outer surface crystal layer. However, increasing the crystallization accelerator concentration promotes crystallization of the outer surface not only in the depth direction but also in the planar direction, which can easily lead to foaming, delamination, and cracking of the outer surface crystal layer.

[0070] During the crystallization of the outer surface of the crucible, point-like crystal nuclei (young nuclei) are first generated. The crystal nuclei grow as the heating time passes, and in this process, they combine with other nearby crystal nuclei to form a planar crystal layer. Ideally, the planar crystal layer thickens without peeling off. However, if the crystal layer reaches the level of strength too quickly, it is prone to foaming, peeling, and cracking. Conversely, if crystallization is too slow, the crucible will deform before it shows strength. So far, it is impossible to optimize the crystallization rate simply by increasing the concentration of the crystallization promoter.

[0071] In contrast, the quartz glass crucible according to this embodiment adjusts factors other than the concentration of the crystallization promoter, namely, the fictive temperature gradient from the outer surface to the depth direction and the concentration of metal impurities such as Ca and Fe, thereby promoting crystallization in the depth direction of the outer surface and optimizing the crystallization rate. This prevents the occurrence of bubbling, delamination, and cracks while forming a sufficiently thick outer surface crystal layer to improve the strength of the crucible.

[0072] Next, a method for manufacturing the quartz glass crucible 1 will be described. The quartz glass crucible 1 of this embodiment can be manufactured by manufacturing the crucible base 10 by so-called rotational molding and then applying a crystallization accelerator to the outer surface 10 o of the crucible base 10 .

[0073] Figure 4 Schematic diagram showing a method for manufacturing a quartz glass crucible by rotational molding.

[0074] like Figure 4 As shown, in the rotational molding method, a carbon mold 14 having a cavity matching the crucible shape is prepared. Natural quartz powder 16a and synthetic quartz powder 16b are sequentially filled along the inner surface 14i of the rotating carbon mold 14, thereby forming a deposited layer 16 of raw quartz powder. The raw quartz powder adheres to the inner surface 14i of the carbon mold 14 due to centrifugal force, remains in a fixed position, and maintains the crucible shape.

[0075] Next, a carbon arc electrode 15 is placed in the carbon mold 14 to arc melt the accumulated layer 16 of the raw quartz powder from the inside of the carbon mold 14. Specific conditions such as the heating time and heating temperature can be appropriately determined in consideration of the properties of the raw quartz powder and the size of the crucible.

[0076] During the arc melting process, the amount of bubbles in the fused silica glass is controlled by vacuuming the accumulated layer 16 of the raw silica powder through a plurality of vent holes 14a provided on the inner surface 14i of the carbon mold 14. Specifically, at the start of arc melting, the accumulated layer 16 of the raw silica powder is vacuumed to form a transparent layer 11. After the formation of transparent layer 11, the vacuuming of the raw silica powder is stopped or the suction force is weakened to form a bubble layer 12.

[0077] Arc heat is transferred from the inside to the outside of the accumulated layer 16 of raw silica powder, gradually melting the raw silica powder. Therefore, by changing the reduced pressure conditions at the moment the raw silica powder begins to melt, the transparent layer 11 and the bubble layer 12 can be formed separately. Specifically, if reduced pressure melting is performed, where the reduced pressure is increased at the moment the raw silica powder melts, the atmospheric gas is not enclosed in the glass, resulting in the fused silica being a silica glass without bubbles. On the other hand, if normal melting (atmospheric pressure melting) is performed, where the reduced pressure is reduced at the moment the raw silica powder melts, the atmospheric gas is enclosed in the glass, resulting in the fused silica being a silica glass containing many bubbles.

[0078] In order to make the Al concentration in the first depth region within 10 mm from the outer surface 10° of the crucible base 10 higher than the Ca and Fe concentrations, it is preferable to use a carbon mold 14 with a higher Al impurity concentration on the inner surface, and to diffuse Al into the region that will become the outer surface 10° of the crucible base 10 during the arc melting process. Alternatively, when filling the carbon mold 14 with quartz raw material powder, the raw material with a higher Al impurity concentration can be filled outside the region that will become the outer surface 10° of the crucible base 10 after arc melting, and to diffuse Al into the region that will become the outer surface 10° of the crucible base 10 during the arc melting process. Furthermore, the raw material with a higher Al impurity concentration can be removed after arc melting. In either method, the Al concentration can be increased and the Ca and Fe concentrations can be decreased near the outer surface 10° of the crucible base 10, and crystallization can be promoted more in the thickness direction than in the in-plane direction.

[0079] The fictive temperature changes with the cooling temperature of the glass. When the molten silica is rapidly cooled, the fictive temperature of the quartz glass becomes higher, and when it is slowly cooled, the fictive temperature of the quartz glass becomes lower. Since the arc electrode 15, which serves as the heat source during the arc melting process, is located on the inner surface of the crucible, the cooling of the inner surface of the crucible begins immediately after the arc ends. On the other hand, there is a carbon mold 14 on the outer surface of the crucible, and the carbon mold remains at a high temperature even after the arc ends. Here, by temporarily stopping the air cooling or water cooling of the carbon mold 14, the cooling rate of the outer surface 10o side of the crucible base 10 becomes slower than that of the inner surface 10i side. In other words, since the outer surface 10o side of the crucible base 10 cools more slowly than the inner surface 10i side, the fictive temperature of the outer surface 10o becomes lower than that of the interior. In this embodiment, the heat preservation is further improved by heating the carbon mold 14 to slow down the cooling rate of the outer surface 10 o of the crucible base 10 , thereby increasing the fictive temperature difference between the outer surface 10 o of the crucible base 10 and the base interior by 50° C. or more.

[0080] The arc melting is then terminated and the crucible is cooled. In this manner, the crucible base 10 is completed, with the transparent layer 11 and the bubble layer 12 arranged sequentially from the inside to the outside of the crucible wall. Thus, the crucible base 10 according to this embodiment can be manufactured by filling a rotating carbon mold 14 with natural quartz powder 16a as the outer layer material, then filling it with synthetic quartz powder 16b as the inner layer material, and arc melting the accumulated layer 16 of the raw quartz powder.

[0081] Next, the crucible base 10 is shaped by cutting the edges and then cleaned with a cleaning solution and rinsed with pure water. The cleaning solution is preferably prepared by diluting semiconductor-grade or higher hydrofluoric acid with pure water having a TOC of ≤ 2 ppb to a concentration of 10-40 w%.

[0082] Next, apply a crystallization accelerator to the outer surface 10o of the crucible base 10. A brush is preferably used for application. To evenly distribute the crystallization accelerator over the outer surface 10o, a coating solution prepared by dissolving the crystallization accelerator in pure water (15-25°C, 17.2 MΩ or higher, TOC ≤ 2 ppb) is preferably used. To increase the solubility of the crystallization accelerator, a stirrer is preferably used to agitate the coating solution.

[0083] When the crystallization promoter is barium, for example, a solution containing a barium compound such as barium carbonate can be used. The coating solution containing the barium compound may be a coating solution containing the barium compound and water, or a coating solution containing no water and anhydrous ethanol and the barium compound. Barium carbonate is preferred as the barium compound, but other barium compounds such as barium chloride, barium acetate, barium nitrate, barium hydroxide, barium oxalate, and barium sulfate may also be used. In addition, as long as the surface concentration of the barium element (atoms / cm 2 ) are the same, the crystallization promoting effect is the same whether it is insoluble or soluble in water, but water-insoluble barium is more difficult to be absorbed by the human body, so it is safer and has advantages in handling.

[0084] The coating liquid comprising barium compound preferably further comprises the higher water-soluble polymer (thickening agent) of viscosity such as carboxyvinyl polymer.In the case of using the coating liquid without thickening agent, due to barium being unstable in the fixing of crucible wall, it is necessary to heat-treat for fixing barium, if this heat-treating is implemented, barium can diffuse and penetrate into the inside of quartz glass, becomes the main cause promoting random growth of crystal.Here, random growth refers to that in crystalline layer, crystal growth direction does not have regularity and crystal grows in all directions.In random growth, due to crystallization stopping in heating initial stage, it is therefore impossible to fully ensure the thickness of crystalline layer.

[0085] However, when using a coating liquid containing a thickener along with a barium compound, the increased viscosity of the coating liquid prevents uneven application to the crucible due to gravity and other factors. Furthermore, when a coating liquid containing a barium compound such as barium carbonate contains a water-soluble polymer, the barium compound disperses in the coating liquid without agglomerating, allowing for uniform application of the barium compound to the crucible surface. This allows for uniform and high-density fixation of high-concentration barium to the crucible wall, promoting the growth of columnar or dome-shaped grains.

[0086] Columnar-oriented crystals refer to a crystal layer composed of a collection of columnar grains. Furthermore, dome-oriented crystals refer to a crystal layer composed of a collection of dome-shaped grains. Columnar or dome-oriented crystals allow for sustained crystal growth, thus forming a crystal layer of sufficient thickness.

[0087] Examples of thickeners include water-soluble polymers with low metal impurity content, such as polyvinyl alcohol, cellulose-based thickeners, high-purity glucomannan, acrylic acid polymers, carboxyvinyl polymers, and polyethylene glycol fatty acid esters. Acrylic acid / alkyl methacrylate copolymers, polyacrylates, polyvinyl carboxamides, and vinyl carboxamides can also be used as thickeners. The viscosity of the coating solution containing barium is preferably in the range of 100 to 10,000 mPa·s, and the boiling point of the solvent is preferably 50 to 100°C.

[0088] For example, a crystallization accelerator coating liquid for coating the outer surface of a 32-inch crucible contains 0.0012 g / mL of barium carbonate and 0.0008 g / mL of carboxyvinyl polymer, and can be prepared by adjusting the ratio of ethanol and pure water and mixing and stirring them.

[0089] Figure 5 This 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 structure of a single crystal pulling apparatus.

[0090] like Figure 5 As shown, a single crystal pulling apparatus 20 is used in the single crystal silicon pulling process according to the CZ method. The single crystal pulling apparatus 20 includes a water-cooled chamber 21, a quartz glass crucible 1 for holding a silicon melt in the chamber 21, a carbon susceptor 22 for holding the quartz glass crucible 1, a rotation shaft 23 for rotatably and vertically supporting the carbon susceptor 22, a shaft driving mechanism 24 for rotating and vertically driving the rotation shaft 23, a heater 25 disposed around the carbon susceptor 22, a single crystal pulling wire 28 disposed above the quartz glass crucible 1 and coaxial with the rotation shaft 23, and a wire winding mechanism 29 disposed above the chamber 21.

[0091] The chamber 21 consists of a main chamber 21a and an elongated cylindrical crystal pulling chamber 21b connected to the upper opening of the main chamber 21a. The quartz glass crucible 1, carbon susceptor 22, and heater 25 are disposed within the main chamber 21a. A gas inlet 21c is provided at the top of the crystal pulling chamber 21b for introducing an inert gas (purge gas) such as argon or a dopant gas into the main chamber 21a. A gas exhaust port 21d is provided at the bottom of the main chamber 21a for exhausting the atmospheric gas within the main chamber 21a.

[0092] The carbon susceptor 22 is used to maintain the shape of the quartz glass crucible 1 softened at high temperature, and holds the quartz glass crucible 1 by enclosing it. The quartz glass crucible 1 and the carbon susceptor 22 constitute a double-structure crucible that supports the silicon melt in the chamber 21 .

[0093] The carbon susceptor 22 is fixed to the upper end of a rotating shaft 23 , and the lower end of the rotating shaft 23 is connected to a shaft driving mechanism 24 that penetrates the bottom of the chamber 21 and is provided outside the chamber 21 .

[0094] The heater 25 melts the polysilicon raw material filled in the quartz glass crucible 1 to generate the silicon melt 3 and maintains the molten state of the silicon melt 3. The heater 25 is a resistance heating carbon heater and is provided to surround the quartz glass crucible 1 in the carbon susceptor 22.

[0095] A wire reel 29 is positioned above the crystal pulling chamber 21b. Wire 28 extends downward from the wire reel 29 through the crystal pulling chamber 21b, with the distal end of wire 28 reaching the interior of the main chamber 21a. This figure shows a silicon single crystal 2 suspended from wire 28 during growth.

[0096] When pulling single silicon crystal 2, wire 28 is slowly pulled while rotating quartz glass crucible 1 and single silicon crystal 2, thereby growing single silicon crystal 2. Although the amount of silicon melt within quartz glass crucible 1 decreases as single silicon crystal 2 grows, quartz glass crucible 1 is raised to maintain a constant melt level. This stabilizes the crystal quality along the growth direction.

[0097] Figure 6 This is a schematic side cross-sectional view showing the crystallization state of a quartz glass crucible caused by heating.

[0098] like Figure 6 As shown, an outer surface crystal layer 31 is formed on the outer surface 10o of the quartz glass crucible 1 during the crystal pulling process. The Ba concentration in the outer surface crystal layer 31 formed on the outer surface 10o of the crucible base 10 by heating or equivalent heat treatment during the crystal pulling process is preferably less than 10 ppm. If the Ba concentration in the outer surface crystal layer 31 is 10 ppm or higher, the concentration of the crystallization promoter applied to the outer surface 10o of the crucible base 10 is high, which excessively promotes crystallization of the outer surface 10o and easily causes foaming and delamination of the outer surface crystal layer 31. However, if the Ba concentration in the outer surface crystal layer 31 is less than 10 ppm, it is possible to promote crystallization of the outer surface while suppressing foaming and delamination of the outer surface crystal layer 31.

[0099] As described above, the quartz glass crucible 1 according to this embodiment includes: a crucible base 10 made of silica glass; and a coating film 13 containing a crystallization accelerator, formed on the outer surface 10o of the crucible base 10. Ten hours after the start of heat treatment in a furnace at a furnace temperature of 1580°C, a furnace pressure of 20 Torr, and an Ar atmosphere, the length of crystal growth in the depth direction from the outer surface 10o of the crucible base 10 is 0.21 to 0.5 mm, and the crystallization rate is 21 to 50 μm / hr. The crystallization rate of the outer surface 10o after 20 hours from the start of the heat treatment is 10 μm / hr or less. Therefore, not only can an outer surface crystal layer 31 having a sufficient thickness of 200 μm or more be formed on the outer surface of the crucible at the high temperature during the single crystal silicon pulling process, but also the outer surface 10o can be crystallized at an appropriate rate that is neither too fast nor too slow. Therefore, it is possible to form the outer surface crystal layer 31 having a sufficient thickness to impart the required strength to the crucible while preventing the outer surface crystal layer 31 from foaming and peeling.

[0100] Furthermore, the quartz glass crucible 1 according to this embodiment has a fictive temperature of the outer surface 10° of the crucible base 10 that is 50°C lower than the fictive temperature of the interior at a depth of 5 mm from the outer surface 10°. This not only promotes crystallization of the crucible's outer surface, but also maintains a moderate strength development time, neither too fast nor too slow. Consequently, the crucible can withstand long single crystal pulling processes while minimizing the gap between the crucible and the carbon susceptor, thereby stably controlling the oxygen concentration and crystal diameter of the silicon single crystal.

[0101] While preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention, which are naturally included in the scope of the present invention.

[0102] Example

[0103] Four crucible substrates with varying concentrations of metal impurities on their outer surfaces were prepared. A barium carbonate solution was applied to a portion of the crucible substrate's outer surface using a brush, and the crucibles were then broken into smaller pieces. Metal impurity analysis was performed from the outer surface of the crucible substrate to the depth of the crucible substrate using the uncoated crucible fragments from the same crucible substrate. The metal impurity analysis involved wet etching to dissolve silica glass to a predetermined depth from the crucible's outer surface. The etchant was then recovered and the amount of metal impurities dissolved in the etchant was measured using ICP-MS (Inductively Coupled Plasma-Mass Spectrometry).

[0104] In the measurement of Al, Ca, and Fe among the metal impurities, the first measurement range was from the outer surface of the crucible base to a depth of 5 mm, the second measurement range was from a depth of 5 to 10 mm, and the third measurement range was from a depth of 10 to 15 mm. The measurement results are shown in Tables 1 and 2.

[0105] [Table 1]

[0106]

[0107] As shown in Table 1, the Fe and Al concentration distributions of the crucible base of Comparative Example 1 show that the Fe concentration is high throughout the entire region from the outer surface to a depth of 15 mm, and the relationship of Fe concentration > Al concentration holds. Furthermore, the Fe and Al concentration distributions of the crucible base of Comparative Example 2 show that the Fe concentration is < Al concentration in the region from the outer surface to a depth of 5 mm, and the Fe concentration > Al concentration in the region from 5 to 15 mm. In contrast, the Fe and Al concentration distributions of the crucible base of Example 1 show that the Fe concentration is < Al concentration in the region from the outer surface to a depth of 10 mm, and the Fe concentration > Al concentration in the region from 10 to 15 mm. Furthermore, in the crucible base of Example 2, the Fe concentration < Al concentration holds throughout the entire region from the outer surface to a depth of 15 mm.

[0108] [Table 2]

[0109]

[0110] As shown in Table 2, the Ca concentration distribution also tends to be similar to that of Fe. That is, with respect to the Ca and Al concentration distributions of the crucible base of Comparative Example 1, the Ca concentration is high in the entire region from the outer surface to a depth of 15 mm, and the relationship of Ca concentration > Al concentration holds. Furthermore, with respect to the Ca and Al concentration distributions of the crucible base of Comparative Example 2, the relationship of Ca concentration < Al concentration holds in the region from the outer surface to a depth of 5 mm, and the relationship of Ca concentration > Al concentration holds in the region from 5 to 15 mm. In contrast, with respect to the Ca and Al concentration distributions of the crucible base of Example 1, the relationship of Ca concentration < Al concentration holds in the region from the outer surface to a depth of 10 mm, and the relationship of Ca concentration > Al concentration holds in the region from 10 to 15 mm. Furthermore, in the crucible base of Example 2, the relationship of Ca concentration < Al concentration holds in the entire region from the outer surface to a depth of 15 mm.

[0111] As described above, in the crucible samples of Comparative Examples 1 and 2, the Fe concentration and the Ca concentration in the depth region from the outer surface to 10 mm were higher than the Al concentration. In contrast, in the crucible samples of Examples 1 and 2, the Al concentration in the depth region from the outer surface to 10 mm was lower than the Fe concentration and the Ca concentration.

[0112] Among the metal impurities, B, Mg, and Cr were measured in a depth range from the outer surface to 2 / 3 of the crucible wall thickness. After dissolving the silica glass by wet etching, the etching solution was recovered and the amount of metal impurities dissolved in the etching solution was measured by ICP-MS. The measurement results are shown in Table 3.

[0113] [Table 3]

[0114] B concentration (ppm) Mg concentration (ppm) Cr concentration (ppm) Comparative Example 1 0.1 0.5 0.1 Comparative Example 2 0.01 0.01 0.01 Example 1 0.02 0.02 0.02 Example 2 0.05 0.4 0.08

[0115] As shown in Table 3, the B concentration of the crucible base of Comparative Example 1 was 0.1 ppm. The B concentration of the crucible base of Comparative Example 2 was 0.01 ppm. On the other hand, the B concentration distribution of the crucible base of Example 1 was 0.02 ppm, and the B concentration of the crucible base of Example 2 was 0.05 ppm.

[0116] As shown in Table 3, the Mg concentration of the crucible base of Comparative Example 1 was 0.5 ppm. The Mg concentration of the crucible base of Comparative Example 2 was 0.01 ppm. On the other hand, the Mg concentration of the crucible base of Example 1 was 0.02 ppm, and the Mg concentration of the crucible base of Example 2 was 0.4 ppm.

[0117] As shown in Table 3, the Cr concentration of the crucible base of Comparative Example 1 was 0.1 ppm. The Mg concentration of the crucible base of Comparative Example 2 was 0.01 ppm. On the other hand, the Cr concentration of the crucible base of Example 1 was 0.02 ppm, and the Cr concentration of the crucible base of Example 2 was 0.08 ppm.

[0118] Next, the fictive temperature of the crucible base's outer surface and the fictive temperature within the base, 5 mm below the outer surface, were measured using Raman spectroscopy. The fictive temperature measurement region for the outer surface was set at a depth of 0 mm to 0.5 mm from the outer surface. Furthermore, the fictive temperature measurement region for the base's interior was set at a depth of 5.0 mm to 5.5 mm from the outer surface. The fictive temperature differences between the outer surface and the interior of the crucible base are shown in Table 4.

[0119] [Table 4]

[0120]

[0121] Next, a heating test was conducted using a crucible piece coated with barium carbonate. In the heating test, a crucible piece with a side of 10 to 20 cm and an area of 200 cm was used. 2 The crucible piece has an aspect ratio as close to 1 as possible. Regarding the heating conditions, the temperature was raised from room temperature to 1580°C over 2.5 hours in an Ar atmosphere furnace, and then maintained at 1580°C for 10 hours. The pressure in the furnace maintained at 1580°C was 20 Torr.

[0122] The crystallization state of the crucible's outer surface was then evaluated. Specifically, the thickness of the outer surface crystal layer was determined, and the ratio of the outer surface crystal layer thickness to the high-temperature holding time (10 hours) at 1580°C was calculated as the crystallization rate. A thickness of 200 μm or greater was considered to indicate a strength-enhancing effect, while a thickness of less than 200 μm was considered to indicate no strength-enhancing effect.

[0123] As shown in Table 4, the crucible samples of Comparative Examples 1 and 2 had a fictive temperature difference of 10°C or less, a crystallization rate of 1 μm / hr or less, and no strength development effect was achieved. In contrast, the crucible samples of Examples 1 and 2 had a fictive temperature difference of 50°C or greater, a crystallization rate of 21 μm / hr or greater, and a strength development effect was achieved. These results demonstrate that a fictive temperature difference of 50°C or greater allows the formation of an outer surface crystal layer of 200 μm or greater on the crucible's outer surface, resulting in a strength development effect.

[0124] Using other crucibles manufactured under the same conditions as Examples 1 and 2 and Comparative Examples 1 and 2, actual single crystal silicon pulling was performed, and the crucible deformation and delamination were visually confirmed. Table 4 also shows the results of crucible deformation and delamination. Here, "deformation" refers to the results of visually observing and evaluating whether the crucible has any deformation such as indentation of the opening, buckling from the sidewalls to the corners, and surface irregularities caused by bonding to the carbon base compared to before use. Furthermore, "delamination" refers to the results of visually observing and evaluating whether a portion of the crystal layer formed on the outer surface of the crucible has peeled off due to bubbling, deformation, etc., exposing an uncrystallized glass surface.

[0125] As shown in Table 4, peeling of the crystal layer was observed in the quartz glass crucible of Comparative Example 1. Furthermore, deformation was observed in the quartz glass crucible of Comparative Example 2. However, neither deformation nor peeling occurred in the quartz glass crucibles of Examples 1 and 2.

[0126] Description of Reference Numerals

[0127] 1-Quartz glass crucible, 2-Single crystal silicon, 3-Silicon melt, 10-Crucible base, 10a-Sidewall, 10b-Bottom, 10c-Corner, 10i-Inner surface, 10o-Outer surface, 11-Transparent layer, 12-Bubble layer, 13-Coating film containing crystallization promoter, 14-Carbon mold, 14a-Vent hole, 14i-Inner surface of carbon mold, 15-Arc electrode, 16-Accumulated layer of raw quartz powder, 16a-Sky Natural quartz powder, 16b-synthetic quartz powder, 20-single crystal pulling device, 21-chamber, 21a-main chamber, 21b-crystal pulling chamber, 21c-gas inlet, 21d-gas outlet, 22-carbon base, 23-rotating axis, 24-axis driving mechanism, 25-heater, 28-wire, 29-winding mechanism, 31-outer surface crystal layer, D1-first depth region, D2-second depth region, D3-third depth region.

Claims

1. A quartz glass crucible, characterized in that: have: a crucible base composed of silica glass; and A coating film containing a crystallization accelerator is formed on the outer surface of the crucible base. Ten hours after the start of the heat treatment at a furnace temperature of 1580° C., a furnace pressure of 20 Torr, and an Ar atmosphere, the thickness of the outer surface crystal layer formed on the outer surface of the crucible base is 0.21 to 0.5 mm, and the crystallization rate is 21 to 50 μm / hr. The crystallization rate of the outer surface 20 hours after the start of the heat treatment is 10 μm / hr or less.

2. The quartz glass crucible according to claim 1, wherein The fictive temperature of the outer surface of the crucible base is 50° C. or more lower than the fictive temperature of the base interior at a depth of 5 mm from the outer surface.

3. The quartz glass crucible according to claim 1, wherein The Al concentration in a first depth region within 10 mm from the outer surface of the crucible base is higher than the Fe concentration in the first depth region.

4. The quartz glass crucible according to claim 1, wherein The Al concentration in a first depth region within 10 mm from the outer surface of the crucible base is higher than the Ca concentration in the first depth region.

5. The quartz glass crucible according to claim 1, wherein The crystallization promoter is Ba, and the Ba concentration in the outer surface crystal layer formed on the outer surface of the crucible base after the heat treatment is less than 10 ppm.

6. The quartz glass crucible according to claim 1, wherein The coating film containing the crystallization accelerator comprises barium carbonate and a thickener, and the Ba concentration in the coating film containing the crystallization accelerator is 1.0×10 15 ~1.0×10 18 atoms / cm 2 .

7. The quartz glass crucible according to claim 1, wherein The B concentration in a second depth region within 2 / 3 of the wall thickness of the crucible base from the outer surface of the crucible base is 0.02 to 0.05 ppm.

8. The quartz glass crucible according to claim 1, wherein The Mg concentration in a second depth region within 2 / 3 of the wall thickness of the crucible base from the outer surface of the crucible base is 0.02 to 0.4 ppm.

9. The quartz glass crucible according to claim 1, wherein The Cr concentration in a second depth region within 2 / 3 of the wall thickness of the crucible base from the outer surface of the crucible base is 0.02 to 0.08 ppm.

10. The quartz glass crucible according to claim 7, wherein The B concentration in a second depth region within 2 / 3 of the wall thickness of the crucible base from the outer surface of the crucible base is higher than the B concentration in a third depth region within 2 mm from the inner surface of the crucible base.

11. The quartz glass crucible according to claim 8, wherein The Mg concentration in a second depth region within 2 / 3 of the wall thickness of the crucible base from the outer surface of the crucible base is higher than the Mg concentration in a third depth region within 2 mm from the inner surface of the crucible base.

12. The quartz glass crucible according to claim 9, wherein The Cr concentration in a second depth region within 2 / 3 of the wall thickness of the crucible base from the outer surface of the crucible base is higher than the Cr concentration in a third depth region within 2 mm from the inner surface of the crucible base.

13. A quartz glass crucible, characterized in that: have: a crucible base composed of silica glass; and A coating film containing a crystallization accelerator is formed on the outer surface of the crucible base. The fictive temperature of the outer surface of the crucible base is 50° C. or more lower than the fictive temperature of the base interior at a depth of 5 mm from the outer surface.

14. A method for producing single crystal silicon, characterized in that: Single crystal silicon is pulled by the CZ method using the quartz glass crucible according to claim 1.

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