Quartz glass crucible and its manufacturing method

Abstract

To provide a quartz glass crucible with improved strength of at least an inner face, and a manufacturing method thereof.SOLUTION: A quartz glass crucible 1 has a cylindrical side wall part 10a, a bottom part 10b provided below the side wall part 10a, and a corner part 10c provided between the side wall part 10a and the bottom part 10b and having curvature larger than that of the bottom part 10b. Virtual temperature of an inner face 10i of the side wall part 10a is lower by 30°C than virtual temperature of an inside inner part deeper than the inner face 10i by at least 3 mm.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Most silicon single crystals used as substrate materials for semiconductor devices 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 the seed crystal is gradually pulled up while rotating the quartz glass crucible and seed crystal, growing a large single crystal at the bottom of the seed crystal. The CZ method can increase the yield of large-diameter silicon single crystals.

[0003] A quartz glass crucible (silica glass crucible) is a container made of silica glass that holds molten silicon. Therefore, quartz glass crucibles must be highly durable so that they do not deform at high temperatures above the melting point of silicon and can withstand long-term use. In addition, quartz glass crucibles must be resistant to cracking and chipping even at room temperature.

[0004] Regarding technology for increasing the strength of quartz glass crucibles, for example, Patent Document 1 describes a method for preventing the crucible wall from collapsing inward due to differences in thermal expansion coefficient and glass density by rapidly cooling the inner surface of the crucible to increase the fictive temperature of the inner surface and by keeping the outer surface of the crucible warm with residual heat after arc melting to decrease the fictive temperature of the outer surface.

[0005] Patent document 2 also describes a silica glass crucible in which a first region, a second region, and a third region are arranged in that order from the inner surface of the crucible toward the outer surface, and the internal residual stress of the first region and the third region is compressive stress, and the internal residual stress of the second region is tensile stress. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-297154 [Patent Document 2] Japanese Patent Application Publication No. 2019-151494 Summary of the Invention [Problem to be solved by the invention]

[0007] A large amount of polycrystalline silicon raw material is filled into a quartz glass crucible, and a large load is applied to the inner surface of the crucible, which can cause damage to the inner surface. In particular, since the individual polycrystalline silicon chunks are crushed into small pieces during the manufacturing process and have sharp corners, the load is concentrated at the sharp tips of the polycrystalline silicon chunks, which can easily cause cracks and breaks on the inner surface of the crucible.

[0008] Furthermore, when the crucible is transported, there is a possibility that the outer surface of the crucible may be hit by something, and if the strength of the outer surface of the crucible is insufficient, there is a risk that cracks or breaks may occur in the outer surface of the crucible.

[0009] Therefore, an object of the present invention is to provide a quartz glass crucible having increased strength at least on its inner surface, and a method for manufacturing the same. [Means for solving the problem]

[0010] In order to solve the above problem, the quartz glass crucible of the present invention has a cylindrical side wall portion, a bottom portion, and a corner portion between the side wall portion and the bottom portion having a larger curvature than the bottom portion, and is characterized in that the fictive temperature of the inner surface of the side wall portion is 30°C or more lower than the fictive temperature of the inner interior at a depth of at least 3 mm from the inner surface.

[0011] According to the present invention, the Si-O structure in the glass matrix near the inner surface of the sidewall can be stabilized to increase the strength of the inner surface of the crucible, thereby suppressing cracking of the crucible when polycrystalline silicon is filled.

[0012] In the present invention, the fictive temperature of the inner surface of the side wall is preferably lower than the fictive temperature of the inner portion by at least 50° C. This makes it possible to further increase the strength of the inner surface of the crucible.

[0013] In the present invention, the OH group concentration on the inner surface of the crucible is preferably 15 ppm to 70 ppm, thereby realizing a silica glass crucible in which the fictive temperature on the inner surface of the side wall is sufficiently lower than the fictive temperature inside the crucible.

[0014] In the present invention, the fictive temperature of the outer surface of the side wall is preferably at least 30°C lower than the fictive temperature of the outer interior at a depth of at least 3 mm from the outer surface, thereby stabilizing the Si-O structure in the glass matrix near the outer surface of the side wall and increasing the strength of the outer surface of the crucible.

[0015] In the present invention, the fictive temperature of the outer surface of the crucible is preferably lower than the fictive temperature of the inside of the outer surface by at least 50° C. This makes it possible to further increase the strength of the outer surface of the crucible.

[0016] In addition, a method for manufacturing a quartz glass crucible according to the present invention comprises the steps of: forming a deposition layer of raw silica powder on the inner surface of a carbon mold that is matched to the outer shape of the quartz glass crucible, the carbon mold having a cylindrical side wall, a bottom located below the side wall, and a corner located between the side wall and the bottom and having a greater curvature than the bottom; arc-melting the deposition layer of raw silica powder from inside the carbon mold; and cooling the molten quartz glass crucible formed in the carbon mold, wherein the cooling step of the quartz glass crucible comprises the steps of: holding a high-temperature arc electrode in the carbon mold for a certain period of time immediately after completion of arc-melting of the raw silica powder, thereby slowly cooling the molten quartz glass crucible in the carbon mold; and, after the slow cooling, retracting the arc electrode above the carbon mold to increase the cooling rate of the quartz glass crucible.

[0017] According to the present invention, it is possible to manufacture a quartz glass crucible whose inner surface is reinforced.

[0018] In the present invention, it is preferable that the step of arc-melting the raw silica powder includes a step of cooling the carbon mold, and the step of cooling the quartz glass crucible includes a step of stopping cooling of the carbon mold for a certain period of time and a step of restarting cooling of the carbon mold, thereby making it possible to manufacture a quartz glass crucible with a reinforced outer surface.

[0019] In the present invention, the step of cooling the quartz glass crucible preferably includes a step of humidifying the chamber in synchronization with the start of the slow cooling, thereby making it possible to manufacture a quartz glass crucible in which the fictive temperatures of the inner and outer surfaces of the crucible are sufficiently lower than those of the inner and outer interiors. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a quartz glass crucible having increased strength at least on its inner surface, and a method for manufacturing the same. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic perspective view showing the configuration of a silica glass crucible according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional side view of the vitreous silica crucible shown in FIG. [Figure 3] FIG. 3 is a schematic diagram for explaining the fictive temperature distribution of the crucible wall of the silica glass crucible according to this embodiment. [Figure 4] FIG. 4 is a schematic diagram showing a method for manufacturing a silica glass crucible by the rotating mold method. [Figure 5] FIG. 5 is a sequence diagram showing the details from the arc melting step to the cooling step. [Figure 6] FIG. 6 is a graph showing the measurement results of the fictive temperature distribution of the silica glass crucible according to Example A1. [Figure 7]FIG. 7 is a graph showing the measurement results of the fictive temperature distribution of the silica glass crucible according to Example A2. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0023] Fig. 1 is a schematic perspective view showing the configuration of a silica glass crucible according to an embodiment of the present invention, and Fig. 2 is a schematic side cross-sectional view of the silica glass crucible shown in Fig. 1.

[0024] As shown in Figures 1 and 2, the quartz glass crucible 1 is a container made of silica glass for holding a silicon melt. It has a cylindrical side wall 10a, a bottom 10b provided below the side wall 10a, and corners 10c provided between the side wall 10a and the bottom 10b. The bottom 10b is preferably a gently curved, so-called rounded bottom, but may also be a so-called flat bottom. The corners 10c are portions having a greater curvature than the bottom 10b. The boundaries between the side wall 10a and the corners 10c and the boundaries between the bottom 10b and the corners 10c can be determined from the points where the curvature of the outer surface changes from a small curvature to a large curvature.

[0025] The bore (diameter) of the quartz glass crucible 1 varies depending on the diameter of the silicon single crystal ingot pulled from the silicon melt, but is generally 18 inches (approximately 450 mm) or larger, preferably 22 inches (approximately 560 mm), and particularly preferably 32 inches (approximately 800 mm) or larger. This is because such large crucibles are used to pull large silicon single crystal ingots with a diameter of 300 mm or larger, and are required to be able to use for long periods of time without affecting the quality of the single crystal.

[0026] The thickness of the crucible varies slightly depending on the location, but is preferably 8 to 20 mm. In particular, the thickness of the side wall 10a of an 18-inch crucible is preferably 8 to 9 mm, the thickness of the side wall 10a of a 24-inch crucible is preferably 10 to 12 mm, the thickness of the side wall 10a of a 28-inch or larger crucible is preferably 13 to 15 mm, and the thickness of the side wall 10a of a 32-inch or larger crucible is preferably 17 to 18 mm. This allows a large amount of silicon melt to be stably held at high temperatures. The thickness of the crucible is preferably thickest at the corners 10c, and thinner at the side wall 10a and bottom 10b than the corners 10c.

[0027] As shown in Figure 2, the silica glass crucible 1 mainly has a two-layer structure, comprising a transparent layer 11 (bubble-free layer) made of silica glass that contains substantially no bubbles, and a bubble layer 12 (opaque layer) made of silica glass that contains a large number of tiny bubbles.

[0028] The transparent layer 11 is a glass layer that forms the inner surface 10i of the crucible that comes into contact with the silicon melt. It is provided to prevent a decrease in the yield of silicon single crystals due to bubbles in the silica glass. Because the inner surface 10i of the quartz glass crucible 1 reacts with the silicon melt and is dissolved, bubbles near the inner surface cannot be contained within the silica glass. Thermal expansion can cause the bubbles to burst, resulting in the separation of crucible fragments (silica fragments). If crucible fragments are released into the silicon melt and carried by melt convection to the growth interface of the silicon single crystal and incorporated into the silicon single crystal, they can cause dislocations in the silicon single crystal. Furthermore, if bubbles released into the silicon melt rise to the solid-liquid interface and are incorporated into the single crystal, they can cause pinholes in the silicon single crystal.

[0029] The phrase "transparent layer 11 is substantially bubble-free" means that the bubble content and bubble size may be such that the single crystal yield is not reduced due to the bubbles. For example, the bubble content is 0.1 vol% or less, and the bubble diameter is 100 μm or less.

[0030] The bubble content per unit volume can be calculated by integrating the bubble content per unit area in the depth direction. To detect bubbles present at a certain depth from the surface, the focus of an optical lens can be scanned from the surface in the depth direction. The bubble content per unit area can be calculated by dividing an image of the crucible inner surface taken with a digital camera into fixed areas and using them as reference areas, and then calculating the ratio of the area occupied by bubbles to this reference area.

[0031] The transparent layer 11 preferably has a thickness of 0.5 to 10 mm, and is set to an appropriate thickness for each portion of the crucible so that it does not disappear completely due to melting during the crystal pulling process, thereby exposing the bubble layer 12. 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 from the upper end portion (rim portion) of the crucible that does not come into contact with the silicon melt.

[0032] The bubble content and bubble diameter of the transparent layer 11 can be measured non-destructively using an optical detection means. The optical detection means includes a light receiving device that receives transmitted or reflected light irradiated onto the crucible. The light receiving device can be a digital camera including an optical lens and an image sensor. The irradiated light can be visible light, ultraviolet light, infrared light, X-rays, laser light, or the like. The measurement results obtained by the optical detection means are input into an image processing device, and the bubble diameter and bubble content per unit volume are calculated.

[0033] The bubble layer 12 is the main glass layer of the quartz glass crucible 1 located outside the transparent layer 11. It is provided to improve the heat retention of the silicon melt in the crucible and to distribute radiant heat from the heater of the single crystal pulling device to heat the silicon melt in the crucible as uniformly as possible. For this reason, the bubble layer 12 is provided throughout the crucible, from the side wall portion 10a to the bottom portion 10b. The thickness of the bubble layer 12 is approximately equal to the thickness of the quartz glass crucible 1 minus the thickness of the transparent layer 11, and varies depending on the part of the crucible. The temperature of the silicon melt is determined by the degree to which the bubble layer 12 transmits radiant heat from the heater, so the state of the bubbles inside the crucible (number, size, and density of bubbles) is important.

[0034] 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%. This is because if the bubble content of the bubble layer 12 is 0.1 vol% or less, the bubble layer 12 will not exhibit the required heat retention function. Furthermore, if the bubble content of the bubble layer 12 exceeds 5 vol%, the thermal expansion of the bubbles may cause deformation of the crucible, resulting in a decrease in the single crystal yield and insufficient heat transfer. From the viewpoint of a balance between heat retention and heat transfer, the bubble content of the bubble layer 12 is particularly preferably 1 to 4 vol%. The bubble content mentioned above is a value measured using an unused crucible at room temperature. The bubble content of the bubble layer 12 can be determined, for example, by measuring the specific gravity (Archimedes' method) of an opaque silica glass piece cut from the crucible.

[0035] In order to increase the strength of the quartz glass crucible 1 at room temperature, the present invention focuses on the fictive temperature of the silica glass that constitutes the crucible. The fictive temperature refers to the freezing temperature of a supercooled liquid. When cooled to a temperature below the melting point at a rate fast enough to prevent crystallization, structural relaxation follows the cooling rate sufficiently at temperatures near the melting point, and the glass structure always reaches the most stable state of the supercooled liquid. However, as the temperature drops further, structural relaxation no longer keeps up with the cooling rate, and the glass structure ultimately fails to reach the thermal equilibrium state of the supercooled liquid and remains in a non-equilibrium state. The fictive temperature indicates the temperature at which the glass structure corresponds to the stable structure ((quasi) thermal equilibrium state) of the supercooled liquid.

[0036] The volume of a substance decreases continuously as the temperature decreases from a high temperature, but the volume changes discontinuously during the phase change from liquid to crystalline solid. However, for some substances, the volume change from liquid to solid occurs continuously, and the substance may become solid while remaining in an amorphous state. The continuous change in volume from liquid to amorphous solid is called the glass transition, and the state below this temperature range is called the glassy state. In other words, glass is defined as an amorphous solid that exhibits the glass transition phenomenon. Unlike crystals, glass is not a thermodynamically stable state, but rather has a disordered structure without long-range order. Therefore, when external energy is applied, glass easily changes its structure, transitioning to a more stable state and constantly changing its structure.

[0037] As mentioned above, even if the glass has the exact same composition, its structure will differ depending on the freezing temperature. If the cooling rate is slow, there is enough time for the structure to relax, and the fictive temperature will decrease in line with the actual temperature. On the other hand, if the cooling rate is fast, the fictive temperature will quickly deviate from the actual temperature of the glass. Compared to slowly cooled glass, rapidly cooled glass freezes its high-temperature structure, making it more unstable and more susceptible to structural changes. It is also more likely to exhibit properties such as transparency, brittleness, and continuity of physical properties.

[0038] FIG. 3 is a schematic diagram for explaining the fictive temperature distribution of the crucible wall of the silica glass crucible according to this embodiment.

[0039] As shown in Fig. 3, the silica glass crucible 1 according to this embodiment is characterized in that when comparing the fictive temperature of the crucible surface with the fictive temperature of the interior of the crucible at least 3 mm deeper than the crucible surface, the fictive temperature of the crucible surface is lower than the fictive temperature of the interior. In detail, the fictive temperature T Vi1 is the fictive temperature T Vi2 The fictive temperature T of the silica glass constituting the outer surface 10o of the crucible is preferably at least 30°C lower, more preferably at least 50°C lower. Vo1 is the fictive temperature T Vo2 It is more preferable that the temperature is at least 30°C lower, and more preferably at least 50°C lower than the temperature.

[0040] Fictive temperature T of the inner surface of the crucible Vi1 In the measurement of the fictive temperature of the crucible, the depth region from the inner surface 10i to 1 / 10 of the crucible's wall thickness is defined as the measurement region di of the crucible's inner surface 10i. In addition, in the measurement of the fictive temperature inside the crucible relative to the crucible's inner surface 10i, the depth region from the crucible's inner surface 10i to a depth position of 1 / 3 to 2 / 3 of the crucible's wall thickness is defined as the measurement region dd inside the crucible. When measuring the inside of the crucible that is at least 3 mm deep from the inner surface 10i, it is sufficient to measure any of these measurement regions dd.

[0041] Also, the fictive temperature T of the outer surface 10° of the crucible Vo1 When measuring the fictive temperature of the inside of the crucible relative to the outer surface 10o, the depth region from the outer surface 10o to a depth of 1 / 10 of the crucible's wall thickness is defined as the measurement region do of the outer surface 10o of the crucible. When measuring the fictive temperature of the inside of the crucible relative to the outer surface 10o, the depth region from the outer surface 10o to a depth position of 1 / 3 to 2 / 3 of the crucible's wall thickness is defined as the measurement region dd of the inside of the crucible. This is the same region as the inside of the crucible relative to the inner surface 10i of the crucible. When measuring the outside inside at least 3 mm deep from the outer surface 10o, it is sufficient to measure any of these measurement regions dd.

[0042] As mentioned above, the wall thickness of a crucible varies depending on the size and location of the crucible, but the wall thickness of the side wall of a crucible of 18 inches or larger is 8 mm or more, and the wall thickness of the side wall of a 32-inch crucible is 17 mm or more. Therefore, for example, for a small-diameter crucible, the fictive temperature inside the crucible can be determined by measuring the fictive temperature at a position at least 3 mm deep from the inner surface 10i of the crucible. Also, the fictive temperature inside the crucible can be measured by measuring the fictive temperature at a position at least 3 mm deep from the outer surface 10o of the crucible.

[0043] The fictive temperature of silica glass can be measured by Raman spectroscopy or FT-IR. In Raman spectroscopy, the surface of the sample to be measured is irradiated with laser light, and the Raman (scattering) spectrum is obtained from the Raman intensity ratio of the peaks derived from the three-membered rings and four-membered rings, which are ring structures of Si. The fictive temperature of the sample can be calculated by plotting the obtained results on a calibration curve obtained from measurements of samples with known fictive temperatures.

[0044] When measuring fictive temperature using the FT-IR method, a thin sample of the glass to be measured is irradiated with laser light, and the peak wavelength derived from the quartz glass structure is detected from the transmission spectrum.The fictive temperature of the sample can be calculated by plotting the obtained results on a calibration curve obtained from measurements of samples with known fictive temperatures.

[0045] At least in the sidewall portion, the silica glass constituting the inner surface 10i and outer surface 10o of the crucible preferably has an OH group concentration of 15 ppm to 70 ppm. By increasing the OH group concentration in the silica glass, the effect of reducing the fictive temperature of the silica glass can be enhanced. Therefore, a silica glass crucible with relatively low fictive temperatures on the inner and outer surfaces can be realized.

[0046] Next, we will explain the method for manufacturing the silica glass crucible 1. The silica glass crucible 1 according to this embodiment can be manufactured by the so-called rotation mold method.

[0047] FIG. 4 is a schematic diagram showing a method for manufacturing a silica glass crucible 1 by the rotating mold method.

[0048] 4, in the rotating mold method, a carbon mold 14 having a cavity that matches the outer shape of the crucible is prepared, and natural silica powder 16a and synthetic silica powder 16b are sequentially filled along the inner surface 14i of the rotating carbon mold 14 to form a deposition layer 16 of raw silica powder. The raw silica powder remains stuck to the inner surface 14i of the carbon mold 14 by centrifugal force, remaining in a fixed position and maintaining the crucible shape.

[0049] Next, the tip of an arc electrode 15 is placed inside the carbon mold 14, and the deposited layer 16 of raw silica powder is arc-melted from inside the carbon mold 14. Specific conditions such as heating time and heating temperature are determined appropriately taking into account the characteristics of the raw silica powder, the size of the crucible, etc.

[0050] During arc melting, the amount of bubbles in the molten silica glass is controlled by evacuating the deposited layer 16 of raw silica powder through a large number of vent holes 14a provided on the inner surface 14i of the carbon mold 14. Specifically, at the start of arc melting, the deposited layer 16 of raw silica powder is evacuated to form a transparent layer 11, and after the transparent layer is formed, the vacuum evacuating the raw silica powder is stopped or the suction force is weakened to form a bubble layer 12.

[0051] Because the arc heat propagates from the inside to the outside of the deposited layer 16 of raw silica powder, melting the raw silica powder, it is possible to produce either the transparent layer 11 or the bubble layer 12 by changing the pressure reduction conditions when the raw silica powder begins to melt. That is, if reduced-pressure melting is performed, in which the pressure reduction is increased when the raw silica powder that forms the inner surface of the crucible melts, atmospheric gases are not trapped in the glass, and the fused silica becomes silica glass that does not contain bubbles. On the other hand, if normal melting (atmospheric pressure melting) is performed, in which the pressure reduction is decreased when the raw silica powder that forms the outer surface of the crucible melts, atmospheric gases are trapped in the glass, and the fused silica becomes silica glass that contains numerous bubbles.

[0052] Thereafter, arc melting is terminated and the crucible is cooled. This completes the quartz glass crucible 1, in which a transparent layer 11 and a bubble layer 12 are sequentially formed from the inside to the outside of the crucible wall. The crucible is then shaped by cutting the rim, etc., and then washed 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 to 40 wt %.

[0053] The fictive temperature of silica glass varies depending on the cooling temperature. Rapidly cooled silica glass has a higher fictive temperature, while slowly cooled silica glass has a lower fictive temperature. Because the arc electrode 15, which serves as the heat source during arc melting, is located on the inner surface of the crucible, cooling of the inner surface of the crucible begins immediately after the arc heating ends. Meanwhile, the carbon mold 14 is located on the outer surface of the crucible, and remains at a high temperature even after the arc ends. Here, by temporarily stopping the air or water cooling of the carbon mold 14, the cooling rate of the outer surface 10o of the quartz glass crucible 1 becomes slower than that of the inner surface 10i. Furthermore, because the outer surface 10o of the quartz glass crucible 1 is cooled more slowly than the interior, the fictive temperature of the outer surface 10o becomes lower than that of the interior. In this embodiment, the heat retention is improved by heating the carbon mold 14, etc., and the cooling rate on the outer surface 10o side of the quartz glass crucible 1 is slowed down, thereby increasing the virtual temperature difference between the outer surface 10o of the quartz glass crucible 1 and the inside of the base by 30°C or more.

[0054] FIG. 5 is a sequence diagram showing the details from the arc melting step to the cooling step.

[0055] As shown in Fig. 5, at the start of the arc melting process, the arc electrode 15 is placed at the discharge position shown in Fig. 4, and arc discharge (arc heating) starts at time t0. At this time, the carbon mold 14 is also cooled, thereby preventing the carbon mold 14 from overheating.

[0056] When the arc discharge ends at time t1, a certain time after the start of the arc discharge (the time until the raw silica powder is completely melted), in this embodiment, the arc electrode 15 is not moved from the discharge position to the retracted position, but is maintained at the discharge position. Conventionally, the arc electrode 15 is retracted above the carbon mold 14 immediately after the end of arc melting in order to rapidly cool the molten crucible, but by maintaining the arc electrode at the discharge position, the crucible can be slowly cooled from the inner surface 10i side. This makes it possible to manufacture a crucible in which the fictive temperature of the inner surface 10i is relatively lower than that of the inside of the crucible.

[0057] Furthermore, when the arc heating is completed, the forced cooling of the carbon mold 14 is temporarily stopped and the mold is allowed to cool naturally. Conventionally, the mold 14 is constantly forcedly cooled, but by temporarily stopping the forced cooling, the crucible can be slowly cooled from the outer surface 10o side. In other words, it is possible to manufacture a crucible in which the fictive temperature of the outer surface 10o is relatively lower than that of the inside of the crucible.

[0058] Furthermore, when the arc heating is completed, the atmosphere in the processing chamber is humidified. The humidification condition is 8 g / cm 3 The humidification time is preferably 60 seconds or more, and the humidification time is preferably 60 seconds or more. This increases the OH group concentration in the silica glass near the inner surface and the outer surface of the crucible, thereby enhancing the effect of reducing the fictive temperature of the inner surface 10i and the outer surface 10o of the crucible. This also has the effect of relaxing the glass structure, thereby further reducing the fictive temperature of the inner surface 10i and the outer surface 10o of the crucible.

[0059] At time t2, after a certain time (e.g., 60 seconds) has elapsed since the start of the slow cooling of the crucible, the slow cooling of the crucible is completed and the arc electrode is moved to the waiting position. At this time, forced cooling of the carbon mold 14 is resumed to promote the cooling of the crucible. This allows the temperature of the crucible to be quickly lowered to room temperature, thereby shortening the time required to complete the arc melting process.

[0060] As explained above, in the quartz glass crucible 1 according to this embodiment, the fictive temperature of the inner surface 10i at least in the side wall portion 10a is 30°C or more lower than the fictive temperature inside the crucible at a depth of at least 5 mm from the inner surface 10i, so the strength of the inner surface 10i of the crucible can be increased at room temperature. Also, in the quartz glass crucible 1 according to this embodiment, the fictive temperature of the inner surface 10i at least in the side wall portion 10a is 30°C or more lower than the fictive temperature inside the crucible at a depth of at least 5 mm from the outer surface 10o, so the strength of the outer surface 10o of the crucible can be increased at room temperature.

[0061] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention.

[0062] For example, in the above embodiment, both the fictive temperature of the inner surface 10i and the fictive temperature of the outer surface 10o of the crucible are lower than the fictive temperature inside the crucible, but it does not matter if only one of them is lower. If only the inner surface of the crucible is made like this, it is possible to improve the strength of only the inner surface of the crucible. Also, if only the outer surface of the crucible is made like this, it is possible to improve the strength of only the outer surface of the crucible. [Example]

[0063] <Evaluation of fictive temperature distribution in a 32-inch crucible> A 32-inch diameter quartz glass crucible was manufactured using the rotating mold method described above. During the arc melting process, the tip of the arc electrode was kept in the mold immediately after the arc heating was completed to slowly cool the inner surface of the crucible. The cooling of the carbon mold was also temporarily stopped to slowly cool the outer surface of the crucible. Furthermore, humidification was started immediately after the arc heating in the chamber was completed.

[0064] The wall thickness, transparent layer thickness, and bubble layer thickness at the 1 / 2 height position (side wall portion) of the quartz glass crucible of Example A1 obtained in this manner were measured, and the wall thickness of the crucible was 17.6 mm, the transparent layer thickness was 5.6 mm, and the bubble layer thickness was 12.0 mm.

[0065] Next, the fictive temperature distribution of the obtained quartz glass crucible was measured using Raman spectroscopy. The measurement position for the fictive temperature distribution was set at 1 / 2 the height of the quartz glass crucible. At this position, 1 / 3 of the crucible's wall thickness was 5.9 mm, and this value was used as the measurement position for the fictive temperature inside the crucible. Specifically, to measure the fictive temperature inside the crucible, the inner surface was polished to 5.9 mm, and then the polished surface was irradiated with laser light to measure the fictive temperature. To measure the fictive temperature inside the crucible, the outer surface was polished to 5.9 mm, and then the polished surface was irradiated with laser light to measure the fictive temperature.

[0066] FIG. 6 is a graph showing the measurement results of the fictive temperature distribution of the quartz glass crucible according to Example A1, with the horizontal axis representing the distance (mm) from the inner surface and the vertical axis representing the fictive temperature (° C.).

[0067] As shown in FIG. 6, the fictive temperature of the inner surface was lower than the fictive temperature of the inner interior, and the fictive temperature of the outer surface was lower than the fictive temperature of the outer interior.

[0068] <Evaluation of fictive temperature distribution in a 24-inch crucible> A 24-inch diameter quartz glass crucible was manufactured using the rotating mold method described above. During the arc melting process, the arc electrode was kept in the mold immediately after the arc heating was completed to slowly cool the inner surface of the crucible. The cooling of the carbon mold was also temporarily stopped to slowly cool the outer surface of the crucible.

[0069] The wall thickness, transparent layer thickness, and bubble layer thickness at the 1 / 2 height position (side wall portion) of the quartz glass crucible of Example A2 obtained in this manner were measured, and the wall thickness of the crucible was 11.5 mm, the transparent layer thickness was 7.5 mm, and the bubble layer thickness was 4.0 mm.

[0070] Next, the fictive temperature distribution of the obtained quartz glass crucible was measured using Raman spectroscopy. The measurement position for the fictive temperature distribution was set at 1 / 2 the height of the quartz glass crucible. At this position, 1 / 3 of the crucible's wall thickness was 3.8 mm, and this value was used as the measurement position for the fictive temperature inside the crucible. Specifically, to measure the fictive temperature inside the crucible, the inner surface was polished to 3.8 mm, and then the polished surface was irradiated with laser light to measure the fictive temperature. To measure the fictive temperature inside the crucible, the outer surface was polished to 3.8 mm, and then the polished surface was irradiated with laser light to measure the fictive temperature.

[0071] FIG. 7 is a graph showing the measurement results of the fictive temperature distribution of the quartz glass crucible according to Example A2, with the horizontal axis representing the distance (mm) from the inner surface and the vertical axis representing the fictive temperature (° C.).

[0072] As shown in FIG. 7, even in the 24-inch crucible, the fictive temperature of the inner surface was lower than the fictive temperature of the inner interior, and the fictive temperature of the outer surface was lower than the fictive temperature of the outer interior.

[0073] <Evaluation of the inner surface of the crucible after pulling the crystal> Five quartz glass crucible samples were prepared, and the fictive temperature of the inner surface of each crucible was measured. The quartz glass crucibles of Examples B1, B2, and B3 were measured using the rotating mold method described above, and in the arc melting process, the arc electrode was kept in the mold even immediately after the end of arc heating to slowly cool the inner surface of the crucible. The quartz glass crucibles of Comparative Examples B1 and B2 were manufactured using the conventional method of rapid cooling after the end of arc heating.

[0074] Next, a silicon single crystal was pulled using a crucible identical to this one, and the condition of the inner surface of the crucible after pulling was visually observed to evaluate the number of silicon pieces that had embedded in the inner surface of the crucible. This embedding is thought to be caused by impacts that the inner surface of the crucible received when the silicon raw material was filled into the crucible or while the silicon raw material was melting. The results are shown in Table 1.

[0075] [Table 1]

[0076] As shown in Table 1, in Example B1, the fictive temperature difference was 30°C and the number of silicon bites was 1. In Example B2, the fictive temperature difference was 30°C and the number of silicon bites was 2. In Example B3, the fictive temperature difference was 50°C and the number of silicon bites was 0.

[0077] On the other hand, in Comparative Example B1, the fictive temperature difference was -10°C, and the number of silicon bites was 13. In Comparative Example B2, the fictive temperature difference was -30°C, and the number of silicon bites was 10. From these results, it was confirmed that the inner surfaces of the quartz glass crucibles of Examples B1, B2, and B3, in which the fictive temperature of the crucible inner surface was 30°C or more lower than that of the crucible interior, suffered little damage and had improved strength.

[0078] <Evaluation of the outer surface of the crucible after pulling the crystal> Three quartz glass crucible samples were prepared, and the fictive temperature of the outer surface of each crucible was measured. The quartz glass crucibles of Examples C1 and C2 were measured using the rotating mold method described above. In the arc melting process, the arc electrode was kept in the mold even immediately after the end of arc heating, and the mold cooling was stopped immediately after the end of arc heating, and the inner and outer surfaces of the crucible were slowly cooled. The quartz glass crucible of Comparative Example C1 was manufactured using the conventional method of rapid cooling after the end of arc heating.

[0079] Next, a silicon single crystal was pulled using a crucible identical to this crucible, and the condition of the outer surface of the crucible after pulling was visually observed to evaluate the number of dents present on the outer surface of the crucible. These dents are thought to be the result of pressure or impact from outside before pulling, such as during transportation, which became apparent during the pulling process. The results are shown in Table 2.

[0080] [Table 2]

[0081] As shown in Table 2, in Example C1, the fictive temperature difference was 40° C. and the number of dents on the outer surface was 0. In Example C2, the fictive temperature difference was 70° C. and the number of dents on the outer surface was 0.

[0082] On the other hand, in Comparative Example C1, the fictive temperature difference was 10°C, and the number of dents on the outer surface was 5. From the above results, it was confirmed that the outer surfaces of the quartz glass crucibles of Examples C1 and C2, in which the fictive temperature of the crucible outer surface was 30°C or more lower than that of the crucible interior, had fewer dents and improved strength. [Explanation of symbols]

[0083] 1. Quartz glass crucible 10a Side wall part 10b bottom 10c Corner 10i inside 10o outer surface 11 Transparent layer 12 Bubble layer 14 Carbon mold 14a Ventilation hole 14i inside 15 Arc electrode 16 Sedimentary layer 16a Natural Silica Powder 16b Synthetic silica powder T Vi1 Inner virtual temperature T Vi2 Internal virtual temperature T Vo1 External virtual temperature T Vo2 External and internal virtual temperature dd Measurement area inside the crucible di Measurement area inside the crucible do Measurement area on the outer surface of the crucible

Claims

1. a cylindrical side wall portion, a bottom portion provided below the side wall portion, and a corner portion provided between the side wall portion and the bottom portion and having a larger curvature than the bottom portion, A quartz glass crucible characterized in that the fictive temperature of the inner surface of the side wall portion is 30°C or more lower than the fictive temperature of the inner interior at a depth of at least 3 mm from the inner surface.

2. The quartz glass crucible according to claim 1, wherein the fictive temperature of the inner surface of the side wall portion is 50°C or more lower than the fictive temperature of the inner portion.

3. The quartz glass crucible according to claim 1, wherein the OH group concentration on the inner surface of the side wall portion is 15 ppm to 70 ppm.

4. 4. A quartz glass crucible according to claim 1, wherein the fictive temperature of the outer surface of the side wall portion is at least 30°C lower than the fictive temperature of the outer interior at a depth of at least 3 mm from the outer surface.

5. The quartz glass crucible according to claim 4, wherein the fictive temperature of the outer surface of the side wall portion is at least 50°C lower than the fictive temperature of the outer interior.

6. A method for manufacturing a quartz glass crucible having a cylindrical side wall portion, a bottom portion provided below the side wall portion, and a corner portion provided between the side wall portion and the bottom portion and having a larger curvature than the bottom portion, forming a deposition layer of raw silica powder on the inner surface of the carbon mold; arc-melting the deposited layer of the raw silica powder from inside the carbon mold; and a step of cooling the fused silica crucible formed in the carbon mold, The step of cooling the quartz glass crucible includes: Immediately after the arc melting of the raw silica powder is completed, a step of holding the arc electrode in a high temperature state in the carbon mold for a certain period of time to slowly cool the fused silica crucible in the carbon mold; and after the slow cooling, the arc electrode is retracted above the carbon mold to increase the cooling rate of the quartz glass crucible.

7. the step of arc-melting the deposited layer of raw silica powder includes a step of cooling the carbon mold; 7. The method for manufacturing a silica glass crucible according to claim 6, wherein the step of cooling the silica glass crucible includes a step of stopping cooling of the carbon mold for a certain period of time and a step of restarting cooling of the carbon mold.

8. The method for manufacturing a silica glass crucible according to claim 6, wherein the step of cooling the silica glass crucible includes a step of humidifying the interior of the chamber in synchronization with the start of the slow cooling.

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