Quartz glass crucible

Abstract

[Problem] To provide a quartz glass crucible in which an inward inclination is less apt to occur at high temperatures during a step for crystal pulling-up. [Solution] A quartz glass crucible 1 according to the present invention comprises a cylindrical sidewall part 10a, a curved bottom part 10b, and a corner part 10c having a greater curvature than the bottom part 10b and provided to between the sidewall part 10a and the bottom part 10b, wherein the radial-direction relative location rb / r of a curvature change point Pb, on the bottom part 10b side, of the outer surface 10o of the crucible with respect to the outer radius r of the sidewall part 10a is within the range of 0.59-0.72.

Description

Quartz glass crucible

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

[0002] Most silicon single crystals used as substrate materials for semiconductor devices are manufactured using the CZ (Crystal Zoning) method. In the CZ method, polycrystalline silicon raw material is melted in a quartz glass crucible to create a silicon melt, a seed crystal is immersed in the silicon melt, and the seed crystal is gradually pulled up while the quartz glass crucible and seed crystal are rotated, allowing a large single crystal to grow at the bottom of the seed crystal. The CZ method makes it possible to increase the yield of large-diameter silicon single crystals.

[0003] A quartz glass crucible is a silica glass container used to hold molten silicon during the silicon single crystal pulling process. Therefore, quartz glass crucibles require high durability to withstand prolonged use without deformation at temperatures exceeding the melting point of silicon. Furthermore, high purity is required to prevent contamination of the silicon single crystal with impurities.

[0004] Regarding quartz glass crucibles for pulling silicon single crystals, for example, Patent Document 1 describes a quartz glass crucible having a cylindrical straight body, a first curved body continuous with the lower end of the straight body and having a first curvature, a second curved body continuous with the first curved body and having a second curvature, and a bottom continuous with the second curved body, wherein the first curvature is greater than the second curvature, and the outer surface of the bottom is a flat surface or a concave surface recessed from the flat surface.

[0005] Japanese Patent Publication No. 2022-025857

[0006] When using conventional quartz glass crucibles to pull silicon single crystals, there is a problem that the crucible is prone to tilting inward. When the crucible tilts inward, it comes into contact with the heat shielding material, making it impossible to rotate the crucible and thus preventing the crystal pulling process from continuing. In addition, the sudden change in the volume of the crucible makes it difficult to control the crystal pulling process.

[0007] The conventional quartz glass crucible described in Patent Document 1 can stand stably in a graphite crucible at the preparation stage before starting the crystal pulling process, but it cannot suppress the inward collapse of the crucible at high temperatures during the crystal pulling process.

[0008] Therefore, an object of the present invention is to provide a quartz glass crucible that is less likely to collapse inward at high temperatures during the crystal pulling process.

[0009] In order to solve the above problems, the quartz glass crucible according to the present invention has a cylindrical side wall portion, a curved bottom portion, and a corner portion provided between the side wall portion and the bottom portion and having a curvature larger than that of the bottom portion. The radial relative position of the curvature change point on the bottom side of the outer surface of the crucible with respect to the outer radius of the side wall portion is within the range of 0.59 to 0.72.

[0010] According to the present invention, since the curvature change point on the bottom side indicating the boundary between the bottom portion and the corner portion is located more inside (toward the center of the crucible) than in the prior art, when the crucible softens at high temperatures during the crystal pulling process, outward opening deformation can be promoted, and inward collapse of the side wall portion can be prevented.

[0011] In the present invention, it is preferable that the curvature of the outer surface of the corner portion is 3 to 7 times larger than the curvature of the outer surface of the bottom portion. Thereby, not only the curvature change point on the bottom side becomes clear, but also the curvature change point can be brought closer to the center side of the crucible. Therefore, when the crucible softens at high temperatures during the crystal pulling process, outward opening deformation can be promoted, and inward collapse of the side wall portion can be prevented.

[0012] In the present invention, the boundary between the corner portion and the side wall portion on the outer surface is preferably between two points at which the absolute value of the curvature change rate between the two end points among three adjacent points first becomes 60% or more when the curvature of the outer surface is measured at a constant pitch from the position of the thickest wall portion toward the rim portion which is the upper end of the side wall portion. Thereby, the boundary between the corner portion and the side wall portion can be clearly specified.

[0013] In the quartz glass crucible according to the present invention, the thickest part of the crucible wall is provided at the corner, and it is preferable that the position of the thickest part is closer to the boundary between the corner and the side wall than to the boundary between the corner and the bottom. In this case, the distance L along the outer surface from the center of the bottom to the upper end of the side wall ０ The distance L along the outer surface from the center of the bottom to the thickest part of the wall. １ Ratio L １ / L ０ It is preferable that the value is within the range of 0.37 to 0.56. When the thickest point of the crucible is within the range of 0.37 to 0.56, deformation due to the weight of the thickest part of the crucible is more likely to occur when the crucible softens at high temperatures. Therefore, outward deformation of the crucible can be promoted, and inward collapse of the side walls can be prevented.

[0014] According to the present invention, it is possible to provide a quartz glass crucible that is less prone to inward collapse at high temperatures during the crystal pulling process.

[0015] Figure 1 is a schematic perspective view showing the configuration of a quartz glass crucible according to an embodiment of the present invention. Figure 2 is a schematic side cross-sectional view of the quartz glass crucible shown in Figure 1. Figure 3 is a schematic diagram showing a method for manufacturing a quartz glass crucible by the rotary molding method. Figure 4 is a diagram illustrating a single crystal pulling process using the quartz glass crucible according to this embodiment, and is a schematic cross-sectional view showing the configuration of a single crystal pulling apparatus. Figure 5 is a schematic diagram illustrating the deformation of a quartz glass crucible during the crystal pulling process. Figure 6 is a schematic diagram illustrating the deformation of a quartz glass crucible during the crystal pulling process.

[0016] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0017] Figure 1 is a schematic perspective view showing the configuration of a quartz glass crucible according to an embodiment of the present invention. Figure 2 is a schematic side cross-sectional view of the quartz glass crucible shown in Figure 1.

[0018] As shown in Figures 1 and 2, the quartz glass crucible 1 is a silica glass container for holding silicon molten liquid, and has a cylindrical side wall portion 10a, a bottom portion 10b provided below the side wall portion 10a, and a corner portion 10c provided between the side wall portion 10a and the bottom portion 10b.

[0019] The side wall portion 10a is a substantially vertical wall, preferably vertical, but may have a slightly outward-facing shape. The bottom portion 10b is a gently curved so-called round bottom, and the corner portion 10c is a portion with a greater curvature than the bottom portion 10b. The boundary point between the bottom portion 10b and the corner portion 10c is the point where the curvature changes from the small curvature of the bottom portion 10b to the large curvature of the corner portion 10c (curvature change point P on the bottom side). ｂ ) The side wall portion 10a is a portion that extends linearly in the vertical direction. The boundary point between the corner portion 10c and the side wall portion 10a is the point where the curvature of the corner portion 10c changes from large to zero in the side wall portion 10a (the curvature change point on the side wall portion side). In this specification, when simply referred to as the "curvature change point," it refers to the curvature change point P at the boundary between the bottom portion 10b and the corner portion 10c. ｂ This refers to the following.

[0020] The curvature of the outer surface 10o at the corner portion 10c is preferably 3 to 7 times greater than the curvature of the outer surface 10o at the bottom portion 10b, and more preferably 3.2 to 6.6 times greater. For example, in the case of a crucible with a diameter of 22 inches (approximately 560 mm), the radius of curvature of the bottom portion 10b is preferably 550 to 560 mm, and the radius of curvature of the corner portion 10c is preferably 100 to 120 mm. Also, in the case of a crucible with a diameter of 32 inches (approximately 810 mm), the radius of curvature of the bottom portion 10b is preferably 705 to 860 mm, and the radius of curvature of the corner portion 10c is preferably 130 to 220 mm. In this way, the curvature of the corner portion 10c is sufficiently greater than the curvature of the bottom portion 10b, so the boundary between the bottom portion 10b and the corner portion 10c (curvature change point P) ｂ Identifying the curvature change point P at the boundary between the bottom 10b and the corner 10c is easy. The bottom 10b and the corner 10c do not necessarily have a single curvature; the curvature may change along the way, but the change should be gradual, and the curvature change point P at the boundary between the bottom 10b and the corner 10c is easy. ｂ The curvature does not change significantly like that.

[0021] The diameter R (outer 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 18 inches (approximately 450 mm) or larger, preferably 22 inches (approximately 560 mm) or larger, and particularly preferably 32 inches (approximately 810 mm) or larger. Such large crucibles are used for pulling large silicon single crystal ingots with a diameter of 200 mm or more, and are required to be resistant to deformation even after prolonged use and not affect the quality of the silicon single crystal.

[0022] The wall thickness of the crucible varies slightly depending on the location, with the corners 10c being the thickest, and the side walls 10a and bottom 10b being thinner than the corners 10c. The wall thickness of the side walls 10a of the crucible is preferably 6 mm or more for 18 inches or larger, 7 mm or more for 22 inches or larger, and 10 mm or more for 32 inches or larger. This allows for the stable retention of a large amount of molten silicon at high temperatures.

[0023] As shown in Figure 2, the quartz glass crucible 1 mainly has a two-layer structure, consisting of a transparent layer 11 (bubble-free layer) that does not contain air bubbles and a bubble layer 12 (opaque layer) that contains numerous minute air bubbles.

[0024] The transparent layer 11 is a layer that constitutes the inner surface 10i of the crucible that comes into contact with the silicon melt, and is provided to prevent a decrease in the yield of silicon single crystals due to air bubbles in the silica glass. Since the inner surface 10i of the crucible reacts with the silicon melt and melts away, air bubbles near the inner surface of the crucible cannot be contained within the silica glass, and there is a risk that the bubbles will burst due to thermal expansion and crucible fragments (silica fragments) will peel off. If crucible fragments released into the silicon melt are carried to the solid-liquid interface by melt convection and incorporated into the silicon single crystal, it can cause dislocations in the single crystal. Also, if air bubbles released into the silicon melt float to the solid-liquid interface and are incorporated into the single crystal, it can cause the formation of pinholes in the silicon single crystal.

[0025] The statement that the transparent layer 11 is bubble-free means that it has a bubble content and bubble size such that the single crystallization rate does not decrease due to bubbles. Such a bubble content is, for example, 0.1 vol% or less, and the diameter of the bubbles is, for example, 100 μm or less.

[0026] The thickness of the transparent layer 11 is preferably 0.5 to 10 mm, and is set to an appropriate thickness for each part of the crucible so that it does not completely disappear due to melting during the crystal pulling process and expose the bubble layer 12. The transparent layer 11 is preferably provided throughout the crucible from the side wall portion 10a to the bottom portion 10b, but it is also possible to omit the transparent layer 11 at the upper end of the crucible where it does not come into contact with the silicon melt.

[0027] The bubble layer 12 is the main layer of the crucible substrate 10, located outside the transparent layer 11. It is provided to improve the heat retention of the silicon melt inside the crucible and to disperse the radiant heat from the heater of the single crystal pulling apparatus to heat the silicon melt inside the crucible as uniformly as possible. For this reason, the bubble layer 12 is provided throughout the entire crucible, from the side wall portion 10a to the bottom portion 10b.

[0028] The bubble content of the bubble layer 12 is preferably higher than that of the transparent layer 11, greater than 0.1 vol%, and 5 vol% or less. This is because if the bubble content of the bubble layer 12 is 0.1 vol% or less, it cannot perform the heat retention function required of the bubble layer 12. Furthermore, if the bubble content of the bubble layer 12 exceeds 5 vol%, the crucible may deform due to the thermal expansion of the bubbles, which may reduce the single crystal yield and result in insufficient heat transfer. From the viewpoint of balancing 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 the value measured in a crucible at room temperature before use.

[0029] To prevent contamination of the silicon melt, it is desirable that the silica glass constituting the transparent layer 11 be of high purity. Therefore, it is preferable that the quartz glass crucible 1 has a two-layer structure consisting of a synthetic silica glass layer (synthetic layer) formed from synthetic quartz powder and a natural silica glass layer (natural layer) formed from natural quartz powder. The synthetic quartz powder is silicon tetrachloride (SiCl４ It can be produced by vapor-phase oxidation (dry synthesis method) as in (1) or hydrolysis of silicon alkoxide (sol-gel method). Natural quartz powder is produced by pulverizing a natural mineral mainly composed of α-quartz into a granular form.

[0030] The two-layer structure of the synthetic silica glass layer and the natural silica glass layer can be produced by depositing natural quartz powder along the inner surface of the mold for crucible production, depositing synthetic quartz powder thereon, and melting these raw material quartz powders by Joule heat generated by arc discharge. In the arc melting process, bubbles are removed by strongly evacuating from the outside of the deposited layer of the raw material quartz powder to form the transparent layer 11, and the bubble layer 12 is formed by stopping or weakening the evacuation. Therefore, the boundary surface between the synthetic silica glass layer and the natural silica glass layer does not necessarily coincide with the boundary surface between the transparent layer 11 and the bubble layer 12, but the synthetic silica glass layer preferably has a thickness such that it does not completely disappear due to the erosion of the inner surface of the crucible during the single crystal pulling process, similar to the transparent layer 11.

[0031] As described above, the quartz glass crucible 1 according to the present embodiment has a cylindrical side wall portion 10a, a curved bottom portion 10b, and a corner portion 10c having a larger curvature than the bottom portion 10b. The relative position in the radial direction of the curvature change point P on the bottom portion 10b side of the outer surface 10o of the crucible with respect to the outer radius r (=R / 2) of the side wall portion 10a ｂ is within the range of 0.59 to 0.72. In other words, when the radial distance from the center P ０ of the bottom portion 10b of the crucible passing through the center axis Z ０ of the crucible to the curvature change point P ｂ is r ｂ (see FIG. 2), 0.59 ≤ r ｂ / r ≤ 0.72. This means that the boundary point between the bottom portion 10b and the corner portion 10c exists more radially inward (toward the center of the crucible) than before.

[0032] The relative position in the radial direction of the curvature change point P on the bottom portion 10b side of the crucible ｂ (r ｂWhen (r) is greater than 0.72, when the crucible is set in the carbon susceptor, a gap is less likely to form between the crucible and the carbon susceptor, and the upper end of the crucible is less likely to deform in the direction that fills the gap (tilts outward) at high temperatures, thus reducing the likelihood of outward deformation. Also, the curvature change point P ｂ Relative position in the radial direction (r ｂ If (r) is less than 0.59, the gap between the crucible and the carbon susceptor is too large, which can easily cause the crucible to wobble. However, the curvature change point P ｂ Relative position in the radial direction (r ｂ If the ratio (r) is within the range of 0.59 to 0.72, it is possible to promote outward deformation while stably holding the crucible at high temperatures.

[0033] The thickness of the side wall portion 10a is preferably constant, and the maximum thickness of the corner portion 10c is preferably thicker than the side wall portion 10a and the bottom portion 10b. That is, the thickest part 10m of the crucible wall is located at the corner portion 10c. The thickest part 10m is at the boundary position (curvature change point P) between the corner portion 10c and the bottom portion 10b. ｂ It is preferable that the corner portion 10c is located closer to the boundary between the corner portion 10c and the side wall portion 10a than the midpoint of the corner portion 10c. In other words, it is preferable that the thickest portion 10m is located closer to the side wall portion 10a (closer to the outside of the crucible) than the midpoint of the range of the corner portion 10c. This promotes outward deformation of the crucible due to the weight of the thickest portion 10m. The boundary between the corner portion 10c and the side wall portion 10a can be determined as the position between two points at which, when the curvature of the outer surface 10o of the crucible is measured at a constant pitch (for example, a 20 mm pitch) from the position of the corner portion 10c (especially the thickest portion 10m) toward the rim portion 10e, which is the upper end of the side wall portion 10a, the absolute value of the rate of change of curvature between the two end points of three adjacent points first exceeds 60%.

[0034] Center P at the bottom 10b of the crucible ０ The distance along the outer surface 10o of the crucible from the upper end of the side wall portion 10a (rim portion 10e) is L. ０ The center P of the bottom 10b ０ Distance L along the outer surface 10o of the crucible from the thickest part of the crucible wall, 10m.１ In that case, L １ / L ０ It is preferable that it is within the range of 0.37 to 0.56. １ / L ０ If the value is greater than 0.56, the thickest part 10m of the wall gets too close to the side wall 10a, causing a large change in the inner diameter from the upper end to the lower end of the side wall 10a. This increases the rate at which the melt level drops due to the consumption of melted silicon during the crystal pulling process, making it difficult to control the pulling of the silicon single crystal. １ / L ０ If L is less than 0.37, the thickest part 10m of the wall gets too close to the bottom part 10b, resulting in less deformation due to the weight of the thickest part 10m, and making outward deformation less likely. However, L １ / L ０ If the value is within the range of 0.37 to 0.56, it is possible to prevent outward deformation of the crucible while ensuring the stability of the silicon single crystal pulling control.

[0035] The quartz glass crucible 1 according to this embodiment can be manufactured by a so-called rotary molding method.

[0036] Figure 3 is a schematic diagram illustrating the manufacturing method of a quartz glass crucible using the rotary molding method.

[0037] As shown in Figure 3, in the rotary molding method, a mold 14 having a cavity that matches the outer shape of the crucible is prepared, and natural quartz powder 16a and synthetic quartz powder 16b are sequentially filled along the inner surface 14i of the rotating mold 14 to form a deposit layer 16 of raw quartz powder. The raw quartz powder adheres to the inner surface 14i of the mold 14 by centrifugal force and remains in a fixed position, maintaining the crucible shape.

[0038] In this embodiment, the crucible shape described above, which is prone to outward deformation during the silicon single crystal pulling process, is achieved by adjusting the shape of the inner surface 14i of the mold 14 and the shape of the scraper used when adjusting the amount of quartz powder packed inside. The scraper consists of a plate-shaped member such as a glass plate whose edge shape is processed to match the inner surface shape of the crucible, and by scraping off excess quartz powder accumulated on the inner surface of the rotating mold, the thickness of the quartz powder deposit layer can be precisely adjusted in each part.

[0039] Next, an arc electrode 15 is placed inside the mold 14, and the deposited layer 16 of raw quartz powder is arc-melted from the inside of the mold 14. Specific conditions such as heating time and heating temperature are determined as appropriate, taking into consideration the characteristics of the raw quartz powder and the size of the crucible. The deposited layer of natural quartz powder 16a cools after arc melting to become a natural silica glass layer 10n, and the deposited layer of synthetic quartz powder 16b cools after arc melting to become a synthetic silica glass layer 10s.

[0040] During arc melting, the amount of bubbles in the molten silica glass is controlled by evacuating the deposited layer 16 of raw quartz powder through numerous ventilation holes 14a provided on the inner surface 14i of the mold 14. Specifically, the raw quartz powder is evacuated at the start of arc melting to form a transparent layer 11, and after the formation of the transparent layer 11, the evacuation of the raw quartz powder is stopped to form a bubble layer 12.

[0041] The arc heat gradually propagates from the inside to the outside of the deposited layer 16 of raw quartz powder, melting the raw quartz powder. By changing the reduced pressure conditions at the moment the raw quartz powder begins to melt, it is possible to create either a transparent layer 11 or a bubble layer 12. Specifically, if reduced pressure melting is performed by increasing the reduced pressure at the moment the raw quartz powder melts, the arc atmosphere gas is not trapped in the glass, and the molten silica becomes silica glass without bubbles. Alternatively, if normal melting (atmospheric pressure melting) is performed by decreasing the reduced pressure at the moment the raw quartz powder melts, the arc atmosphere gas is trapped in the glass, and the molten silica becomes silica glass containing many bubbles. After that, the arc melting is terminated and the crucible is cooled. As a result, a crucible substrate is completed in which the transparent layer 11 and the bubble layer 12 are sequentially formed from the inside to the outside of the crucible wall.

[0042] Next, the crucible base is shaped into a predetermined form by cutting the rim portion, then washed with a cleaning solution, and finally rinsed with pure water. This completes the quartz glass crucible 1 according to this embodiment.

[0043] Figure 4 is a diagram illustrating the single crystal pulling process using the quartz glass crucible 1 according to this embodiment, and is a schematic cross-sectional view showing the configuration of the single crystal pulling apparatus.

[0044] As shown in Figure 4, a single crystal pulling apparatus 20 is used in the silicon single crystal pulling process by the CZ method. The single crystal pulling apparatus 20 comprises a water-cooled chamber 21, a quartz glass crucible 1 that holds the silicon melt inside the chamber 21, a carbon susceptor 22 that holds the quartz glass crucible 1, a rotating shaft 23 that supports the carbon susceptor 22 so that it can rotate and move up and down, a shaft drive mechanism 24 that drives the rotating shaft 23 to rotate and move up and down, a heater 25 arranged around the carbon susceptor 22, a heat insulating material 26 arranged outside the heater 25 and along the inner surface of the chamber 21, a heat shielding member 27 arranged above the quartz glass crucible 1, a single crystal pulling wire 28 arranged above the quartz glass crucible 1 and coaxially with the rotating shaft 23, and a wire winding mechanism 29 arranged above the chamber 21.

[0045] Chamber 21 consists of a main chamber 21a and an elongated cylindrical pull chamber 21b connected to the upper opening of the main chamber 21a. The quartz glass crucible 1, carbon susceptor 22, and heater 25 are located inside the main chamber 21a. A gas inlet 21c is provided at the top of the pull chamber 21b for introducing an inert gas (purge gas) such as argon gas or a dopant gas into the main chamber 21a, and a gas outlet 21d is provided at the bottom of the main chamber 21a for discharging the atmospheric gas inside the main chamber 21a.

[0046] The carbon susceptor 22 is used to maintain the shape of the quartz glass crucible 1, which has softened at high temperatures, and holds the quartz glass crucible 1 by enclosing it. The quartz glass crucible 1 and the carbon susceptor 22 constitute a double-layered crucible that supports the silicon molten liquid within the chamber 21.

[0047] The carbon susceptor 22 is fixed to the upper end of the rotating shaft 23, and the lower end of the rotating shaft 23 passes through the bottom of the chamber 21 and is connected to a shaft drive mechanism 24 provided on the outside of the chamber 21.

[0048] The heater 25 is used to melt the polycrystalline silicon raw material packed inside the quartz glass crucible 1 to produce a silicon melt 3, and to maintain the molten state of the silicon melt 3. The heater 25 is a resistance heating type carbon heater and is installed so as to surround the quartz glass crucible 1 inside the carbon susceptor 22.

[0049] The heat shielding member 27 is provided to suppress temperature fluctuations in the silicon melt 3, to form an appropriate hot zone near the crystal growth interface, and to prevent heating of the silicon single crystal 2 by radiant heat from the heater 25 and the quartz glass crucible 1. The heat shielding member 27 is a substantially cylindrical graphite member and is provided to cover the area above the silicon melt 3, excluding the pulling path for the silicon single crystal 2.

[0050] The diameter of the opening at the lower end of the heat shielding member 27 is larger than the diameter of the silicon single crystal 2, thereby ensuring a path for pulling up the silicon single crystal 2. Furthermore, the outer diameter of the lower end of the heat shielding member 27 is smaller than the diameter of the quartz glass crucible 1, and the lower end of the heat shielding member 27 is located inside the quartz glass crucible 1. Therefore, even if the upper end of the rim of the quartz glass crucible 1 is raised above the lower end of the heat shielding member 27, the heat shielding member 27 will not interfere with the quartz glass crucible 1.

[0051] The wire winding mechanism 29 is positioned above the pull chamber 21b, and the wire 28 extends downward from the wire winding mechanism 29 through the pull chamber 21b, with the tip of the wire 28 reaching the internal space of the main chamber 21a. This figure shows a silicon single crystal 2 in the process of being grown suspended from the wire 28. When pulling up the silicon single crystal 2, the wire 28 is gradually pulled up while the quartz glass crucible 1 and the silicon single crystal 2 are rotated, thereby growing the silicon single crystal 2.

[0052] As the silicon single crystal 2 grows, the amount of silicon melt in the quartz glass crucible 1 decreases. However, by raising the quartz glass crucible 1 so that the height of the melt surface remains constant, temperature fluctuations of the silicon melt 3 can be suppressed, and the amount of dopant evaporation from the silicon melt 3 can be controlled by keeping the flow velocity of the gas flowing near the melt surface constant. Therefore, the stability of the crystal defect distribution, oxygen concentration distribution, resistivity distribution, etc., in the pulling axis direction of the silicon single crystal 2 can be improved.

[0053] In the production of silicon single crystal 2, a quartz glass crucible 1 is first placed inside a carbon susceptor 22, and then polycrystalline silicon raw material is placed inside the quartz glass crucible. Generally, the internal shape of the carbon susceptor 22 is not precisely matched to the external shape of a specific quartz glass crucible 1, but is a general-purpose shape. Therefore, when designing the quartz glass crucible 1, it is necessary to make it fit inside the carbon susceptor 22, and in particular, the diameter R (outer diameter) of the quartz glass crucible must be slightly smaller than the opening diameter of the carbon susceptor 22. In addition, the curvature of the bottom of the crucible must be approximately equal to or slightly larger than the curvature of the bottom of the carbon susceptor 22, and the curvature of the corners of the crucible must be smaller than the curvature of the corners of the carbon susceptor 22.

[0054] When such a quartz glass crucible 1 is placed inside a carbon susceptor 22, at least a portion of the bottom of the quartz glass crucible 1 is in contact with and supported by the bottom of the carbon susceptor 22. However, the corner portion 10c and the side wall portion 10a of the quartz glass crucible 1 do not come into contact with the inner surface of the carbon susceptor 22, and a small gap exists between them. Here, the curvature change point P on the bottom 10b side of the crucible is... ｂ If the curvature change point P is too far outward (upward) in the radial direction, a gap will not easily form between the crucible and the carbon susceptor 22, and the crucible will not be able to deform outward. ｂ If it is too far inward (downward) in the radial direction, the rattle will increase when the crucible is set in the carbon susceptor 22. However, the curvature change point P on the bottom 10b side. ｂ If the radial relative position is within the range of 0.59 to 0.72, it is possible to promote outward deformation of the crucible and prevent rattling when the crucible is set in the carbon susceptor.

[0055] Next, the raw materials in the quartz glass crucible 1 are heated and melted by the heater 25 to generate a silicon melt 3. Furthermore, a seed crystal attached to the lower end of the wire 28 is lowered and placed into the silicon melt 3. Then, while maintaining contact with the silicon melt 3, the seed crystal is gradually pulled up to grow a silicon single crystal 2. In the crystal pulling process, the diameter is gradually increased to form a shoulder portion, and then the diameter is kept constant to form a straight body portion. After forming a straight body portion of the desired length, the diameter is gradually decreased to separate it from the silicon melt 3. Thus, a silicon single crystal ingot is completed.

[0056] During the crystal pulling process, the quartz glass crucible 1 softens, but the side walls 10a and corners 10c of the crucible tilt outward and fit to the inner surface of the carbon susceptor 22, thereby suppressing the inward tilting of the crucible. Therefore, it is possible to prevent the crucible from coming into contact with the heat shielding member 27 and to prevent changes in the volume of the crucible from causing fluctuations in the liquid level of the molten silicon 3.

[0057] Figures 5 and 6 are schematic diagrams illustrating the deformation of a quartz glass crucible during the crystal pulling process.

[0058] As shown in Figure 5, the conventional quartz glass crucible 1C has a curvature change point P on the bottom 10b side of the crucible. ｂ Because the (contact end) is located towards the radially outer side of the crucible, the contact area between the bottom 10b of the crucible and the carbon susceptor 22 is large, and the side wall 10a and corner 10c are less likely to collapse outwards. Therefore, when the crucible is heated and softened, the corner 10c sinks in, and this tends to cause the side wall 10a to collapse inwards.

[0059] In contrast, the quartz glass crucible 1 according to the present invention has a curvature change point P on the bottom 10b side of the crucible. ｂ Because the contact end is located closer to the center of the bottom 10b than in conventional crucibles, the area in contact between the bottom 10b of the crucible and the carbon susceptor 22 is smaller, and the side walls 10a and corners 10c are more easily deformed. The side walls 10a and corners 10c do not contact the carbon susceptor 22, and there is a suitable gap between the side walls 10a and corners 10c and the carbon susceptor 22. When the crucible is heated and softened, the side walls 10a and corners 10c tilt in a direction that fills the gap between them and the inner surface of the carbon susceptor 22, using the contact point with the carbon susceptor 22 as a fulcrum. As a result, the side walls 10a of the crucible are more likely to deform into an outward-opening shape. Therefore, inward tilting of the side walls 10a can be prevented.

[0060] As shown in Figure 6, in the conventional quartz glass crucible 1C, the thickest part 10m of the crucible wall is located closer to the center of the bottom of the crucible (below the crucible), making it difficult for the corner portion 10c to sink due to its own weight and the resulting outward deformation of the side wall portion 10a to occur under high temperatures during the crystal pulling process. In contrast, in the quartz glass crucible 1 according to the present invention, the thickest part 10m of the crucible wall is located closer to the side wall portion 10a (above the crucible), which promotes the sinking of the corner portion 10c due to its own weight and the resulting outward deformation of the side wall portion 10a.

[0061] As described above, the quartz glass crucible 1 according to this embodiment has a cylindrical side wall portion 10a, a curved bottom portion 10b, and a corner portion 10c provided between the side wall portion 10a and the bottom portion 10b, and the point of change of curvature P on the bottom portion 10b side of the outer surface 10o of the crucible with respect to the outer radius r of the side wall portion 10a. ｂ Since the relative radial position of the elements is within the range of 0.59 to 0.72, it is possible to promote outward deformation of the crucible at high temperatures during the crystal pulling process and prevent inward tilting of the side wall portion 10a.

[0062] Although preferred embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the invention, and these modifications are also included within the scope of the present invention.

[0063] Point of change in curvature at the bottom of the crucible (P ｂ We investigated the effect of differences in the position of the crucible on its deformation. In the evaluation test, we examined the position of the curvature change point and the thickest part of the wall of each crucible sample before use. Then, we used them in the crystal pulling process and visually observed and evaluated whether or not the crucibles had deformed after use. We also evaluated whether or not the crucibles rattled when they were set in the carbon susceptor.

[0064] The crucible samples were manufactured using a rotary molding method. The position of the curvature change point on the outer surface of the crucible was adjusted by the amount of silica powder packed into the mold. The outer surface shape of the crucible is affected not only by the inner surface shape of the mold but also by the thickness of the silica powder deposit layer packed into the mold. Increasing the thickness of the silica powder deposit layer packed into the mold increases the amount of unmelted silica powder remaining between the inner surface of the mold and the outer surface of the crucible after arc melting, thereby changing the outer surface shape of the crucible. The thickness distribution of the silica powder deposit layer is adjusted by a scraper used to smooth the silica powder deposited on the inner surface of the rotating mold. By changing the edge shape of the scraper to adjust the thickness distribution of the silica powder deposit layer packed into the mold, the position of the curvature change point on the outer surface of the crucible can be adjusted.

[0065] The location of the curvature change point on the outer surface of the crucible can be measured non-destructively using a laser rangefinder. Coordinate data is acquired at 20 mm intervals along the outer surface of the crucible from the center of the bottom to an arbitrary position at the top of the rim. The curvature is calculated from the coordinate data of three adjacent points, and the point where the curvature changes significantly in the range from the center of the bottom to the thickest part of the corner is identified as the curvature change point on the bottom side. In other words, the curvature change point on the bottom side is determined as the midpoint between the two end points of a sequence of three consecutive points in the range from the center of the bottom to the thickest part of the corner, at the position where the rate of curvature change between the two end points is greatest.

[0066] Radius of curvature r of the outer surface of the crucible ｃ This is determined by acquiring coordinate data at equal intervals along the outer surface of the crucible and using the coordinate data of three adjacent points. That is, the radius of curvature r ｃ This is point X on the bottom center side. １ The coordinates (x １ ,y １ ), midpoint X ２ The coordinates (x ２ ,y ２ ), point X on the rim side ３ The coordinates (x ３ ,y ３ Using ), it can be calculated using the following formula.

[0067] 3 points {X ｉ = (x ｉ , y ｉ )} ｉ＝１，２，３ The center (a, b) of the circle passing through is given by the following equation.

[0068] The radius r of this circle is given by the following formula. However, i is one of the values ​​1, 2, or 3.

[0069] The radius r of the circle obtained in this way is the midpoint X ２ radius of curvature r ｃ２ Let the radius of curvature be r. ｃ２ The reciprocal of (1 / r) ｃ２ ) to midpoint X ２ This is the curvature at [location].

[0070] Point X on the bottom center side １ radius of curvature r ｃ１ Point X on the rim side ３ radius of curvature r ｃ３ In this case, the midpoint X ２ Curvature change rate Δr ｃ２ The percentage (%) is given by the following formula:

[0071] Table 1 shows the evaluation results of the crucible samples from Examples 1 to 5 and Comparative Examples 1 and 2.

[0072]

[0073] In Example 1, the position of the curvature change point at the bottom of the crucible sample (relative value) was 0.59, and the position of the thickest part (relative value) was 0.37. In Example 2, the position of the curvature change point at the bottom of the crucible sample was 0.67, and the position of the thickest part was 0.5. In Example 3, the position of the curvature change point at the bottom of the crucible sample was 0.72, and the position of the thickest part was 0.56. These crucible samples from Examples 1 to 3 showed no rattling within the carbon susceptor, and outward deformation was observed after use.

[0074] In Example 4, the curvature change point at the bottom of the crucible sample was 0.59, and the position of the thickest part of the wall was 0.3. This crucible sample did not rattle inside the carbon susceptor, and although outward deformation was observed after use, the deformation due to its own weight at the thickest part of the wall was small. Therefore, the degree of outward deformation was small. In Example 5, the curvature change point at the bottom of the crucible sample was 0.59, and the position of the thickest part of the wall was 0.6. This crucible sample did not rattle inside the carbon susceptor, and although outward deformation was observed after use, the change in the inner diameter of the side wall was large.

[0075] On the other hand, the curvature change point at the bottom of the crucible sample in Comparative Example 1 was 0.50, and there was significant rattle within the carbon susceptor, so its use in the crystal pulling process was discontinued. In addition, the curvature change point at the bottom of the crucible sample in Comparative Example 2 was 0.80, and no rattle was observed within the carbon susceptor, but inward deformation was observed after use, and the inner diameter of the side wall changed significantly.

[0076] Semiconductor products are indispensable in modern society and are used in a variety of fields. This invention provides a quartz glass crucible used in the manufacture of silicon single crystals that serve as substrates for semiconductor products, and which has a structure that is less prone to inward tilting even at high temperatures. When a crucible tilts inward, a portion of it comes into contact with the heat shielding material, making it impossible to rotate the crucible and thus preventing the pulling process from continuing. In addition, the sudden change in the volume of the crucible makes it difficult to control the pulling of the single crystal stabilization process. This invention solves these problems and improves the productivity of silicon single crystals, thereby contributing to the production of semiconductor products. As a result, this invention will promote technological progress in various industries and contribute to achieving SDG Goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation." Furthermore, this invention will reduce the waste of resources such as silicon raw materials, quartz crucibles, and inert gases generated by the inward tilting of quartz crucibles, and will contribute to achieving SDG Goal 12, "Responsible Consumption and Production."

[0077] 1,1C Quartz glass crucible 2 Silicon single crystal 3 Silicon melt 10 Crucible substrate 10a Side wall 10b Bottom 10c Corner 10e Rim (upper end of side wall) 10i Inner surface of crucible 10m Thickest part 10n Natural silica glass layer (natural layer) 10o Outer surface of crucible 10s Synthetic silica glass layer (synthetic layer) 11 Transparent layer 12 Bubble layer 14 Mold 14a Ventilation hole 14i Inner surface 15 Arc electrode 16 Deposited layer 16a Natural quartz powder 16b Synthetic quartz powder 20 Single crystal pulling device 21 Chamber 21a Main chamber 21b Pull chamber 21c Gas inlet 21d Gas outlet 22 Carbon susceptor 23 Rotating shaft 24 Shaft drive mechanism 25 Heater 26 Insulation material 27 Heat shielding member 28 Single crystal pulling wire 29 Wire winding mechanism P ０ Center of the bottom (center of the crucible) P ｂ Curvature change point (boundary between the bottom and corner) r Distance from the central axis of the crucible to the outer surface of the side wall (outer radius of the crucible) r ｂRadial distance Z from the central axis of the crucible to the point of curvature change. ０ Crucible central axis

Claims

1. A quartz glass crucible having a cylindrical side wall, a curved bottom, and a corner portion having a greater curvature than the bottom and provided between the side wall and the bottom, wherein the radial relative position of the point of curvature change on the bottom side of the outer surface of the crucible with respect to the outer radius of the side wall is within the range of 0.59 to 0.

72.

2. The quartz glass crucible according to claim 1, wherein the curvature of the outer surface at the corner portion is 3 to 7 times greater than the curvature of the outer surface at the bottom portion.

3. The quartz glass crucible according to claim 2, wherein the thickest part of the crucible wall is located at the corner, and the position of the thickest part is closer to the boundary between the corner and the side wall than to the boundary between the corner and the bottom.

4. The quartz glass crucible according to claim 3, wherein the boundary between the corner portion and the side wall portion on the outer surface is located between two points at the position where, when the curvature of the outer surface is measured at a constant pitch from the position of the thickest portion toward the upper end of the side wall portion, the absolute value of the rate of change of curvature between the two end points of three adjacent points first becomes 60% or more.

5. The distance L along the outer surface from the center of the bottom to the upper end of the side wall. ０ The distance L along the outer surface from the center of the bottom to the thickest part of the wall. １ Ratio L １ / L ０ A quartz glass crucible according to claim 3 or 4, wherein the coefficient is in the range of 0.37 to 0.56.

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