Quarts glass crucible

Abstract

[Problem] To provide a quartz glass crucible for pulling a silicon single crystal, capable of preventing silicon single crystal dislocation caused by exfoliation of brown rings. [Solution] This quartz glass crucible 1 comprises a crucible base body 10 having a cylindrical side wall portion 10a, a bottom portion 10b, and a corner portion 10c provided between the side wall portion 10a and the bottom portion 10b. The crucible base body 10 includes a bubble layer 11 composed of a silica glass containing numerous bubbles, and a transparent layer 12 provided on the inner surface 11i side of the bubble layer 11 and composed of a silica glass that does not contain bubbles. The thickest portion 10m of the crucible base body 10 is positioned at the corner portion 10c, and the intersection angle θT between the tangent TL1 on the outer surface 11o side and the tangent TL2 on the inner surface 11i side of the bubble layer 11 at the thickest portion 10m is 0° to 8.5°.

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 example, Patent Document 1 describes a quartz glass crucible in which the curvature of the inner surface of the curved portion is 0.8 to 1.2 times the curvature of the outer surface. Patent Document 2 describes a quartz glass crucible in which the ratio of the infrared transmittance at the position of maximum wall thickness of the corner portion to the infrared transmittance of the side wall portion is 0.3 or more and 0.99 or less, and the absolute value of the rate of change of infrared transmittance in the height direction along the wall surface of the crucible from the center of the bottom portion toward the upper end of the side wall portion is 3% / cm or less. Furthermore, Patent Document 2 describes a quartz glass crucible in which the absolute value of the rate of change of the thickness of the bubble layer in the height direction along the wall surface of the crucible from the center of the bottom portion toward the upper end of the side wall portion is 2.5 mm / cm or less.

[0005] Japanese Patent Publication No. 2008-162840, International Publication No. 2020 / 137647, Pamphlet

[0006] A quartz glass crucible has a two-layer structure consisting of a bubble layer and a transparent layer, with the inner surface of the crucible covered by the transparent layer. The reason for including the transparent layer is that if bubbles are present near the inner surface of the crucible, when the bubbles burst due to thermal expansion, pieces of the crucible are released into the silicon molten state, travel with the convection currents of the molten state, and are incorporated into the silicon single crystal at the solid-liquid interface, causing dislocation formation in the silicon single crystal.

[0007] In a two-layered quartz glass crucible like this, if the interface shape between the bubble layer and the transparent layer differs significantly from the outer surface shape of the crucible, the scattering of light passing through the bubble layer becomes uneven, resulting in an uneven temperature distribution on the inside of the crucible. In areas with higher temperatures, the reaction with the molten silicon is accelerated, leading to more rapid formation of Brown rings than in other areas. Ultimately, the center of the Brown ring is eroded, becoming a glass dissolution surface. When this happens, the glass becomes more easily detached from the glass dissolution surface, moves with the molten convection, and is incorporated into the solid-liquid interface of the silicon single crystal, causing dislocation formation in the silicon single crystal.

[0008] Therefore, the object of the present invention is to provide a quartz glass crucible capable of preventing dislocation formation of silicon single crystals caused by the peeling of Brown rings.

[0009] To solve the above problems, the quartz glass crucible according to the present invention comprises a crucible base having a cylindrical side wall portion, a bottom portion, and a corner portion provided between the side wall portion and the bottom portion, wherein the crucible base includes a bubble layer made of silica glass containing a large number of bubbles, and a transparent layer made of silica glass without bubbles provided on the inner surface side of the bubble layer, the thickest part of the crucible base is located at the corner portion, and the intersection angle between the tangent on the outer surface and the tangent on the inner surface of the bubble layer at the thickest part is 0° to 8.5°.

[0010] The corners of a quartz glass crucible are the hottest parts, and temperature unevenness occurs. In areas that become even hotter, the reaction with the molten silicon progresses more rapidly, making it prone to Brown ring formation and subsequent glass leaching. Furthermore, delamination also progresses from these high-temperature corners. In addition, the extremely high temperatures increase the risk of the quartz softening and buckling deformation due to its own weight.

[0011] According to the present invention, it is possible to prevent the temperature of the inner surface of the crucible from becoming uneven during the silicon single crystal pulling process. Therefore, it is possible to prevent dislocation formation of the silicon single crystal caused by the peeling of Brown rings from the inner surface of the crucible. In addition, by stabilizing the heat transfer at the thickest part located at the corner of the crucible, it is possible to prevent inward collapse.

[0012] In the present invention, the intersection angle is preferably 0.8° to 5.7°. Furthermore, the ratio of the radius of curvature of the outer surface to the radius of curvature of the inner surface of the bubble layer at the thickest part of the corner is preferably 0.65 to 1.22. This further improves the uniformity of temperature on the inner surface of the corner of the crucible.

[0013] When a first perpendicular line is drawn perpendicular to the outer surface of the bubble layer at the position of the thickest part of the wall, the intersection of the first perpendicular line and the outer surface is defined as the first intersection point, the intersection of the first perpendicular line and the inner surface of the bubble layer is defined as the second intersection point, a second perpendicular line is drawn perpendicular to the outer surface of the bubble layer at a position 20 mm above or below the first intersection point along the outer surface of the bubble layer, the intersection of the second perpendicular line and the outer surface is defined as the third intersection point, and the intersection of the second perpendicular line and the inner surface of the bubble layer is defined as the fourth intersection point, it is preferable that the tangent line on the outer surface side of the bubble layer at the thickest part of the corner is a straight line connecting the first intersection point and the second intersection point, and the tangent line on the inner surface side of the bubble layer at the thickest part of the corner is a straight line connecting the third intersection point and the fourth intersection point.

[0014] A first perpendicular line is drawn perpendicular to the outer surface of the bubble layer at the position of the thickest part of the wall, the intersection of the first perpendicular line and the outer surface is designated as the first intersection point, the intersection of the first perpendicular line and the inner surface of the bubble layer is designated as the second intersection point, a second perpendicular line is drawn perpendicular to the outer surface of the bubble layer at a position 20 mm above the first intersection point along the outer surface of the bubble layer, the intersection of the second perpendicular line and the outer surface is designated as the third intersection point, the intersection of the second perpendicular line and the inner surface of the bubble layer is designated as the fourth intersection point, and from the first intersection point the bubble When a third perpendicular line is drawn perpendicular to the outer surface of the bubble layer at a position 20 mm below the outer surface of the layer, the intersection point of the third perpendicular line and the outer surface is defined as the fifth intersection point, and the intersection point of the second perpendicular line and the inner surface of the bubble layer is defined as the sixth intersection point, it is preferable that the radius of curvature of the outer surface of the bubble layer is the radius of the arc passing through the three points of the third intersection point, the first intersection point, and the fifth intersection point, and the radius of curvature of the inner surface of the bubble layer is the radius of the arc passing through the three points of the fourth intersection point, the second intersection point, and the sixth intersection point.

[0015] According to the present invention, it is possible to provide a quartz glass crucible for pulling silicon single crystals that can prevent dislocation formation of silicon single crystals caused by the peeling of Brown rings.

[0016] 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 an explanatory diagram of the intersection angle between the outer and inner tangent lines of the bubble layer at a corner. Figures 4(a) and 4(b) are schematic diagrams for explaining the effects of the quartz glass crucible according to the present invention, with Figure 4(a) showing a conventional crucible and Figure 4(b) showing the crucible of the present invention. Figure 5 is an explanatory diagram of the ratio of the radius of curvature between the outer and inner surfaces of the bubble layer at a corner. Figure 6 is an explanatory diagram of a method for measuring the shapes of the outer and inner surfaces of the bubble layer. Figure 7 is a graph of the brightness levels of an image taken using the measurement method in Figure 6. Figure 8 is a schematic diagram showing a method for manufacturing a quartz glass crucible by the rotary molding method. Figures 9(a) to 9(c) are explanatory diagrams for controlling the shape of the inner surface of the bubble layer of the crucible.

[0017] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0018] 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.

[0019] As shown in Figures 1 and 2, the quartz glass crucible 1 is a container for holding a silicon melt and comprises a silica glass crucible base 10. The crucible base 10 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.

[0020] The side wall portion 10a is a part that extends linearly in the vertical direction and is preferably vertical, but it may also 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 part that has a greater curvature than the bottom portion 10b.

[0021] The diameter R 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 24 inches (approximately 610 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 it is required that they do not deform easily even after prolonged use and do not affect the quality of the silicon single crystal.

[0022] The thickness of the crucible substrate 10 varies slightly depending on the location, with the corner portion 10c being the thickest, and the side walls 10a and bottom portion 10b being thinner than the corner portion 10c. The thickness of the side walls 10a is preferably 6 mm or more for 18 inches or larger, 7 mm or more for 24 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, comprising a bubble layer 11 (opaque layer) containing numerous minute bubbles, and a substantially bubble-free transparent layer 12 (bubble-free layer) provided on the inner side of the transparent layer 12.

[0024] The bubble layer 11 is the main layer of the crucible substrate 10 and 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, it is desirable that the bubble layer 11 be provided throughout the entire crucible from the side wall portion 10a to the bottom portion 10b.

[0025] The bubble content of the bubble layer 11 is preferably sufficiently higher than that of the transparent layer 12, and is 1 vol% or more. This is because if the bubble content of the bubble layer 11 is lower than 1 vol%, it will not be able to perform the heat retention function required of the bubble layer 11. Furthermore, it is preferable that the bubble content of the bubble layer 11 is 5 vol% or less. This is because if the bubble content of the bubble layer 11 exceeds 5 vol%, the crucible may deform due to the thermal expansion of the bubbles, which may reduce the yield of silicon single crystals, and the heat transfer performance may also be insufficient. The bubble content mentioned above is the value measured in a crucible at room temperature before use.

[0026] The transparent layer 12 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 by melt convection to the solid-liquid interface of the silicon single crystal and incorporated into the silicon single crystal, it can cause dislocation formation in the silicon 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.

[0027] The transparent layer 12 has a sufficiently low bubble content so 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.

[0028] The thickness of the transparent layer 12 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 11. The transparent layer 12 is preferably provided throughout the entire crucible from the side wall portion 10a to the bottom portion 10b, but it is also possible to omit the transparent layer 12 at the upper end of the crucible where it does not come into contact with the silicon melt.

[0029] To prevent contamination of the silicon melt, it is desirable that the silica glass constituting the transparent layer 12 be of high purity. Therefore, it is preferable that the crucible substrate 10 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 (SiCl ４ It can be produced by gas-phase oxidation (dry synthesis method) of ) or hydrolysis of silicon alkoxides (sol-gel method). Natural quartz powder is produced by crushing natural minerals, mainly composed of α-quartz, into granules.

[0030] As will be described in detail later, the two-layer structure of a synthetic silica glass layer and a natural silica glass layer can be manufactured by depositing natural quartz powder along the inner surface of a crucible manufacturing mold, depositing synthetic quartz powder on top of it, and melting these raw quartz powders by Joule heating due to arc discharge. In the arc melting process, bubbles are removed by strongly drawing a vacuum from the outside of the deposited layer of raw quartz powder to form a transparent layer 12, and a bubble layer 11 is formed by stopping or weakening the vacuum. Therefore, the interface between the synthetic silica glass layer and the natural silica glass layer does not necessarily coincide with the interface between the transparent layer 12 and the bubble layer 11, but it is preferable that the synthetic silica glass layer, like the transparent layer 12, has a thickness such that it does not completely disappear due to melting of the inner surface of the crucible during the single crystal pulling process.

[0031] 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 having a larger curvature than the bottom portion 10b. The thickest portion 10m of the crucible substrate 10 is provided at the corner portion 10c. The tangent TL １ (or TL １ ') on the outer surface 11o side of the bubble layer 11 at the thickest portion 10m of the corner portion 10c and the tangent TL ２ (or TL ２ ') on the inner surface 11i side, the intersection angle θ Ｔ (or θ Ｔ ') is preferably 0° to 8.5°, and particularly preferably 0.8° to 5.7°.

[0032] The tangent TL １ on the outer surface 11o side of the bubble layer 11 and the tangent TL ２ on the inner surface 11i side are defined as follows. As shown in FIG. 3, a perpendicular line PL １ perpendicular to the outer surface 11o of the bubble layer 11 is drawn at the position of the thickest portion 10m of the corner portion 10c of the crucible, and the intersection of the perpendicular line PL １ and the outer surface 11o of the bubble layer 11 is set as P １ , and the intersection of the perpendicular line PL １ and the inner surface 11i of the bubble layer 11 is set as P ２ .

[0033] Next, a perpendicular line PL １ perpendicular to the outer surface 11o of the bubble layer 11 is drawn at a position 20 mm above along the outer surface 11o of the bubble layer 11 from the intersection P ２ , and the intersection of the perpendicular line PL ２ and the outer surface 11o of the bubble layer 11 is set as P ３ , and the intersection of the perpendicular line PL ２ and the inner surface 11i of the bubble layer 11 is set as P ４ .

[0034] Similarly, a perpendicular line PL １ perpendicular to the outer surface 11o of the bubble layer 11 is drawn at a position 20 mm below along the outer surface 11o of the bubble layer 11 from the intersection P ３ , and the intersection of the perpendicular line PL ３ and the outer surface of the bubble layer 11 is set as P ５ , and the intersection of the perpendicular line PL ３ and the inner surface of the bubble layer 11 is set as P ６Let's assume that.

[0035] And then, intersection P １ and intersection point P ３ The straight line passing through is the tangent TL on the outer surface 11o side of the bubble layer 11. １ Let P be the intersection point. ２ and intersection point P ４ The straight line passing through the inner surface 11i side of the bubble layer 11 is tangential TL. ２ This means that the tangent TL on the outer surface 11o side of the bubble layer 11 １ and the tangent TL on the inner surface 11i side ２ The angle θ at the intersection with Ｔ It is possible to find this.

[0036] Also, intersection P １ and intersection point P ５ The straight line passing through is the tangent TL on the outer surface 11o side of the bubble layer 11. １ Let's assume the intersection point P ２ and intersection point P ６ The straight line passing through the inner surface 11i side of the bubble layer 11 is tangential TL. ２ This means that the tangent TL on the outer surface 11o side of the bubble layer 11 １ ' and the tangent TL on the inner surface 11i side ２ 'Intersection angle θ Ｔ ' can be calculated.

[0037] Tangent TL on the outer surface 11o side １ and the tangent TL on the inner surface 11i side ２ The intersection angle θ obtained from Ｔ and the tangent TL on the outer surface 11o side １ ' and the tangent TL on the inner surface 11i side ２ The intersection angle θ obtained from ' Ｔ ' will not necessarily have the same value, but will be approximately the same, so it is sufficient to find and evaluate either one. Alternatively, θ Ｔ and θ Ｔ' You can also find both values ​​and choose the one with the larger value.

[0038] intersection angle θ Ｔ (or θ) Ｔ' If ) is less than 0°, and the intersection angle θ Ｔ (or θ) Ｔ'In all cases where the intersection angle θ is greater than 8.5°, as shown in Figure 4(a), the change in shape of the inner surface 11i becomes steeper in response to the change in shape of the outer surface 11o of the bubble layer 11, resulting in uneven scattering of light passing through the bubble layer 11 and large temperature variations in the inner surface 11i. Ｔ (or θ) Ｔ' If the temperature is between 0° and 8.5°, as shown in Figure 4(b), the light passing through the bubble layer 11 can be uniformly scattered and transmitted to the silicon melt, suppressing localized heating of the inner surface of the crucible and achieving stable heat transfer. This stabilizes the temperature of the inner surface of the crucible, stabilizes the melting rate of the Brown ring, and suppresses the peeling of the Brown ring.

[0039] In this embodiment, the radius of curvature r of the outer surface 11o of the bubble layer 11 at the thickest part 10m of the corner portion 10c of the crucible ｏ and the radius of curvature r of the inner surface 11i ｉ In comparison to ｉ / r ｏ It is preferable that the value is between 0.65 and 1.22.

[0040] Radius of curvature r on the outer surface 11o of the bubble layer 11 ｏ and the radius of curvature r on the inner surface 11i side ｉ It is defined as follows: As shown in Figure 5, the perpendicular line PL is perpendicular to the outer surface 11o of the bubble layer 11 at the position of the thickest part of the corner portion 10c of the crucible. １ Draw a perpendicular line PL １ The intersection point between the outer surface 11o of the bubble layer 11 is P １ , perpendicular line PL １ The intersection point between the bubble layer 11 and the inner surface 11i is P ２ Let's assume that.

[0041] Also, intersection P １ A perpendicular line PL is perpendicular to the outer surface 11o of the bubble layer 11, at a position 20 mm above along the outer surface 11o of the bubble layer 11. ２ Draw a perpendicular line PL ２ The intersection point between the outer surface 11o of the bubble layer 11 is P ３ , perpendicular line PL ２ The intersection point between the bubble layer 11 and the inner surface 11i is P ４ Let's assume that.

[0042] Furthermore, intersection P １A perpendicular line PL that is perpendicular to the outer surface 11o of the bubble layer 11 and is 20 mm below along the outer surface 11o of the bubble layer 11 ３ is drawn, and the perpendicular line PL ３ and the intersection point of the outer surface 11o of the bubble layer 11 is P ５ , the perpendicular line PL ３ and the intersection point of the inner surface 11i of the bubble layer 11 is P ６ is set.

[0043] Then, the radius of the arc passing through the three intersection points P ３ , P １ , P ５ is defined as the radius of curvature r ｏ on the outer surface 11o side of the bubble layer 11. Also, the radius of the arc passing through the three intersection points P ４ , P ２ , P ６ is defined as the radius of curvature r ｉ on the inner surface 11i side of the bubble layer 11.

[0044] When the radius of curvature ratio r ｉ / r ｏ is less than 0.65 and when the radius of curvature ratio r ｉ / r ｏ is greater than 1.22, the scattering of light passing through the bubble layer 11 becomes non-uniform, the inner surface of the crucible is locally heated, and the temperature unevenness on the inner surface increases. However, if the radius of curvature ratio r ｉ / r ｏ is within the range of 0.65 to 1.22, the light from the heater can be uniformly scattered by the bubble layer 11 and transmitted to the silicon melt, suppressing local heating of the inner surface of the crucible and realizing stable heat transfer. Thereby, the temperature of the inner surface of the crucible can be stabilized, the melting rate of the brown ring is stabilized, and the peeling of the brown ring can be suppressed.

[0045] The surface shapes of the outer surface 11o and the inner surface 11i of the bubble layer 11 can be measured non-destructively by the following method.

[0046] Fig. 6 is an explanatory diagram of the measurement method for the shapes of the outer surface 11o and the inner surface 11i of the bubble layer 11. Fig. 7 is a graph of the luminance levels of the images taken by the measurement method of Fig. 6.

[0047] As shown in Figure 6, the method for measuring the bubble layer 11 involves irradiating the inner surface of the crucible from the inside with a laser beam 20 at an oblique angle, while the irradiation area of ​​the laser beam 20 is photographed with a camera 22 to acquire a photographic image 30 of the reflected / scattered light. The laser beam 20 emitted from the laser device 21 is reflected by the mirror 23 and incident on the crucible. By adjusting the angle of the mirror 23, the incident angle on the inner surface of the crucible (inner surface 12i of the transparent layer 12) can be easily adjusted.

[0048] A portion of the laser beam 20 irradiated onto the crucible is reflected by the inner surface of the crucible, causing a bright spot to appear at the intersection of the inner surface 12i of the transparent layer 12 and the laser beam 20. The laser beam 20 that enters the crucible travels through the transparent layer 12 with almost no scattering and reaches the inner surface 11i of the bubble layer 11. As the laser beam travels through the bubble layer 11, it is scattered by the bubbles, and a linear, weak scattered light appears in the captured image 30. When the laser beam 20 reaches the outer surface 11o of the bubble layer 11 (i.e., the outer surface of the crucible), the reflection of the laser beam 20 increases, causing a bright spot to appear at the intersection of the outer surface 11o of the bubble layer 11 and the laser beam 20.

[0049] As can be seen from Figure 7, a steep peak in brightness level occurs at the inner surface of the crucible due to the reflection of laser light, and a steep peak in brightness level also occurs at the outer surface of the crucible due to the reflection of laser light. Therefore, the wall thickness of the crucible can be determined by calculating the distance between these peaks as a pixel value, correcting the measurement distance using the incident angle of the laser light 20, and further converting the pixel value to actual dimensions (millimeters).

[0050] Furthermore, since an increase in brightness level due to scattered light is observed at the boundary between the transparent layer 12 and the bubble layer 11, the position of the boundary between the transparent layer 12 and the bubble layer 11 can be identified by binarizing the captured image 30 using an appropriate threshold.Then, the distance from the inner surface of the crucible to the boundary between the transparent layer 12 and the bubble layer 11 is determined in pixel values, the measurement distance is corrected using the incident angle of the laser light 20, and the pixel values ​​are further converted to actual dimensions (millimeters) to determine the thickness of the transparent layer 12.Furthermore, the thickness of the bubble layer 11 is calculated by subtracting the thickness of the transparent layer 12 from the wall thickness of the crucible.

[0051] As described above, the wall thickness of the crucible, the thickness of the transparent layer 12, and the thickness of the bubble layer 11 can be measured at any position on the inner surface of the crucible. From these measurement results and the shape of the outer surface of the crucible, the shapes of the outer surface 11o and inner surface 11i of the bubble layer 11 can be determined. The shape of the outer surface of the crucible can be measured by moving a laser displacement meter along the outer surface of the crucible.

[0052] The shapes of the outer surface 11o and inner surface 11i of the bubble layer 11 can be evaluated not only by the non-destructive testing described above, but also by destructive testing. In the case of destructive testing, a large cutting machine is used to cut the crucible so that the cutting line passes through the center of the bottom, and a cross-sectional sample with a thickness of, for example, 20 mm is cut out so that the contour shapes of the side wall portion 10a, bottom portion 10b, and corner portion 10c of the crucible can be seen. Then, using the cut cross-sectional sample, the position of the thickest part of the crucible is identified and it is determined whether or not the thickest part is located at the corner portion 10c. In this way, the shapes of the outer surface 11o and inner surface 11i of the bubble layer 11 can be determined.

[0053] Figure 8 is a schematic diagram illustrating the manufacturing method of a quartz glass crucible 1 by the rotary molding method.

[0054] As shown in Figure 8, the quartz glass crucible 1 according to this embodiment can be manufactured by a so-called rotary molding method. 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 15a and synthetic quartz powder 15b are sequentially filled along the inner surface 14i of the rotating mold 14 to form a deposit layer 15 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.

[0055] In this embodiment, the desired crucible shape is achieved by adjusting the shape of the inner surface 14i of the mold 14 and the shape of the scraper 16 used when adjusting the amount of quartz powder filled. The scraper 16 is made 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 14, the thickness of the raw quartz powder deposit layer 15 can be precisely adjusted in each part.

[0056] Next, an arc electrode 17 is placed inside the mold 14, and the deposited layer 15 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 15a cools after arc melting to become a natural silica glass layer, and the deposited layer of synthetic quartz powder 15b cools after arc melting to become a synthetic silica glass layer.

[0057] During arc melting, the amount of bubbles in the molten silica glass is controlled by evacuating the deposited layer 15 of raw quartz powder through numerous slit-shaped vents 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 12, and after the formation of the transparent layer 12, the evacuation of the raw quartz powder is stopped or weakened to form a bubble layer 11.

[0058] The arc heat gradually propagates from the inside to the outside of the deposited layer 15 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 12 or a bubble layer 11. 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 base 10 is completed in which the transparent layer 12 and the bubble layer 11 are sequentially formed from the inside to the outside of the crucible wall.

[0059] The viscosity of the raw material quartz powder changes due to melting. While the raw material quartz powder adhering to the side surface of the mold 14 flows down due to gravity, the raw material quartz powder at the bottom of the mold 14 moves outward due to centrifugal force. Therefore, the wall thickness of the crucible is the thickest at the corner portion 10c.

[0060] The radius of curvature ro of the outer surface 11o of the bubble layer 11 can be changed by controlling the radius of curvature of the inner surface of the mold 14 and the heating conditions. Also, the radius of curvature r of the inner surface 11i of the bubble layer 11 ｉ can be changed by controlling the thickness of the deposited layer 15 of the raw material quartz powder, the rotation speed of the mold 14, and the time of evacuation. Thus, the intersection angle θ between the tangent line on the outer surface 11o side and the tangent line on the inner surface 11i side of the bubble layer 11 at the thickest part 10m of the wall thickness at the corner portion 10c Ｔ is 0° to 8.5°, and further, the ratio r of the radius of curvature r of the outer surface 11o of the bubble layer 11 to the radius of curvature r of the inner surface 11i at the thickest part 10m of the wall thickness at the corner portion 10c ｏ and the radius of curvature r of the inner surface 11i ｉ and the ratio r ｉ / r ｏ is 0.65 to 1.22, and the crucible base 10 is completed.

[0061] A method for controlling the intersection angle θ formed by the inner surface 11i and the outer surface 11o of the bubble layer 11 will be described. The intersection angle θ Ｔ is an angle that depends on the shapes of the inner surface 11i and the outer surface 11o of the bubble layer 11. Therefore, the intersection angle θ Ｔ can be controlled by controlling the shapes of the inner surface 11i and the outer surface 11o of the bubble layer 11. The shape of the outer surface 11o of the bubble layer 11 can be controlled by the shape of the inner surface of the mold 14. Ｔ

[0062] The shape of the inner surface 11i of the bubble layer 11 can, firstly, be controlled by the shape of the scraper 16. As described above, the transparent layer 12 is formed by vacuuming during arc melting. The formation of the transparent layer 12 is facilitated by melting and vitrifying the inner surface of the crucible, and the molten glass acts like a lid covering the inner surface of the crucible, forming a sealing layer that seals the inner surface of the crucible. When the entire packed raw material powder is melted uniformly, the shape of the outer surface of the transparent layer 12 (inner surface 11i of the bubble layer 11) can be made to almost coincide with the inner surface shape of the crucible (shape of the scraper 16). In other words, the shape of the inner surface 11i of the bubble layer 11 can be changed by changing the shape of the scraper 16.

[0063] Secondly, the shape of the inner surface 11i of the bubble layer 11 can also be controlled by adjusting the position of the arc electrode 17, the opening of the arc electrode 17, the vacuuming time, etc. The thickness of the transparent layer 12 can be changed by biasing the creation of the seal layer when forming the transparent layer 12, thereby changing the shape of the inner surface 11i of the bubble layer 11. The formation speed and position of the seal layer can be adjusted by the position and opening of the arc electrode 17, the vacuuming time, the arc heat, etc.

[0064] Figures 9(a) to 9(c) are explanatory diagrams illustrating a method for controlling the shape of the inner surface 11i of the bubble layer 11 of the crucible.

[0065] As shown in Figure 9(a), in the production of quartz glass crucibles by the rotary molding method, raw material powder 18 deposited on the inner surface of the rotary mold 14 is heated and melted from the inside of the mold 14. When the melting of the raw material powder 18 begins, a thin layer of molten quartz, called a seal layer 18s, is formed on the inner surface of the deposited layer of raw material powder 18. Subsequently, a vacuum is drawn from the outside of the raw material powder 18 to form a transparent layer 12. This forms an outer surface 12o of the transparent layer 12 that conforms to the shape of the inner surface of the crucible. The outer surface 12o of the transparent layer 12 is the inner surface 11i of the bubble layer 11.

[0066] As shown in Figure 9(b), when arc heating is performed with the tip of the arc electrode 17 positioned as far down as possible inside the mold 14, the melting of the raw material powder 18 proceeds rapidly at the bottom of the mold 14, and a seal layer 18s is formed. As a result, when vacuum is applied, the pressure inside the raw material powder 18 is accelerated, and a thick transparent layer 12 is formed at the bottom 10b of the crucible.

[0067] As shown in Figure 9(c), when the opening of the tip of the arc electrode 17 is widened and arc heating is performed so that heat is applied to the wall side of the mold 14, the melting of the raw material powder 18 proceeds rapidly at the side wall of the mold 14, and a seal layer 18s is formed. As a result, when vacuum is drawn, the pressure inside the raw material powder 18 is promoted, and a thick transparent layer 12 is formed on the side wall 10a of the crucible.

[0068] On the other hand, at the bottom of the mold 14, the melting of the raw material powder 18 is slow, and a seal layer 18s is not formed. As a result, even when vacuuming is performed, the pressure inside the raw material powder 18 is not reduced, and the transparent layer 12 is not formed. Consequently, the thickness of the transparent layer 12 becomes relatively thicker at the side walls 10a of the crucible and relatively smaller at the corners 10c and the bottom 10b.

[0069] As described above, by adjusting the height position of the arc electrode 17, the thickness of the transparent layer 12 in each part of the crucible can be controlled, and by adjusting the thickness of the transparent layer 12, the shape of the inner surface 11i of the bubble layer 11 can be controlled.

[0070] Next, the crucible base 10 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.

[0071] As described above, the quartz glass crucible 1 according to this embodiment has a cylindrical side wall portion 10a, a bottom portion 10b provided below the side wall portion 10a, and a corner portion 10c provided between the side wall portion 10a and the bottom portion 10b, the thickest part 10m of the crucible base 10 is located at the corner portion 10c, and the tangent intersection angle θ between the outer surface 11o side and the inner surface 11i side of the bubble layer 11 at the thickest part 10m Ｔ , θ ＴSince the temperature range is 0° to 8.5°, it is possible to prevent the temperature of the inside of the crucible from becoming uneven during the silicon single crystal pulling process. Therefore, it is possible to prevent dislocation formation of the silicon single crystal caused by the peeling of Brown rings from the inside of the crucible.

[0072] 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.

[0073] The effect of the interface shape between the bubble layer and the transparent layer at the corner of a quartz glass crucible used for silicon single crystal pulling on the yield of silicon single crystals was evaluated. In the evaluation test, multiple samples of quartz glass crucibles were manufactured using the rotary mold method, and then the intersection angle of the tangents to the inner / outer surfaces of the bubble layer and the radius of curvature ratio were measured at the corner of each crucible sample. The sizes of the crucible samples were 24 inches and 32 inches.

[0074] As described above, the radius of curvature of the outer surface of the crucible's bubble layer was adjusted by changing the radius of curvature of the mold and the heating conditions. The thickness of the bubble layer and the radius of curvature of the inner surface were adjusted by changing the thickness of the raw material powder deposit layer, the mold rotation speed, and the vacuuming time, respectively.

[0075] Next, the tangent intersection angle and radius of curvature ratio of the inner and outer surfaces of the bubble layer at the corner of each crucible sample were determined. The method for determining the tangent intersection angle and radius of curvature ratio was as described above: the crucible was cut, and the curvature shape of the inner and outer surfaces of the bubble layer revealed in the cross-section was visually observed to determine the tangent intersection angle and radius of curvature ratio of the bubble layer. Thus, the measurement of the tangent intersection angle and radius of curvature ratio of the bubble layer was performed by destructive testing. The results of the tangent intersection angle and radius of curvature ratio are shown in Table 1.

[0076] Next, silicon single crystal pulling experiments were conducted using separate crucible samples manufactured under the same conditions as the crucible samples prepared for evaluating crucible properties. In the pulling experiments, one single crystal was pulled from each crucible. In the single crystal pulling experiment using a 24-inch crucible, more than 100 kg of polycrystalline silicon raw material was used to grow a silicon single crystal with a diameter of approximately 200 mm. In the single crystal pulling process using a 32-inch crucible, several hundred kg of polycrystalline silicon raw material was used to grow a silicon single crystal with a diameter of approximately 300 mm.

[0077] Subsequently, the single-crystallization rate of the obtained silicon single crystals was evaluated. The single-crystallization rate is the weight ratio of the single crystal to the polycrystalline raw material packed in the crucible, and a single-crystallization rate of 80% or higher is considered acceptable. This is because even if the pulling of the single crystal is perfectly successful, a small amount of silicon raw material will always remain in the crucible, making it impossible to achieve 100%.

[0078] The single crystallization rate was calculated by averaging the single crystallization rates of five silicon single crystals obtained using five virtually identical quartz glass crucibles. Specifically, in the silicon single crystal pulling experiment, five crystal pulling crucible samples, each virtually identical to one of the eight crucible samples used for property measurement, were prepared. Using these 8 × 5 = 40 crucible samples, 8 × 5 = 40 silicon single crystals were pulled. The single crystallization rates are shown in Table 1.

[0079]

[0080] As can be seen from Table 1, when the tangent intersection angle was between 0.8° and 8.5° and the radius of curvature ratio was between 0.65 and 1.22, the single crystallization rate was 80% or higher. On the other hand, when the tangent intersection angle was 9.2° or higher and the radius of curvature ratio was 1.55 or higher, the single crystallization rate was less than 80%. Also, when the radius of curvature ratio was 0.49, the single crystallization rate was below 80%.

[0081] Semiconductor products are indispensable in modern society and are widely used in various fields. This invention provides a quartz glass crucible used in the manufacture of silicon single crystals that serve as substrates for semiconductor products, which suppresses the peeling of Brown rings. When Brown ring peeling occurs, dislocations may occur in the silicon single crystal, potentially adversely affecting the silicon single crystal manufacturing process. This invention solves this problem and contributes to the stable production of semiconductor products by improving the yield of silicon single crystals. As a result, this invention will ultimately promote technological innovation in various industrial fields and contribute to achieving SDG Goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation."

[0082] 1. Quartz glass crucible 10. Crucible base 10a. Side wall 10b. Bottom 10c. Corner 10i. Inner surface 10m. Thickest part 11. Bubble layer 11i. Inner surface of bubble layer 11o. Outer surface of bubble layer 12. Transparent layer 14. Mold 14a. Ventilation hole 14i. Inner surface of mold 15. Deposited layer of raw quartz powder 15a. Natural quartz powder 15b. Synthetic quartz powder 16. Scraper 17. Arc electrode 18. Raw material powder 18s. Seal layer 20. Laser light 21. Laser device 22. Camera 23. Mirror 30. Captured image P １ Intersection (first intersection) P ２ Intersection (second intersection) P ３ Intersection (third intersection) P ４ Intersection (Fourth intersection) P ５ Intersection (5th intersection) P ６ Intersection (6th intersection) PL １ Perpendicular line (first perpendicular line) PL ２ Perpendicular line (second perpendicular line) PL ２ Perpendicular line (third perpendicular line) R Crucible diameter TL １ , TL １ 'Tangential line on the outer surface TL ２ , TL ２ ' Tangent line r on the inner side ｏ Radius of curvature r on the outer surface ｉ Radius of curvature r on the inner side ｉ / r ｏ Curvature radius ratio θＴ Intersection angle θ Ｔ 'Intersection Angle'

Claims

1. A quartz glass crucible comprising a crucible base having a cylindrical side wall portion, a bottom portion, and a corner portion provided between the side wall portion and the bottom portion, wherein the crucible base comprises a bubble layer made of silica glass containing a large number of bubbles, and a transparent layer made of silica glass without bubbles provided on the inner surface side of the bubble layer, the thickest part of the crucible base is located at the corner portion, and the intersection angle between the tangent on the outer surface and the tangent on the inner surface of the bubble layer at the thickest part is 0° to 8.5°.

2. The quartz glass crucible according to claim 1, wherein the intersection angle is 0.8° to 5.7°.

3. The quartz glass crucible according to claim 1 or 2, wherein the ratio of the radius of curvature of the outer surface to the radius of curvature of the inner surface of the bubble layer at the thickest part of the corner is 0.65 to 1.

22.

4. A quartz glass crucible according to claim 1, wherein a first perpendicular line is drawn perpendicular to the outer surface of the bubble layer at the position of the thickest part of the wall, the intersection of the first perpendicular line and the outer surface is defined as the first intersection point, the intersection of the first perpendicular line and the inner surface of the bubble layer is defined as the second intersection point, a second perpendicular line is drawn perpendicular to the outer surface of the bubble layer at a position 20 mm above or below the first intersection point along the outer surface of the bubble layer, the intersection of the second perpendicular line and the outer surface is defined as the third intersection point, and the intersection of the second perpendicular line and the inner surface of the bubble layer is defined as the fourth intersection point, the tangent line on the outer surface side of the bubble layer at the thickest part of the corner is a straight line connecting the first intersection point and the second intersection point, and the tangent line on the inner surface side of the bubble layer at the thickest part of the corner is a straight line connecting the third intersection point and the fourth intersection point.

5. When a first perpendicular line is drawn perpendicular to the outer surface of the bubble layer at the position of the thickest part of the wall thickness, and the intersection of the first perpendicular line and the outer surface is defined as the first intersection point, and the intersection of the first perpendicular line and the inner surface of the bubble layer is defined as the second intersection point, when a second perpendicular line is drawn perpendicular to the outer surface of the bubble layer at a position 20 mm above the first intersection point along the outer surface of the bubble layer, and the intersection of the second perpendicular line and the outer surface is defined as the third intersection point, and the intersection of the second perpendicular line and the inner surface of the bubble layer is defined as the fourth intersection point, when a third perpendicular line is drawn perpendicular to the outer surface of the bubble layer at a position 20 mm below the first intersection point along the outer surface of the bubble layer, and the intersection of the third perpendicular line and the outer surface is defined as the fifth intersection point, and the intersection of the second perpendicular line and the inner surface of the bubble layer is defined as the sixth intersection point, The quartz glass crucible according to claim 3, wherein the radius of curvature of the outer surface of the bubble layer is the radius of the arc passing through the three points of the third intersection, the first intersection, and the fifth intersection, and the radius of curvature of the inner surface of the bubble layer is the radius of the arc passing through the three points of the fourth intersection, the second intersection, and the sixth intersection.

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