Quartz glass crucible for pulling up a silicon monocrystal and method for producing a silicon monocrystal using the same

Abstract

[Task] A quartz glass crucible for pulling up a silicon monocrystal is provided, wherein a thickness of the crystal layer at a time of crystallization of an outer surface of the crucible is large and the crucible can withstand a long-term crystal pulling up step. [Solution] A quartz glass crucible 1 includes a crucible main body 10 made of silica glass, and a semi-molten layer 13 consisting of a fusion-bonded layer of unmelted or semi-molten quartz powder formed on the outer surface of the crucible main body 10. A number of recesses 14 with a diameter of 0.2 mm or more and 5.0 mm or less and a depth of 50 μm or more are formed on a surface of the semi-molten layer 13. Some of the recesses 14 are through-holes that penetrate the semi-molten layer 13 to reach the outer surface 10o of the crucible main body 10, and the density of the through-holes is 1 through-hole / cm 2 or more and 50 through holes / cm 2 or less.

Description

TECHNICAL AREA

[0001] The present invention relates to a quartz glass crucible for pulling up a silicon monocrystal and a method for producing the same. Furthermore, the present invention relates to a method for producing a silicon monocrystal using such a quartz glass crucible. STATE OF THE ART

[0002] A quartz crucible (silica crucible) is used to produce a silicon monocrystal using the Czochralski process (CZ process). In the CZ process, a polycrystalline silicon raw material is melted in a quartz crucible to create a silicon melt. A seed crystal is immersed in the silicon melt, and the seed crystal is gradually pulled upward while the quartz crucible and seed crystal are rotated, allowing large monocrystals to grow at the bottom of the seed crystal. The CZ process can increase the yield of large-diameter silicon monocrystals.

[0003] The quartz glass crucible is a silica glass container that holds the silicon melt during a silicon monocrystal pull-up step. The inner side portion (inner layer) of the quartz glass crucible is formed from a transparent glass layer that comes into contact with the silicon melt and therefore contains essentially no bubbles. The outer side portion (outer layer) is formed from a bubble-containing layer containing a number of bubbles to distribute the radiant heat from the outside and evenly heat the interior of the crucible.

[0004] As a method for manufacturing a quartz glass crucible, the rotary molding method is known. This manufacturing method is a method for manufacturing a crucible. The method includes heating quartz powder deposited on an inner surface of a rotary mold from a central side of the mold to vitrify the quartz powder, thereby producing a crucible in which a transparent glass layer can be formed inside the crucible by sucking air into a quartz powder deposit layer from the mold side during melting and removing bubbles in a glass layer.

[0005] For example, regarding a quartz glass crucible, Patent Literature 1 describes a quartz glass crucible in which a roughness of an outer surface from a lower portion to an R portion of a straight body portion of an opaque outer layer is greater than a roughness of an outer surface from an upper portion to a middle portion of the straight body portion and greater than a roughness of an outer surface of a bottom portion, and a method for manufacturing the same. The roughness of the outer surface from the upper portion to the middle portion of the straight body portion is 5 μm or more and 50 μm or less, while the roughness of the outer surface from the lower portion to the R portion of the straight body portion is 30 μm or more and 100 μm or less.

[0006] Furthermore, Patent Literature 2 describes a quartz glass crucible having an outer surface layer formed of a quartz glass layer containing bubbles, an inner surface layer formed of a quartz glass layer in which no bubbles are visible to the naked eye, and a semi-molten quartz layer formed of an unmelted or semi-molten quartz layer formed on one surface of the outer surface layer, wherein the average center line roughness (Ra) of the semi-molten quartz layer is 50 μm to 200 μm.

[0007] Recently, with the increase in the size of a crucible, the temperature of the crucible also increases during lifting. As the temperature of the crucible increases, the viscosity of the glass decreases, and there is a risk of the crucible deformation during use. As a countermeasure, a method is known in which a crystallization accelerator is applied to or incorporated into a surface of a crucible and glass is crystallized at a high temperature to increase the strength of the crucible. In addition, a quartz glass crucible with a three-layer structure is also known, in which an outer layer of the crucible is a quartz layer to which Al is added, an intermediate layer is a natural quartz layer or a high-purity synthetic quartz layer, and an inner layer is a transparent high-purity synthetic quartz layer (see Patent Literature 3). LITERATURE ON THE STATE OF THE ART PATENT LITERATURE Patent Literature 1: Japanese Patent Laid-Open Publication No. 2020-200199 Patent Literature 2: Japanese Laid-Open Patent Publication No. 2009-84114 Patent Literature 3: Japanese Laid-Open Patent Publication No. 2000-247778 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] As described above, it is essential that the quartz glass crucible be durable so that the quartz glass crucible can withstand a long-term crystal pulling step, and a method of crystallizing an outer surface of the crucible or a method of adding Al is effective, but further improvement of the durability of the crucible is required.

[0009] Therefore, an object of the present invention is to provide a quartz glass crucible in which a thickness of a crystal layer at the time of crystallization of an outer surface of the crucible is large and the crucible can withstand a long-term crystal pulling step, and a method for producing the same. Another object of the present invention is to provide a method for producing a silicon monocrystal that makes it possible to grow a long and high-quality silicon monocrystal by performing a long-term crystal pulling step. MEANS FOR SOLVING THE TASKS

[0010] To achieve the objects, a quartz glass crucible for pulling up a silicon monocrystal according to one aspect of the present invention includes a crucible main body made of silica glass, and a semi-molten layer consisting of a fusion-bonded layer of unmelted or semi-molten quartz powder formed on an outer side of an outer surface of the crucible main body, wherein a number of recesses having a diameter of 0.2 mm or more and 5.0 mm or less are formed on a surface of the semi-molten layer, some of the recesses are through holes penetrating the semi-molten layer to reach the outer surface of the crucible main body, and a density of the through holes of 1 through hole / cm 2 or more and 50 through holes / cm 2 or less.

[0011] According to the present invention, the crystallization rate of the outer surface of the crucible can be increased to form a thick crystal layer. Therefore, it is possible to improve the durability of the crucible at a high temperature during crystal pulling, and it is also possible to provide a crucible that can withstand a long-term crystal pulling step. Although recesses are also provided on an outer surface of a quartz glass crucible in the prior art, the number of deep recesses that penetrate the semi-molten layer to reach the glass layer is small. Thus, the crystallization rate of the outer surface is low, and the thickness of the crystal layer at the time of outer surface crystallization is thin. Therefore, the durability of the quartz glass crucible was low, and the quartz glass crucible could not withstand a long-term crystal pulling step.However, according to the present invention, the number of recesses reaching the glass layer is large, so that crystallization into the wall is likely to occur at the time of crystallization of an outer surface of the crucible, and the thickness of the crystal layer can be increased.

[0012] In the present invention, the thickness of the semi-molten layer is preferably 50 μm or more. When the thickness of the semi-molten layer is 50 μm or more, crystallization of the outer surface of the crucible is promoted, allowing the formation of a thick crystal layer.

[0013] Preferably, the quartz glass crucible according to the present invention includes a cylindrical side wall portion, a bottom portion, and a corner portion provided between the side wall portion and the bottom portion, wherein a wall thickness of the corner portion is greater than the wall thickness of the side wall portion and the bottom portion, and a region where the through-holes are formed is provided at least over an entire circumference of the corner portion. Since the deep recesses penetrating the semi-molten layer are distributed at least over the entire circumference of the corner portion as described above, crystallization of the corner portion of the crucible can be promoted, and deformations such as crucible subsidence can be effectively suppressed.

[0014] Furthermore, the method for producing a quartz glass crucible according to the present invention includes a step of heating quartz powder deposited on an inner surface of a rotary mold from a central side of the mold to vitrify the quartz powder, a step of taking out the quartz glass crucible from the mold after cooling, and a step of subjecting a semi-molten layer consisting of a fusion-bonded layer of unmelted or semi-molten quartz powder formed on an outer surface of the quartz glass crucible to a honing treatment, in which a thermal conductivity of the quartz powder forming a natural quartz glass layer of the quartz glass crucible at 750 °C is 0.5 W / (m·K) or more and 10 W / (m·K) or less.

[0015] According to the present invention, it is possible to manufacture a quartz glass crucible in which a semi-molten layer consisting of a fusion-bonded layer of unmelted or semi-melted quartz powder is formed on an outer surface of a crucible main body made of silica glass, a number of recesses having a diameter of 0.2 mm or more and 5.0 mm or less are formed on a surface of the semi-molten layer, some of the recesses are through-holes reaching the outer surface of the crucible main body, and a density of the through-holes is 1 through-hole / cm 2 or more and 50 through holes / cm 2 or less.

[0016] In the present invention, the average particle diameter of the quartz powder is preferably 150 µm or more and less than 400 µm. By using such a quartz powder, the production yield of the quartz glass crucible with these properties can be increased.

[0017] In the present invention, the mold preferably has a cavity that conforms to an outer shape of the quartz glass crucible, and an opening size of the cavity corresponding to the side wall portion of the quartz glass crucible is 1.01 times or more and 1.15 times or less of a target outer diameter of the side wall portion. By using such a mold, the production yield of the quartz glass crucible with these characteristics can be increased.

[0018] Furthermore, in the method for producing a silicon monocrystal according to the present invention, a silicon melt is produced by melting a polycrystalline silicon raw material in a quartz glass crucible having these properties, and the silicon monocrystal is pulled up from the silicon melt. According to the present invention, it is possible to grow a long and high-quality silicon crystal by performing a long-duration crystal pulling step. EFFECTS OF THE INVENTION

[0019] According to the present invention, it is possible to provide a quartz glass crucible in which a thickness of a crystal layer at the time of crystallization of an outer surface of the crucible is large and the quartz glass crucible can withstand a long-term crystal pulling step, and a method for producing the same. Furthermore, according to the present invention, it is possible to provide a method for producing a silicon monocrystal that makes it possible to grow a long and high-quality silicon monocrystal by performing a long-term crystal pulling step. BRIEF DESCRIPTION OF THE CHARACTERS [ Fig. 1] is a schematic perspective view showing a configuration of a quartz glass crucible according to an embodiment of the present invention. [ Fig.2] is a schematic side view of the quartz glass crucible according to the present embodiment, in which the left half is a cross-sectional view and the right half is an external view. [ Fig. 3] is a schematic cross-sectional view of a semi-molten layer in which recesses are formed. [ Fig. 4] is a schematic cross-sectional view showing a state of the semi-molten layer according to the present invention before and after heating in comparison with the prior art. In [ Fig. 4] (a) shows a state of a crucible according to the prior art before heating, (b) shows a state of the crucible according to the prior art after heating, (c) shows a state of a crucible according to the present invention before heating, and (d) shows a state of the crucible according to the present invention after heating. [ Fig.5] is a schematic view showing a method for manufacturing a quartz glass crucible according to an embodiment of the present invention. [ Fig. 6] is a view for explaining a step of pulling up a monocrystal using the quartz glass crucible according to the present embodiment, which is a schematic cross-sectional view showing a configuration of a monocrystal pulling-up apparatus. [ Fig. [Figure 7] is a graph showing the results of a one-way analysis of the deformation amounts of crucible samples 1 to 10 after a heating test. MODE FOR CARRYING OUT THE INVENTION

[0020] Hereinafter, preferred embodiments of the present invention are described in detail with reference to the accompanying figures.

[0021] Fig.1 is a schematic perspective view showing the configuration of a quartz glass crucible according to an embodiment of the present invention.

[0022] As in Fig.1, a quartz glass crucible 1 is a silica glass container for holding a silicon melt, the container having a cylindrical side wall portion 10a, a bottom portion 10b provided below the side wall portion 10a, and a corner portion 10c provided between the side wall portion 10a and the bottom portion 10b. The bottom portion 10b is preferably a so-called round bottom, which is slightly curved, but may also be a so-called flat bottom. The corner portion 10c is a portion that has a greater curvature than the bottom portion 10b. The boundary between the side portion 10a and the corner portion 10c, as well as the boundary between the corner portion 10c and the bottom portion 10b, can be determined based on curvature change points. The boundary between the side wall portion 10a and the corner portion 10c in Fig.2 is slightly shifted from the point of curvature change, which differs from the explanation given here. Therefore, Fig. 2 may be slightly modified.

[0023] The opening (diameter) of the quartz glass crucible 1 also depends on the diameter of a silicon monocrystal ingot pulled up from the silicon melt, but is 18 inches (approximately 450 mm) or more, preferably 22 inches (approximately 560 mm), and more preferably 32 inches (approximately 800 mm) or more. This is because such a large crucible is used to pull up a large silicon monocrystal ingot with a diameter of 300 mm or more, and the quality of the monocrystal must not be deteriorated even after extended use.

[0024] The wall thickness of the crucible varies slightly depending on the part, but preferably, the wall thickness of the side wall portion 10a of the crucible with a diameter of 18 inches or more is 6 mm or more, the wall thickness of the side wall portion 10a of the crucible with a diameter of 22 inches or more is 7 mm or more, and the wall thickness of the side wall portion 10a of the crucible with a diameter of 32 inches or more is 10 mm or more. This allows a large amount of silicon melt to be stably maintained at a high temperature. Preferably, the wall thickness of the corner portion 10c of the crucible is the largest, and the wall thickness of the side wall portion 10a and the bottom portion 10b of the crucible is smaller than that of the corner portion 10c of the crucible.

[0025] Fig.2 is a schematic side view of the quartz glass crucible 1 according to the present embodiment, in which the left half is a cross-sectional view and the right half is an external view.

[0026] As in Fig. As shown in Figure 2, the quartz glass crucible 1 includes a crucible main body 10 made of silica glass and a semi-molten layer 13 formed on an outer surface 10o of the crucible main body 10. The crucible main body 10 is a two-layer structure including a transparent layer 11 containing no bubbles (bubble-free layer) and a bubble layer 12 containing a number of tiny bubbles (opaque layer). The semi-molten layer 13 is provided outside the bubble layer 12. A crystallization accelerator may be coated or added to the outer surface of the semi-molten layer 13.

[0027] The transparent layer 11 is a glass layer forming an inner surface 10i of the crucible main body 10. The glass layer comes into contact with the silicon melt and is designed to prevent a decrease in the yield of silicon monocrystals due to bubbles in the silica glass. Since the inner surface 10i of the crucible reacts with the silicon melt to melt away, the bubbles near the inner surface of the crucible cannot be trapped in the silica glass, and the bubbles burst due to thermal expansion, causing the crucible fragments (silica fragments) to detach. In a case where the crucible fragments released into the silicon melt are transported to a growth interface of the silicon monocrystal by melt convection and incorporated into the silicon monocrystal, they cause dislocations in the monocrystal.In a case where the bubbles released into the silicon melt rise upwards, reach a solid-liquid interface and are incorporated into the monocrystal, they also cause the formation of pinholes in the silicon monocrystal.

[0028] The term "bubble-free" in the transparent layer 11 means a bubble content and bubble size such that the monocrystallization rate is not reduced by the bubbles. Such a bubble content is, for example, 0.1 vol% or less and such a bubble diameter is, for example, 100 µm or less.

[0029] 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 the bubble layer 12 is not exposed due to complete disappearance of the transparent layer 11 due to melting during a crystal pulling-up step. The transparent layer 11 is preferably provided over the entire crucible from the side wall portion 10a to the bottom portion 10b of the crucible, but it is also possible to omit the transparent layer 11 in the upper end portion of the crucible that does not come into contact with the silicon melt.

[0030] The bubble layer 12 is a main glass layer of the crucible main body 10, located on the outer side compared to the transparent layer 11. It is provided to improve the heat retention property of the silicon melt in the crucible and to heat the silicon melt in the crucible as evenly as possible by distributing radiant heat from a heater in a monocrystal pulling device. Therefore, the bubble layer 12 is provided over the entire crucible from the sidewall portion 10a to the bottom portion 10b.

[0031] The bubble content of the bubble layer 12 is greater than that of the transparent layer 11 and is preferably more than 0.1 vol% and 5 vol% or less. The reason for this is that in a case where the bubble content of the bubble layer 12 0.1 vol% or less, the bubble layer 12 may not exhibit the required heat retention function. Another reason is that in a case where the bubble content of the bubble layer 12 is more than 5 vol%, the crucible may deform due to thermal expansion of the bubbles, and the yield of the monocrystals may decrease, and further, the heat transfer property may be insufficient. From the viewpoint of balancing the heat retention property and the heat transfer property, the bubble content of the bubble layer 12 is particularly preferably 1 to 4 vol%. Note that the bubble content described above is a value obtained by measuring an unused crucible in a room-temperature environment.

[0032] The semi-molten layer 13 is a layer formed on the outer surface of the crucible when a part of the quartz powder used as the raw material for the crucible is cooled in an incompletely molten state (semi-molten state). The semi-molten layer 13 has a surface rich in waves and a thickness of 50 to 2,000 μm. The thickness of the semi-molten layer 13 is thinner when a temperature gradient is steeper near the outer surface during the manufacture of the crucible, and thicker when the temperature gradient is shallower. Since the temperature gradient is different for each part of the crucible, the thickness of the semi-molten layer 13 varies slightly for each part of the crucible. The thickness of the semi-molten layer 13 can be determined by measuring the cross-section of the sample cut out of the crucible.

[0033] Whether the semi-molten layer 13 is formed on the outer surface of the crucible can be determined by whether a halo pattern, in which a diffraction pattern unique to an amorphous material is blurred, is present along with a peak indicating crystallinity when the outer surface of the crucible is measured using an X-ray diffraction method. If the target to be measured is a crystal layer, the peak indicating crystallinity is detected, but the halo pattern, in which a diffraction pattern is blurred, is not. If the semi-molten layer 13 is removed, a surface of the glass is exposed, and thus no peak is detected.

[0034] A number of recesses 14 are formed on one surface of the semi-molten layer 13 (the outer surface of the crucible). The recesses 14 serve to promote crystallization of the outer surface of the crucible. In particular, by forming a large number of deep recesses 14 that penetrate the semi-molten layer 13 to reach the glass layer 15, a thick crystal layer can be formed on the outer surface of the crucible.

[0035] The recess 14 can be easily confirmed and distinguished by visual observation and has a concave shape that stands out clearly from the surroundings. The diameter of the recess 14 is 0.2 to 5.0 mm, more preferably 0.3 to 2.0 mm, and even more preferably 0.5 to 1.0 mm. If the diameter is less than 0.2 mm, crystallization does not progress to a crystal layer thickness at which deformation of the crucible can be suppressed. On the other hand, if the thickness is more than 5.0 mm, the outer surface of the crucible is excessively crystallized, which may cause cracks in the crystal layer and deformation of the crucible. The opening shape of the recess is often elliptical, and the diameter in this case is defined as the maximum diameter of the opening.

[0036] The depth of the recess 14 is 50 to 2,100 µm, more preferably 50 to 1,000 µm, and even more preferably 50 to 300 µm. If the depth of the recess 14 is less than 50 µm, crystallization does not progress to a crystal layer thickness at which deformation of the crucible can be suppressed. On the other hand, if the thickness exceeds 2,100 µm, the outer surface of the crucible is excessively crystallized, which may cause cracks in the crystal layer and deformation of the crucible.

[0037] Fig. 3 is a schematic cross-sectional view of the semi-molten layer in which recesses are formed.

[0038] As in Fig.3, some of the recesses 14 are through-holes 14d that penetrate the semi-molten layer 13, and the bottom portions of which reach the glass layer 15 (i.e., the bubble layer 12) constituting the crucible main body 10, and some of which reach the interior of the glass layer 15. Since the glass layer 15 is exposed through the recesses 14, heat is easily transferred to the glass layer 15 and can crystallize the glass layer 15. When comparing the crystallization rate of the glass layer 15 with that of the semi-molten layer 13, the crystallization rate of the glass layer 15 is faster. Since some of the recesses 14 reach the glass layer 15, crystallization in the wall is likely to occur at the time of crystallization of the outer surface of the crucible, and the thickness of the crystal layer can be increased.

[0039] The density of the deep recesses 14 (through holes 14d) penetrating the semi-molten layer 13 is preferably 1 to 50 recesses / cm 2 , more preferably 2 to 30 recesses / cm 2 and even more preferably 5 to 20 recesses / cm 2 . If the density of the deep recesses 14 penetrating the semi-molten layer 13 is less than 1 recess / cm 2 , crystallization does not progress to a thickness of the crystal layer at which deformation of the crucible can be suppressed. However, if the number of deep recesses is more than 50 recesses / cm 2 If the outer surface of the crucible is excessively crystallized, cracks in the crystal layer and deformation of the crucible may occur.

[0040] The thickness d1 of the semi-molten layer 13 is less than the maximum depth d2 of the recesses 14. The thickness of the semi-molten layer 13 is preferably in a range of 50 to 2,000 µm, more preferably in a range of 100 to 1,000 µm, and even more preferably in a range of 100 to 500 µm. When the thickness of the semi-molten layer 13 is less than 50 µm, crystallization does not progress to a crystal layer thickness at which deformation of the crucible can be suppressed. On the other hand, when the thickness exceeds 2,000 µm, the possibility of the crucible deformation increases due to peeling of the outer surface caused by a difference in thermal expansion coefficient between the semi-molten layer 13 and the glass layer 15 during pulling up of the silicon monocrystal.

[0041] Preferably, the through-hole 14d is provided at least in the corner portion 10c of the crucible and distributed over the entire circumference of the corner portion 10c. Preferably, the through-hole 14d is provided over the entire circumference of the crucible from the bottom portion 10a2 of the side wall portion 10a to the corner portion 10c. As described above, since a number of through-holes 14d are provided in the corner portion 10c of the crucible, crystallization of the outer surface of the crucible can be promoted to improve the strength of the crucible, and in particular, bulging and sinking at the corner portion of the crucible can be effectively suppressed.

[0042] The corner portion 10c is a portion likely to be heated to high temperatures, so bulging and sinking are likely to occur. Recently, multiple pull-ups are frequently performed and the crucible is exposed to high temperatures for a long time. Therefore, bulging and sinking of the corner portion is likely to occur. When bulging or sinking of the crucible occurs, the probability of fine crucible pieces (silicon dioxide pieces) peeling off from the inner surface of the corner portion 10c increases. In a case where the crucible pieces are transported to a growth interface of the silicon monocrystal by melt convection and are incorporated into the silicon monocrystal, they cause dislocations in the monocrystal.However, if the strength of the crucible is improved by promoting the crystallization of the corner portion of the crucible as described above, the detachment of the fine silicon dioxide pieces can be suppressed and the dislocations of the silicon monocrystal can be prevented.

[0043] The region where the recesses 14 are formed may or may not be provided in the upper portion 10a1 of the sidewall portion 10a or the bottom portion 10b. When the recesses 14 are formed in the sidewall portion 10a or the bottom portion 10b, the recesses 14 may be deep recesses (through holes 14d) that reach the glass layer 15 or shallow recesses (non-through holes) that do not reach the glass layer 15.

[0044] Fig.4 is a schematic cross-sectional view showing a state of the semi-molten layer 13 according to the present invention before and after heating in comparison with the prior art.

[0045] As in Fig. As shown in Figure 4(a), the recesses 14 were present in a semi-molten layer 13 of a prior art quartz glass crucible, but the depth of the recesses 14 was small and did not reach a glass layer 15. Therefore, as shown in Fig. 4(b), the crystal layer 16 cannot be made thick even at a time of crystallization of the outer surface of the crucible by heating in the crystal pulling-up step.

[0046] On the other hand, as in Fig.As shown in Fig. 4(c), most of the recesses 14 formed in the semi-molten layer 13 of the quartz glass crucible according to the present invention surround the glass layer 15, and some of the recesses 14 extend deeper than the surface of the glass layer 15. In this way, heat is easily transferred to the deep portion of the crucible. Therefore, as shown in Fig. 4(d), at the time of crystallizing an outer surface of the crucible by heating during the crystal pulling-up step, the crystal layer 16 can be formed thick, whereby the strength of the crucible can be improved.

[0047] To prevent contamination of the silicon melt, the silica glass constituting the transparent layer 11 desirably has high purity. Therefore, the quartz glass crucible 1 preferably has a two-layer structure consisting of a synthetic silica glass layer (synthetic layer) formed of synthetic quartz powder (synthetic silica powder) and a natural silica glass layer (natural layer) formed of natural quartz powder. The synthetic quartz powder can be produced by vapor-phase oxidation (dry synthesis method) of silicon tetrachloride (SiCl4) or hydrolysis of silicon alkoxide (sol-gel method) and is preferably used as a raw material for forming an inner surface of a crucible in contact with a silicon melt. In addition, the natural quartz powder is produced by pulverizing a natural mineral with α-quartz as the main component into granules.Natural quartz powder is a naturally produced crystalline quartz powder and is relatively inexpensive. Therefore, natural quartz powder is preferably used as the main raw material for crucibles.

[0048] The two-layer structure comprising the synthetic silica layer and the natural silica layer can be manufactured by depositing natural quartz powder along an inner surface of a mold for making a crucible, depositing synthetic quartz powder thereon, and melting this raw quartz powder with Joule heat generated by arc discharge. During arc melting, bubbles are removed from the outer surface of the quartz powder deposit layer by strong evacuation to form the transparent layer 11, and the evacuation is stopped or weakened to form the bubble layer 12.Therefore, the interface between the synthetic silica layer and the natural silica layer does not necessarily coincide with the interface between the transparent layer 11 and the bubble layer 12, but like the transparent layer 11, the synthetic silica layer preferably has a thickness to the extent that it does not completely disappear due to the melting away of the inner surface of the crucible during the step of pulling up the monocrystal.

[0049] The quartz glass crucible 1 according to the present embodiment can be manufactured by a so-called rotary molding method.

[0050] [ Fig. 5] is a schematic view showing a method of manufacturing the quartz glass crucible 1 according to the embodiment of the present invention.

[0051] As in Fig.As shown in Figure 5, in the manufacture of the quartz glass crucible 1 by the rotary forming method, a mold 20 having a cavity corresponding to the outer shape of the crucible is used. The inner diameter of the mold 20 is preferably 1% to 15% wider than the target outer diameter of the side wall portion of the crucible. That is, the opening size of the cavity is preferably 1.01 to 1.15 times the target diameter of the crucible. In this way, the diameter of the finished crucible can be adjusted to the target diameter by making the opening size of the mold cavity wider than before.

[0052] Subsequently, the natural quartz powder 21a and the synthetic quartz powder 21b are sequentially poured along the inner surface 20i of the rotary mold 20 to form a quartz powder deposition layer 21. The quartz powder remains in a fixed position by centrifugal force while adhering to the inner surface 20i of the mold 20 and is held in a crucible shape. The thickness (height) of the quartz powder deposition layer 21 is preferably greater than the target wall thickness in each part of the crucible and is 1.06 to 1.1 times the target wall thickness.

[0053] The thermal conductivity of the natural quartz powder 21a is preferably 0.2 to 10 W / (m·K), more preferably 0.3 to 1.0 W / (m·K), and even more preferably 0.45 to 0.6 W / (m·K) at 750°C. When raw material powder having a thermal conductivity in this range is used, a number of recesses with a desired depth can be easily formed in the semi-molten layer 13 formed on the outer surface of the crucible. When the thermal conductivity is less than 0.2 W / (m·K), no recesses are formed. On the other hand, when the thermal conductivity is more than 10 W / (m·K), excessive recesses are formed, the outer surface of the crucible crystallizes excessively during the crystal pulling-up step, cracks in the crystal layer are likely to occur, and deformation of the crucible occurs.In addition, there is the problem that the melting of the raw material powder does not progress, the outer diameter of the crucible increases, and the crucible does not enter the carbon susceptor used at the time of pulling up the silicon monocrystal.

[0054] The average particle diameter of the natural quartz powder 21a is preferably 150 to 400 μm. If the average particle diameter is less than 150 μm, the raw material powder will melt excessively, making it impossible to remove the crucible from the mold. On the other hand, if the average particle diameter is more than 400 μm, there is a problem that the melting of the raw material powder will not progress, the outer diameter of the crucible will increase, and the crucible cannot be installed in a carbon susceptor used for pulling up the silicon monocrystal.

[0055] Subsequently, an arc electrode 22 is installed in the mold 20, and the quartz powder deposit layer 21 is melted with an arc from the inside of the mold 20. Specific conditions such as a heating time and a heating temperature are appropriately determined by considering conditions such as the properties of the quartz powder and a size of the crucible.

[0056] When quartz powder with a thermal conductivity of 0.2 to 10 W / (m K) at 750 °C is used, even when the quartz powder deposition layer 21 is heated, no heat is retained in the deposition layer 21 and easily escapes. Thus, the outer diameter of the crucible tends to increase less. However, if the opening size of the cavity of the mold 20 is increased as described above to thicken the deposition layer 21, heat is likely to remain in the deposition layer 21, and the outer diameter of the crucible can thus be set to a desired diameter. As described above, the thickness of the quartz powder deposition layer 21 is preferably 1.5 to 3.0 times the wall thickness of the crucible. As the thickness of the quartz powder deposition layer 21 increases, the mold 20 must be rotated at a higher speed.

[0057] During arc melting, the amount of bubbles in the molten silica glass is controlled by evacuating the quartz powder deposition layer 21 through a number of vent holes 20a located on the inner surface 20i of the mold 20. Specifically, at the beginning of arc melting, the quartz powder deposition layer 21 is evacuated to form the transparent layer 11, and after the formation of the transparent layer 11, the evacuation is stopped or the suction force is reduced to form the bubble layer 12.

[0058] Since the arc heat is gradually transferred from the inside to the outside of the quartz powder deposition layer 21 to melt the quartz powder, the transparent layer 11 and the bubble layer 12 can be formed separately by changing the decompression conditions at a time when the quartz powder begins to melt. That is, in a case where decompression melting is performed to enhance decompression at a time when the quartz powder is melting, the atmospheric arc gas is not trapped in the glass, and thus the molten quartz becomes silica glass containing no bubbles.In addition, in a case where normal melting (melting under atmospheric pressure) is carried out to weaken the decompression at the time when the quartz powder melts, the atmospheric arc gas is trapped in the glass, and thus the molten silica becomes silica glass containing a number of bubbles.

[0059] Subsequently, the arc melting is stopped, and the crucible is cooled. Specifically, by stopping the arc heating before the quartz powder near the inner surface of the mold 20 is completely melted, it is possible to prevent the mold 20 from being tightly adhered to the glass layer, and thus the crucible can be easily removed from the mold 20. Furthermore, by stopping the arc heating before the quartz powder near the inner surface of the mold 20 is completely melted, the semi-molten layer 13, consisting of a fusion-bonded layer of the unmelted or semi-melted quartz powder, can be formed on the outer surface of the crucible.

[0060] As described above, the quartz glass crucible 1 in which the transparent layer 11, the bubble layer 12 and the semi-molten layer 13 are provided sequentially from the inside to the outside is completed.

[0061] After the crucible is formed into a predetermined shape by cutting the edge portion or the like, the outer surface of the crucible is subjected to honing to remove residual quartz powder. During the honing treatment, the excess quartz powder is preferably removed by spraying it with pure water under high pressure. This honing treatment can expose the recesses 14 on the surface of the semi-molten layer 13.

[0062] The crucible is then cleaned with a cleaning fluid and rinsed with pure water. The cleaning fluid is preferably prepared by diluting semiconductor-grade or higher hydrofluoric acid with pure water with a TOC of ≤ 2 ppb to adjust it to 10 to 40 wt.%. This completes a series of steps for manufacturing the quartz glass crucible 1.

[0063] As described above, the quartz glass crucible 1 according to the present embodiment includes the crucible main body 10 made of silica glass and the semi-molten layer 13 formed on the outer surface 10o of the crucible main body 10. A number of recesses 14 are formed on the surface of the semi-molten layer 13, and some of the recesses 14 reach the crucible main body 10. Thus, the crystallization of the outer surface of the crucible can be promoted to form a thick crystal layer, whereby the durability of the crucible can be improved.

[0064] Moreover, in the method for manufacturing the quartz glass crucible 1 according to the present embodiment, the quartz glass crucible is manufactured using quartz powder having a thermal conductivity of 0.2 W / (m·K) or more and 10 W / (m·K) or less at 750°C, which has a relatively high thermal conductivity, so that a quartz glass crucible having a number of deep recesses formed on the surface of the semi-molten layer can be manufactured.

[0065] Fig. 6 is a view for explaining a step of pulling up a monocrystal using the quartz glass crucible 1 according to the present embodiment, the view being a schematic cross-sectional view showing a configuration of a monocrystal pulling-up apparatus.

[0066] As in Fig.6, a monocrystal pulling-up apparatus 30 is used for the step of pulling up silicon monocrystals by the CZ method.The monocrystal pulling-up apparatus 30 includes a water-cooled chamber 31, a quartz glass crucible 1 holding a silicon melt in the chamber 31, a carbon susceptor 32 holding the quartz glass crucible 1, a rotary shaft 33 supporting the carbon susceptor 32 so as to be rotatable and vertically movable, a shaft drive mechanism 34 driving the rotary shaft 33 so as to be rotated and vertically moved, a heater 35 arranged around the carbon susceptor 32, a substantially cylindrical heat shielding member 36 arranged above the quartz glass crucible 1, a monocrystal pulling-up wire 38 arranged above the quartz glass crucible 1 and coaxial with the rotary shaft 33, and a wire winding mechanism 39 arranged above the chamber 31.

[0067] The chamber 31 consists of a main chamber 31a and a narrow cylindrical pulling chamber 31b connected to an upper opening of the main chamber 31a. The quartz glass crucible 1, the carbon susceptor 32, and the heater 35 are installed in the main chamber 31a. A gas inlet 31c for introducing an inert gas (purge gas) such as argon gas or a doping gas into the main chamber 31a is provided in the upper portion of the pulling chamber 31b, and a gas outlet 31d for discharging the atmospheric gas within the main chamber 31a is provided in the lower portion of the main chamber 31a.

[0068] The carbon susceptor 32 is used to maintain the shape of the quartz glass crucible 1, which softens at high temperatures, and holds the quartz glass crucible 1 in a manner that encloses it. The quartz glass crucible 1 and the carbon susceptor 32 constitute a dual-structure crucible that supports the silicon melt in the chamber 31.

[0069] The carbon susceptor 32 is fixed to the upper end portion of the rotary shaft 33, and the lower end portion of the rotary shaft 33 penetrates the bottom portion of the chamber 31 and is connected to a shaft drive mechanism 34 provided outside the chamber 31.

[0070] The heater 35 serves to melt the polycrystalline silicon raw material filled into the quartz glass crucible 1 to produce the silicon melt 2 and to maintain the silicon melt 2 in a molten state. The heater 35 is a resistance heating type carbon heater and is provided surrounding the quartz glass crucible 1 in the carbon susceptor 32.

[0071] The heat shielding member 36 is a member made of graphite that covers an upper portion of the silicon melt 2 except for the pull-up path of the silicon monocrystal 3 and is provided to suppress a temperature fluctuation of the silicon melt 2, to form a suitable hot zone near the solid-liquid interface, and to prevent the silicon monocrystal 3 from being heated by the radiant heat of the heater 35 and the quartz glass crucible 1.

[0072] A circular opening whose diameter is larger than the diameter of the silicon monocrystal 3 is formed in the center of the lower end of the heat shielding member 36. Since the diameter of the opening 17a of the heat shielding member 36 is smaller than the diameter of the quartz glass crucible 1 and the lower portion of the heat shielding member 36 is located inside the quartz glass crucible 1, the heat shielding member 36 does not interfere with the quartz glass crucible 1 even if the upper end of the rim of the quartz glass crucible 1 rises above the lower end of the heat shielding member 36.

[0073] The heat shielding member 36 also functions as a gas rectification member, rectifying the gas flow near the surface of the silicon melt 2. The amount of melt decreases with the growth of the silicon monocrystal 3, and the melting area in the quartz glass crucible 1 gradually decreases. However, by gradually raising the quartz glass crucible 1, the distance (gap value) from the melting surface of the silicon melt 2 to the bottom of the heat shielding member 36 can be kept constant, so that the flow rate of the gas flowing near the melting surface can be kept constant.Therefore, it is possible to suppress the temperature fluctuations of the silicon melt 2 and to control the amount of the dopant evaporated from the silicon melt 2, and it is possible to improve the stability of the distribution of crystal defects, the distribution of oxygen concentration, the distribution of resistivity, and the like in the pull-up axis direction of the monocrystal.

[0074] The wire winding mechanism 39 is arranged above the pulling chamber 31b. The wire 38 extends downward from the wire winding mechanism 39 and passes through the interior of the pulling chamber 31b. A tip portion of the wire 38 reaches the interior of the main chamber 31a. This figure shows a state in which the silicon monocrystal 3 is suspended from the wire 38 in the middle of growth. When the silicon monocrystal 3 is pulled up, the wire 38 is gradually pulled up while the quartz glass crucible 1 and the silicon monocrystal 3 are individually rotated to grow the silicon monocrystal 3.

[0075] During the monocrystal pulling-up step, the quartz glass crucible 1 becomes soft, but as the crystallization of the outer surface of the crucible progresses, the strength of the crucible can be increased, and deformations such as sinking and inward collapse of the crucible can be suppressed. This prevents the position of the melting surface of the silicon melt 2 from rapidly changing due to the volume change of the crucible, or prevents the crucible from coming into contact with the heat shielding member 36.

[0076] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the scope of the present invention, and such modifications are of course included within the scope of the present invention.

[0077] For example, in the embodiments, the semi-molten layer 13 is formed on the entire crucible from the bottom portion 10b to the top of the side wall portion 10a of the crucible, but the semi-molten layer 13 may not be formed in the bottom portion 10b, and the semi-molten layer 13 may not be formed near the top of the rim. [Examples]

[0078] Samples 1 to 10 of quartz glass crucibles produced by the rotary forming method were prepared, and the diameters (mm) of recesses formed over the entire circumference of the corner portion, the depths (µm) of the recesses, and the density (recesses / cm 2) of the deep recesses (through holes) reaching the glass layer were evaluated. A surface roughness gauge, SURFTEST SJ-301, manufactured by Mitutoyo Corporation, was used to measure the diameter and depth of the recess. The measurement was performed at a measuring speed of 0.5 mm / s. The diameter of the recess was measured by cutting out a sample from the quartz crucible. The arrival position of a tip of the recess was determined by irradiating the quartz crucible with a fluorescent lamp from the inner surface side and by visual observation from the outer surface side of the quartz crucible. That is, the diameter and depth of the recess were measured by machine, but the evaluation of whether the tip of the recess reached the glass layer or not was performed by visual confirmation. The measurement results are shown in Table 1.Crucible samples 1 to 6 are comparative examples and samples 7 to 10 are examples. [Table 1] sample Diameter of the recess (mm) Depth of the recess (µm) Density of the recesses reaching the glass layer (recesses / cm 2 ) Amount of deformation (mm) 1 0,13 149,3 23,8 7,9 2 7,90 102,9 19,4 9,3 3 2,41 21,8 19,0 8,5 4 4,03 47,1 31,5 10,3 5 0,27 56,0 0,8 8,7 6 1,58 179,5 52,1 9,7 7 0,24 51,2 1,3 2,3 8 1,85 94,9 12,6 2,9 9 3,16 79,4 29,2 2,5 10 4,51 127,6 46,1 3,4

[0079] Subsequently, the thermal deformation resistance of the quartz glass crucibles of samples 1 to 10 was evaluated. For the thermal deformation resistance evaluation, the sample was installed in a test furnace, and after maintaining the temperature at 1,500 °C for 50 hours, the crucible was removed to evaluate the presence or absence of deformation. Specifically, the thermal deformation resistance was quantitatively evaluated by measuring the amount of change (deformation amount) in the height of the crucible before and after the test. The results of the thermal deformation resistance evaluation are shown in Table 1.

[0080] As can be seen from Table 1, the height of the crucible changed for crucible samples 1 to 6, and the crucible sank significantly. On the other hand, no significant sinking of the crucible was observed for crucible samples 7 to 10.

[0081] Fig. Figure 7 is a graph showing the results of one-way analysis of the deformation amounts of crucible samples 1 to 10 after the heating test in which the temperature was kept at 1,500 °C for 50 hours.

[0082] As in Fig. As shown in Figure 7, the deformation amounts of crucible samples 1 to 6 were approximately 7.9 to 10.3 mm, while the deformation amounts of crucible samples 7 to 10 were approximately 2.3 to 3.4 mm. Thus, it was confirmed that the sinking amounts of crucible samples 7 to 10 were smaller. DESCRIPTION OF REFERENCE SYMBOLS 1 quartz glass crucible 2 silicon melt 3 silicon monocrystal 10 Crucible main body 10a Side wall section 10a1 Upper section of the side wall section 10a2 Lower section of the side wall section 10b Floor section 10c corner section 10i inner surface 10o exterior surface 11 Transparent layer 11 quartz crucibles 12 bubble layer 13 Semi-molten layer 14 Recess 14d through hole (deep recess) 15 glass layers 16 crystal layers 17a Opening 20 Shape 20a vent hole 20i inner surface of the mold 21 Deposit layer 21a Natural quartz powder 21b Synthetic quartz powder 22 Arc electrode 30 Device for pulling up a monocrystal 31 Chamber 31a Main Chamber 31b Drawing chamber 31c Gas inlet 31d Gas outlet 32 Carbon susceptor 33 Rotating shaft 34 Shaft drive mechanism 35 Heating device 36 Heat shielding element 38 Wire for pulling up monocrystals 39 Wire winding mechanism

Claims

[1] A quartz glass crucible for pulling up a silicon monocrystal, the quartz glass crucible comprising: a crucible main body made of silica glass; and a semi-molten layer consisting of a fusion-bonded layer of unmelted or semi-melted quartz powder formed on an outer side of an outer surface of the crucible main body, wherein a number of recesses having a diameter of 0.2 mm or more and 5.0 mm or less and a depth of 50 µm or more are formed on a surface of the semi-molten layer, wherein some of the recesses are through holes penetrating the semi-molten layer to reach the outer surface of the crucible main body, and where a density of the through holes is 1 through hole / cm 2 or more and 50 through holes / cm 2 or less. [2] The quartz glass crucible according to claim 1, wherein a thickness of the semi-molten layer is 50 µm or more. [3] Quartz glass crucible according to claim 1, wherein the quartz glass crucible has a cylindrical side wall portion, a bottom portion and a corner portion provided between the side wall portion and the bottom portion, wherein a wall thickness of the corner section is greater than the wall thickness of the side wall section and the bottom section, and wherein a region in which the through holes are formed is provided at least over an entire circumference of the corner portion. [4] A method of producing a silicon monocrystal by a Czochralski process, the method comprising: Melting a polycrystalline silicon raw material in the quartz glass crucible according to any one of claims 1 to 3 to produce a silicon melt; and Pulling up a silicon monocrystal from the silicon melt.

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