Quartz glass crucible for pulling silicon single crystals and method for producing silicon single crystals using the same

Abstract

To provide a quartz glass crucible for pulling a silicon single crystal that can form a uniform and thin crystal layer at an inner surface by heating during a step of crystal pulling.SOLUTION: A quartz glass crucible 1 includes: a crucible substrate 10 made of silica glass; and a crystallization promoter-containing coating film 13 formed at an inner surface 10i of the crucible substrate 10. Density of Fe included in a first depth region of at least 0.5 mm or less from the inner surface 10i of the crucible substrate 10 is greater than density of Al included in the first depth region.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Most silicon single crystals used as substrate materials for semiconductor devices are manufactured by the CZ method. In the CZ method, polycrystalline silicon raw material is melted in a quartz glass crucible to produce silicon melt, a seed crystal is immersed in the silicon melt, and the seed crystal is gradually pulled up while rotating the quartz glass crucible and seed crystal, growing a large single crystal at the bottom of the seed crystal. The CZ method can increase the yield of large-diameter silicon single crystals.

[0003] A quartz glass crucible (silica glass crucible) is a container made of silica glass that holds molten silicon during the silicon single crystal pulling process. Therefore, quartz glass crucibles must be highly durable so that they do not deform at high temperatures above the melting point of silicon and can withstand long-term use. They also need to be highly pure to prevent impurity contamination of the silicon single crystal.

[0004] It is known that brown ring-shaped cristobalite crystals, known as brown rings, grow on the inner surface of a quartz glass crucible that comes into contact with the silicon melt during the pulling process of silicon single crystals. If the brown rings peel off from the crucible surface and become mixed into the silicon melt, they may be carried by the melt convection current to the solid-liquid interface and be incorporated into the single crystal. The peeling of cristobalite can cause dislocations in the silicon single crystal. For this reason, crystallization accelerators are used to actively crystallize the inner surface of the crucible to prevent the peeling of crystal grains.

[0005] Regarding methods for crystallizing and strengthening the inner surface of a crucible, for example, Patent Document 1 describes a method for manufacturing a highly durable crucible using calcium, strontium, or barium as a crystallization promoter. Patent Document 2 describes a devitrification agent for a crucible with improved efficiency compared to conventional methods. This devitrification agent contains barium, tantalum, tungsten, germanium, tin, or a combination of two or more thereof, and is dissolved in the crucible during construction, applied to the surface of the final crucible, and / or added to the silicon melt used in pulling the crystal.

[0006] Patent Document 3 describes a surface-treated crucible with improved dislocation-free performance. The crucible includes first and second devitrification promoters distributed on the inner and outer surfaces, respectively, of a sidewall formation of a vitreous silica body. The first devitrification promoter is distributed such that a first layer of substantially devitrified silica is formed on the inner surface of the crucible that contacts the molten semiconductor material when the semiconductor material melts in the crucible during crystal growth. The second devitrification promoter is distributed such that a second layer of substantially devitrified silica is formed on the outer surface of the crucible when the semiconductor material melts in the crucible during crystal growth.

[0007] Patent Document 4 describes a quartz glass crucible that can withstand extremely long single crystal pulling processes such as multi-pulling. This quartz glass crucible comprises a crucible base made of quartz glass and first and second crystallization accelerator-containing coating films formed on the inner and outer surfaces of the crucible base, respectively. The first and second crystallization accelerator-containing coating films contain a polymer, and the crystallization accelerator is a water-insoluble barium compound. The action of the crystallization accelerator forms a crystal layer consisting of an aggregate of dome-shaped or columnar crystal grains on the surface layer of the inner and outer surfaces of the crucible base.

[0008] Patent Document 5 describes a method for measuring the impurity concentration profile in the depth direction from the surface of a quartz crucible sample by bringing an etching solution into contact with a specific region on the surface of the sample to dissolve the surface, and then repeating the process of recovering the etching solution multiple times, and measuring the concentration of impurities contained in the recovered etching solution, and a measuring jig used for this method. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-211082 [Patent Document 2] Special Publication No. 2019-509969 [Patent Document 3] Japanese Patent Application Publication No. 9-110590 [Patent Document 4] Japanese Patent Publication No. 2020-200236 [Patent Document 5] Japanese Patent Application Publication No. 2019-066262 Summary of the Invention [Problem to be solved by the invention]

[0010] As described above, applying a crystallization accelerator is effective for uniformly crystallizing the inner surface of the crucible. Techniques for applying the crystallization accelerator include brush application and spray application. Brush application is prone to in-plane concentration unevenness, leading to the formation of non-crystallized areas within the coated area. Spray application tends to result in the atomized crystallization accelerator scattering, leading to the formation of non-crystallized areas near the boundary between the coated and uncoated areas. The inner surface of the crucible is melted upon contact with the silicon melt, but because the non-crystallized glass portion melts faster than the crystallized portion, the crystallized portion remains and is prone to detach from the glass surface as the pulling process progresses. When crystal grains detached from the inner surface of the crucible enter the silicon melt, they cause dislocations in the silicon single crystal, adversely affecting the single crystal yield.

[0011] In order to prevent any uncrystallized areas from remaining, it is effective to increase the concentration of the crystallization promoter to promote crystallization. However, increasing the concentration of the crystallization promoter increases the crystallization rate not only in the in-plane direction but also in the depth direction, resulting in an excessively thick crystal layer. The formation of such a thick crystal layer on the inner surface of the crucible presents a problem: the crystal layer becomes more susceptible to peeling.

[0012] The present invention has been made in view of the above-mentioned problems, and its object is to provide a quartz glass crucible capable of forming a uniform and thin crystal layer on its inner surface by heating during the crystal pulling process, and a method for manufacturing the same. Another object of the present invention is to provide a method for manufacturing a silicon single crystal using such a quartz glass crucible. [Means for solving the problem]

[0013] As a result of extensive research into the mechanism of crystallization of the inner surface of a crucible when a crystallization promoter is applied, the inventors of the present application discovered that by setting the impurity concentration in the depth direction near the inner surface of the crucible within a specific range, crystallization of the inner surface due to heating during crystal pulling can sometimes be faster in the in-plane direction than in the depth direction, thereby enabling the present invention.

[0014] The present invention is based on this technical finding. The quartz glass crucible for pulling silicon single crystals according to the present invention comprises a crucible base made of silica glass and a coating film containing a crystallization promoter formed on the inner surface of the crucible base, and is characterized in that the Fe concentration in a first depth region at least 0.5 mm from the inner surface is higher than the Al concentration in the first depth region. In this way, the quartz glass crucible according to the present invention has a higher iron concentration in a depth region at least 0.5 mm from the inner surface of the crucible than the aluminum concentration in the same depth region, thereby accelerating the crystallization rate in the in-plane direction of the inner surface. As a result, even if the coating of the crystallization promoter is uneven on the inner surface, the inner surface of the crucible is ultimately covered with a uniform crystal surface, thereby suppressing peeling of the crystallized portion and preventing dislocations in the silicon single crystal pulled from the silicon melt in the crucible.

[0015] In the present invention, the concentration of Ca contained in the first depth region is preferably higher than the concentration of Al contained in the first depth region. Calcium also acts in the same way as iron, and facilitates the crystallization of the inner surface of the crucible to spread in the in-plane direction, thereby forming a uniform crystal plane on the inner surface of the crucible and suppressing peeling of the crystallized portion.

[0016] In the present invention, the concentration of the metal element contained in the second depth region, which is 2 mm or less from the inner surface, is lower than the concentration of the metal element contained in the third depth region, which is 2 mm or more and 5 mm or less from the inner surface, and the metal element is preferably B, Mg, or Cr. When boron, magnesium, or chromium is present in the glass, the microstructure around the atoms becomes a regularly arranged crystalline structure. If the above impurities are present to a certain depth from the inner surface, the crystallization rate in the depth direction from the inner surface to the outer surface increases, so it is desirable to have a small amount of impurities. Furthermore, contamination of the silicon melt due to melting of the inner surface of the crucible can be prevented.

[0017] In the present invention, the concentration of the crystallization accelerator in the crystallization accelerator-containing coating film is 1.0 × 10 12 ~2.6×1015 atoms / cm 2 It is preferable that the concentration of the crystallization promoter is 2.6×10 15 atoms / cm 2 If the concentration of the crystallization accelerator is higher than 2.6 × 10, the crystallized particles will not crystallize randomly but will be oriented in the depth direction, which will increase the crystallization speed in the depth direction, resulting in the crystallization accelerator being consumed (diffused) in that direction, making it difficult for the crystallization to spread in the in-plane direction. 15 atoms / cm 2 When the thickness is equal to or less than this, crystallization in the depth direction can be suppressed and crystallization in the in-plane direction can be promoted.

[0018] When the quartz glass crucible according to the present invention is heat-treated at 1580°C, the ratio of the crystallization rate in the in-plane direction to the crystallization rate in the depth direction is preferably 1.5 to 400. If the ratio of the crystallization rate in the in-plane direction to the crystallization rate in the depth direction is less than 1.5, the crystal layer becomes too thick, making it more likely for crystal grains to peel off. If the ratio of the crystallization rate in the in-plane direction to the crystallization rate in the depth direction is greater than 400, the crystal layer may not be thick enough, and there is a risk that parts of the crystal layer will disappear due to a reaction with the silicon melt during pulling. If the ratio of the crystallization rate in the in-plane direction to the crystallization rate in the depth direction is 1.5 to 400, it is possible to prevent such problems from occurring.

[0019] In the present invention, the heat treatment is preferably carried out with a temperature rise time from room temperature to 1580°C of 2.5 hours, a holding time at 1580°C of 10 hours, and a pressure of 20 Torr during the heat treatment. When the heat treatment is carried out under these conditions, if the crystallization rate in the in-plane direction on the inner surface is higher than the crystallization rate in the depth direction, then the crystallization in the in-plane direction will similarly proceed during the actual pulling of the crystal, and a thin, uniform crystal layer can be formed evenly on the inner surface of the crucible base.

[0020] In the present invention, the in-plane length of the crystallization that spreads on the inner surface after the heat treatment is preferably 1 to 60 mm. If the crystallization length is shorter than 1 mm, there is a possibility that non-crystallized regions will occur due to unevenness in the crystallization promoter applied to the inner surface. If the crystallization length is longer than 60 mm, crystallization will occur up to the upper end of the crucible opening, and there is a high risk that the crystal layer that is peeled off due to excessive crystallization will fall into the silicon melt, causing dislocations.

[0021] In the present invention, it is preferable that the crystallization accelerator contained in the crystallization accelerator-containing coating film is Ba, and that the concentration of Ba in the crystal layer formed after the heat treatment is less than 1 ppm.

[0022] In the present invention, the crucible base has a cylindrical side wall portion, a bottom portion, and a corner portion provided between the side wall portion and the bottom portion, and of the inner surface of the crucible base, the region near the rim extending at least 20 mm downward from the upper end of the rim is an uncoated region of the crystallization promoter, and it is preferable that the crystallization promoter-containing coating film is formed on the entire inner surface excluding the uncoated region.

[0023] The present invention also provides a method for producing a quartz glass crucible, comprising the steps of producing a crucible base made of silica glass and forming a coating film containing a crystallization promoter on the inner surface of the crucible base. The crucible base production step comprises: sequentially charging natural quartz powder and synthetic quartz powder onto the inner surface of a rotating mold to form a deposited layer of raw material powder; and an arc process for arc-melting the deposited layer of raw material powder from inside the mold. The arc process comprises a first heating step, a second heating step that is arc-heating with lower power and for a longer period than the first heating step, and a third heating step that is arc-heating with lower power and for a longer period than the second heating step. In this case, the output of the first heating step is preferably 110% of the output of the second heating step, and the output of the third heating step is preferably 55% of the output of the second heating step. According to the present invention, a quartz glass crucible can be produced in which the crystallization rate in the in-plane direction of the inner surface of the crucible base is faster than the crystallization rate in the depth direction.

[0024] In the present invention, the arc step includes a transparent layer forming step in which the deposited layer of raw material powder is arc-melted while evacuating the layer from inside the mold, and a bubble layer forming step in which the raw material powder is arc-melted while stopping the evacuation or reducing the suction force, and the first heating step is preferably started at the start of the transparent layer forming step and ended midway through the transparent layer forming step, thereby reducing the aluminum concentration in the region up to 0.5 mm deep from the inner surface of the crucible base.

[0025] Furthermore, the method for producing a silicon single crystal according to the present invention is characterized in that the silicon single crystal is pulled using the quartz glass crucible according to the present invention having the above-mentioned characteristics. According to the present invention, the production yield of the silicon single crystal can be increased. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a quartz glass crucible capable of forming a uniform and thin crystal layer on its inner surface by heating during the crystal pulling process, and a method for manufacturing the same. Furthermore, according to the present invention, it is possible to provide a method for manufacturing a silicon single crystal that can perform a long crystal growth process by using such a quartz glass crucible. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic perspective view showing the configuration of a silica glass crucible according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional side view of the vitreous silica crucible shown in FIG. [Figure 3] FIG. 3 is a schematic diagram for explaining the metal impurity profile in the depth direction from the inner surface of the crucible base. [Figure 4] FIG. 4 is a schematic diagram showing a method for manufacturing a silica glass crucible by the rotating mold method. [Figure 5] FIG. 5 is a diagram for explaining the method for producing a silicon single crystal using the silica glass crucible 1 according to this embodiment, and is a schematic cross-sectional view showing the configuration of a single crystal pulling device. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0029] Fig. 1 is a schematic perspective view showing the configuration of a silica glass crucible according to an embodiment of the present invention, and Fig. 2 is a schematic side cross-sectional view of the silica glass crucible shown in Fig. 1.

[0030] As shown in Figures 1 and 2, the quartz glass crucible 1 is a container made of silica glass for holding a silicon melt, and has a cylindrical side wall 10a, a bottom 10b provided below the side wall 10a, and corners 10c provided between the side wall 10a and the bottom 10b. The bottom 10b is preferably a gently curved, so-called rounded bottom, but may also be a so-called flat bottom. The corners 10c are portions having a greater curvature than the bottom 10b. The boundary positions between the side wall 10a and the corners 10c and the boundary positions between the bottom 10b and the corners 10c are positions where the curvature begins to change from small to large.

[0031] The bore (diameter) of the quartz glass crucible 1 varies depending on the diameter of the silicon single crystal ingot pulled from the silicon melt, but is generally 18 inches (approximately 450 mm) or larger, preferably 22 inches (approximately 560 mm) or larger, and particularly preferably 32 inches (approximately 800 mm) or larger. This is because such large crucibles are used to pull large silicon single crystal ingots with a diameter of 300 mm or larger, and are required to be able to use for long periods of time without affecting the quality of the single crystal.

[0032] The thickness of the crucible varies slightly depending on the location, but it is preferable that the thickness of the side wall 10a of a crucible of 18 inches or larger is 6 mm or more, the thickness of the side wall 10a of a crucible of 22 inches or larger is 7 mm or more, and the thickness of the side wall 10a of a crucible of 32 inches or larger is 10 mm or more. This allows a large amount of silicon melt to be stably held at high temperatures. It is preferable that the thickness of the crucible is thickest at the corners 10c, and that the side wall 10a and bottom 10b are thinner than the corners 10c.

[0033] 2, the quartz glass crucible 1 includes a crucible base 10 made of silica glass and a crystallization promoter-containing coating film 13 formed on the inner surface 10i of the crucible base 10. The crucible base 10 mainly has a two-layer structure, including a transparent layer 11 that does not contain bubbles (a bubble-free layer) and a bubble layer 12 that contains a large number of tiny bubbles (an opaque layer), and the crystallization promoter-containing coating film 13 is provided on the inside of the transparent layer 11.

[0034] The transparent layer 11 is a glass layer that forms the inner surface 10i of the crucible base 10, which comes into contact with the silicon melt. It is provided to prevent a decrease in the yield of silicon single crystals due to bubbles in the silica glass. Because the inner surface 10i of the crucible reacts with the silicon melt and dissolves, bubbles near the inner surface of the crucible cannot be confined within the silica glass. Thermal expansion can cause the bubbles to burst, potentially resulting in crucible fragments (silica fragments) being detached. If crucible fragments released into the silicon melt are carried by melt convection to the growth interface of the silicon single crystal and are incorporated into the silicon single crystal, they can cause dislocations in the silicon single crystal. Furthermore, if bubbles released into the silicon melt float to the solid-liquid interface and are incorporated into the single crystal, they can cause pinholes in the silicon single crystal.

[0035] The transparent layer 11 being bubble-free means that the bubble content and bubble size are such that the single crystallization rate is not reduced due to the bubbles. For example, the bubble content is 0.1 vol% or less, and the bubble diameter is 100 μm or less.

[0036] The transparent layer 11 preferably has a thickness of 0.5 to 10 mm, and is set to an appropriate thickness for each portion of the crucible so that it does not disappear completely due to melting during the crystal pulling process, thereby exposing the bubble layer 12. The transparent layer 11 is preferably provided over the entire crucible from the side wall portion 10a to the bottom portion 10b, but it is also possible to omit the transparent layer 11 from the upper end portion of the crucible that does not come into contact with the silicon melt.

[0037] The bubble content and bubble diameter of the transparent layer 11 can be measured non-destructively using an optical detection means. The optical detection means includes a light receiving device that receives transmitted or reflected light irradiated onto the crucible. The light receiving device can be a digital camera including an optical lens and an image sensor. The irradiated light can be visible light, ultraviolet light, infrared light, X-rays, laser light, or the like. The measurement results obtained by the optical detection means are input into an image processing device, and the bubble diameter and bubble content per unit volume are calculated.

[0038] The bubble layer 12 is the main glass layer of the crucible base 10 located outside the transparent layer 11, and is provided to improve the heat retention of the silicon melt in the crucible and to distribute radiant heat from the heater of the single crystal pulling device to heat the silicon melt in the crucible as uniformly as possible. For this reason, the bubble layer 12 is provided throughout the entire crucible, from the side wall portion 10a to the bottom portion 10b. The thickness of the bubble layer 12 is approximately equal to the thickness of the crucible base 10 minus the thickness of the transparent layer 11, and varies depending on the part of the crucible.

[0039] The bubble content of the bubble layer 12 is higher than that of the transparent layer 11, and is preferably greater than 0.1 vol% and less than 5 vol%. This is because if the bubble content of the bubble layer 12 is less than 0.1 vol%, the bubble layer 12 will not exhibit the required heat retention function. Furthermore, if the bubble content of the bubble layer 12 exceeds 5 vol%, the thermal expansion of the bubbles may cause deformation of the crucible, resulting in a decrease in the single crystal yield and insufficient heat transfer. From the viewpoint of a balance between heat retention and heat transfer, the bubble content of the bubble layer 12 is particularly preferably 1 to 4 vol%. The bubble content mentioned above is a value measured at room temperature for the crucible before use. The bubble content of the bubble layer 12 can be determined, for example, by measuring the specific gravity (Archimedes' method) of an opaque silica glass piece cut from the crucible.

[0040] To prevent contamination of the silicon melt, it is desirable that the silica glass constituting the innermost layer of the transparent layer 11 be highly pure. Therefore, it is preferable that the crucible base 10 have a two-layer structure consisting of a synthetic silica glass layer (synthetic layer) made from synthetic silica powder and a natural silica glass layer (natural layer) made from natural silica powder. Synthetic silica powder can be produced by the vapor-phase oxidation of silicon tetrachloride (SiCl4) (dry synthesis method) or the hydrolysis of silicon alkoxide (sol-gel method). Natural silica powder is produced by crushing and granulating natural minerals primarily composed of α-quartz.

[0041] The two-layer structure of a synthetic silica glass layer and a natural silica glass layer can be produced by depositing natural silica powder along the inner surface of a crucible mold, depositing synthetic silica powder on top of that, and melting the raw silica powder using Joule heat generated by arc discharge. In the arc melting process, a strong vacuum is applied from the outside of the deposited layer of raw silica powder to remove bubbles, forming transparent layer 11, and the vacuum is then stopped or weakened to form bubble layer 12. Therefore, the interface between the synthetic silica glass layer and the natural silica glass layer does not necessarily coincide with the interface between transparent layer 11 and bubble layer 12. However, like transparent layer 11, the synthetic silica glass layer preferably has a thickness sufficient to prevent it from being completely lost due to melting of the inner surface of the crucible during the single crystal pulling process.

[0042] The quartz glass crucible 1 according to this embodiment has a configuration in which the inner surface 10i of the crucible base 10 is covered with a coating film 13 containing a crystallization promoter. The crystallization promoter serves to promote crystallization of the inner surface 10i of the crucible base 10 during the single crystal pulling process. The crystallization promoter is preferably barium (Ba) or strontium (Sr), which are Group 2a elements, with barium being particularly preferred. This is because barium has a smaller segregation coefficient than silicon, is stable at room temperature, and is easy to handle. Barium also has the advantage that its crystallization rate does not decrease with crystallization and induces more oriented growth than other elements.

[0043] The crystallization promoter-containing coating film 13 is preferably formed on the entire inner surface 10i of the crucible base 10, excluding the region near the rim extending at least 20 mm downward from the upper end of the rim. The reason for excluding the region near the rim is that the region near the upper end of the rim does not come into contact with the silicon melt and does not necessarily need to be crystallized, and the region near the upper end of the rim is prone to peeling when crystallized, and crystal grains mixed in the silicon melt can cause dislocations in the silicon single crystal.

[0044] The concentration of the crystallization accelerator contained in the crystallization accelerator-containing coating film 13 is 1.0×10 12 ~2.6×10 15 atoms / cm 2It is preferable that the concentration of the crystallization promoter is 2.6×10 15 atoms / cm 2 If the concentration is higher than , the orientation of the crystallized particles is not random but rather crystallizes in a depth-oriented manner, which increases the crystallization rate in the depth direction, resulting in the consumption (diffusion) of the crystallization promoter in that direction, making it difficult for the crystallization to spread in the in-plane direction. However, if the concentration of the crystallization promoter is relatively low, it is possible to suppress the crystallization in the depth direction of the inner surface 10i of the crucible base 10 and promote the crystallization in the in-plane direction. Therefore, uniform crystallization can be achieved on the inner surface 10i of the crucible base 10.

[0045] The thickness of the crystallization accelerator-containing coating film 13 is not particularly limited, but is preferably 0.1 to 50 μm, and particularly preferably 1 to 20 μm. If the thickness of the crystallization accelerator-containing coating film 13 is too thin, the peel strength of the crystallization accelerator-containing coating film 13 is weak, and peeling of the crystallization accelerator-containing coating film 13 causes non-uniform crystallization. If the crystallization accelerator-containing coating film 13 is too thick, the peel strength is reduced and crystallization becomes non-uniform.

[0046] In order to crystallize the inner surface of the crucible as uniformly and thinly as possible by heating during the crystal pulling process, it is necessary that the crystallization rate in the in-plane direction of the crystal layer be higher than the crystallization rate in the depth direction. In particular, the ratio of the crystallization rate in the in-plane direction to the crystallization rate in the depth direction is preferably 1.5 to 400. If the ratio of the crystallization rate in the in-plane direction to the crystallization rate in the depth direction is less than 1.5, the crystal layer becomes too thick, making it more likely for crystal grains to peel off. Furthermore, if the ratio of the crystallization rate in the in-plane direction to the crystallization rate in the depth direction is greater than 400, the crystal layer may not be thick enough, and some parts of the crystal layer may disappear due to a reaction with the silicon melt during pulling.

[0047] FIG. 3 is a schematic diagram for explaining the metal impurity profile in the depth direction from the inner surface 10i of the crucible base 10. As shown in FIG.

[0048] 3, in order to increase the crystallization rate in the in-plane direction of the inner surface 10i of the crucible base 10 compared to the depth direction, the concentration of aluminum (Al) contained in the very surface layer portion of the crucible base 10 is preferably lower than the concentrations of iron (Fe) and calcium (Ca) contained in the very surface layer portion. Specifically, the concentration of Al contained in a depth region D1 (first depth region) extending from the inner surface 10i of the crucible base 10 to at least 0.5 mm is preferably lower than the concentration of Fe contained in the depth region D1. Furthermore, the concentration of Al contained in the depth region D1 extending from the inner surface 10i of the crucible base 10 to at least 0.5 mm is preferably lower than the concentration of Ca contained in the depth region D1.

[0049] Al forms an anion (Al - ) and attracts cations. Therefore, when Al is present in the glass, it inhibits the diffusion of the crystallization promoter, slowing down the crystallization rate. However, Fe and Ca do not trap the crystallization promoter and promote crystallization. Therefore, if Fe and Ca are present in higher concentrations than Al, crystallization tends to spread in the in-plane direction. Furthermore, by lowering the Al concentration on the inner surface 10i of the crucible base 10, it is possible to prevent the viscosity of the glass behind the crystal layer from decreasing, thereby reducing the risk of the crystal layer peeling off due to deformation.

[0050] Although Fe and Ca on the inner surface 10i of the crucible base 10 cause impurity contamination of the silicon single crystal, even small amounts serve as starting points for crystallization on the inner surface 10i, facilitating the crystallization to spread in the in-plane direction. In the present invention, the Al content on the inner surface 10i of the crucible base 10 is even lower than that of Fe and Ca. If a large amount of Al is present on the inner surface 10i, the action of the Al weakens the action of the Fe and Ca, making it difficult for the crystallization of the inner surface 10i to proceed in the in-plane direction. However, since the Al concentration is lower than the Fe and Ca concentrations, it is possible to promote the crystallization of the inner surface 10i in the in-plane direction.

[0051] As will be described in detail later, this concentration balance of Al, Fe, and Ca can be achieved by using synthetic quartz powder with a low Al concentration as the raw material for the inner surface 10i of the crucible base 10 and by performing a long low-power arc discharge at the end of the arc melting of the raw material powder. If the low-power arc time is too short, no change in the Fe and Ca concentrations on the inner surface 10i is observed, while if the low-power arc time is too long, the impurity concentration on the inner surface 10i becomes too high. Therefore, the arc time must be adjusted appropriately. In this way, by performing a low-power arc, the Fe and Ca concentrations can be made higher than those of Al. Furthermore, it is preferable to increase the arc power during the transparent layer 11 formation process at the beginning of the arc melting process. This reduces the aluminum concentration in the region of the crucible base 10 down to a depth of 0.5 mm from the inner surface 10i.

[0052] In this embodiment, the boron (B) concentration in the depth region D2 (second depth region) of the crucible base 10, which is 2 mm or less from the inner surface 10i, is preferably lower than the B concentration in the depth region D3 (third depth region) of 2 mm or more and 5 mm or less from the inner surface 10i. The same applies to magnesium (Mg) and chromium (Cr). When B, Mg, and Cr are present in glass, the microstructure around these atoms becomes a regularly arranged crystalline structure. Therefore, if a large amount of the above impurities is present in the depth region D2 of the crucible base 10, which is 2 mm or less from the inner surface 10i, crystallization in the depth direction from the inner surface 10i becomes rapid, making it difficult to promote crystallization in the in-plane direction at the inner surface 10i. However, if the amount of the above impurities is small in the depth region D2 of 2 mm or less from the inner surface 10i, crystallization in the depth direction from the inner surface 10i can be suppressed and crystallization in the in-plane direction can be promoted. Furthermore, contamination of the silicon melt with impurities due to melting of the inner surface 10i of the crucible base 10 can be prevented.

[0053] When the quartz glass crucible according to this embodiment is heat-treated at 1500°C to 1600°C, the crystallization rate in the in-plane direction of the inner surface of the crucible is higher than the crystallization rate in the depth direction, so that crystallization in the in-plane direction of the inner surface of the crucible can be promoted during the crystal pulling process. The heat treatment conditions are to raise the temperature from room temperature to 1580°C over 2.5 hours, and then hold at 1580°C for 10 hours. When the atmospheric pressure is 20 Torr, the ratio of the crystallization rate in the in-plane direction to the crystallization rate in the depth direction of the inner surface of the crucible after heat treatment is preferably 1.5 to 400.

[0054] The length of the crystallization in the in-plane direction that spreads on the inner surface after the evaluation heat treatment is preferably 1 to 60 mm. If the length of the crystallization in the in-plane direction is shorter than 1 mm, unevenness in the crystallization promoter applied to the inner surface is likely to result in non-crystallized areas, while if the length of the crystallization in the in-plane direction is longer than 60 mm, crystallization will extend up to the upper end of the crucible opening, increasing the risk that the crystal layer peeled off due to excessive crystallization will fall into the silicon melt and cause dislocations.

[0055] The length of crystallization (crystal growth) can be calculated as the longest distance from the starting point of crystallization to the outermost periphery of the crystallized region, or as the difference ΔB = B2 - B1 between the boundary position B1 between the region coated with the crystallization promoter and the uncoated region and the boundary position B2 between the crystallized region and the non-crystallized region after heat treatment.

[0056] The barium concentration in the crystal layer formed on the inner surface 10i of the crucible base 10 after the heat treatment is preferably less than 1 ppm. By crystallizing the inner surface 10i of the crucible base 10 in this way without using a large amount of a crystallization promoter, it is possible to promote crystallization in the in-plane direction of the crucible, and to form a thin crystal layer evenly on the inner surface 10i of the crucible base 10.

[0057] The vitreous silica crucible 1 according to this embodiment can be manufactured by manufacturing the crucible base 10 by the so-called rotational molding method, and then applying a crystallization promoter to the inner surface of the crucible base 10.

[0058] FIG. 4 is a schematic diagram showing a method for manufacturing a silica glass crucible by the rotating mold method.

[0059] 4, in the rotating mold method, a carbon mold 14 is prepared having a cavity that matches the outer shape of the crucible, and natural quartz powder 16a and synthetic quartz powder 16b are sequentially filled along the inner surface 14i of the rotating carbon mold 14 to form a deposition layer 16 of raw quartz powder. The raw quartz powder is adhered to the inner surface 14i of the carbon mold 14 by centrifugal force and remains in a fixed position, maintaining the crucible shape.

[0060] Next, an arc electrode 15 is placed inside the carbon mold 14, and the deposited layer 16 of raw quartz powder is arc-melted from inside the carbon mold 14. Specific conditions such as heating time and heating temperature are determined appropriately taking into account the characteristics of the raw quartz powder, the size of the crucible, etc.

[0061] During arc melting, the amount of bubbles in the molten quartz glass is controlled by evacuating the deposited layer 16 of raw quartz powder through a large number of vent holes 14a provided on the inner surface 14i of the carbon mold 14. Specifically, at the start of arc melting, the deposited layer 16 of raw quartz powder is evacuated to form a transparent layer 11, and after the transparent layer 11 is formed, the vacuum evacuating the raw quartz powder is stopped or the suction force is weakened to form a bubble layer 12.

[0062] Since the arc heat propagates from the inside to the outside of the deposited layer 16 of raw silica powder, melting the raw silica powder, it is possible to produce either the transparent layer 11 or the bubble layer 12 by changing the decompression conditions when the raw silica powder begins to melt. That is, if reduced-pressure melting is performed, in which the decompression is increased when the raw silica powder melts, the atmospheric gas is not trapped in the glass, and the molten quartz becomes silica glass that does not contain bubbles. On the other hand, if normal melting (atmospheric pressure melting) is performed, in which the decompression is decreased when the raw silica powder melts, the atmospheric gas is trapped in the glass, and the molten quartz becomes silica glass that contains many bubbles.

[0063] In order to make the Fe and Ca concentrations higher than Al on the inner surface 10i side of the crucible base 10, arc melting at low power is performed for a long time at the end of the arc melting process. The Fe and Ca concentrations on the inner surface 10i of the crucible base 10 tend to increase as the low-power arc melting time is longer. If the low-power arc melting time is too short, there will be no change in the Fe and Ca concentrations on the inner surface 10i, but if it is too long, the impurity concentration on the inner surface 10i will become excessively high, so it is necessary to set the time appropriately.

[0064] Thereafter, arc melting is terminated, and the crucible is cooled. This completes the crucible base 10, on which the transparent layer 11 and the bubble layer 12 are sequentially formed from the inside to the outside of the crucible wall. Thus, the crucible base 10 of this embodiment can be manufactured by filling a rotating carbon mold 14 with natural quartz powder 16a as the outer layer raw material, then filling it with synthetic quartz powder 16b as the inner layer raw material, and arc melting the deposited layer 16 of raw quartz powder.

[0065] Next, the shape of the crucible base 10 is adjusted by cutting the rim portion or the like, and then the crucible base 10 is washed with a cleaning solution and further rinsed with pure water. The cleaning solution is preferably prepared by diluting hydrofluoric acid of semiconductor grade or higher with pure water of TOC≦2 ppb to a concentration of 10 to 40 wt %.

[0066] Next, a crystallization accelerator is applied to the inner surface 10i of the crucible base 10. A brush is preferably used to apply the coating liquid. To uniformly disperse the crystallization accelerator on the inner surface 10i, it is preferable to use a coating liquid in which the crystallization accelerator is dissolved in pure water (15 to 25°C, 17.2 MΩ or more, TOC≦2 ppb). To increase the solubility of the crystallization accelerator, it is preferable to stir the coating liquid using a stirrer.

[0067] FIG. 5 is a diagram for explaining the single crystal pulling process using the silica glass crucible 1 according to this embodiment, and is a schematic cross-sectional view showing the configuration of a single crystal pulling apparatus.

[0068] 5, a single crystal pulling apparatus 20 is used in the silicon single crystal pulling process by the CZ method. The single crystal pulling apparatus 20 includes a water-cooled chamber 21, a quartz glass crucible 1 that holds a silicon melt within the chamber 21, a carbon susceptor 22 that holds the quartz glass crucible 1, a rotating shaft 23 that supports the carbon susceptor 22 so that it can rotate and move up and down, a shaft drive mechanism 24 that drives the rotating shaft 23 to rotate and move up and down, a heater 25 arranged around the carbon susceptor 22, a single crystal pulling wire 28 that is arranged above the quartz glass crucible 1 of the heater 25 and coaxially with the rotating shaft 23, and a wire winding mechanism 29 arranged above the chamber 21.

[0069] The chamber 21 is composed of a main chamber 21a and a long, cylindrical pull chamber 21b connected to the upper opening of the main chamber 21a, and the quartz glass crucible 1, carbon susceptor 22, and heater 25 are provided inside the main chamber 21a. A gas inlet 21c is provided at the top of the pull chamber 21b for introducing an inert gas (purge gas) such as argon gas or a dopant gas into the main chamber 21a, and a gas outlet 21d is provided at the bottom of the main chamber 21a for discharging the atmospheric gas inside the main chamber 21a.

[0070] The carbon susceptor 22 is used to maintain the shape of the quartz glass crucible 1 softened at high temperatures, and encases and holds the quartz glass crucible 1. The quartz glass crucible 1 and the carbon susceptor 22 form a double-structure crucible that supports the silicon melt within the chamber 21.

[0071] The carbon susceptor 22 is fixed to the upper end of a rotating shaft 23 , and the lower end of the rotating shaft 23 passes through the bottom of the chamber 21 and is connected to a shaft driving mechanism 24 provided outside the chamber 21 .

[0072] The heater 25 is used to melt the polycrystalline silicon raw material filled in the quartz glass crucible 1 to generate the silicon melt 3, and to maintain the molten state of the silicon melt 3. The heater 25 is a resistance heating type carbon heater, and is provided so as to surround the quartz glass crucible 1 inside the carbon susceptor 22.

[0073] As the silicon single crystal 2 grows, the amount of silicon melt in the quartz glass crucible 1 decreases, but the quartz glass crucible 1 is raised so that the height of the melt surface remains constant.

[0074] The wire winding mechanism 29 is disposed above the pull chamber 21b, and the wire 28 extends downward from the wire winding mechanism 29 through the pull chamber 21b, with the tip of the wire 28 reaching the internal space of the main chamber 21a. This figure shows a silicon single crystal 2 in the middle of growth suspended from the wire 28. When pulling the silicon single crystal 2, the wire 28 is gradually pulled up while the quartz glass crucible 1 and the silicon single crystal 2 are each rotated, and the silicon single crystal 2 is grown.

[0075] During the single crystal pulling process, the inner surface of the crucible crystallizes, but the crystallization accelerator ensures that crystallization on the inner surface of the crucible proceeds uniformly, preventing dislocations in the silicon single crystal due to peeling of the brown ring. Furthermore, although the quartz glass crucible 1 softens, the crystallization on the inner surface of the crucible proceeds uniformly, ensuring the strength of the crucible and suppressing deformation. Therefore, it is possible to prevent contact with furnace interior components due to deformation of the crucible and fluctuations in the liquid surface position of the silicon melt 3 due to changes in the crucible volume.

[0076] As described above, the quartz glass crucible 1 according to this embodiment comprises a crucible base 10 made of silica glass and a coating film 13 containing a crystallization promoter formed on the inner surface 10i of the crucible base 10, and the concentration of Al contained in the depth region D1 extending from the inner surface 10i of the crucible base 10 to at least 0.5 mm is lower than the concentrations of Fe and Ca contained in the depth region D1, and the crystallization rate in the in-plane direction when the inner surface crystallizes at high temperatures during the crystal pulling process is greater than the crystallization rate in the depth direction. Therefore, even if unevenness occurs in the application of the crystallization promoter on the inner surface 10i, the inner surface of the crucible can ultimately be covered with a uniform crystal surface, preventing peeling of crystal grains.

[0077] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention, and it goes without saying that these modifications are also included in the scope of the present invention. [Example]

[0078] Four crucible bases with different metal impurity concentrations on the inner surface were prepared. A barium carbonate solution was applied to a portion of the inner surface of the crucible base with a brush, and the crucible was then crushed into small pieces. Several crucible pieces obtained from the same crucible base that had not been coated with barium carbonate were used to perform a metal impurity analysis in the depth direction from the inner surface of the crucible base. For the metal impurity analysis, silica glass was dissolved to a certain depth from the inner surface of the crucible by wet etching, and the etchant was recovered. The amount of metal impurities dissolved in the etchant was measured using ICP-MS (Inductively Coupled Plasma-Mass Spectrometry).

[0079] Among the metal impurities, Fe, Ca, and Al were measured in the first measurement range from the inner surface of the crucible base to a depth of 0.3 mm, in the second measurement range from 0.3 to 0.5 mm, and in the third measurement range from 0.5 to 0.7 mm. The measurement results are shown in Tables 1 and 2.

[0080] [Table 1]

[0081] As shown in Table 1, for the ladle substrate of Comparative Example 1, the Fe and Al concentration profiles showed a low Fe concentration throughout the depth range from the inner surface to 0.7 mm, and the relationship Fe concentration < Al concentration was established. Also, for the ladle substrate of Comparative Example 2, the relationship Fe concentration > Al concentration was established in the depth range from the inner surface to 0.3 mm, and the relationship Fe concentration < Al concentration was established in the depth range from 0.3 to 0.7 mm. In contrast, for the ladle substrate of Example 1, the relationship Fe concentration > Al concentration was established in the depth range from the inner surface to 0.5 mm, and the relationship Fe concentration < Al concentration was established in the depth range from 0.5 to 0.7 mm. Furthermore, for the ladle substrate of Example 2, the relationship Fe concentration > Al concentration was established throughout the depth range from the inner surface to 0.7 mm.

[0082] [Table 2] <0​​​​​​As described above, in the crucible samples of Comparative Examples 1 and 2, the Fe concentration and Ca concentration in the depth region from the inner surface to 0.5 mm were lower than the Al concentration, whereas in the crucible samples of Examples 1 and 2, the Al concentration in the depth region from the inner surface to 0.5 mm was lower than the Fe concentration and Ca concentration.

[0085] For the measurement of metal impurities B, Mg, and Cr, the first measurement range was from the inner surface to a depth of 1.0 mm, the second measurement range was from 1.0 to 2.0 mm, the third measurement range was from 2.0 to 3.0 mm, the fourth measurement range was from 3.0 to 4.0 mm, and the fifth measurement range was from 4.0 to 5.0 mm. The measurement results are shown in Tables 3 to 5.

[0086] [Table 3]

[0087] As shown in Table 3, the B concentration profile of the crucible base of Comparative Example 1 was 0.1 ppm in the entire depth region from the inner surface to 5 mm or less. The B concentration profile of the crucible base of Comparative Example 2 was 0.01 ppm in the depth region from the inner surface to 1 mm, but 0.1 ppm in the depth region from 1 to 5 mm. The B concentration profile of the crucible base of Example 1 was 0.02 ppm or less in the depth region from the inner surface to 2 mm, but 0.1 ppm in the depth region from 2 to 5 mm. The B concentration profile of the crucible base of Example 2 was 0.02 ppm or less in the depth region from the inner surface to 3 mm, but 0.1 ppm in the depth region from 3 to 5 mm.

[0088] [Table 4]

[0089] As shown in Table 4, the Mg concentration profile of the crucible base of Comparative Example 1 was 0.14 ppm in the entire depth region from the inner surface to 5 mm or less. The Mg concentration profile of the crucible base of Comparative Example 2 was 0.01 ppm in the depth region from the inner surface to 1 mm, but 0.14 ppm in the depth region from 1 to 5 mm. The Mg concentration profile of the crucible base of Example 1 was 0.01 ppm or less in the depth region from the inner surface to 2 mm, but 0.14 ppm in the depth region from 2 to 5 mm. The Mg concentration profile of the crucible base of Example 2 was 0.01 ppm or less in the depth region from the inner surface to 3 mm, but 0.14 ppm in the depth region from 3 to 5 mm.

[0090] [Table 5]

[0091] As shown in Table 5, the Cr concentration profile of the crucible base of Comparative Example 1 was 0.08 ppm in the entire depth region from the inner surface to 5 mm or less. The Cr concentration profile of the crucible base of Comparative Example 2 was 0.01 ppm in the depth region from the inner surface to 1 mm, but 0.08 ppm in the depth region from 1 to 5 mm. The Cr concentration profile of the crucible base of Example 1 was 0.02 ppm or less in the depth region from the inner surface to 2 mm, but 0.08 ppm in the depth region from 2 to 5 mm. The Cr concentration profile of the crucible base of Example 2 was 0.02 ppm or less in the depth region from the inner surface to 3 mm, but 0.08 ppm in the depth region from 3 to 5 mm.

[0092] As described above, in the crucible samples of Comparative Examples 1 and 2, the B concentration in the depth region from the inner surface to 2.0 mm was higher than the B concentration in the depth region from 2.0 to 5.0 mm from the inner surface, whereas in the crucible samples of Examples 1 and 2, the B concentration in the depth region of 2.0 mm or less from the inner surface was lower than the B concentration in the depth region from 2.0 to 5.0 mm from the inner surface. A similar tendency was observed for Mg and Cr.

[0093] Next, a heating test was conducted using a crucible piece coated with barium carbonate. 2 The crucible pieces used had an aspect ratio as close to 1 as possible. The heating conditions were as follows: the furnace in an Ar atmosphere was heated from room temperature to 1580°C over 2.5 hours, and then held at 1580°C for 10 hours. The pressure inside the furnace held at 1580°C was 20 Torr.

[0094] The crystallization state of the inner surface of the crucible substrate was then evaluated. Specifically, the in-plane crystallization rate and the depth crystallization rate were determined from the width and thickness of the crystal layer on the inner surface of the crucible substrate, and the presence or absence of crystallization unevenness was visually confirmed. Here, the in-plane crystallization rate was the value obtained by dividing the length of crystallization in the in-plane direction by 10 hours, which is the time it was held at a high temperature of 1580°C. Similarly, the depth crystallization rate was the value obtained by dividing the length of crystallization in the depth direction by 10 hours. The in-plane crystallization length is the maximum distance indicating the spread of the crystal layer from the starting point of crystallization. Furthermore, the depth crystallization length is the maximum thickness of the crystal layer in the cross section of the sample. Crystallization unevenness refers to the presence of areas in the barium carbonate-coated area of ​​the crucible substrate that remain glassy without devitrification, particularly when 5% or more of the area is not devitrified.

[0095] As a result, as shown in Tables 1 to 5, crystallization unevenness was observed on the inner surface of the crucible samples of Comparative Examples 1 and 2, but no crystallization unevenness was observed on the inner surface of the crucible samples of Examples 1 and 2, and the entire surface was uniformly crystallized. When the ratio of the crystallization rate in the in-plane direction to the crystallization rate in the depth direction of each crucible sample was calculated, it was 0.5 for Comparative Example 1, 1 for Comparative Example 2, 1.5 for Example 1, and 100 for Example 2. From these results, it was found that the inner surface of the crucible can be crystallized evenly if the crystallization rate ratio is 1.5 or more. [Explanation of symbols]

[0096] 1. Quartz glass crucible 2. Silicon single crystal 3. Silicon melt 10 Crucible base 10a Side wall part 10b bottom 10c Corner 10i inner surface 11 Transparent layer 12 Bubble layer 13 Coating film containing crystallization promoter 14 Carbon mold 14a Ventilation hole 14i carbon mold inner surface 15 Arc electrode 16 Sedimentary layer of raw quartz powder 16a natural quartz powder 16b Synthetic quartz powder 20 Single crystal pulling equipment 21 Chamber 21a Main Chamber 21b Pull Chamber 21c Gas inlet 21d Gas outlet 22 Carbon susceptor 23 Rotating shaft 24 Shaft drive mechanism 25 Heater 28 Crystal pulling wire 29 Wire winding mechanism

Claims

1. A quartz glass crucible for pulling silicon single crystals, a crucible base made of silica glass; a coating film containing a crystallization promoter formed on the inner surface of the crucible base, A quartz glass crucible characterized in that the concentration of Fe contained in a first depth region at least 0.5 mm or less from the inner surface is higher than the concentration of Al contained in the first depth region.

2. The silica glass crucible according to claim 1 , wherein the concentration of Ca contained in the first depth region is higher than the concentration of Al contained in the first depth region.

3. The silica glass crucible according to claim 1, wherein the concentration of B contained in the second depth region 2 mm or less from the inner surface is lower than the concentration of B contained in the third depth region 2 mm or more and 5 mm or less from the inner surface.

4. The silica glass crucible according to claim 1 , wherein the concentration of Mg contained in the second depth region is lower than the concentration of Mg contained in the third depth region.

5. The silica glass crucible according to claim 1 , wherein the concentration of Cr contained in the second depth region is lower than the concentration of Cr contained in the third depth region.

6. The concentration of the crystallization accelerator in the crystallization accelerator-containing coating film is 1.0×10 １２ ~2.6 x 10 １５ atoms / cm ２ The quartz glass crucible according to claim 1,

7. 2. The quartz glass crucible according to claim 1, wherein the ratio of the crystallization rate in the in-plane direction to the crystallization rate in the depth direction of the inner surface is 1.5 to 400 when heat treated at 1580°C.

8. The quartz glass crucible according to claim 7, wherein the heat treatment is carried out with a temperature rise time from room temperature to 1580°C of 2.5 hours, a holding time at 1580°C of 10 hours, and an atmospheric pressure of 20 Torr during the heat treatment.

9. The quartz glass crucible according to claim 8, wherein the length of the crystallization spreading on the inner surface after the heat treatment in the in-plane direction is 1 mm to 60 mm.

10. The quartz glass crucible according to claim 7, wherein the crystallization promoter contained in the crystallization promoter-containing coating film is Ba, and the concentration of Ba in the crystal layer formed after the heat treatment is less than 1 ppm.

11. the crucible base has a cylindrical side wall portion, a bottom portion, and a corner portion provided between the side wall portion and the bottom portion, a rim-near region of the inner surface of the crucible base extending from the upper end of the rim to at least 20 mm downward is a region not coated with a crystallization accelerator; 2. The quartz glass crucible according to claim 1, wherein the crystallization promoter-containing coating film is formed on the entire inner surface except for the uncoated region.

12. A method for producing a silicon single crystal, comprising pulling a silicon single crystal using the quartz glass crucible according to any one of claims 1 to 11.

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