Method for manufacturing a quartz glass crucible

Abstract

To provide a method for manufacturing a quartz glass crucible, capable of reducing a rate of a bubble content in an inner transparent layer of a crucible without any particular pretreatment or strong heating to a raw material quartz powder.SOLUTION: A method according to the present invention for manufacturing a quartz glass crucible includes the steps of: depositing a quartz powder on an inner surface 14i of a rotating mold 14; heating a deposited layer 16 of the quartz powder from inside the mold 14 to melt the quartz powder, wherein thermal conductivity at 1300°C of the quartz powder tapped-filled into the container is 0.4 W / (m_K) or more and 1.0 W / (m_K) or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a quartz glass crucible and a method for producing the same, and more particularly to a method for producing a quartz glass crucible used in the production of silicon single crystals by the Czochralski process (CZ process). The invention also relates to quartz powder used as a raw material for such a quartz glass crucible. [Background technology]

[0002] In the production of silicon single crystals using the CZ method, a quartz glass crucible is used. In the CZ method, silicon raw material is heated and melted in a quartz glass crucible, a seed crystal is immersed in this molten silicon, and the seed crystal is gradually pulled up while the crucible is rotated to grow the single crystal. The CZ method makes it possible to produce large-diameter, high-quality silicon single crystals for semiconductor devices with a high yield.

[0003] It is desirable that there are no air bubbles near the inner surface of a quartz glass crucible. If air bubbles near the inner surface of the crucible that come into contact with the silicon melt burst due to thermal expansion, tiny silica fragments will detach from the crucible and mix into the silicon melt, becoming incorporated into the growing single crystal and causing dislocation formation in the single crystal. For this reason, a transparent layer free of air bubbles is provided near the inner surface of the quartz glass crucible.

[0004] To improve the quality of the transparent inner layer of a quartz glass crucible, for example, Patent Document 1 describes a method for producing a quartz glass crucible with an inner layer that has few bubbles while keeping energy and material costs as low as possible. This method involves covering a molten mold with a heat shield, supplying a light gas into the molten mold through a gas inlet of the heat shield, and vitrifying SiO2 inner layer granules in the molten mold in an atmosphere containing the light gas to obtain a transparent inner layer.

[0005] Patent Document 2 describes a method for manufacturing a quartz glass crucible, which includes the steps of: producing a synthetic quartz glass material by a direct method or a soot method; processing the synthetic quartz glass material into a crucible shape without crushing it; and welding silica powder to the outer wall of the crucible-shaped synthetic quartz glass material. By processing the synthetic quartz glass material produced by a direct method or a soot method into a crucible shape without crushing it, a synthetic quartz glass material that is substantially free of air bubbles can be obtained.

[0006] Patent Document 3 describes a method for producing a quartz glass crucible by supplying quartz raw material powder into a mold to form a silica powder molded body having a straight section, a corner section, and a bottom section, and then arc melting this silica powder molded body in an oxygen atmosphere, in which a carbon member is placed in contact with the open end of the silica powder molded body. By preventing oxygen from entering the silica powder molded body from the open end through reaction with the carbon member, combustion, etc., it is possible to suppress the increase of oxygen excess defects in the transparent layer of the resulting silica glass crucible and suppress the expansion of bubbles in the transparent layer during silicon single crystal pulling. Patent Document 4 also describes suppressing oxygen excess defects by supplying hydrogen along the inner surface of the crucible.

[0007] Patent Document 5 includes a filling step of filling a melting furnace with quartz raw material powder, a preheating step of applying a preheating treatment to the quartz raw material powder filled in the melting furnace to remove moisture and gas, a melting step of heating and melting the preheated quartz raw material powder, and a cooling step of cooling the molten quartz glass in the melting furnace to form a quartz glass block, wherein in the filling step the filling density of the quartz raw material powder filled in the melting furnace is 1.4 g / cm³. 3 More than 1.6g / cm 3 The following conditions apply to the dense packing, and the pre-heat treatment process includes vacuuming and introduction of a rare gas or H2 gas. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-521882 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-218980 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-065621 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-065622 [Patent Document 5] Japanese Patent Application Laid-Open No. 2009-096674 [Summary of the Invention] [[ID=,21]] [Problems to be Solved by the Invention]

[0009] In the conventional method for manufacturing a quartz glass crucible, in order to eliminate bubbles near the inner surface of the crucible as much as possible, a method of pretreating raw material quartz powder or a method of strongly heating during melting of the raw material quartz powder has been adopted.

[0010] However, in the method of pretreating raw material quartz powder, an increase in the manufacturing cost of the crucible due to such pretreatment becomes a problem. Also, in the method of strongly heating during melting of the raw material quartz powder, there are problems of an increase in power consumption and an increase in manufacturing cost due to improvement / enhancement of manufacturing equipment.

[0011] Therefore, an object of the present invention is to provide a method for manufacturing a quartz glass crucible capable of reducing the bubble content rate of the transparent layer inside the crucible without performing special pretreatment or strong heating on the raw material quartz powder. Another object of the present invention is to provide quartz powder capable of manufacturing a quartz glass crucible in which the bubble content rate of the transparent layer is reduced. Furthermore, the present invention aims to provide a high-quality quartz glass crucible in which the bubble content rate of the transparent layer is reduced. [Means for Solving the Problems]<,

[0012] [[ID=4,1]] In order to solve the above problems, a method for manufacturing a quartz glass crucible according to the present invention includes a step of depositing quartz powder on the inner surface of a rotating mold, and a step of heating the deposited layer of the quartz powder from the inside of the mold to melt the quartz powder, and is characterized in that the thermal conductivity of the quartz powder tap-filled in a container is 0.4 W / (m·K) or more and 1.0 W / (m·K) or less at 1300°C.

[0013] According to the present invention, it is possible to manufacture a quartz glass crucible with a low bubble content in the transparent layer without performing any special pretreatment or intense heating on the raw material quartz powder. When using raw material quartz powder with a low thermal conductivity, heat is difficult to escape to the outside when the deposited layer of quartz powder is heated from the inside, so the temperature of the inner surface of the deposited layer of quartz powder can be maintained at a high temperature. When the inner surface of the deposited layer of quartz powder becomes high in temperature, the melting rate of the quartz powder increases, and the bubble size of the surface layer (sealing layer) of the transparent silica glass layer with a slightly high bubble content formed at the initial stage of melting of the quartz powder can be reduced. When the bubble size of the sealing layer is small, the internal pressure of the bubble is large, so the gas constituting the bubble is likely to dissolve into the glass during subsequent heating, and thus the bubble can be eliminated. Therefore, the bubble content in the transparent layer on the inner surface side of the crucible can be reduced.

[0014] In this specification, the "thermal conductivity of quartz powder" means the thermal conductivity of an aggregate of a large number of quartz powders, not the thermal conductivity of a single quartz powder. The reason for evaluating the thermal conductivity at 1300°C is that it is appropriate as a representative index indicating the degree of heat transfer in the temperature range from 1000°C to 1650°C at which the quartz powder melts during the process of heating and melting the deposited layer of quartz powder. 1300°C is a high temperature, but it is a temperature at which the measurement of thermal conductivity is possible.

[0015] In the present invention, the quartz powder deposit layer comprises a deposit layer of natural quartz powder formed on the inner surface of the mold and a deposit layer of synthetic quartz powder formed on the inner surface of the natural quartz powder deposit layer. The thickness of the natural quartz powder deposit layer is at least twice the thickness of the synthetic quartz powder deposit layer, and it is preferable that the thermal conductivity of the natural quartz powder at 1300°C is at least 0.4 W / (m·K) or 1.0 W / (m·K). By controlling the thermal conductivity of the natural quartz powder in this way, the bubble content of the transparent layer on the inner surface of the crucible can be reduced.

[0016] In the present invention, the thermal conductivity of the natural quartz powder at 1300°C is preferably 0.5 W / (m·K) or more and 0.8 W / (m·K) or less, and more preferably 0.6 W / (m·K) or more and 0.8 W / (m·K) or less. This makes it possible to increase the manufacturing yield of quartz glass crucibles with a low bubble content in the transparent layer.

[0017] In the present invention, the immersion heat of the synthetic quartz powder in water at 25°C is preferably 250 J / g or more and 450 J / g or less. This makes it possible to reduce the air bubble content of the transparent layer on the inner surface of the crucible.

[0018] The step of heating and melting the quartz powder deposit layer preferably includes a transparent layer forming step, in which a transparent layer made of silica glass without air bubbles is formed by melting the quartz powder deposit layer while drawing vacuum from the inner surface of the mold, and a bubble layer forming step, in which a bubble layer made of silica glass containing numerous air bubbles is formed by weakening or stopping the suction force of the vacuum drawing from the inner surface of the mold. According to this, a two-layer quartz glass crucible having a transparent layer and a bubble layer can be manufactured.

[0019] Furthermore, the method for manufacturing a quartz glass crucible according to the present invention comprises the steps of forming a deposit layer of natural quartz powder on the inner surface of a rotating mold, forming a deposit layer of synthetic quartz powder on the inner surface of the deposit layer of natural quartz powder, and heating the deposit layers of natural quartz powder and synthetic quartz powder from the inside of the mold to melt the quartz powder, characterized in that the immersion heat of the synthetic quartz powder in water at 25°C is 250 J / g or more and 450 J / g or less. According to the present invention, the bubble content of the transparent layer on the inner surface of the quartz glass crucible can be reduced.

[0020] Furthermore, the quartz powder according to the present invention is a raw material for quartz glass crucibles, is made of natural quartz, and is characterized by having a thermal conductivity of 0.4 W / (m·K) or more and 1.0 W / (m·K) or less at 1300°C when tapped and filled in a container. According to the present invention, the bubble content of the transparent layer on the inner surface of the quartz glass crucible can be reduced.

[0021] Furthermore, the quartz powder according to the present invention is a raw material for a quartz glass crucible, and is preferably made of synthetic quartz with an immersion heat of 250 J / g or more and 450 J / g or less. According to the present invention, the bubble content of the transparent layer on the inner surface of the quartz glass crucible can be reduced.

[0022] Furthermore, the quartz glass crucible according to the present invention comprises a bubble layer made of quartz glass containing numerous bubbles formed by heating and melting natural quartz powder, and a bubble-free quartz glass formed by heating and melting synthetic quartz powder, and has a transparent layer provided inside the bubble layer, wherein the natural quartz powder has a thermal conductivity of 0.4 W / (m·K) or more and 1.0 W / (m·K) or less at 1300°C when tap-filled in the container, and the average bubble content of the surface layer of the transparent layer with a depth of 2 mm or less is 0.05 vol% or less. In this case, it is preferable that the immersion heat of the synthetic quartz powder in water at 25°C is 250 J / g or more and 450 J / g or less. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a method for manufacturing a quartz glass crucible that can reduce the bubble content of the transparent layer inside the crucible without requiring special pretreatment or strong heating of the raw quartz powder. Furthermore, according to the present invention, it is possible to provide quartz powder that can be used to manufacture a quartz glass crucible with a reduced bubble content in the transparent layer. Moreover, the present invention can provide a high-quality quartz glass crucible with a reduced bubble content in the transparent layer. [Brief explanation of the drawing]

[0024] [Figure 1] Figure 1 shows the configuration of a quartz glass crucible according to an embodiment of the present invention, where (a) is a substantially perspective view and (b) is a substantially side cross-sectional view. [Figure 2] Figure 2 is a schematic diagram illustrating the manufacturing method of a quartz glass crucible. [Figure 3] Figure 3 is a schematic diagram illustrating the effect of the thermal conductivity of the deposit layer of raw quartz powder on the bubble content near the inner surface of the crucible. [Figure 4] Figure 4 is an explanatory diagram of the immersion heat of synthetic quartz powder. [Figure 5] Figure 5 is a schematic diagram illustrating an example of a method for measuring the thermal conductivity of a deposit of raw quartz powder. [Figure 6] Figure 6 is a table showing the quality and evaluation results of quartz glass crucibles according to Comparative Examples 1-4 and Examples 1-3. [Modes for carrying out the invention]

[0025] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0026] Figure 1 shows the configuration of a quartz glass crucible according to an embodiment of the present invention, where (a) is a substantially perspective view and (b) is a substantially side cross-sectional view.

[0027] As shown in Figures 1(a) and (b), the quartz glass crucible 1 is a silica glass container for supporting a silicon melt, and has a cylindrical side wall portion 10a, a bottom portion 10b, and a corner portion 10c provided between the side wall portion 10a and the bottom portion 10b. The bottom portion 10b is preferably a gently curved so-called round bottom, but it may also be a so-called flat bottom. The corner portion 10c is located between the side wall portion 10a and the bottom portion 10b and has a larger curvature than the bottom portion 10b. The boundary position between the side wall portion 10a and the corner portion 10c is the position where the side wall portion 10a begins to bend. The boundary position between the corner portion 10c and the bottom portion 10b is the position where the large curvature of the corner portion 10c begins to change to the small curvature of the bottom portion 10b.

[0028] The diameter of the quartz glass crucible 1 varies depending on the diameter of the silicon single crystal ingot being pulled using it, but it is preferably 22 inches (approximately 560 mm) or larger, and particularly preferably 32 inches (approximately 800 mm) or larger. Such large-diameter crucibles are used to pull large silicon single crystal ingots with a diameter of 300 mm or more, and it is required that they do not affect the manufacturing yield or quality of the single crystals even when used for a long time.

[0029] The wall thickness of the crucible varies slightly depending on the location, but for crucibles 22 inches or larger, the wall thickness of the side wall portion 10a is preferably 7 mm or more, and for large crucibles 32 inches or larger, the wall thickness of the side wall portion 10a is preferably 10 mm or more. This allows for the stable retention of a large amount of molten silicon at high temperatures.

[0030] As shown in Figure 1(b), the quartz glass crucible 1 has a transparent layer 11 (bubble-free layer) made of silica glass that does not contain air bubbles, and a bubble layer 12 (opaque layer) made of silica glass that contains numerous tiny air bubbles and is provided on the outside of the transparent layer 11.

[0031] The transparent layer 11 is a layer that constitutes the inner surface 10i of the crucible that comes into contact with the silicon melt, and is provided to prevent a decrease in single crystal yield due to air bubbles in the silica glass. Since the inner surface 10i of the crucible reacts with the silicon melt and melts away, air bubbles near the inner surface of the crucible cannot be contained within the silica glass, and there is a risk that crucible fragments (silica fragments) will peel off when the air bubbles burst due to thermal expansion. If crucible fragments released into the silicon melt are carried by melt convection to the single crystal growth interface and incorporated into the single crystal, it can cause dislocations in the single crystal. Also, if air bubbles released into the silicon melt float to the solid-liquid interface and are incorporated into the single crystal, it can cause pinholes in the silicon single crystal.

[0032] The statement that the transparent layer 11 is "bubble-free" means that it has a bubble content and bubble size such that the single crystallization rate does not decrease due to bubbles. Such a bubble content is, for example, 0.1 vol% or less, and the average diameter of the bubbles is, for example, 100 μm or less.

[0033] The thickness of the transparent layer 11 is preferably 0.5 to 10 mm, and is set to an appropriate thickness for each part of the crucible so that it does not completely disappear due to melting during the single crystal pulling process and expose the bubble layer 12. The transparent layer 11 is preferably provided throughout the crucible from the side wall portion 10a to the bottom portion 10b, but it is also possible to omit the transparent layer 11 at the upper end of the crucible where it does not come into contact with the silicon melt.

[0034] 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 from light irradiated onto the crucible. The light receiving device can be a digital camera including an optical lens and an image sensor. In addition to visible light, ultraviolet light, and infrared light, X-rays or laser light can be used as the irradiated light. The measurement results from the optical detection means are input into an image processing device, and the bubble diameter and bubble content per unit volume are calculated.

[0035] The bubble layer 12 is a layer that makes up the outer surface 10o of the crucible. It is provided to improve the heat retention of the silicon molten inside the crucible and to disperse the radiant heat from the heaters that surround the crucible in the single crystal pulling apparatus, thereby heating the silicon molten inside the crucible as uniformly as possible. For this reason, the bubble layer 12 is provided throughout the entire crucible, from the side walls 10a to the bottom 10b. The thickness of the bubble layer 12 is approximately equal to the thickness of the crucible minus the thickness of the transparent layer 11, and varies depending on the part of the crucible.

[0036] The bubble content of the bubble layer 12 is preferably higher than that of the transparent layer 11, greater than 0.1 vol%, and 5 vol% or less. This is because if the bubble content of the bubble layer 12 is 0.1 vol% or less, it cannot exhibit the heat retention function required of the bubble layer 12. Furthermore, if the bubble content of the bubble layer 12 exceeds 5 vol%, the crucible may deform due to the thermal expansion of the bubbles, potentially reducing the single crystal yield and resulting in insufficient heat transfer. From the viewpoint of balancing heat retention and heat transfer, a bubble content of 1 to 4 vol% in the bubble layer 12 is particularly preferable. The numerous bubbles contained in the bubble layer 12 can be easily recognized by visual inspection. The bubble content mentioned above is the value measured in a crucible at room temperature before use. The bubble content of the bubble layer 12 can be determined, for example, by measuring the specific gravity of an opaque silica glass piece cut from the crucible (Archimedes method).

[0037] To prevent contamination of the silicon melt, it is desirable that the silica glass constituting the transparent layer 11 be of high purity. Therefore, the quartz glass crucible 1 according to this embodiment preferably has a two-layer structure consisting of a synthetic silica glass layer (synthetic layer) formed from synthetic quartz powder and a natural silica glass layer (natural layer) formed from natural quartz powder. Synthetic quartz powder can be produced by gas-phase oxidation of silicon tetrachloride (SiCl4) (dry synthesis method) or hydrolysis of silicon alkoxide (sol-gel method). Natural quartz powder is quartz powder produced by crushing natural minerals mainly composed of α-quartz into granules.

[0038] As will be described in detail later, the two-layer structure of synthetic silica glass and natural silica glass can be manufactured by depositing natural quartz powder along the inner surface of a crucible manufacturing mold, depositing synthetic quartz powder on top of it, and melting these quartz powders by Joule heating due to arc discharge. In the initial stages of the arc melting process, bubbles are removed by strongly drawing a vacuum from the outside of the deposited quartz powder layer to form a transparent layer 11 (transparent layer formation step). Subsequently, a bubble layer 12 is formed on the outside of the transparent layer 11 by weakening the suction force of the vacuum or stopping the vacuum (bubble layer formation step). Therefore, the boundary position between the synthetic silica glass layer and the natural silica glass layer does not necessarily coincide with the boundary position between the transparent layer 11 and the bubble layer 12, but it is preferable that the synthetic silica glass layer, like the transparent layer 11, has a thickness such that it does not completely disappear due to melting of the inner surface of the crucible during the single crystal pulling process.

[0039] Figure 2 is a schematic diagram illustrating the manufacturing method of the quartz glass crucible 1.

[0040] As shown in Figure 2, the quartz glass crucible 1 can be manufactured by the so-called rotary molding method. In the rotary molding method, a mold 14 having a cavity that matches the outer diameter of the crucible is prepared, and natural quartz powder 13a and synthetic quartz powder 13b are sequentially filled along the inner surface 14i of the rotating mold 14 to form a deposit layer 16 of raw quartz powder. The raw quartz powder adheres to the inner surface 14i of the mold 14 by centrifugal force and remains in a fixed position, maintaining the crucible shape.

[0041] Next, an arc electrode 15 is placed inside the mold 14, and the deposited layer 16 of raw quartz powder is arc-melted from the inside of the mold 14. Specific conditions such as heating time and heating temperature are determined as appropriate, taking into consideration the characteristics of the raw quartz powder and the size of the crucible.

[0042] During arc melting, the amount of bubbles in the molten silica glass is controlled by evacuating the deposited layer 16 of raw quartz powder through numerous vents 14a provided on the inner surface 14i of the mold 14. Specifically, the reduced pressure on the raw quartz powder is increased at the start of arc melting to form a transparent layer 11, and after the formation of the transparent layer 11, the reduced pressure on the raw quartz powder is decreased to form a bubble layer 12. The reduced pressure when forming the transparent layer 11 is preferably -70 to -95 kPa, and the reduced pressure when forming the bubble layer 12 is preferably atmospheric pressure to -35 kPa.

[0043] The arc heat gradually propagates from the inside to the outside of the deposited layer 16 of raw quartz powder, melting the raw quartz powder. By changing the reduced pressure conditions at the moment the raw quartz powder begins to melt, it is possible to create either a transparent layer 11 or a bubble layer 12. In other words, if reduced pressure melting is performed by increasing the reduced pressure at the moment the quartz powder melts, the arc atmosphere gas is not trapped in the glass, and the fused silica becomes silica glass without bubbles. On the other hand, if normal melting (atmospheric pressure melting) is performed by decreasing the reduced pressure at the moment the quartz powder melts, the arc atmosphere gas is trapped in the glass, and the fused silica becomes silica glass containing many bubbles.

[0044] Afterward, the arc melting is terminated and the crucible is cooled. This completes the quartz glass crucible 1, which is made of silica glass with a transparent layer 11 and a bubble layer 12 arranged sequentially from the inside to the outside of the crucible wall.

[0045] In order to reduce the bubble content of the transparent layer 11, the present invention uses raw quartz powder with low thermal conductivity. Specifically, the thermal conductivity of the raw quartz powder, especially natural quartz powder, is between 0.4 W / (m·K) and 1.0 W / (m·K). This is because if the thermal conductivity of the raw quartz powder is higher than 1.0 W / (m·K), the bubble content near the inner surface of the crucible will be higher. When the thermal conductivity of the raw quartz powder is high, a lot of heat escapes, so the inner surface temperature of the crucible does not rise, the melting rate of the raw quartz powder is slow, and it is thought that the quartz powder partially melts and forms spheres, incorporating voids and making it easier for relatively large bubbles to be embedded in the silica glass. In addition, when the thermal conductivity of the raw quartz powder is high, there is also the problem that the thickness of the crucible becomes thin.

[0046] On the other hand, if the thermal conductivity of the raw quartz powder is lower than 0.4 W / (m·K), the thermal insulation is too high and the melting rate is too fast, resulting in a thick initial seal layer. This makes it impossible to remove air bubbles, and bubbles remain in a region slightly deeper than the inner surface. In this case, while bubbles directly below the inner surface can be removed, if a crucible with a layer of microbubbles remaining in a slightly deeper region is used for pulling silicon single crystals, the microbubble layer will become exposed on the inner surface of the crucible after some time has passed since use, which will reduce the pulling performance.

[0047] The thermal conductivity of the raw quartz powder, especially natural quartz powder, is preferably 0.5 W / (m·K) or more and 0.8 W / (m·K) or less, and particularly preferably 0.6 W / (m·K) or more and 0.8 W / (m·K) or less. By keeping the thermal conductivity of the raw quartz powder low in this way, the bubble content of the transparent layer 11 can be reduced, and in particular, the manufacturing yield of quartz glass crucibles 1 with a low bubble content in the transparent layer 11 can be increased.

[0048] As described above, the thermal conductivity of quartz powder refers not to the thermal conductivity of a single grain of quartz powder, but to the thermal conductivity of an aggregate of many quartz powders. The thermal conductivity of such an aggregate of many quartz powders can be measured when it is tapped into a container.

[0049] The majority of the deposit layer 16 of raw quartz powder consists of natural quartz powder 13a, and the thickness of the deposit layer of synthetic quartz powder 13b is much thinner than that of the deposit layer of natural quartz powder 13a. Typically, the thickness of the deposit layer of natural quartz powder 13a is more than twice the thickness of the deposit layer of synthetic quartz powder 13b. Therefore, the thermal conductivity of natural quartz powder 13a has a large influence on the overall thermal conductivity of the deposit layer 16 of raw quartz powder, while the thermal conductivity of synthetic quartz powder 13b has a small influence on the overall thermal conductivity of the deposit layer 16 of raw quartz powder. Consequently, as long as the thermal conductivity of natural quartz powder 13a is within the above range, it is not a problem even if the thermal conductivity of synthetic quartz powder 13b is somewhat higher. However, it is particularly preferable if the thermal conductivity of not only the deposit layer of natural quartz powder 13a but also the deposit layer of synthetic quartz powder 13b is within the above range, as this ensures that the overall thermal conductivity of the deposit layer 16 of raw quartz powder is kept within the above range.

[0050] Figure 3 is a schematic diagram illustrating the effect of the thermal conductivity of the deposited layer 16 of raw quartz powder on the bubble content near the inner surface of the crucible.

[0051] As shown in Figure 3, when the thermal conductivity of the raw quartz powder deposit layer 16 is high, the heat applied to the raw quartz powder deposit layer 16 escapes easily, resulting in a lower internal temperature of the raw quartz powder deposit layer 16. When the internal temperature of the raw quartz powder deposit layer 16 is low, the melting rate of the raw quartz powder deposit layer 16 is slow, the surface tension of the glass decreases, and the internal pressure of the bubbles also decreases. As a result, bubbles easily dissolve into the glass, and the size of the bubbles in the glass cannot be reduced, causing bubbles to remain in the transparent layer 11.

[0052] On the other hand, if the thermal conductivity of the raw quartz powder deposit layer 16 is low, the heat applied to the raw quartz powder deposit layer does not easily escape, so the internal temperature of the raw quartz powder deposit layer 16 becomes high. When the internal temperature of the raw quartz powder deposit layer is high, the melting rate of the raw quartz powder deposit layer 16 is fast, the surface tension of the glass increases, and the internal pressure of the bubbles also increases. As a result, bubbles can easily dissolve into the glass, thereby eliminating bubbles in the transparent layer 11.

[0053] Unlike bulk quartz, the thermal conductivity of quartz powder varies depending on differences in physical properties such as the average particle size, particle shape, and specific surface area of ​​the quartz powder, and also depends on the bulk density or tap density of the quartz powder deposit layer 16. To lower the thermal conductivity of the quartz powder deposit layer 16, for example, it is preferable that the average particle size of the quartz powder be small, and that the particle shape be flatter than spherical. Furthermore, the larger the specific surface area of ​​the quartz powder particles, the lower the thermal conductivity. In addition, the lower the bulk density or tap density of the quartz powder deposit layer, the lower the thermal conductivity.

[0054] It is preferable to measure the thermal conductivity of the raw quartz powder at the highest possible temperature, for example, measuring the thermal conductivity at 1000 to 1300°C. This is because the thermal conductivity during the melting and vitrification of the quartz powder is important in the manufacture of the quartz glass crucible 1, and also because the difference in thermal conductivity between different raw quartz powders becomes clearer the higher the temperature at which it is measured. In other words, the reason for evaluating the thermal conductivity at 1000 to 1300°C is that, in the process of heating and melting the deposited layer 16 of quartz powder, the way heat is transferred in the temperature range from a high temperature of 1000°C to 1650°C, where the quartz powder melts, is important. In this embodiment, the thermal conductivity at 1300°C is used as a representative indicator. Although 1300°C is a high temperature, it is a temperature at which thermal conductivity can be measured.

[0055] The thermal conductivity of an aggregate of natural quartz powder at high temperatures such as 1300°C is influenced by a complex array of factors, including the thermal conductivity within the quartz particles, the surface area and emissivity of the particles, and the voids between particles. However, by setting the thermal conductivity of the aggregate of natural quartz powder at 1300°C to between 0.4 W / (m·K) and 1.0 W / (m·K), and further setting the average particle aspect ratio of the natural quartz powder to between 1.7 and 2.1, it is possible to enhance the effect of reducing the bubble content in the transparent layer on the inner surface of the crucible.

[0056] In this embodiment, the immersion heat of the synthetic quartz powder 13b, which is the raw material for the transparent layer 11 that constitutes the inner surface of the crucible, should be as high as possible, and the immersion heat of the synthetic quartz powder 13b in water at 25°C is preferably 250 to 450 J / g. Here, "immersion heat" (also called "wetting heat") refers to the heat generated when a liquid comes into contact with a solid surface, and the amount of heat generated can be used to determine the surface area of ​​the powder, its properties, and its mixability.

[0057] As shown in Figure 4, using synthetic quartz powder with a high immersion heat on the inner surface of the crucible increases its affinity with the liquid (fused quartz 17). This increases the contact area between adjacent quartz particles when they melt, allowing gases present in the voids between particles to be removed under reduced pressure. Conversely, using synthetic quartz powder with a low immersion heat results in lower affinity with the liquid (fused quartz 17), making it difficult for bubbles present in the voids between particles to escape. As a result, bubbles tend to remain in the transparent layer 11, as shown in the figure.

[0058] While there are no particular limitations on the method for measuring the thermal conductivity of quartz powder, the hot-wire method is a well-known method for measuring the thermal conductivity of powders. The hot-wire method is one of the transient methods for measuring thermal conductivity and is specified in JIS R2616 and ASTM D5930. The immersion heat of quartz powder can be measured, for example, by a direct thermometering method using a thermistor.

[0059] Figure 5 is a schematic diagram illustrating an example of a method for measuring the thermal conductivity of a deposit of raw quartz powder.

[0060] As shown in Figure 5, the thermal conductivity of raw quartz powder can be determined by the hot-wire method. In measuring the thermal conductivity of quartz powder using the hot-wire method, a linear heater 42 is placed inside a sample 41 (test specimen) of quartz powder, which is assumed to be infinite. When a constant DC current is passed through the heater 42, its temperature is measured with a thermocouple 43, and the thermal conductivity of the sample is determined from the temperature rise of the heater 42 itself. In this way, the transient method calculates the thermal conductivity from the temperature response of the sample when transient heat flow energy is applied to the sample and it is heated transiently. The hot-wire method is an absolute measurement method and does not require a standard sample, however, a standard sample with a known thermal conductivity is necessary to check whether the obtained measurement value is valid.

[0061] As described above, the method for manufacturing a quartz glass crucible according to this embodiment includes the steps of forming a deposit layer 16 of raw quartz powder along the inner surface of a rotating mold 14, and heating the deposit layer 16 of raw quartz powder from the inside of the mold 14 to melt the raw quartz powder. Since the thermal conductivity of the raw quartz powder at 1300°C is 0.4 W / (m·K) or more and 1.0 W / (m·K) or less, the bubble content of the transparent layer 11 on the inside of the crucible can be reduced without any special pretreatment or strong heating of the raw quartz powder.

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

[0063] In quartz glass crucibles using synthetic quartz powder on the inner layer and natural quartz powder on the outer layer, the influence of the thermal conductivity of the natural quartz powder and the immersion heat of the synthetic quartz powder on the quality and performance of the crucible was evaluated. Therefore, as shown in Figure 6, 32-inch diameter quartz glass crucibles were manufactured using the rotary molding method according to Comparative Examples 1-4 and Examples 1-3, each using synthetic and natural quartz powders with different physical properties. Subsequently, silicon single crystals were pulled using the CZ method with these crucible samples, and the single crystal yield (dislocation-free pulling rate) was evaluated. The single crystal yield is expressed as a percentage of the weight ratio of silicon single crystals to polycrystalline silicon raw material placed in the crucible; a yield of 75% or higher is considered acceptable.

[0064] In evaluating the physical properties of synthetic quartz powder, the heat of immersion in water at 25°C [mJ / m 2 ], average particle diameter [μm], specific surface area [m 2 [g], bulk density [g / cm³] 3 The following were measured: ]. Furthermore, in the evaluation of the physical properties of natural quartz powder, the thermal conductivity at 1300°C [W / (m·K)], average particle aspect ratio, and bulk density [g / cm³] were measured. 3 ] was measured.

[0065] In measuring the thermal conductivity of natural quartz powder, a heat-resistant sample container made of Al2O3 (approximately 230 mm x 115 mm x 130 mm) was filled with quartz powder, and then the container was dropped from a height of approximately 50 mm and tapped 10 times. The direction of tapping (direction of free fall) was from the right end to the left end of sample 41 in Figure 5. Subsequently, the thermal conductivity of the natural quartz powder was measured in air using a hot-wire thermal conductivity measuring device.

[0066] For the measurement of the immersion heat, a multi-micro calorimeter MMC-5111 manufactured by Tokyo Institute of Technology was used. Quartz powder was immersed in distilled water at 25 °C, and the immersion heat per unit area was calculated from the amount of heat generated at that time. The specific surface area of the quartz powder was measured by the BET method. The average aspect ratio of the particles of natural quartz powder was calculated by measuring the long diameter and short diameter of the particles by image analysis of SEM photographs, and the aspect ratio was calculated. The additive average value of the aspect ratio was calculated from 100 measured particles. A multi-functional powder physical property measuring instrument was used to measure the bulk density of the quartz powder.

[0067] The immersion heat of the synthetic quartz powder used in the production of the quartz glass crucible according to Comparative Example 1 in water at 25 °C was 200 mJ / m 2 , the average particle size was 105 μm, the specific surface area was 0.040 m 2 / g, and the bulk density was 1.10 g / cm 3 . Also, the thermal conductivity of natural quartz powder at 1300 °C was 0.35 W / (m·K), the average particle aspect ratio was 2.6, and the bulk density was 1.08 g / cm 3 .

[0068] Subsequently, the average bubble content of the surface layer part of the transparent layer within a depth of 2 mm from the inner surface of the completed crucible was measured by non-destructive inspection. Also, the thickness of the unmelted layer formed on the outer surface of the crucible was evaluated. For the evaluation of the thickness of the unmelted layer, a certain reference value was set, and if the thickness was above the reference value, it was judged as OK, and if the thickness was below the reference value, it was judged as NG. As a result, the average bubble content was 0.135 vol%, which was a high result of 0.1 vol% or more. Also, the thickness of the unmelted layer was below the reference value (NG). As a result of pulling up a silicon single crystal using the crucible according to this Comparative Example 1, the single crystal yield was 71%, which was a result below 75%.

[0069] The immersion heat of the synthetic quartz powder used in the production of the quartz glass crucible according to Comparative Example 2 was 3I6 mJ / m 2 , the average particle size was 190 μm, the specific surface area was 0.036 m 2 / g, and the bulk density was 1.23 g / cm 3 . Also, the thermal conductivity of natural quartz powder was 0.38 W / (m·K), the average particle aspect ratio was 2.4, and the bulk density was 1.12 g / cm3 That was the case.

[0070] Next, the average bubble content within 2 mm of the inner surface of the completed crucible and the thickness of the unmelted layer were determined. As a result, the average bubble content was 0.151 vol%, and the thickness of the unmelted layer was NG (below the standard value). When silicon single crystals were pulled using the crucible from this Comparative Example 2, the single crystal yield was 70%.

[0071] The immersion heat of the synthetic quartz powder used in the production of the quartz glass crucible in Comparative Example 3 was 225 mJ / m³. 2 The average particle size is 90 μm, and the specific surface area is 0.026 m². 2 The bulk density is 1.05 g / cm³ / g. 3 Furthermore, the thermal conductivity of the natural quartz powder was 1.05 W / (m·K), the average particle aspect ratio was 1.5, and the bulk density was 1.37 g / cm³. 3 That was the case.

[0072] Next, the average bubble content within 2 mm of the inner surface of the completed crucible and the thickness of the unmelted layer were determined. As a result, the average bubble content was 0.175 vol%, and the thickness of the unmelted layer was NG (below the standard value). When silicon single crystals were pulled using the crucible from this Comparative Example 3, the single crystal yield was 72%.

[0073] The immersion heat of the synthetic quartz powder used in the production of the quartz glass crucible according to Comparative Example 4 was 480 mJ / m³. 2 The average particle size is 450 μm, and the specific surface area is 0.015 m². 2 The bulk density is 1.7 g / cm³ / g. 3 Furthermore, the thermal conductivity of the natural quartz powder was 1.12 W / (m·K), the average particle aspect ratio was 1.2, and the bulk density was 1.41 g / cm³. 3 That was the case.

[0074] Next, the average bubble content within 2 mm of the inner surface of the completed crucible and the thickness of the unmelted layer were determined. As a result, the average bubble content was 0.198 vol%, and the thickness of the unmelted layer was NG (below the standard value). When silicon single crystals were pulled using the crucible from this Comparative Example 4, the single crystal yield was 70%. As described above, in the crucible samples of Comparative Examples 1 to 4, the single crystals underwent dislocation formation, resulting in a low single crystal yield of 72% or less.

[0075] The immersion heat of the synthetic quartz powder used in the production of the quartz glass crucible according to Example 1 was 250 mJ / m³. 2 The average particle size is 87 μm, and the specific surface area is 0.071 m². 2 The bulk density is 0.99 g / cm³ / g. 3 Furthermore, the thermal conductivity of the natural quartz powder was 0.43 W / (m·K), the average particle aspect ratio was 2.1, and the bulk density was 1.16 g / cm³. 3 That was the case.

[0076] Next, the average bubble content within 2 mm of the inner surface of the completed crucible and the thickness of the unmelted layer were determined. As a result, the average bubble content was 0.025 vol%, which is a good result of less than 0.05 vol%, indicating that bubbles on the inner surface of the crucible were sufficiently removed. In addition, the thickness of the unmelted layer was above the standard value. When silicon single crystals were pulled using the crucible according to this Example 1, the single crystal yield was 86%.

[0077] The immersion heat of the synthetic quartz powder used in the production of the quartz glass crucible according to Example 2 was 450 mJ / m³. 2 The average particle size is 222 μm, and the specific surface area is 0.035 m². 2 The bulk density is 1.27 g / cm³ / g. 3 Furthermore, the thermal conductivity of the natural quartz powder was 0.71 W / (m·K), the average particle aspect ratio was 1.9, and the bulk density was 1.25 g / cm³. 3 That was the case.

[0078] Next, the average bubble content within 2 mm of the inner surface of the completed crucible and the thickness of the unmelted layer were determined. As a result, the average bubble content was 0.020 vol%, which is a good result of 0.05 vol% or less. In addition, the thickness of the unmelted layer was above the standard value. When silicon single crystals were pulled using the crucible according to this Example 2, the single crystal yield was 89%.

[0079] The immersion heat of the synthetic quartz powder used in the production of the quartz glass crucible according to Example 3 was 365 mJ / m³. 2 The average particle size is 235 μm, and the specific surface area is 0.040 m². 2 The bulk density is 1.33 g / cm³ / g. 3 Furthermore, the thermal conductivity of the natural quartz powder was 0.95 W / (m·K), the average particle aspect ratio was 1.7, and the bulk density was 1.33 g / cm³. 3 That was the case.

[0080] Next, the average bubble content within 2 mm of the inner surface of the completed crucible and the thickness of the unmelted layer were determined. As a result, the average bubble content was 0.024 vol%, which is a good result of 0.05 vol% or less. In addition, the thickness of the unmelted layer was above the standard value. When silicon single crystals were pulled using the crucible according to this Example 3, the single crystal yield was 93%. [Explanation of Symbols]

[0081] 1 Quartz glass crucible 10a Side wall part 10b bottom 10c Corner section 10i Crucible interior 100 Outer surface of the crucible 11 Transparent layer 12. Bubble layer 13a Natural quartz powder 13b Synthetic quartz powder 14 molds 14a Ventilation holes 14i mold inner surface 15 Arc electrode 16. Quartz powder deposits 17. Fused silica (fused glass) 41 Samples (test specimens) 42 Heater 43 Thermocouples

Claims

1. The process includes the steps of depositing quartz powder on the inner surface of a rotating mold, and heating the deposited layer of quartz powder from the inside of the mold to melt the quartz powder. The quartz powder deposit layer comprises a natural quartz powder deposit layer formed on the inner surface of the mold and a synthetic quartz powder deposit layer formed on the inner surface of the natural quartz powder deposit layer. A method for manufacturing a quartz glass crucible, characterized in that the thickness of the deposited layer of natural quartz powder is at least twice the thickness of the deposited layer of synthetic quartz powder, and the thermal conductivity of the natural quartz powder tap-filled in the container at 1300°C is 0.43 W / (m·K) or more and 0.95 W / (m·K) or less.

2. The method for producing a quartz glass crucible according to claim 1, wherein the thermal conductivity of the natural quartz powder at 1300°C is 0.5 W / (m·K) or more and 0.8 W / (m·K) or less.

3. A method for producing a quartz glass crucible according to claim 1, wherein the immersion heat of the synthetic quartz powder in water at 25°C is 250 J / g or more and 450 J / g or less.

4. The method for manufacturing a quartz glass crucible according to claim 1, wherein the step of heating and melting the deposited layer of quartz powder includes a transparent layer forming step of forming a transparent layer made of silica glass without air bubbles by melting the deposited layer of quartz powder while drawing vacuum from the inner surface side of the mold, and a bubble layer forming step of forming a bubble layer made of silica glass containing a large number of air bubbles by weakening or stopping the suction force of the vacuum drawing from the inner surface side of the mold.

Images