JP5473878B2 - Method for producing quartz glass crucible for pulling silicon single crystal - Google Patents

Description

  The present invention relates to a quartz glass crucible for pulling a silicon single crystal and a method for manufacturing the same, and more particularly to a layer structure of a quartz glass crucible.

  A quartz glass crucible is used for manufacturing a silicon single crystal. In the Czochralski method (CZ method), polysilicon is heated and melted in a quartz glass crucible, the seed crystal is immersed in this silicon melt, and the crucible and the seed crystal are gradually pulled up while rotating in opposite directions. To grow a single crystal. In order to produce a high-purity silicon single crystal for semiconductor devices, it is required that the silicon single crystal is not contaminated by elution of impurities contained in the quartz glass crucible, and the temperature control of the silicon melt in the crucible is easy. It is also necessary to have a sufficient heat capacity. Therefore, a quartz glass crucible having a two-layer structure having an opaque outer layer containing a large number of minute bubbles and a transparent inner layer having a bubble content of 0.1% or less and an average bubble diameter of 100 μm or less is preferable. It is used (see Patent Document 1). In addition, the outer layer of the crucible is made of natural quartz to increase the strength of the crucible at high temperatures, while the inner layer of the crucible in contact with the silicon melt is made of synthetic quartz to prevent impurities from entering. A quartz glass crucible having a structure is also used (see Patent Document 2).

  In recent years, quartz glass crucibles with large diameters of 700 mm or more have been used with the increase in size of silicon wafers, and the distance from the heater in the crucible to the single crystal has increased, the amount of melting has increased, the pulling time has been longer than 100 hours. The heat load on the quartz crucible increases due to the fact that it is farther and more intense than before, and a phenomenon of subduction in which the lower part of the quartz crucible is deformed by its own weight during pulling has occurred. One method of preventing deformation is a three-layer quartz glass crucible in which the outer layer of the crucible is an Al-added quartz layer, the intermediate layer is a natural quartz layer or a high-purity synthetic quartz layer, and the inner layer is a transparent high-purity synthetic quartz layer. It has been proposed (see Patent Document 3). As another method for preventing deformation, a quartz crucible in which the inner surface and outer surface of the crucible are crystallized and strengthened is known. For example, Patent Document 4 describes that a crystallization accelerator is applied to the outer surface of the crucible, and the crucible is crystallized and strengthened during pulling. Patent Document 5 describes that an oxyhydrogen flame is sprayed on the outer surface of the crucible to form a crystallized glass layer on the outer surface of the crucible. Patent Document 6 describes a quartz crucible in which the entire inner surface of the crucible is polished by sandblasting and the polished surface is further heat treated with an oxyhydrogen flame and smoothed.

JP-A-1-197381 JP-A-1-261293 JP 2000-247778 A JP 09-110590 A JP-A-10-203893 JP 2001-328831 A

  However, in the conventional crucible described in Patent Document 3, the crystallization accelerator applied to the outer surface of the crucible is an impurity for the silicon single crystal and may adversely affect the electrical characteristics of the manufactured wafer. is there. Further, according to the crucible described in Patent Document 4, an oxyhydrogen flame can be sprayed on the outer surface of the crucible to form a crystallized glass layer on the outer surface of the crucible, but the softening point (about 1700 ° C.) of quartz glass in an oxygen atmosphere. When heated to the above, cristobalite crystals precipitate during the cooling process. Since quartz glass and cristobalite have greatly different coefficients of thermal expansion, the cristobalite layer formed by this method is easy to peel off and is not suitable for practical use. Further, the conventional crucible described in Patent Document 5 has an advantage that the inner surface does not contain bubbles and the purity is high, so that the single crystallization rate can be improved. The problem of the subduction phenomenon that deforms has not been solved.

  The present invention solves the above-described problems, and an object of the present invention is to provide a quartz glass crucible in which sinking is suppressed at a high temperature during pulling of a silicon single crystal and a method for manufacturing the same.

In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, the specific gravity of the opaque quartz glass layer in the upper part of the crucible is made smaller than that in the lower part of the crucible. It has been found that subsidence due to a high heat load of 1500 ° C. or higher can be prevented, and for that purpose, the OH group concentration of the quartz powder used can be adjusted. The present invention has been made on the basis of such technical knowledge, and the present invention is a quartz glass crucible having a side wall portion, a curved portion and a bottom portion, and a large number of bubbles provided on the outer surface side of the crucible. And a transparent quartz glass layer provided on the inner surface side of the crucible, and the opaque quartz glass layer belongs to a range from the upper end of the crucible to a first intermediate position below the upper end. A first opaque quartz glass portion provided at the upper part of the crucible, and a lower part of the crucible belonging to a range from the second intermediate position below the upper part of the crucible and below the first intermediate position to the lower end of the crucible. and a second opaque quartz glass portion provided, the height _{h 1} of the first quartz glass portion is at 0.1 h ₀ or 0.6 h ₀ or less with respect to the height _{h 0} of the entire crucible, Second opaque quartz glass The specific gravity of the portion is 1.7 or more and 2.1 or less, the specific gravity of the first opaque quartz glass portion is 1.4 or more and 1.8 or less, which is smaller than the specific gravity of the second opaque quartz glass portion, The OH group concentration in the first opaque quartz glass portion is higher than the OH group concentration in the second opaque quartz glass layer, and the Al concentration in the first opaque quartz glass portion is 10 ppm or more.

  The crucible whose viscosity has been improved by adding more Al can be enlarged, but since such a large quartz glass crucible is very heavy, a new problem that subduction is likely to occur due to its own weight Has occurred. For this reason, it is not sufficient to increase the viscosity with Al, and further contrivances are required to withstand long-time use. According to the present invention, since the specific gravity of the opaque quartz glass layer at the upper part of the crucible is small, it is possible to reduce the load due to the own weight applied to the lower part of the crucible, and to suppress the sinking of the crucible. In addition, since the opaque quartz glass layer on the upper part of the crucible contains more bubbles, the heat retaining property on the upper part of the crucible can be improved. For example, the generation of cracks in the silicon single crystal due to rapid cooling such as a cooling rate of 3.0 ° C./min. Can be prevented.

  The present invention also relates to a method for producing a quartz glass crucible having a side wall portion, a curved portion and a bottom portion, wherein quartz powder is introduced into the mold while rotating a hollow mold having an inner surface adapted to the outer shape of the quartz glass crucible. A step of filling and forming a layer of quartz powder along the inner surface of the mold and a step of forming an opaque quartz glass layer by heating the layer of quartz powder to melt the quartz powder. Forming the first quartz powder at a position corresponding to the upper part of the crucible belonging to the range from the upper end of the crucible to the first intermediate position below the upper end, and below the upper part of the crucible. And filling the second quartz powder into a position corresponding to the crucible lower part belonging to the range from the second intermediate position below the first intermediate position to the lower end of the crucible; 2 quartz powder And a step of filling the crack crucible third quartz powder on the inner surface of, OH group concentration of the first quartz powder is characterized by higher than the second silica powder.

  According to the present invention, the quartz powder used for forming the upper part of the crucible has a relatively high OH group concentration, thereby forming a quartz glass having a high bubble content. Can be reduced. If the specific gravity of the opaque quartz glass layer at the upper part of the crucible is small, the load applied to the lower part of the crucible can be reduced, so that the crucible sinking, which is particularly problematic in large crucibles, can be suppressed. Moreover, since the opaque quartz glass layer on the upper part of the crucible contains more bubbles, the heat retention of the silicon single crystal immediately after the pulling can be improved, and the occurrence of cracks in the silicon single crystal due to rapid cooling can be prevented. On the other hand, the quartz powder used in the lower portion of the crucible has a relatively low OH group concentration, thereby forming a quartz glass having a low bubble content, and thus the specific gravity of the lower portion of the crucible can be increased. Therefore, the strength of the crucible lower portion can be secured, and the crucible sinking can be suppressed together with the lightened crucible upper portion.

  In the present invention, the OH group concentration of the first quartz powder is preferably 30 ppm or more and 60 ppm or less, and the OH group concentration of the second quartz powder is preferably less than 30 ppm. Further, the Al concentration of the first quartz powder is preferably 10 ppm or more. When the OH group concentration and Al concentration of these quartz powders used for forming the first and second quartz glass portions satisfy the above conditions, the crucible upper portion and the crucible lower portion can have appropriate specific gravity, and the high temperature The crucible sinking can be sufficiently suppressed while keeping the crucible high in strength.

  In the present invention, it is preferable to generate a second quartz powder having a lower OH group concentration than the first quartz powder by dehydrating the first quartz powder. According to this, since the first and second quartz powders having only different OH group concentrations can be generated from a common raw material, various controls for manufacturing a quartz glass crucible that satisfies a desired condition are easily performed. be able to. Alternatively, quartz powders having different impurity concentrations as well as OH group concentrations may be prepared.

  In the method for producing a quartz glass crucible according to the present invention, when a quartz powder layer is heated to melt the quartz powder, the quartz powder being heated is degassed from a vent hole provided in the mold, thereby the inner surface side of the crucible. It is preferable to include a step of forming a transparent quartz glass layer and a step of forming an opaque quartz glass layer on the outer surface side of the crucible by weakening or stopping decompression for deaeration.

  According to the present invention, it has an opaque quartz glass layer containing many bubbles provided on the outer surface side of the crucible, and a transparent quartz glass layer substantially free of bubbles provided on the inner surface side of the crucible. A quartz glass crucible with a relatively small specific gravity of the opaque quartz glass layer on the upper part of the crucible can be reliably formed.

  In the present invention, a large effect can be confirmed with a quartz glass crucible for pulling a large silicon single crystal having a diameter of 812 mm or more. A large crucible having a diameter of 812 mm or more is used for pulling up an ingot for a silicon wafer having a diameter of 300 mm, and has a large capacity and a large weight. However, according to the present invention, sinking can be prevented in a large crucible having a diameter of 812 mm or more, and the production yield of silicon single crystals can be improved.

  According to the present invention, it is possible to provide a manufacturing method for easily manufacturing a quartz glass crucible in which the crucible is effectively prevented from sinking at a high temperature during pulling of the silicon single crystal.

It is a schematic sectional drawing which shows the structure of the quartz glass crucible by the 1st Embodiment of this invention. It is a flowchart for demonstrating the manufacturing method of a quartz glass crucible. It is a 1st schematic diagram for demonstrating the manufacturing method of a quartz glass crucible. It is the 2nd schematic diagram for demonstrating the manufacturing method of a quartz glass crucible. It is a schematic sectional drawing which shows the structure of the quartz glass crucible by the 2nd Embodiment of this invention.

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

  FIG. 1 is a schematic cross-sectional view showing the structure of a quartz glass crucible for pulling a silicon single crystal according to a first embodiment of the present invention.

  As shown in FIG. 1, the quartz glass crucible 10 according to the present embodiment has a two-layer structure, and includes an opaque quartz glass layer 11 constituting an outer layer and a transparent quartz glass layer 12 constituting an inner layer.

  The opaque quartz glass layer 11 is a crystalline silica glass layer containing a large number of minute bubbles. In the present specification, “opaque” means a state in which a large number of bubbles are inherently present in quartz glass, and it is apparently clouded. The opaque quartz glass layer 11 plays a role of uniformly transferring heat from a heater disposed on the outer periphery of the crucible to the silicon melt in the quartz glass crucible. Since the opaque quartz glass layer 11 has higher heat retention than the transparent quartz glass layer 12, the temperature of the silicon melt can be easily maintained constant.

The opaque quartz glass layer 11 has a first opaque quartz glass portion 11a located at the upper portion of the crucible and a second opaque quartz glass portion 11b located at the lower portion of the crucible, and the bubble content and specific gravity are different. Yes. Here, the “crucible upper part” means a part belonging to the range from the upper end P _{0 of} the crucible to the intermediate position P ₁ , and the “crucible lower part” is lower than the “crucible upper part” and the intermediate position P ₁ refers to a portion that belongs to range up to the lower end P ₂ of the crucible from. When the crucible overall height _{h 0,} it is preferable that the height _{h 1} of the first opaque vitreous silica portion 11a is 0.1h ₀ ~0.6h _0. If h ₁ is less than 0.1h _{0, the} effect of providing the first opaque quartz glass portion 11a is not obtained, and if h ₁ exceeds 0.6h ₀ , the strength of the crucible decreases. This is because the crucible is likely to be deformed.

  The first opaque quartz glass portion 11a contains more bubbles than the second opaque quartz glass portion 11b, and its specific gravity is relatively small. Specifically, the specific gravity of the first opaque quartz glass portion 11a is 1.4 to 1.8, and the specific gravity of the second opaque quartz glass portion 11b is 1.7 to 2.1. It is larger than the opaque quartz glass portion 11a. The specific gravity difference between the two is preferably 0.1 to 0.3, and particularly preferably 0.2 to 0.28. In order to realize such a specific gravity, quartz powder having an OH group concentration of about 30 ppm to 60 ppm is used as a raw material for the first opaque quartz glass portion 11a. On the other hand, quartz powder having an OH group concentration of less than 30 ppm is used as a raw material for the second opaque quartz glass portion 11b. Quartz powder having an OH group concentration of less than 30 ppm is a raw material that is preferably used for forming an opaque quartz glass layer of a crucible, whereas an OH group concentration of 30 to 60 ppm has a higher OH group concentration than usual. It has quartz powder.

  By using the raw material quartz powder as described above, the specific gravity of the first opaque quartz glass portion 11a is smaller than that of the second opaque quartz glass portion 11b, and the OH group concentration of the first opaque quartz glass portion 11a. Is larger than the second opaque quartz glass portion 11b. Here, the Al concentration of the first quartz glass portion 11a is preferably 10 ppm or more. It is known that when the OH group concentration is high, the viscosity of the quartz glass decreases. However, when the Al concentration is high, the viscosity of the quartz glass can be increased. The desired viscosity can be ensured by offsetting.

  The difference between the OH group concentration of the raw quartz powder of the first opaque quartz glass portion 11a and the OH group concentration of the raw quartz powder of the second opaque quartz glass portion 11b is more preferably 15 ppm or more. If the difference in OH group concentration is 15 ppm or more, the difference in the bubble content and specific gravity of the first and second opaque quartz glass portions 11a and 11b described above can be ensured, and the crucible sinking can be effectively performed. Can be suppressed.

  In this way, opaque quartz glass portions 11a and 11b having different specific gravities are formed by properly using quartz powders having different OH group concentrations. It is known that the viscosity of quartz glass having a high OH group concentration is lowered, and therefore there is a possibility that deformation such as inward tilting may occur in a crucible side wall portion made of quartz glass having a high OH group concentration. However, the use of quartz powder having a high Al concentration can increase the viscosity at a high temperature, and can suppress a decrease in viscosity due to the influence of OH groups. In a crucible in which subsidence is suppressed, it is possible to prevent a situation in which the crucible side wall portion is slightly inclined starting from the subsidence, and the inclination proceeds and a large deformation occurs.

  The opaque quartz glass layer 11 is preferably made of natural quartz glass. Natural quartz glass means silica glass produced by melting natural raw materials such as natural quartz and quartzite. In general, natural quartz has the characteristics that the concentration of metal impurities is higher and the concentration of OH groups is lower than that of synthetic quartz. For example, the concentration of Al contained in natural quartz is 1 ppm or more, the concentration of alkali metals (Na, K, and Li) is 0.05 ppm or more, and the concentration of OH groups is less than 60 ppm. It should be noted that whether or not it is natural quartz should not be determined based on one element, but should be comprehensively determined based on a plurality of elements. Since natural quartz has a higher viscosity at high temperatures than synthetic quartz, the heat resistance of the entire crucible can be increased. Natural materials are cheaper than synthetic quartz and are advantageous in terms of cost.

  The transparent quartz glass layer 12 is an amorphous silica glass layer substantially free of bubbles. According to the transparent quartz glass layer 12, it is possible to prevent an increase in the number of quartz pieces peeled from the inner surface of the crucible, and to increase the silicon single crystallization rate. Here, “substantially free of bubbles” means that the bubble content and bubble size are such that the single crystallization rate does not decrease due to bubbles, and is not particularly limited, It means that the bubble content is 0.1% or less and the average diameter of the bubbles is 100 μm or less. The change in the bubble content from the opaque quartz glass layer 11 to the transparent quartz glass layer 12 is relatively steep, and 30 μm from the position where the bubble content of the transparent quartz glass layer 12 starts to increase toward the outer surface of the crucible. At a certain degree of progress, the bubble content of the substantially opaque quartz glass layer 11 is reached. Therefore, the opaque quartz glass layer 11 and the transparent quartz glass layer 12 can be clearly distinguished apparently.

  The bubble content of the transparent quartz glass layer 12 can be measured nondestructively using an optical detection means. The optical detection means includes a light receiving device that receives transmitted light or reflected light of light irradiated on the crucible. The light emitting means for irradiating light may be built-in or may use an external light emitting means. As the optical detection means, one that can be rotated along the inner surface of the quartz crucible is used. As the irradiation light, in addition to visible light, ultraviolet light and infrared light, X-rays or laser light can be used, and any light can be applied as long as it can reflect and detect bubbles. The light receiving device is selected according to the type of irradiation light. For example, a digital camera including an optical lens and an image sensor can be used. In order to detect bubbles existing at a certain depth from the surface, the focal point of the objective lens may be scanned in the depth direction from the surface.

  The measurement result by the optical detection means is taken into the image processing apparatus, and the bubble content P (%) is calculated. More specifically, an image of the inner surface of the crucible is taken using an optical camera, the inner surface of the crucible is divided into a predetermined volume to obtain a reference volume W1, and an occupied volume W2 of bubbles with respect to the reference volume W1 is obtained, and P (% ) = (W2 / W1) × 100.

  The transparent quartz glass layer 12 is preferably made of synthetic quartz glass. Synthetic silica glass means silica glass produced by melting a synthetic raw material obtained by, for example, hydrolysis of silicon alkoxide. In general, synthetic quartz has the characteristics that the concentration of metal impurities is lower than that of natural quartz and the concentration of OH groups is high. For example, the concentration of each metal impurity contained in synthetic quartz is less than 0.05 ppm, and the concentration of OH groups is 30 ppm or more. However, since synthetic quartz to which metal impurities such as Al are added is also known, whether or not it is synthetic quartz should not be determined based on one element, but comprehensively based on a plurality of elements. It should be judged. Thus, since synthetic quartz glass has fewer impurities than natural quartz glass, it is possible to prevent an increase in impurities eluted from the crucible into the silicon melt, and to increase the silicon single crystallization rate.

  Both the opaque quartz glass layer 11 and the transparent quartz glass layer 12 are provided on the entire crucible from the side wall 10A to the bottom 10B of the crucible. The crucible side wall 10A is a cylindrical portion parallel to the central axis (Z axis) of the crucible, and extends substantially directly below the opening of the crucible. However, the side wall portion 10A does not have to be completely parallel to the Z axis, and may be inclined so as to gradually spread toward the opening. Further, the side wall portion 10A may be straight or may be gently curved. Although not particularly limited, the side wall portion 10A can be defined as a region where the tangential inclination angle of the crucible wall surface with respect to the XY plane orthogonal to the Z axis is 80 degrees or more.

  The bottom 10B of the crucible is a relatively flat portion including the intersection with the Z-axis of the crucible, and a curved portion 10C is formed between the bottom 10B and the side wall 10A. The bottom 10B preferably covers the projection surface of the silicon single crystal to be pulled up. The shape of the crucible bottom 10B may be a so-called round bottom or a flat bottom. Further, the curvature and angle of the bending portion 10C can be arbitrarily set. When the crucible bottom portion 10B has a round bottom, the bottom portion 10B also has an appropriate curvature, so that the difference in curvature between the bottom portion 10B and the curved portion 10C is very small compared to the flat bottom. When the crucible bottom portion 10B is a flat bottom, the bottom portion 10B has a flat or extremely gentle curved surface, and the curvature of the curved portion 10C is very large. Although not particularly limited, in the case of a flat bottom, the bottom portion 10B can be defined as a region where the tangential inclination angle of the crucible wall surface with respect to the XY plane orthogonal to the Z axis is 30 degrees or less.

  The thickness of the crucible is preferably 10 mm or more, and more preferably 13 mm or more. Usually, the thickness of large crucibles with a diameter of 812 mm (32 inches) or more is 10 mm or more, and the thickness of large crucibles of 1016 mm (40 inches) or more is 13 mm or more. Because it is used, sinking is likely to occur, and the effect of the present invention is remarkable. The thickness of the crucible need not be constant from the side wall portion 10A to the bottom portion 10B. For example, the thickness of the curved portion 10C is the largest, and the thickness is reduced toward the upper end of the side wall portion 10A or the center of the bottom portion 10B. It may be.

  The thickness of the transparent quartz glass layer 12 is preferably 0.5 mm or more, and more preferably 1.0 mm or more. This is because when the transparent quartz glass layer 12 is thinner than 0.5 mm, the transparent quartz glass layer 12 may be completely melted during the pulling of the silicon single crystal, and the opaque quartz glass layer 11 may be exposed. The thickness of the transparent quartz glass layer 12 does not need to be constant from the side wall portion 10A to the bottom portion 10B. For example, the thickness of the transparent quartz glass layer 12 of the curved portion 10C is the largest, and the upper end or bottom portion of the side wall portion 10A is You may be comprised so that it may become thin as it goes to the center of 10B.

  As described above, according to the present embodiment, the specific gravity of the first opaque quartz glass part 11a at the upper part of the crucible is smaller than that of the second opaque quartz glass part 11b at the lower part of the crucible, so that the crucible resulting from the enlargement of the crucible. Can be suppressed. In addition, since the first opaque quartz glass portion 11a contains more bubbles, it is possible to increase the heat retention of the upper part of the crucible, to retain the temperature of the silicon single crystal being pulled up, and to generate cracks due to rapid cooling. Can be prevented.

  Next, a method for manufacturing the quartz glass crucible 10 will be described in detail with reference to FIGS.

  FIG. 2 is a flowchart schematically showing a manufacturing process of the quartz glass crucible 10. 3 and 4 are schematic views for explaining a method for manufacturing the quartz glass crucible 10.

  The quartz glass crucible 10 can be manufactured by a rotational mold method. In the rotary mold method, as shown in FIG. 3, a carbon mold 14 having a cavity that matches the outer shape of the quartz glass crucible 10 is prepared, and quartz powder is filled while rotating the mold 14, and the quartz along the inner surface of the mold is prepared. Form a layer of powder. At this time, the upper part of the cavity corresponding to the upper part of the crucible is filled with the first quartz powder 13a, and the lower part of the cavity corresponding to the lower part of the crucible is filled with the second quartz powder 13b (step S11). The order of filling the first and second quartz powders 13a and 13b is not particularly limited. Since the carbon mold 14 rotates at a constant speed, the filled quartz powder stays at a fixed position while being stuck to the inner surface by centrifugal force, and its shape is maintained.

  Both the first and second quartz powders 13a and 13b become the opaque quartz glass layer 11. In particular, the first quartz powder 13a becomes the first opaque quartz glass portion 11a, and the second quartz powder is the second quartz powder. It becomes an opaque quartz glass part. Therefore, the first quartz powder 13a has a higher OH group concentration than the second quartz powder 13b.

  In the present embodiment, the first quartz powder 13a is preferably natural quartz powder having an OH group concentration of 30 ppm to 60 ppm, and the second quartz powder 13b is a natural stone having an OH group concentration of less than 30 ppm. It is preferably an English powder. In the present embodiment, the first quartz powder having an OH group concentration higher than that of the second quartz powder 13b can be generated by adding the synthetic quartz powder to the second quartz powder 13b. Since the OH group concentration of synthetic quartz powder made from silicon alkoxide or the like is much higher than that of natural quartz powder, the first quartz is mixed by mixing the second quartz powder and synthetic quartz powder at a predetermined ratio. Powder can be obtained.

  Moreover, in this embodiment, you may produce | generate the 2nd quartz powder 13b whose OH group density | concentration is lower than the said 1st quartz powder 13a by dehydrating the 1st quartz powder 13a. According to this, since the 1st and 2nd quartz powder 13a, 13b from which only OH group concentration differs from a common raw material can be generated, a quartz glass crucible having stable quality can be easily manufactured. . The method of dehydration is not particularly limited. For example, a method in which quartz powder is heated to about 1400 ° C. and dried, or a method in which quartz powder is brought into contact with chlorine gas or a chlorine gas-containing compound gas at a temperature of 1000 to 1500 ° C. (See JP-A-6-40713).

  Next, as shown in FIG. 4, the first material used as the raw material for the transparent quartz glass layer 12 in the mold 14 in which the layers of the first and second quartz powders 13a and 13b used as the raw material for the opaque quartz glass layer 11 are formed. 3 quartz powder 13c is filled to form a thicker quartz powder layer (step S12). The third quartz powder 13c is filled in the entire mold with a predetermined thickness. The third quartz powder 13c may be natural quartz powder or synthetic quartz powder.

The OH group concentration of the quartz powder can be determined by Fourier transform infrared spectrophotometry (FT-IR), and utilizes the principle that the chemical structure of the compound has an absorption spectrum in the unique infrared region. FT-IR is an infrared spectrum obtained by Fourier transforming an interferogram obtained by plotting the intensity of interference light of two infrared lights that have passed through different routes from the same light source against the difference in optical path length. Is a method for analyzing the molecular structure and the like. The infrared absorption position of the OH group is 3672 cm ⁻¹ .

  Then, the arc electrode 15 is installed in the cavity, arc discharge is performed from the inside of the mold, and the entire quartz powder layer is heated to 1720 ° C. or more to melt. Simultaneously with this heating, the pressure is reduced from the mold side, the gas inside the quartz is sucked to the outer layer side through the vents provided in the mold, and the quartz powder being heated is degassed, thereby removing bubbles on the inner surface of the crucible. Then, the transparent quartz glass layer 12 substantially free of bubbles is formed (step S13). Here, “substantially free of bubbles” means that the bubble content and bubble size are such that the single crystallization rate does not decrease due to bubbles, and is not particularly limited, It means that the bubble content is 0.1% or less and the average diameter of the bubbles is 100 μm or less. Thereafter, the decompression for deaeration is weakened or stopped while continuing the heating, and the bubbles remain, thereby forming the opaque quartz glass layer 11 containing a large number of minute bubbles (step S14). At this time, the bubble content of the first opaque quartz glass portion 11a is higher than that of the second opaque quartz glass portion 11b due to the difference in raw materials, and the specific gravity of one opaque quartz glass portion 11a is the second opaque quartz glass portion. It becomes smaller than the part 11b. As described above, the quartz glass crucible according to the present embodiment is completed.

  As described above, the method for producing the quartz glass crucible according to the present embodiment is different from the first opaque quartz glass portion 11a by changing the OH group concentration of the raw material powder of the opaque quartz glass layer 11 between the upper part and the lower part of the crucible. Since the second opaque quartz glass portion 11b is formed separately, the specific gravity of the opaque quartz glass layer above the crucible and the opaque quartz glass layer below the crucible without partial heating or suction to the crucible. Can be made very different.

  In the first embodiment, the specific gravity of the opaque quartz glass layer 11 is divided into two stages, that is, the upper part of the crucible and the lower part of the crucible. However, the present invention is not limited to two stages, but three or more stages. It is also possible to divide and configure.

  FIG. 5 is a schematic cross-sectional view showing the structure of a quartz glass crucible for pulling a silicon single crystal according to a second embodiment of the present invention.

  As shown in FIG. 5, the quartz glass crucible 20 according to the present embodiment includes a first opaque quartz glass part 11 a located at the upper part of the crucible, a second opaque quartz glass part 11 b located at the lower part of the crucible, and an intermediate part of the crucible. And the third opaque quartz glass portion 11c located in the region, wherein the bubble content and specific gravity of each portion are different. That is, the change in specific gravity of the opaque quartz glass layer 11 has three steps in the height direction, and the specific gravity is higher in the lower part.

Here, the “crucible upper part” means a part belonging to the range from the upper end P _{0 of} the crucible to the first intermediate position P ₁₁ , and the “crucible lower part” is lower than the “crucible upper part”, A portion belonging to a range from the second intermediate position P ₁₂ lower than the first intermediate position P ₁₁ to the lower end P ₂ of the crucible, and the “crucible intermediate portion” refers to the second intermediate position P ₁₁ to the second intermediate position P ₁₁ . It refers to the portion that belongs in the range up to the intermediate position P _12. Specifically, the height h ₁ of the first opaque quartz glass portion 11a is 0.3h ₀ , the height of the second opaque quartz glass portion 11a is 0.4h ₀ , and the height of the third opaque quartz glass portion 11c is the height can be set to 0.3h _0. Also, the height h ₁ of the first opaque quartz glass portion 11a is 0.1h ₀ , the height of the second opaque quartz glass portion 11a is 0.4h ₀ , and the height of the third opaque quartz glass portion 11c is 0.5h may be set to _0. Each of these specific examples satisfies the condition that the height h _{1 of} the first opaque quartz glass portion 11a shown in the first embodiment is 0.1 h _{0 to} 0.6 h ₀ .

  The bubble contents and specific gravity of the first and second opaque quartz glass portions 11a and 11b are the same as those of the quartz glass crucible 10 according to the first embodiment. That is, the specific gravity of the first opaque quartz glass portion 11a is 1.4 to 1.8, and the specific gravity of the second opaque quartz glass portion 11b is 1.7 to 2.1. It is larger than the portion 11a. The bubble content and specific gravity of the third opaque quartz glass portion 11c are intermediate values of the first and second opaque quartz glass portions 11a and 11b, and are larger than the specific gravity of the first opaque quartz glass portion 11a. 2 and less than the specific gravity of the opaque quartz glass portion 11b.

  The first quartz powder 13a, which is a raw material of the first opaque quartz glass portion 11a, preferably has an OH group concentration of 30 to 60 ppm. Moreover, it is preferable that the 2nd quartz powder 13b which is a raw material of the 2nd opaque quartz glass part 11b is less than 30 ppm in OH group concentration.

  Further, as the raw material for the third opaque quartz glass portion 11c, it is preferable to use a material obtained by mixing the first quartz powder 13a and the second quartz powder 13b at a predetermined ratio. In this way, the third opaque quartz glass portion 11c having a specific gravity larger than that of the first opaque quartz glass portion 11a and smaller than that of the second opaque quartz glass portion 11 can be easily formed.

As described above, the quartz glass crucible 20 according to the present embodiment is provided with the crucible middle part between the crucible upper part and the crucible lower part, and the height h ₁ of the first opaque quartz glass part 11a is set to 0.1 h ₀ to. and 0.6 h _0, is made smaller than the larger and the crucible bottom than the specific gravity of the crucible upper part of the third opaque quartz glass portion 11c located crucible middle section, the same effects as the first embodiment Can play.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. It goes without saying that the present invention is included in the scope of the present invention.

Example 1
A quartz glass crucible sample A1 having a diameter of 812 mm was prepared. The size of the quartz glass crucible sample A1 was 812 mm in diameter and 500 mm in height. The thickness of the crucible was 18 mm at the side wall, 20 mm at the curved portion, and 18 mm at the bottom, and the thickness of the transparent quartz glass layer 12 on the side wall was 1.0 mm.

The quartz glass crucible sample A1 is manufactured by a rotational mold method, and natural quartz powder having an average OH group concentration of 30 ppm and an average Al concentration of 15 ppm is used as a raw material for the first opaque quartz glass portion 11a. Natural quartz powder having an average OH group concentration of 15 ppm was used as the raw material for the portion 11b. Further, synthetic quartz powder having an average OH group concentration of 90 ppm was used as a raw material for the transparent quartz glass layer 12. The average OH group concentration of the quartz powder was determined using FT-IR. The measuring method by FT-IR is shown in JIS K0117. When quartz powder is measured by FT-IR, it is necessary to use a liquid such as carbon tetrachloride having a refractive index similar to that of quartz powder as a solvent, and to closely fill the sample cell. First, the cell is filled with the solvent to be used for measurement, and the OH group concentration is calculated from the height of the absorption peak at the OH group measurement wavelength of 2.73 μm (the infrared absorption position of the OH group is 3672 cm ⁻¹ ). And Then, the absorption peak in the infrared absorption position 3672 cm < ^-1 > of OH group is measured for the sample cell filled with quartz powder by FT-IR. The calculation method of the OH group concentration from the absorption peak is OH group concentration = peak height ÷ sample cell thickness ÷ quartz powder filling rate × 1000.

  The average Al concentration of the quartz powder was determined by ICP-AES (inductively coupled plasma emission spectroscopy). Specifically, quartz powder that has been washed in advance is subjected to pressurized acid vapor decomposition with a mixed acid of hydrofluoric acid and other inorganic acids (such as nitric acid), sulfuric acid is added to the decomposition solution, and then solidified by distillation until white smoke is produced. Thereafter, the solid substance that had been allowed to cool was dissolved in pure water to prepare an aqueous solution. In quantitative analysis, a calibration curve is first prepared by the luminescence intensity method. Four or more types of calibration curve preparation solutions having different Al concentrations are prepared, and a relationship line between the emission intensity and the concentration is prepared using these solutions to obtain a calibration curve. Using this calibration curve, the pretreated aqueous solution was used as an analysis target sample, and the luminescence intensity was measured by ICP-AES to obtain the Al concentration corresponding to the calibration curve. The meaning of the concentration here is a mole fraction. The measurement wavelength of Al is 237.312 nm. The measuring method by ICP-AES is shown in JIS K0116.

The height h ₁ of the first opaque vitreous silica portion of the crucible sample A1 is 0.6 h 0 with respect to the height h ₀ of the entire _crucible, the height h ₂ of the second opaque vitreous silica portion of the entire crucible High It was 0.4h ₀ against is _{h 0.}

  When the specific gravity of the first and second opaque quartz glass portions 11a and 11b was determined by the Archimedes method from another sample manufactured under the same conditions as the crucible sample A1, the specific gravity of the first opaque quartz glass portion 11a was 1. 62, and the specific gravity of the second opaque quartz glass portion 11b was 1.86.

  Next, after filling the quartz glass crucible with 300 kg of polycrystalline silicon fragments, the quartz glass crucible is loaded into a single crystal pulling apparatus, and the polycrystalline silicon in the crucible is melted in a furnace to obtain a silicon single crystal having a diameter of about 300 mm. Raised the ingot.

  Thereafter, deformation of the crucible after use was confirmed. Further, the single crystallization rate of the pulled silicon single crystal was determined. The results are shown in Table 1. The single crystallization rate is defined as the weight ratio of the single crystal to the silicon raw material. However, not all the silicon melt in the crucible is used, and only the straight body part excluding the top part and tail part of the silicon single crystal ingot is subject to calculation of the single crystallization rate. Even if a sufficient silicon single crystal is pulled up, the single crystallization rate is 100% or less, and it is good if it is 80% or more.

  As shown in Table 1, the quartz glass crucible sample A1 according to this example had almost no crucible sink after use. Moreover, the single crystallization rate of the silicon ingot pulled up using this quartz glass crucible sample A1 was 86%, and a good single crystallization rate was obtained.

(Example 2)
A quartz glass crucible sample A2 having the same size and shape as the quartz glass crucible sample A1 according to Example 1 was prepared. The quartz glass crucible sample A2 was manufactured by the rotational mold method, but unlike Example 1, natural quartz powder having an average OH group concentration of 60 ppm and an average Al concentration of 15 ppm was used as a raw material for the first opaque quartz glass portion 11a. Natural quartz powder having an average OH group concentration of 15 ppm was used as a raw material for the second opaque quartz glass portion 11b. Synthetic quartz powder having an average OH group concentration of 90 ppm was used as a raw material for the transparent quartz glass layer 12.

The height h ₁ of the first opaque vitreous silica portion of the crucible sample A2 is 0.6 h 0 with respect to the height h ₀ of the entire _crucible, the height h ₂ of the second opaque vitreous silica portion of the entire crucible High It was 0.4h ₀ against is _{h 0.}

  Thereafter, the quartz single crystal ingot was pulled up using the quartz glass crucible A2, and the deformation of the crucible after use and the silicon single crystallization rate were determined. The results are shown in Table 1.

  As shown in Table 1, the quartz glass crucible sample A2 according to this example had almost no crucible sink after use. Moreover, the single crystallization rate of the silicon ingot pulled up using this quartz glass crucible sample A2 was 88%, and a good single crystallization rate was obtained.

(Example 3)
A quartz glass crucible sample A3 having the same size and shape as the quartz glass crucible sample A1 according to Example 1 was prepared. The quartz glass crucible sample A3 was manufactured by the rotational mold method, but unlike Example 1, natural quartz powder having an average OH group concentration of 30 ppm and an average Al concentration of 15 ppm was used as the raw material of the first opaque quartz glass portion 11a. Natural quartz powder having an average OH group concentration of 15 ppm was used as a raw material for the second opaque quartz glass portion 11b. Synthetic quartz powder having an average OH group concentration of 90 ppm was used as a raw material for the transparent quartz glass layer 12.

The height h ₁ of the first opaque vitreous silica portion of the crucible sample A3 is 0.1 h 0 with respect to the height h ₀ of the entire _crucible, the height h ₂ of the second opaque vitreous silica portion of the entire crucible High It was 0.9h ₀ against is _{h 0.}

  When the specific gravity of the first and second opaque quartz glass portions 11a and 11b was determined from another sample manufactured under the same conditions as the crucible sample A3, the specific gravity of the first opaque quartz glass portion 11a was 1.60. The specific gravity of the second opaque quartz glass portion 11b was 1.87.

  Thereafter, the silicon single crystal ingot was pulled up using this quartz glass crucible A3, and the deformation of the crucible after use and the silicon single crystallization rate were determined. The results are shown in Table 1.

  As shown in Table 1, the quartz glass crucible sample A3 according to this example had almost no crucible sink after use. Moreover, the single crystallization rate of the silicon ingot pulled up using this quartz glass crucible sample A3 was 89%, and a good single crystallization rate was obtained.

(Comparative Example 1)
A quartz glass crucible sample B1 having the same size and shape as the quartz glass crucible sample A1 according to Example 1 was prepared. The quartz glass crucible sample B1 was manufactured by the rotational mold method. Unlike the first embodiment, the raw materials of the first opaque quartz glass portion 11a and the second opaque quartz glass portion 11b both have an average OH group concentration of 15 ppm. As a raw material for the transparent quartz glass layer 12, synthetic quartz powder having an average OH group concentration of 90 ppm was used. Thereafter, using this quartz glass crucible B1, the silicon single crystal ingot was pulled up, and the deformation of the crucible after use was confirmed and the silicon single crystallization rate was determined. The results are shown in Table 1.

  As shown in Table 1, the quartz glass crucible sample B1 according to Comparative Example 1 was submerged by about 38 mm after the completion of the pulling. Moreover, the single crystallization rate of the silicon ingot pulled up using this quartz glass crucible sample B1 was 61%, and the single crystallization rate was greatly reduced.

10 quartz glass crucible 10A crucible side wall 10B crucible bottom 10C crucible curved portion 11 opaque quartz glass layer 11a first opaque quartz glass portion 11b second opaque quartz glass portion 11c third opaque quartz glass portion 12 transparent quartz Glass layer 13a First quartz powder 13b Second quartz powder 13c Third quartz powder 14 Carbon mold 14a Vent hole 15 Arc electrode 20 Quartz glass crucible h ₀ Crucible total height h ₁ Crucible top height h ₂ Crucible bottom height H ₃ Height of crucible middle portion P ₀ Crucible upper end P ₁ Crucible intermediate position P ₂ Crucible lower end P ₁₁ Crucible first intermediate position P ₁₂ Crucible second intermediate position

Claims (3)

A method for producing a quartz glass crucible for pulling a silicon single crystal having a side wall, a curved portion and a bottom,
Filling the mold with quartz powder while rotating a hollow mold having an inner surface matched to the outer shape of the quartz glass crucible, and forming a layer of quartz powder along the inner surface of the mold;
A step of heating the quartz powder layer to melt the quartz powder to form an opaque quartz glass layer,
The step of forming the quartz powder layer includes:
Filling a predetermined position in the mold corresponding to the upper part of the crucible with a first quartz powder made of natural quartz powder having an OH group concentration of 30 ppm or more and 60 ppm or less ;
Natural stone produced by dehydrating the first quartz powder at a predetermined position in the mold corresponding to the lower part of the crucible and having an OH group concentration of 15 ppm or more lower than the first quartz powder and less than 30 ppm. Filling a second quartz powder made of English powder ;
Filling the entire inner surface of the mold covered with the first and second quartz powders with a third quartz powder made of synthetic quartz powder having an OH group concentration of 30 ppm or more ,
The step of forming the opaque quartz glass layer includes:
The first quartz powder is melted to form a first opaque quartz glass portion having a specific gravity of 1.4 to 1.8, and the second quartz powder is melted to have a specific gravity of 1.7 to 2. Forming a second opaque quartz glass portion that is less than or equal to 1 and has a greater specific gravity than the first opaque quartz glass portion;
The OH group concentration in the portion of the third quartz powder in contact with the first quartz powder is the same as the OH group concentration in the portion of the third quartz powder in contact with the second quartz powder. A method for producing a quartz glass crucible. The method for producing a quartz glass crucible according to claim 1 , wherein the Al concentration of at least the first quartz powder is 10 ppm or more. When the quartz powder layer is heated to melt the quartz powder, a transparent quartz glass layer is formed on the inner surface side of the crucible by degassing the quartz powder being heated from a vent hole provided in the mold. Process,
Method for manufacturing a silica glass crucible according to claim 1 or 2, characterized in that it comprises a step of forming the opaque quartz glass layer on the outer surface of the crucible under reduced pressure to weaken or stop for the degassing.

Images