Method for manufacturing quartz glass crucible and quartz glass crucible

Abstract

To provide a method for manufacturing a quartz glass crucible, capable of forming a non-air bubble layer on the inner surface of the quartz glass crucible.SOLUTION: A method for manufacturing a quartz glass crucible, manufactures a quartz glass crucible having a transparent layer (an inner layer) on the inner surface side and an opaque layer (an outer layer) on an outer surface side by supplying a raw material powder into a crucible molding die rotating at a first rotation frequency. The method concretely comprises: the molding steps (S1 and S2) of obtaining a raw material powder laminate by laminating the raw material powder in the crucible molding die so that a mouth side is thicker than the other areas; the steps of vitrifying the raw material powder laminate by heating; and the melting steps (S3 and S4) of gradually reducing the first rotation frequency capable of holding the shape of the raw material powder laminate up to a second rotation frequency allowing glass on the mouth side formed in a thick shape to flow in the gravity direction by viscous flow.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a quartz glass crucible used for pulling a silicon single crystal ingot, and to a quartz glass crucible manufactured by this manufacturing method. [Background technology]

[0002] The Czochralski method (CZ method) is widely used for growing silicon single crystals. In this method, a seed crystal is brought into contact with the surface of silicon melt formed in a quartz glass crucible (hereinafter sometimes simply referred to as "crucible"), and while the crucible is rotated, the seed crystal is pulled upward while rotating in the opposite direction, thereby growing a single crystal at the bottom of the seed crystal.

[0003] The quartz glass crucible used to contain this silicon melt generally has a two-layer structure, with a transparent layer made of high-purity synthetic quartz glass on the inner surface and an opaque layer made of natural quartz glass with excellent thermal properties on the outer surface.

[0004] The rotating mold method is known as one example of a method for manufacturing such a quartz glass crucible. In the rotating mold method, a raw material powder of natural quartz glass is first layered on the inner surface of a rotating crucible-forming mold, and then a raw material powder of synthetic quartz glass is layered on the surface of this raw material powder layer to form a raw material powder layer. Next, this raw material powder layer is heated and melted from the inside to the outside by arc discharge, and then cooled, resulting in a quartz glass crucible with a two-layer structure in which a synthetic quartz glass layer (transparent layer) is formed on the inner surface and a natural quartz glass layer (opaque layer) is formed on the outer surface (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-17246 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the above-mentioned Patent Document 1, it is described that a two-layered quartz glass crucible is produced in which a transparent layer that is essentially bubble-free and contains only very small bubbles is formed on the inner surface, and an opaque layer containing a large number of bubbles is formed on the outer surface.

[0007] However, while the manufacturing method described in Patent Document 1 can suppress bubbles that are trapped on the inner surface when the raw material powder is vitrified, it cannot form a completely bubble-free layer on the inner surface. That is, when the raw material is vitrified using an arc heat source, bubbles originating from the raw material particles and voids between the particles are trapped. Furthermore, bubbles near the inner surface of the quartz glass crucible can cause air pockets when pulling a silicon single crystal ingot.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a method for manufacturing a quartz glass crucible that forms a bubble-free layer of a predetermined thickness on the inner surface of the quartz glass crucible, and a quartz glass crucible manufactured by this manufacturing method. [Means for solving the problem]

[0009] The method for manufacturing a quartz glass crucible according to the present invention is a method for manufacturing a quartz glass crucible having a transparent layer (inner layer) on the inner surface side and an opaque layer (outer layer) on the outer surface side by supplying raw material powder into a crucible molding die rotating at a first rotation speed, and is characterized by comprising: a molding process for obtaining a raw material powder stack by stacking the raw material powder inside the crucible molding die so that the mouth side is thicker than other areas; and a melting process for vitrifying the raw material powder stack by heating, and then gradually reducing the first rotation speed, which is capable of maintaining the shape of the raw material powder stack, to a second rotation speed, which is capable of causing the glass on the mouth side, which has been formed into a thick shape, to flow in the direction of gravity by viscous flow.

[0010] In the transparent layer of the quartz glass crucible manufactured by the above manufacturing method, in the region ranging from the apex of the corner portion to the mouth of the straight portion, bubbles are crushed by the viscous flow of glass from the mouth side, and a first bubble-free layer is formed in a region 0.4 mm deep from the inner surface. Furthermore, in the transparent layer, bubbles are crushed by the viscous flow of a small amount of glass that wraps around from the straight portion in the silicon single crystal ingot projection region, and a second bubble-free layer is formed in a region 0.2 mm deep from the inner surface. Furthermore, in the transparent layer, in the region sandwiched between the first and second bubble-free layers, a third bubble-free layer is formed in a region 0.2 mm deep to 0.4 mm deep from the inner surface.

[0011] That is, according to the method for manufacturing a silica glass crucible of the present invention, it is possible to significantly reduce the bubbles remaining in the inner layer of the silica glass crucible.

[0012] Furthermore, in the manufacturing method of the silica glass crucible according to the present invention, in the molding process, it is desirable to spray and deposit 40% to 60% of the total weight of the inner layer raw material powder onto a first region that is in the range of the upper 50% from the mouth side of the straight portion of the raw material powder stack.

[0013] Furthermore, in the method for manufacturing a quartz glass crucible according to the present invention, it is desirable that in the molding process, 10% to 20% of the total weight of the inner layer raw material powder is sprayed and deposited onto a second region, which is the bottom inner surface of the raw material powder stack centered on the silicon single crystal ingot projection region.

[0014] Furthermore, in the method for manufacturing a silica glass crucible according to the present invention, it is desirable that the average particle size of the inner layer raw material powder deposited in the first region and the second region be 150 μm or less and be equal to or less than the average particle size of the inner layer raw material powder deposited in regions other than the first region and the second region.

[0015] The quartz glass crucible of the present invention has a transparent layer (inner layer) made of synthetic quartz glass on the inner surface side and an opaque layer (outer layer) made of natural quartz glass on the outer surface side, and is composed of a straight section, corner sections, and a bottom section in this order from the mouth side. The crucible also has a first bubble-free layer in a region from the apex of the corner section to the mouth of the straight section, extending to a depth of 0.4 mm from the inner surface, and further has a bubble diameter of 15 μm to 30 μm and a bubble density of 0.2 (pcs / mm 3 The silicon single crystal ingot projection area in the bottom portion has a second bubble-free layer in a depth region from the inner surface to 0.2 mm, and further, in a region from the inner surface to more than 0.2 mm, the bubble diameter is 15 μm or more and 30 μm or less and the bubble density is 0.2 (pcs / mm 3 ) or less. In addition, a third bubble-free layer is provided in a region sandwiched between the first bubble-free layer and the second bubble-free layer, in a depth region of 0.2 mm to 0.4 mm from the inner surface. [Effects of the Invention]

[0016] According to the method for manufacturing a silica glass crucible of the present invention, a bubble-free layer of a predetermined thickness can be formed on the inner surface of the silica glass crucible, thereby suppressing air pockets during pulling of silicon single crystals. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram showing an example of a silica glass crucible manufacturing apparatus used in the method for manufacturing a silica glass crucible according to the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of a silica glass crucible manufacturing apparatus used in the method for manufacturing a silica glass crucible according to the present invention. [Figure 3] FIG. 3 is a flowchart showing an example of a method for manufacturing a silica glass crucible according to the present invention. [Figure 4] FIG. 4 is a cross-sectional view of the raw material powder laminate. [Figure 5]FIG. 5 is a diagram showing the melting procedure in the method for producing a silica glass crucible according to the present invention. [Figure 6] FIG. 6 shows an example of a silica glass crucible manufactured by the method for manufacturing a silica glass crucible according to the present invention. [Figure 7] FIG. 7 is a diagram showing the results of comparing bubble densities. [Figure 8] FIG. 8 is a diagram showing the results of comparing bubble diameters. [Figure 9] FIG. 9 is a diagram showing the results of comparing the depth of the inner surface where bubbles exist. [Figure 10] FIG. 10 is a diagram showing the results of comparing the depth of the inner surface where bubbles exist. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the method for manufacturing a silica glass crucible and the silica glass crucible according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments.

[0019] <Crucible manufacturing equipment> 1 is a schematic diagram showing an example of a quartz glass crucible manufacturing apparatus used in the method for manufacturing a quartz glass crucible according to the present invention, and particularly shows the configuration for forming a raw material powder laminate. The quartz glass crucible manufacturing apparatus 1 of this embodiment uses a rotational mold method to manufacture, as an example, a quartz glass crucible with a two-layer structure, which has a transparent layer (inner layer) formed on the inner surface from high-purity synthetic quartz glass and an opaque layer (outer layer) formed on the outer surface from natural quartz glass with excellent thermal properties.

[0020] In Figure 1, the crucible forming mold 2 of the silica glass crucible manufacturing apparatus 1 is composed of an inner member 3, which is, for example, a mold having multiple through holes (not shown) drilled therein, and a holder 5 which holds the inner member 3 and has a ventilation section 4 on its outer periphery.

[0021] Furthermore, a rotating shaft 6 connected to a rotary drive source (not shown) is fixed to the lower part of the holder 5, and rotatably supports the crucible forming mold 2. The ventilation part 4 is connected to an exhaust port 8 provided in the center of the rotating shaft 6 via an opening 7 provided in the lower part of the holder 5, and this ventilation part 4 is connected to a pressure reducing mechanism 9. The silica glass crucible manufacturing apparatus 1 of this embodiment is configured so that the atmosphere inside the inner member 3 is sucked from the inner peripheral surface by operating the pressure reducing mechanism 9.

[0022] The silica glass crucible manufacturing apparatus 1 of this embodiment also includes a silica glass raw material powder supply mechanism 10 for supplying silica glass raw material powder into the inside of the inner member 3. This silica glass raw material powder supply mechanism 10 includes a nozzle 11 for spraying the silica glass raw material powder, a raw material cartridge 12 containing the silica glass raw material powder, and a raw material powder supply hose 13 connecting the nozzle 11 and the raw material cartridge 12. A carrier gas supply hose 14 for supplying a carrier gas is attached to the nozzle 11.

[0023] The nozzle 11, raw material powder supply hose 13, and carrier gas supply hose 14 are attached to a horizontally movable table 15, which is configured to be horizontally movable relative to the base 16, as shown by arrow X in Fig. 1. The nozzle 11 is also configured to be rotatable, as shown by arrow Z in Fig. 1, so that the spray angle relative to the inner member 3 can be adjusted.

[0024] Furthermore, the support portion 12a of the raw material cartridge 12 is attached to a vertically movable table 18. Furthermore, this vertically movable table 18 is configured to be vertically movable (movable in the axial direction of the inner member 3) relative to a base 17 fixed to the outer peripheral surface of the holder 5, as shown by arrow Y in FIG.

[0025] Therefore, the nozzle 11 is configured to be movable in the radial direction of the inner member 3 and in the axial direction (vertical direction) of the inner member 3, and is also configured to be rotatable so as to adjust the spray angle relative to the inner member 3.

[0026] Here, examples of silica glass raw material powders that can be accommodated in the raw material cartridge 12 include natural silica glass raw material powders and either purified or calcined powders of synthetic silica glass (synthetic silica glass raw material powders). The particle size of these silica glass raw material powders is preferably in the range of 5 μm to 500 μm. The same raw material powder may be used for the outer and inner layers of the silica glass crucible, but different silica glass raw material powders may be used for the inner and outer layers, for example, by forming the outer layer of the crucible using natural silica glass raw material powder and the inner layer of the crucible using synthetic silica glass raw material powder. Furthermore, silica glass raw material powders containing different elements may be used in each layer.

[0027] An organic binder may be added to the silica glass raw material powder. Various organic materials can be used as the organic binder. Examples include polyvinyl alcohol and methyl cellulose. Considering the sprayability and fixability, as well as the ease of handling and the prevention of carbon residues in the molten glass, it is also preferable to use ethanol or pure water.

[0028] The carrier gas supplied to the nozzle may be air, nitrogen, oxygen, argon, or other gas. By using a carrier gas, the silica glass raw material powder can be sprayed onto the inner member 3 or onto a layer of silica glass raw material powder that has already been sprayed. By spraying the silica glass raw material powder using a carrier gas, a denser raw material powder layer can be obtained. The flow rate of the supplied carrier gas is preferably 0.5 to 6.5 m / s.

[0029] Furthermore, by operating the pressure reducing mechanism 9, the atmosphere inside the inner member 3 is sucked out, and the pressure on the inner surface of the inner member 3 is set to 1 to 101.3 kPa. When the silica glass raw material powder is sprayed under such a pressure environment, a denser raw material powder laminate can be obtained.

[0030] In this embodiment, the raw material powder layer is formed by spraying silica glass raw material powder onto the inner surface of the inner member 3 of the rotating crucible forming mold 2 in a non-heated and non-melting environment.

[0031] 2 is a schematic diagram showing an example of a silica glass crucible manufacturing apparatus used in the method for manufacturing a silica glass crucible according to the present invention, and particularly shows the configuration of the heating and melting section. As shown in Fig. 2, the silica glass crucible manufacturing apparatus 1 of this embodiment is provided with a heating and melting section 20 that heats and melts a raw material powder stack formed by a silica glass raw material powder supply mechanism 10. This heating and melting section 20 is provided with an arc electrode 21 for arc discharge at its upper part facing the inner member 3, and a nozzle 22 that sprays a gas such as air, nitrogen, oxygen, or argon onto a predetermined portion of the crucible.

[0032] <Crucible manufacturing method> Next, a method for manufacturing a silica glass crucible according to this embodiment will be described in detail. Fig. 3 is a flowchart showing an example of the method for manufacturing a silica glass crucible according to this embodiment.

[0033] First, the rotary drive source (not shown) of the vitreous silica crucible manufacturing apparatus 1 is operated to rotate the rotary shaft 6 in the direction of the arrow (see FIGS. 1 and 2), thereby rotating the crucible forming mold 2 at a predetermined speed (first rotation speed). Further, the pressure reducing mechanism 9 is operated to evacuate the atmosphere inside the inner member 3, and the pressure on the inner surface of the inner member 3 is set to 1 to 101.3 kPa.

[0034] Then, in a non-heated and non-melting environment, a silica glass raw material powder is sprayed from the nozzle 11 onto the inner member 3 to form a raw material powder laminate. When spraying the silica glass raw material powder into the crucible forming mold 2 rotated as described above, for example, first, coarse-grained natural silica glass raw material powder is sprayed (step S1), and then fine-grained synthetic silica glass raw material powder is sprayed onto the surface (step S2).

[0035] Specifically, the natural silica glass raw material powder first sprayed into the crucible forming mold 2 is layered on the inner surface of the inner member 3 of the crucible forming mold 2 by the centrifugal force of the rotary drive source and the suction force of the pressure reducing mechanism 9. This forms a natural silica glass raw material powder layer (outer layer) (step S1).

[0036] Thereafter, the natural silica glass raw material powder is sprayed into the crucible forming mold 2, followed by the synthetic silica glass raw material powder, and this synthetic silica glass raw material powder is laminated on the inner surface of the natural silica glass raw material powder layer by the centrifugal force of the rotary drive source and the suction force of the pressure reducing mechanism 9 (step S2).

[0037] FIG. 4 is a cross-sectional view of a raw material powder laminate obtained by the manufacturing method of this embodiment, and particularly shows the shape of the synthetic silica glass raw material powder layer (inner layer) formed on the inner surface of the natural silica glass raw material powder layer (outer layer).

[0038] In this embodiment, when forming the synthetic silica glass raw material powder layer 30a (inner layer), for example, the synthetic silica glass raw material powder is layered so that the inner layer opening side is thicker (thicker) than other regions. Specifically, as shown in Fig. 4, 40% to 60% of the total weight of the synthetic silica glass raw material powder is allocated to the region of the inner surface of the natural silica glass raw material powder layer 30b (outer layer) in the range of the upper 50% (upper half of the inner surface) from the opening side of the straight part of the raw material powder layer. This layered region on the opening side of the inner layer is called the first thick region (see Fig. 4).

[0039] Furthermore, when forming the synthetic silica glass raw material powder layer 30a (inner layer), for example, the synthetic silica glass raw material powder is layered so that the inner surface on the bottom side of the inner layer also has a thickness (<thickness of the first thick region). Specifically, as shown in Fig. 4, 10% to 20% of the total weight of the synthetic silica glass raw material powder is allocated to the region on the bottom side inner surface of the natural silica glass raw material powder layer 30b (outer layer) centered on the silicon single crystal ingot projected region of the raw material powder layer. This layered region on the bottom side of the inner layer is called the second thick region (see Fig. 4). The reason for layering the synthetic silica glass raw material powder thickly on the bottom side of the inner layer will be described later.

[0040] In addition, in the area other than the first and second thick areas on the inner surface of the natural silica glass raw material powder layer 30b (outer layer), the remaining synthetic silica glass raw material powder other than the above-mentioned allocated amount is layered to a uniform thickness. This layered area is called the uniform thickness area (see Figure 4).

[0041] In this embodiment, the synthetic silica glass raw material powder allocated in the above proportions is sprayed onto each region (first thick region, second thick region, uniform thickness region) of the inner surface of the natural silica glass raw material powder layer 30b (outer layer) to deposit it. As a result, the synthetic silica glass raw material powder layer 30a (inner layer) is formed in the shape shown in Figure 4, and a raw material powder layer 30 having a predetermined thickness on the opening side and bottom side is obtained (step S2).

[0042] Thereafter, as shown in FIG. 2, in an atmospheric environment, while maintaining the reduced pressure by the pressure reducing mechanism 9 and the rotation speed (first rotation speed) of the crucible forming mold 2, electricity is passed through the arc electrode 21 to heat the raw material powder laminate 30 from the inside.

[0043] 5 is a diagram showing the melting procedure in the manufacturing method of this embodiment. In this embodiment, when current is applied to the arc electrode 21, the raw material powder layer 30 is heated and melted from the inside, and the surface layer is first vitrified (a synthetic silica glass layer 40a is formed). Thereafter, the pressure is reduced by the pressure reduction mechanism 9, the crucible forming mold 2 is rotated (at the first rotation speed), and the heating and melting by the arc electrode 21 are continued, and the raw material powder layer 30 is vitrified all the way to the outer surface (a natural silica glass layer 40b is formed). Note that the first rotation speed is a rotation speed (rpm) that can maintain the shape of the raw material powder layer 30 shown in FIG. 4, i.e., the shape of the synthetic silica glass raw material powder layer 30a (the first thickness region, the second thickness region, and the uniform thickness region), and it is desirable to continue this for 5 minutes or more from the start of application of current to the arc electrode 21. That is, the synthetic silica glass layer 40a is formed by the strong centrifugal force (the force that sticks to the sides) caused by the first rotation speed, without causing viscous flow due to gravity, while maintaining the shape of the synthetic silica glass raw material powder layer 30a (the first thickness region, the second thickness region and the uniform thickness region), as shown in FIG. 5(a) (step S3).

[0044] After vitrification as described above, while continuing the decompression by the decompression mechanism 9 and the heating and melting by the arc electrode 21, the rotation drive source (not shown) is controlled to gradually reduce the rotation speed (first rotation speed) of the crucible forming mold 2 to a second rotation speed (<first rotation speed) within a range of 40 rpm to 100 rpm with a drop of 10 rpm or more. The second rotation speed is preferably within a range of 40 rpm to 60 rpm and is continued for 5 minutes or more until the heating and melting is completed. Note that the second rotation speed is a rotation speed that can destroy the shape of the first thickness region shown in FIG. 5(a), i.e., the shape of the synthetic silica glass layer 40a (first thickness region, second thickness region, and uniform thickness region) due to the viscous flow of the glass. That is, the glass in the first thickness region of the synthetic silica glass layer 40a undergoes viscous flow in the direction of gravity due to the influence of the centrifugal force, which is weakened by the reduction in rotation speed from the first rotation speed to the second rotation speed (the influence of gravity, which is relatively increased), thereby forming a synthetic silica glass layer 40c in which the layer thickness of the straight portion is uniform, or a synthetic silica glass layer 40c in which the layer thickness of the straight portion becomes thinner toward the mouth side (see Figure 5(b)), and further, the shape of this synthetic silica glass layer 40c is maintained by rotating the crucible forming mold 2 at the second rotation speed (step S4).

[0045] Regarding the shape of the synthetic silica glass layer 40c formed as described above, a shape in which the layer thickness of the straight portion is uniform and a shape in which the layer thickness of the straight portion becomes thinner toward the mouth side are preferable, and a shape in which the layer thickness of the straight portion becomes thinner toward the mouth side is even more preferable. This is because if the layer thickness of the mouth side is thicker than the other layer thicknesses, the upper portion becomes heavier, increasing the risk of deformation such as collapse.

[0046] In the above-mentioned spraying step, 10% to 20% of the total weight of the synthetic silica glass raw material powder is sprayed onto the bottom inner surface of the natural silica glass raw material powder layer 30b (outer layer) centered on the silicon single crystal ingot projection area of ​​the raw material powder stack shown in Figure 4, to deposit the synthetic silica glass raw material powder.The reason for this is to prevent the bottom from becoming thinner than other parts, since after vitrification, the glass that flows downward due to viscous flow does not flow uniformly to the center of the bottom (because only a small amount of glass flows to the center of the bottom).In other words, by depositing a larger amount of synthetic silica glass raw material powder on the bottom in advance, the thickness is ensured to be the same as other parts.

[0047] 5(b), the synthetic silica glass layer 40c is formed, and then the heating and melting by the arc electrode 21 is terminated. As a result, a two-layered molded crucible 40 is obtained (step S4), which has a synthetic silica glass layer (transparent layer) 40c as an inner layer and a natural silica glass layer (opaque layer) 40b as an outer layer, as shown in FIG.

[0048] Finally, nitrogen gas or helium gas is sprayed onto the molded crucible 40 to cool it, and after cooling, the upper end of the molded crucible 40 is cut off to obtain a silica glass crucible (step S5).

[0049] 6 shows an example of a silica glass crucible manufactured by the method for manufacturing a silica glass crucible according to this embodiment. The silica glass crucible 50 according to this embodiment has a two-layer structure, with a transparent layer (inner layer) 50a made of high-purity synthetic silica glass on the inner surface and an opaque layer (outer layer) 50b made of natural silica glass with excellent thermal properties on the outer surface.

[0050] The quartz glass crucible 50 of this embodiment is configured in this order from the mouth side to the straight section, corner section, and bottom section, and further has an overlapping layer in the transparent layer (inner layer) 50a where the glass of the first thickness region and the glass of the second thickness region that have flowed down due to viscous flow overlap each other. This overlapping layer is formed within the range from the apex of the corner section to the silicon single crystal ingot projection area.

[0051] In the transparent layer (inner layer) 50a of the vitreous silica crucible 50 of this embodiment, in the region ranging from the apex of the corner portion to the mouth of the straight portion, bubbles are crushed by the viscous flow of glass from the mouth side, and a bubble-free layer (first bubble-free layer) is formed in the region to a depth of 0.4 mm from the inner surface. Furthermore, in the region to a depth of more than 0.4 mm from the inner surface, the bubble diameter is 15 μm or more and 30 μm or less and the bubble density is 0.2 (pcs / mm 3 ) is as follows.

[0052] In the transparent layer (inner layer) 50a of the vitreous silica crucible 50 of this embodiment, bubbles are crushed in the silicon single crystal ingot projection area by the viscous flow of a small amount of glass that flows around from the straight portion, and a bubble-free layer (second bubble-free layer) is formed in the area up to a depth of 0.2 mm from the inner surface. Furthermore, in the area exceeding 0.2 mm from the inner surface, the bubble diameter is 15 μm or more and 30 μm or less and the bubble density is 0.2 (pcs / mm 3 ) is as follows.

[0053] In addition, in the transparent layer (inner layer) 50a of the silica glass crucible 50 of this embodiment, the overlapping layer sandwiched between the first bubble-free layer and the second bubble-free layer has a bubble-free layer (third bubble-free layer) formed in a depth region of 0.2 mm to 0.4 mm from the inner surface.

[0054] In the manufacturing method of this embodiment, synthetic silica glass raw material powder is used as the silica glass raw material powder for the inner layer (inner layer raw material), but this is not limited to this. For example, the inner layer raw material deposited in the first and second thick-walled regions may be either synthetic silica glass raw material powder or natural silica glass raw material powder, but it is preferable to deposit synthetic silica glass raw material powder, which has a lower viscosity. Furthermore, it is preferable that the average particle size of the inner layer raw material deposited in the first and second thick-walled regions be 150 μm or less and be equal to or less than the average particle size of the inner layer raw material deposited in regions other than the above-mentioned respective thick-walled regions.

[0055] <Effects> As described above, in the method for manufacturing a silica glass crucible of this embodiment, a two-layered silica glass crucible 50 having a transparent layer (inner layer) on the inner surface side and an opaque layer (outer layer) on the outer surface side is manufactured by supplying raw material powder into the crucible molding die 2 rotating at a first rotation speed. Specifically, the raw material powder is layered in the crucible molding die 2 so that the neck side is thicker than other regions, thereby obtaining a raw material powder stack 30. Then, after vitrifying the raw material powder stack 30 by heating, the first rotation speed, at which the shape of the raw material powder stack 30 can be maintained, is gradually reduced to a second rotation speed, at which the thick-walled glass on the neck side can flow in the direction of gravity due to viscous flow, thereby manufacturing the silica glass crucible 50 shown in FIG. 6.

[0056] In the transparent layer 50a of the quartz glass crucible 50 manufactured as described above, in the region ranging from the apex of the corner portion to the mouth of the straight portion, bubbles are crushed by the viscous flow of glass from the mouth side, and a first bubble-free layer is formed in the region to a depth of 0.4 mm from the inner surface. Furthermore, in the region to a depth of more than 0.4 mm from the inner surface, the bubble diameter is 15 μm or more and 30 μm or less and the bubble density is 0.2 (pcs / mm 3 ) is as follows.

[0057] In the transparent layer 50a, bubbles are crushed in the silicon single crystal ingot projection area by the viscous flow of a small amount of glass that flows around from the straight portion, forming a second bubble-free layer in a region up to 0.2 mm deep from the inner surface. Furthermore, in the region beyond 0.2 mm deep from the inner surface, the bubble diameter is 15 μm to 30 μm and the bubble density is 0.2 pcs / mm3 or less. In the transparent layer 50a, a third bubble-free layer is formed in the overlapping layer sandwiched between the first and second bubble-free layers in a region 0.2 mm to 0.4 mm deep from the inner surface.

[0058] That is, according to the method for manufacturing a silica glass crucible of this embodiment, it is possible to significantly reduce the bubbles remaining in the inner layer of the manufactured silica glass crucible.

[0059] In addition, by covering the inner surface of the crucible with viscous, flowing glass during the heating and melting process, it is expected that the exposure of contamination (such as unburned carbon electrode dust) during the initial stage of arc melting will be reduced. [Example]

[0060] Next, examples of quartz glass crucibles manufactured by the method for manufacturing a quartz glass crucible according to the present invention will be described. Note that the present invention is not limited to the following examples.

[0061] Example 1 Using the quartz glass crucible manufacturing apparatus 1 shown in Figure 1, the crucible forming mold 2 was rotated at a rotation speed of 70 rpm while the pressure reducing mechanism 9 was operated to evacuate the atmosphere inside the inner member 3 and set the pressure on the inner surface of the inner member 3 to 80 kPa.

[0062] Thereafter, a total weight of 80 kg of natural silica glass raw material powder (average particle size 180 μm) was sprayed from the nozzle 11 onto the inner surface of the inner member 3. The natural silica glass raw material powder was layered by the centrifugal force of the rotary drive source and the suction force of the pressure reducing mechanism 9, thereby forming a natural silica glass raw material powder layer (outer layer) on the inner surface of the inner member 3 of the crucible forming mold 2. The flow rate of the carrier gas at this time was 2.8 m / s.

[0063] Then, under the same conditions as above, a total weight of 12 kg of synthetic silica glass raw material powder (average particle size 150 μm) was sprayed onto the inner surface of the layer of natural silica glass raw material powder (outer layer). At this time, 45% (5.4 kg) of the total weight of the synthetic silica glass raw material powder was sprayed onto the upper 50% region of the inner surface of the natural silica glass raw material powder layer on the mouth side (the upper half of the inner surface), to give a thickness to this region. Also, 15% (1.8 kg) of the total weight of the synthetic silica glass raw material powder was sprayed onto the region of the bottom side inner surface of the natural silica glass raw material powder layer centered on the silicon single crystal ingot projection region, to give a thickness to this region as well. The spraying procedure was as follows: first, 4.8 kg of synthetic quartz glass raw material powder, excluding the synthetic quartz glass raw material powder (45% + 15%), was sprayed uniformly onto the entire inner surface of the natural quartz glass raw material powder layer, and then 5.4 kg and 1.8 kg of synthetic quartz glass raw material powder were sprayed onto each of the above regions. As a result, a synthetic quartz glass raw material powder layer (inner layer) with the shape shown in Figure 4 was formed on the inner surface of the natural quartz glass raw material powder layer. The flow rate of the carrier gas at this time was also 2.8 m / s.

[0064] As a result, a raw material powder layer having a predetermined thickness at the mouth and bottom was obtained inside the crucible forming die 2.

[0065] Thereafter, the pressure was reduced by the pressure reducing mechanism 9 and the rotation speed of the crucible molding die 2 was maintained at 70 rpm. Under conditions where the melting temperature of SiO2 (estimated 2000°C) was obtained, the arc electrode 21 was energized to heat and vitrify the raw material powder stack from the inside for 10 minutes, thereby forming a synthetic silica glass layer (inner layer) and a natural silica glass layer (outer layer) having the shape shown in Figure 5(a).

[0066] After vitrification as described above, the rotation speed of the crucible forming mold 2 was reduced to 50 rpm while continuing the decompression by the decompression mechanism 9 and the heating and melting by the arc electrode 21, and a synthetic silica glass layer (inner layer) having the shape shown in Figure 5(b) was formed by viscous flow, and heating by the arc electrode 21 was terminated. The time from reducing the rotation speed of the crucible forming mold 2 to 50 rpm to terminating heating by the arc electrode 21 was set to 20 minutes. Finally, a predetermined cooling process and cutting process were performed, and the quartz glass crucible of Example 1 was obtained.

[0067] <Comparative Example 1> As in Example 1 above, using the quartz glass crucible manufacturing apparatus 1 shown in Figure 1, the crucible forming mold 2 was rotated at a rotation speed of 70 rpm while the pressure reducing mechanism 9 was operated to evacuate the atmosphere inside the inner member 3 and set the pressure on the inner surface of the inner member 3 to 80 kPa.

[0068] Thereafter, under the same conditions as in Example 1, a layer of natural silica glass raw material powder (outer layer) was formed on the inner surface of the inner member 3 of the crucible forming mold 2. Then, under the same conditions as above (rotation speed, pressure, carrier gas flow rate, etc.), a total weight of 12 kg of synthetic silica glass raw material powder (average particle size 150 μm) was sprayed onto the inner surface of the layer of natural silica glass raw material powder (outer layer). The synthetic silica glass raw material powder was layered by the centrifugal force of the rotation drive source and the suction force of the pressure reducing mechanism 9, thereby forming a layer of synthetic silica glass raw material powder (inner layer) on the inner surface of the layer of natural silica glass raw material powder.

[0069] As a result, a raw material powder laminate having a two-layer structure and a crucible shape as a whole was obtained inside the crucible molding die 2.

[0070] Thereafter, the pressure was reduced by the pressure reducing mechanism 9 and the rotation speed (70 rpm) of the crucible forming mold 2 was maintained, and current was passed through the arc electrode 21 to heat the raw material powder stack from the inside under conditions of obtaining the melting temperature of SiO (estimated 2000°C).The raw material powder stack was then melted and vitrified sequentially from the inside, and the specified cooling and cutting processes were performed to obtain the quartz glass crucible of Comparative Example 1.

[0071] <Result> 7 is a diagram showing the results of comparing bubble densities. The bubble densities (psc / mm ) of the quartz glass crucibles of Example 1 and Comparative Example 1 are 3 ) and the average bubble density of the quartz glass crucible of Comparative Example 1 was 0.263 psc / mm 3 The average bubble density of the quartz glass crucible of Example 1 was 0.089 psc / mm 3 From these results, it was confirmed that the quartz glass crucible manufactured by the method for manufacturing a quartz glass crucible according to the present invention can crush and remove bubbles that are contained inside when the raw material powder is vitrified by actively generating viscous flow of the glass.

[0072] 8 is a diagram showing the results of a comparison of bubble diameters. Comparing the average bubble diameter (μm) of the silica glass crucibles of Example 1 and Comparative Example 1, the average bubble diameter of the silica glass crucible of Comparative Example 1 was 30.07 μm, while the average bubble diameter of the silica glass crucible of Example 1 was 24.55 μm. From these results, it was also confirmed that the average bubble diameter was reduced for the silica glass crucible manufactured by the method for manufacturing a silica glass crucible according to the present invention.

[0073] 9 and 10 are diagrams showing the results of comparing the depth of the inner surface where bubbles exist. No bubble-free layer was observed on the inner surface of the quartz glass crucible of Comparative Example 1, but a bubble-free layer of a uniform thickness (depth of about 0.4 mm) was observed on the straight part of the quartz glass crucible of Example 1, and a bubble-free layer of a uniform thickness (depth of about 0.2 mm) was observed on the bottom of the quartz glass crucible of Example 1.

[0074] That is, the silica glass crucible of Example 1 achieved a reduction in bubble density of approximately 40 to 70% and a reduction in bubble diameter of approximately 10 to 20% compared to the silica glass crucible of Comparative Example 1, and furthermore was able to form a bubble-free surface layer of approximately 0.2 to 0.4 mm. [Explanation of symbols]

[0075] 1. Quartz glass crucible manufacturing equipment 2 Crucible mold 3 Inner member 4 Ventilation section 5 Holder 6 Rotation Axis 7 Openings 8 exhaust port 9 Pressure reduction mechanism 10. Quartz glass raw powder supply mechanism 11,22 nozzle 12 Raw material cartridge 12a Support part 13 Raw powder supply hose 14 Carrier gas supply hose 15 Horizontal moving platform 16,17 Base 18 Vertical moving platform 20 Heat melting section 21 Arc electrode 30 Raw material powder laminate 30a Synthetic quartz glass raw material powder layer 30b Natural silica glass raw material powder layer 30 Raw material powder laminate 40 Crucible molding 40a Synthetic silica glass layer 40b Natural silica glass layer 40c synthetic silica glass layer 50 Quartz glass crucible 50a transparent layer (inner layer) 50b Opaque layer (outer layer)

Claims

1. A method for manufacturing a quartz glass crucible, which manufactures a quartz glass crucible having a transparent layer (inner layer) on the inner surface side and an opaque layer (outer layer) on the outer surface side, by supplying raw material powder into a crucible molding die rotating at a first rotation speed, comprising: a molding step of stacking the raw material powder in the crucible molding die so that the mouth side is thicker than other regions to obtain a raw material powder laminate; a melting step in which, after vitrifying the raw material powder stack by heating, the first rotation speed at which the shape of the raw material powder stack can be maintained is gradually reduced to a second rotation speed at which the glass on the mouth side, which has been formed into a thick shape, can flow in the direction of gravity by viscous flow; Including, A method for manufacturing a quartz glass crucible.

2. In the molding step, 40% to 60% of the total weight of the inner layer raw material powder is sprayed and deposited on a first region that is in a range from the mouth side of the straight portion of the raw material powder stack to the upper 50%.

2. The method for manufacturing a quartz glass crucible according to claim 1.

3. In the molding step, 10% to 20% of the total weight of the inner layer raw material powder is sprayed and deposited on a second region, which is the bottom inner surface of the raw material powder stack centered on the silicon single crystal ingot projection region.

3. The method for manufacturing a quartz glass crucible according to claim 2.

4. the average particle size of the inner layer raw material powder deposited in the first region and the second region is 150 μm or less and is equal to or less than the average particle size of the inner layer raw material powder deposited in regions other than the first region and the second region; 4. The method for manufacturing a quartz glass crucible according to claim 3.

5. A quartz glass crucible having a transparent layer (inner layer) formed of synthetic quartz glass on the inner surface side and an opaque layer (outer layer) formed of natural quartz glass on the outer surface side, From the mouth side, it is composed of a straight section, a corner section and a bottom section. In the range from the apex of the corner portion to the mouth of the straight portion, a first bubble-free layer is provided in a region up to 0.4 mm deep from the inner surface, and further, in a region more than 0.4 mm deep from the inner surface, a bubble diameter is 15 μm or more and 30 μm or less and a bubble density is 0.2 (pcs / mm 3 ) has the following non-bubble-free layers: The silicon single crystal ingot projection area in the bottom has a second bubble-free layer in a depth region from the inner surface to 0.2 mm, and further has a bubble diameter of 15 μm or more and 30 μm or less and a bubble density of 0.2 (pcs / mm 3 ) has the following non-bubble-free layers: a third bubble-free layer is provided in a region sandwiched between the first bubble-free layer and the second bubble-free layer at a depth of 0.2 mm to 0.4 mm from the inner surface; A quartz glass crucible characterized by:

Images