Quartz glass crucible for pulling up monocrystalline silicon ingot

Abstract

The present invention is a quartz glass crucible for pulling up a monocrystalline silicon ingot, the quartz glass crucible having a crucible shape comprising a straight torso section, a rounded section, and a bottom section and having an outer layer formed from an opaque quartz glass containing air bubbles, and an inner layer formed from a transparent quartz glass and having a wall thickness of 1.5 mm or greater. At a position 1 mm from an inner surface of the quartz glass crucible, the concentration of Na is less than 5 mass ppb, the concentration of K is less than 5 mass ppb, and the concentration of Li is less than 100 mass ppb. Further, in the wall thickness direction of the bottom section and the rounded section, the average concentration of Na is less than 10 mass ppb, the average concentration of K is less than 50 mass ppb, and the average concentration of Li is less than 180 mass ppb in the outer layer. Through such a configuration, a quartz glass crucible for pulling up a monocrystalline ingot is provided by which the occurrence of pinholes in the pulled up monocrystalline silicon ingot can be suppressed.

Description

Quartz glass crucible for pulling single crystal silicon ingots

[0001] The present invention relates to a quartz glass crucible for pulling single crystal silicon ingots.

[0002] The so-called Czochralski method (CZ method) is widely used in the production of single crystal silicon (single crystal silicon ingots). In this CZ method, a silicon melt is placed in a quartz glass crucible, a seed crystal is brought into contact with the surface of the silicon melt, and the quartz glass crucible is rotated while the seed crystal is pulled upward while rotating in the opposite direction, thereby growing single crystal silicon at the bottom end of the seed crystal.

[0003] Single crystal silicon ingots manufactured using quartz glass crucibles can contain bubbles called pinholes, which are several microns to several millimeters in size. Silicon wafers containing these bubbles can be detected by visual inspection or infrared inspection, but even a single pinhole can reduce yield.

[0004] The sources of bubbles that cause pinholes in the single crystal silicon ingot being pulled include gas inside the pulling device, bubbles contained on the inner surface of the quartz glass crucible, and gas generated by the reaction between the silicon melt and the quartz glass crucible, and measures have been taken to deal with these bubbles (for example, Patent Document 1).

[0005] International Publication No. 2013 / 140706

[0006] As described above, various measures have been taken to prevent bubbles that can cause pinholes in pulled single crystal silicon ingots. However, pinholes that cannot be explained by these measures alone sometimes occur, and there has been a demand for a quartz glass crucible that reduces the number of pinholes in the pulled single crystal silicon ingots.

[0007] The present invention has been made to solve the above-mentioned problems, and has an object to provide a quartz glass crucible for pulling single crystal silicon ingots that can suppress pinholes in the pulled single crystal silicon ingots.

[0008] The present invention has been made to solve the above-mentioned problems, and provides a quartz glass crucible for pulling single crystal silicon ingots, which has a crucible shape consisting of a straight body portion, a curved portion, and a bottom portion, and which has an outer layer made of opaque quartz glass containing bubbles, and an inner layer made of transparent quartz glass and having a thickness of 1.5 mm or more, wherein the concentrations of Na, K, and Li in the inner layer at a position 1 mm from the inner surface of the quartz glass crucible are less than 5 ppb by mass for Na, less than 5 ppb by mass for K, and less than 100 ppb by mass for Li, and the average concentrations of Na, K, and Li in the thickness direction of the outer layer at the curved portion and the bottom portion are less than 10 ppb by mass for Na, less than 50 ppb by mass for K, and less than 180 ppb by mass for Li.

[0009] Such a quartz glass crucible can promote crystallization in the depth direction in the brown ring that forms on the inner surface of the quartz glass crucible during pulling of a single crystal silicon ingot, thereby suppressing the release of bubbles that form inside the brown ring and preventing pinholes from forming in the pulled single crystal silicon ingot.

[0010] In this case, it is preferable that the concentrations of Na, K, and Li in the inner layer at a position 1 mm from the inner surface of the quartz glass crucible are less than 5 mass ppb for Na, less than 5 mass ppb for K, and less than 50 mass ppb for Li, and that the average concentrations of Na, K, and Li in the thickness direction of the outer layer at the R portion and the bottom are less than 5 mass ppb for Na, less than 50 mass ppb for K, and less than 100 mass ppb for Li.

[0011] By satisfying the concentrations of these impurity elements (note that in the following description, Na, K, and Li may be collectively referred to as impurity elements) in the inner and outer layers of the quartz glass crucible, it is possible to more effectively suppress pinholes in the pulled single crystal silicon ingot.

[0012] Furthermore, it is preferable that the average concentrations of Na, K, and Li in the thickness direction of the straight body portion of the outer layer satisfy at least one of 10 mass ppb or more for Na, 50 mass ppb or more for K, and 180 mass ppb or more for Li.

[0013] By satisfying the impurity concentration in the body portion of the outer layer, it is possible to prevent the quartz glass crucible from collapsing or sinking when heated at high temperatures, rather than by making the entire crucible highly pure.

[0014] The quartz glass crucible may have an outer diameter of 800 mm or more.

[0015] In this way, the present invention can be suitably applied to a quartz glass crucible having a large diameter of 800 mm or more.

[0016] The quartz glass crucible holds a silicon melt therein, and after a single crystal silicon ingot is pulled up from the silicon melt, a brown ring is formed on the inner surface of the quartz glass crucible, and the density of bubbles having a diameter of 3.0 μm or more in the inner layer within the inner region of the brown ring is 4.0 bubbles / mm ２ It is preferable that the above is true.

[0017] When such a brown ring is formed on the inner surface of a quartz glass crucible after pulling a single crystal silicon ingot, pinholes in the pulled single crystal silicon ingot can be more effectively suppressed.

[0018] Furthermore, the quartz glass crucible holds a silicon melt therein, and after a single crystal silicon ingot is pulled up from the silicon melt, a brown ring is formed on the inner surface of the quartz glass crucible, where a bisecting line of the brown ring running in the circumferential direction of the quartz glass crucible is defined as an outer diameter reference line of the brown ring, and the length of the outer diameter reference line is in the range of 10 mm to 13 mm. When the length of the outer diameter reference line of the brown ring is x [mm], the top of the brown ring at the end of the outer diameter reference line is set to a reference height of 0 [μm], and the convex height, which is the height of the top of the inner region of the brown ring on the outer diameter reference line, is set to y [μm], the brown ring having a length of the outer diameter reference line in the range of 10 mm to 13 mm satisfies the following formula (1): y≧10x−70 (1)

[0019] Even if such brown rings are formed, pinholes in the pulled single crystal silicon ingot can be more effectively suppressed.

[0020] The quartz glass crucible of the present invention can promote crystallization of the brown ring in the depth direction during pulling of the single crystal silicon ingot, thereby suppressing the release of bubbles generated inside the brown ring and preventing pinholes from forming in the pulled single crystal silicon ingot.

[0021] FIG. 1 is a schematic cross-sectional view showing parts of a typical quartz glass crucible. FIG. 2 is a photograph of a brown ring that occurs on the inner surface of a quartz glass crucible. FIG. 3 is a graph showing the diameter of bubbles inside a brown ring. FIG. 4 is a graph showing the relationship between the Li concentration in the inner layer of a quartz glass crucible and the bubble density inside a brown ring. FIG. 5 is a graph showing the correlation between the Na concentration in the outer layer and the Na concentration in the inner layer of a quartz glass crucible. FIG. 6 is a graph showing the correlation between the K concentration in the outer layer and the K concentration in the inner layer of a quartz glass crucible. FIG. 7 is a graph showing the correlation between the Li concentration in the outer layer and the Li concentration in the inner layer of a quartz glass crucible. FIG. 8 is a graph showing the uneven shape of the brown ring in Experimental Examples 1 to 4. FIG. 9 is a schematic diagram explaining a brown ring.

[0022] As mentioned above, various measures have been taken to deal with bubbles, which are the source of pinholes. However, pinholes can occur that cannot be explained by these measures alone, and the present inventors have attempted to clarify this.

[0023] As a result, after the single crystal silicon ingot is pulled up, a brown ring called a brown ring appears on the inner surface of the quartz glass crucible. Upon detailed investigation of this brown ring, it was discovered that bubbles with diameters of several μm to several tens of μm exist inside the brown ring, and it was predicted that these bubbles became pinholes when exposed to the silicon melt.

[0024] Furthermore, as described above, bubbles ranging in size from several μm to several tens of μm exist inside the brown ring, but according to research by the present inventors, it has been found that by reducing the concentrations of Na, K, and Li in the inner layer of the quartz glass crucible, the diameter of the bubbles inside the brown ring can be reduced, and crystallization in the depth direction inside the brown ring can be promoted, thereby reducing melting damage to the silicon melt. In other words, it is possible to prevent the bubbles inside the brown ring from opening into the silicon melt, thereby reducing the number of bubbles that are incorporated into the single crystal silicon ingot and reducing pinhole defects in silicon wafers.

[0025] The present invention will be described in more detail below. The present invention relates to a quartz glass crucible for pulling single-crystal silicon ingots, which has a crucible shape consisting of a body portion, a curved portion, and a bottom portion, an outer layer made of opaque quartz glass containing bubbles, and an inner layer made of transparent quartz glass and having a thickness of 1.5 mm or more, wherein the concentrations of Na, K, and Li in the inner layer at a position 1 mm from the inner surface of the quartz glass crucible are less than 5 ppb by mass for Na, less than 5 ppb by mass for K, and less than 100 ppb by mass for Li, and the average concentrations of Na, K, and Li in the thickness direction of the outer layer in the curved portion and the bottom portion are less than 10 ppb by mass for Na, less than 50 ppb by mass for K, and less than 180 ppb by mass for Li. These requirements must be met before pulling a single-crystal silicon ingot.

[0026] First, the components of the silica glass crucible of the present invention will be described with reference to Figure 1. The silica glass crucible 10 of Figure 1 has an outer layer 21 made of opaque silica glass containing bubbles, and an inner layer 22 made of transparent silica glass. As shown in Figure 1, the crucible shape of the silica glass crucible 10 typically consists of a bottom portion 12, a rounded portion 13, and a straight body portion 14. The bottom portion 12 is centered at the bottom center 11, and the bottom portion 12 is sometimes called the large rounded portion, and the rounded portion 13 is sometimes called the small rounded portion.

[0027] As described above, the silica glass crucible 10 of the present invention has an inner layer 22 having a thickness of 1.5 mm or more, and the concentrations of Na, K, and Li at a position 1 mm from the inner surface of the quartz glass crucible are less than 5 ppb by mass for Na, less than 5 ppb by mass for K, and less than 100 ppb by mass for Li. By providing the inner layer 22 of the quartz glass crucible 10 with such high purity and specified concentrations of Na, K, and Li, crystallization of the brown ring in the depth direction during pulling of the single-crystal silicon ingot can be promoted. This can suppress the release of bubbles that form inside the brown ring. Furthermore, the silica glass crucible 10 of the present invention has an outer layer 21 in which the average concentrations of Na, K, and Li in the thickness direction in the rounded portion 13 and bottom portion 12 are less than 10 ppb by mass for Na, less than 50 ppb by mass for K, and less than 180 ppb by mass for Li. By satisfying the element concentrations in the rounded portion 13 and bottom portion 12 of the outer layer 21, the diffusion of the impurity elements to the inner surface of the crucible can be suppressed, and the inner layer 22 of the crucible can be maintained at a high purity.

[0028] The above impurity concentrations are preferably further increased as follows. That is, in the inner layer 22, the concentrations of Na, K, and Li at a position 1 mm from the inner surface of the quartz glass crucible are preferably less than 5 ppb by mass for Na, less than 5 ppb by mass for K, and less than 50 ppb by mass for Li. In addition, in the outer layer 21, the average concentrations of Na, K, and Li in the thickness direction in the R portion 13 and the bottom portion 12 are preferably less than 5 ppb by mass for Na, less than 50 ppb by mass for K, and less than 100 ppb by mass for Li. By satisfying these impurity element concentrations, pinholes in the pulled single crystal silicon ingot can be more effectively suppressed.

[0029] The impurity element concentration in each layer of the silica glass crucible of the present invention can be measured by preparing a sample from the silica glass crucible 10 and using ICP-MS (inductively coupled plasma mass spectrometry) or the like. The measurement points are at least one each in the body portion 14, the rounded portion 13, and the bottom portion 12 of both the inner layer 22 and the outer layer 21. Two or more measurement points may be taken for each portion, and the average value may be calculated.

[0030] The diffusion of each impurity element between the outer layer 21 and the inner layer 22 will be described with reference to Figures 5 to 7. Figures 5 to 7 respectively show the correlation between the concentration of Na, K, and Li in the outer layer 21 of the quartz glass crucible (average concentration in the crucible thickness direction) and the concentration in the inner layer 22 (concentration at a position 1 mm from the inner surface of the quartz glass crucible 10). The correlations shown in these figures were measured by preparing a quartz glass crucible 10 with an outer diameter of 32 inches (800 mm) and preparing samples from the quartz glass crucible. As can be seen from these figures, when Na is less than 10 mass ppb in the outer layer 21, it can be less than 5 mass ppb in the inner layer 22; when K is less than 50 mass ppb in the outer layer 21, it can be less than 5 mass ppb in the inner layer 22; and when Li is less than 180 mass ppb in the outer layer 21, it can be less than 100 mass ppb in the inner layer 22.

[0031] On the other hand, in the silica glass crucible 10 of the present invention, the average concentrations of Na, K, and Li in the thickness direction in the body portion 14 of the outer layer 21 preferably satisfy at least one of the following: 10 mass ppb or more for Na, 50 mass ppb or more for K, and 180 mass ppb or more for Li. In the body portion 14, the lower limits of the impurity element concentrations are preferably set as described above in order to prevent the silica glass crucible 10 from collapsing or sinking inward during high-temperature heating. However, since the inner layer 22 of the silica glass crucible 10 must satisfy the above-mentioned high purity requirement, it is best not to make the impurity element concentrations in the body portion 14 of the outer layer 21 too high to avoid contamination by diffusion.

[0032] The reason for separating the outer layer 21 into the bottom portion 12 to the R portion 13 and the body portion 14 is that the bottom portion 12 to the R portion 13 of the quartz glass crucible has a longer contact time with the silicon melt, and therefore the diameter of the brown ring is more likely to expand than the body portion 14. Therefore, by reducing the Na, K, and Li concentrations, particularly on the inner surface of the bottom portion 12 to the R portion 13, and promoting crystallization of the brown ring in the depth direction, it is possible to suppress the release of bubbles that occur inside the brown ring. Furthermore, by reducing the Na, K, and Li concentrations in the outer layer 21 only of the bottom portion 12 to the R portion 13, it is possible to suppress deformation of the body portion 14 during use of the quartz glass crucible 10 while suppressing pinhole defects.

[0033] Furthermore, the present invention can be suitably applied to quartz glass crucibles 10 having an outer diameter of 800 mm or more. Such quartz glass crucibles 10 can pull single crystal silicon ingots with larger diameters, and can pull single crystal silicon ingots with such large diameters with pinholes suppressed. The pinhole standards for single crystal silicon wafers with a diameter of 12 inches (300 mm) or more are strict, and the quality requirements for quartz glass crucibles with an outer diameter of 800 mm or more used therefor are also high. In such cases, both the single crystal silicon wafer and the quartz glass crucible are large, and there is a high probability that bubbles will be trapped on the underside of the single crystal silicon ingot being pulled, making it necessary to apply the present technology.

[0034] The relationship between the state of the brown ring on the surface of the inner layer of the quartz glass crucible and the concentration of impurity elements in the inner layer of the quartz glass crucible will be described below.

[0035] As described above, brown rings called "brown rings" are formed on the inner surface of a quartz glass crucible upon contact with molten silicon, and it has been found that bubbles of several μm to several tens of μm in size are found inside these rings. When comparing cases where the Na and K concentrations in the inner layer of the quartz glass crucible are less than 5 ppb by mass with cases where they are 50 ppb by mass or more, it has been found that the bubble diameter is smaller when the Na and K concentrations are less than 5 ppb by mass.

[0036] Figure 2 shows a photograph of brown rings that form on the inner surface of a quartz glass crucible. Figure 2(a) shows the state of the inner surface of a quartz glass crucible. The circular objects in Figure 2(a) are brown rings. Brown rings can be isolated, but as shown in Figure 2(a), multiple rings can also be fused together. Figure 2(b) is an enlarged view of a portion of Figure 2(a). As shown in Figure 2(b), bubbles ranging in size from several μm to several tens of μm can be seen inside the brown rings.

[0037] Figure 3 shows the results of an investigation into the diameter of bubbles inside the brown ring shown in Figure 2(b). Figure 3 compares the impurity element concentrations in the inner layer of a quartz glass crucible, where both Na and K are less than 5 ppb by mass and the Li concentration is less than 50 ppb by mass, with those where both Na and K are greater than 50 ppb by mass and the Li concentration is less than 50 ppb by mass. As can be seen from this figure, when the Li concentration is commonly less than 50 ppb by mass, the bubble diameter becomes smaller when both the Na concentration and the K concentration are less than 5 ppb by mass.

[0038] 4, when comparing the Li concentration of the inner layer of the quartz glass crucible at 180 mass ppb or more with that at less than 100 mass ppb, it was found that the bubble density near the center of the brown ring was higher when the Li concentration was less than 100 mass ppb. Here, a high bubble density means that bubbles remain without being released, and in this case, the bubbles are present at a deep position and are not incorporated into the silicon melt.

[0039] In addition to this finding, it has been found that when the Na and K concentrations in the inner layer of the quartz glass crucible are each less than 5 ppb by mass and the Li concentration is less than 100 ppb by mass, there are few pinholes having a size of several μm to several tens of μm when a single crystal silicon ingot is pulled up.

[0040] From these findings, it is presumed that reducing the concentrations of Na and K in the inner layer of the quartz glass crucible reduces the bubble diameter, and reducing the Li concentration suppresses the release of bubbles into the silicon melt, thereby improving the occurrence of pinholes in the pulled single crystal silicon ingot. To summarize the effects of the impurity element specifications of the present invention, the advantage of using low concentrations of Na and K is that reducing the concentrations of Na and K suppresses the size of bubbles in the brown ring. The advantage of using low concentrations of Li is that the brown ring crystallizes rapidly in the depth direction, allowing bubbles generated by crystallization to reside at relatively deep positions, and that the crystallization slows the melting speed, preventing bubbles from releasing into the silicon melt.

[0041] As described above, since the brown ring is caused by crystallization of the inner surface of the quartz glass crucible, it was presumed that the degree of crystallization varies depending on the Na, K, and Li concentrations of the inner surface of the quartz glass crucible, and that the lower the Na, K, and Li concentrations, the more the crystallization inside the brown ring, that is, the crystallization in the depth direction from the inner surface of the quartz glass crucible, progresses, and the more the melting damage to the silicon melt is reduced. Therefore, as shown in the following experimental example, the uneven shapes of brown rings with a diameter of 12 mm that occurred in quartz glass crucibles with different Na, K, and Li concentrations on the inner surface were measured with a surface roughness measuring device.

[0042] [Experimental Examples 1 to 4] Four types of quartz glass crucibles were prepared, each with different concentrations of Na, K, and Li in the inner layer. The impurity element concentrations at a depth of 1 mm from the inner surface of each quartz glass crucible were as follows: Experimental Example 1: Na: 3 mass ppb, K: 1 mass ppb, Li: 200 mass ppb Experimental Example 2: Na: 2 mass ppb, K: 3 mass ppb, Li: 200 mass ppb Experimental Example 3: Na: 3 mass ppb, K: 2 mass ppb, Li: 70 mass ppb Experimental Example 4: Na: 4 mass ppb, K: 1 mass ppb, Li: 70 mass ppb

[0043] The uneven shape of the brown ring with a diameter of 12 mm that occurred in these quartz glass crucibles with different concentrations of Na, K, and Li in the inner layer was measured using a surface roughness measuring device, and the results are shown in Figure 8.

[0044] As can be seen from Figure 8, when the Na concentration and K concentration of the inner layer of the quartz glass crucible are each less than 5 mass ppb and the Li concentration is less than 100 mass ppb (Experimental Examples 3 and 4), the convexity is about 10 to 20 μm higher than when the Na concentration and K concentration are each less than 5 mass ppb and the Li concentration is 100 mass ppb or more (Experimental Examples 1 and 2). In other words, when the Na concentration and K concentration are each less than 5 mass ppb and the Li concentration is less than 100 mass ppb, crystallization inside the brown ring is promoted and damage to the silicon melt is suppressed. It is believed that this difference in damage of 10 to 20 μm affects the opening of bubbles several μm to several tens of μm in size.

[0045] Furthermore, while a high alkali metal content generally promotes the crystallization of silica glass, the opposite phenomenon occurs inside the brown ring that is formed by the reaction between silica glass with a low metal concentration and silicon melt. From this, it is presumed that by setting the impurity element concentrations in the inner layer of the silica glass crucible to less than 5 mass ppb for Na, less than 5 mass ppb for K, and less than 100 mass ppb for Li, crystallization inside the brown ring is promoted and the exposure of bubbles inside the brown ring can be suppressed.

[0046] As described above, the quartz glass crucible satisfying the impurity element concentration specification of the present invention can promote the crystallization of the brown ring in the depth direction during the pulling of the single crystal silicon ingot. As a result, the quartz glass crucible of the present invention can be specified as follows based on the brown ring after the pulling of the single crystal silicon ingot. That is, the quartz glass crucible of the present invention holds a silicon melt therein, and after the single crystal silicon ingot is pulled from the silicon melt, a brown ring is formed on the inner surface of the quartz glass crucible, and the density of bubbles having a diameter of 3.0 μm or more in the inner layer within the inner region of the brown ring is 4.0 bubbles / mm ２ It is preferable that the above-mentioned brown ring is formed on the inner surface of the quartz glass crucible after the single crystal silicon ingot is pulled up, and this can more effectively suppress pinholes in the pulled single crystal silicon ingot.

[0047] It is becoming common to use a multi-pulling method to pull multiple single crystal silicon ingots from a single quartz glass crucible, but the specification based on the bubbles in the brown ring after pulling in the quartz glass crucible of the present invention applies to the period after the first single crystal silicon ingot is pulled. In this case, the usage time of the quartz glass crucible is approximately several tens of hours to 100 hours. This is because when multiple ingots are pulled, the usage time becomes longer and the brown ring that has formed may disappear.

[0048] Furthermore, the quartz glass crucible of the present invention has a brown ring on its inner surface after holding a silicon melt therein and pulling up a single crystal silicon ingot from the silicon melt. In this case, it is preferable that the height of the convex portion of the brown ring satisfy the following condition. That is, when the bisecting line of the brown ring running in the circumferential direction of the quartz glass crucible is defined as the outer diameter reference line of the brown ring, it is preferable that the length of the outer diameter reference line is 10 mm or more and 13 mm or less. Furthermore, when the length of the outer diameter reference line of the brown ring is x [mm], the top of the brown ring at the end of the outer diameter reference line is set to a reference height of 0 [μm], and the convex portion height, which is the height of the top of the inner region of the brown ring on the outer diameter reference line, is y [μm], it is preferable that the brown ring having the length of the outer diameter reference line in the range of 10 mm or more and 13 mm or less satisfies the following formula (1): y≧10x−70 (1)

[0049] Even if such brown rings are formed, pinholes in the pulled single crystal silicon ingot can be more effectively suppressed.

[0050] A more detailed explanation is as follows. Figure 9 shows a schematic diagram of a brown ring. The density of bubbles inside the brown ring, the outer diameter, and the reference height in the present invention are for a single brown ring as shown in Figure 9. A combination of multiple brown rings is not used in the calculation of these values.

[0051] Figure 9 illustrates the direction from the bottom side of the quartz glass crucible to the end face side of the crucible (the upper end side of the straight body portion), i.e., the vertical direction. The bisecting line running in the circumferential direction of the crucible is a line that divides the brown ring in half on a plane perpendicular to the vertical direction of the quartz glass crucible. The outer diameter reference line refers to the line segment between two points where the bisecting line intersects with the outer circumference of the brown ring. In the present invention, it is preferable that after the first single crystal silicon ingot is pulled, the length of the outer diameter reference line is in the range of 10 mm to 13 mm. The length of the outer diameter reference line can also be said to be the outer diameter of the brown ring, but it is defined in this way because the brown ring is not necessarily perfectly circular.

[0052] The uppermost point of the brown ring at the end of the outer diameter reference line is the higher of the two points. This will be explained with reference to FIG. 8. FIG. 8 shows the results of measuring the height of the brown ring in FIG. 9 on the inner surface of a quartz glass crucible using a surface roughness measuring instrument. The uppermost point at the end of the outer diameter reference line shown on the right side of FIG. 8 is set to the reference height 0 [μm]. The convex height, which is the height of the uppermost point on the outer diameter reference line in the inner region of the brown ring, is set to y [μm]. In Experimental Example 4 of FIG. 8, the length of the outer diameter reference line is approximately 12.2 mm. The position of the reference height 0 [μm] is approximately 15.5 mm on the horizontal axis in the figure. To set this position as the reference height 0 [μm], the height of the uppermost point on the outer diameter reference line at a position approximately 10 mm on the horizontal axis in the figure is approximately 54 μm. That is, y = 54 and x = 12.2, which satisfies Equation (1).

[0053] The reason for the convex shape of the brown ring is presumably that crystallization proceeds simultaneously with the occurrence of dissolution damage to the silicon melt, and the crystallized portion is prevented from dissolution, resulting in the convex shape. In other words, the portion corresponding to the left side of the maximum value of the curve for each experimental example in Figure 8 is presumably dissolved by the flow of silicon melt, and as a result, most of the brown portion (crystallized portion) disappeared.

[0054] [Method for Manufacturing a Quartz Glass Crucible] The quartz glass crucible of the present invention can be manufactured by known methods, except for controlling the concentrations of impurity elements in the inner and outer layers. For example, it can be manufactured by a method known as the arc rotary melting method. In this method, silicon dioxide powder (silica powder, quartz powder) is first fed into a rotating mold as raw material powder and centrifugal force forms a crucible-shaped molded body. The molded body is then heated and melted from the inside using an arc flame to form a translucent quartz glass crucible base (outer layer) (base formation process). Furthermore, during or after the formation of the crucible base, new silicon dioxide powder is fed into the heated atmosphere within the crucible base to form a transparent quartz glass inner layer on the inner surface of the crucible base (inner layer formation process). The method of forming an inner layer made of transparent quartz glass by heating while spraying quartz powder is also known as the spraying method. The impurity element concentrations in the inner and outer layers can be adjusted, for example, by adjusting the impurity element concentrations in the raw material powder of each layer.

[0055] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples.

[0056] [Examples 1 to 3, Comparative Examples 1 to 4] Quartz glass crucibles with an outer diameter of 800 mm were manufactured by the arc rotary melting method. At this time, the impurity concentrations in the inner layer, outer layer (R portion and bottom portion), and outer layer (straight body portion) of the manufactured quartz glass crucibles were adjusted to be as shown in Table 1. That is, each impurity concentration shown in Table 1 is the concentration (unit: mass ppb) at each portion of the quartz glass crucible before pulling up the single crystal silicon ingot. Note that, as mentioned above, the impurity concentration in the inner layer is the concentration at a position 1 mm from the inner surface of the quartz glass crucible, and the impurity concentration at each portion of the outer layer is the average concentration in the thickness direction.

[0057] Next, a single crystal silicon ingot was pulled using the manufactured quartz glass crucible. The brown ring formed on the inner surface of the quartz glass crucible after the first single crystal silicon ingot was pulled was observed. Brown rings with the above-mentioned outer diameter reference line length ranging from 10 mm to 13 mm were selected as the brown rings to be observed. Table 2 shows the state of bubbles in the inner layer within the inner region of the brown ring, including the diameter of the largest bubble contained and the density of bubbles with a diameter of 3.0 μm or more within the brown ring. Table 2 also shows the length x of the outer diameter reference line and the convex height y, which is the height of the top of the outer diameter reference line, in the above formula (1), obtained by observing the brown ring. Table 2 also shows the state of pinholes formed after the first single crystal silicon ingot was pulled, as "pinhole performance." The pinhole performance was evaluated using three levels: "particularly good," "good," and "poor," which are defined here for convenience as follows: The number of pinholes detected when a single crystal silicon wafer was produced from a single crystal silicon ingot was determined based on the number of pinholes detected in Comparative Example 1. A number higher than this was rated as "poor," a number equal to or less than half of "poor" was rated as "good," and a number equal to or less than half of "good" was rated as "particularly good."

[0058]

[0059]

[0060] As can be seen from Tables 1 and 2, it was found that pinhole performance was good when the impurity concentrations of Na, K, and Li in the inner layer were less than 5 mass ppb for Na, less than 5 mass ppb for K, and less than 100 mass ppb for Li, and the Na, K, and Li concentrations in the R and bottom of the outer layer were less than 10 mass ppb for Na, less than 50 mass ppb for K, and less than 180 mass ppb for Li. Furthermore, when these impurity concentration specifications were met, the density of bubbles with a diameter of 3.0 μm or more in the brown ring was 4.0 bubbles / mm ２or more. Thus, a high number density means that bubbles remain without being released, and in that case, the bubbles are present at a deep position within the brown ring and are not incorporated into the silicon melt. Furthermore, as can be seen from Table 2, in Examples 1-3, the brown rings having an outer diameter reference line length in the range of 10 mm or more and 13 mm or less satisfied the above formula (1), and in this case, the pinhole performance was "particularly good" or "good." On the other hand, in Comparative Examples 1-4, the above formula (1) was not satisfied.

[0061] Furthermore, in the outer layer of the manufactured quartz glass crucible, the impurity elements in the straight body portion had high concentrations in all of the examples and comparative examples (satisfying at least one of 10 mass ppb or more for Na, 50 mass ppb or more for K, and 180 mass ppb or more for Li), so collapse and sinking were suppressed.

[0062] The present invention is not limited to the above-described embodiments, which are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention.

Claims

1. It has a crucible shape consisting of a straight section, a curved section, and a bottom section. The outer layer is made of opaque quartz glass containing air bubbles, It consists of transparent quartz glass, with an inner layer having a thickness of 1.5 mm or more. A quartz glass crucible for pulling single crystal silicon ingots, having the following characteristics: The concentrations of Na, K, and Li in the inner layer at a position 1 mm from the inner surface of the quartz glass crucible are less than 5 mass ppb for Na, less than 5 mass ppb for K, and less than 100 mass ppb for Li. A quartz glass crucible for pulling single-crystal silicon ingots, characterized in that the average concentrations of Na, K, and Li in the thickness direction at the R portion and the bottom portion of the outer layer are less than 10 mass ppb for Na, less than 50 mass ppb for K, and less than 180 mass ppb for Li.

2. The concentrations of Na, K, and Li in the inner layer at a position 1 mm from the inner surface of the quartz glass crucible are less than 5 mass ppb for Na, less than 5 mass ppb for K, and less than 50 mass ppb for Li. The quartz glass crucible for pulling single crystal silicon ingots according to claim 1, characterized in that the average concentrations of Na, K, and Li in the thickness direction at the R portion and the bottom portion of the outer layer are less than 5 mass ppb for Na, less than 50 mass ppb for K, and less than 100 mass ppb for Li.

3. The quartz glass crucible for pulling single crystal silicon ingots according to claim 1, characterized in that the average concentrations of Na, K, and Li in the thickness direction in the straight body portion of the outer layer satisfy at least one of the following conditions: 10 mass ppb or more for Na, 50 mass ppb or more for K, and 180 mass ppb or more for Li.

4. The quartz glass crucible for pulling single crystal silicon ingots according to claim 2, characterized in that the average concentrations of Na, K, and Li in the thickness direction in the straight body portion of the outer layer satisfy at least one of the following conditions: 10 mass ppb or more for Na, 50 mass ppb or more for K, and 180 mass ppb or more for Li.

5. The quartz glass crucible for pulling single crystal silicon ingots according to claim 1, characterized in that the outer diameter of the quartz glass crucible is 800 mm or more in diameter.

6. The quartz glass crucible for pulling single crystal silicon ingots according to claim 2, characterized in that the outer diameter of the quartz glass crucible is 800 mm or more in diameter.

7. The quartz glass crucible for pulling single crystal silicon ingots according to claim 3, characterized in that the outer diameter of the quartz glass crucible is 800 mm or more in diameter.

8. The quartz glass crucible for pulling single crystal silicon ingots according to claim 4, characterized in that the outer diameter of the quartz glass crucible is 800 mm or more in diameter.

9. The aforementioned quartz glass crucible is The crucible holds a silicon melt inside, and after a single-crystal silicon ingot is pulled out from the silicon melt, a Brown ring is formed on the inner surface of the quartz glass crucible. The density of bubbles with a diameter of 3.0 μm or more in the inner layer within the inner region of the Brown ring is 4.0 bubbles / mm². ２ A quartz glass crucible for pulling single crystal silicon ingots according to any one of claims 1 to 8, characterized in that it is as described above.

10. The aforementioned quartz glass crucible is A molten silicon is held inside the quartz glass crucible, and after a single-crystal silicon ingot is pulled out from the molten silicon, a Brown ring is formed on the inner surface of the quartz glass crucible, with the length of the Brown ring being in the range of 10 mm to 13 mm, where the bisection line of the Brown ring across the circumferential direction of the quartz glass crucible is defined as the outer diameter reference line of the Brown ring. Let x [mm] be the length of the outer diameter reference line of the Brown ring. The uppermost point at the end of the outer diameter reference line of the Brown ring is taken as the reference height 0 [μm], When the height of the protrusion, which is the height of the uppermost part on the outer diameter reference line in the inner region of the Brown ring, is denoted as y [μm], A quartz glass crucible for pulling single crystal silicon ingots according to any one of claims 1 to 8, characterized in that the Brown ring, in which the length of the outer diameter reference line is in the range of 10 mm to 13 mm, satisfies the following formula (1). y ≥ 10x - 70 ... (1)

11. The aforementioned quartz glass crucible is A molten silicon is held inside the quartz glass crucible, and after a single-crystal silicon ingot is pulled out from the molten silicon, a Brown ring is formed on the inner surface of the quartz glass crucible, with the length of the Brown ring being in the range of 10 mm to 13 mm, where the bisection line of the Brown ring across the circumferential direction of the quartz glass crucible is defined as the outer diameter reference line of the Brown ring. Let x [mm] be the length of the outer diameter reference line of the Brown ring. The uppermost point at the end of the outer diameter reference line of the Brown ring is taken as the reference height 0 [μm], When the height of the protrusion, which is the height of the uppermost part on the outer diameter reference line in the inner region of the Brown ring, is denoted as y [μm], The quartz glass crucible for pulling single crystal silicon ingots according to claim 9, characterized in that the Brown ring, in which the length of the outer diameter reference line is in the range of 10 mm to 13 mm, satisfies the following formula (1). y ≥ 10x - 70 ... (1)