Patent ID: 12252804

MODE FOR CARRYING OUT THE INVENTION

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

FIG.1is a schematic side cross-sectional view illustrating the structure of a quartz glass crucible according to a first embodiment of the present invention. Further,FIG.2shows schematic side cross-sectional views illustrating the use state of the quartz glass crucibleFIG.1, where (a) illustrates a state where a raw material is charged, and (b) illustrates a state where the raw material is melted.

As illustrated inFIG.1andFIG.2, a quartz glass crucible1according to the present embodiment is a cylindrical container having a bottom for supporting a silicon melt5, and includes a quartz glass crucible body (hereinafter, referred to as a “crucible body”)10, and an inner-surface coating film13A which contains a crystallization accelerator and is formed on an inner surface10iof the crucible body10. The crucible body10has a cylindrical side wall portion10a, a bottom portion10bwhich is gently curved, and a corner portion10cwhich has a larger curvature than that of the bottom portion10band connects the side wall portion10aand the bottom portion10bto each other.

The aperture of the quartz glass crucible1is 22 inches (about 560 mm) or more, preferably 24 inches (about 600 mm) or more, and more preferably 32 inches (about 800 mm) or more. This is because such a crucible having a large aperture is used for pulling a large-size silicon single crystal ingot having a diameter of 300 mm or more, and is required to be less likely to be deformed even when used for a long period of time and not to affect the quality of the silicon single crystal. In recent years, with an increase in the size of silicon single crystals and an increase in the time for a crystal pulling step, the thermal environment of the crucible becomes more severe, and improvement in durability of the crucible is an important issue.

Although the thickness of the crucible body10slightly varies depending on its part, the thickness of the side wall portion10aof a crucible of 22 inches or more is preferably 7 mm or more, and the thickness of the side wall portion10aof a crucible of 24 inches or more is preferably 8 mm or more. In addition, the thickness of the side wall portion10aof a large crucible of 32 inches or more is preferably 10 mm or more, and the thickness of the side wall portion10aof a large crucible of 40 inches (about 1000 mm) or more is more preferably 13 mm or more.

The crucible body10has a two-layer structure, and includes a transparent layer11(bubble-free layer) made of quartz glass containing no bubbles, and an opaque layer12(bubble layer) which is made of quartz glass containing a large number of minute bubbles and is provided on the outer side of the crucible from the transparent layer11.

The transparent layer11is a layer that forms the inner surface10iof the crucible body10that is in contact with the silicon melt5, and is provided to prevent a single crystal yield from being reduced due to bubbles in quartz glass. The thickness of the transparent layer11is preferably 0.5 to 10 mm, and is set to an appropriate thickness for each part of the crucible so as not to cause the opaque layer12to be exposed due to the transparent layer11completely eroding during a single crystal pulling step. The transparent layer11is preferably provided over the entire crucible from the side wall portion10ato the bottom portion10bof the crucible. However, in a rim upper end portion of the crucible that is not in contact with the silicon melt, the transparent layer11may be omitted.

The expression the transparent layer11“contains no bubbles” means that the bubble content and the bubble size are such that single crystal yield is not reduced due to the bubbles. This is because there is concern that when bubbles are present in the vicinity of the inner surface of the crucible, the bubbles in the vicinity of the inner surface of the crucible cannot be confined in the quartz glass due to erosion of the inner surface of the crucible, the bubbles in the quartz glass may burst due to thermal expansion during crystal pulling, and crucible fragments (quartz pieces) may delaminate. In a case where crucible fragments released into the melt are carried to the growth interface of the single crystal by convection of the melt and are incorporated into the single crystal, this causes dislocation of the single crystal. In addition, in a case where bubbles released into the melt due to erosion of the inner surface of the crucible float up to the solid/liquid interface and are incorporated into the single crystal, this causes pinholes. The bubble content of the transparent layer11is preferably 0.1 vol % or less, and the average diameter of the bubbles is preferably 100 μm or less.

The bubble content of the transparent layer11can be measured nondestructively using optical detecting means. The optical detecting means includes a light-receiving device which receives transmitted light or reflected light of the light irradiating the crucible. Light-emitting means of the irradiation light may be built into the light-receiving device, or external light-emitting means may also be used. In addition, as the optical detecting means, one that can be turned along the inner surface of the crucible is preferably used. As the irradiation light, X-rays, laser light, and the like as well as visible light, ultraviolet light, and infrared light can be used. As the light-receiving device, a digital camera including an optical lens and an image element can be used. A bubble content per unit volume can be obtained by integrating bubble contents per unit area in a depth direction. In order to detect bubbles present at a certain depth from the surface, the focal point of the optical lens may be scanned from the surface in the depth direction. Measurement results obtained by the optical detecting means are received by an image processing device to calculate the bubble content per unit area. The bubble content per unit area can be obtained as a ratio of the area occupied by bubbles to a reference area, the reference area obtained by dividing an image of the inner surface of the crucible taken using the digital camera into predetermined areas.

The opaque layer12is a layer that is provided outside the transparent layer11and forms an outer surface10oof the crucible body10. The opaque layer12is provided to enhance heat retention of the silicon melt5in the crucible, and heat the silicon melt5in the crucible as uniformly as possible by dispersing radiant heat from a heater6provided to surround the crucible in a single crystal pulling apparatus (seeFIG.2(b)). Therefore, it is preferable that the opaque layer12is provided over the entire crucible from the side wall portion10ato the bottom portion10bof the crucible. The thickness of the opaque layer12is a value obtained by subtracting the thickness of the transparent layer11from the thickness of the crucible wall, and varies depending on the part of the crucible.

It is preferable that the thickness of the opaque layer12at the bottom portion10bof the crucible body10is larger than other parts, particularly the opaque layer12at the side wall portion10a. By causing the opaque layer12at the bottom portion10bof the crucible body10to be as thick as possible, the temperature of the inner surface of the crucible can be lowered, thereby suppressing generation of pinholes in the silicon single crystal.

The bubble content of the opaque layer12is 0.8% or more, and preferably 1 to 5%. A change in the bubble content at the boundary between the opaque layer12and the transparent layer11is steep, and the boundary between the two is apparent with the naked eye. The bubble content of the opaque layer12can be obtained, for example, by specific gravity measurement (Archimedes' method) by comparing the weight per unit volume of an opaque quartz glass piece cut out of the crucible to the weight per unit volume of quartz glass containing no bubbles.

The crucible body10preferably includes two layers, an inner surface layer formed from a synthetic silica powder (hereinafter, referred to as “synthetic layer”) and an outer surface layer formed from a natural silica powder (hereinafter, referred to as “natural layer”). The natural silica powder is a silica powder manufactured by pulverizing into particles a natural mineral containing α-quartz as a primary component. The synthetic silica powder can be manufactured by vapor phase oxidation of silicon tetrachloride (SiCl4) (dry synthesis method) or hydrolysis of silicon alkoxide (sol-gel method).

As will be described in detail later, the crucible body10having the two-layer structure of the synthetic layer and the natural layer can be manufactured by depositing the natural silica powder along the inner surface of a mold for manufacturing a crucible, depositing the synthetic silica powder thereon, and dissolving the silica powders by Joule heat through arc discharge. In an initial stage of the arc dissolution step, strong vacuum drawing is conducted at the outside of the deposition layers of the silica powders to remove bubbles, whereby the transparent layer11is formed. Thereafter, the vacuum drawing is stopped or weakened, whereby the opaque layer12is formed outside the transparent layer11. For this reason, although the interface between the synthetic layer and the natural layer does not always coincide with the interface between the transparent layer and the opaque layer, like the transparent layer11, the synthetic layer preferably has a thickness that does not completely disappear by erosion of the inner surface of the crucible during the crystal pulling step.

In the present embodiment, a compressive stress layer Lc is formed in the vicinity of the inner surface10iof the crucible body10. In a case where internal residual stress in the vicinity of the inner surface10iof the crucible body10is compressive stress, a dense crystal layer can be formed on the inner surface10iof the crucible body10, and strength of the inner surface10ican be improved. As illustrated inFIG.2(a), at the start of manufacturing of a silicon single crystal, the inside of the crucible is filled with a large amount of a polycrystalline silicon raw material4, and the sharp tips of the polycrystalline silicon masses are pressed against the inner surface10iof the crucible, so that an impact is likely to be applied to the inner surface10i. However, in a case where compressive stress is applied to the inner surface10iof the crucible, durability against impact at the time of filling with the raw material can be improved.

The thickness of the compressive stress layer Lc is preferably 0.5 mm or more. In this case, the thickness of the compressive stress layer Lc may differ for each part of the crucible, and for example, the compressive stress layer Lc in the bottom portion10bof the crucible may be thicker. In this case, impact resistance of the inner surface of the bottom portion10bof the crucible can be improved, generation of irregularities can be suppressed, and the probability of bubbles being trapped at the bottom portion10bof the crucible can be reduced.

Stress strength of the compressive stress layer Lc may differ for each part of the crucible. For example, compressive stress of the bottom portion10band the corner portion10cmay be greater than that of the side wall portion10a. Since the corner portion10csupports the weight of the side wall portion, deformation of the corner portion10ccan be suppressed by increasing compressive stress of the corner portion10c. Furthermore, by increasing compressive stress of the bottom portion10b, it is possible to form a crystal layer which has a reduced number of irregularities which cause pinholes and is dense.

A tensile stress layer Lt may be formed on the inner side (outer surface side) of the compressive stress layer Lc. In this case, the rate of change in stress from compressive stress to tensile stress is preferably gentle. Accordingly, deformation of the crucible such as sagging or collapse to the inside can be suppressed. The tensile stress layer Lt is preferably formed in the transparent layer11together with the compressive stress layer Lc. This is because when the tensile stress layer Lt is formed in the opaque layer12, fine cracks are likely to be generated between the bubbles, and there is concern that the cracks may spread and cause large cracks.

When the crystal layer formed on the inner surface10iof the crucible body10becomes thicker rapidly, strength of the crucible body10increases, and this has an effect in a good way in terms of crucible strength. Therefore, compressive stress of the inner surface of the crucible is preferably as strong as possible, and the compressive stress layer Lc is preferably as thick as possible. Furthermore, tensile stress of the tensile stress layer Lt is preferably strong, but the thickness of the tensile stress layer Lt is preferably as thin as possible. In a case where the growth rate of the crystal layer formed on the inner surface10iof the crucible body10is slow or the crystal layer is thin, the crystal layer ceases to exist. Therefore, the inner surface10iof the crucible body10having stronger compressive stress can withstand an environment in which the dissolution rate of the inner surface of the crucible is fast. In addition, when the compressive stress layer Lc of the inner surface10iof the crucible body10is thick, the crystal layer can be formed thick, so that the inner surface10ican withstand a crystal pulling step taken for a long period of time.

Whether internal residual stress in the vicinity of the inner surface10iof the crucible body10is compressive stress or tensile stress can be determined by observing the cross section of the crucible wall with a strain measuring device.

FIG.3is a schematic view illustrating the principle of the strain measuring device.

As illustrated inFIG.3, a strain measuring device20includes two polarizing plates21and22combined in a crossed Nicols state. The crucible is cut in the thickness direction, and a cut crucible piece23is installed as a sample between the two polarizing plates21and22, and observed through white light. In a case where there is no strain in the crucible piece23, the crucible piece23does not give an optical path difference to white polarized light, so that the white polarized light cannot pass through the orthogonal polarizing plate22(analyzer). On the other hand, in a case where there is strain in the crucible piece23, the crucible piece23gives an optical path difference to the white polarized light, so that the plane of polarization of the white polarized light is rotated, and a component passing through the orthogonal polarizing plate22(analyzer) is observed.

As described above, when white polarized light is passed through the crucible piece23having strain, an optical path difference corresponding to the strain occurs for each wavelength, and the amount of light passing through the polarizing plate22differs for each wavelength. As a result, a color is observed in the crucible piece23observed through the polarizing plate22(analyzer). The strain of the crucible piece23can be evaluated from this color. For example, the strain of the crucible piece23can be evaluated by using an interference color chart or a polarization color chart showing the relationship between chromaticity and birefringence. In addition, when a sensitive tint color method is used, it is possible to determine whether the stress is compressive stress or tensile stress based on the color, so that the interface between residual compressive stress and residual tensile stress can be observed.

FIG.4is a grayscale image of a cross section of the crucible body10seen through the strain measuring device20.

As shown inFIG.4, when the cross section of the crucible body10having internal residual stress is observed using the strain measuring device20, a color indicating compressive stress (for example, blue) and a color indicating tensile stress (for example, orange) are respectively shown. The quartz glass crucible according to the present embodiment has a compressive stress layer present in the vicinity of the inner surface of the crucible and a tensile stress layer present on the inner side of the compressive stress layer as shown in the figure.

In addition, it is also possible to measure the stress of the strain by installing a quarter-wave plate24between the crucible piece23and the polarizing plate22(Sénarmont method). A specific measuring method is as follows. First, a polarizing plate22(analyzer) is installed so as to be in a crossed Nicols state with respect to the polarizing plate21(polarizer) installed in front of a light source25. At this time, the rotation angle of the analyzer is set to 0°. Next, the sample is observed from the analyzer side, and the sample is rotated relative to the analyzer so that the sample portion whose stress is to be measured becomes brightest. Furthermore, the analyzer is rotated in a horizontal direction so that the sample portion whose stress is to be measured is darkest. When the rotation angle from the brightest state to the darkest state is referred to as θ, the stress F of the strain can be obtained by the following formula.
F=(λ×θ/180)/(C×L)

Here, λ is the wavelength (nm) of the light source, C is the photoelastic constant (nm/cm)/MPa, and L is the optical path length (cm). The photoelastic constant C of silica glass is 3.5±0.2 (nm/cm)/MPa. As the wavelength λ of the light source25, a wavelength suitable for the quarter-wave plate24to be used is selected. Alternatively, a quarter-wave plate suitable for the wavelength λ of the light source25to be used may be selected. The optical path length L is the thickness of the sample in an optical axis direction.

On the inner surface10iof the crucible body10, an inner-surface coating film13A which is a crystallization-accelerator-containing coating film is formed. The inner-surface coating film13A plays a role of accelerating crystallization of the surface layer portion of the crucible body10through heating in a step of pulling a silicon single crystal. Since the transparent layer11is formed on the inner surface10iside of the crucible body10, the inner-surface coating film13A is formed on the transparent layer11. The inner-surface coating film13A contains a water-soluble polymer acting as a thickener, whereby a hard film is formed on the inner surface10iof the crucible body10.

The thickness of the inner-surface coating film13A is preferably 0.3 to 100 μm. The concentration of the crystallization accelerator applied to the inner surface10iof the crucible body10is controlled by changing the thickness of the inner-surface coating film13A. It should be noted that elements that can act as a crystallization accelerator are not intentionally added to the crucible body10made of quartz glass, and for example, in a case where the crucible body10is formed of a natural silica powder, it is preferable that the concentration of barium contained in the crucible body10is less than 0.10 ppm, the concentration of magnesium is less than 0.10 ppm, and the concentration of calcium is less than 2.0 ppm. Furthermore, in a case of using a synthetic silica powder as the constituent raw material of the inner surface of the crucible body10, it is preferable that the concentrations of both magnesium and calcium contained in the crucible body10are less than 0.02 ppm.

The crystallization accelerator contained in the inner-surface coating film13A is an element in group2a, such as magnesium, calcium, strontium, barium, and the like. In particular, barium is particularly preferred because of its small segregation coefficient to silicon, and characteristics that the crystallization rate does not attenuate with crystallization, and growth in an orientation is caused most strongly compared to other elements. In addition, barium is stable at room temperature and easy to handle, and has substantially the same nuclear radius as that of glass (Si), so that there is also an advantage that crystal growth is easy to continue. The crystallization-accelerator-containing coating film can be formed by applying a coating solution containing the crystallization accelerator to the wall surface of the crucible. Examples of the crystallization accelerator include lithium (Li), zinc (Zn), lead (Pb), and the like in addition to the elements in group2a. Thus, the inner-surface coating film13A can be formed by applying the coating solution containing barium or the like to the wall surface of the crucible.

The inner-surface coating film13A is preferably formed in a region excluding a rim upper-end surface10tand the vicinity of the rim upper end in the inner surface10i. That is, the vicinity of the rim upper end is preferably an uncoated region15A to which the crystallization accelerator has not been applied. In a case where the inner-surface coating film13A is formed over the entire inner surface including the vicinity of the rim upper end, a rim upper-end portion (upper-end surface) is also crystallized, and there is concern that particles generated from the crystallized region of the crucible body10may be incorporated into the silicon melt in the crucible, and yield of the silicon single crystals may decrease. However, by providing the uncoated region15A extending downward from the rim upper end within a certain range to suppress crystallization of the rim upper-end portion, yield of silicon single crystals can be improved.

It is preferable that the uncoated region15A extends downward from the rim upper end within a range of 2 mm or more and 40 mm or less. This is because, in a case where the width of the uncoated region15A is smaller than 2 mm, the effect of providing the uncoated region15A is hardly obtained. Furthermore, in a case where the width of the uncoated region15A is greater than 40 mm, there is a higher possibility that the position of the upper end of the inner-surface coating film13A may be lower than the initial melt surface position of the silicon melt5(seeFIG.2(b)). When the boundary between the crystal layer and the glass layer is immersed in the silicon melt5, there is a higher possibility that cracks may be generated by stress concentration on the boundary region and particles of small crystal pieces may be generated. However, yield of the silicon single crystals can be improved by providing the uncoated region15A above the initial melt surface position of the silicon melt to suppress crystallization of the rim upper-end portion.

Normally, the quartz glass crucible1during the crystal pulling step is accommodated in a carbon susceptor8, and the rim upper-end portion of the quartz glass crucible1protrudes upward beyond the upper end of the carbon susceptor8. Below a melt surface5aof the silicon melt5, the crucible wall is pressed outward by the liquid pressure and adapts to the carbon susceptor. However, above the melt surface5a, no liquid pressure is applied, so that the crucible wall is not pressed against the carbon susceptor. Therefore, the rim upper-end portion is always in a self-sustaining state without being supported by the carbon susceptor8(seeFIG.2). It is preferable that the uncoated region15A is provided in a region protruding upward beyond the upper end of the carbon susceptor8. Stress is likely to be applied to the rim upper-end portion in a self-sustaining state without being in contact with the carbon susceptor8, and in a case where the rim upper-end portion is crystallized, particles are likely to be generated due to cracks or the like. By causing the rim upper-end portion to become the uncoated region, dust generation due to the crystallization of the rim upper-end portion can be suppressed, and yield of silicon single crystals can be improved.

It is preferable that the range of the width of the uncoated region15A is 0.02 times to 0.1 times the length of the side wall portion10aof the crucible. This is because, in a case where the width of the uncoated region15A is smaller than 0.02 times the length of the side wall portion10aof the crucible, the effect of providing the uncoated region15A is insufficient. Furthermore, in a case where the width of the uncoated region15A is larger than 0.1 times the length of the side wall portion10aof the crucible, the uncoated region is formed to reach the region supported by the carbon susceptor8and there is concern of deterioration of the yield of silicon single crystals.

As described above, the quartz glass crucible1according to the present embodiment includes the inner-surface coating film13A formed on the inner surface10iof the crucible body10made of quartz glass. When this quartz glass crucible1is used in an actual crystal pulling step, quartz glass is crystallized by the action of the crystallization accelerator, and a dense crystal layer is formed on the surface of the crucible body10, thereby improving the strength of the crucible.

FIG.5is a cross-sectional view of the quartz glass crucible1used for pulling a silicon single crystal, and is a view illustrating a state where the surface is crystallized by heating during the crystal pulling step.

As illustrated inFIG.5, on the surface of the quartz glass crucible1to which the crystallization accelerator is applied, crystallization of the quartz glass is accelerated by heating during the crystal pulling step, so that an inner crystal layer14A is formed on the inner surface10iof the crucible body10. Heating during the step of pulling a silicon single crystal is performed even for several tens of hours or longer at a temperature of the melting point of silicon (about 1400° C.) or higher. However, how the crystal layer is formed on the surface layer portion of the crucible body10can be evaluated, as well as by actually performing the step of pulling a silicon single crystal, by performing a heat treatment at a temperature equal to or higher than 1400° C. and equal to or lower than the softening point of silica glass for 1.5 hours or longer.

The thickness of the inner crystal layer14A is 200 μm or more, and preferably 400 μm or more. The inner crystal layer14A that comes into contact with the silicon melt during the single crystal pulling is gradually eroded, but by gradually growing the inner crystal layer14A, the thickness of the inner crystal layer14A can be 200 μm or more, and even can be maintained at 400 μm or more.

In order for the quartz glass crucible1to stably hold the silicon melt at a high temperature during the crystal pull-up step for a long period of time, it is not good that just any crystal layer is formed on the crucible body10, but that a desirable crystal grain size and a crystal orientation are present. This is because in a case where the crystal layer does not satisfy desired crystal quality, the crystal growth cannot be maintained during the crystal pulling step, the strength of the crucible body10is insufficient, deformation such as sagging occurs, and single crystal yield decreases.

FIGS.6(a) and (b)are model diagrams of crystal grains constituting a crystal layer. As shown in the drawing, the crystal orientation of the crystal grains in the crystal layer is preferably perpendicular to the main surface (crucible surface) of the crystal layer, and preferably has a columnar orientation. InFIG.6, the principal plane of a crystal layer is an XY plane, and the crystal grains have a columnar orientation elongated in a Z-axis direction. Accordingly, not only can the surface of the crucible body10be uniformly crystallized, but also the crystal growth can be maintained, and deformation of the crucible body10can be suppressed, thereby improving single crystal yield. Even if the crystal grains have the same orientation, there are cases where the crystal grain size is large (seeFIG.6(a)) or small (seeFIG.6(b)). When the crystal grain size is too large, the crystal layer is not densified, and deformation of the crucible and delamination of the crystal layer tend to occur due to insufficient strength. On the other hand, when the crystal grain size is too small, the crystal layer does not grow continuously, the thickness of the crystal layer is insufficient, and the strength of the crucible decreases.

For this reason, the average grain size of the crystal grains constituting the inner crystal layer14A is preferably 0.1 to 100 μm, and the peak of the frequency distribution of the crystal grain sizes is preferably in a range of 0.1 to 100 μm. This is because in a case where the average grain size of the crystal grains is larger than 100 μm, the denseness of the crystal layer is insufficient and the strength of the crucible decreases, while in a case where the average grain size of the crystal grains is smaller than 0.1 μm, the crystal grains are too small and the strength of the crystal layer is weakened. Furthermore, in a case where the peak of the frequency distribution of the crystal grain size is in a range of 0.1 to 100 μm, the crystal grain size is concentrated near the average grain size, so that reliability of the measured value of the average grain size can be increased.

In addition, the sum of the first and second highest ranks in the area ratios of the plane orientations of the crystal grains constituting the crystal layer is preferably 50% or more, and particularly preferably 80% or more. Furthermore, it is preferable that the plane orientations accounting for the first and second highest ranks in the area ratios are a (200) plane and a (112) plane. As described above, in a case where the orientation of the crystal layer is strong, crystal growth can be maintained to form a crystal layer having a sufficient thickness, or a crystal layer having high strength can be formed even when the thickness is small. Accordingly, the strength of the crucible can be improved.

In a case where the plane orientations accounting for the first and second highest ranks in the area ratios are the (200) plane and the (112) plane, the area ratio of the (200) plane is preferably larger than the area ratio of the (112) plane. In a case where the area ratio of the (200) plane is larger than the area ratio of the (112) plane, the orientation of the crystal grains can be strong, and the growth of the crystal layer can be maintained for a long period of time, thereby increasing the strength of the crucible.

It is considered that the orientation of the crystal grains constituting the crystal layer is affected by the surface density of the crystallization accelerator. When the distance between crystal nuclei formed increases, various orientation growths that occur during the growth of the crystal layer are less likely to disappear, and variation in the orientation of the crystal grains increases. Furthermore, the orientation of the crystal grains is considered to be affected by the internal diffusion of the crystallization accelerator. When the crystallization accelerator diffuses from the surface toward the inside of the crucible wall, variation in the position where the crystal nuclei are generated occurs in the depth direction from the surface, and variation in the orientation of the crystal grains increases. The internal diffusion of the crystallization accelerator is caused by preheating of the crucible in a step of applying the crystallization accelerator, or by lowering a temperature rise in a temperature-raising step during pulling.

The crystal grain size and crystal orientation of the crystal layer can be evaluated by an electron backscatter diffraction pattern (EBSD) method. The EBSD method is a crystal analysis method in a submicron region using an electron channeling pattern (ECP) method, which is one of crystal analysis methods using a scanning electron microscope (SEM). The ECP method requires a special electron optical system for irradiating one point on a sample with an electron beam to irradiate the sample while sequentially changing the angle, whereas in the EBSD method, it is only necessary to stop an electron beam on an analyzed crystal grain, and there is no need to add a special device to an electron optical system.

FIG.7is a schematic view illustrating the principle of the EBSD method. As shown in the figure, an EBSD device40has a simple configuration in which an EBSD detector41(CCD camera) is added to the SEM. When a sample42inclined at about 60 to 70° is irradiated with an electron beam43, the electron beam is scattered on each crystal plane in a shallow region up to about 50 nm from the surface of the sample42. However, in the case of a crystalline sample, the electron beam is diffracted, and a pattern corresponding to the crystal orientation (EBSD pattern) appears. By photographing and analyzing the EBSD pattern with the EBSD detector41, information regarding the crystal orientation of the sample can be obtained, and the orientation distribution, texture, and crystal phase distribution of crystal grains can be analyzed.

It should be noted that, in the EBSD measurement, it is necessary to set an allowable angle (tolerance) of a misorientation angle between adjacent measurement points, but in the present embodiment, the tolerance is preferably set to 1 to 5°.

FIGS.8(a) to (c)are views showing an example of an EBSD analysis result of a crucible cross section, where (a) is an image quality (IQ) map, (b) is a signal map, and (c) is an IQ map (ND).

As shown inFIGS.8(a) to (c), according to the EBSD method, the crystal orientation of each crystal grain can be specified, and the crystal orientations can be displayed, for example, by color. In particular, as shown inFIG.8(a), streaky crystal grain boundaries can be observed from the cross section of the crystal layer (XZ plane or YZ plane inFIG.6), and it can be seen that the crystal grains have a columnar orientation extending in the depth direction. Furthermore, the frequency distribution of the crystal grain sizes can be obtained by aggregating the area of each crystal grain in the IQ map for each crystal orientation. As described above, according to the EBSD method, the average grain size, the grain size distribution, and the crystal orientation of the crystal grains constituting the crystal layer can be accurately obtained.

FIG.9is a graph showing the frequency distribution of the crystal grain sizes obtained from the measurement result by the EBSD method. According to the EBSD method, the frequency distribution of the crystal grain sizes can be obtained from a crystal orientation map obtained when an evaluation is performed in a direction (Z-axis direction inFIG.6) perpendicular to the surface of the crystal layer (XY plane inFIG.6), and furthermore, the area ratio of each plane orientation of the crystal grains constituting the crystal layer can be obtained. In the present embodiment, the average grain size of the crystal grains is preferably 0.1 to 100 μm, and the peak of the frequency distribution of the crystal grain sizes is preferably in a range of 0.1 to 100 μm. InFIG.9, the average grain size of the crystal grains is 5.5 μm, and the peak of the frequencies of the crystal grain sizes is 3 μm.

The crystal orientation of the crystal layer can also be evaluated based on a texture coefficient obtained from the measurement result of an X-ray diffraction method. The texture coefficient is a coefficient indicating the magnitude of the orientation of a crystalline sample, and the larger the value, the stronger the orientation of a specific orientation. A texture coefficient Tc (hkl) of an (hkl) plane of a sample is represented by the following formula.

Tc⁡(hkl)=I⁡(hkl)/Io⁡(hkl)1N⁢{∑NI⁡(hkl)/Io⁡(hkl)}[Formula⁢1]

Here, I(hkl) indicates the measured intensity of X-rays from the (hkl) plane of the sample, Io(hkl) indicates the standard intensity from the (hkl) plane of a powder sample, and N indicates the number of diffraction lines. In the case of a sample having no orientation, Tc(hkl) is 1.

Then, when the texture coefficient Tc of each plane orientation of the crystal layer viewed from the surface of the crucible body10is measured by the X-ray diffraction method, the ratio (Tc occupancy ratio) of the first and second highest ranks in the texture coefficients Tc to the sum of the texture coefficients Tc of the plane orientations is preferably 50% or more, and particularly preferably 80% or more. In this case, it is preferable that the plane orientations accounting for the first and second highest ranks in the texture coefficients Tc are the (200) plane and the (112) plane, and it is particularly preferable that the texture coefficient Tc(200) of the (200) plane is larger than the texture coefficient Tc(112) of the (112) plane. As described above, in a case where the orientation of the crystal layer is strong, crystal growth can be maintained to form a crystal layer having a sufficient thickness, or a crystal layer having high strength can be formed even when the thickness is small. Accordingly, the strength of the crucible can be improved.

As described above, in a case where the average grain size and the plane orientation of the crystal grains constituting the crystal layer satisfy the above conditions, a crystal layer having high strength can be formed even if the thickness is small. Therefore, deformation such as sagging of the crucible can be suppressed, and single crystal yield can be improved.

In a case where the inner-surface coating film13A is formed on the inner surface10iof the crucible body10, formation of scratches and indentations on the inner surface10iof the crucible body10can be suppressed. In a case where the inner-surface coating film13A is not formed, when the inside of the crucible is filled with the polycrystalline silicon raw material4, the sharp tips of the polycrystalline silicon masses come into direct contact with the inner surface10iof the crucible body10, and a very large load from a large amount of the polycrystalline silicon raw material is concentrated on the sharp tips of the polycrystalline silicon masses, so that scratches and indentations are likely to be formed on the inner surface10i. However, in a case where the inner surface10iof the crucible body10is covered with the inner-surface coating film13A, it is possible to protect the inner surface of the crucible by avoiding a situation where the inner surface10iis directly damaged.

In the initial stage of a step of melting the polycrystalline silicon raw material4, recessed portions such as scratches or indentations are formed on the inner surface10iof the crucible body10, and the recessed portions capture gas. In a quartz glass crucible in the related art in which a coating film containing a crystallization accelerator is formed on the inner surface10iof the crucible body10and the inner surface10ihas no compressive stress, crystallization of the inner surface10iproceeds in the latter half of the step of melting the raw material, and the viscosity of the inner surface of the crucible increases, so that the shape of the recessed portions is maintained. Accordingly, the gas adhering to the surface of the crucible is less likely to be separated from the surface of the crucible. The gas that has continued to adhere to the surface of the crucible is separated from the surface during the crystal pull-up step and is released into the melt, so that a pinhole is more easily generated in a single crystal than in a normal quartz glass crucible where crystallization of the inner surface is not accelerated.

In the quartz glass crucible in the related art in which the crystallization accelerator is not applied to the inner surface10i, the inner surface of the crucible is hardly crystallized in the latter half of the step of melting the raw material, has a low viscosity because of its vitreous state, and has a reduced ability to capture the gas adhered to the surface of the crucible. Therefore, the gas adhered to the surface of the crucible is released away from the surface of the crucible in the latter half of the step of melting the raw material. That is, it is considered that the crucible on which the inner-surface coating film13A is formed can withstand crystal pulling for a longer period of time than a crucible without the inner-surface coating film13A formed thereon, but has a property of easily generating pinholes in a single crystal.

Contrary to this, in the quartz glass crucible according to the present invention in which compressive stress is applied to the inner surface, the inner surface of the crucible is dense, the number of recessed portions is small, and the depth of the recessed portions is small, so that the recessed portions cannot catch gas. Therefore, the pinhole generation ratio in the single crystal can be reduced.

FIG.10is a flowchart showing a method of manufacturing the quartz glass crucible1.FIG.11is a schematic view for describing a method of manufacturing the crucible body10according to a rotational molding method.

As shown inFIG.10andFIG.11, the quartz glass crucible1according to this embodiment can be manufactured by manufacturing the crucible body10having the compressive stress layer Lc formed on the inner surface10iby a so-called rotational molding method, and then forming the inner-surface coating film13A on the inner surface10iof the crucible body10. In the manufacturing of the crucible body10by the rotational molding method, a natural silica powder16A and a synthetic silica powder16B are sequentially deposited on an inner surface30iof a rotating mold30to form a deposition layer16of the raw material silica powders (step S11). It is also possible to use only the natural silica powder as the raw material of the crucible body10. These raw material silica powders remain in a certain position while being adhered to the inner surface30iof the mold30by centrifugal force, and are maintained in the shape of the crucible.

Next, an arc electrode31is set in the mold30, and the deposition layer16of the raw material silica powders is arc-melted from the inner surface30iside of the mold (step S12). Specific conditions such as heating time and heating temperature need to be appropriately determined in consideration of conditions such as the raw materials and size of the crucible. In this case, the amount of bubbles in the melted quartz glass is controlled by suctioning the deposition layer16of the raw material silica powders from a large number of vent holes32provided on the inner surface30iof the mold30. Specifically, at the start of arc melting, the suction force from the large number of vent holes32provided on the inner surface30iof the mold30is strengthened to form the transparent layer11(step S13), and after the formation of the transparent layer11, the suction force is weakened to form the opaque layer12(step S14).

Since the arc heat is gradually transferred from the inner side to the outer side of the deposition layer16of the raw material silica powders to melt the raw material silica powders, by changing decompression conditions at the timing at which the raw material silica powders start to melt, the transparent layer11and the opaque layer12can be separately formed. When decompression melting is performed to strengthen decompression at the timing at which the silica powders melt, the arc atmosphere gas is not confined in the glass, and quartz glass containing no bubbles is formed. In addition, during normal melting (atmospheric pressure melting) in which decompression is weakened at the timing at which the silica powders melt, the arc atmosphere gas is confined in the glass and quartz glass containing a large number of bubbles is formed.

Thereafter, the arc heating is ended, and the crucible is cooled so that compressive stress remains in the inner surface10iof the crucible (step S15). As a rapid cooling method, it is preferable that the arc electrode is kept as far away from the crucible as possible immediately after the end of the arc heating, and cold air is sent toward the inside of an arc furnace, particularly the inner surface of the crucible to cool the inner surface of the crucible. It should be noted that since the structure of SiO2does not change at a temperature of 1200° C. or lower, it is preferable to cool the crucible at a cooling rate of 150° C./min or more in a high temperature range of 1200° C. or higher, and a cooling rate of 280 to 300° C./min is particularly preferable. Accordingly, the crucible body10in which the transparent layer11and the opaque layer12are sequentially provided from the inside toward the outside of the crucible wall is completed.

Next, the inner-surface coating film13A is formed on the inner surface10iof the crucible body10thus manufactured (step S16). As described above, the inner-surface coating film13A can be formed by applying a coating solution containing a crystallization accelerator and drying the coating solution. The application of the crystallization accelerator coating solution to the surface of the crucible can be performed by brushing and spraying. After the application, water and the like evaporate such that a hard film is formed by the thickener.

The crystallization-accelerator-containing coating solution applied to the crucible body10contains a crystallization accelerator such as a barium compound. The average particle size of the crystallization accelerator is preferably 0.1 to 100 μm, and more preferably 0.1 to 10 μm. In addition, the peak of the frequency distribution of the particle sizes of the crystallization accelerator is preferably in a range of 0.1 to 100 μm, and more preferably in a range of 0.1 to 10 μm. When the particle size of the crystallization accelerator is smaller than 0.1 μm, the crystal grains grown become small, and it becomes difficult to achieve continuous crystal growth. In addition, in a case where the particle size of the crystallization accelerator is larger than 100 μm, or small particles of the crystallization accelerator are aggregated to form an aggregate larger than 100 μm, the grown crystal grains also become large, decrease in strength, and tend to delaminate.

However, by causing the average particle size of the crystallization accelerator to be 0.1 to 100 μm, the average grain size of the crystal grains of the crystal layer can be 0.1 to 100 μm.

The aspect ratio (major axis/minor axis) of the primary particles of the crystallization accelerator is preferably 1.0 or more and less than 10, and particularly preferably 1.0 or more and 3.0 or less. This is because when the aspect ratio of the particles of the crystallization accelerator is 10.0 or more (acicular), the particles are entangled with each other, and the dispersibility on the surface of the crucible deteriorates.

FIG.12is a flowchart showing a method of preparing the crystallization-accelerator-containing coating solution.

As shown inFIG.12, in the preparation of the crystallization-accelerator-containing coating solution, in order to cause the average particle size and particle size distribution of the crystallization accelerator to be within the above ranges, the crystallization accelerator is crushed by ultrasonic irradiation (step S21), the viscosity of a solvent is adjusted to 100 mPa·s or more (step S22). Thereafter, the fine crystallization accelerator is dispersed in the solvent (Step S23). By such preparation, the grain size distribution and crystal orientation of the crystal grains in the crystal layer can be made as described above, and it becomes possible to increase the strength of the crystal layer. The particle size distribution of the crystallization accelerator crushed by ultrasonic irradiation can be measured by, for example, a Microtrac method.

The crushing of the crystallization accelerator by ultrasonic irradiation can be performed by, for example, providing a vibrator that oscillates and generates ultrasonic waves at the bottom of a water tank to crush the crystallization accelerator immersed in a liquid, and making the particles of the crystallization accelerator finer.

Alternatively, an oscillator such as an ultrasonic homogenizer may be immersed in a liquid to make the crystallization accelerator in the liquid finer. The liquid containing the fine crystallization accelerator is stored in a container with a liquid stirring function, and is maintained in a state where the crystallization accelerator does not precipitate. In order to uniformly disperse the fine crystallization accelerator, it is preferable to add a thickener to cause the viscosity of the liquid to be 100 mPa·s or more.

In a case where crushing of the crystallization accelerator by ultrasonic irradiation is not performed, that is, in a state where the peak of the particle size distribution of the crystallization accelerator is more than 100 μm, variation in the particle size of the crystallization accelerator applied to the crucible is large, and this increases the kinds of orientation of the crystal layer. As a result, the occupancy ratio of a specific crystal orientation cannot be increased, and the strength of the crystal layer decreases. In contrast, in a case where crushing of the crystallization accelerator by ultrasonic irradiation is performed for a long period of time, that is, when the peak of the particle size distribution of the crystallization accelerator is 0.1 μm or less, it becomes difficult to achieve continuous crystal growth of the crystal layer. Alternatively, the crystallization accelerator may aggregate to particles larger than 100 μm, and this increases the kinds of orientation of the crystal layer.

The crystallization-accelerator-containing coating solution may be a coating solution containing a barium compound and water, or may be a coating solution which does not contain water but contains a barium compound and anhydrous ethanol. Examples of the barium compound include barium carbonate, barium chloride, barium acetate, barium nitrate, barium hydroxide, barium oxalate, barium sulfate, and the like. A barium compound insoluble in water is more preferable, and barium carbonate is particularly preferable. This is because in a case where a water-soluble barium compound such as barium hydroxide is used, the average value of the crystal grain sizes constituting the crystal layer becomes 0.1 μm or less, and the crystal grain size becomes too small, so that the strength of the crystal layer is reduced. Furthermore, barium, which is insoluble in water, is less likely to be taken into the human body, and is thus highly safe and advantageous in terms of handling.

It is preferable that the crystallization-accelerator-containing coating solution further contains a highly viscous water-soluble polymer (thickener) such as carboxyvinyl polymer. In a case of using a coating solution without a thickener contained therein, fixing of the crystallization accelerator to the wall surface of the crucible is unstable, so that a heat treatment for fixing the crystallization accelerator is necessary. When such a heat treatment is performed, the crystallization accelerator diffuses and penetrates into the quartz glass, and becomes the cause of acceleration of random growth of crystal, which will be described later. However, in a case of using a coating solution containing a thickener together with the crystallization accelerator, the viscosity of the coating solution increases, so that it is possible to prevent the coating solution from flowing with gravity when applied to the crucible and thus becoming uneven.

Furthermore, in a case where the coating solution contains the water-soluble polymer, the crystallization accelerator does not cohere in the coating solution but diffuses, so that it is possible to uniformly apply the crystallization accelerator to the surface of the crucible. Therefore, the crystallization accelerator at a high concentration can be uniformly and densely fixed to the wall surface of the crucible, thereby accelerating the growth of highly oriented crystal grains.

Examples of the thickener include water-soluble polymers having few metal impurities such as polyvinyl alcohol, a cellulosic thickener, high-purity glucomannan, an acrylic polymer, a carboxyvinyl polymer, a polyethylene glycol fatty acid ester, and the like. In addition, an acrylic acid-alkyl methacrylate copolymer, polyacrylate, polyvinyl carboxylic acid amide, vinylcarboxylic acid amide, or the like may also be used as the thickener. The viscosity of the coating solution is preferably in a range of 100 to 10000 mPa·s, and the boiling point of the solvent is preferably 50 to 100° C. When the viscosity of the coating solution is lower than 100 mPa·s, the dispersed state of the crystallization accelerator cannot be maintained, and the crystallization accelerator may aggregate and increase in particle size. However, when the viscosity of the solvent is 100 mPa·s or more, the fine crystallization accelerator can be uniformly dispersed in the solvent.

The application of the crystallization accelerator coating solution to the inner surface10iof the crucible body10(step S16) can be performed by brushing and spraying. After the application, water and the like evaporate such that a hard film is formed by the thickener. It should be noted that it is not preferable to heat the crucible to reach a surface temperature of 200 to 300° C. for the purpose of fixing the crystallization accelerator. This is because when the surface of the crucible is heated to 100° C. or higher after applying water or alcohols containing the crystallization accelerator, barium on the surface of the crucible diffuses to the inside, and crystal nuclei are simultaneously generated, so that a desired crystal orientation is not obtained, and the strength of the crystal layer cannot be obtained.

It is preferable that the concentration of the crystallization accelerator in the surface layer portion of the crucible body10on which the crystallization-accelerator-containing coating film is formed is low. Elements that can act as a crystallization accelerator are not intentionally added to the crucible body10made of quartz glass, and for example, in a case where the crucible body10is formed of a natural quartz powder, it is preferable that the concentration of barium contained in the crucible body10is less than 0.10 ppm, the concentration of magnesium is less than 0.10 ppm, and the concentration of calcium is less than 2.0 ppm. Furthermore, in a case of using, in the crucible body10, a synthetic quartz powder as the constituent raw material of the inner surface, it is preferable that the concentrations of both magnesium and calcium contained in the crucible body10are less than 0.02 ppm.

In a case where the concentration of the crystallization accelerator in the crucible body10is high, random growth occurs in the surface layer portion of the crucible body10and the crystallization accelerator in the crystallization-accelerator-containing coating film is trapped at the crystal interface, whereby it is difficult to form a crystallization-accelerator-enriched layer. However, in a case where the crystallization-accelerator-containing coating film is formed on the surface of the crucible body10, the crystallization accelerator can be localized on the surface of the crucible body10at a uniform concentration. In particular, in a case where the concentration of the crystallization accelerator in the quartz glass is low, the crystallization accelerator having a high concentration is uniformly localized on the surface of the crucible body10, so that random growth is not attained when the crystallization proceeds due to heat applied by subsequent crystal pulling and a crystallization-accelerator-enriched layer is more likely to be formed.

Accordingly, the quartz glass crucible1according to the present embodiment is completed. Thereafter, when a step of pulling a silicon single crystal is performed using the quartz glass crucible1, a crystal layer having the above-described crystal grain size and crystal orientation is formed on the surface of the crucible. Therefore, it is possible to provide the quartz glass crucible1which is hardly cracked even when the thickness of the crystal layer is small and has high strength. Accordingly, deformation of the crucible such as sagging can be suppressed even when used under a high temperature for a long period of time during crystal pulling, and even in a case where a brown ring or the like is generated on the inner surface of the crucible, delamination thereof can be prevented, thereby improving yield of the silicon single crystals.

As described above, the quartz glass crucible1according to the present embodiment includes the crucible body10and the inner-surface coating film13A containing the crystallization accelerator formed on the inner surface10iof the crucible body10, the inner surface10iof the crucible body10is under compressive stress, and the inner-surface coating film13A is formed on the inner surface10i. Therefore, it is possible to obtain a crystal layer which is denser and stronger than that in the related art. Therefore, it is possible to provide a quartz glass crucible (silica glass crucible) having few irregularities which become the origin of generation of bubbles during the crystal pulling step. In addition, since the crystallization rate of the quartz glass under compressive stress is high, by adding the action of the crystallization accelerator thereto, the quartz glass can be crystallized at a temperature as low as 1200° C. or lower at which compressive stress is not released. Therefore, the inner surface10ican be crystallized before strain due to compressive stress is released, so that it is possible to obtain a crystal layer which is denser and stronger than that in the related art.

In addition, the quartz glass crucible1according to the present embodiment includes the cylindrical crucible body10having a bottom made of quartz glass, and the inner-surface coating film13A formed on the inner surface10iof the crucible body10so as to form the inner crystal layer14A in the vicinity of the inner surface of the crucible body10by being heated during the step of pulling a silicon single crystal, the average grain size of the crystal grains in the inner crystal layer14A is 0.1 to 100 μm, the peak of the frequency distribution of the crystal grains is in a range of 0.1 to 100 μm, and when the area ratio of each plane orientation of the inner crystal layer14A as viewed from the inner surface side of the crucible body10is measured by the EBSD method, the sum of the first and second highest ranks in the area ratios is 50% or more. Therefore, deformation of the crucible can be suppressed and single crystal yield can be improved.

In addition, in the method of manufacturing the quartz glass crucible1according to the present embodiment, the coating solution which is obtained by crushing a crystallization accelerator insoluble in water, such as barium carbonate or the like, by ultrasonic irradiation or the like, and then dispersing the crystallization accelerator in the solvent together with the thickener, and which has a viscosity of 100 mPa·s or more is used, so that a good crystallization-accelerator-containing coating film can be formed on the surface of the crucible body10. In particular, since the coating solution is applied to the crucible in a state where the crystallization accelerator is uniformly dispersed in the coating solution within a predetermined particle size range, the crystallized portion has a uniform particle size and oriented state within a predetermined range. Therefore, the strength of the crystal layer formed on the surface of the crucible body10can be increased.

FIG.13is a schematic side cross-sectional view illustrating the structure of a quartz glass crucible according to a second embodiment of the present invention.

As illustrated inFIG.13, a quartz glass crucible2according to the present embodiment is characterized in that the inner-surface coating film13A and an outer-surface coating film13B are formed on the inner surface10iand the outer surface10oof the crucible body10, respectively. Similarly to the inner-surface coating film13A, the outer-surface coating film13B is a film containing a crystallization accelerator, and can be formed using the same coating solution as the inner-surface coating film13A. In this case, the thickness of the outer-surface coating film13B is preferably smaller than that of the inner-surface coating film13A.

The compressive stress layer Lc is formed on the outer surface10oof the crucible body10, and the outer-surface coating film13B is formed on the outer surface10ounder compressive stress. Therefore, a dense and strong crystal layer can be also formed on the outer surface10oside of the crucible body10.

The outer-surface coating film13B is also preferably formed in a region excluding the rim upper-end surface10tand the vicinity of the rim upper end on the outer surface10o. That is, the vicinity of the rim upper end is preferably an uncoated region15B to which the crystallization accelerator has not been applied. In a case where the outer-surface coating film13B is formed on the entire outer surface including the vicinity of the rim upper end, the rim upper-end portion (upper end surface) is also crystallized, and there is concern that particles generated from the crystallized region may be incorporated into the silicon melt in the crucible, and yield of the silicon single crystals may decrease. However, by providing the uncoated region15B extending downward from the rim upper end within a certain range to suppress crystallization of the rim upper-end portion, yield of silicon single crystals can be improved.

It is preferable that the uncoated region15B extends downward from the rim upper end within a range of 2 mm or more and 40 mm or less. This is because, in a case where the width of the uncoated region15B is smaller than 2 mm, the effect of providing the uncoated region15B is hardly obtained. Furthermore, in a case where the width of the uncoated region15B is greater than 40 mm, strengthening of the outer surface10oof the crucible body10by the outer-surface coating film13B is insufficiently achieved.

As described above, although the quartz glass crucible1during the crystal pulling step is accommodated in the carbon susceptor8, the rim upper-end portion of the quartz glass crucible1protrudes upward beyond the upper end of the carbon susceptor8, and is always in a self-sustaining state without being supported by the carbon susceptor8(seeFIG.2). It is preferable that the uncoated region15B is provided in a region protruding upward beyond the upper end of the carbon susceptor8. By causing the rim upper-end portion of the quartz glass crucible1that is not in contact with the carbon susceptor8to become the uncoated region, dust generation due to crystallization of the rim upper-end portion can be suppressed, and yield of the silicon single crystals can be improved.

It is preferable that the range of the width of the uncoated region15B is 0.02 times to 0.1 times the length of the side wall portion10aof the crucible. This is because, in a case where the width of the uncoated region15B is smaller than 0.02 times the length of the side wall portion10aof the crucible, the effect of providing the uncoated region15B is insufficient. Furthermore, in a case where the width of the uncoated region15B is larger than 0.1 times the length of the side wall portion10aof the crucible, the uncoated region is formed to reach the region supported by the carbon susceptor8and there is concern of deterioration of yield of silicon single crystals.

The bubble content in the vicinity of the outer surface10oof the crucible body10is 5% or less, and particularly preferably 0.8 to 5%. In a case where the bubble content in the vicinity of the outer surface10oof the crucible body10is very high, when the outer surface10oof the crucible body10is crystallized, there is concern that the outer crystal layer may foam and delaminate due to the bubbles and the crucible may deform. However, in a case where the bubble content in the vicinity of the outer surface10ois 5% or less, deformation of the crucible due to foaming and delamination of the outer crystal layer can be prevented. In a case where a crystallization accelerator containing an element in group2ais used, although the crystallization rate of the quartz glass is high, crystal growth stops at a certain thickness, and crystal growth does not continue for a long period of time. Therefore, when the bubble content in the vicinity of the outer surface10oof the crucible body10is 5% or less, foaming and delamination of the outer crystal layer can be sufficiently suppressed. In a case where the bubble content in the vicinity of the outer surface is higher than 5%, even if the growth of the crystal layer stops at a certain thickness, the probability that the outer crystal layer foams and delaminates increases, which is not preferable. Furthermore, in a case where the bubble content is lower than 0.8%, a translucent layer or a transparent layer is formed on the outer surface10oof the crucible body10, and the heat retention and heat insulation of the crucible body10are reduced, which is not preferable.

As described above, the quartz glass crucible2according to the present embodiment has not only the inner-surface coating film13A formed on the inner surface10iof the crucible body10, but also the outer-surface coating film13B formed on the outer surface10o. Therefore, in addition to the effects of the first embodiment, it is possible to suppress a decrease in single crystal yield due to deformation of the crucible.

FIG.14is a cross-sectional view of the quartz glass crucible2according to the second embodiment used for pulling a silicon single crystal, and is a view illustrating a state where the surface is crystallized by heating during the crystal pulling step.

As illustrated inFIG.14, on the surface of the quartz glass crucible2to which the crystallization accelerator is applied, crystallization of the quartz glass is accelerated by heating during the crystal pulling step, so that the inner crystal layer14A and an outer crystal layer14B are respectively formed on the inner surface10iand the outer surface10oof the crucible body10.

As described above, the thickness of the inner crystal layer14A is 200 μm or more, and preferably 400 μm or more. The inner crystal layer14A that comes into contact with the silicon melt during the single crystal pulling is gradually eroded, but by gradually growing the inner crystal layer14A, the thickness of the inner crystal layer14A can be 200 μm or more, and even can be maintained at 400 μm or more.

On the other hand, the thickness of the outer crystal layer14B is 200 μm or more, but is preferably thinner than the inner crystal layer14A, and the orientation of the crystal grains is preferably weaker than that of the inner crystal layer14A. Accordingly, the continuity of the crystal growth is weakened, so that it is possible to prevent the outer crystal layer14B from becoming excessively thick. Therefore, delamination of the crystal layer due to expansion of bubbles at the interface between the thick crystal layer and the quartz glass can be prevented, and generation of cracks along the crystal grain boundaries can be prevented.

The inner crystal layer14A and the outer crystal layer14B have the same crystal grain size and crystal orientation as the inner crystal layer14A in the first embodiment. The average grain size of the crystal grains constituting the inner crystal layer14A and the outer crystal layer14B is preferably 0.1 to 100 μm, and the peak of the frequency distribution of the crystal grain sizes is preferably in a range of 0.1 to 100 μm. In addition, the sum of the first and second highest ranks in the area ratios of the plane orientations of the crystal grains constituting the crystal layer is preferably 50% or more, and particularly preferably 80% or more. Furthermore, it is preferable that the plane orientations accounting for the first and second highest ranks in the area ratios are a (200) plane and a (112) plane. When the crystal layer satisfies desired crystal quality, crystal growth can be maintained during the crystal pulling step, and both the strength of the crucible body10and the single crystal yield can be improved.

FIG.15is a schematic side cross-sectional view illustrating the structure of a quartz glass crucible according to a third embodiment of the present invention.

As illustrated inFIG.15, a quartz glass crucible3according to the present embodiment is characterized in that the outer-surface coating film13B is formed only on the outer surface10oof the crucible body10. The compressive stress layer Lc is formed on the inner surface10iand the outer surface10oof the crucible body10, and the outer-surface coating film13B is formed on the outer surface10ounder compressive stress.

The outer-surface coating film13B is preferably formed in a region excluding the rim upper-end surface10tand the vicinity of the rim upper end on the outer surface10o. That is, the vicinity of the rim upper end is preferably an uncoated region15B to which the crystallization accelerator has not been applied. It is preferable that the uncoated region15B extends downward from the rim upper end within a range of 2 mm or more and 40 mm or less.

As described above, although the quartz glass crucible1during the crystal pulling step is accommodated in the carbon susceptor8, the rim upper-end portion of the quartz glass crucible1protrudes upward beyond the upper end of the carbon susceptor8, and is always in a self-sustaining state without being supported by the carbon susceptor8(seeFIG.2). It is preferable that the uncoated region15B is provided in a region protruding upward beyond the upper end of the carbon susceptor8. By causing the rim upper-end portion of the quartz glass crucible1that is not in contact with the carbon susceptor8to become the uncoated region, dust generation due to the crystallization of the rim upper-end portion can be suppressed, and yield of silicon single crystals can be improved.

The bubble content in the vicinity of the outer surface10oof the crucible body10is 5% or less, and particularly preferably 0.8 to 5%. When the bubble content in the vicinity of the outer surface10oof the crucible body10is 5% or less, foaming and delamination of the outer crystal layer can be sufficiently suppressed. Furthermore, when the bubble content is 0.8% or more, it is possible to prevent a decrease in heat retention and heat insulation due to the formation of a translucent layer or a transparent layer on the outer surface10oof the crucible body10.

According to the present embodiment, a dense and strong crystal layer can be formed on both the inner surface10iand the outer surface10oof the crucible body10. Furthermore, by forming the compressive stress layer Lc on the inner surface10iof the crucible, the number of recessed portions such as scratches and indentations formed on the inner surface10iof the crucible can be reduced, and the depth of the recessed portions can be reduced.

In particular, in a temperature range from the start of crystallization to 1200° C. in which strain in the crucible is not released, the outer crystal layer rapidly grows and increases in thickness, and force for compressing the crucible toward the inside (contraction in the horizontal direction) is applied. Accordingly, compressive stress on the inner surface side of the crucible is increased, the thickness of the compressed layer of the inner surface is further increased, so that strength on the inner surface side of the crucible is improved. Furthermore, in a temperature range from 1200° C. to the melting point of silicon, compressive and tensile stresses are released. However, since the thickness of the outer crystal layer is increased, deformation of the crucible, such as collapse to the inside, is suppressed. In addition, as the compression of the inner surface of the crucible is maintained by the load of the polycrystalline silicon in the crucible in a state where the outer surface of the crucible is not deformed, the denseness of the inner surface of the crucible is maintained, so that strength of the crucible inner surface is also maintained. Therefore, generation of pinholes in the single crystal can be suppressed by reducing the number of bubbles trapped in the inner surface of the crucible.

FIG.16is a cross-sectional view of the quartz glass crucible1used for pulling a silicon single crystal, and is a view illustrating a state where the surface is crystallized by heating during the crystal pulling step.

As illustrated inFIG.16, on the surface of the quartz glass crucible1to which the crystallization accelerator is applied, crystallization of the quartz glass is accelerated by heating during the crystal pulling step, so that the outer crystal layer14B is formed on the outer surface10oof the crucible body10.

As described above, the thickness of the outer crystal layer14B is 200 μm or more, but is preferably thinner than the inner crystal layer14A, and the orientation of the crystal grains is preferably weaker than that of the inner crystal layer14A. Accordingly, the continuity of the crystal growth is weakened, so that it is possible to prevent the outer crystal layer14B from becoming excessively thick. Therefore, delamination of the crystal layer due to expansion of bubbles at the interface between the thick crystal layer and the quartz glass can be prevented, and generation of cracks along the crystal grain boundaries can be prevented.

The outer crystal layer14B has the same crystal grain size and crystal orientation as the outer crystal layer14B in the second embodiment. The average grain size of the crystal grains constituting the outer crystal layer14B is preferably 0.1 to 100 μm, and the peak of the frequency distribution of the crystal grain sizes is preferably in a range of 0.1 to 100 μm. In addition, the sum of the first and second highest ranks in the area ratios of the plane orientations of the crystal grains constituting the crystal layer is preferably 50% or more, and particularly preferably 80% or more. Furthermore, it is preferable that the plane orientations accounting for the first and second highest ranks in the area ratios are a (200) plane and a (112) plane. When the crystal layer satisfies desired crystal quality, crystal growth can be maintained during the crystal pulling step, and both the strength of the crucible body10and the single crystal yield can be improved.

While the preferred embodiments of the present invention have been described above, the present invention is not limited to the embodiments and may be variously modified without departing from the scope of the present invention. Accordingly, all such modifications are naturally included in the scope of the present invention.

For example, in the above-described embodiment, the rim upper-end portion is the uncoated region of the crystallization accelerator, but the inner-surface coating film13A and the outer-surface coating film13B can also be formed up to the rim upper-end portion.

EXAMPLES

Example A1

A quartz glass crucible of Example A1 was prepared in which the inner-surface coating film13A containing the crystallization accelerator was formed on the inner surface10iof the crucible body10in which the inner surface10iand the outer surface10owere under compressive stress. However, the inner surface and the outer surface present on the rim upper-end surface10tand a range of the inner surface10iextending downward to 20 mm from the upper end thereof were the uncoated regions of the crystallization accelerator. Furthermore, the bubble content in the region in the vicinity of the outer surface from the outer surface10oof the crucible body10to a depth of 2 mm was 4%.

Next, after pulling up a silicon single crystal using this quartz glass crucible, the obtained silicon single crystal was processed into a wafer product, and the pinhole generation ratio and the single crystal yield were evaluated. The pinhole generation ratio is the ratio of the number of wafers having pinholes to the total number of wafers obtained from one silicon single crystal, and the presence or absence of pinholes was visually inspected. The single crystal yield is the weight ratio of the silicon single crystal to the input weight of a polycrystalline silicon raw material. Table 1 shows the results.

TABLE 1ComparativeExampleExampleExampleExampleExampleExampleExampleExampleExampleA1A2A3A4A5A6A1A7A8Crystallization-InnerInnerInnerInnerInnerInnerInnerInnerOuteraccelerator-surfacesurfacesurfacesurfacesurfacesurfacesurfacesurfacesurfacecontainingonlyonlyonlyonlyonlyonlyonly+ outeronlycoating filmsurfaceInnerCompressiveCompressiveCompressiveCompressiveCompressiveCompressiveAbsentCompressiveCompressivesurfacestrainOuterCompressiveCompressiveAbsentCompressiveAbsentCompressiveAbsentCompressiveCompressivesurfacestrainBubble483338944content ofoutersurface (%)Coating ofAbsentAbsentAbsentPresentPresentPresentPresentAbsentAbsentrim upper-end surfaceCoating ofAbsentAbsentAbsentPresentPresentPresentPresentAbsentAbsentrim upper-end portion(2 to 40 mm)Pinhole0.210.220.180.220.170.1840.140.19generationratio (%)Yield of867977787372558882siliconsinglecrystal (%)

As shown in Table 1, the pinhole generation ratio of the silicon single crystal manufactured using the quartz glass crucible was 0.21%, and the single crystal yield was 86%.

Example A2

A quartz glass crucible having substantially the same characteristics as in Example A1, except that the bubble content in a region in the vicinity of the outer surface of the crucible body10was as high as 8%, was prepared, and pulling of a silicon single crystal was performed using the quartz glass crucible. As a result, as shown in Table 1, the pinhole generation ratio of the silicon single crystal was 0.22%, and the single crystal yield was 79%.

Example A3

A quartz glass crucible having substantially the same characteristics as in Example A1, except that compressive stress was present in the inner surface10iof the crucible body10but was not present in the outer surface10o, and the bubble content in a region in the vicinity of the outer surface was 3%, was prepared, and pulling of a silicon single crystal was performed using the quartz glass crucible. As a result, as shown in Table 1, the pinhole generation ratio of the silicon single crystal was 0.18%, and the single crystal yield was 77%.

Example A4

A quartz glass crucible having substantially the same characteristics as in Example A1, except that the crystallization accelerator was applied to the inner surface10iand the outer surface10oof the rim upper-end surface and the upper-end portion of the crucible body10, was prepared, and pulling of a silicon single crystal was performed using the quartz glass crucible. As a result, as shown in Table 1, the pinhole generation ratio of the silicon single crystal was 0.22%, and the single crystal yield was 78%.

Example A5

A quartz glass crucible having substantially the same characteristics as in Example A1, except that compressive stress was present in the inner surface10iof the crucible body10but was not present in the outer surface10o, and furthermore, the crystallization accelerator was applied to the inner surface and the outer surface of the rim upper-end surface and the upper end-portion of the crucible body10, was prepared, and pulling of a silicon single crystal was performed using the quartz glass crucible. As a result, as shown in Table 1, the pinhole generation ratio of the silicon single crystal was 0.17%, and the single crystal yield was 73%.

Example A6

A quartz glass crucible having substantially the same characteristics as in Example A1, except that the bubble content in a region in the vicinity of the outer surface of the crucible body was as high as 8%, and furthermore, the crystallization accelerator was applied to the inner surface and the outer surface of the rim upper-end surface and the upper-end portion of the crucible body, was prepared, and pulling of a silicon single crystal was performed using the quartz glass crucible. As a result, as shown in Table 1, the pinhole generation ratio of the silicon single crystal was 0.18%, and the single crystal yield was 72%.

Comparative Example A1

A quartz glass crucible having substantially the same characteristics as in Example A1, except that no compressive stress layer was present in both the inner surface10iand the outer surface10oof the crucible body10, the bubble content in a region in the vicinity of the outer surface of the crucible body10was as high as 9%, and furthermore, the crystallization accelerator was applied to the inner surface and the outer surface on the rim upper-end surface and in the vicinity of the rim upper end of the crucible body10, was prepared, and pulling of a silicon single crystal was performed using the quartz glass crucible. As a result, as shown in Table 1, the pinhole generation ratio of the silicon single crystal was as high as 4%, and the single crystal yield was as extremely low as 55%.

From the above results, it could be seen that in the quartz glass crucible in which the crystallization-accelerator-containing coating film is formed on the inner surface10iof the crucible body10in which the inner surface10iis under compressive stress, the pinhole generation ratio and the single crystal yield can be improved.

Example A7

A quartz glass crucible having substantially the same characteristics as in Example A1, except that a coating film containing the crystallization accelerator was formed not only on the inner surface10ibut also on the outer surface10oof the crucible, was prepared, and pulling of a silicon single crystal was performed using the quartz glass crucible. As a result, as shown in Table 1, the pinhole generation ratio of the silicon single crystal was 0.14%, and the single crystal yield was 88%.

Example A8

A quartz glass crucible having substantially the same characteristics as in Example A1, except that a coating film containing the crystallization accelerator was formed only on the outer surface10oof the crucible, was prepared, and pulling of a silicon single crystal was performed using the quartz glass crucible. As a result, as shown in Table 1, the pinhole generation ratio of the silicon single crystal was 0.19%, and the single crystal yield was 82%.

Example B1

(Crystallization Accelerator Application Conditions)

A quartz glass crucible body having an aperture of 32 inches manufactured by a rotational molding method was prepared, and a crystallization accelerator was applied to the inner surface and the outer surface of the crucible body. The crystallization accelerator coating solution was produced by including each of 0.0012 g/mL of barium carbonate and 0.0008 g/mL of a carboxyvinyl polymer, adjusting the ratio between ethanol and pure water, and mixing and stirring the resultant. Barium carbonate was crushed by ultrasonic irradiation so that the average particle size became 100 μm or less, and then mixed and stirred in a solvent to produce a crystallization-accelerator-containing coating solution. The average particle size of the crystallization accelerator particles in the coating solution was 1 μm, the peak of the particle size frequency was 2 μm, and the liquid viscosity of the solution was 400 mPa·s. This coating solution was applied to the inner surface and the outer surface of the crucible body and dried to complete a sample of a quartz glass crucible for pulling a silicon single crystal (Example B1a).

(Evaluation Conditions)

Next, using this crucible sample, a step of pulling a silicon single crystal was performed by the CZ method. After the pulling was ended, the degree of sagging of the crucible sample used was measured. As shown in Table 2, the degree of sagging at the upper end of the crucible was about 2 mm. In addition, the single crystal yield (weight ratio of the pulled single crystal to the input raw material) was 86%, which was a good result exceeding 70%.

(Evaluation of Crystallinity by EBSD)

Next, the state of the crystal layer formed on the surface of the crucible sample used was evaluated by the EBSD method. For the crystal analysis by the EBSD method, a Schottky field emission scanning electron microscope (JSM-7800FPRIME manufactured by JEOL Ltd.) was used. The allowable angle (tolerance) of the misorientation angle was set to 5°. As a result, as shown in Table 2, the average grain size of the crystal grains was 0.11 μm, and the peak of the frequency distribution of the crystal grain sizes was 0.18 μm. Furthermore, the highest three ranks in the area ratios of the plane orientation were (200) plane: 30.5%, (112) plane: 23.6%, and (113) plane: 16.2%. The sum of the area ratios of the (200) plane and the (112) plane as the plane orientations accounting for the first and second highest ranks was 54%, so that the orientation of the crystal grains was high.

TABLE 2Sum ofDegreeareasofParticleratiosOrientationsaggingAveragesize atofplanes ofofcrystalposition offirstfirst andcrucibleYield ofgrainpeak ofandseconduppersiliconsizefrequencysecondranks inOrder ofendsingle(μm)distributionranksarea ratiosarea ratios(mm)crystalsExample B1a0.110.1854200112(200) > (112)286Example B2a8.18.467200112(200) > (112)383Example B3a948479200112(200) > (112)384Example B4a0.530.4851200112(200) > (112)1176Example B5a797630200112(200) > (112)1574Example B6a0.530.4866200202(200) > (112)1472Example B7a0.890.7671200112(200) < (112)1075Comparative0.070.0651200112(200) > (112)3742Example B1aComparative11011260200112(200) > (112)3338Example B2a
(Evaluation of Crystallinity by X-Ray Diffraction Method)

Using another crucible sample (Example B1b) manufactured under the same conditions as the crucible sample (Example B1a), a step of pulling a silicon single crystal by the CZ method was performed. After the pulling was ended, the degree of sagging of the crucible sample used was measured. As shown in Table 3, the degree of sagging at the upper end of the crucible was about 1 mm. In addition, the single crystal yield was 88%, which was a good result exceeding 70%. Furthermore, the crucible sample used was evaluated by the EBSD method. As shown in Table 3, the average grain size of the crystal grains was 0.13 μm, and the peak of the frequency distribution of the crystal grain sizes was 0.19 μm.

Next, the state of the crystal layer formed on the surface of the crucible sample (Example B1b) was evaluated by the X-ray diffraction method. In the evaluation by the X-ray diffraction method, an X-ray diffractometer RINT 2500 manufactured by Rigaku Corporation was used, and target: Cu (λ=1.5418 nm), scanning axis: 28, measurement method: continuous, 28 angle scanning range: 10 to 70°, light-receiving slit: 0.15 mm, divergence slit: 1°, scattering slit: 1°, sampling width: 0.02°, and scanning speed: 10°/min were set. The depth (detection depth) from the surface being evaluated by X-rays varied depending on the incident angle of X-rays, and was set to several nanometers to several tens of micrometers here. X-rays were irradiated perpendicularly to the surface of the sample on which the crystal layer was formed.

Next, the texture coefficient Tc of the crystal layer was calculated based on the measurement results. As a result, the highest three ranks in the texture coefficients Tc of the plane orientations were Tc(200): 33.5%, Tc(112): 30.3%, and Tc(113): 12.6%. In addition, as shown in Table 3, the Tc occupancy ratio of the first and second highest ranks was 64%, and it could be confirmed from the measurement results by the X-ray diffraction method that the orientation was high.

TABLE 3DegreeParticleOrientationofsize atTcplanes ofsaggingAverageposition ofoccupancyfirst andofYield ofcrystalpeak ofratio ofsecond ranksOrder ofcruciblesilicongrainfrequencyfirst andin texturetextureuppersinglesizedistributionsecondcoefficientscoefficientsendcrystals(μm)(μm)ranks (%)TcTc(mm)(%)Example B1b0.130.1964200112(200) > (112)188Example B2b7.87.471200112(200) > (112)384Example B3b979180200112(200) > (112)288Example B4b0.490.4933200112(200) > (112)981Example B5b777551200112(200) > (112)979Example B6b0.530.4871200202(200) > (112)1374Example B7b0.860.8174200112(200) < (112)1473Comparative0.080.0853200112(200) > (112)3141Example B1bComparative10811255200112(200) > (112)3833Example B2b

Example B2

A crucible was manufactured under the application conditions of the crystallization accelerator different from that of Example B1, and pulling of a silicon single crystal was performed using the crucible sample (Example B2a). The average particle size of the crystallization accelerator particles in the coating solution was 8 μm, the peak of the particle size frequency was 10 μm, and the liquid viscosity of the solution was 400 mPa·s. As a result, the degree of sagging of the crucible was about 3 mm. In addition, the single crystal yield was 83%, which was a good result exceeding 70%.

The crystal layer of the crucible sample used was evaluated by the EBSD method. The average grain size of the crystal grains was 8.1 μm, and the peak of the frequency distribution of the crystal grain sizes was 8.4 μm. In addition, the highest three ranks in the area ratios of the plane orientations were (200) plane: 34.8%, (112) plane: 32.0%, and (113) plane: 10.7%. Furthermore, the sum of the area ratios of the plane orientations accounting for the first and second highest ranks was 67%, and the orientation of the crystal grain was high.

Using another crucible sample (Example B2b) manufactured under the same conditions as the crucible sample (Example B2a), a step of pulling a silicon single crystal by the CZ method was performed, and thereafter the degree of sagging of the crucible sample used was measured. As shown in Table 3, the degree of sagging at the upper end of the crucible was about 3 mm. In addition, the single crystal yield was 84%, which was a good result exceeding 70%. Furthermore, the crucible sample used was evaluated by the EBSD method. As shown in Table 3, the average grain size of the crystal grains was 7.8 μm, and the peak of the frequency distribution of the crystal grain sizes was 7.4 μm.

Next, the crucible sample used was evaluated by the X-ray diffraction method. The highest three ranks in the texture coefficients Tc of the plane orientations of the crystal layer were Tc(200): 39.2%, Tc(112): 31.9%, and Tc(113): 9.7%. In addition, the Tc occupancy ratio of the first and second highest ranks was 71%, and it could be confirmed from the measurement results by the X-ray diffraction method that the orientation of the crystal grains was high.

Example B3

A crucible was manufactured under the application conditions of the crystallization accelerator different from those of Examples B1 and B2, and pulling of a silicon single crystal was performed using the crucible sample (Example B3a). The average particle size of the crystallization accelerator particles in the coating solution was 20 μm, the peak of the particle size frequency was 30 μm, and the liquid viscosity of the solution was 400 mPa·s. As a result, the degree of sagging of the crucible was about 3 mm. In addition, the single crystal yield was 84%, which was a good result exceeding 70%.

The crystal layer of the crucible sample used was evaluated by the EBSD method. The average grain size of the crystal grains was 94 μm, and the peak of the frequency distribution of the crystal grain sizes was 84 μm. In addition, the highest three ranks in the area ratios of the plane orientations were (200) plane: 42.1%, (112) plane: 37.1%, and (113) plane: 7.3%. Furthermore, the sum of the area ratios of the plane orientations accounting for the first and second highest ranks was 79%, and the orientation of the crystal grain was very high.

Using another crucible sample (Example B3b) manufactured under the same conditions as the crucible sample (Example B3a), a step of pulling a silicon single crystal by the CZ method was performed, and thereafter the degree of sagging of the crucible sample used was measured. As shown in Table 3, the degree of sagging at the upper end of the crucible was about 2 mm. In addition, the single crystal yield was 88%, which was a good result exceeding 70%. Furthermore, the crucible sample used was evaluated by the EBSD method. As shown in Table 3, the average grain size of the crystal grains was 97 μm, and the peak of the frequency distribution of the crystal grain sizes was 91 μm.

Next, the crucible sample used was evaluated by the X-ray diffraction method. The highest three ranks in the texture coefficients Tc of the plane orientations of the crystal layer were Tc(200): 41.1%, Tc(112): 39.0%, and Tc(113): 6.8%. In addition, the Tc occupancy ratio of the first and second highest ranks was 80%, and it could be confirmed from the measurement results by the X-ray diffraction method that the orientation of the crystal grains was very high.

Example B4

A crucible was manufactured under the application conditions of the crystallization accelerator different from those of Examples B1 to B3, and pulling of a silicon single crystal was performed using the crucible sample (Example B4a). The average particle size of the crystallization accelerator particles in the coating solution was 1 μm, the peak of the particle size frequency was 3 μm, and the liquid viscosity of the solution was 90 mPa·s. As a result, the degree of sagging of the crucible was about 11 mm. In addition, the single crystal yield was 76%, which was a good result exceeding 70%.

The crystal layer of the crucible sample used was evaluated by the EBSD method. The average grain size of the crystal grains was 0.53 μm, and the peak of the frequency distribution of the crystal grain sizes was 0.48 μm. In addition, the highest three ranks in the area ratios of the plane orientations were (200) plane: 25.9%, (112) plane: 25.5%, and (113) plane: 15.1%. Furthermore, the sum of the area ratios of the plane orientations accounting for the first and second highest ranks was 51%, and the orientation of the crystal grain was slightly low.

Using another crucible sample (Example Bob) manufactured under the same conditions as the crucible sample (Example B4a), a step of pulling a silicon single crystal by the CZ method was performed, and thereafter the degree of sagging of the crucible sample used was measured. As shown in Table 3, the degree of sagging at the upper end of the crucible was about 9 mm. In addition, the single crystal yield was 81%, which was a good result exceeding 70%. Furthermore, the crucible sample used was evaluated by the EBSD method. As shown in Table 3, the average grain size of the crystal grains was 0.49 μm, and the peak of the frequency distribution of the crystal grain sizes was 0.49 μm.

Next, the crucible sample used was evaluated by the X-ray diffraction method. The highest three ranks in the texture coefficients Tc of the plane orientations of the crystal layer were Tc(200): 16.8%, Tc(112): 16.2%, and Tc(113): 16.0%. In addition, the Tc occupancy ratio of the first and second highest ranks was 33%, and it could be confirmed from the measurement results by the X-ray diffraction method that the orientation of the crystal grains was slightly low.

Example B5

A crucible was manufactured under the application conditions of the crystallization accelerator different from those of Examples B1 to B4, and pulling of a silicon single crystal was performed using the crucible sample (Example B5a). The average particle size of the crystallization accelerator particles in the coating solution was 8 μm, the peak of the particle size frequency was 9 μm, and the liquid viscosity of the solution was 80 mPa·s. As a result, the degree of sagging of the crucible was about 15 mm. In addition, the single crystal yield was 74%, which was a good result exceeding 70%.

The crystal layer of the crucible sample used was evaluated by the EBSD method. The average grain size of the crystal grains was 79 μm, and the peak of the frequency distribution of the crystal grain sizes was 76 μm. In addition, the highest three ranks in the area ratios of the plane orientations were (200) plane: 15.7%, (112) plane: 14.6%, and (113) plane: 14.2%. Furthermore, the sum of the area ratios of the plane orientations accounting for the first and second highest ranks was 30%, and the orientation of the crystal grain was low.

Using another crucible sample (Example B5b) manufactured under the same conditions as the crucible sample (Example B5a), a step of pulling a silicon single crystal by the CZ method was performed, and thereafter the degree of sagging of the crucible sample used was measured. As shown in Table 3, the sagging amount at the upper end of the crucible was about 9 mm. In addition, the single crystal yield was 79%, which was a good result exceeding 70%. Furthermore, the crucible sample used was evaluated by the EBSD method. As shown in Table 3, the average grain size of the crystal grains was 77 μm, and the peak of the frequency distribution of the crystal grain sizes was 75 μm.

Next, the crucible sample used was evaluated by the X-ray diffraction method. The highest three ranks in the texture coefficients Tc of the plane orientations of the crystal layer were Tc(200): 27.7%, Tc(112): 23.7%, and Tc(113): 14.0%. In addition, the Tc occupancy ratio of the first and second highest ranks was 51%, and it could be confirmed from the measurement results by the X-ray diffraction method that the orientation of the crystal grains was slightly low.

Example B6

A crucible was manufactured under the application conditions of the crystallization accelerator different from those of Examples B1 to B5, and pulling of a silicon single crystal was performed using the crucible sample (Example B6a). The average particle size of the crystallization accelerator particles in the coating solution was 1 μm, the peak of the particle size frequency was 3 μm, and the liquid viscosity of the solution was 30 mPa·s. As a result, the degree of sagging of the crucible was about 14 mm. In addition, the single crystal yield was 72%.

The crystal layer of the crucible sample used was evaluated by the EBSD method. The average grain size of the crystal grains was 0.53 μm, and the peak of the frequency distribution of the crystal grain sizes was 0.48 μm. In addition, the highest three ranks in the area ratios of the plane orientations were (200) plane: 33.6%, (202) plane: 32.1%, and (112) plane: 11.2%. Furthermore, the sum of the area ratios of the plane orientations accounting for the first and second highest ranks was 66%, and the orientation of the crystal grain was high.

Using another crucible sample (Example B6b) manufactured under the same conditions as the crucible sample (Example B6a), a step of pulling a silicon single crystal by the CZ method was performed, and thereafter the degree of sagging of the crucible sample used was measured. As shown in Table 3, the degree of sagging at the upper end of the crucible was about 13 mm. In addition, the single crystal yield was 74%, which was a good result exceeding 70%. Furthermore, the crucible sample used was evaluated by the EBSD method. As shown in Table 3, the average grain size of the crystal grains was 0.53 μm, and the peak of the frequency distribution of the crystal grain sizes was 0.48 μm.

Next, the crucible sample used was evaluated by the X-ray diffraction method. The highest three ranks in the texture coefficients Tc of the plane orientations of the crystal layer were Tc(200) plane: 36.4%, Tc(202) plane: 34.9%, and Tc(112) plane: 9.2%. In addition, the Tc occupancy ratio of the first and second highest ranks was 71%, and it could be confirmed from the measurement results by the X-ray diffraction method that the orientation of the crystal grains was high.

Example B7

A crucible was manufactured under the application conditions of the crystallization accelerator different from those of Examples B1 to B6, and pulling of a silicon single crystal was performed using the crucible sample (Example B7a). The average particle size of the crystallization accelerator particles in the coating solution was 160 μm, the peak of the particle size frequency was 150 μm, the liquid viscosity of the solution was 50 mPa·s, and variation in the surface density of the crystallization accelerator was large. As a result, the degree of sagging of the crucible was about 10 mm. In addition, the single crystal yield was 75%, which was a good result exceeding 70%.

The crystal layer of the crucible sample used was evaluated by the EBSD method. The average grain size of the crystal grains was 0.89 μm, and the peak of the frequency distribution of the crystal grain sizes was 0.76 μm. In addition, the highest three ranks in the area ratios of the plane orientations were (200) plane: 34.5%, (112) plane: 36.6%, and (113) plane: 8.1%. Furthermore, the sum of the area ratios of the plane orientations accounting for the first and second highest ranks was 71%, and the orientation of the crystal grain was high.

Using another crucible sample (Example B7b) manufactured under the same conditions as the crucible sample (Example B7a), a step of pulling a silicon single crystal by the CZ method was performed, and thereafter the degree of sagging of the crucible sample used was measured. As shown in Table 3, the degree of sagging at the upper end of the crucible was about 14 mm. In addition, the single crystal yield was 73%, which was a good result exceeding 70%. Furthermore, the crucible sample used was evaluated by the EBSD method. As shown in Table 3, the average grain size of the crystal grains was 0.86 μm, and the peak of the frequency distribution of the crystal grain sizes was 0.81 μm.

Next, the crucible sample used was evaluated by the X-ray diffraction method. The highest three ranks in the texture coefficients Tc of the plane orientations of the crystal layer were Tc(200): 35.9%, Tc(112): 37.9%, and Tc(113): 7.8%. In addition, the Tc occupancy ratio of the first and second highest ranks was 74%, and it could be confirmed from the measurement results by the X-ray diffraction method that the orientation of the crystal grains was high.

Comparative Example B1

A crucible was manufactured under the application conditions of the crystallization accelerator different from those of Examples B1 to B7. Specifically, ultrasonic crushing of the crystallization accelerator was performed for a long period of time to make the particles fine, whereby a coating solution was produced. Therefore, the average particle size of the crystallization accelerator particles in the coating solution was 0.5 μm, and the peak of the particle size frequency was 0.5 μm. Thereafter, pulling of a silicon single crystal was performed using the crucible sample (Comparative Example B1a). As a result, the degree of sagging of the crucible was about 37 mm, which means that the degree of sagging was extremely large. In addition, the single crystal yield was 42%, which was a result significantly lower than 70%.

The crystal layer of the crucible sample used was evaluated by the EBSD method. The average grain size of the crystal grains was 0.07 μm, and the peak of the frequency distribution of the crystal grain sizes was 0.06 μm, which means that the crystal grain size was extremely small. In addition, the highest three ranks in the area ratios of the plane orientations were (200) plane: 26.1%, (112) plane: 25.2%, and (113) plane: 15.2%. Furthermore, the sum of the area ratios of the plane orientations accounting for the first and second highest ranks was 51%, and the orientation of the crystal grain was slightly high.

Using another crucible sample (Comparative Example B1b) manufactured under the same conditions as the crucible sample (Comparative Example B1a), a step of pulling a silicon single crystal by the CZ method was performed, and thereafter the degree of sagging of the crucible sample used was measured. As shown in Table 3, the degree of sagging at the upper end of the crucible was about 31 mm. In addition, the single crystal yield was 41%, which was a result lower than 70%. Furthermore, the crucible sample used was evaluated by the EBSD method. As shown in Table 3, the average grain size of the crystal grains was 0.08 μm, and the peak of the frequency distribution of the crystal grain sizes was 0.08 μm.

Next, the crucible sample used was evaluated by the X-ray diffraction method. The highest three ranks in the texture coefficients Tc of the plane orientations of the crystal layer were Tc(200): 26.7%, Tc(112): 26.1%, and Tc(113): 14.0%. In addition, the Tc occupancy ratio of the first and second highest ranks was 53%, and it could be confirmed from the measurement results by the X-ray diffraction method that the orientation of the crystal grains was slightly high.

Comparative Example B2

A crucible was manufactured under the application conditions of the crystallization accelerator different from those of Examples B1 to B7 and Comparative Example B1. Since ultrasonic crushing of the crystallization accelerator was not performed, the average particle size of the crystallization accelerator particles in the coating solution was 110 μm, and the peak of the particle size frequency was 150 μm. Thereafter, pulling of a silicon single crystal was performed using the crucible sample (Comparative Example B2a). As a result, the degree of sagging of the crucible was about 33 mm, which means that the degree of sagging was extremely large. In addition, the single crystal yield was 38%, which was a result significantly lower than 70%.

The crystal layer of the crucible sample used was evaluated by the EBSD method. The average grain size of the crystal grains was 110 μm, and the peak of the frequency distribution of the crystal grain sizes was 112 μm, which means that the crystal grain size was extremely large. In addition, the highest three ranks in the area ratios of the plane orientations were (200) plane: 31.8%, (112) plane: 28.0%, and (113) plane: 14.2%. Furthermore, the sum of the area ratios of the plane orientations accounting for the first and second highest ranks was 60%, and the orientation of the crystal grain was slightly high.

Using another crucible sample (Comparative Example B2b) manufactured under the same conditions as the crucible sample (Comparative Example B2a), a step of pulling a silicon single crystal by the CZ method was performed, and thereafter the degree of sagging of the crucible sample used was measured. As shown in Table 3, the degree of sagging at the upper end of the crucible was about 38 mm. In addition, the single crystal yield was 33%, which was a result lower than 70%. Furthermore, the crucible sample used was evaluated by the EBSD method. As shown in Table 3, the average grain size of the crystal grains was 108 μm, and the peak of the frequency distribution of the crystal grain sizes was 112 μm.

Next, the crucible sample used was evaluated by the X-ray diffraction method. The highest three ranks in the texture coefficients Tc of the plane orientations of the crystal layer were (200) plane: 28.2%, (112) plane: 26.8%, and (113) plane: 16.2%. In addition, the Tc occupancy ratio of the first and second highest ranks was 55%, and it could be confirmed from the measurement results by the X-ray diffraction method that the orientation of the crystal grains was slightly high.

REFERENCE SIGNS LIST

1,2,3quartz glass crucible4polycrystalline silicon raw material5silicon melt5amelt surface (initial melt surface position)6heater8carbon susceptor10quartz glass crucible body (crucible body)10aside wall portion of crucible body10bbottom portion of crucible body10ccorner portion of crucible body10iinner surface of crucible body10oouter surface of crucible body10trim upper-end surface of crucible body11transparent layer12opaque layer13A inner-surface coating film13B outer-surface coating film14A inner crystal layer14B outer crystal layer15A uncoated region15B uncoated region16deposition layer of raw material silica powder16A natural silica powder16B synthetic silica powder20strain measuring device21polarizing plate (polarizer)22polarizing plate (analyzer)23crucible piece24quarter-wave plate25light source30mold30iinner surface of mold31arc electrode32vent hole40EBSD device41EBSD detector42sample43electron beamLc compressive stress layerLt tensile stress layer