Method for evaluating and manufacturing quartz glass crucibles

Abstract

To provide an evaluation method of a quartz glass crucible capable of easily evaluating nondestructively a state of an oxygen deficiency defect generated by hydrogen doping, steam introduction or the like in a quartz glass crucible.SOLUTION: An evaluation method of a quartz glass crucible evaluates a quartz glass crucible having an outer layer made of opaque quartz glass containing air bubbles and an inner layer made of transparent quartz glass. The evaluation method includes a step for preparing a quartz glass crucible of the evaluation object, a step for irradiating the quartz glass crucible of the evaluation object with ultraviolet rays as excitation light, a step for detecting blue fluorescence emitted from the quartz glass crucible irradiated with the ultraviolet rays, and a step for evaluating a state of an oxygen deficiency defect in the outer layer of the quartz glass crucible based on the presence or absence of the blue fluorescence.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating and manufacturing a quartz glass crucible. [Background technology]

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

[0003] These quartz glass crucibles are generally manufactured by a method known as the arc rotary melting method. First, silicon dioxide powder (silica powder, quartz powder) is supplied as raw material powder into a rotating mold and formed into a crucible-shaped body by centrifugal force. The body is then heated and melted from the inside by an arc flame to form a translucent quartz glass crucible base (outer layer) (base formation step). Furthermore, during or after the formation of the crucible base, new silicon dioxide powder is supplied into the heated atmosphere within the crucible base, and a transparent quartz glass inner layer is formed on the inner surface of the crucible base (inner layer formation step). The method of forming an inner layer made of transparent quartz glass by heating while scattering quartz powder is also called the scattering method.

[0004] Furthermore, the outer layer of a quartz glass crucible is often formed using natural silicon dioxide powder, while the inner layer is often formed using synthetic silicon dioxide powder.

[0005] In the manufacture of such quartz glass crucibles, it is known to dope the inner layer of the quartz glass crucible with hydrogen. This hydrogen doping has the effect of suppressing the generation of bubbles. For example, Patent Document 1 describes a manufacturing method in which quartz raw material powder is fed into a mold to form a silica powder molded body having a crucible shape, and this silica powder molded body is heated and melted by arc discharge to obtain a silica glass crucible, in which hydrogen gas is supplied to the inner surface of the silica powder molded body during heating and melting by arc discharge. Furthermore, Patent Document 2 describes heating and holding a quartz glass crucible manufactured by the arc rotation melting method in a hydrogen or hydrogen-containing atmosphere.

[0006] Another known method for hydrogen doping a silica glass crucible is to dope the raw material powder with hydrogen (Patent Documents 3 and 4). This hydrogen-doped silica powder (often synthetic silica powder) is used to form a transparent silica glass layer, which is the inner layer of the silica glass crucible, using the above-mentioned scattering method.

[0007] Furthermore, in the manufacture of a silica glass crucible, it is also known to introduce water vapor into the silica glass crucible (Patent Document 5). Patent Document 5 describes that the introduction of water vapor in this manner can also suppress bubble expansion near the inner surface of the silica glass crucible. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-65622 [Patent Document 2] Japanese Patent Application Publication No. 05-208838 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-335513 [Patent Document 4] Japanese Patent Application Publication No. 2017-031007 [Patent Document 5] Japanese Patent Application Laid-Open No. 2001-348240 [Patent Document 6] Japanese Patent Application Publication No. 2018-35029 [Patent Document 7] Japanese Patent Application Laid-Open No. 2006-89301 Summary of the Invention [Problem to be solved by the invention]

[0009] As described above, hydrogen-doped silica powder as described in Patent Documents 3 and 4 is used to form a transparent silica glass layer using a spraying method. However, in transparent silica glass layers formed by the spraying method, hydrogen doping may not be sufficiently performed at intended locations in the inner layer. In particular, there may be variations in the state of hydrogen doping depending on the position. Furthermore, if hydrogen doping is insufficient, the bubble expansion suppression effect may not be fully achieved. In order to identify such locations, it has conventionally been necessary to perform heat treatment evaluation by cutting. For example, after cutting a sample from a quartz glass crucible, bubbles are expanded and made visible by VBT (vacuum baking test), and evaluation is performed based on the occurrence status. In this case, for example, in a vacuum of 2×10 -2 The test required a temperature of 1650°C and a pressure of 100 Pa or less for 2 hours and 10 minutes. This test was destructive and took a long time.

[0010] The present invention has been made to solve the above-mentioned problems, and aims to provide a method for evaluating a silica glass crucible that can easily and non-destructively evaluate the state of oxygen deficiency defects that have occurred in the outer layer of a silica glass crucible by hydrogen doping, introducing water vapor, etc. [Means for solving the problem]

[0011] The present invention has been made to solve the above-mentioned problems, and provides a method for evaluating a quartz glass crucible having an outer layer made of opaque quartz glass containing bubbles and an inner layer made of transparent quartz glass, comprising the steps of: preparing a quartz glass crucible to be evaluated; irradiating the quartz glass crucible to be evaluated with ultraviolet light as excitation light; detecting blue fluorescence emitted from the quartz glass crucible irradiated with the ultraviolet light; and evaluating the state of oxygen deficiency defects in the outer layer of the quartz glass crucible based on the presence or absence of the blue fluorescence.

[0012] With this method for evaluating a quartz glass crucible, the state of oxygen deficiency defects in the outer layer made of opaque quartz glass of the quartz glass crucible can be easily evaluated non-destructively based on the presence or absence of blue fluorescence. Since oxygen deficiency defects in the outer layer reflect the state of hydrogen doping and introduction of water vapor in the inner layer, the method for evaluating a quartz glass crucible of the present invention makes it possible to easily evaluate the state of hydrogen doping and introduction of water vapor in the inner layer non-destructively.

[0013] In this case, the distribution of oxygen deficiency defects in the outer layer of the silica glass crucible can be evaluated based on the distribution of the blue fluorescence in the outer layer of the silica glass crucible.

[0014] As described above, in the present invention, the distribution of oxygen deficiency defects in the outer layer of a silica glass crucible can be evaluated simply and non-destructively based on the distribution of blue fluorescence.

[0015] In addition, in the method for evaluating a quartz glass crucible of the present invention, the blue fluorescence can be fluorescence having a peak at a wavelength of around 395 nm.

[0016] In the method for evaluating a quartz glass crucible of the present invention, the ultraviolet light to be irradiated may have a peak wavelength near 254 nm.

[0017] In this way, the evaluation method for a quartz glass crucible of the present invention can easily evaluate the state of oxygen deficiency defects in the outer layer made of opaque quartz glass by detecting blue fluorescence that is generated as fluorescence having a peak wavelength around 395 nm when exposed to ultraviolet light having a peak wavelength around 254 nm.

[0018] Furthermore, it is preferable to detect the blue fluorescence by measuring a peak intensity A of the blue fluorescence and a peak intensity B of Rayleigh scattered light generated as a result of irradiating the ultraviolet light, and defining that the blue fluorescence has been detected when A and B satisfy the following formula (1): (A / B)×1000≧20...Equation (1)

[0019] In this way, by defining whether blue fluorescence is detected or not based on the intensity of blue fluorescence relative to the Rayleigh scattered light of the incident light, it is possible to more objectively evaluate the state of oxygen-deficient defects in the outer layer made of opaque quartz glass.

[0020] It is also preferable that the irradiation angle of the ultraviolet light is an angle shifted from the perpendicular direction to the inner surface of the quartz glass crucible, and that the detection of the blue fluorescence is carried out at an angle shifted from the specular reflection of the ultraviolet light.

[0021] By setting the irradiation angle of the irradiation light and the detection angle of the blue fluorescence in this way, it is possible to eliminate the influence of specular reflection of the irradiation light and to detect the Rayleigh scattered light and the blue fluorescence.

[0022] In the method for evaluating a silica glass crucible of the present invention, it is preferable to perform the evaluation without destroying the silica glass crucible.

[0023] The present invention makes it possible to non-destructively and simply evaluate the state of oxygen deficiency defects in the outer layer of a quartz glass crucible. Therefore, by performing the evaluation without destroying the quartz glass crucible, evaluation results can be obtained quickly and all quartz glass crucibles can be evaluated.

[0024] It is also preferable that the quartz glass crucible to be evaluated has an inner layer formed using hydrogen-doped raw silica powder, or that moisture is additionally introduced into the inner layer.

[0025] In this way, the method for evaluating a quartz glass crucible of the present invention is particularly suitable for evaluating a quartz glass crucible that uses a raw material silica powder doped with hydrogen for forming an inner layer, or a quartz glass crucible in which moisture has been introduced into the inner layer, and allows for easy evaluation of the state of oxygen deficiency defects in the outer layer of such a quartz glass crucible.

[0026] The present invention also provides a method for manufacturing a quartz glass crucible, comprising the steps of: manufacturing a quartz glass crucible having an outer layer made of opaque quartz glass containing bubbles and an inner layer made of transparent quartz glass; evaluating the manufactured quartz glass crucible as the quartz glass crucible to be evaluated using any of the above-mentioned methods for evaluating a quartz glass crucible; setting manufacturing conditions for manufacturing a new quartz glass crucible based on the results of evaluating the state of oxygen deficiency defects in the outer layer of the manufactured quartz glass crucible; and manufacturing a new quartz glass crucible under the set manufacturing conditions.

[0027] In this way, by using the method for evaluating a quartz glass crucible of the present invention, the evaluation results can be fed back to the manufacture of quartz glass crucibles. Because the method for evaluating a quartz glass crucible of the present invention can be carried out non-destructively and simply, the results can be fed back quickly to the manufacture of quartz glass crucibles, thereby improving productivity and quality. [Effects of the Invention]

[0028] The silica glass crucible evaluation method of the present invention allows for easy, non-destructive evaluation of the state of oxygen deficiency defects in the outer layer of a silica glass crucible, which reflects the state of hydrogen doping or water vapor introduction, based on the presence or absence of blue fluorescence. This allows for rapid evaluation of the inner layer of a silica glass crucible, improving productivity and eliminating the need to destroy the silica glass crucible that will be used as a product. Furthermore, the silica glass crucible evaluation method of the present invention can be used to feed back evaluation results into the manufacture of silica glass crucibles. Because the silica glass crucible evaluation method of the present invention can be performed non-destructively and easily, feedback can be quickly provided to the manufacture of silica glass crucibles. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a flowchart showing an outline of a method for evaluating a quartz glass crucible of the present invention. [Figure 2] 10 is a graph showing the relationship between blue fluorescence intensity and the density of bubbles exposed on the inner surface after VBT in Experimental Examples 1-1 to 1-8. [Figure 3] 10 is a photograph showing the state of blue fluorescence generation at various locations in a quartz glass crucible and the state of bubble generation after VBT in Experimental Examples 2-1 and 2-2. [Figure 4] 1 is a photograph of the quartz glass crucible in Example 1, irradiated with ultraviolet light and observed for blue fluorescent light emission, according to the method for evaluating a quartz glass crucible of the present invention. [Figure 5] FIG. 1 is a schematic cross-sectional view showing parts of a typical quartz glass crucible. DETAILED DESCRIPTION OF THE INVENTION

[0030] As described above, in the past, if the inner layer of a quartz glass crucible was not sufficiently doped with hydrogen, the bubble expansion suppression effect was not sufficient. In order to identify such areas, it was necessary to perform a heat treatment evaluation by cutting out the crucible, which was not a simple and quick method.

[0031] According to the inventors' research, the following mechanism is believed to be responsible for the insufficient hydrogen-doped areas. When hydrogen-doped silica powder is dispersed as raw material powder using the dispersion method and attached to a quartz glass crucible substrate, there are areas formed by direct adhesion of the raw material powder and areas formed by inertia during melting (e.g., areas where the raw material powder adhered and then moved in a glassy state). The areas formed by inertia have a reduced hydrogen concentration, resulting in insufficient bubble suppression. To determine this, heat treatment evaluation using the cutting process described above was previously required. This conventional method involves examining variations in the hydrogen-doped state by cutting a sample from a quartz glass crucible and actually heating the sample to generate bubbles. This is a destructive and time-consuming evaluation method. For example, it takes approximately 10 hours in total: 1 hour for destruction and marking of the quartz glass crucible, 1 hour for sample cutting, 30 minutes for pretreatment, 5 hours for VBT (vacuum bake test) including warming, 3 hours for cooling, and 30 minutes for evaluation. In this case, the evaluation takes time, and even if feedback is to be provided, production must be stopped during the evaluation, which reduces productivity.

[0032] To solve this problem, the inventors focused on oxygen deficiency defects that occur in the outer layer of a quartz glass crucible when hydrogen-doped silica powder is used as the raw material powder for manufacturing the crucible. By using hydrogen-doped silica powder, hydrogen diffuses from the inner layer (transparent silica glass layer) of the quartz glass crucible to the outer layer (opaque silica glass layer). This causes oxygen deficiency defects to form when oxygen absorbed from the silica and the melting atmosphere, which are the main causes of bubbles in the outer layer, combines with hydrogen. The presence of these oxygen deficiency defects generates fluorescence (blue fluorescence) when irradiated with ultraviolet light, allowing the state of oxygen deficiency defects in the outer layer of the quartz glass crucible to be determined, and ultimately the state of hydrogen doping. Note that the blue fluorescence occurs in the shallower portion of the boundary between the inner and outer layers, closer to the outer layer. Blue fluorescence does not necessarily occur throughout the entire thickness of the outer layer. Based on these findings, the inventors arrived at the present invention.

[0033] The present invention will be described in more detail below. The method for evaluating a silica glass crucible of the present invention is a method for evaluating a silica glass crucible having an outer layer made of opaque silica glass containing bubbles and an inner layer made of transparent silica glass, and is characterized by comprising the steps of: preparing a silica glass crucible to be evaluated; irradiating the silica glass crucible to be evaluated with ultraviolet light as excitation light; detecting blue fluorescence emitted from the quartz glass crucible irradiated with the ultraviolet light; and evaluating the state of oxygen deficiency defects in the outer layer of the silica glass crucible based on the presence or absence of the blue fluorescence.

[0034] First, the components of a typical silica glass crucible will be described with reference to Figure 5. The silica glass crucible 10 in Figure 5 has an outer layer 21 made of opaque silica glass containing bubbles, and an inner layer 22 made of transparent silica glass. As shown in Figure 5, the crucible shape of the silica glass crucible 10 typically consists of a bottom portion 12, a curved portion 13, and a straight body portion 14. The center of the bottom portion 12 is the bottom center 11, and the bottom portion 12 is also called the large R portion, and the curved portion 13 is also called the small R portion.

[0035] An outline of the silica glass crucible evaluation method of the present invention is shown in Figure 1. First, as shown in step S1, a silica glass crucible to be evaluated is prepared. The silica glass crucible prepared here can be a regular silica glass crucible, but the silica glass crucible evaluation method of the present invention is suitable for evaluating the state of oxygen deficiency defects, and is therefore suitable for evaluating a silica glass crucible in which the inner layer 22 is formed using hydrogen-doped raw silica powder, or an inner layer 22 to which moisture has been added. The present invention can also be applied without problem to silica glass crucibles in which only a portion of the inner layer 22 is doped with hydrogen or moisture, in addition to silica glass crucibles in which the entire inner layer 22 is doped with hydrogen or moisture.

[0036] Next, as shown in step S2, ultraviolet light is irradiated onto the silica glass crucible to be evaluated as excitation light. Next, as shown in step S3, blue fluorescence emitted from the quartz glass crucible irradiated with ultraviolet light is detected. It is preferable that the ultraviolet light irradiated here has a peak wavelength around 254 nm. In this case, the detected blue fluorescence will have a peak wavelength around 395 nm. Ultraviolet light with a wavelength around 254 nm can be easily obtained from a mercury lamp. Thus, in the silica glass crucible evaluation method of the present invention, the state of oxygen deficiency defects in the outer layer made of opaque silica glass can be more easily evaluated by detecting blue fluorescence with a peak wavelength around 395 nm generated by ultraviolet light with a peak wavelength around 254 nm. It is known that fluorescence with a peak wavelength around 395 nm in silica glass is due to oxygen deficiency defects (B2β). Furthermore, fluorescence with a wavelength of around 395 nm often has a peak at wavelengths of 394 to 396 nm, but this may vary slightly depending on the measuring device, and the peak may also be around 390 to 400 nm.

[0037] Next, as shown in step S4, the state of oxygen deficiency defects in the outer layer of the quartz glass crucible is evaluated based on the presence or absence of blue fluorescence. If blue fluorescence is generated by the operations of steps S2 and S3, it means that oxygen deficiency defects are present. If blue fluorescence is not generated, it means that oxygen deficiency defects are not present or their density is low.

[0038] The silica glass crucible evaluation method of the present invention allows for easy, non-destructive evaluation of the state of oxygen deficiency defects in the outer layer made of opaque silica glass of a silica glass crucible based on the presence or absence of blue fluorescence. Because oxygen deficiency defects in the outer layer reflect the state of hydrogen doping or water vapor introduction in the inner layer, the silica glass crucible evaluation method of the present invention allows for easy, non-destructive evaluation of the state of hydrogen doping or water vapor introduction. As described above, the location where blue fluorescence occurs, i.e., where oxygen deficiency defects occur, is the shallower portion of the boundary between the inner and outer layers near the outer layer. For example, if natural silica powder is used as the raw silica powder for the outer layer and synthetic silica powder is used as the raw silica powder for the inner layer, the outer layer will be a natural silica glass layer. In this case, oxygen in the outer layer (natural silica glass layer) combines with hydrogen introduced by hydrogen doping or water vapor introduction to form a natural transparent layer with few bubbles and oxygen deficiency defects. This natural transparent layer will emit blue fluorescence. Blue fluorescence does not necessarily occur throughout the entire thickness of the outer layer.

[0039] The above steps S1 to S4 make it possible to evaluate the state of oxygen deficiency defects in the entire or part of the outer layer of the quartz glass crucible. Therefore, when evaluating a quartz glass crucible in which an inner layer is formed using hydrogen-doped raw silica powder, the state of hydrogen doping in the inner layer by the diffusion method can be known, and feedback can be provided immediately to manufacturing. Similarly, when evaluating a quartz glass crucible in which moisture has been added to the inner layer, the state of the added moisture in the inner layer can be known, and feedback can be provided immediately to manufacturing.

[0040] Specifically, feedback can be provided in the method for manufacturing a silica glass crucible as follows. First, a silica glass crucible 10 (see FIG. 5) having an outer layer 21 made of opaque silica glass containing bubbles and an inner layer 22 made of transparent silica glass is manufactured by a normal method (Step A). Next, the manufactured silica glass crucible is used as the silica glass crucible to be evaluated and evaluated by the silica glass crucible evaluation method of the present invention in accordance with the above steps S1 to S4 (Step B). Based on the results of evaluating the state of oxygen deficiency defects in the outer layer 21 of the manufactured silica glass crucible 10 in Step B, manufacturing conditions for manufacturing a new silica glass crucible are set (Step C). Next, a new silica glass crucible is manufactured under the manufacturing conditions set in Step C (Step D).

[0041] In this way, the silica glass crucible evaluation method of the present invention can be used to feed back evaluation results in the manufacture of silica glass crucibles. Because the silica glass crucible evaluation method of the present invention can be performed non-destructively and easily, feedback can be quickly provided to the manufacture of silica glass crucibles, thereby improving productivity. With the silica glass crucible evaluation method of the present invention, by determining the fluorescence state of the outer layer of a silica glass crucible in a cooled state after melting, it is possible to determine the state of oxygen deficiency defects in the outer layer, and ultimately the state of hydrogen doping and moisture introduction in the inner layer, allowing for immediate feedback to the manufacture. As described above, while in the past it required, for example, about 10 hours after melting to obtain evaluation results, the present invention allows feedback in about 1 hour. Furthermore, since the present invention does not require destructive evaluation, 100% evaluation is possible.

[0042] In the method for evaluating a quartz glass crucible of the present invention, blue fluorescence can be confirmed visually. Specifically, ultraviolet light is irradiated onto the quartz glass crucible in a dark room, and the generation of blue fluorescence can be confirmed. The distribution of blue fluorescence in the outer layer of the quartz glass crucible can also be confirmed visually.

[0043] Furthermore, in the method for evaluating a quartz glass crucible of the present invention, the detection of blue fluorescence can be quantitatively defined based on numerical values. Specifically, this is as follows: The peak intensity (peak height) of blue fluorescence generated when irradiated with ultraviolet light as excitation light is measured as peak intensity A. Furthermore, the peak intensity (peak height) of Rayleigh scattered light generated as a result of irradiating with ultraviolet light is measured as peak intensity B. Here, it can be defined that blue fluorescence has been detected when the above A and B satisfy the following formula (1): (A / B)×1000≧20...Equation (1)

[0044] In this way, blue fluorescence can be detected without relying on visual inspection. The reason for using the above formula (1) is as follows.

[0045] Patent Documents 6 and 7 describe measuring red fluorescence to detect excess oxygen defects in a quartz glass crucible. In the case of red fluorescence, Raman scattered light and fluorescence are measured using an Ar laser with a wavelength of 514 nm as excitation light.

[0046] In the case of blue fluorescence, 254 nm ultraviolet light is used as excitation light, resulting in a fluorescence wavelength of 395 nm, so the same measurement method as for red fluorescence cannot be used. Because fluorescence intensity is affected by the intensity of the excitation light, it is preferable to normalize it using the ratio of these two. Normalization requires knowledge of the excitation light intensity, but excitation light intensity is not constant due to variations in equipment and deterioration over time. Therefore, Rayleigh scattered light, which has the same wavelength as the excitation light, is used as the standard. While Rayleigh scattered light theoretically has the same wavelength as the incident light, it often peaks around 253 nm to 256 nm, varying slightly depending on the measurement equipment.

[0047] However, even if Rayleigh scattered light is used as the standard, as described above, specularly reflected light of the excitation light, which is unnecessary for measurement, may be mixed into the light receiving unit. Therefore, it is preferable to set the irradiation angle of the UV light at an angle shifted from the perpendicular direction to the inner surface of the quartz glass crucible and to detect the blue fluorescence at an angle shifted from the specularly reflected UV light. For example, the irradiation surface of the quartz glass crucible can be tilted so that the angle of incidence of the excitation light is 60 degrees, and measurements can be performed with a spectrofluorometer.

[0048] The experimental example from which the above formula (1) was derived is shown below.

[0049] [Experimental Examples 1-1 to 1-8] The conventional silica glass crucible 10 shown in Fig. 5 was manufactured using hydrogen-doped synthetic silica powder as the raw material powder for the inner layer 22. Eight similar silica glass crucibles 10 were manufactured while varying the manufacturing conditions (Experimental Examples 1-1 to 1-8).

[0050] (Sample production) For each of the quartz glass crucibles 10 produced in Experimental Examples 1-1 to 1-8, a measurement sample was cut out from the inner layer 22 located in the straight body portion 14.

[0051] (Blue fluorescence measurement) Each sample was irradiated with ultraviolet light with a peak wavelength near 254 nm, and blue fluorescence with a peak wavelength near 395 nm was detected. The measurement device used was a JASCO FP-8500 spectrofluorometer. The measurement was performed by tilting the irradiated surface of the quartz glass crucible so that the angle of incidence of the excitation light was 60 degrees. The measurement conditions were set to a sensitivity that allowed the peak intensity of Rayleigh scattered light to be measured. The intensity of Rayleigh scattered light depends on the wavelength of the incident light, and at 254 nm, it is approximately 0.1% of the incident light intensity. The peak intensity ratio, normalized by the above formula (1) based on the peak intensity A of blue fluorescence and the peak intensity B of Rayleigh scattered light, was used as the fluorescence intensity ratio.

[0052] (Measurement of bubble density) After the blue fluorescence measurement, the bubble density after VBT, which is a conventional evaluation method, was measured for each sample of the quartz glass crucible 10 of Experimental Examples 1-1 to 1-8. -2 The sample was then held at 1650°C for 2 hours and 10 minutes at a pressure of 1 Pa or less to generate bubbles. After that, the density of bubbles exposed on the surface of each sample was visually confirmed.

[0053] The results of Experimental Examples 1-1 to 1-8 are shown in Table 1 and FIG.

[0054] [Table 1]

[0055] As can be seen from Table 1 and Figure 2, the bubble density after VBT is significantly suppressed when the fluorescence intensity ratio (A / B) × 1000 is 20 or more. This indicates that when formula (1) is satisfied, it can be determined that there are sufficient oxygen-deficient defects.

[0056] If it is difficult to measure the fluorescence intensity without destroying the quartz glass crucible, when actually checking the fluorescence of the quartz glass crucible, it is possible to grasp the quality state of the inner layer of the quartz crucible (the state of oxygen deficiency defects in the outer layer) by using a standard sample with a fluorescence intensity of 20 or more as calculated by equation (1) and comparing them.

[0057] When using the standard sample to feed back to the manufacturing conditions of the next quartz glass crucible to be manufactured, the following feedback can be carried out, for example.

[0058] First, if the fluorescence is the same as or stronger than that of a standard sample, the manufactured quartz glass crucible is deemed an acceptable product and sent to the next process.

[0059] On the other hand, if the fluorescence is weaker than the standard sample, this information is fed back to the manufacturing conditions of the next quartz crucible, for example, by setting the conditions so that the hydrogen-doped raw material powder adheres directly to the area where the fluorescence is weak.

[0060] Furthermore, quartz glass crucibles with weak fluorescence may not be used in products because the only way to actually confirm the bubble suppression effect is to destroy them.

[0061] The evaluation method of the present invention using blue fluorescence from a quartz glass crucible makes it possible to grasp the overall condition of the quartz glass crucible and also to provide immediate feedback for the next production.

[0062] Next, in the evaluation method of the silica glass crucible of the present invention, it will be shown with reference to the following Experimental Examples 2-1 and 2-2 that there is a correlation between visual observation of blue fluorescence and the state of bubble generation after VBT.

[0063] [Experimental Example 2-1] In a similar manner to Experimental Examples 1-1 to 1-8, but with slight changes to the manufacturing conditions, a conventional quartz glass crucible 10 shown in FIG. 5 was manufactured using hydrogen-doped synthetic quartz powder as the raw material powder for the inner layer 22 (Experimental Example 2-1).

[0064] (Sample production) For each of the produced quartz glass crucibles 10, samples of approximately 4 cm x approximately 8 cm were cut out every 100 mm from the bottom center 11 to the straight body portion 14. Of these, the portion at a distance of 0 mm (bottom center) from the bottom center 11 is the portion that includes the bottom center 11. The portions at distances of 100 mm, 200 mm, and 300 mm from the bottom center 11 are located in the bottom portion 12 (i.e., the large R portion). The portion at a distance of 400 mm from the bottom center 11 is located in the curved portion 13 (i.e., the small R portion). The portions at distances of 500 mm, 600 mm, and 700 mm from the bottom center 11 are located in the straight body portion 14. Of these, the portion at a distance of 500 mm from the bottom center 11 is located near the bottom of the straight body portion 14.

[0065] (Blue fluorescence measurement) Each sample was irradiated with ultraviolet light with a peak wavelength of approximately 254 nm, and the presence or absence of blue fluorescence with a peak wavelength of approximately 395 nm was visually confirmed. Photographs taken under ultraviolet light irradiation are shown in the "Fluorescence Generation Status" column in Figure 3. Blue fluorescence appears as a bright area on the left side of each sample in Figure 3. No blue fluorescence was observed in the bottom portion 12 (i.e., the large R portion), which is 300 mm away from the bottom center 11, or in the areas corresponding to the straight body portion 14 at 500 mm, 600 mm, and 700 mm.

[0066] (Measurement of bubble density) After the blue fluorescence measurement, the bubble density after VBT, which is a conventional evaluation method, was measured for each sample of the quartz glass crucible 10 of Experimental Example 2-1. -2 The sample was heated to 1000 Pa or less and held at 1650°C for 2 hours and 10 minutes to generate bubbles. The density of bubbles exposed on the surface of each sample was then visually confirmed. A sample with the bubble locations marked is shown in Figure 3 (column "Bubble generation status after VBT"). As a result, the number of exposed bubbles was greater in areas where blue fluorescence was not observed (distances of 300 mm, 500 mm, 600 mm, and 700 mm from the bottom center 11) than in other areas. This means that hydrogen doping in these areas was insufficient, and the bubble generation suppression effect was not sufficient.

[0067] [Experimental Example 2-2] Using the same method as in Experimental Examples 1-1 to 1-8 and Experimental Example 2-1, but with slight changes to the manufacturing conditions, a conventional quartz glass crucible 10 shown in Figure 5 was fabricated using hydrogen-doped synthetic quartz powder as the raw material powder for the inner layer 22 (Experimental Example 2-2).

[0068] For the quartz glass crucible 10 produced in Experimental Example 2-2, sample preparation, measurement of blue fluorescence, and measurement of bubble density were performed in the same manner as in Experimental Example 2-1. The results are shown in Figure 3. In Experimental Example 2-2, blue fluorescence was observed in all samples. Furthermore, in the bubble generation test after VBT, bubbles were suppressed in all samples.

[0069] The results of Experimental Examples 2-1 and 2-2 show that there is a correlation between the visual observation of blue fluorescence and the state of bubble generation after VBT. [Example]

[0070] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples.

[0071] [Example 1-1] The ordinary quartz glass crucible 10 shown in FIG. 5 was manufactured using hydrogen-doped synthetic quartz powder as the raw material powder for the inner layer 22 (Example 1-1).

[0072] The silica glass crucible 10 manufactured in Example 1-1 was irradiated from the inner surface with ultraviolet light having a wavelength of 254 nm as excitation light. As a result, a distribution of blue fluorescence was observed, as shown in Figure 4. As shown in Figure 4, blue fluorescence was observed in the curved portion 13 (small R portion) in Figure 4, but blue fluorescence was not observed or was weak from the bottom center 11 to the bottom portion 12 and the straight body portion 14. This shows that hydrogen doping was sufficient in the curved portion 13 of the manufactured silica glass crucible 10, resulting in a bubble suppression effect, but was insufficient in other portions.

[0073] [Examples 2-1 to 2-8] The conventional quartz glass crucible 10 shown in Figure 5 was manufactured using hydrogen-doped synthetic quartz powder as the raw material powder for the inner layer 22 in the same manner as in Example 1-1, except that the manufacturing conditions were slightly changed (Examples 2-1 to 2-8).

[0074] (Preparation of standard samples) Quartz glass crucibles were manufactured under various manufacturing conditions, and measurement samples were cut out from the quartz glass crucibles. From these samples, standard samples were prepared, which satisfied the above formula (1) where the fluorescence intensity (A / B) × 1000 was 20 or more and less than 25.

[0075] The silica glass crucibles 10 manufactured in Examples 2-1 to 2-8 were non-destructively irradiated from the inner surface with ultraviolet light having a wavelength of 254 nm as excitation light. The state of blue fluorescence generation was visually observed for the straight body portion 14 of the silica glass crucibles 10 of each Example. As a result, as shown in Table 2, blue fluorescence that was equal to or stronger than that of the standard sample was observed in Examples 2-1 to 2-4. On the other hand, blue fluorescence that was weaker than that of the standard sample was observed in Examples 2-5 to 2-8. This means that in Examples 2-1 to 2-4, the fluorescence intensity (A / B) × 1000 in the above formula (1) was 20 or greater (i.e., the amount of hydrogen doping was large and there were many oxygen deficiency defects), and in Examples 2-5 to 2-8, the fluorescence intensity (A / B) × 1000 in the above formula (1) was less than 20 (i.e., the amount of hydrogen doping was small and there were few oxygen deficiency defects).

[0076] [Table 2]

[0077] Furthermore, to confirm the above results, the actual bubble generation was investigated for the quartz glass crucibles 10 manufactured in Examples 2-1 to 2-8. Measurement samples were cut out from the quartz glass crucibles 10 of Examples 2-1 to 2-8, and the bubble density after VBT was measured. For each sample, a vacuum of 2×10 -2 The specimens were heated to 1650°C for 2 hours and 10 minutes at a pressure of 1000 Pa or less to generate bubbles. The density of the bubbles exposed on the surface of each specimen was then visually confirmed. The results are shown in Table 2.

[0078] As can be seen from Table 2, the amount of oxygen deficiency defects evaluated in the quartz glass crucibles 10 manufactured in Examples 2-1 to 2-8 in an undestructed state reflects the bubble density after VBT. That is, those with high fluorescence intensity (Examples 2-1 to 2-4) have a low exposed bubble density, and those with low fluorescence intensity (Examples 2-5 to 2-8) have a high exposed bubble density.

[0079] The present invention is not limited to the above-described embodiments, which are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0080] 10...quartz glass crucible, 11...bottom center, 12...bottom, 13...curved portion, 14...straight body portion, 21...outer layer, 22...inner layer.

Claims

1. A method for evaluating a quartz glass crucible having an outer layer made of opaque quartz glass containing bubbles and an inner layer made of transparent quartz glass, comprising: A step of preparing a quartz glass crucible to be evaluated; a step of irradiating the quartz glass crucible to be evaluated with ultraviolet light as excitation light; detecting blue fluorescence emitted from the quartz glass crucible irradiated with ultraviolet light; a step of evaluating the state of oxygen deficiency defects in the outer layer of the quartz glass crucible based on the presence or absence of the blue fluorescence; A method for evaluating a quartz glass crucible, comprising:

2. 2. The method for evaluating a silica glass crucible according to claim 1, wherein the distribution of oxygen deficiency defects in the outer layer of the silica glass crucible is evaluated based on the distribution of the blue fluorescence in the outer layer of the silica glass crucible.

3. 3. The method for evaluating a silica glass crucible according to claim 1, wherein the blue fluorescence has a peak at a wavelength of about 395 nm.

4. 4. The method for evaluating a quartz glass crucible according to claim 1, wherein the ultraviolet light to be irradiated has a peak wavelength near 254 nm.

5. detecting the blue fluorescence measuring a peak intensity A of the blue fluorescence and a peak intensity B of the Rayleigh scattered light generated as a result of irradiating the ultraviolet light; The method for evaluating a quartz glass crucible according to any one of claims 1 to 4, characterized in that the blue fluorescence is defined as being detected when A and B satisfy the following formula (1): (A / B)×1000≧20...Formula (1)

6. The irradiation angle of the ultraviolet light is set to an angle shifted from a direction perpendicular to the inner surface of the quartz glass crucible, The blue fluorescence is detected at an angle shifted from the specular reflection of the ultraviolet light.

6. The method for evaluating a quartz glass crucible according to claim 1, wherein the quartz glass crucible is a quartz glass crucible.

7. 7. The method for evaluating a silica glass crucible according to claim 1, wherein the evaluation is performed without destroying the silica glass crucible.

8. A method for evaluating a quartz glass crucible according to any one of claims 1 to 7, characterized in that the quartz glass crucible to be evaluated has an inner layer formed using raw silica powder doped with hydrogen, or has moisture additionally introduced into the inner layer.

9. A method for manufacturing a quartz glass crucible, comprising: A step of manufacturing a quartz glass crucible having an outer layer made of opaque quartz glass containing bubbles and an inner layer made of transparent quartz glass; A step of evaluating the manufactured quartz glass crucible as the quartz glass crucible to be evaluated by the method for evaluating a quartz glass crucible according to any one of claims 1 to 8; A step of setting manufacturing conditions for manufacturing a new quartz glass crucible based on the results of evaluating the state of oxygen deficiency defects in the outer layer of the manufactured quartz glass crucible; a step of manufacturing a new quartz glass crucible under the set manufacturing conditions; A method for manufacturing a quartz glass crucible, comprising the steps of:

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