JP7724066B2 - Method for evaluating and manufacturing quartz glass crucibles - Google Patents

Description

The present invention relates to a method for evaluating and manufacturing a quartz glass crucible.

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

These quartz glass crucibles are generally manufactured using 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 centrifugal force forms a crucible-shaped molded body. The molded body is then heated and melted from the inside using an arc flame to form a translucent quartz glass crucible base (outer layer) (base formation process). Furthermore, during or after the formation of the crucible base, additional silicon dioxide powder is supplied into the heated atmosphere within the crucible base, forming a transparent quartz glass inner layer on the inner surface of the crucible base (inner layer formation process). The method of forming an inner layer made of transparent quartz glass by heating while spraying quartz powder is also known as the spraying method.

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

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 supplied 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.

It is also known that a method of hydrogen doping a silica glass crucible involves doping 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.

It is also known that in the manufacture of quartz glass crucibles, water vapor is introduced into the quartz glass crucible (Patent Document 5). Patent Document 5 states that the introduction of water vapor in this manner can also suppress bubble expansion near the inner surface of the quartz glass crucible.

JP 2014-65622 A Japanese Patent Application Publication No. 05-208838 Japanese Patent Application Laid-Open No. 2003-335513 Japanese Patent Application Laid-Open No. 2017-031007 Japanese Patent Application Laid-Open No. 2001-348240 Japanese Patent Application Laid-Open No. 2018-35029 Japanese Patent Application Laid-Open No. 2006-89301

As described above, hydrogen-doped silica powders such as those described in Patent Documents 3 and 4 are used to form transparent silica glass layers using a spraying method. However, in transparent silica glass layers formed using the spraying method, hydrogen doping may not be sufficiently achieved at intended locations in the inner layer. In particular, the state of hydrogen doping may vary depending on the location. Furthermore, insufficient hydrogen doping may result in insufficient bubble expansion suppression. To identify such locations, heat treatment evaluation using cutting processing has traditionally been required. For example, after cutting a sample from a quartz glass crucible, bubbles are expanded and manifested by VBT (vacuum baking test), and evaluation is performed based on the bubble expansion status. In this case, for example, the sample must be held at 1650°C for 2 hours and 10 minutes at a vacuum of 2×10 ⁻² Pa or less. This test is destructive and time-consuming.

The present invention was made to solve the above-mentioned problems, and aims to provide a method for evaluating quartz glass crucibles that can easily and non-destructively evaluate the state of oxygen deficiency defects that occur in the outer layer of a quartz glass crucible through hydrogen doping, water vapor introduction, etc.

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.

This method for evaluating a silica glass crucible makes it possible to easily and non-destructively evaluate the state of oxygen deficiency defects in the outer layer of the silica glass crucible, which is made of opaque silica glass, based on the presence or absence of blue fluorescence. Since oxygen deficiency defects in the outer layer reflect the state of hydrogen doping and water vapor introduction in the inner layer, the method for evaluating a silica glass crucible of the present invention makes it possible to easily and non-destructively evaluate the state of hydrogen doping and water vapor introduction in the inner layer.

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

In this way, the present invention makes it possible to easily and non-destructively evaluate the distribution of oxygen deficiency defects in the outer layer of a quartz glass crucible based on the distribution of blue fluorescence.

Furthermore, in the method for evaluating a quartz glass crucible of the present invention, the blue fluorescence can be fluorescence having a peak wavelength around 395 nm.

Furthermore, in the method for evaluating a quartz glass crucible of the present invention, the ultraviolet light irradiated can be ultraviolet light having a peak wavelength around 254 nm.

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

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 irradiation with ultraviolet light, and defining that the blue fluorescence has been detected when A and B satisfy the following formula (1):
(A/B)×1000≧20...Formula (1)

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 deficiency defects in the outer layer made of opaque quartz glass.

It is also preferable that the irradiation angle of the ultraviolet light be offset from the perpendicular direction to the inner surface of the quartz glass crucible, and that the blue fluorescence be detected at an angle offset from the specular reflection of the ultraviolet light.

By using these illumination angles for the irradiated light and detection angles for the blue fluorescence, it is possible to eliminate the influence of specular reflection of the irradiated light and detect Rayleigh scattered light and blue fluorescence.

Furthermore, in the method for evaluating a quartz glass crucible of the present invention, it is preferable to perform the evaluation without destroying the quartz glass crucible.

This invention makes it possible to easily and non-destructively 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.

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

As such, the silica glass crucible evaluation method of the present invention is particularly suitable for evaluating silica glass crucibles that use raw silica powder doped with hydrogen to form the inner layer, or silica glass crucibles 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 these silica glass crucibles.

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 one 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.

In this way, 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, thereby improving productivity and quality.

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 quartz glass crucible that will become the product. Furthermore, the silica glass crucible evaluation method of the present invention can be used to feed back evaluation results into the manufacture of quartz glass crucibles. Because the silica glass crucible evaluation method of the present invention can be performed non-destructively and easily, it allows for rapid feedback into the manufacture of quartz glass crucibles.

1 is a flowchart showing an outline of a method for evaluating a quartz glass crucible of the present invention. 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. 10 is a photograph showing the state of blue fluorescence generation at each location of the quartz glass crucible and the state of bubble generation after VBT in Experimental Examples 2-1 and 2-2. 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. FIG. 1 is a schematic cross-sectional view showing parts of a typical quartz glass crucible.

As mentioned 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, which was not a simple and quick method.

According to the inventors' research, the following mechanism is believed to be responsible for insufficient hydrogen doping. When hydrogen-doped silica powder is dispersed as raw material powder using the dispersion method and attached to a quartz glass crucible substrate, some areas are formed by direct deposition of the raw material powder, while others are formed by inertia during melting (e.g., areas where the raw material powder adheres and then moves in a glassy state). These inertial areas have a reduced hydrogen concentration, resulting in insufficient bubble suppression. To determine this, a heat treatment evaluation using the cutting process described above was previously required. This conventional method involves examining variations in the hydrogen doping state by cutting a sample from the quartz glass crucible and heating it 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, evaluation took time, and even if feedback was to be provided, production had to be stopped during the evaluation, resulting in a decline in productivity.

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, the main cause of bubbles in the outer layer, and from the molten atmosphere combines with hydrogen. The presence of these oxygen deficiency defects produces 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 ascertained, and ultimately the state of hydrogen doping. Note that the blue fluorescence occurs in the shallow 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. These findings led the inventors to arrive at the present invention.

The present invention will be described in more detail below. The method for evaluating a quartz glass crucible of the present invention is 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, and is characterized by 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.

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

An outline of the silica glass crucible evaluation method of the present invention is shown in Figure 1. First, as shown in step S1, the 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 those in which the inner layer 22 is formed using hydrogen-doped raw silica powder, or those in which moisture has been added to the inner layer 22, in order to evaluate the state of oxygen deficiency defects. Furthermore, in addition to silica glass crucibles in which the entire inner layer 22 is doped with hydrogen or moisture, the present invention can also be applied without problem to silica glass crucibles in which only a portion is doped with hydrogen or moisture.

Next, as shown in step S2, ultraviolet light is irradiated onto the quartz 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 near 254 nm. In this case, the detected blue fluorescence has a peak wavelength near 395 nm. Ultraviolet light with a wavelength near 254 nm can be easily obtained from a mercury lamp. Thus, the quartz glass crucible evaluation method of the present invention detects blue fluorescence with a peak wavelength near 395 nm generated by ultraviolet light with a peak wavelength near 254 nm, making it easier to evaluate the state of oxygen deficiency defects in the outer layer made of opaque quartz glass. It is known that fluorescence with a peak wavelength near 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 between 394 and 396 nm, but this can vary slightly depending on the measuring device, and the peak may also be around 390 to 400 nm.

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 produced by the operations of steps S2 and S3, it means that oxygen deficiency defects are present. If blue fluorescence is not produced, it means that oxygen deficiency defects are not present or their density is low.

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 opaque silica glass outer layer 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 generates blue fluorescence. Blue fluorescence does not necessarily occur throughout the entire thickness of the outer layer.

The above steps S1 to S4 make it possible to evaluate the state of oxygen deficiency defects in the entire or partial outer layer of a quartz glass crucible. Therefore, when evaluating a quartz glass crucible whose 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 determined, allowing for immediate feedback to manufacturing. Similarly, when evaluating a quartz glass crucible whose inner layer has had additional moisture introduced, the state of the added moisture in the inner layer can be determined, allowing for immediate feedback to manufacturing.

Specifically, feedback can be provided in the manufacturing method of a silica glass crucible as follows. First, a silica glass crucible 10 (see Figure 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 conventional method (Step A). Next, the manufactured silica glass crucible is used as the quartz glass crucible to be evaluated and evaluated using the silica glass crucible evaluation method of the present invention, following steps S1 to S4 above (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 using the manufacturing conditions set in Step C (Step D).

In this way, 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, thereby improving productivity. With the silica glass crucible evaluation method of the present invention, by understanding the state of fluorescence in the outer layer of a silica glass crucible after it has melted and cooled, 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, because the present invention does not require destructive evaluation, 100% evaluation is possible.

In the silica glass crucible evaluation method of the present invention, blue fluorescence can be confirmed visually. Specifically, ultraviolet light is irradiated onto the silica glass crucible in a dark room, and the generation of blue fluorescence can be confirmed. The distribution of blue fluorescence on the outer layer of the silica glass crucible can also be confirmed visually.

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, the method 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, blue fluorescence can be defined as being detected when the above A and B satisfy the following formula (1):
(A/B)×1000≧20...Formula (1)

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

Patent documents 6 and 7 describe measuring red fluorescence to detect excess oxygen defects in quartz glass crucibles. 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.

In the case of blue fluorescence, 254 nm ultraviolet light is used as excitation light, and the resulting fluorescence wavelength is 395 nm, so it cannot be measured in the same way as red fluorescence. Because fluorescence intensity is affected by the intensity of the excitation light, it is preferable to normalize using the ratio of these two. Normalization requires knowledge of the excitation light intensity, but excitation light intensity is not constant as it differs depending on the device and deteriorates over time. For this reason, Rayleigh scattered light, which has the same wavelength as the excitation light, is used as the standard. In principle, Rayleigh scattered light has the same wavelength as the incident light, but this varies slightly depending on the measurement device, and there is often a peak around 253 nm to 256 nm.

However, even when Rayleigh scattered light is used as the standard as described above, specularly reflected excitation light that is unnecessary for measurement may be mixed into the light receiving unit. For this reason, it is preferable to set the irradiation angle of the ultraviolet 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 ultraviolet 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 taken with a spectrofluorometer.

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

[Experimental Examples 1-1 to 1-8]
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. Eight similar quartz glass crucibles 10 were manufactured while varying the manufacturing conditions (Experimental Examples 1-1 to 1-8).

(Sample preparation)
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 body portion 14 .

(Measurement of blue fluorescence)
Each sample was irradiated with ultraviolet light having a peak at a wavelength of approximately 254 nm, and blue fluorescence having a peak at a wavelength of approximately 395 nm was detected. The measurement device used was a JASCO FP-8500 spectrofluorometer. The measurement was performed by tilting the irradiation 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 achieve 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 the blue fluorescence and the peak intensity B of the Rayleigh scattered light, was used as the fluorescence intensity ratio.

(Measurement of bubble density)
After measuring the blue fluorescence, 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. Bubbles were generated in each sample by maintaining the sample at a vacuum of 2×10 ⁻² Pa or less and at 1650° C. for 2 hours and 10 minutes. The density of bubbles exposed on the surface of each sample was then visually confirmed.

The results of Experimental Examples 1-1 to 1-8 are shown in Table 1 and Figure 2.

As can be seen from Table 1 and Figure 2, when the fluorescence intensity ratio (A/B) x 1000 is 20 or greater, the bubble density after VBT is significantly suppressed. This indicates that when formula (1) is satisfied, it can be determined that sufficient oxygen deficiency defects are present.

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 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.

When using a standard sample to provide feedback to the manufacturing conditions of the next quartz glass crucible to be produced, the following feedback can be used, for example:

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

On the other hand, if the fluorescence is weaker than the standard sample, this can be fed back into the manufacturing conditions for the next quartz crucible. For example, the conditions can be set so that the hydrogen-doped raw material powder adheres directly to areas with weak fluorescence.

Furthermore, quartz glass crucibles with weak fluorescence can be avoided from being used in products, as the only way to actually confirm the bubble suppression effect is to destroy them.

The evaluation method of the present invention, which uses the blue fluorescence of a quartz glass crucible, makes it possible to grasp the overall condition of the quartz glass crucible and provide immediate feedback for the next production run.

Next, we will demonstrate, with reference to Experimental Examples 2-1 and 2-2 below, that there is a correlation between visual observation of blue fluorescence and the bubble generation status after VBT in the evaluation method for quartz glass crucibles of the present invention.

[Experimental Example 2-1]
In a similar manner to Experimental Examples 1-1 to 1-8, but with slight changes to the manufacturing conditions, 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 (Experimental Example 2-1).

(Sample preparation)
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.

(Measurement of blue fluorescence)
Each sample was irradiated with ultraviolet light having a peak wavelength of approximately 254 nm, and the presence or absence of blue fluorescence having 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 areas corresponding to the straight body portion 14 at 500 mm, 600 mm, and 700 mm.

(Measurement of bubble density)
After measuring the blue fluorescence, the bubble density after VBT, a conventional evaluation method, was measured for each sample of the quartz glass crucible 10 of Experimental Example 2-1. Bubbles were generated in each sample by maintaining the sample at a vacuum of 2×10 ⁻² Pa or less and at 1650°C for 2 hours and 10 minutes. The density of bubbles exposed on the surface of each sample was then visually confirmed. Samples with markings on the bubble locations are shown in FIG. 3 (the "Bubble Generation Status After VBT" column). As a result, the number of exposed bubbles was greater in areas where blue fluorescence was not observed (distances from the bottom center 11 of 300 mm, 500 mm, 600 mm, and 700 mm) than in other areas. This means that hydrogen doping was insufficient in these areas, and the bubble generation suppression effect was insufficient.

[Experimental Example 2-2]
In a manner similar to that of Experimental Examples 1-1 to 1-8 and Experimental Example 2-1, but with slight changes to the manufacturing conditions, the normal 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 2-2).

For the quartz glass crucible 10 produced in Experimental Example 2-2, sample preparation, blue fluorescence measurement, and bubble density measurement 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.

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

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

[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).

The quartz 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 indicates that the curved portion 13 of the manufactured quartz glass crucible 10 was sufficiently hydrogen-doped, resulting in a bubble-suppressing effect, but that this was insufficient in other areas.

[Examples 2-1 to 2-8]
The 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 in the same manner as in Example 1-1, except that the manufacturing conditions were slightly changed (Examples 2-1 to 2-8).

(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) of the fluorescence intensity (A/B)×1000 being 20 or more and less than 25.

The quartz 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 straight body portion 14 of the quartz glass crucibles 10 of each Example was visually observed for the generation of blue fluorescence. As a result, as shown in Table 2, blue fluorescence observed in Examples 2-1 to 2-4 was either the same or stronger than that of the standard sample. On the other hand, blue fluorescence observed in Examples 2-5 to 2-8 was weaker than that of the standard sample. This means that in Examples 2-1 to 2-4, the fluorescence intensity (A/B) x 1000 in the above formula (1) was 20 or greater (i.e., the amount of hydrogen doping was high and there were many oxygen deficiency defects). In Examples 2-5 to 2-8, the fluorescence intensity (A/B) x 1000 in the above formula (1) was less than 20 (i.e., the amount of hydrogen doping was low and there were few oxygen deficiency defects).

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, bubbles were generated by maintaining the sample at a vacuum of 2×10 ⁻² Pa or less and 1650°C for 2 hours and 10 minutes. The density of bubbles exposed on the surface of each sample was then visually confirmed. The results are also shown in Table 2.

As can be seen from Table 2, the amount of oxygen deficiency defects evaluated in the non-destructive quartz glass crucibles 10 manufactured in Examples 2-1 to 2-8 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, while those with low fluorescence intensity (Examples 2-5 to 2-8) have a high exposed bubble density.

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

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

Claims (9)

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;
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. The method for evaluating a silica glass crucible described in claim 1, characterized in that 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. The method for evaluating a quartz glass crucible according to claim 1 or 2, characterized in that the blue fluorescence has a peak wavelength around 395 nm. A method for evaluating a quartz glass crucible according to any one of claims 1 to 3, characterized in that the ultraviolet light irradiated has a peak wavelength around 254 nm. 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) 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 method for evaluating a quartz glass crucible according to any one of claims 1 to 5, characterized in that the detection of the blue fluorescence is performed at an angle shifted from the specularly reflected light of the ultraviolet light. A method for evaluating a quartz glass crucible according to any one of claims 1 to 6, characterized in that the evaluation is performed without destroying the quartz glass crucible. 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. 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;
and a step of manufacturing a new quartz glass crucible under the set manufacturing conditions.