JP2001342030A - Remelted quartz glass crucible and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high quality quartz glass crucible that is substantially free from a fine bubble and a foreign matter in an internal surface layer of the crucible and a method of manufacturing it. SOLUTION: The quartz glass crucible that a luminous point occurs in a heated region after heating the internal surface of the crucible at 800-1500 deg.C is held at <1500 deg.C, while the internal surface of the crucible is exposed to local heating at 1850-2400 deg.C by an oxyhydrogen flame or a plasma flame, thus removing the luminous point by remelting its region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-quality quartz glass crucible free from irregularities and dirt on the inner surface and containing substantially no fine bubbles or foreign matter in the inner surface layer. The quartz glass crucible of the present invention is suitable as a crucible for pulling a silicon single crystal.

[0002]

2. Description of the Related Art In a method of manufacturing a silicon single crystal in which a silicon single crystal is pulled from a silicon melt, a quartz glass crucible containing the silicon melt is heated to a temperature higher than the melting point of silicon, and an inner surface of the crucible in contact with the silicon melt. If the layer contains air bubbles or foreign matter, or has irregularities or dirt on the inner surface, it reacts with the silicon melt to produce local crystals such as cristobalite, and the silicon that is pulled up This is one of the causes for lowering the crystallization rate. Therefore, the inner layer of the quartz crucible is formed as a transparent layer free of bubbles and foreign matter on the inner surface layer, with the surface being as smooth and free of dirt as possible.

However, the conventional quartz glass crucible has a very thin surface layer (inner surface layer: inner surface layer) in contact with the inner surface even if the amount of bubbles in the entire inner transparent layer (about 0.5 to 3.5 mm thick) is small. (About 0.5 mm thick from the surface), there may be a case where a large number of fine bubbles which are difficult to recognize with the naked eye are included. When a quartz glass crucible is manufactured by the rotary molding method, the inner surface layer is the part where the quartz powder melts first and becomes a coating of the molten layer, so when fine bubbles are taken in this part, the quartz fused layer is depressurized. However, it is difficult to remove the fine bubbles by sucking them to the outside, and there is a problem that the fine bubbles are likely to remain in this portion.

[0004] Since the bubbles contained in the inner surface layer are transparent fine bubbles, it is difficult to find them with the naked eye. Although it can be detected by using a microscope, it is necessary to cut out a sample with a normal detection method using a microscope, which is not suitable for inspection of shipped products. Further, according to the inspection method of observing the image of the microscope on a monitor, it is not necessary to cut out the observation sample, but it is not suitable for observing the entire crucible because the field of view is limited. Further, in this method, it is difficult to observe dirt and irregularities on the inner surface of the crucible, and even if bubbles or foreign substances are detected, they cannot be removed immediately. Further, there is a problem that the cost of the system configuration increases.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the conventional quartz glass crucible. The quartz glass crucible has fine bubbles and foreign matter contained in an inner surface layer thereof.
Another object of the present invention is to provide a high-quality quartz glass crucible from which irregularities on the inner surface and contaminants attached to the inner surface are easily detected and removed.

[0006]

According to the present invention, there is provided (1) a quartz glass crucible in which, when the inner peripheral surface of a crucible is heated to a temperature higher than the red heat temperature and lower than the softening temperature, a bright spot is generated in a heated area, the outer surface of the crucible is maintained lower than the softening temperature. On the other hand, the present invention relates to a re-melted quartz glass crucible characterized by locally heating an inner surface layer of a crucible to a softening temperature or higher by an oxyhydrogen flame or a plasma flame to re-melt a bright spot generating portion to remove a bright spot.

Further, the present invention relates to (2) a quartz glass crucible in which, when the inner peripheral surface of the crucible is heated to 800 ° C. to 1500 ° C., a bright spot is generated in the heated area,
While maintaining the temperature below 0 ° C., the inner surface of the crucible is locally heated to 1850 ° C. to 2400 ° C. by an oxyhydrogen flame or a plasma flame to re-melt the bright spot generating portion to remove the bright spot. The present invention relates to a method for manufacturing a quartz glass crucible.

The production method of the present invention comprises: (3) a method of sandblasting the inner surface layer of the quartz glass crucible before re-melting, with respect to the quartz glass crucible from which a bright spot is detected;
(4) A method in which a cooled quartz glass crucible is placed in a heating furnace after annealing and then annealed to remove thermal distortion. (5) Using a quartz burner, scan the quartz burner along the inner surface of the crucible. And heating the inner surface layer of the crucible.

[0009] The quartz glass crucible of the present invention is manufactured by heating the inner surface of the quartz glass crucible to a constant temperature and observing the bright spots emerging on the inner surface. Alternatively, it is a high-quality crucible in which fine bubbles and foreign substances contained in the inner surface layer are detected, and these are removed by re-melting the inner surface layer by oxyhydrogen flame or plasma flame. Since these fine bubbles and foreign matter are easily removed by re-melting or sandblasting after detection, a high-quality quartz glass crucible can be obtained at low cost. In addition, since this quartz glass crucible is free from irregularities and dirt on the inner surface, and does not substantially contain fine bubbles or foreign matter in the inner surface layer, it can be used for pulling a silicon single crystal to achieve an excellent single crystal yield. Obtainable. Further, according to the manufacturing method of the present invention, the above quartz glass crucible can be obtained at low cost.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. The quartz glass crucible of the present invention is a quartz glass crucible that produces a bright spot in the heating region when the inner peripheral surface of the crucible is heated to a temperature higher than the red heat temperature and lower than the softening temperature.
The crucible outer surface is maintained at a temperature lower than the softening temperature, while the crucible inner surface is locally heated to a temperature higher than the softening temperature by an oxyhydrogen flame or a plasma flame, and the bright spot generating portion is re-melted to remove the bright spot. It is a re-melted quartz glass crucible. In addition, the manufacturing method of the quartz glass crucible used for re-melting is not limited. A quartz glass crucible manufactured by a rotary molding method or another method can be widely used.

The present invention uses an oxyhydrogen flame or a plasma flame as a heating means for re-melting. Since the oxyhydrogen flame is a local heating using a burner, it is possible to selectively and quickly re-melt a portion where a bright spot occurs. Further, the heating density per unit area is very high, and therefore the crucible inner surface layer is mainly heated in a short time, so that the temperature of the crucible outer surface layer can be kept low. The plasma flame can also be locally heated. The heating burner is preferably mounted on the moving means so that the outlet of the flame runs along the inner surface of the crucible. The heating burner is preferably a quartz burner so that impurities are not mixed.

The heating temperature of the inner surface of the quartz glass crucible during the observation of the bright spot is higher than the red heat temperature and the softening temperature of the quartz glass.
(Softening point). The red heat temperature is a temperature at which a heated portion of a quartz glass crucible starts to show a red color, and is approximately 800 ° C.
It is. If the heated part does not glow red, no bright spot due to fine bubbles or foreign matter is observed. On the other hand, if the heating temperature exceeds the softening temperature of the quartz glass (about 1700 ° C.), the crucible is deformed and unevenness is generated, which is not preferable. 1500 ° C. or lower is suitable for clearly distinguishing the bright spot, and 1400 ° C. or lower is preferable. If the temperature exceeds 1500 ° C., the bright spot on the crucible surface and its surroundings have the same brightness, so that it is difficult to distinguish the bright spot. The surface temperature may be measured with an infrared thermometer or the like.

[0013] The inner surface of the crucible is heated to above the red heat temperature and below the softening temperature of quartz glass, preferably from 800 ° C to 1500 ° C.
When the crucible is heated to a temperature above, the crucible whose inner surface layer contains microbubbles or whose crucible inner surface has irregularities will reflect light because the refractive index of this part is different from that of the surroundings. Observed as a brighter spot. In addition, when a foreign substance is contained in the inner surface layer of the crucible or a contaminant adheres to the inner surface, a material having a higher emissivity than quartz glass is observed to be brighter than the surroundings. Therefore, it is possible to determine the presence or absence of irregularities and dirt on the inner surface, or fine bubbles and foreign substances contained in the inner surface layer, based on the bright spot. Since the emissivity of most foreign substances and contaminants is larger than that of quartz glass, many of them are observed as bright spots.

Next, for those in which a bright spot is generated in the heating area, the temperature of the outer surface of the crucible is kept lower than the softening temperature, while the calorific value of the oxyhydrogen flame or the plasma flame is increased to raise the softening temperature of the inner surface layer of the crucible. Heating is performed as described above, and re-melting is performed to remove bright spots. If the inner surface layer is remelted while the temperature of the outer surface of the crucible is higher than its softening temperature, the crucible may be deformed. Specifically, the outer surface of the crucible is maintained at, for example, 1500 ° C or lower, preferably 1400 ° C or lower, and the inner surface of the crucible is maintained at 1850 ° C to 2400 ° C, preferably 2000 ° C to 2 ° C.
Heat to 350 ° C. to re-melt. By controlling the temperature of the outer surface and the inner surface of the crucible within the above range, the crucible does not deform even if the inner surface layer of the crucible is re-melted.

In the case of re-melting, if the outer surface of the crucible is exposed to cold air without using a mold to promote heat dissipation of the crucible,
The temperature of the outer surface of the crucible is 1500 ° C. or less, preferably 14 ° C.
It can be suppressed to not more than 00 ° C. By the way, as already mentioned, since oxyhydrogen flame and plasma flame are local heating,
It is easy to suppress the temperature of the crucible outer surface to 1400 ° C. or less even when the bright spot generating portion on the crucible inner surface is heated to a temperature higher than the softening temperature.

[0016] By remelting the inner surface layer of the crucible, the fine bubbles contained in this portion are extruded and burst to the inner surface, and the pinholes are filled with the fused quartz glass to substantially remove the bubbles. It becomes a quartz glass layer that does not contain. The surface irregularities disappear and become smooth, and the foreign matter is volatilized and removed.

The inner surface of the crucible is kept at 1850 ° C. to 240 ° C.
In order to re-melt by heating to 0 ° C., the calorific value of the oxyhydrogen flame or plasma flame should be 500 to 3000 W / cm ² , preferably 10 to
At a rate of 00 to 2500 W / cm ² , re-melting takes about 1 minute.
The optimum distance from the burner tip to the crucible inner surface depends on the burner. If the distance is too short, the unburned gas hits the inner surface of the crucible, which is not preferable. On the other hand, if the distance is long, the heating area of the inner surface of the crucible increases, but the amount of heat per heating area decreases, so that the heating efficiency decreases.

The quartz glass crucible having a bright spot can be sandblasted on the inner surface of the crucible prior to remelting the inner surface layer, thereby reducing the burden of the remelting process. By performing the sandblasting, a portion containing fine bubbles and foreign matter is scraped off, so that the remelting time can be reduced. The sandblasting is performed, for example, by blowing silica particles with high-pressure air of ^{2 to} 7 kg / cm ² .

Further, when the quartz glass crucible is locally heated by an oxyhydrogen flame or a plasma flame, the quartz glass crucible is somewhat heat-strained. Therefore, after re-melting, the quartz glass crucible is put into a heating furnace and annealed to remove the heat distortion. Is preferred.
As a specific example of the annealing treatment, a temperature of room temperature (about 25 ° C.)
The temperature may be raised to 200 ° C. in 2 hours, maintained at 1200 ° C. for 2 hours, gradually cooled from 1200 ° C. to 700 ° C. at a rate of 1 ° C./min, and then forcedly cooled or naturally cooled to 700 ° C. to room temperature.

The quartz glass crucible where the bright spots are observed is subjected to the above-mentioned re-melting treatment to remove the bright spots,
A quartz glass crucible substantially free of luminescent spots can be obtained. When the number of bright spots is 10 / cm ² or less, preferably 3 / cm ² or less, the devitrification area of the crucible can be suppressed in the devitrification test, and a high average single crystallization ratio is achieved. can do. Specifically, the number of bright spots is 10
/ cm ² or less crucible under argon atmosphere, 5-20 Tor
r, Under heating conditions of 1500 ± 50 ° C. and 20 to 50 hours, the devitrification area of the inner surface is approximately 30% in area ratio.
When the silicon single crystal is pulled up using this crucible, a single crystallization ratio of about 70% on average can be obtained. In addition, a crucible having 3 or less bright spots does not substantially cause devitrification of the inner surface, and has an average of 7 / cm ^2.
A high single crystallization ratio of about 7% can be obtained. In addition,
In the present invention, the number of bright spots is preferably 3 / c when it is said that the crucible inner surface layer is substantially free of fine bubbles and foreign matter.
It refers to that at m ² or less. Further, the remelting of the present invention may be applied to the entire inner surface of the crucible, or may be locally applied to a portion where a bright spot exists.

[0021]

EXAMPLE A quartz glass crucible having a diameter of 22 inches (inner transparent layer: 2 mm, outer opaque layer: 10 m) by a rotary molding method.
m) were produced. About this quartz glass crucible,
Using a quartz burner, the inner surface of the
After heating to 100 ° C., the number of bright spots was checked. Next, the calorific value of the oxyhydrogen flame was increased, and the crucible inner surface layer was re-melted under the conditions shown in Table 1. The remelted crucible was inspected for any change in shape. Further, after the re-melted crucible was annealed under the conditions shown in Table 1, the crucible was placed in an electric heating furnace, and was subjected to 20 To
A devitrification test was performed by heating at a constant temperature of 1500 ° C. for 24 hours in an argon atmosphere of rr. Further, a silicon single crystal was pulled up using another re-melted crucible, and a single crystallization ratio was obtained. The results are shown in Table 1.

[0022]

[Table 1]

[0023]

According to the quartz glass crucible of the present invention, the inner surface layer of the crucible is heated to a certain temperature by an oxyhydrogen flame or a plasma flame to detect a bright spot, and the inner surface of the crucible is further heated to a softening temperature or higher. A crucible from which fine bubbles and foreign substances contained in the surface layer have been removed.There is no irregularity or dirt on the inner surface, and the inner surface layer contains substantially no fine bubbles or foreign substances. A single crystal yield can be obtained. Further, since the present invention is a local heating using an oxyhydrogen flame or a plasma flame, a portion where a luminescent spot occurs can be selectively and quickly re-melted. Furthermore, since the crucible inner surface is rapidly and intensively heated, the temperature of the crucible outer surface can be kept low.

Continued on the front page (72) Inventor Takahiro Sato 5-14-3 Ibarjima, Akita City, Akita Prefecture Mitsubishi Materials Quartz Co., Ltd. Development Center F-term (reference) 4G014 AH23 5F053 AA12 BB04 BB13 FF04 RR04 RR07

Claims (5)

[Claims] 1. A quartz glass crucible in which a heating area has a bright spot when the inner peripheral surface of the crucible is heated to a temperature higher than the red heat temperature and lower than the softening temperature, while maintaining the outer surface of the crucible lower than the softening temperature, while maintaining an oxyhydrogen flame or a plasma flame. A remelted quartz glass crucible characterized in that a crucible inner surface layer is locally heated to a temperature equal to or higher than a softening temperature, and a bright spot generating portion is remelted to remove a bright spot. 2. The crucible has an inner peripheral surface of 800 ° C. to 1500 ° C.
In the case of a quartz glass crucible that produces a bright spot in the heating area when heated, the crucible outer surface is maintained at less than 1500 ° C., and the crucible inner surface is locally heated to 1850 ° C. to 2400 ° C. by oxyhydrogen flame or plasma flame, A method for producing a re-melted quartz glass crucible, characterized by re-melting a generated portion to remove a bright spot. 3. The method according to claim 1, wherein the inner surface layer of the quartz glass crucible for which a bright spot is detected is subjected to sandblasting before remelting. 4. The method according to claim 2, wherein after remelting, the cooled quartz glass crucible is placed in a heating furnace and annealed to remove thermal distortion. 5. The method according to claim 2, wherein the crucible inner surface layer is heated by scanning the quartz burner along the inner surface of the crucible using the quartz burner.