JP2012017240A - Method for manufacturing silica glass crucible for pulling silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a silica glass crucible for pulling a silicon single crystal, by which a crucible inner surface having a high OH-group concentration and high purity is formed at a low cost in order to prevent the liquid surface vibration of a polysilicon melt that is a cause of reduction in yield of the silicon single crystal caused by crucible and to suppress the occurrence of brown mold.SOLUTION: In the manufacturing of a silica glass crucible having a straight body part and a bottom part, an inner layer is formed on the inner surface from an opening part to the straight body part of the crucible by depositing transparent silica glass by using a silica powder having particle diameters of 70-300 μm and an oxyhydrogen flame.

Description

  The present invention relates to a method for producing a silica glass crucible for containing a raw material silicon melt used when pulling up a silicon single crystal by the Czochralski method (hereinafter referred to as CZ method).

The CZ method is widely used in the production of silicon single crystals. In this method, the seed crystal is brought into contact with the surface of the raw material silicon melt (polysilicon melt) contained in the crucible, the crucible is rotated, and the seed crystal is pulled upward while rotating in the opposite direction. Thus, a single crystal ingot is grown at the lower end of the seed crystal.
In the above method, a silica glass crucible made of transparent silica glass for the inner layer and opaque silica glass for the outer layer containing many bubbles is generally used for the crucible for containing the polysilicon melt.

  Conventionally, the silica glass crucible as described above is generally manufactured by a method in which silica powder is put into a rotating crucible molding mold, and is melted by arc discharge. In this manufacturing method, there is a possibility that the inner surface, which is required to have high purity, is contaminated with impurities due to the entrainment of outer layer raw material powder during molding, the atmosphere during arc melting, or the like.

Such impurities on the inner surface of the crucible not only cause a decrease in the purity of the silicon single crystal to be pulled up, but also a brown ring generated on the inner surface of the crucible when the polysilicon melt is contained in the crucible. Cristobalite, a so-called brown mold (also referred to as brown ring or brown mark).
In this brown mold, the crystal nuclei of cristobalite produced by crystallization of silica glass are gradually grown and expanded by heating, and the inner surface of the crucible is roughened and peeled off. As a result, exfoliated crystal pieces and the like are mixed in the polysilicon melt, causing dislocations in the silicon single crystal, resulting in a decrease in the yield of the silicon single crystal.

  Moreover, in the conventional manufacturing method as described above, the OH group concentration on the inner surface of the crucible was about 200 ppm at most. When the OH group concentration on the inner surface of the crucible is low, the wettability of the inner surface of the crucible with respect to silicon is inferior. This was one of the causes of a decrease in the yield of silicon single crystals, such as the dislocation-free rate.

  For the problem of the inner surface of the crucible formed by such an arc melting method, for example, Patent Document 1 discloses a method in which such an inner surface of the crucible is polished and then heat-treated with an oxyhydrogen burner. Has been proposed.

  Patent Document 2 discloses a method in which a crucible opening is disposed downward, heated from the outer wall surface of the crucible, and a transparent silica glass layer is formed on the inner wall surface of the crucible with a silane-based gas and an oxyhydrogen burner. ing.

JP 2001-328831 A Japanese Patent Laid-Open No. 11-11956

  However, the method described in Patent Document 1 is intended to make the transparent layer of the crucible inner layer non-bubble, and even if the purity of the inner surface of the crucible is improved, In this case, impurities at the time of arc melting remain, and the impurities may be eluted into the polysilicon melt accommodated in the crucible.

In addition, the method described in Patent Document 2 uses a general method for producing synthetic silica glass using a silane-based gas and an oxyhydrogen burner. In such a method, the transparent layer is formed on the inner wall surface of the crucible. On the other hand, it is formed in a layered state and is easily peeled. For this reason, this exfoliation piece mixes in the polysilicon melt accommodated in the crucible, and as a result, dislocation occurs in the silicon single crystal, leading to a decrease in the yield of the silicon single crystal.
Furthermore, in this method, since a high-purity silane-based gas is used instead of the silica powder raw material used in the conventional arc melting method or the like, there is a problem that the raw material and the apparatus cost are increased.

  Therefore, in order to prevent the liquid surface vibration of the polysilicon melt, which is a cause of the yield reduction of the silicon single crystal due to the crucible, and to suppress the generation of the brown mold, a crucible having a high OH group concentration and a high purity. There is a need for a method that can form the inner surface at low cost.

  The present invention has been made to solve the above technical problem, and prevents liquid level vibration of the polysilicon melt, which is a cause of a decrease in the yield of the silicon single crystal due to the crucible. In order to suppress the occurrence of the above, an object of the present invention is to provide a method for producing a silica glass crucible for pulling up a silicon single crystal, which can form a high OH group concentration and high purity crucible inner surface at low cost. .

The method for producing a silica glass crucible for pulling up a silicon single crystal according to the present invention, in the production of a silica glass crucible having a straight body part and a bottom part, on the inner surface from the opening part of the crucible to the straight body part, A transparent silica glass is deposited with 300 μm silica powder and an oxyhydrogen flame to form an inner layer.
According to such a method, a transparent silica glass layer having a high OH group concentration and high purity can be formed on the inner surface of the crucible.

In the above production method, the oxyhydrogen flame is melted at 1800 to 2000 ° C. for 2 to 5 minutes and sprayed onto the inner surface of the crucible with oxygen and hydrogen flow rates of 20 to 50 liters / min. It is preferable to adjust so that.
According to the oxyhydrogen flame under such conditions, a uniform transparent silica glass layer can be suitably formed.

The inner layer preferably has a thickness of 2 to 10 mm.
By setting the thickness within the above range, the vibration of the polysilicon melt contained in the crucible and the generation of the brown mold can be effectively suppressed.

According to the method for producing a silica glass crucible for pulling a silicon single crystal according to the present invention, a high OH group concentration and high purity crucible inner surface can be formed at low cost using a silica powder raw material.
Therefore, by using the silica glass crucible obtained by the manufacturing method according to the present invention, when the silicon single crystal is pulled up, the liquid level vibration of the polysilicon melt and the generation of the brown mold are effectively suppressed. The yield of crystal pulling can be improved.

Hereinafter, the present invention will be described in more detail.
The method for producing a silica glass crucible for pulling a silicon single crystal according to the present invention relates to a method for producing a silica glass crucible used in pulling a silicon single crystal by a CZ method having a straight body portion and a bottom portion. The inner layer is formed by depositing transparent silica glass on the inner surface from the opening of the crucible to the straight body with silica powder having a particle size of 70 to 300 μm and an oxyhydrogen flame. .
By forming the crucible inner layer by such a method, the crucible inner surface in the melt line of the polysilicon melt can be made a transparent silica glass layer having a high OH group concentration and a high purity.

In the above production method, the production method of the outer crucible layer is not particularly limited, and the silica crucible mold is put into a rotating crucible molding mold, and an arc electrode is inserted into the crucible outer mold to perform reduced-pressure arc melting. It can be produced by a conventional general rotary molding method and arc melting method.
The crucible outer layer is usually composed of a transparent layer made of transparent silica glass and an opaque layer made of opaque silica glass formed outside the transparent layer, and the shape and strength of the crucible when the silicon single crystal is pulled up. It is formed so as to have a thickness capable of holding. The thickness of the outer crucible layer is preferably about 20 to 40 mm. Usually, it is about 25 mm.
The opaque layer is generally formed of a natural silica raw material such as quartz, which is excellent in heat resistance, although it is low in purity. However, the opaque layer is a high-purity synthetic material obtained by hydrolysis of silicon alkoxide or the like. Silica raw materials may be used. The transparent layer is formed using a high-purity synthetic silica raw material obtained by hydrolysis of silicon alkoxide.

In the present invention, after the crucible outer layer is formed as described above, the inner layer is formed by spraying and depositing transparent silica glass on the inner surface with silica powder and an oxyhydrogen flame.
Thus, by using the same silica powder raw material as that used for forming the outer transparent layer together with the oxyhydrogen flame, the inner transparent silica glass layer is different from the case of using the silane-based gas raw material. It can be formed in a state in which it is difficult to peel off from the outer layer without generating an interface.

Moreover, since silica powder is melted and sprayed by an oxyhydrogen flame as described above, the deposited transparent silica glass can contain OH groups at a high concentration of 500 to 1500 ppm.
For this reason, the inner surface of the crucible has a high OH group concentration, the wettability with respect to the polysilicon melt is improved, and the effect of suppressing the liquid level vibration is obtained.

Moreover, if high-purity synthetic silica powder as described above is used as the silica powder raw material, there is little risk of containing impurities due to the atmosphere or electrodes during arc discharge, as in the arc melting method, and high-purity melting. Silica glass can be deposited.
Thereby, the purity fall of the silicon single crystal pulled up can be controlled.

The inner layer may be formed on the inner surface from the crucible opening to the straight body.
When pulling up the silicon single crystal, the vibration of the polysilicon melt or brown mold, which is the cause of the decrease in the yield of the silicon single crystal due to the crucible, is caused by the crucible near the melt line, which is the liquid surface of the polysilicon melt. It is affected by the condition of the inner surface.
For this reason, it is not necessary to form the inner layer by the said transparent silica glass layer to the crucible bottom part which a melt line does not reach | attain, and the round part from a straight body part to a bottom part.
In addition, if only the cylindrical portion from the opening of the crucible to the straight body portion is used in this way, there is an advantage that the spraying with the silica powder and the oxyhydrogen flame can be easily performed and the processing is easy.
In addition, as long as it forms as a uniform transparent silica glass layer, even if it forms in the whole crucible inner surface, it does not interfere.

  The transparent silica glass layer may be formed by arc melting only the outer opaque layer and then the outer transparent layer and the inner transparent silica glass layer with an oxyhydrogen flame, or alternatively, After forming the transparent layer and the opaque layer by arc melting, an inner transparent silica glass layer may be formed by an oxyhydrogen flame. In the latter case, since the high OH group concentration region in the thickness direction of the formed silica glass layer is smaller and the high viscosity is maintained, the risk of deformation of the crucible during pulling of the silicon single crystal is reduced. More preferred.

  The transparent silica glass layer is formed by the oxyhydrogen flame. After the arc melting as described above, the arc electrode is pulled up, the oxyhydrogen burner is lowered into the crucible, and the transparent silica glass is melted and deposited in a clean state. Can be performed.

The silica powder to be melted by the oxyhydrogen flame has a particle size of 70 to 300 μm, and more preferably has a particle size of 70 to 200 μm. Further, both the mode diameter and the median diameter are preferably 100 to 170 μm, and more preferably 130 to 150 μm.
When the particle diameter exceeds 300 μm, bubbles are easily taken in during melt deposition by an oxyhydrogen flame, and it is difficult to obtain a transparent layer.
On the other hand, when the particle size is less than 70 μm, the fluidity of the melted silica powder is lowered, it is difficult to spray uniformly with an oxyhydrogen flame, and bubbles are easily taken in by increasing the grain boundary, Also in this case, it becomes difficult to form a transparent layer.

Further, the oxyhydrogen flame has a flow rate of oxygen and hydrogen of 20 to 50 liters / min, respectively, from the viewpoint of sufficiently melting the silica powder and depositing it as a uniform transparent silica glass layer on the inner surface of the crucible. It is preferable to adjust so that the silica powder is melted at 2000 ° C. for 2 to 5 minutes and sprayed on the inner surface of the crucible.
If the flow rates of oxygen and hydrogen are too large or too small, it is difficult to melt the silica powder on the inner surface of the crucible and spray it uniformly on the inner surface of the crucible.
Further, the melting temperature of the silica powder is preferably such that the temperature in the vicinity of the inner surface of the crucible to be sprayed is within the above range, whereby the transparent silica glass layer can be brought into close contact with the inner surface of the outer crucible layer.
In order to form a transparent silica glass layer having a uniform thickness, the melting time of the silica powder is preferably 2 to 5 minutes in consideration of the fluidity of the melted silica powder. In addition, the melting time here represents the time when the flame by a burner has reached.

Specifically, the step of melting and spraying the silica powder with the oxyhydrogen flame is preferably performed as follows.
The spraying operation is carried out while changing the spraying position of the oxyhydrogen burner so as not to overlap this position after the spraying at the first position is completed.
At this time, from the viewpoint of preventing cracking and uneven thickness due to local heating of the outer layer of the crucible, it is preferable to carry out while rotating the crucible at 5 to 10 rpm.

As the oxyhydrogen burner, a quartz burner is preferably used from the viewpoint of preventing the mixing of metal impurities. Then, from the viewpoint of preventing melting of the quartz burner itself due to reflected heat from the spraying surface, the quartz burner is used by being inclined downward and at an angle of 30 to 45 ° with respect to the spraying surface in the crucible.
In addition, if the diameter of the burner is too large, a difference occurs in the amount of fused silica glass deposited between the central portion and the peripheral portion of the spray position. On the other hand, if the aperture is too small, the silica powder tends to clog in the burner tube. For this reason, it is preferable that the internal diameter of the pipe | tube with which silica powder flows is about 10-30 mm, and the aperture diameter of a burner is about 30-60 mm.

  In the spraying step, clean air at 80 to 120 ° C. is sprayed at 10 to 15 liter / min together with the oxyhydrogen flame in order to prevent adhesion of unfused silica powder and deposition of soot on the untreated portion. This air blowing is performed from a method other than the oxyhydrogen burner method in order to stabilize the oxyhydrogen burner and to prevent the crucible inner surface temperature from decreasing.

Moreover, when supplying silica powder from the center part of a burner mouth, in order to supply stably, it sprays using the carrier gas by oxyhydrogen gas. The oxyhydrogen gas has a volume ratio of oxygen and hydrogen, and oxygen: hydrogen = 1: 2-3. The flow rate is 5 to 10 liters / min.
When the flow rate is less than 5 liters / min, the silica powder may melt at the mouth of the burner due to insufficient flow rate. On the other hand, when the flow rate exceeds 50 liters / min, the stability of the oxyhydrogen burner is deteriorated and it becomes difficult to form a uniform transparent silica glass layer.

The inner layer preferably has a thickness of 2 to 10 mm.
When the thickness is less than 2 mm, it is too thin and it is difficult to suppress the vibration of the polysilicon melt contained in the crucible and the occurrence of brown mold.
On the other hand, even if the thickness exceeds 10 mm, the effect of suppressing the occurrence of liquid level vibration and brown mold corresponding to the thickness cannot be improved, so that the thickness of the region is sufficient to be 10 mm or less.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not restrict | limited by the following Example.
[Example 1]
After forming the crucible outer layer by the rotary molding method and the arc melting method, the silica powder having a particle size of 70 to 300 μm and a mode diameter and a median diameter of 140 μm on the inner surface from the opening of the crucible outer layer to the straight body portion. And an oxyhydrogen flame to deposit a transparent silica glass to form an inner layer having a thickness of 2 mm, an outer diameter of 600 mm, a height of 400 mm, an inner layer made of transparent silica glass having an OH group concentration of 1500 ppm, and a transparent thickness of 25 mm A silica glass crucible provided with an outer layer having a silica glass layer and an opaque silica glass layer was produced.

[Example 2]
A silica glass crucible was prepared in the same manner as in Example 1 except that silica powder having a particle diameter of 100 to 200 μm and a mode diameter and a median diameter of 150 μm were used.

[Comparative Example 1]
A conventional silica glass crucible was produced in the same manner as in Example 1 except that the inner layer was not formed in Example 1.

[Comparative Examples 2 and 3]
As a silica powder, in Comparative Example 2, a particle size of 30 to 60 μm and a mode diameter and a median diameter of 40 μm are used. In Comparative Example 3, a particle diameter of 300 to 350 μm, a mode diameter and a median diameter are used. A silica glass crucible was prepared in the same manner as in Example 1 except that both were 320 μm.

Four silica glass crucibles prepared in the above examples and comparative examples were fitted and set in a carbon crucible, heated by a heater from the outer periphery of the crucible, about 70 kg of raw material silicon was melted in the crucible, A silicon single crystal having a diameter of 8 inches was pulled up.
Then, the inner surface of the crucible after the pulling of the silicon single crystal was observed, and the number of brown molds generated in the straight body portion at a position of 100 mm from the initial melt line toward the bottom of the crucible was visually measured. In addition, the measured value was made into the average value of the number of brown molds in the range of 40 mm x 40 mm, respectively at four places (equal intervals) in the circumferential direction.
In addition, the number of reapplying seed crystals by the liquid level vibration of the polysilicon melt during pulling of the silicon single crystal was measured.
These evaluation and measurement results are summarized in Table 1. In addition, the number of times of repeated liquid deposition in Table 1 is represented by a relative ratio when Comparative Example 1 (conventional example) is set to 100.

  As can be seen from the results shown in Table 1, according to the silica glass crucible according to the present invention, it is recognized that the liquid level vibration of the polysilicon melt and the generation of the brown mold can be suppressed as compared with the conventional crucible. It was.

Claims (3)

In producing a silica glass crucible having a straight body and a bottom,
For pulling up a silicon single crystal, characterized in that an inner layer is formed by depositing transparent silica glass with silica powder having a particle size of 70 to 300 μm and an oxyhydrogen flame on the inner surface from the opening of the crucible to the straight body portion A method for producing a silica glass crucible.   The oxyhydrogen flame is adjusted so that each flow rate of oxygen and hydrogen is 20 to 50 liters / min, and silica powder is melted at 1800 to 2000 ° C. for 2 to 5 minutes and sprayed on the inner surface of the crucible. The method for producing a silica glass crucible for pulling up a silicon single crystal according to claim 1.   The method for producing a silica glass crucible for pulling a silicon single crystal according to any one of claims 1 and 2, wherein the inner layer has a thickness of 2 to 10 mm.