JP5191003B2 - Silica glass crucible for silicon single crystal pulling - Google Patents

Description

  The present invention relates to 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 contained in the crucible, the crucible is rotated, and the seed crystal is pulled upward while rotating the seed crystal in the opposite direction. Single crystal ingots are nurtured.
In the above method, a silica glass crucible is used as the crucible for containing the raw material silicon melt, and the silica glass crucible is set so as to be fitted into the carbon crucible when the silicon single crystal is pulled up, Heated by the heater.

Conventionally, the silica glass crucible has a two-layer structure in which the inner layer is a synthetic silica glass layer and the outer layer is a natural silica glass layer (see, for example, Patent Document 1), or alternatively, between the outer layer and the inner layer of the two-layer structure. For example, a three-layer structure such as that described in Patent Document 2 is generally sandwiched between opaque (semi-transparent) intermediate layers made of silica glass.
Since the synthetic silica glass mainly constituting the inner layer is obtained with high purity, impurity contamination of the pulled silicon single crystal can be suppressed. On the other hand, natural silica glass constituting the outer layer has a feature that it is excellent in heat resistance, although its purity is lower than that of synthetic silica glass.

  In Patent Document 3, a crystallization accelerator-added silica glass layer is formed on the outside of the outer layer other than the bottom of the two-layered silica glass crucible as described above, and the three-layer structure other than the bottom has a durability. And a silica glass crucible with improved support stability with a carbon crucible.

Japanese Patent No. 2811290 JP 2001-348294 A JP 2008-81374 A

By the way, in recent years, from the viewpoint of improving the production efficiency of silicon single crystals, silicon single crystal ingots pulled by the above method have become larger in diameter, and accordingly, the amount of raw material silicon melt required for one pulling increases. The silica glass crucible is also enlarged.
In addition, the use environment of the silicon crucible has become severe, such as refilling of raw material silicon into the silica glass crucible and rapid temperature rise and fall.
In particular, before pulling up the silicon single crystal, the crucible is rapidly heated by the heater heating from the outer periphery in order to shorten the time for melting the raw material silicon in the crucible.

At this time, in the silica glass crucible as described in Patent Documents 1 and 2, because the natural silica glass of the outer layer has a high viscosity at high temperature, it is difficult to be familiar with the carbon crucible covering the outer periphery of the crucible and has sufficient adhesion. Sex cannot be obtained.
Further, even if the crucible is formed with a crystallization accelerator-added silica glass layer as described in Patent Document 3, when the crucible is rapidly heated, before the sufficient adhesion to the carbon crucible is obtained. In addition, crystallization at the portion in contact with the carbon crucible is completed at an early stage.

  As described above, when the heater is heated from the outer periphery of the crucible, if the adhesion between the silica glass crucible and the carbon crucible outside thereof is not sufficient, the larger the crucible, the larger the raw material silicon melt contained in the crucible. In addition, temperature irregularities are likely to occur, and the silica glass crucible itself may be heated and deformed, leading to a decrease in the single crystallization rate of the pulled silicon single crystal.

  The present invention has been made in order to solve the above technical problem, and at the time of pulling a silicon single crystal, immediately after the start of heating for melting the raw material silicon in the crucible, the carbon crucible in contact with the outer periphery is sufficiently adhered. It is an object of the present invention to provide a silica glass crucible for pulling up a silicon single crystal capable of obtaining the properties.

A silica glass crucible for pulling up a silicon single crystal according to the present invention is a silica glass crucible having a three-layer structure having an arcuate corner portion between a bottom portion and a cylindrical side wall portion. An OH group-containing concentration formed at a position within ± 5 ° around the center of curvature with respect to a straight line connecting the center of curvature with a portion having the largest curvature of the corner portion in a vertical cross section passing through the center. A first layer made of synthetic silica glass having a thickness of ˜300 ppm, a second layer being an opaque layer made of natural silica glass, formed on the inner surface side of the first layer over the entire crucible, Natural silica glass formed on the inner surface side of the second layer, or high-purity synthetic silica having a metal impurity content of Na, K, Al of 1 ppm or less each. And a third layer which is a transparent layer made of mosquito glass.
According to the silica glass crucible having the above-described structure, when the silicon single crystal is pulled, the adhesion with the carbon crucible immediately after the start of the crucible heating is improved, initial deformation is suppressed, and temperature unevenness of the raw material silicon melt is suppressed. The generation of silicon can be suppressed, and the single crystallization rate of the pulled silicon single crystal can be improved.

In the silica glass crucible, the first layer is preferably thinner at the corner than at the center of the bottom. In particular, in the silica glass crucible, it is preferable that the thickness of the first layer continuously decreases from the center of the bottom toward the corner.
In this case, the first layer has a ratio t _c / t _p between the thickness t _c at the center of the bottom of the crucible and the thickness t _{p at} the portion having the largest curvature in the vertical cross section passing through the center of the crucible. 1.2 to 2.4 is preferable.
By adopting such a configuration, the silica glass crucible and the carbon crucible can be brought into close contact with each other from the center of the bottom of the crucible, and the close contact speed can be kept moderate, and uniform adhesiveness can be obtained.

According to the silica glass crucible for pulling up a silicon single crystal according to the present invention, at the time of pulling up the silicon single crystal, immediately after the start of heating for melting the raw silicon in the crucible, sufficient adhesion with the carbon crucible in contact with the outer periphery is obtained. be able to.
Therefore, according to the silica glass crucible according to the present invention, it is possible to suppress the occurrence of temperature unevenness of the raw material silicon melt contained in the crucible, and to prevent the crucible from being deformed at the initial temperature rise. As a result, it becomes possible to pull up the silicon single crystal with high efficiency and high single crystallization rate.

It is typical sectional drawing of the silica glass crucible for silicon single crystal pulling concerning the present invention. It is an expanded sectional view around the corner part of the silica glass crucible of FIG. It is an expanded sectional view of the corner part periphery of the silica glass crucible for silicon single crystal pulling of another mode concerning the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a cross-sectional view of a silica glass crucible according to the present invention. The silica glass crucible shown in FIG. 1 has a U-shaped cross section having a rounded corner portion 3 between a bottom portion 1 and a cylindrical side wall portion 2. This silica glass crucible has a three-layer structure. Then, a first layer 4 made of synthetic silica glass formed from a bottom portion 1 to a predetermined position of the corner portion 2 and an opaque layer made of natural silica glass formed over the entire crucible on the inner surface side of the first layer 4. From a certain second layer 5 and a natural silica glass formed on the inner surface side of the second layer 5 over the entire crucible, or a high-purity synthetic silica glass having a metal impurity content of Na, K, Al of 1 ppm or less. And a third layer 6 which is a transparent layer.

Thus, by providing the first layer 4 made of synthetic silica glass having a viscosity lower than that of natural silica glass on the outer layer from the bottom 1 to the corner 2, rapid melting of the raw material silicon in the silica glass crucible is possible. Even if it is a case where it heats, immediately after a heating start, adhesiveness with the carbon crucible which touches outer periphery can be improved.
As a result, the occurrence of temperature unevenness in the raw material silicon melt contained in the crucible can be suppressed, and the silicon single crystal can be pulled with high single crystallization rate and high efficiency.

  Here, the synthetic silica glass is a silica glass produced by melting a synthetic silica raw material synthesized by, for example, hydrolysis of silicon alkoxide, and the natural silica glass is a natural silica raw material such as quartz. This means silica glass produced in the same manner.

In general, synthetic silica glass has a lower viscosity than natural silica glass. However, in order to obtain sufficient adhesion with the above-described carbon crucible, the synthetic silica glass is composed of the first layer 4 from the viewpoint of appropriate viscosity. In silica glass, the OH group-containing concentration is preferably 30 to 300 ppm, and more preferably 80 to 200 ppm.
When the OH group concentration is less than 30 ppm, the viscosity of the synthetic silica glass is high, and it is difficult to improve the adhesion with the carbon crucible in contact with the outer periphery immediately after the start of the crucible heating.
On the other hand, when the OH group concentration exceeds 300 ppm, the viscosity of the synthetic silica glass is too low, the initial deformation immediately after the start of heating of the crucible is remarkable, and the shape stability of the crucible base material itself becomes insufficient.

FIG. 2 is an enlarged cross-sectional view around the corner portion of the silica glass crucible of FIG. As shown in FIG. 2, the formation range of the first layer 4 is in a vertical cross section passing through the center of the crucible, with respect to a straight line PO connecting a point P having the largest curvature of the corner portion 3 and the center of curvature O. It is preferable that the end portion is located at a position within ± 5 ° around the curvature center O.
In the above position, by forming the first layer 4 made of synthetic silica glass as an outer layer, immediately after the start of heating of the crucible, sufficient adhesion with the carbon crucible in contact with the outer periphery is obtained, and the side wall of the crucible In the part 2, the initial deformation immediately after the start of heating of the crucible can be suppressed by adopting a two-layer structure in which the second layer 5 which is an opaque layer made of natural silica glass is used as the outer layer.

With respect to the straight line PO, when the rotation in the crucible side wall 2 direction around the point O is a positive direction, the end of the formation range of the first layer 4 is a position where the rotation angle is less than −5 °. As soon as the crucible starts heating, sufficient adhesion with the carbon crucible in contact with the outer periphery cannot be obtained, and temperature fluctuation occurs in the raw material silicon melt in the crucible, and the single crystal ratio of the silicon single crystal to be pulled up is increased. Cause a decline.
On the other hand, when the first layer 4 is formed up to a position where the rotation angle exceeds + 5 °, the viscosity of the outer layer is lowered in the side wall portion 2 and the crucible is likely to buckle.

Moreover, it is preferable that the thickness of the said 1st layer 4 is 1-5 mm, and it is more preferable that it is 2-4 mm.
When the thickness is less than 1 mm, sufficient adhesion with the carbon crucible as described above cannot be obtained.
On the other hand, when the thickness exceeds 5 mm, the synthetic silica glass layer having a relatively low viscosity is too thick, so that the initial deformation immediately after the start of heating of the crucible is remarkable, and the shape stability of the crucible base material itself becomes insufficient. .

  The thickness of each of the second layer 5 and the third layer 6 formed inside the first layer 4 is appropriately determined depending on the size of the crucible. From the viewpoint of strength, cost, etc., for example, In the case of a crucible having an outer diameter of 800 mm and a height of 500 mm, the second layer 5 is preferably 15 to 28 mm, and the inner third layer 6 is preferably 2 to 6 mm.

The second layer 5 is formed of natural silica glass having excellent heat resistance, although the purity is lower than that of the synthetic silica glass, and usually contains a larger number of bubbles than the transparent layer. The opaque layer has a low light transmittance and mainly has a function of maintaining the strength of the entire crucible.
The third layer 6 constitutes a surface in contact with the silicon single crystal raw material silicon melt, and depending on the quality required for the silicon single crystal, natural silica glass, or Na, K, Al It is formed of a high-purity synthetic silica glass having a metal impurity content of 1 ppm or less, and is usually a transparent layer containing almost no bubbles and having a smooth inner surface.

In FIG. 3, the expanded sectional view of the corner part periphery of the silica glass crucible of the other aspect which concerns on this invention is shown.
Within the above range, the thickness of the first layer 4 is preferably smaller at the corner 3 than at the center of the bottom 1, and particularly, as shown in FIG. 3, from the center of the bottom 1 toward the corner 3. It is preferable that the thickness is continuously reduced so that the center of the bottom 1 is thicker and the corner 3 (end) side is thinner.
By forming the first layer with such a thickness, the crucible bottom 1 can be brought into close contact with the carbon crucible immediately after the start of heating of the crucible, and then toward the end of the first layer. By gradually adhering, the first layer and the carbon crucible can be uniformly adhered.

As described above, when the thickness of the first layer is not uniform and inclined, the thickness t _c at the center C of the crucible bottom 1 and the vertical curvature passing through the center of the crucible have the most curvature of the corner portion 3. the ratio t _c / t _p of the thickness t _p of large portions P is preferably 1.2 to 2.4, more preferably 1.5 to 2.2.
Is less than the ratio t _c / t _p is 1.2, after the start of heating of the crucible, there is also a case where the first layer and the carbon crucible is not begin to close contact from the bottom 1 center, it may contact becomes nonuniform.
In contrast, if it exceeds the ratio t _c / t _p is 2.4, since the adhesion rate of the carbon crucible at the bottom 1 center is too large, the bottom 1 center and a near corner portions of an end portion of the first layer 4 The time difference until the carbon crucible comes into close contact with the carbon crucible increases, and initial crucible deformation tends to occur.

The silica glass crucible according to the present invention as described above can be manufactured using a conventional manufacturing method. Although an example of a specific manufacturing method is demonstrated below, the manufacturing method of the silica glass crucible which concerns on this invention is not limited to this.
First, synthetic silica raw material powder is supplied into a crucible molding mold that rotates around the central axis of the crucible, and is applied from the bottom of the inner surface of the mold to a predetermined position of the corner portion by centrifugal force and mechanical pressing. A layered compact is formed. Note that the thickness and shape of the first layer can be controlled by appropriately adjusting the amount of the synthetic silica raw material powder and the degree of mechanical pressing.
Next, the natural silica raw material powder is supplied into the mold, and the molded product of the second layer is formed over the entire crucible inside the first layer by centrifugal force and mechanical pressing. This second layer is preferably an opaque layer.
Thereafter, natural silica raw material powder or high-purity synthetic silica raw material powder having a metal impurity content of Na, K, or Al of 1 ppm or less is supplied as a whole, and the inside of the second layer is obtained by centrifugal force and mechanical pressing. A molded body of the third layer is formed on the surface. This third layer is preferably a transparent layer.
And the silica glass crucible which concerns on this invention is obtained by vitrifying the whole crucible molded object obtained as mentioned above by an arc melting method.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.
[Example 1]
A silica glass crucible having an outer diameter of 800 mm and a height of 500 mm as shown in FIG. 3 was manufactured by the same manufacturing method as that described in the above embodiment. The first layer of the crucible has a thickness t _c of 2.5 mm at the center C of the crucible bottom 1 of the first layer, the position of the end of the first layer is a point P having the largest curvature of the corner portion, and t _c / the t _p of 2.0, was also constructed by synthetic silica glass containing OH groups concentration 85 ppm. Moreover, the 2nd layer was comprised with the natural silica glass, and the thickness in a side wall part was 20 mm. The third layer was made of natural silica glass and had a thickness of 3 mm.
This silica glass crucible is set in a carbon crucible, heated by a heater from the outer periphery of the crucible, about 350 kg of raw silicon is melted in the crucible, and a silicon single crystal having a diameter of 12 inches is pulled by the CZ method. It was. The temperature increase rate before pulling the single crystal was set to twice the normal rate.

[Examples 2 to 4]
The thickness of the first layer, the end position, OH group content level, the t _c / t _p was varied as shown in Examples 2-4 of Table 1, in the same manner as in Example 1 except that silica Glass crucibles were manufactured, and using these crucibles, a silicon single crystal was pulled in the same manner as in Example 1.

[Comparative Example 1]
In Example 1 above, a silica glass crucible having a two-layer structure having only the second layer and the third layer was produced without forming the first layer, and this crucible was used in the same manner as in Example 1. The silicon single crystal was pulled up.

[Examples 5 to 10, Comparative Examples 2 to 7]
The thickness of the first layer, the end position, OH group content level, examples 5-10 of Table 1 t _c / t _p, varied as shown in Comparative Examples 2 to 7, also, the third layer A silica glass crucible is manufactured in the same manner as in Example 1 except that the metallic impurity content of Na, K, and Al is 1 ppm or less, and the rest is carried out using each of these crucibles. In the same manner as in Example 1, the silicon single crystal was pulled.

About the silica glass crucible manufactured in the said Example and comparative example, the deformation | transformation of the crucible after using for a silicon single crystal pulling, and the single crystallization rate of the silicon single crystal pulled up were evaluated.
These evaluation results are summarized in Table 1.

In Table 1, the judgment criteria for the presence or absence of deformation of the crucible were as follows: ◯: No visual deformation, Δ: Visually confirmed the occurrence of deformation, ×: Discontinuation of pulling due to the occurrence of deformation.
The criteria for determining the single crystallization rate were: ○:> 95%, Δ: 90-95%, x: <90%.

As can be seen from the evaluation results shown in Table 1, in Examples 1 to 10, the crucible was not deformed, and the single crystallization rate of the pulled silicon single crystal was also good, exceeding 95%.
Incidentally, less inclined ratio t _c / t _p of the thickness of the first layer is 1.2 or, if it exceeds 2.4 (Examples 9 and 10), no significant deformation of the crucible, pulling of a silicon single crystal However, the single crystallization rate of the silicon single crystal was slightly inferior to those of Examples 1-8.

On the other hand, when the crucible of the conventional two-layer structure (Comparative Example 1), the first layer is thin (Comparative Example 2), and the end of the first layer is too close to the crucible bottom, the formation range is narrow ( In Comparative Example 4), the function of the first layer was not sufficiently performed, the adhesion with the carbon crucible was poor, and undulation deformation occurred at the bottom immediately after the start of heating of the crucible.
In addition, when the first layer is thick (Comparative Example 3) and when the OH group-containing concentration of the first layer is high (Comparative Example 6), the viscosity of the crucible base material itself is lowered and deformation occurs. Single crystal pulling was stopped.
When the end portion of the first layer spreads too far to the crucible sidewall portion side and the formation range is wide (Comparative Example 5), buckling deformation occurred in the crucible sidewall portion, and the silicon single crystal pulling was stopped.
Further, when the OH group-containing concentration of the first layer is low (Comparative Example 7), the viscosity of the crucible base material itself is high, the adhesion with the carbon crucible is poor, the temperature unevenness of the raw material silicon melt occurs, The single crystallization rate of the crystal was lowered.

From the above, according to the silica glass crucible formed with the first layer according to the present invention, immediately after the start of heating of the crucible, sufficient adhesion with the carbon crucible in contact with the outer periphery is obtained, and initial deformation is suppressed. It was recognized that it is possible to improve the production efficiency by rapid heating for melting silicon.
In addition, it was confirmed that the occurrence of temperature unevenness in the raw material silicon melt contained in the crucible was suppressed, and the silicon single crystal could be pulled at a high single crystallization rate.

DESCRIPTION OF SYMBOLS 1 Bottom part 2 Side wall part 3 Corner part 4 1st layer 5 2nd layer 6 3rd layer

Claims (4)

A silica glass crucible having a three-layer structure having a rounded corner portion between a bottom portion and a cylindrical side wall portion,
Formed from the center of the bottom to a position within ± 5 ° around the center of curvature with respect to a straight line connecting the center of curvature with a portion having the largest curvature of the corner in a vertical section passing through the center of the crucible. A first layer having a thickness of 1 to 5 mm made of synthetic silica glass having an OH group-containing concentration of 30 to 300 ppm,
A second layer, which is an opaque layer made of natural silica glass, formed over the entire crucible on the inner surface side of the first layer;
A transparent layer made of natural silica glass or high-purity synthetic silica glass having a metal impurity content of Na, K, or Al of 1 ppm or less, formed on the inner surface side of the second layer over the entire crucible. A silica glass crucible for pulling up a silicon single crystal.   2. The silica glass crucible for pulling up a silicon single crystal according to claim 1, wherein the first layer is thinner at the corner than at the center of the bottom.   The silica glass crucible for pulling up a silicon single crystal according to claim 1 or 2, wherein the thickness of the first layer continuously decreases from the center of the bottom toward the corner. The first layer has a thickness t _c at the center of the crucible bottom and a ratio t _c / t _p of the thickness t _{p at} the corner where the curvature is the largest in the vertical cross section passing through the center of the crucible. The silica glass crucible for pulling a silicon single crystal according to any one of claims 1 to 3, wherein the silica glass crucible is 2 to 2.4.

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