JP7051392B2 - Method for manufacturing quartz glass crucible and quartz glass crucible - Google Patents

Description

The present invention relates to a quartz glass rutsubo and a method for manufacturing a quartz glass rutsubo, and to a quartz glass rutsubo and a quartz glass rutsubo for accommodating a raw material silicon melt, which are used when pulling up a silicon single crystal.

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 in the opposite direction, thereby pulling the lower end of the seed crystal upward. It is intended to grow single crystal ingots.
In the above method, as the crucible for accommodating the silicon melt, a quartz glass crucible made of natural quartz glass, which has an inner layer made of high-purity quartz glass and an outer layer having a lower purity than the inner layer and is inexpensive, is generally used. Has been done.

In recent years, in order to improve the efficiency of silicon single crystal production, the diameter of the silicon single crystal to be pulled up has been increased, and along with this, the time required for producing the silicon single crystal has become longer, and the crucible usage time, that is, the heating time has also increased. As it gets longer, the crucible is exposed to high temperatures for extended periods of time. Therefore, there is a concern that the viscosity of the quartz glass constituting the crucible will decrease and the crucible will be easily deformed.

On the other hand, it is known that the viscosity of quartz glass is increased by adding aluminum (Al) to the quartz raw material powder in order to suppress the deformation of the crucible at high temperature.
For example, Patent Document 1 describes a crucible manufactured by using quartz powder having an aluminum concentration of 5 to 45 ppm and a lithium concentration of 2% or more at least on the outer peripheral portion of the crucible, and has a viscosity of 9 at 1500 ° C. A crucible that is 6 × 10 ⁹ poise or more is shown.

Japanese Unexamined Patent Publication No. 2006-16240

By the way, a phenomenon was observed in which a large number of wrinkles were generated on the inner surface of the quartz glass crucible in the crucible in which the viscosity of the quartz glass was increased by adding aluminum (Al) to the quartz raw material powder.
The occurrence of this wrinkle will be specifically described with reference to FIG.
As shown in FIG. 1, the quartz glass crucible 1 includes an inner layer 2 made of high-purity quartz glass and an outer layer 3 made of natural quartz glass having aluminum (Al) added to quartz raw material powder to increase the viscosity. A straight body portion 4, a curved portion 5, and a bottom portion 6 are formed from the open end portion, and are formed in a bottomed cylindrical shape as a whole.
When the quartz glass crucible 1 is exposed to a high temperature for a long time, as shown in FIG. 1, a large number of quartz glass crucibles 1 are formed on the inner surface of the quartz glass crucible 1 in the region from the lower part of the straight body portion 4 to the curved portion 5. Wrinkles (unevenness) occur.

The present inventor has diligently studied the suppression of wrinkles generated on the inner surface of the quartz glass crucible in the region from the lower part of the straight body portion to the curved portion of the quartz glass crucible.
As a result, even if aluminum (Al) is added to the quartz raw material powder in the outer layer of the quartz glass crucible to increase the viscosity of the quartz glass, if the difference in viscosity between the inner layer and the outer layer is large, the inner layer with less viscosity sinks. It was found that (movement in the direction of the arrow in FIG. 1) became large, and a large number of wrinkles (unevenness) occurred in the region from the lower part of the straight body portion to the curved portion.
In addition, the crack width (crack width: width in the width direction (short direction), not in the crack length direction (longitudinal direction)) tends to be large on the inner surface crystallized by the occurrence of this wrinkle, and the silicon melt. The gas generated by the reaction between the crystallized glass and the inner surface of the quartz glass tends to accumulate. It was found that the accumulated gas escaped, moved into the silicon melt, reached the solid-liquid interface, was taken into the silicon single crystal, and became an air pocket.

The present invention has been made to solve the above technical problems, and by setting the viscosity difference between the inner layer and the outer layer within a specific range, wrinkles generated on the inner surface in the region from the lower part of the straight body portion to the curved portion. It is an object of the present invention to provide a quartz glass crucible and a method for manufacturing a quartz glass crucible, which suppresses (unevenness) and further reduces the crack width (crack width) generated on the inner surface.

The quartz glass rutsubo according to the present invention made to achieve the above object has an inner layer made of high-purity quartz glass and an outer layer made of natural quartz glass having aluminum (Al) added to quartz raw material powder to increase the viscosity. The inner layer has an Al concentration of 10 ppm or less, the outer layer has an Al concentration of 7 ppm or more and 20 ppm or less, and the inner layer and the outer layer have viscosity at 1400 ° C. It is characterized in that the difference is 0.8 × 10 ⁺¹⁰ (poise) or less.

As described above, since the viscosity difference between the inner layer and the outer layer at 1400 ° C. is 0.8 × 10 ⁺¹⁰ (poise) or less, the inner layer sinks (moves downward of the inner layer) when the silicon single crystal is pulled up. Can be suppressed, and wrinkles (unevenness) generated from the inner surface of the lower part of the straight body portion of the crucible to the inner surface of the curved portion can be suppressed.
In addition, cracks caused by the generation of wrinkles (unevenness) can be suppressed, and the width thereof can be made smaller.
In this way, cracks, which are gas pools generated by the reaction between the silicon melt and the inner surface of the quartz glass, are suppressed, and as a result, air pockets in the silicon single crystal are also suppressed.

Further, in the quartz glass crucible according to the present invention, the Al concentration of the inner layer is 10 ppm or less, and the Al concentration of the outer layer is 7 ppm or more and 20 ppm or less.
The inner layer is made of high-purity quartz glass in order to suppress the diffusion of impurities into the silicon melt. Therefore, the Al concentration needs to be 10 ppm or less.
Further, in order for the viscosity difference between the inner layer and the outer layer at 1400 ° C. to be 0.8 × 10 ⁺¹⁰ (poise) or less, the Al concentration of the outer layer needs to be 7 ppm or more and 20 ppm or less.
When the Al concentration of the outer layer is less than 7 ppm, the deformation of the crucible cannot be suppressed under high temperature, which is not preferable. On the other hand, when the Al concentration of the outer layer exceeds 20 ppm, the viscosity difference between the inner layer and the outer layer at 1400 ° C. cannot be less than 0.8 × 10 ⁺¹⁰ (poise), and the inside of the curved portion from the lower part of the straight body portion. It is not preferable because a large number of wrinkles (unevenness) occur in the surface region.

The method for producing a quartz glass rut according to the present invention, which has been made to achieve the above object, has an inner layer made of high-purity quartz glass and an outer layer made of natural quartz glass, and is used for pulling out a silicon single crystal. It is a method for producing a glass rut, in which the Al component is added to the quartz raw material powder for forming the outer layer without adding the Al component to the quartz raw material powder for forming the inner layer, and the inner layer is added. The Al concentration of the outer layer is 10 ppm or less, and the Al concentration of the outer layer is adjusted to 7 ppm or more and 20 ppm or less.

As described above, by adding a predetermined amount of the Al component to the quartz raw material powder forming the outer layer, it is possible to easily produce quartz glass capable of suppressing the generation of wrinkles in the inner surface region of the curved portion from the lower part of the straight body portion. be able to.

According to the present invention, by setting the difference in viscosity between the inner layer and the outer layer within a specific range, wrinkles (unevenness) generated on the inner surface in the region from the lower part of the straight body portion to the curved portion are suppressed, and the generation of the inner surface is suppressed. It is possible to obtain a quartz glass crucible and a method for manufacturing a quartz glass crucible in which the crack width (crack width) is further reduced.

FIG. 1 is a schematic view for explaining wrinkles generated on the inner surface of the region of the curved portion from the lower part of the straight body portion of the quartz glass crucible. FIG. 2 is a diagram showing cracks generated in the quartz crucible used.

Hereinafter, an embodiment of a quartz glass crucible and a method for manufacturing a quartz glass crucible according to the present invention will be described.
The quartz glass rutsubo according to the present invention is a quartz glass rutsubo for pulling a silicon single crystal having an inner layer made of high-purity quartz glass and an outer layer made of natural quartz glass, and at 1400 ° C. of the inner layer and the outer layer. It is characterized in that the viscosity difference is 0.8 × 10 ⁺¹⁰ (poise) or less.

This quartz glass crucible is formed in the same shape as the quartz glass crucible shown in FIG. That is, it is provided with an inner layer made of high-purity quartz glass formed of high-purity quartz raw material powder and an outer layer made of highly viscous natural quartz glass made of quartz raw material powder added with aluminum (Al). The overall shape is a bottomed cylindrical shape, and a straight body portion, a curved portion, and a bottom portion are formed from the open end portion.

The inner layer is formed of high-purity quartz raw material powder, and a high-purity quartz raw material having an Al concentration of 10 ppm or less in the inner layer and other impurities such as Na, K, Li of less than 1 ppm is used.
Al is an element contained in a relatively large amount in the quartz raw material, while Na and K have a low viscosity and tend to deform the crucible, so a low concentration is preferable. Further, among the impurities contained in the high-purity quartz raw material powder, Al, Na, K or Li are particularly likely to diffuse in the quartz glass, which has a great influence on the formation of a brown mold and further on the roughness and peeling of the inner surface of the crucible. To exert. Therefore, it is preferable that these impurities are hardly contained.
That is, it is preferable that the Al concentration of the inner layer is 10 ppm or less, and the concentration of other impurities such as Na, K, and Li is less than 1 ppm.

Further, the inner layer is formed by melting the high-purity quartz raw material powder, and is formed as transparent quartz glass containing no bubbles.
The high-purity quartz raw material powder may be a synthetic quartz powder or a natural quartz powder purified to the same level as the synthetic quartz powder. As the synthetic quartz powder, for example, one synthesized by hydrolysis of silicon alkoxide or the like can be used, and as the natural quartz powder, for example, a natural quartz raw material such as crystal can be used.

The outer layer is formed of a natural quartz raw material powder to which aluminum (Al) has been added. The outer layer may be formed of synthetic quartz powder, but it is preferable to use natural quartz raw material powder from the viewpoint of cost.
The aluminum (Al) is added to the natural quartz raw material powder so that the Al concentration of the outer layer is 7 ppm or more and 20 ppm or less.

Further, the outer layer is formed by melting natural quartz raw material powder, and is formed as quartz glass containing a large number of closed pores (air bubbles). Further, as the natural quartz powder, for example, a natural quartz raw material such as crystal can be used.

When the amount of the aluminum (Al) added to the natural quartz raw material powder is small and the Al concentration of the outer layer is less than 7 ppm, the deformation of the crucible cannot be suppressed at a high temperature, which is not preferable.
On the other hand, when the amount of the aluminum (Al) added to the natural quartz raw material powder is large and the Al concentration of the outer layer exceeds 20 ppm, the viscosity difference between the inner layer and the outer layer at 1400 ° C. is 0.8 × 10 ⁺¹⁰ . (Poise) or less, and a large number of wrinkles (unevenness) are generated from the lower part of the straight body portion to the inner surface region of the curved portion, which is not preferable.

By the way, when the viscosity difference between the inner layer and the outer layer at 1400 ° C. exceeds 0.8 × 10 ⁺¹⁰ (poise), as described above, when the quartz glass crucible is exposed to high temperature for a long time, quartz is used. On the inner surface of the glass crucible, a large number of wrinkles (unevenness) occur in the region from the lower part of the straight body portion to the inner surface of the curved portion.
The reason is that when the viscosity difference between the inner layer and the outer layer is large, the inner layer moves slightly downward (subduction) with respect to the outer layer, as shown by the arrow X in FIG. On the other hand, because the outer layer is highly viscous (to crystallize), it does not move downward (no subduction). As a result, there is a difference in the amount of movement (subduction amount) between the inner layer and the outer layer, and since the amount of subduction of the inner layer in the curved part and the bottom part is smaller than that in the straight body part, it is curved from the lower part of the straight body part. It is presumed that a large number of wrinkles (unevenness) occur in the area of the inner surface of the portion. In particular, when a crystallization accelerator is added to the inner surface (inner layer surface) of the crucible, wrinkles are more likely to occur.

Further, the thickness of the entire quartz glass crucible including the inner layer and the outer layer is preferably about 5 to 30 mm in consideration of the strength and weight of the crucible. Normally, it is about 15 mm.
The thickness of the outer layer is not particularly limited, but is preferably about 3 to 28 mm from the same viewpoint.
The thickness of the inner layer is not particularly limited, but is preferably about 2 mm from the same viewpoint.

The quartz glass crucible according to the present invention can be manufactured by using a conventional manufacturing method. Generally, it is manufactured by a rotary molding method and an arc melting method.
An example of a specific manufacturing method will be described below, but the manufacturing method of the quartz glass crucible according to the present invention is not limited to this.
First, the impurity concentration of the high-purity quartz raw material powder forming the inner layer is measured, and a high-purity quartz raw material having an Al, Na, K, Li concentration of less than 10 ppm is selected. As described above, it is preferable that the Al concentration of the inner layer is 10 ppm or less, and the concentration of other impurities such as Na, K, and Li is less than 1 ppm.
By using such high-purity quartz raw material powder, the Al concentration in the inner layer can be reduced to 10 ppm or less. Further, the concentration of other impurities such as Na, K and Li can be set to less than 1 ppm.

Next, the Al concentration of the natural quartz raw material powder forming the outer layer is measured, and a predetermined amount of aluminum (Al) is added to the natural quartz raw material powder so that the Al concentration of the outer layer is 7 ppm or more and 20 ppm or less.
The Al component is preferably added to the natural quartz raw material powder as an aqueous solution of aluminum nitrate nine hydrate (Al (NO ₃ ) _{3.9H 2} O).
Each aqueous solution is appropriately adjusted in concentration so that it can be added as uniformly as possible according to the amount of the natural quartz raw material powder, and after being uniformly added to the natural quartz raw material powder, it is dried and powdered again before use. It is preferable to do so.
By adding such an aqueous solution of nitrate, the concentration of Al can be adjusted uniformly and easily. In addition, excess water and nitric acid can be easily removed by drying and heating, and are easy to handle.

Then, a natural quartz raw material powder to which a predetermined amount of aluminum (Al) for forming an outer layer is added is supplied into the crucible molding mold that rotates around the central axis of the crucible, and the outer layer is subjected to centrifugal force and mechanical pressing. To mold.
Next, high-purity quartz raw material powder is supplied to the entire inner surface of the outer layer molded body in the crucible molding mold, and the inner layer is molded inside the outer layer molded body by centrifugal force and mechanical pressing.
Then, by vitrifying the whole crucible molded body having a two-layer structure obtained as described above by an arc melting method, the outer layer is a natural quartz glass containing bubbles, and the inner layer is high-purity without containing bubbles. A quartz glass crucible made of quartz glass is manufactured.

(Example 1)
As the high-purity quartz raw material powder forming the inner layer, synthetic quartz raw material powder having an Al, Na, K, Li concentration of less than 1 ppm is used, and as the quartz raw material powder forming the outer layer, the Al concentration is 12 ppm (Al addition amount). 6 ppm) of natural quartz raw material powder was used.
Then, using these high-purity quartz raw material powder and quartz raw material powder, a quartz glass crucible for pulling a silicon single crystal was manufactured by a general rotary molding method.

Using the obtained crucible, a dopant agent or a silicon raw material is filled in the quartz crucible, the raw material is melted in a reduced pressure / inert atmosphere, and then a desired silicon single crystal is controlled while controlling the melt temperature. Pull up. Then, the number of air pockets generated per unit volume was calculated from the number of air pockets that could be confirmed when the obtained silicon ingot was sliced to a thickness of about 1 mm.
The air pocket slices the silicon ingot to a thickness of about 1 mm to create a wafer, then irradiates infrared light from the back surface of the wafer, captures the transmitted light with the camera on the front surface, and performs image processing (binarization). And shape determination), the air pocket was measured.

The difference in viscosity between the inner layer and the outer layer was measured by the beam bending method.
First, an unused quartz glass crucible is cut into 4 × 4 × 40 mm, processed, and mirror-polished to produce an inner layer sample and an outer layer sample. Then, in the measurement, a load was applied to each sample at 1400 ° C. for 10 minutes, the displacement amount was measured, and the viscosity value was calculated. Then, the viscosity difference was obtained from the viscosity values of the inner layer sample and the outer layer sample.

In addition, the surface roughness of the wrinkled portion was measured.
For the surface roughness of this wrinkled portion, the wrinkled portion was cut out from the used quartz crucible and used as a sample. The surface roughness of the wrinkled portion was measured by setting a reference length and an evaluation length with a surface roughness meter, tracing the surface of the sample, and electrically detecting the vertical movement of the stylus.

Furthermore, the width of the crack generated in the quartz crucible used was measured.
The surface width of the crack was measured by a method of measuring the width of the crack portion by enlarging the sample surface portion with a microscope. The results are shown in Table 1.
As shown in FIG. 2, the width of the crack X was measured not in the length direction (longitudinal direction) of the crack but in the width direction (short direction) as shown in FIG.

In Table 1, the surface roughness ratio indicates the wrinkle unevenness ratio, the surface width ratio indicates the crack gap (width) ratio, and the AP (air pocket) generation ratio indicates the air pocket density ratio. It is shown by the ratio when it is done.

(Example 2)
As the high-purity quartz raw material powder forming the inner layer, natural quartz raw material powder having an Al, Na, K, Li concentration of less than 10 ppm is used, and as the quartz raw material powder forming the outer layer, the Al concentration is 8.5 ppm (Al added). A natural quartz raw material powder having an amount of 2.5 ppm) was used. Then, using these high-purity quartz raw material powder and quartz raw material powder, a quartz glass crucible for pulling a silicon single crystal was manufactured by a general rotary molding method.
Then, in the same manner as in Example 1, the viscosity value, the number of air pockets generated per unit volume, the viscosity of the inner layer and the outer layer, the surface roughness of the wrinkled portion, and the surface width of the crack were measured. The results are shown in Table 1.

(Example 3)
As the high-purity quartz raw material powder forming the inner layer, synthetic quartz raw material powder having an Al, Na, K, Li concentration of less than 1 ppm is used, and as the quartz raw material powder forming the outer layer, the Al concentration is 10 ppm (Al addition amount 4 ppm). ), A natural quartz raw material powder having a Na concentration of about 0.6 ppm, a K concentration of about 0.3 ppm, a Li concentration of about 0.1 ppm and a total alkali content of 1 ppm was used.
Then, using these high-purity quartz raw material powder and quartz raw material powder, a quartz glass crucible for pulling a silicon single crystal was manufactured by a general rotary molding method.
Then, in the same manner as in Example 1, the viscosity value, the number of air pockets generated per unit volume, the viscosity of the inner layer and the outer layer, the surface roughness of the wrinkled portion, and the surface width of the crack were measured. The results are shown in Table 1.

(Comparative Example 1)
As the high-purity quartz raw material powder forming the inner layer, synthetic quartz raw material powder having an Al, Na, K, Li concentration of less than 1 ppm is used, and as the quartz raw material powder forming the outer layer, the Na concentration is about 2 ppm, K, Li. A natural quartz raw material powder having a concentration of about 1 ppm, a total amount of alkali of 4 ppm, and no addition of Al was used. The Al concentration of this natural quartz raw material was 6 ppm.
Then, using these high-purity quartz raw material powder and quartz raw material powder, a quartz glass crucible for pulling a silicon single crystal was manufactured by a general rotary molding method.
Then, in the same manner as in Example 1, the viscosity value, the number of air pockets generated per unit volume, the viscosity of the inner layer and the outer layer, the surface roughness of the wrinkled portion, and the surface width of the crack were measured. The results are shown in Table 1.

(Comparative Example 2)
As the high-purity quartz raw material powder forming the inner layer, synthetic quartz raw material powder having an Al, Na, K, Li concentration of less than 1 ppm is used, and as the quartz raw material powder forming the outer layer, a natural quartz raw material having an Al addition amount of 15 ppm is used. Powder was used. The Al concentration of the natural quartz raw material at this time was 21 ppm.
Then, using these high-purity quartz raw material powder and quartz raw material powder, a quartz glass crucible for pulling a silicon single crystal was manufactured by a general rotary molding method.
Then, in the same manner as in Example 1, the viscosity value, the number of air pockets generated per unit volume, the viscosity of the inner layer and the outer layer, the surface roughness of the wrinkled portion, and the surface width of the crack were measured. The results are shown in Table 1.

As shown in Examples 1 to 3, by reducing the viscosity difference between the inner layer and the outer layer, the amount of subduction of the quartz glass crucible at the time of pulling up the silicon single crystal can be reduced, and wrinkles on the inner surface are generated. It was confirmed that it became difficult to do so and the generation of air pockets could be reduced.

1 Quartz glass crucible 2 Inner layer 3 Outer layer 4 Straight body 5 Curved part 6 Bottom X Inner layer movement direction (sinking direction)

Claims (2)

A silicon single crystal pull-up quartz glass rutsubo having an inner layer made of high-purity quartz glass and an outer layer made of natural quartz glass whose viscosity has been increased by adding aluminum (Al) to the quartz raw material powder.
The Al concentration of the inner layer is 10 ppm or less, and the Al concentration of the outer layer is 7 ppm or more and 20 ppm or less.
A quartz glass crucible characterized in that the viscosity difference between the inner layer and the outer layer at 1400 ° C. is 0.8 × 10 ⁺¹⁰ (poise) or less. The method for producing a quartz glass crucible for pulling a silicon single crystal according to claim 1, which has an inner layer made of high-purity quartz glass and an outer layer made of natural quartz glass.
The Al component was not added to the quartz raw material powder for forming the inner layer, and the Al component was added to the quartz raw material powder for forming the outer layer.
A method for producing a quartz glass crucible, wherein the Al concentration of the inner layer is 10 ppm or less, and the Al concentration of the outer layer is adjusted to 7 ppm or more and 20 ppm or less.

Images