JPH07196397A - Production of quartz glass crucible for pulling up silicon single crystal - Google Patents

Abstract

PURPOSE:To decrease the amount of metallic impurities taken into a silicon single crystal, shorten the time necessary for etching and decrease the etching thickness to prevent the roughening of the inner surface a crucible. CONSTITUTION:The inner surface of a crucible having the 1st high-OH layer exposed to the inner surface, having a thickness of <=100mum and containing 350-1,500ppm of OH group and the 2nd low-OH layer unexposed to the inner surface, having a thickness of >=5mm and containing <=100ppm of OH group is etched to remove at least the surface part of the 1st layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a quartz glass crucible for pulling a silicon single crystal used for pulling a silicon single crystal.

[0002]

2. Description of the Related Art A silicon single crystal used as a substrate of a semiconductor device is mainly manufactured by the CZ method (Czochralski method). In this method, in principle, the polycrystalline silicon raw material is loaded in the crucible, and the polycrystalline silicon raw material is melted by heating from the surroundings, and then the seed crystal is hung from above and immersed in the silicon melt. By pulling up, the silicon single crystal ingot is pulled up.

In semiconductor devices, it is well known that the element characteristics are adversely affected by the influence of metal impurities contained in the silicon substrate. Even during the above-described silicon single crystal pulling operation, the silica glass crucible is eroded by the silicon melt, and the metal impurities in the silica glass crucible are taken into the silicon single crystal. Efforts are also being made to reduce metallic impurities. Actually, in the conventionally used quartz glass crucible, the content of alkali metal or the like is 0.1 ppm or less in the average value of the total wall thickness, and Al (aluminum) is also 7
It is extremely small, about 8 ppm.

However, the above-mentioned Al content is an average value as a whole, and in reality, the Al concentration is extremely high at 150 ppm to 1000 ppm on the inner surface side of the quartz glass crucible, and it rapidly decreases toward the inside. Has a distribution. Therefore, when the inner surface of the quartz glass crucible is eroded by the silicon melt, more than expected Al is taken into the silicon single crystal, and the pulled silicon single crystal cannot be ignored from the viewpoint of the influence on the characteristics of the semiconductor device. There is a problem that Al is contained to some extent.

In order to solve such a problem, a quartz glass crucible and a method for producing the same have been proposed in Japanese Patent Laid-Open No. 63-166791.

This quartz glass crucible is characterized in that the Al concentration on the inner surface is 10 ppm or less. The production method of a quartz glass crucible is to make a SiO ₂ (silicon dioxide) raw material into a crucible shape by a usual arc melting method, and then to etch the inner surface of the quartz glass crucible with an HF aqueous solution for 30 μm or more. The treatment condition with this HF (hydrogen fluoride) aqueous solution is, for example, 30 minutes or more with a 50% HF aqueous solution.

According to such a quartz glass crucible, even if the inner surface is eroded by the molten silicon, Al taken in the silicon single crystal can be reduced, which in turn has an adverse effect on the element characteristics of the semiconductor device. It can be reduced.

[0008]

However, in the quartz glass crucible and the manufacturing method thereof described in the above-mentioned JP-A-63-166791, the contaminated inner surface layer is etched as described above. It takes a long time of 30 minutes or more.

Moreover, since the inner surface is roughened by etching to a thickness of 30 μm or more as described above, impurities are likely to adhere to the inner surface, and when the silicon single crystal is pulled, the silicon single crystal pulled up is transferred. There is a problem that it has an adverse effect such as occurrence.

Further, when the inner surface is roughened, the amount of melting loss of the quartz glass crucible in the silicon melt during pulling up of the silicon single crystal increases, and the oxygen concentration in the silicon single crystal excessively increases. .

The present invention can reduce the metal impurities taken in the silicon single crystal, can shorten the time required for etching, and further can reduce the etching thickness to prevent the inner surface from being roughened. In addition, for pulling a silicon single crystal, it is possible to prevent an increase in the melt loss of the quartz glass crucible in the silicon melt during pulling the silicon single crystal and prevent an excessive increase in the oxygen concentration in the silicon single crystal. An object of the present invention is to provide a method for manufacturing a quartz glass crucible.

[0012]

In order to solve the above-mentioned problems, the present invention is exposed on the inner surface, has a thickness of 100 μm or less, and has an OH group content of 350 ppm to 1.
A crucible having a first layer with a high OH concentration of 500 ppm and a second layer not exposed on the inner surface and having a thickness of 5 mm or more and an OH group content of 100 ppm or less. The gist is a method for manufacturing a quartz glass crucible for pulling a silicon single crystal, which comprises etching at least the surface portion of the first layer by etching the inner surface of the crucible.

[0013]

The metal impurities such as alkali metal substitute for the H (hydrogen) atom of the OH group (hydroxyl group), and thus are condensed in a portion having a large OH group content. According to the present invention, the first layer having a high OH concentration, which is exposed on the inner surface and has a thickness of 100 μm or less and the OH group content is 350 ppm to 1500 ppm, and the first layer are exposed on the inner surface. Since the second layer has a thickness of 5 mm or more and a low OH concentration having an OH group content of 100 ppm or less, the metal impurities are condensed on the surface portion of the first layer.

Therefore, by removing at least the surface portion of the first layer, the concentration of metal impurities on the inner surface of the crucible can be made sufficiently low for practical use.

[0015]

EXAMPLE A method of manufacturing a quartz glass crucible for pulling a silicon single crystal according to a preferred embodiment of the present invention will be described.

First, a powder layer of SiO ₂ (silicon dioxide) is molded in a rotary mold, and the powder layer is melted by an electric arc to manufacture a crucible. In this way, in the electric arc melting of the powder layer in the rotary mold, until the end of melting or immediately before the end of melting, it is melted in an atmosphere with less water, and at the end of melting or immediately before and after the end of melting,
An atmosphere containing more water than the atmosphere before that. The atmosphere can be the same as the conventional one, for example, normal atmosphere.

The adjustment of the amount of water in the atmosphere will be described in more detail. By introducing (steam + air) into the melting crucible during the melting just before the end of melting,
A layer having many OH groups is formed on the inner surface layer. Further, the OH group content can be arbitrarily changed to some extent by changing the ratio of steam to air and the total amount.

By adjusting the water content in such an atmosphere,
The crucible described below is obtained by adjusting the OH group content of the crucible. That is, it is exposed on the inner surface, has a thickness of 100 μm or less, and has an OH group content of 350 ppm to 1
A crucible having a first layer having a high OH concentration of 500 ppm and a second layer which is not exposed on the inner surface and has a thickness of 5 mm or more and an OH group content of 100 ppm or less. obtain.

The OH group content indicates the total ratio of OH groups (hydroxyl groups) in parts per million.

Since metal impurities such as alkali metal substitute for H (hydrogen) atoms in the OH group, they are condensed in a portion having a large OH group content. Therefore, in the crucible described above, the metal impurities are condensed on the surface portion of the first layer. For example, even when the concentration of metal impurities in the crucible is as high as that of the conventional crucible, unlike the conventional case, the metal impurities do not diffuse and
Condensates on the surface of the layer. In this description, "condensation"
For example, when the alkali metal Na is taken as an example, the H atom of the OH group is replaced with Na to form ONa, and
It means that the alkali is concentrated on the surface portion of the layer to increase.

Explaining the thickness of the surface portion of the first layer, that is, the condensed portion of the metal impurities, the OH group content in the inner layer tends to increase as it approaches the inner surface.
It is preferable that the OH concentration of 0 to 1500 ppm is concentrated within 20 μm. Furthermore, the thickness of the condensed part is 10
It is preferably within μm. This can be arbitrarily changed by adjusting the water content of the atmosphere during the production of the crucible.

The second layer having a low OH concentration prevents diffusion of metal impurities. Therefore, it is possible to prevent metal impurities from diffusing and penetrating from the outer surface to the inner surface of the crucible, and to prevent the inner surface of the crucible from being contaminated by the metal impurities.

Next, by etching the inner surface of the crucible,
At least the surface portion of the high OH first layer is removed. For example, the inner surface of the crucible is etched by putting a 50% HF (hydrogen fluoride) aqueous solution in the crucible and holding it for 15 minutes. Thereby, the condensed portion of the metal impurities is removed. The metal impurity concentration in the first layer excluding the condensed portion of the metal impurities is sufficiently low in practical use. Therefore, the concentration of metal impurities on the inner surface of the etched crucible is practically sufficiently low.

In the manufacturing method described above, a conventional crucible manufacturing method, for example, the adjustment of the amount of moisture in the atmosphere and the etching of the inner surface, such as the rotary molding method described in Japanese Patent Publication No. 2-24797 can be employed.

As described above, unlike the conventional case, the metal impurities are not diffused and are condensed on the surface portion of the first layer, so that the etching amount of the inner surface can be reduced as compared with the conventional case. Therefore, it is possible to prevent the inner surface of the crucible from being roughened by etching. For example, the etching amount is 5 to 20 μ.
It is preferably m.

The thickness of the first layer having a high OH concentration is preferably 5 μm or more and 100 μm or less, more preferably 50 μm.
Hereinafter, the optimum condition is about 20 μm. In this case, the thickness of the condensed portion of the metal impurities can be made smaller, and the etching amount of the inner surface can be made smaller.

If the thickness of the first layer having a high OH concentration is larger than 100 μm, the alkaline impurities will be condensed in the layer having a thickness of 100 μm or more, so that it is necessary to increase the etching amount of the inner surface. As a result, the inner surface of the crucible becomes rough and impurities are likely to adhere to the inner surface, which causes adverse effects such as the dislocation of the pulled silicon single crystal due to the attached impurities when pulling the silicon single crystal. Moreover, the etching takes a long time, which is inefficient.

When the OH group content in the high OH concentration first layer is less than 350 ppm, the amount of metal impurities condensed on the surface of the first layer is small and the OH group content is 1%.
If it is more than 500 ppm, the OH groups are likely to diffuse during melting of the crucible at a high temperature, so that it is difficult to make the thickness of the first layer having a high OH concentration 100 μm or less.

When the OH group content in the second layer having a low OH concentration exceeds 100 ppm, it becomes difficult to condense metal impurities into the first layer having a high OH concentration.

The thickness of the second layer having a low OH concentration is 5
Even if it is less than mm, the same problem occurs.

Next, Examples 1 to 3 and Comparative Examples 1 and 2 will be described in order.

Example 1 Using a high-purity SiO ₂ powder as a raw material, a crucible having a diameter of 14 inches and a wall thickness of about 7 mm was prepared by the above-mentioned manufacturing method. The thickness and OH of the high OH concentration first layer of this crucible
The group content is shown in Table 1.

[0033]

[Table 1] A block-shaped sample having a total thickness was cut out from this glass crucible and crushed to obtain five kinds of metal elements {Al (aluminum), Fe (iron), Na (sodium), Li.
(Lithium), K (potassium)} concentration (chemical analysis value)
Was measured. The results are shown in the column of T (abbreviation of total) in Table 1. The symbols shown in the column of chemical analysis values in Table 1 ↓
Indicates less than. In other words, "0.1 ↓" and "0.01
“↓” indicates “less than 0.1” and “less than 0.01”, respectively.

Then, the inner surface of the crucible was etched by putting a 50% HF aqueous solution in the crucible and holding it for 15 minutes, and then the HF aqueous solution was recovered and the recovered HF was recovered.
The amount of SiO ₂ dissolved in the aqueous solution and the concentration of the metal element were measured. Then, the thickness (etching thickness) of the fused quartz glass crucible is obtained from the amount of SiO ₂ , and
The concentration of the metal element with respect to the quartz glass having that thickness was obtained. The results are shown in the column of S1 (abbreviation of surface1) in Table 1.

Next, 50% is put in this quartz glass crucible.
The inner surface of the crucible was etched by re-inserting the HF aqueous solution and holding it for 15 minutes, and then the HF aqueous solution was recovered and SiO ₂ dissolved in the recovered HF aqueous solution was recovered.
The amount and the concentration of the metal element were measured. Then, the thickness (etching thickness) of the fused quartz glass crucible was determined from the amount of SiO ₂ , and the concentration of the metal element in the quartz glass of that thickness was determined. This result is S in Table 1.
It is shown in column 2.

Examples 2 and 3 and Comparative Examples 1 and 2 In Examples 2 and 3 and Comparative Examples 1 and 2, the thickness and the OH group content of the first layer having a high OH concentration are shown in Table 1. To prepare a crucible. Then, the same measurement as that of the above-described Example 1 was performed. The results are shown in Table 1.

As is clear from Table 1, in each of the crucibles of Examples 1 to 3, the concentration of the metal element S2 was sufficiently low for practical use, and the first etching caused the condensed portion of the metal impurities near the inner surface. Had been removed. Therefore, in Examples 1 to 3, the second etching is not always necessary.

On the other hand, in Comparative Examples 1 and 2, the concentration of the metal element S2 was higher than that in Examples 1 to 3, and the first etching did not sufficiently remove the condensed portion of the metal impurities near the inner surface. It was

The present invention is not limited to the embodiments described above.

For example, the manufacturing method of the crucible is not limited to the above-mentioned manufacturing method, and other manufacturing methods can be adopted. Also in that case, the crucible having the above-described structure may be manufactured by adjusting the OH group content. For example, in the production method of the above-described embodiment or the conventional production method, the OH group content of the crucible may be adjusted by gas burning the crucible inner surface with an oxyhydrogen burner immediately after completion of melting. Other configurations are similar to those of the above-described embodiment.

The production method using the oxyhydrogen burner will be described in more detail. An oxyhydrogen burner made of quartz glass is used to maintain high purity, and the flame of the oxyhydrogen burner is kept at 2000 ° C. or higher in the crucible. By melting on the surface and near the inner surface, H ₂ O in the flame diffuses to the inner surface of the crucible and OH groups are formed in the crucible.

Further, the etching is not limited to the above-mentioned etching using the HF aqueous solution, and other etching can be adopted. Also in that case, at least the surface portion of the first layer may be removed.

In the present invention, the second layer having a low OH concentration does not necessarily reach the outer surface of the quartz glass crucible and may have a thickness of 5 mm or more. That is, the outer surface can have any OH concentration.

For example, the crucible is composed of an inner layer region, an intermediate layer region and an outer layer region, the inner layer region is the first layer, the intermediate layer region is the second layer, and the outer layer region is the third layer having an arbitrary OH concentration.
It may be a layer. Seen from the inner surface, the first layer, the second layer, the third layer
The layers may be formed sequentially.

[0045]

According to the present invention, it is exposed to the inner surface, has a thickness of 100 μm or less, and has a high OH concentration of OH group content of 350 to 1500 ppm.
Layer and low OH that is not exposed on the inner surface and has a thickness of 5 mm or more and an OH group content of 100 ppm or less
Since the second layer has a concentration, the metal impurities can be condensed on the surface portion of the first layer to prevent its diffusion. Then, the inner surface of the crucible is etched to remove at least the surface portion of the first layer, so that the condensed portion of the metal impurities can be removed. As a result, the amount of metal impurities taken into the silicon single crystal can be reduced, which in turn can reduce the adverse effect on the element characteristics of the semiconductor device. Moreover, since the metal impurities are condensed, the etching thickness can be reduced and the inner surface can be prevented from being roughened. Furthermore, the time required for etching can be shortened.

Claims (1)

[Claims] 1. Exposed on the inner surface, having a thickness of 100 μm or less, and having an OH group content of 350 ppm to 15
Crucible having a first layer with a high OH concentration of 00 ppm and a second layer not exposed on the inner surface and having a thickness of 5 mm or more and a low OH concentration having an OH group content of 100 ppm or less. A method of manufacturing a quartz glass crucible for pulling a silicon single crystal, wherein at least a surface portion of the first layer is removed by etching an inner surface of the crucible.