JP4774355B2 - Protective sheet for crucible and melting apparatus - Google Patents

Description

The present invention relates to a crucible protective sheet and a melting instrument. A crucible is used for the production of single crystal silicon or the like by the CZ method. Such crucibles include an outer crucible heated by a heater or the like and an inner crucible in which raw materials such as polycrystalline silicon are accommodated. Usually, a quartz crucible is used for the inner crucible due to problems with silicon reactivity and purity, and the outer crucible is made of carbon composite (C / C) or graphite due to purity, heat resistance and strength problems. A crucible is used, and the inner crucible is inserted into the outer crucible.
During the manufacture of single crystal silicon, etc., damage is prevented when the quartz inner crucible is inserted, and the outer crucible is prevented from becoming SiC due to reaction with SiO gas, etc. generated from the quartz crucible. In order to secure the structure, a member for protecting both the crucibles is provided between the outer crucible and the inner crucible.
The present invention relates to a crucible protective sheet disposed between the outer crucible and the inner crucible, and a melting instrument used in the production of single crystal silicon or the like.

In the production of single crystal silicon by the CZ method, in order to improve the quality of the produced single crystal silicon, the polycrystalline silicon used as a raw material is required to be as highly pure as possible, in other words, to have as few impurities as possible. Is done.
However, in actual production of single crystal silicon, in order to obtain single crystal silicon having desired electrical characteristics, a small amount of an arbitrary impurity is added as a doping element to polycrystalline silicon as a raw material. Single crystal silicon is manufactured from the included polycrystalline silicon.

Here, if the amount of the doping element present in the molten silicon is not controlled, a quality abnormality of the manufactured single crystal silicon will occur, but a melting tool used for melting polycrystalline silicon during manufacturing, Specifically, there is a concern that the impurities may evaporate from the inner crucible, the outer crucible, and the sheet disposed between the crucibles, and a problem may occur in which the impurities are mixed into the molten silicon.
Since it is impossible to control the amount of impurities mixed in from such a melting tool, at present, by reducing the amount of impurities contained in the melting tool itself as much as possible, there is a possibility that impurities will be mixed into molten silicon. Lowering is performed (Patent Documents 1 to 3).

  However, it is possible to suppress the mixing of impurities into the molten silicon by using a melting device with a very small amount of impurities, in other words, a very high quality melting device, but such a very high quality melting The equipment is very expensive, which causes an increase in the price of the silicon manufacturing equipment and leads to an increase in the production cost of single crystal silicon. In addition, such high-quality melting equipment requires strict quality control to prevent contamination after the equipment is manufactured, but it is difficult to perform quality control to maintain the quality at a certain level or higher, and this management cost is also reduced to a single crystal. It is reflected in the production cost of silicon.

  In particular, it is difficult to reuse the sheet, and it is fundamental to use a new sheet almost every time. For this reason, although the sheet cost required for one melting operation is not so high, the production cost of single crystal silicon increases by using a high-quality sheet in the long term.

In addition, it is difficult to increase the purity of the sheet, and there is a problem that the working efficiency of increasing the purity is not good as compared with the graphite crucible.
This is because a normal graphite crucible is a so-called porous material with microscopic holes, and impurities can escape through these holes, so high-purity treatment can be easily performed in a relatively short time for its volume. On the other hand, the graphite sheet has an extremely layered structure, and because it is made of a material having no holes on its surface, it takes time to purify the interior even though its volume is small. And the fact that the sheet is flexible and needs to be handled with a large-area product is one reason that the efficiency of the work of purifying the sheet deteriorates compared to the work of purifying the graphite crucible. It has become.

  As described above, the quality of single crystal silicon can be improved by improving the quality of the melting tool, but the production cost has been increased. Since the increase in the production cost of silicon is promoted, it is desired to develop a melting apparatus that can suppress the production cost of the single crystal silicon while suppressing the production cost.

Japanese Patent Publication No.6-2637 Patent No. 2923260 Japanese Patent No. 3410380

  In view of the circumstances described above, the present invention has an object to provide a crucible protective sheet and a melting instrument that can suppress an increase in production cost and can also effectively suppress a deterioration in quality of a manufactured product. To do.

The melting instrument of the first invention comprises a crucible having an inner crucible and an outer crucible, and a sheet made of expanded graphite disposed between both crucibles, wherein the sheet has a total ash content of more than 50 massppm and less than 100 massppm, and Among the mixed impurities, the weight ratio of one or more specific elements selected from boron, phosphorus, arsenic, iron, antimony, indium, and bismuth is 3 massppm or less. The ratio of the total ash content of the ash content and the ash content of the outer crucible to the total weight of the total weight of the sheet and the outer crucible is 30 massppm or less.
The melting instrument of the second invention is characterized in that, in the first invention, the outer crucible is a graphite crucible having an ash content of 20 massppm or less.
The melting instrument of the third invention is characterized in that, in the first invention, the outer crucible is a carbon composite crucible having an ash content of 20 massppm or less.
The melting instrument of the fourth invention is characterized in that, in the first, second or third invention, the total weight ratio of the specific elements contained in the sheet is 10 massppm or less .

According to the first invention, since the total amount of ash combined with the sheet and the crucible is small, the total amount of impurities mixed into the material can be suppressed. In addition to prescribing the total amount of ash content, paying attention to the weight ratio of specific elements and making the weight ratio below a specific amount, the melting equipment can be used without making the ash content reduction process excessive. The manufacturing cost of a product to be manufactured (hereinafter simply referred to as a product) can be reduced, and the product quality can be kept high. In addition, since the amount of the specific element having a great influence on the quality of the product is suppressed, the quality of the entire sheet is not so high, but the occurrence of product quality abnormality can be prevented. Since the quality of the entire sheet is not so high, the manufacture of the sheet and the quality control of the sheet are facilitated, and the product quality can be kept high while suppressing the manufacturing cost of the product.
According to the second invention, the outer crucible is a graphite crucible, and the ash content thereof is kept low. Therefore, the total amount of ash in the entire apparatus can be reduced, and the occurrence of product quality abnormalities can be suppressed. In addition, since it is not necessary to make the sheet quality so high, sheet manufacturing and sheet quality control are facilitated, and the product quality can be kept high while suppressing the manufacturing cost of the product.
According to the third invention, the outer crucible is a carbon composite (C / C) crucible, and its ash content is kept low, so that the total amount of ash in the entire apparatus is reduced, and product quality abnormalities are generated. Can be suppressed. In addition, since it is not necessary to make the sheet quality so high, sheet manufacturing and sheet quality control are facilitated, and the product quality can be kept high while suppressing the manufacturing cost of the product.
According to the fourth aspect of the present invention , since the amount of mixing of a plurality of specific elements is suppressed, it is possible to more reliably suppress the occurrence of product quality abnormality .

Next, an embodiment of the present invention will be described with reference to the drawings.
An apparatus for producing polycrystalline silicon in which the melting apparatus of the present invention is used will be briefly described.
FIG. 1A is a schematic explanatory view of equipment for manufacturing a silicon single crystal and the like, and FIG. 1B is a partially enlarged explanatory view of a crucible 1.
In FIG. 1, reference numeral 1 is a crucible for accommodating polycrystalline silicon which is a raw material such as a silicon single crystal. A heater 5 is disposed around the crucible 1, and the crucible 1 is heated by radiant heat from the heater 5. For this reason, when the crucible 1 is heated by the heater 5, the polycrystalline silicon is heated and melted by heat conduction from the crucible 1, so that a silicon single crystal is manufactured by bringing the seed crystal into contact with the molten silicon and pulling it up. can do.
The crucible 1 is usually composed of an inner crucible 2 and an outer crucible 3 that accommodates the inner crucible 2 therein. Further, the inner crucible 2 is inserted into the outer crucible 3 to prevent breakage, and due to the difference in thermal expansion coefficient between the materials forming the crucibles 2 and 3 when the crucible 1 is cooled after the production of silicon single crystal or the like is finished. In order to prevent damage, a sheet 4 is disposed between the crucibles 2 and 3.
And the melting instrument of this invention is used for said crucible 1 and sheet | seat 4 (FIG. 1 (B)).

Next, the melting instrument of the present invention will be described in detail.
As described above, the melting instrument of the present invention is composed of the crucible 1 and the sheet 4.
The crucible 1 is composed of an inner crucible 2 made of quartz that accommodates polycrystalline silicon as a raw material such as a silicon single crystal, and an outer crucible 3 that accommodates the inner crucible 2 therein.
The outer crucible 3 is made of, for example, graphite or carbon composite (C / C), and has a weight of about 20 to 100 kg, for example. And the outer crucible 3 is adjusted so that the ash content may be 20 massppm or less, More preferably, it is 10 massppm or less. The reason why the ash content of the outer crucible 3 is adjusted to the above range will be described later.

The sheet 4 is formed from expanded graphite. Specifically, expanded graphite formed by immersing natural graphite, quiche graphite, or the like in a liquid such as sulfuric acid or nitric acid and then performing a heat treatment at 400 ° C. or higher is formed into a sheet shape. Expanded graphite has a cotton or fiber shape, that is, its axial length is longer than its radial length. For example, the length in the axial direction is about 1 to 3 mm and the length in the radial direction is about 300 to 600 μm, and the expanded graphite is entangled with each other inside the sheet 4. .
In addition, although the sheet | seat 4 may be formed only with expanded graphite as mentioned above, binders, such as a phenol resin and a rubber component, may be mixed a little (for example, about 5%).

The sheet 4 is adjusted (purified) so that the content of impurities mixed therein, that is, the total ash content is 100 massppm or less, preferably 50 massppm or less.
In recent years, the demand for purity of products has become increasingly severe. For this reason, higher purity is required for the crucible 1 and the sheet 4 to be used, and in order to meet this demand, the sheet disposed between the inner crucible 2 and the outer crucible 3 is also highly purified. Things are being developed.
However, in the melting device of the present invention, by setting the ash content of the outer crucible 3 to 20 massppm or less, it is possible to obtain a high-purity product even if the ash content is the same as the conventional sheet 4, for example, more than 50 massppm and less than 100 massppm. It became.

More specifically, for example, in the case of the outer crucible 3 having an inner diameter of 18 inches, the weight is about 30 kg. Therefore, if the ash content is 20 massppm, the ash content is about 0.6 g. When the entire inner surface of the outer crucible 3 is covered with the sheet 4, the dimension of the sheet 4 is about φ480 mm. Therefore, if the thickness is 1 mm and the bulk density is 1.5 Mg / m ³ , the weight is about 270 g. It becomes. In this case, if the ash content of the sheet 4 is 100 massppm, the ash content contained in the sheet 4 is about 0.03 g, and the total ash content in the entire melting apparatus is about 0.63 g, that is, the ash content for the entire melting apparatus is about 20 massppm. It becomes.
Then, considering that the weight of the polycrystalline silicon melted by the melting tool having the outer crucible 3 as described above is about 60 kg, the total amount of ash contained in the melting tool relative to the weight of the polycrystalline silicon is relatively small. it is conceivable that.

As described above, in the melting device of the present invention, since the total amount of ash combined with the ash contained in the outer crucible 3 and the sheet 4 is small, the amount of impurities mixed into the material can be suppressed. Moreover, it is not necessary to increase the quality of each member more than necessary. In particular, since it is not necessary to increase the quality of the sheet 4 more than necessary, the production and quality control of the outer crucible 3 and the sheet 4 are easy, and the product quality can be kept high while suppressing the production cost of the product.
In particular, if the ash content of the outer crucible 3 is 20 massppm or less, preferably 10 massppm or less, the outer crucible 3 can be manufactured and quality controlled and product quality can be efficiently maintained. Similarly, if the ash content of the sheet 4 is about 100 massppm, preferably about 50 massppm, it is preferable because the production and quality control of the sheet 4 and product quality maintenance can be performed efficiently.

  The method for adjusting the outer crucible 3 and the sheet 4 to ash as described above is not particularly limited, but impurities can be removed by, for example, bringing the outer crucible 3 or the sheet 4 into contact with a halogen gas.

Further, it is preferable that the sheet 4 is adjusted so that the weight ratio of the specific element among the plurality of impurities mixed therein is 3 massppm or less, preferably 1 massppm or less. The specific element is, for example, an element such as boron, phosphorus, arsenic, iron, antimony, indium, or bismuth. When these elements are mixed in polycrystalline silicon as a raw material for single crystal silicon, they have a great influence on the quality of the manufactured single crystal silicon and the manufacturing process thereof.
Then, since the sheet 4 suppresses the amount of the specific element having a large influence on the quality of the single crystal silicon, although the quality of the sheet 4 as a whole is not so high, the occurrence of product quality abnormality or the manufacturing process The occurrence of defects in can be effectively suppressed.
Therefore, manufacture of the sheet 4 and quality control of the sheet 4 are facilitated, and the product quality can be kept high while suppressing the manufacturing cost of the product.

  Note that all the specific elements do not necessarily have to be 3 massppm or less, and the specific elements that have a large influence on the properties required for the single crystal silicon to be manufactured have to be 3 massppm or less, preferably 1 massppm or less.

  Furthermore, if the properties of single crystal silicon to be produced are affected by the amount of a plurality of specific elements, the total weight ratio of the selected plurality of specific elements may be 10 massppm or less, preferably 5 massppm or less. Good.

  The melting instrument of the present invention is suitable for the production of silicon single crystals and the like by the CZ method.

(A) is schematic explanatory drawing of the equipment which manufactures a silicon single crystal etc., (B) is a partial expansion explanatory drawing of crucible 1.

1 crucible 2 inner crucible 3 outer crucible 4 sheet

Claims (4)

Consisting of a crucible having an inner crucible and an outer crucible, and a sheet of expanded graphite disposed between the crucibles,
The sheet is
The total ash content is greater than 50 massppm and less than 100 massppm , and among the mixed impurities, the weight ratio of one or more specific elements selected from boron, phosphorus, arsenic, iron, antimony, indium, bismuth is A sheet of 3 massppm or less,
A melting apparatus, wherein the total ash amount of the ash content of the sheet and the ash content of the outer crucible is 30 massppm or less in terms of the total weight of the weight of the sheet and the outer crucible. The melting instrument according to claim 1, wherein the outer crucible is a graphite crucible having an ash content of 20 massppm or less. The melting instrument according to claim 1, wherein the outer crucible is a carbon composite crucible having an ash content of 20 massppm or less. The total weight ratio of the said specific element contained in the said sheet | seat is 10 massppm or less, The melting instrument of Claim 1, 2, or 3 characterized by the above-mentioned.