JP2002195758A - Melting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that conventionally when there is used a melting apparatus of the type where a stock material put in a crucible in a vacuum container is heated and melted with heating means into a molten solution, and then the crucible is inclined and cast iron is poured into a mold, resistance heating type heater is difficult to use as the heating means so that an expensive induction heating type heating means has had to be used. SOLUTION: A melting apparatus is provided, in which a stock material put in a crucible in a vacuum container is heated and melted with heating means into a molten solution, and then the crucible is inclined to pour cast iron into a mold. In the melting apparatus, a heat-insulating material is provided on the side surface of the crucible, and a resistance heating heater is provided at an upper portion and a lower portion of the crucible, and further, the crucible is inclined toward the mold, independently of the foregoing resistance-heating type heater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a melting apparatus, and more particularly to a melting apparatus used for a casting apparatus for casting a semiconductor material such as silicon.

[0002]

2. Description of the Related Art Conventionally, a raw material such as silicon put in a crucible in a vacuum vessel is heated and melted by a heating means, and after the raw material turns into a melt, the crucible is tilted and poured into a mold. As the casting apparatus, there was one as shown in FIG.
In FIG. 4, reference numeral 21 denotes a casting chamber, 22 denotes an induction heating type melting apparatus for heating and melting a semiconductor material (not shown) such as silicon, and 23 denotes a mold for solidifying the melted semiconductor material.

The interior of the casting chamber 21 is kept in an atmosphere in which an inert gas such as an argon gas is introduced after evacuation is performed so that the semiconductor material is not oxidized. A melting device 22 and a mold 23 are provided in the casting chamber 21. The melting device 22 is provided with a tilting mechanism (not shown) for tilting the melting device 22 to a predetermined angle so that the molten metal can be poured. , Heater 2 for controlling the solidification state of mold 23 from the pouring position
A transport mechanism 25 for transporting the mold 4 to the position where the mold 4 is provided is provided so that the mold 23 can move up and down and horizontally in the casting chamber 21.

In this casting apparatus, the raw material charged into the melting apparatus 22 is heated and melted in the melting apparatus 22 while maintaining the interior of the casting chamber 21 in an inert gas atmosphere. And poured into the casting mold 23, conveyed to a solidification position where a heater 24 for controlling the solidification state was provided, and solidified.

[0005] Although not a tilting type melting apparatus, in a silicon single crystal pulling apparatus which is the most common as a silicon melting apparatus, as shown in FIG. 5, a resistance heating type heater 31 made of graphite is used as a heating means. Have been. The resistance heater 31 is provided around a crucible having a cylindrical shape. In FIG. 5, 32 is a quartz crucible, 33 is a graphite crucible, 34 is a seed crystal, 35 is a lifting shaft,
36 is a suction port.

[0006]

However, if a melting apparatus using a resistance heater 31 as shown in FIG. 5 is replaced with a tilting melting apparatus as shown in FIG. 4, the structure becomes complicated, and In addition, a large vacuum container is required.
Therefore, when the melting apparatus is of a tilting type, an induction heating type has conventionally been used as a heating means.

However, the induction heating type heating means has a problem in that the power supply device is much more expensive than the resistance heating type heating means.

[0008] In addition, in a melting apparatus of the induction heating type, when a raw material such as silicon which has a large electric resistance and is difficult to directly inductively heat is melted, a graphite crucible is induction-heated and the heat such as silicon is used. The graphite crucible reacts with silicon, so that a quartz crucible is put inside the graphite crucible and melted in the quartz crucible. However,
When a crucible that has been emptied by pouring is cooled, there is a problem that the crucible subjected to thermal stress is broken due to the difference in thermal expansion coefficient between quartz and graphite.

Therefore, it is conceivable that the graphite crucible may be divided to absorb the thermal stress due to the difference in the coefficient of thermal expansion. However, if the graphite crucible is divided, an arc discharge occurs on the divided surface and the graphite crucible is consumed. Problem occurs. Therefore, there is a problem that the divided graphite crucible cannot be used in the induction heating type melting apparatus.

The present invention has been made in view of the above-mentioned problems of the conventional apparatus. If the melting apparatus using the resistance heating type heater is made to be a tilting type, the structure becomes complicated and the induction heating is performed. In the melting device using the heater of the formula,
It is an object of the present invention to provide a melting apparatus which solves the problem of the conventional apparatus that a graphite crucible cannot be divided.

[0011]

In order to achieve the above object, in the melting apparatus according to the first aspect, a raw material put in a crucible in a vacuum vessel is heated and melted by heating means, and the raw material is melted. After that, in a melting apparatus in which the crucible is tilted and poured into a mold, a heat insulating material is provided on the side surface of the crucible, and a resistance heating heater is provided on the upper and lower parts of the crucible, and the crucible is provided on the mold. It is characterized in that it is inclined separately from the resistance heater.

In the above melting apparatus, it is preferable that the upper heater is rotated about a horizontal rotation axis located on the upper side of the crucible to secure an inclined region of the crucible.

In the above melting apparatus, it is desirable that the crucible be tilted while the position of the resistance heating type heater below the crucible is maintained.

Further, in the melting apparatus described above, it is preferable that the crucible is composed of an inner crucible made of quartz and an outer crucible made of graphite, and the outer crucible is a crucible divided in a vertical direction.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing one embodiment of a melting apparatus according to the present invention, wherein 1 (1a, 1b) is a crucible, 2 is an upper heater, 3 is a lower heater, 4 is a heat insulator on the side of the crucible, and 5 is Heat insulator for upper heater, 6 for lower heater,
7 is a tilting axis of the crucible.

These are all housed in a vacuum container. In order to prevent the material from being oxidized, the inside of the container is kept in a vacuum or the inside of the container is evacuated and then kept in an inert gas atmosphere such as argon gas.

The crucible 1 heats and melts a semiconductor material such as silicon and pours a melt into a mold (not shown). The crucible 1 includes a quartz crucible 1a provided inside and a graphite crucible 1b provided outside. Become. The silicon material melted in the quartz crucible 1a, poured into a mold, and solidified is used, for example, for a silicon substrate for a solar cell. The quartz crucible 1a dissolves a semiconductor material such as silicon that has been put into it, and is generally made of quartz in consideration of fire resistance and that no impurities are mixed into the semiconductor material. Since the quartz crucible 1a is softened at a high temperature and cannot keep its shape, the quartz crucible 1b is held by the graphite crucible 1b. The size of the crucible 1 is determined by the amount of the semiconductor material to be dissolved and the like.

An upper heater 2 is provided on the crucible 1, and a lower heater 3 is provided below the crucible 1. These heaters 2 and 3 are resistance heating type heaters heated by Joule heat generated by an electric current. Semiconductor materials such as silicon filled in the crucible 1 are heated and melted by the heaters 2 and 3. The upper heater 2 and the lower heater 3 may be connected in series or in parallel and may be heated by one power supply, or the respective heaters 2 and 3 may be separately heated by independent power supplies. As for the heaters 2 and 3, only the upper heater 2 can be provided, or only the lower heater 3 can be provided. However, installing the heaters 2 and 3 on both the upper and lower sides is advantageous in terms of thermal efficiency.

The upper heater 2 and the surrounding heat insulating material 5 are shown in FIG.
As shown in (1), it is structured to rotate and move to the side of the crucible 1. Before tilting the crucible 1, the upper heater 2 and the heat insulating material 5 of the upper heater are rotated and moved upward as shown in FIG. Thus, the present invention is not limited to the case where the upper heater 2 and the heat insulating material 5 of the upper heater are rotated to move upward, but may be rotated in the horizontal direction or linearly moved in the horizontal direction. However, the moving method as shown in FIG. 2 is advantageous when the melting apparatus is to be housed in a vacuum vessel as small as possible.

If an additional raw material charging mechanism is provided on the upper part of the crucible 1, it becomes possible to additionally charge the raw material during melting. In this case, when the raw material is additionally charged into the crucible 1, the upper heater 2 and the heat insulator 5 of the upper heater are moved as shown in FIG.

Around the crucible 1, a heat insulating material 4 on the side of the crucible 1 for preventing heat from escaping from the side of the crucible 1 is provided. The heat insulating material 4 on the side of the crucible 1 is the crucible 1
Are supported, and the crucible 1 is rotated about a rotation axis 7 for tilting. As shown in FIGS. 1 and 3, when the rotating shaft 7 is located near a casting mold (not shown), the heat insulating material 4 on the side of the crucible 1 is inclined toward the casting mold until the casting is completed. The lower heater 3 and the heat insulator 6 of the lower heater. Therefore, by setting the rotation axis 7 of the crucible 1 to such a position, it is not necessary to move the lower heater 3, and the lower heater 3 may be of a fixed type. When all of the semiconductor material such as silicon in the crucible 1 is melted, the heat insulating material 4 on the side of the crucible 1 is tilted about the rotation axis 7 of the crucible 1 with the crucible 1 supported, and the crucible 1 The melt is poured into a mold (not shown). FIG. 3 shows a state in which the heat insulating material 4 on the side surface of the crucible 1 is tilted.

Further, the graphite crucible 1b is arranged in the vertical direction in FIG.
Has been split. If the graphite crucible 1b is of an integral type, when the crucible 1 is cooled by pouring, thermal stress acts on the crucible 1 due to the difference in the coefficient of thermal expansion between quartz and graphite.
Crucible 1 breaks. By forming the graphite crucible 1b into a two-part structure, damage to the crucible 1 during cooling can be prevented.

By making the melting apparatus have the above structure,
Although it is a melting device using a resistance heating type heater as a heating means, it can be installed with a simple structure and in the same space as a melting device using an induction heating type heating means.

As a dissolving apparatus for silicon, one having a structure in which a cylindrical resistance heating type heater is installed around a crucible 1 like a silicon single crystal pulling apparatus shown in FIG. 5 has been used. With this structure it is difficult to make it tiltable,
Obviously, even if it could be done, it would be a fairly large device when compared to the present invention.

Further, in the case of the apparatus of the present invention, since the surface area inside the heat insulating material is smaller than that of a melting apparatus such as a silicon single crystal pulling apparatus, heat does not easily escape, and thermal efficiency is easily improved. Further, in the case of the apparatus of the present invention, a relatively small flat heater is sufficient without requiring a large cylindrical heater, so that the cost of the heater can be reduced.

Furthermore, in the case of the induction heating type, if the cooling water flowing through the induction coil is stopped during melting, the induction coil may be damaged by the heat of the crucible 1 or the melt. If the induction coil is damaged, there is a danger of steam explosion caused by leaking cooling water. For this reason, in the case of the induction heating type melting furnace, it is common to install an emergency cooling water facility. On the other hand, in the case of the resistance heating type of the present invention, since a water-cooled induction coil is not used, there is no danger of steam explosion and the safety is high.

[0027]

As described above, according to the melting apparatus of the present invention, the raw material put in the crucible in the vacuum vessel is heated and melted by the heating means. In a melting apparatus in which a crucible is tilted and poured into a mold, a heat insulating material is provided on the side of the crucible, and a resistance heating type heater is provided on an upper portion and a lower portion of the crucible, and the crucible faces the mold with the resistance heating type. Since it is tilted separately from the heater, it is a melting apparatus using a resistance heating type heater as a heating means, but it can be installed in a space with a simple structure and equivalent to a melting apparatus using an induction heating type heating means. As a result, it is not necessary to use expensive induction heating type heating means even in the tilting pouring type melting apparatus.

Further, by using the resistance heating type heater as the heating means, the divided type graphite crucible 1b can be used, so that the crucible can be easily prevented from being damaged by thermal stress during cooling. Become.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a melting apparatus according to the present invention.

FIG. 2 is a view showing a state in which an upper heater and a heat insulating material of the upper heater are moved in the melting apparatus according to the present invention.

FIG. 3 is a view showing a state in which a crucible and a heat insulator on the side of the crucible are inclined in the melting apparatus according to the present invention.

FIG. 4 is a view showing a casting apparatus using a conventional melting apparatus.

FIG. 5 is a view showing another conventional melting apparatus.

[Explanation of symbols]

1 (1a, 1b): crucible, 2: upper heater, 3: lower heater, 4: heat insulator on the side of crucible, 5: heat insulator of upper heater,
6: Insulation material of lower heater, 7: Rotating axis of tilting crucible

Claims (4)

[Claims] 1. A raw material put in a crucible in a vacuum vessel is heated and melted by a heating means, and after the raw material turns into a melt,
In a melting apparatus in which the crucible is tilted and poured into a mold,
A melting apparatus, wherein a heat insulating material is provided on a side surface of the crucible, and a resistance heating heater is provided at an upper portion and a lower portion of the crucible, and the crucible is inclined toward the mold separately from the resistance heating heater. . 2. The crucible according to claim 1, wherein the upper heater is rotated about a horizontal rotation axis located on the upper side of the crucible, so that the crucible is separately tilted. The dissolving apparatus according to claim 1. 3. The melting apparatus according to claim 1, wherein the crucible is separately tilted while the position of the resistance heater below the crucible is maintained. 4. The melting apparatus according to claim 1, wherein the crucible is composed of an inner crucible made of quartz and an outer crucible made of graphite, and the outer crucible is a crucible divided in a vertical direction.