JP3872233B2 - Silicon casting method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a silicon casting apparatus, and more particularly to a silicon casting apparatus that supplies a silicon raw material into a mold, heats and melts it, and then solidifies in one direction to form an ingot.
[0002]
[Prior art]
A conventional silicon casting apparatus is shown in FIG. In FIG. 2, 11 is a mold made of graphite, 12 is a cooling plate in which a coolant such as water circulates, 13 is a resistance heater, 14 is a heat insulating wall made of graphite, and 15a and 15b are upper portions of the heat insulating wall. It is the raw material supply tank provided in. Such a mold 11 and a heat insulating wall 14 are all installed in a vacuum vessel (not shown) (see, for example, JP-A-10-139586).
[0003]
In this silicon casting apparatus, a mold release material mainly composed of silicon nitride or silicon carbide is applied to the inner wall of the mold 11, a silicon raw material 17 is placed in the mold 11, and the silicon raw material 17 is heated by the heater 13. And melt. Next, when the silicon raw material 17 is melted and a space is formed above the mold 11, the silicon raw material in the first raw material supply tank 15 a is supplied into the mold 11. Next, when the additionally supplied silicon raw material is melted and a space is formed above the mold 11, the silicon raw material in the second raw material supply tank 15 b is supplied into the mold 11. Finally, when all the silicon raw materials are melted, the mold 11 is gradually lowered and the silicon melt 17 is gradually separated from the heater 13 to cool, or the temperature of the heater 13 is lowered while the position of the mold 11 remains unchanged. Then, the silicon melt is unidirectionally solidified in the mold 11 to form an ingot.
[0004]
The ingot of the unidirectionally solidified silicon melt 17 is taken out from the mold 11 by breaking the mold 11, or in the case of an assembly mold, the mold 11 is disassembled and taken out.
[0005]
[Problems to be solved by the invention]
However, in such a silicon casting method, it takes a long time to dissolve the raw materials in order to heat and melt all the raw materials 17 in one mold 11. In order to shorten the melting time with the conventional technique, it is necessary to increase the temperature of the heater 13, but if the temperature of the heater 13 is excessively increased, the release material applied to the inner wall surface of the mold 11 is damaged. Therefore, it was difficult to shorten the dissolution time.
[0006]
The present invention was invented in view of such problems of the conventional apparatus, and an object of the present invention is to provide a silicon casting apparatus that solves the problem of the conventional apparatus that it takes a long time to dissolve the silicon raw material. .
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a silicon casting method according to the present invention includes a step of introducing a silicon raw material into a mold, a step of introducing a silicon raw material into a melting crucible, and the silicon raw material in the mold in a mold. Heating and melting the silicon raw material in the melting crucible, heating and melting the silicon raw material in the melting crucible, and discharging the molten silicon melt in the melting crucible from the bottom of the melting crucible. And a step of additionally supplying the inside .
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing an embodiment of a silicon casting apparatus using a silicon casting method according to the present invention. 1 is a mold made of graphite or the like, 2 is a cooling plate in which a coolant such as water circulates. 3 is a resistance heater, 4 is a heat insulating wall made of graphite, 5a is a quartz crucible, 5b is a graphite crucible, and 6 (6a, 6b) is a resistance heater for the crucible. Such mold 1 and heat insulating wall 4 are all installed in a vacuum container (not shown).
[0009]
In the present invention, a melting crucible 5 composed of a quartz crucible 5a and a graphite crucible 5b is provided on the upper part of the mold 1. At the bottom of the melting crucible 5, a hole 5c for discharging the melt is provided. This melting crucible 5 is also installed in the vacuum container together with the mold 1. A crucible resistance heater 6 (6a, 6b) is installed on or around the melting crucible 5 or both.
[0010]
The casting method according to the present invention includes a step of introducing a silicon raw material into a mold, a step of introducing a silicon raw material into a melting pot, a step of heating and melting the silicon raw material in the mold in the mold, and the melting A step of heating and melting a silicon raw material in a crucible in a melting crucible, and a step of additionally supplying the silicon melt melted in the melting crucible from the bottom of the melting crucible into the mold. Have. Specifically , the casting method in the casting apparatus using the present invention is as follows. First, about half of the silicon raw material 7 is put into the mold 1 and the remaining half of the silicon raw material 8 is put into the quartz crucible 5a. Next, the silicon raw material 7 in the mold 1 and the silicon raw material 8 in the quartz crucible 5a are heated and melted by the heater 3 and the heater 6 (6a, 6b). The silicon melted in the quartz crucible 5 a flows out from the hole 5 c at the bottom of the crucible and is additionally supplied into the mold 1. Finally, when all the silicon raw materials 7 and 8 are melted, the output of the heater 6 (6a, 6b) is turned off and the output of the heater 3 is adjusted to solidify in one direction.
[0011]
If enough silicon raw material 7 is put in the mold 1 and the remaining raw materials are put in the quartz crucible 5a, the required size of the quartz crucible 5a becomes the smallest. The bulk specific gravity of a general silicon raw material is 1.0 to 1.5, which is about half of the specific gravity of silicon 2.33. For this reason, about half of the silicon raw material can be placed in a mold of a size suitable for casting. Therefore, if about half of the silicon raw material 7 is put into the mold 1 and the remaining half of the silicon raw material 8 is put into the quartz crucible 5a, the mold and the crucible can be used most effectively. . However, there is no particular problem even if the amount of silicon raw material put into the mold 1 is less than half regardless of the above description. When melting mainly with the melting crucible 5a, the size of the melting crucible 5a is slightly increased, and the melting crucible 5a may be filled with more than half of the raw material.
[0012]
The melting crucible 5 and the heater 3 can be partitioned by a heat insulating material made of graphite or the like. However, a hole necessary for hot water is provided in the heat insulating material. If a heat insulating partition is inserted, the output of the heater 3 during solidification can be reduced, thus saving power.
[0013]
The crucible 5 is taken in and out from the upper part of the casting apparatus. At this time, the heater 6a and the heat insulation wall 4 on the crucible 5 are moved sideways. The raw material is introduced by moving the heater 6a and the heat insulating wall 4 sideways while the crucible 5 is contained. Alternatively, the crucible 5 in which raw materials are previously placed is placed in the casting apparatus. In the case of the mold 1, raw materials are put in the mold 1 in advance, and the mold 1 is put in a casting apparatus.
[0014]
When the raw material is melted with the mold 1 and the crucible 5, the melting time is almost halved. However, when the silicon raw material is melted, the crucible 5 can be melted in a shorter time. If the amount dissolved in 1 is reduced and the amount dissolved in the crucible 5 is increased, the dissolution time can be made shorter than 1/2.
[0015]
When only the mold 1 is melted, the melting time is long and the mold 1 is exposed to a high temperature state for a long time, so that the release material on the inner surface of the mold 1 is easily damaged. When the release material is damaged, the yield of good ingots decreases. In the case of the present invention, since the melting time is short, the release material is easily damaged, and the yield of good ingots is high.
[0016]
In the case of the present invention, the melting time is shortened to about half and the productivity is improved, whereas the increase in the equipment cost is slight. The size of the vacuum vessel may be the same as or slightly smaller than that of the conventional apparatus shown in FIG. In the conventional apparatus shown in FIG. 2, a driving device is required for the lid 15d and the heat insulating wall 14b of the raw material tank. However, in the present invention, such a driving device is unnecessary.
[0017]
In the present invention, automation is easier compared to the conventional apparatus of FIG. In the conventional apparatus shown in FIG. 2, it is necessary to observe the melting state of the raw material in the mold 11 and supply the raw material in the tanks 15a and 15b into the mold at an appropriate time. It is not necessary to observe and control this, so automatic dissolution is easy.
[0018]
【The invention's effect】
As described above, according to the silicon casting method of the present invention, the step of introducing the silicon raw material into the mold, the step of introducing the silicon raw material into the melting crucible, and the silicon raw material in the mold within the mold A step of heating and melting; a step of heating and melting the silicon raw material in the melting crucible; and a step of discharging the silicon melt melted in the melting crucible from the bottom of the melting crucible to within the mold. And at least the step of additionally supplying to the substrate, the silicon can be heated and melted not only in the mold but also in the melting crucible in parallel, and the melting time is significantly shortened.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a silicon casting apparatus using a silicon casting method according to the present invention .
FIG. 2 is a view showing a conventional silicon casting apparatus.
[Explanation of symbols]
1 ... Mold, 2 ... Cooling plate, 3 Heater, 4 Heat insulation wall, 5 (5a, 5b) Melting crucible, 6 (6a, 6b) Heater for crucible

Claims (1)

A step of introducing silicon raw material into a mold;
Adding silicon raw material into a melting crucible;
A step of heating and melting the silicon raw material in the mold in the mold;
A step of heating and melting the silicon raw material in the melting crucible in the melting crucible;
A step of additionally supplying the silicon melt melted in the melting crucible from the bottom of the melting crucible into the mold;
A silicon casting method characterized by comprising:

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