JPH07138012A - Device for casting silicon - Google Patents

Abstract

PURPOSE:To continuously and efficiently cast silicon improved in the quality and prevented in the generation of cracks by disposing a prescribed casting section, a heat-insulating container, and an ingot-lowering means for inserting a support bar into the heat-insulating container and subsequently lowering the ingot. CONSTITUTION:A bottom-less crusible 22 whose axially directional part is divided into plural pieces in the circumferential direction is disposed, and silicon is melted in the crucible 22 by an electromagnetic induction method in a state not contacting with the inner wall of the crucible. The obtained silicon molten liquid 11 is supplied in a casting section 20, downward lowered and simultaneously solidified. The obtained bar-like ingot 10 is lowered, guided into a cylindrical heat-insulating container 30 and subsequently subjected to heat insulation. The support bar 41 of an ingot-lowering means 40 is inserted into the lower part of a container 30. The ingot 10 is supported with a support bed 42 from the lower direction, and the support bar 41 is simultaneously pulled down in the lower direction to continuously produce the ingot 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon casting apparatus for producing a polycrystalline solidified ingot of silicon used in a solar cell or the like, and in particular, the polycrystalline solidified ingot is continuously produced by electromagnetic melting. The present invention relates to a continuous casting device for manufacturing.

[0002]

2. Description of the Related Art As a method for producing a polycrystalline solidified ingot of silicon used as a material for a solar cell or the like, a continuous casting method by electromagnetic melting has been proposed, for example, in Japanese Patent Laid-Open No. 2-30698. The continuous casting method of silicon by electromagnetic melting uses an induction coil and a conductive bottomless crucible installed therein. At least a part of the bottomless crucible in the axial direction is divided into a plurality in the circumferential direction. The raw material silicon charged in the bottomless crucible is melted in a non-contact state with the inner wall of the crucible by electromagnetic induction by the induction coil.
Then, while supplying the raw material silicon into the bottomless crucible,
A polycrystalline solidified ingot of silicon is continuously produced by gradually lowering and solidifying the melt in the bottomless crucible.

In such a continuous casting method of silicon by electromagnetic induction, as long as the raw material silicon is continuously supplied to the bottomless crucible, the casting is continued, which contributes to a significant improvement in casting efficiency. However, it is impossible to manufacture an extremely long ingot due to restrictions of manufacturing equipment and the like. Therefore, it becomes necessary to collect ingots that are continuously manufactured by a certain length and carry them to another place.
As a specific method thereof, for example, in Japanese Patent Laid-Open No. 2-51493, a cutter provided below the chamber is supported while supporting the ingot below the casting part, lowering it downward, and carrying it out below the chamber. Discloses that the ingot is cut into a certain length.

[0004]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2-51493
According to the method disclosed in the publication, the ingot can be cut and carried to another place during casting, so that it is not necessary to stop the casting. Therefore, there is no concern that the casting efficiency will be reduced. However, in order to cut the ingot, the outer peripheral surface of the ingot must be firmly held above and below the cut portion.

According to experiments conducted by the present inventors, it has been found that a large mechanical stress acts on the ingot due to holding the outer peripheral surface of the ingot. That is, the outer peripheral surface of the ingot, that is, the ingot surface is not smooth and has large unevenness, and when such an ingot surface is forcibly held, the ingot is displaced with respect to the device center, and the ingot is impossible. A large mechanical stress is applied to the ingot mainly due to the application of such a force. Then, due to this large mechanical stress, a serious operational problem such as cracking of the ingot or inability to pull it down occurred.

Further, since the cutter is provided at an intermediate position between the casting part and the floor, the distance from the casting part to the cutter is limited, and the ingot is not sufficiently cooled at the cutter. When cutting with a cutter in such a state, the cutting portion is rapidly cooled by a lubricant such as water, and a large temperature gradient in the central axis direction is generated in the ingot. As a result, ingot cracking and deterioration of crystal quality were caused.

Further, it has been found that there is a problem with the impurity concentration in continuous casting by this method. That is, in this method, as shown in FIG. 3, there is no change in the conversion efficiency up to a casting length of 5 m, but a decrease in the conversion efficiency is observed at a casting length of more than 5 m, and at a casting length of 10 m, it becomes 5 m or less. In comparison, the conversion efficiency is reduced by about 5%. It is considered that this is because impurities in the raw material silicon are discharged into the melt due to segregation, and the impurity concentration in the melt increases as the casting is continued.

An object of the present invention is to provide a silicon casting apparatus capable of solving all of these problems. Also,
Another object of the present invention is to provide a silicon casting apparatus capable of solving all of these problems without substantially lowering the casting efficiency.

[0009]

In the silicon casting apparatus of the present invention, a conductive bottomless crucible having at least a part in the axial direction divided into a plurality of parts in the circumferential direction is installed in the induction coil, and the bottomless crucible. Inside of the crucible, the silicon is melted by electromagnetic induction in a state of non-contact with the inner wall of the crucible, and the casting part is set below the casting part, which is set below the casting part by solidifying the melt that descends downward to solidify the melt. The tubular incubator that introduces the ingot that descends downward from the part and keeps it warm, and is installed below the set position of the insulative container, inserts the support rod from below into the insulative container, and Ingot lowering means for lowering the ingot by pulling down the support rod while supporting the ingot from below with the support head.

Preferably, a plurality of the heat-retaining containers are provided, each of which is movable so as to be attachable to and detachable from a casting part, and the supporting head of the supporting rod can be separated from the supporting rod main body. The structure according to claim 2 is adopted in which the holding mechanism for holding is provided in the lower portion of the heat insulating container.

[0011]

In the silicon casting apparatus of the present invention, the ingot continuously produced in the casting section is lowered while being supported from below by the support rod and drawn into the heat retaining container. When the drawing is completed, the supply of the raw material silicon is stopped, and the manufactured ingot is completely housed in the heat insulation container and cooled.

Since the manufactured ingot is supported from below,
The mechanical stress acting on the ingot is reduced. The ingot can be cooled in the heat-retaining container for a sufficient time, and since no lubricant is used for cutting, the temperature gradient in the central axis direction of the slab becomes extremely small. Since the ingot is stopped at a length that can be accommodated in the heat insulation container, the increase of the impurity concentration in the melt can be suppressed.

When a desirable structure is adopted, the ingot can be held inside the heat retaining container without depending on the ingot lowering means. Then, by moving the heat insulating container containing the ingot from the lower part of the casting part to another place, and cooling the ingot in another case, by setting another heat insulating container below the casting part, cooling is performed. Casting can also be performed during.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical cross-sectional view showing the structure of an example of a silicon casting apparatus according to the present invention.

The present casting apparatus includes a casting unit 20 for continuously producing the ingot 10, an ingot lowering unit 40 installed below the casting unit 20 with an interval of, for example, several meters, and a horizontal arrangement in parallel between them. The two vertical heat insulation containers 30 and 30 are provided.

The casting part 20 has an induction coil 21, a bottomless crucible 22 installed inside the induction coil 21, and a heat insulation furnace 23 installed below the bottomless crucible 22. Bottomless crucible 22
Is a water-cooled tubular body made of copper, and is divided into a plurality of pieces in the circumferential direction except for the upper part. These are provided inside the chamber 24, and a raw material feeder 25 is provided outside the chamber 24.

The ingot lowering means 40 has a vertical support rod 41. The upper end of the support rod 41 is a support head 42 that directly supports the ingot 10, and is attachable to and detachable from the lower support rod body 43. The support rod main body 43 is movably supported in the axial direction by a frame body 44, and is vertically moved by a lower drive mechanism 46.

Each of the heat retaining containers 30, 30 is a cylindrical body having a heat retaining function. The upper portion of each heat insulation container 30 is supported by a cart 33 placed on a horizontal rail 32,
As the trolley 33 travels, it linearly moves between the area directly below the casting portion 20 and the side thereof. The upper end opening of the heat insulating container 30 is airtightly communicated with the inside of the chamber 24 by the seal 34, and is closed airtightly by the upper lid 35. Insulation container 30
A holding mechanism 36 for clamping the support head 42 from the outside and holding the support head 42 in the heat insulating container 30 is provided at the lower end of the. While the lower end opening of the heat insulating container 30 is sealed between the outer peripheral surface of the support rod 41 by the seal 37,
The lower lid 38 is airtightly closed.

On the side of the ingot lowering means 40, the heat insulating means 3 is provided.
The ingot extracting means 50 is installed at a predetermined interval in the moving direction of 0 and 30. The ingot extracting means 50 has an elevating head 52 that is vertically moved along a guide 51.
The elevating head 52 is connected to the support head 42 held in the heat retaining container 30, and lowers the support head 42 while supporting the load of the ingot 10 on the support head 42 to remove the ingot 10 from the heat retaining container 30. Pull it down.

Next, a silicon casting method using this casting apparatus will be described.

One heat retaining means 30 is located between the casting section 20 and the ingot lowering means 40, and the heat retaining container 30 is hermetically connected to the chamber 24 of the upper casting section 20. The support head 42 is attached to the tip end portion of the support rod 41 of the ingot lowering means 40, the support rod 41 is raised, and the support head 42 is inserted into the heat retaining container 30. After the support head 42 is clapped by the holding mechanism 36, the support head 42 is separated from the support rod main body 43, and the support rod main body 43 is once lowered.

After the lower end opening of the heat retaining container 30 is closed by the lower lid 38, the inside of the chamber 24 and the heat retaining container 30 are closed.
The inside is replaced with argon gas. The gas may be of any type as long as it is inert to the silicon melt. The substitution method may be vacuum substitution, upward substitution, or downward substitution.

After the argon substitution is complete, the pressure is reduced to 1
The pressure is made slightly higher than the atmospheric pressure, and the lower lid 38 is removed. Since the inside of the chamber 24 and the inside of the heat retaining container 30 are in a weakly pressurized state of argon, the atmosphere does not enter the heat retaining container 30 even if the lower lid 38 is removed.

The support rod body 43 is raised again and connected to the support head 42 in the heat insulation container 30. The support rod body 43 is further raised and inserted into the chamber 24 from below. Continue to raise until the support head 42 is inserted into the bottomless crucible 22 to form the bottom of the bottomless crucible 22.
When the support rod main body 43 is inserted into the heat retaining container 30, the outer peripheral surface of the support rod main body 43 and the inner peripheral surface of the heat retaining container 30 are sealed by the seal 37, so that the invasion of the atmosphere can be prevented more reliably.

Raw material silicon is put into the bottomless crucible 22 by the raw material feeder 25, and electric power is supplied to the induction coil 21 to form the silicon melt 11 on the support head 42 in the bottomless crucible 22. At this time, the silicon melt 11 is held in a non-contact state with the inner surface of the bottomless crucible 22 by the electromagnetic force.

While the raw material charging machine 25 continues to charge the raw material silicon, the support rod 41 is gradually lowered. As a result, the silicon melt 11 continuously formed in the bottomless crucible 22 is gradually solidified while descending below the bottomless crucible 22 to become the ingot 10. At this time, the silicon melt 11
The descending speed of the support rod 41 is controlled so that the two are located at the same height in the bottomless crucible 22. Thus, the ingot 10 is continuously manufactured.

The manufactured ingot 10 passes through the heat insulation furnace 23. The heat insulation furnace 23 has a temperature gradient of 35 ° C./cm or less at 1300 to 500 ° C. of the ingot 10, preferably 30 ° C.
The temperature gradient in the central axis direction is controlled so as to be not more than / cm.

As the casting proceeds, the ingot 10 enters the heat retaining container 30. The heat-retaining container 30 has a heat-retaining function in order to reduce the temperature gradient in the central axis direction of the ingot 10. However, the heat-retaining container 30 may be either heat-retaining only with a heat-retaining material or heat-retaining including heat generation by resistance heating or the like.

When the casting proceeds to the vicinity of the maximum length at which the ingot 10 can be inserted into the heat insulation container 30, the raw material charging from the raw material charging machine 25 is stopped, the output of the induction coil 21 is reduced, and the bottomless bottom is reached. The silicon melt 11 in the crucible 22 is solidified. After the solidification is completed, the ingot 10 is slowly moved down.
This is because a rapid change in ingot temperature causes ingot cracking. Also at this time, the temperature gradient similar to the above is given to the heat retention furnace 23.

When the ingot 10 is completely inserted into the heat retaining container 30, the support head 42 is clamped by the holding mechanism 36 to retain the ingot 10 in the heat retaining container 30. The support head 42 is separated from the support rod main body 43, and only the support rod main body 43 is lowered to be pulled out from the heat retaining container 30. The lower end opening of the heat insulating container 30 is closed by the lower lid 38.

The heat insulation container 30 holding the ingot 10 inside is separated from the casting part 20 and moved laterally from just below the casting part 20 to just above the ingot removing means 50. Immediately below the casting part 20, another warm container 30 having an empty inside is moved,
Argon replacement is performed in the same manner as above, and casting is restarted.

At the same time that the heat-retaining container 30 moves to just above the ingot extracting means 50, the upper end opening of the heat-retaining container 30 is closed by the upper lid 35, so that the ingot 10 inside has sufficient time for circulation of cooling gas. Cool over. When the ingot 10 is cooled to a temperature at which it can be taken out, the lower lid 38 is removed,
The elevating head 52 is raised and connected to the supporting head 42. By releasing the clamp by the holding mechanism 36 and lowering the elevating head 52, the ingot 10 is extracted below the heat retaining container 30.

The above operation was repeated to obtain a cross section of 210 m.
Twenty ingots each having a square of m and a length of 2000 mm were continuously manufactured. As a result, no mechanical obstacles occurred, and the photoelectric conversion efficiency of the cells produced from the produced ingots was the same in all the ingots, and uniform crystal quality was obtained.

Regarding the casting efficiency, although casting is suspended,
Since the production of the ingot and the cooling of the produced ingot are performed in parallel at the same time, no significant difference was observed as compared with the case of cutting the ingot while continuing the casting.

The number of the heat retaining containers 30 can be appropriately increased. Further, the container moving means for circulating and using the plurality of heat retaining containers 30 is not limited to the above-mentioned embodiment, and various ones can be adopted.

FIG. 2 is a plan view showing another embodiment of the present invention.

In this embodiment, three heat insulation containers 30A, 30 are used.
Equipped with B and 30C. These are arranged symmetrically around the vertical axis 39 and rotate around them to make the casting part 2
It has a revolver structure that moves directly below 0. According to this structure, even if the casting is completed while the ingot being cooled remains in the heat retaining container, the casting can be immediately restarted.

That is, when casting is completed and the ingot 10 is inserted into the heat retaining container 30A immediately below the casting portion 20, even if the ingot 10 in the heat retaining container 30B is not completely cooled,
If the heat retaining containers 30A, 30B, 30C are rotated and the heat retaining container 30C is moved directly below the casting part 20, the casting operation can be restarted.

Therefore, the loss time is completely eliminated, and the casting efficiency is further improved.

[0040]

As is apparent from the above description, the silicon casting apparatus of the present invention supports the ingot continuously manufactured by electromagnetic melting from below and further pulls the ingot into the heat insulation container, By stopping the ingot at a length that can be accommodated in the heat retaining container, cracking of the ingot can be prevented and its quality can be improved.

When the desirable configuration according to the second aspect is adopted, it is possible to suppress the reduction of the casting efficiency due to stopping the casting as much as possible.

[Brief description of drawings]

FIG. 1 is a side view showing the configuration of an example of a silicon casting apparatus embodying the present invention.

FIG. 2 is a plan view showing another embodiment of the present invention.

FIG. 3 is a chart showing the influence of casting length on quality.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ingot 11 Silicon melt 20 Casting part 21 Induction coil 22 Bottomless crucible 23 Insulating furnace 25 Raw material charging machine 30 Insulating container 33 Cart 36 Holding mechanism 40 Ingot lowering means 41 Support rod 42 Supporting head 50 Ingot removing means

Claims (2)

[Claims] 1. An induction coil is provided with a conductive bottomless crucible having at least a part in the axial direction divided into a plurality in the circumferential direction, and silicon is placed in the bottomless crucible without contacting the inner wall of the crucible. In the state, it is melted by electromagnetic induction, and the casting part that solidifies the melt that descends downward to form a rod-shaped ingot, and the casting part that is set below the casting part and that descends downward from the casting part is introduced. A cylindrical heat-retaining container that keeps it warm, and a support rod that is installed below the set position of the heat-retaining container, inserts a support rod into the heat-retaining container from below, and supports the ingot while supporting it from below with the support head at the upper end. An ingot lowering means for pulling a rod downward to lower an ingot, the silicon casting apparatus. 2. A plurality of the heat insulating containers are provided, each of which is movable so as to be attachable to and detachable from a casting part, and a supporting head of the supporting rod is separable from a supporting rod main body.
The silicon casting apparatus according to claim 1, wherein a holding mechanism for holding the support head is provided in a lower portion of the heat insulating container.