JP4784089B2 - Solid-liquid interface detection apparatus, casting apparatus and casting method - Google Patents

Description

  The present invention relates to a solid-liquid interface detection device that detects a solid-liquid interface generated in the process of dissolving and sequentially solidifying a substance in one direction, and a casting apparatus and a casting method for forming an ingot.

For example, as a device for casting polycrystalline ingots of semiconductors such as silicon, a raw material is put into a melting crucible (mold) made of graphite or silica, and the material in the melting crucible is melted by heating means such as a heater. A casting apparatus is known which forms an ingot that is shaped like a melting crucible (mold) by forming a melt and cooling the melt (for example, Patent Document 1).
U.S. Pat. No. 3,898,051

  In a casting apparatus as shown in Patent Document 1, in order to align the solidification direction of the ingot to be formed in one direction, for example, the relative position between the heater and the melting crucible is changed by lowering the heater and the melting crucible (mold). The melting crucible is moved away from the heater from the bottom surface side, so that the melt is sequentially solidified from the bottom surface to the top surface of the melting crucible.

  In this process of changing the relative position of the heater and the melting crucible, the position of the solid-liquid interface is properly grasped by appropriately grasping the interface between the solidified part in the melting crucible and the part as the melt. It is necessary to optimally control the descending speed of the melting crucible so that the interface gradually rises in the melting crucible.

  That is, if the descending speed of the melting crucible is too fast (the cooling speed is too fast), solidification occurs simultaneously at various portions of the melting crucible, and a good ingot with the solidification direction aligned in one direction cannot be obtained. For this reason, in order to cast a good polycrystalline ingot with the crystal orientation kept constant, the position of the solid-liquid interface in the melting crucible is grasped in real time, and the descending speed of the melting crucible is controlled (that is, the cooling crucible). It is important to feed back to temperature distribution control.

  However, in a conventional casting apparatus such as the casting apparatus described in Patent Document 1, it is difficult to grasp the position of the solid-liquid interface in the molten crucible that has been heated to a high temperature. The rod was inserted to confirm the approximate position of the solid-liquid interface. For this reason, it has been difficult to obtain a good ingot with a good yield by detecting the exact position of the solid-liquid interface and feeding back to the control of the solidification direction of the melt. Further, in such a method of inserting a search rod into the melt, impurities may be mixed into the melt, and there is a concern about operational danger.

  The present invention has been made in view of the above circumstances, and a solid-liquid interface detection device capable of easily and accurately grasping the position of a solid-liquid interface in a melting crucible and solidifying using the same It is an object of the present invention to provide a casting apparatus and a casting method capable of casting a high-quality ingot whose direction is appropriately controlled.

In order to achieve the above object, according to the present invention, basically,
A solid-liquid interface detection device used in a melting furnace for heating and melting silicon as a substance having different electrical conductivity between a solid state and a liquid state, and further solidifying the molten silicon in one direction;
A detection coil installed so as to surround the periphery of the melting furnace;
A current circuit including a resonance circuit having the detection coil as an inductance element, and generating a magnetic field in the detection coil;
A detection circuit for detecting a change in the magnetic field generated in the detection coil as a change in the resonance frequency of the resonance circuit ;
Storage means for storing the correlation between the resonance frequency and the interface position obtained in advance by experiment or simulation;
Solid-liquid interface detection means for detecting a solid-liquid interface in the melting furnace based on the correlation from the change in the resonance frequency detected by the detection circuit ,
A solid-liquid interface detection device characterized by comprising :
Is provided.

According to the present invention,
A crucible containing silicon as a substance having different conductivity in a solid state and a liquid state, and a heater for heating the crucible, and for solidifying molten silicon in the crucible in one direction from below to above In casting equipment;
A lift that changes a relative position in the vertical direction between the heater and the crucible;
A detection coil installed so as to surround the periphery of the crucible;
A current circuit including a resonance circuit having the detection coil as an inductance element, and generating a magnetic field in the detection coil;
A detection circuit for detecting a change in the magnetic field generated in the detection coil as a change in the resonance frequency of the resonance circuit;
Storage means for storing the correlation between the resonance frequency and the interface position obtained in advance by experiment or simulation;
Control means for controlling the lift based on the correlation according to a change in the resonance frequency detected by the detection circuit ;
There is provided a casting apparatus characterized by comprising:

Moreover, according to the present invention,
A crucible containing silicon as a substance having different conductivity in a solid state and a liquid state, and a heater unit heater comprising a plurality of heaters for heating the crucible, with the molten silicon in the crucible facing upward from below In a casting device for solidifying in one direction;
A detection coil installed so as to surround the periphery of the crucible;
A current circuit including a resonance circuit having the detection coil as an inductance element, and generating a magnetic field in the detection coil;
A detection circuit for detecting a change in the magnetic field generated in the detection coil as a change in the resonance frequency of the resonance circuit;
Storage means for storing the correlation between the resonance frequency and the interface position obtained in advance by experiment or simulation;
Control means for controlling the heat generation distribution in the vertical direction of the heater unit based on the correlation in accordance with a change in the resonance frequency detected by the detection circuit;
A casting apparatus characterized by comprising :
Is provided.

  The detection coil may be composed of two or more independent coils, and each coil may be formed at a position corresponding to at least the upper surface and the lower surface of the molten material formed on the crucible. The resonance circuit of the current circuit may be a series resonance circuit or a parallel resonance circuit having the detection coil as an inductance.

According to the present invention,
A step of melting silicon as a substance having different electrical conductivity between a solid state and a liquid state contained in a crucible with a heater, and then solidifying the crucible in one direction from below to above;
Generating a magnetic field in a detection coil installed so as to surround the periphery of the crucible;
Detecting a change in the magnetic field of the detection coil as a change in the resonance frequency of a resonance circuit including the detection coil as an inductance element;
And a step of controlling the relative position in the vertical direction of the crucible and the heater according to the detection result of the change in the resonance frequency based on the correlation between the resonance frequency and the interface position obtained in advance by experiment or simulation . A casting method characterized by that,
Is provided.

Moreover, according to the present invention,
Melting silicon in a heater unit composed of a plurality of heaters in a solid state and a liquid state housed in a crucible, and then solidifying the crucible in one direction from the bottom to the top;
Generating a magnetic field in a detection coil installed so as to surround the periphery of the crucible;
Detecting a change in the magnetic field of the detection coil as a change in the resonance frequency of a resonance circuit including the detection coil as an inductance element;
Based on the correlation between the resonance frequency obtained by experiment or simulation in advance and the interface position, the operation of each heater constituting the heater unit is controlled according to the detection result of the change in the resonance frequency, and A casting method comprising a step of controlling the heat generation distribution in the direction,
Is provided.

According to the present invention, the position of the silicon solid-liquid interface in the melting crucible can be detected in real time in a non-contact manner by monitoring the fluctuation of the resonance frequency due to the distribution change of the magnetic flux lines around the coil. It is possible to obtain a high-quality silicon ingot that is aligned in one direction. In addition, since the solid-liquid interface can be detected in real time without contact, the melt is not contaminated, and the position of the solid-liquid interface in the melting crucible can be known with high accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a casting apparatus of the present invention. Casting apparatus 1 is suitably used for an ingot casting of silicon, which is the conductivity is greatly different substances in a solid body state and the liquid state. The casting apparatus 1 includes a melting furnace 3 and a housing 2 for housing the melting furnace 3. The storage housing 2 may be formed of a heat-insulating refractory or metal.

  The melting furnace 3 includes a melting crucible (mold) 11 and a heater 12 disposed around the melting crucible (mold) 11 for heating the melting crucible (mold) 11. The melting crucible (mold) is a separable mold formed of, for example, graphite or silica, and may be selected according to the shape of the ingot to be formed.

The heater 12 is a heat source that melts a silicon lump that is a semiconductor as a raw material contained in the melting crucible 11 to form the melt 8, and is formed so as to surround the melting crucible 11. In addition to the method of heating the melting crucible 11 to obtain the melt 8, a method of introducing the melt melted in another step into the melting crucible 11 may be used. In this case, vertical movement is unnecessary by the lift 14 described later. In addition to the electric heater, the heater 12 may be, for example, induction heating by a coil or melting by an electron beam, and is not limited.

  A table 13 that supports the melting crucible 11 is formed at the bottom of the melting crucible 11. The table 13 can be moved up and down by a lift 14. Thereby, the melting crucible 11 can change the position with respect to the heater 12 in the vertical direction by the operation of the lift 14. The lift 14 is controlled by a lift driver 15 and the table 13 is moved up and down.

  A cooling pipe (cooling means) 16 is disposed inside the table 13. For example, cooling water is passed through the cooling pipe (cooling means) 16 to cool the table 13. Thereby, the melting crucible 11 placed on the table 13 is cooled from the bottom surface.

  A coil 22 constituting the solid-liquid interface detecting device 21 of the present invention is formed below the melting crucible 11. The coil 22 may be a single-turn or multiple-turn coil formed so as to surround the periphery of the melting crucible 11. As shown in FIG. 2, such a coil 22 is connected to a current circuit 24 including an AC power supply 33 and a capacitor 34 for parallel resonance, and generates a magnetic field at the periphery of the coil 22. The current circuit 24 may use a series resonance capacitor in addition to the parallel resonance capacitor 24.

  The solid-liquid interface detection device 21 includes a coil 22 connected to such a current circuit 24 and an interface detection circuit 35. The interface detection circuit 35 may be configured by a circuit that detects a change in inductance of the coil 22. The interface detection circuit 35 is connected to the lift driver 15 and outputs a control signal for controlling the descending speed of the table 13 to the lift driver 15 in accordance with a change in the inductance of the coil 22. Such an interface detection circuit 35 may be, for example, a circuit that detects a change in the output voltage or output current of the current circuit 24 in addition to a circuit that detects a change in the inductance of the coil 22.

  The operation of the solid-liquid interface detection device 21 will be described with reference to FIG. When a current flows from the current circuit 24 to the coil 22, a magnetic field is generated at the periphery of the coil 22. In the cross-sectional view shown in FIG. These magnetic flux lines M are uniformly distributed without being affected by a dielectric or the like. However, when a conductor is present, the magnetic flux lines M are formed so as to avoid the conductor.

When the melting crucible (mold) 11 contains and melts silicon , which is a substance whose electrical conductivity is greatly different between the solid state and the liquid state, and starts to solidify the molten silicon 42 by cooling from the bottom surface of the melting crucible 11, In the melting crucible 11, two regions having significantly different electrical conductivity are formed in the melting crucible 11 with the solid-liquid interface S between the solidified silicon 41 already solidified and the molten silicon 42 not yet solidified as a boundary.

Magnetic flux lines M generated in the coil 22 surrounding the periphery of the melting crucible 11 in such a state pass through the region of the solidified silicon 41 having a low conductivity as it is, but the molten silicon having a high conductivity at the solid-liquid interface S as a boundary. It distorts so that the area | region of 42 may be avoided (magnetic flux line Ma part in FIG. 3). Thus, when the magnetic flux lines M generated in the coil 22 are in contact with a substance having high conductivity in a specific region and are disturbed, the inductance of the coil 22 changes. The relationship between the inductance and the resonance frequency is expressed by the following equation (1).
f = 1 / 2π√LC (1)
(Where f = resonance frequency, L = inductance, C = resonance capacitor)

  Thereby, for example, when the position of the coil 22 is fixed and the position of the solid-liquid interface S varies, the distribution of the magnetic flux lines M generated in the coil 22 changes, and the resonance frequency changes. The interface detection circuit 35 detects a change in resonance frequency due to a change in the inductance of the coil 22. In this way, the position of the solid-liquid interface S in the melting crucible 11 can be reliably detected without contact. Then, the lowering speed of the table 13 is controlled via the lift driver 15 based on the detection result of the position of the solid-liquid interface S.

  Next, the operation and action of the casting apparatus of the present invention will be described. For example, it is assumed that a polycrystalline silicon ingot is cast using the casting apparatus 1 shown in FIG. First, a silicon lump as a raw material is put into the melting crucible 11 and the heater 12 is operated to melt the silicon lump in the melting crucible 11 to obtain the melt 8.

  Next, a current is passed from the current circuit 24 (see FIG. 2) to the coil 22 to form magnetic flux lines around the coil 22. Then, the lift 14 is operated to start lowering the table 13. The melting crucible 11 placed on the table 13 moves away from the bottom surface with respect to the heater 12, and as shown in FIG. 4, the melt 8 is solidified from the bottom surface in the melting crucible 11 to form the solid phase 9, and the melting crucible 11 is melted. A solid-liquid interface S is generated between the liquid 8 and the solid phase 9.

  In order to obtain a high-quality polycrystalline silicon ingot having the same solidification direction of crystals, it is important to gradually increase the position of the solid-liquid interface S in the melting crucible 11 while maintaining this solidification rate appropriately. The solid-liquid interface detection device 21 monitors the fluctuation of the resonance frequency due to the change in the distribution of the magnetic flux lines around the coil 22 so that the table 13 descends at such a speed that the change rate of the position obtained from the resonance frequency becomes constant. In addition, a control signal is output to the lift driver 15.

  If there is no fluctuation in the resonance frequency, the position of the solid-liquid interface S in the melting crucible 11 is maintained at a certain level. If all the melts 8 in the melting crucible 11 are solidified, the solidification direction is changed. A high-quality polycrystalline silicon ingot aligned in one direction can be obtained. Further, since the solid-liquid interface S can be detected in real time without contact, the melt 8 is not contaminated, and the position of the solid-liquid interface S in the melting crucible 11 can be known safely and with high accuracy. it can.

  In addition to the casting apparatus that solidifies the melt by changing the relative position between the melting crucible and the heater as in the above-described embodiment, a heater unit including a plurality of heaters as in the casting apparatus shown in FIG. May be used to control the operation of the individual heaters to solidify the melt. In the casting apparatus 51 shown in FIG. 5, in order to form the melt 53 in the melting crucible 52, a heater unit 56 in which a plurality of heaters 55a to 55f are stacked is provided.

  In such a casting apparatus 51, in order to solidify the melt 53 formed in the melting crucible 52 in one direction upward from the bottom surface of the melting crucible 52, the electric power of the heater 55a is first reduced, and thereafter the heater 55b to the heater 55f. The power is sequentially decreased toward the power source. As a result, the melt 53 in the melting crucible 52 is solidified in one direction from the bottom to the top.

  In controlling the plurality of heaters 55 a to 55 f constituting such a heater unit 56, a current is passed through the coil 62 of the solid-liquid interface detecting device 61 to generate a magnetic flux line, and the inductance change of the coil 62 is monitored. The heaters 55a to 55f are controlled from the interface detection circuit 63 via the heater control circuit 65 so that the position of the solid-liquid interface in the inside increases at a constant speed. Thereby, a good quality ingot with the solidification direction aligned in one direction can be obtained.

  The present applicant verified the relationship between the height (position) of the melt in the melting crucible and the resonance frequency of the coil formed so as to surround the melting crucible. In the verification, as shown in FIG. 6, the position of the coil of the solid-liquid interface detector is placed at the bottom of the melting crucible, and the verification example a in which the solid-liquid interface is at the coil position regardless of solidification, The relation between the resonance frequency and the solid-liquid interface (melt height) in the melting crucible was measured for two examples of the verification example b in which the relation with the upper surface of the melt was constant and the solid-liquid interface increased. Such verification results are shown in the graph of FIG.

  According to the verification result shown in FIG. 6, when the solid-liquid interface is set to be at the position of the coil, the relationship between the resonance frequency and the solid-liquid interface (melt height) changes so as to gently curve downward. If the relationship between the coil position and the upper surface of the melt is fixed and the solid-liquid interface rises, the relationship between the resonance frequency and the solid-liquid interface (melt height) curves gently upward. Change. Then, as shown in FIG. 7, when the coils are respectively placed at the positions of the bottom surface of the melting crucible and the upper surface of the melt before solidification and the upper surface or the lower surface of the melt in the middle of solidification is set to the coil position, The frequency and height are almost linear. In addition, as shown in FIG. 8, it can be seen that if the melt is between the upper end coil and the lower end coil and the melt height is constant (20 mm height), the detection frequency is substantially constant. If the frequency is determined according to the relationship with FIG. 7 described above, the height of the melt can be uniquely determined. It has been found that the relationship between the resonance frequency and the solid-liquid interface (melt height) changes almost linearly.

FIG. 1 is a cross-sectional view showing a casting apparatus of the present invention. FIG. 2 is an explanatory view showing the solid-liquid interface detecting device of the present invention. FIG. 3 is an explanatory diagram showing a solid-liquid interface detection step. FIG. 4 is an explanatory view showing the casting method of the present invention. FIG. 5 is a cross-sectional view showing another embodiment of the present invention. FIG. 6 is a graph showing the verification results of the present invention. FIG. 7 is a graph showing the verification results of the present invention. FIG. 8 is a graph showing the verification results of the present invention.

Explanation of symbols

1 Casting equipment (casting equipment)
3 Melting furnace 11 Molten crucible 14 Lift 21 Solid-liquid interface detection device 22 Coil 24 Current circuit 35 Interface detection circuit (detection circuit)
56 Heater unit

Claims (7)

A solid-liquid interface detection device used in a melting furnace for heating and melting silicon as a substance having different electrical conductivity between a solid state and a liquid state, and further solidifying the molten silicon in one direction;
A detection coil installed so as to surround the periphery of the melting furnace;
A current circuit including a resonance circuit having the detection coil as an inductance element, and generating a magnetic field in the detection coil;
A detection circuit for detecting a change in the magnetic field generated in the detection coil as a change in the resonance frequency of the resonance circuit ;
Storage means for storing the correlation between the resonance frequency and the interface position obtained in advance by experiment or simulation;
Solid-liquid interface detection means for detecting a solid-liquid interface in the melting furnace based on the correlation from the change in the resonance frequency detected by the detection circuit ,
And a solid-liquid interface detecting device. A crucible containing silicon as a substance having different conductivity in a solid state and a liquid state, and a heater for heating the crucible, and for solidifying molten silicon in the crucible in one direction from below to above In casting equipment;
A lift that changes a relative position in the vertical direction between the heater and the crucible;
A detection coil installed so as to surround the periphery of the crucible;
A current circuit including a resonance circuit having the detection coil as an inductance element, and generating a magnetic field in the detection coil;
A detection circuit for detecting a change in the magnetic field generated in the detection coil as a change in the resonance frequency of the resonance circuit ;
Storage means for storing the correlation between the resonance frequency and the interface position obtained in advance by experiment or simulation;
Control means for controlling the lift based on the correlation according to a change in the resonance frequency detected by the detection circuit ;
And a casting apparatus. A crucible containing silicon as a substance having different conductivity in a solid state and a liquid state, and a heater unit heater comprising a plurality of heaters for heating the crucible, with the molten silicon in the crucible facing upward from below In a casting device for solidifying in one direction;
A detection coil installed so as to surround the periphery of the crucible;
A current circuit including a resonance circuit having the detection coil as an inductance element, and generating a magnetic field in the detection coil;
A detection circuit for detecting a change in the magnetic field generated in the detection coil as a change in the resonance frequency of the resonance circuit ;
Storage means for storing the correlation between the resonance frequency and the interface position obtained in advance by experiment or simulation;
Control means for controlling the heat generation distribution in the vertical direction of the heater unit based on the correlation in accordance with a change in the resonance frequency detected by the detection circuit;
And a casting apparatus.   The detection coil includes two or more independent coils, and each coil is formed at a position corresponding to at least an upper surface and a lower surface of a molten material formed on the crucible. 3. The casting apparatus according to 3.   The casting apparatus according to any one of claims 2 to 4, wherein the resonance circuit of the current circuit is a series resonance circuit or a parallel resonance circuit having the detection coil as an inductance. A step of melting silicon as a substance having different electrical conductivity between a solid state and a liquid state contained in a crucible with a heater, and then solidifying the crucible in one direction from below to above;
Generating a magnetic field in a detection coil installed so as to surround the periphery of the crucible;
Detecting a change in the magnetic field of the detection coil as a change in the resonance frequency of a resonance circuit including the detection coil as an inductance element;
And a step of controlling the relative position in the vertical direction of the crucible and the heater according to the detection result of the change in the resonance frequency based on the correlation between the resonance frequency and the interface position obtained in advance by experiment or simulation . A casting method characterized by the above. Melting silicon in a heater unit composed of a plurality of heaters in a solid state and a liquid state housed in a crucible, and then solidifying the crucible in one direction from the bottom to the top;
Generating a magnetic field in a detection coil installed so as to surround the periphery of the crucible;
Detecting a change in the magnetic field of the detection coil as a change in the resonance frequency of a resonance circuit including the detection coil as an inductance element;
Based on the correlation between the resonance frequency obtained by experiment or simulation in advance and the interface position, the operation of each heater constituting the heater unit is controlled according to the detection result of the change in the resonance frequency, and And a step of controlling the heat generation distribution in the direction.

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