JP2015137210A - Method and unit for melting silicon and silicon single crystal manufacturing apparatus including unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To completely, efficiently melt a silicon raw material by further reducing an occurrence frequency of high frequency noise.SOLUTION: The method for melting silicon comprises: pre-heating a silicon raw material by supplying AC to an induction coil in the state of surrounding the outer periphery of a melting vessel storing the silicon raw material by a cylindrical pre-heating mechanism; and induction-heating the pre-heated silicon raw material by supplying AC to the induction coil in the state of removing the preheating mechanism from the periphery of the silicon raw material after the silicon raw material reaches a predetermined temperature by the pre-heating. A frequency of AC supplied to the induction coil is set to 5 kHz or more and less than 100 kHz, preferably, 10 kHz or more and 80 kHz, and the predetermined temperature is set to more than 800°C and less than 1412°C, preferably, 1000°C or more and 1200°C or less.

Description

  The present invention relates to a silicon melting method and apparatus. More specifically, the present invention relates to a method and apparatus for melting a silicon raw material by induction heating. The present invention also relates to a silicon single crystal manufacturing apparatus equipped with this silicon melting apparatus.

  Conventionally, a silicon rapid melting method has been disclosed in which a rod-like carbon heating element is inserted into a crucible containing silicon raw material, the heating element is heated at high frequency, and the silicon raw material is preheated (for example, Patent Documents). 1). According to this method, there is no contamination of impurities and silicon can be heated rapidly. However, since this carbon heating element is rod-shaped, the distance between the induction coil and the carbon heating element is increased. As a result, sufficient preheating cannot be performed, and it is necessary to insert the rod-shaped carbon heating element into the crucible. Therefore, the amount of charge of the silicon raw material is reduced correspondingly, and in order to avoid contact between the silicon raw material and the carbon heating element, the carbon heating element must be accommodated in a silica container, and the structure becomes complicated. There was a problem.

  As a silicon melting method that solves the above problems, the present applicant pre-heats the silicon raw material by radiation by passing an alternating current through the induction coil in a state of surrounding the silicon raw material by a cylindrical pre-heating mechanism, A silicon melting method was proposed in which the preheated silicon material is induction-heated by passing an alternating current through the induction coil with the preheating mechanism removed from the periphery of the silicon material (see, for example, Patent Document 2). ). In this method, the frequency of the alternating current that flows through the induction coil during preheating is preferably 100 kHz or more and 200 kHz, and the frequency of the alternating current that flows through the induction coil when the preheated silicon raw material is induction heated is preferably 100 kHz or more and less than 2 MHz. And more preferably 100 kHz or more and less than 300 kHz. Further, the temperature when removing the preheating mechanism is preferably set in the range of 700 ° C. or higher and 800 ° C. or lower. And according to this method, first, it becomes possible to efficiently perform preliminary heating before induction heating of the silicon raw material, and secondly, there is less risk of the induction coil causing discharge. It is possible to increase the working efficiency, and thirdly, by setting the frequency of the alternating current to 100 kHz or more and less than 300 kHz, the depth of current penetrating into the silicon raw material is optimized and more efficient. The silicon raw material is often completely dissolved.

JP-A-11-130581 (Claim 3, paragraphs [0014], [0026] to [0028], FIG. 1) JP 2010-150100 A (Claim 1, paragraphs [0012], [0013], [0027], [0029], FIGS. 1 and 2)

  In the above-mentioned Patent Document 2, in order to dissolve silicon raw materials whose maximum length of each chip raw material is 2 mm or more and less than 100 mm by direct heating with high frequency, the frequency of the alternating current flowing through the induction coil during preheating is set to 100 kHz or more. Preferably, the temperature when removing the preheating mechanism (direct heating start temperature) is set in the range of 700 ° C. or higher and 800 ° C. or lower, and the frequency of the alternating current flowing through the induction coil during direct heating is preferably 100 kHz or higher. It was good. The reason why the frequency is set to 100 kHz or more is that the silicon raw material is heated and melted by intensively applying a high frequency to the skin of the silicon raw material. When the frequency is less than 100 kHz, a sufficient calorific value cannot be obtained to dissolve the silicon raw material, which is insufficient to completely dissolve the silicon raw material by direct heating. On the other hand, when the frequency of the alternating current flowing through the induction coil during preheating and direct heating is set to 100 kHz or more, the heating atmosphere is good under heating at a reduced pressure of 500 Torr or less, but the heating efficiency is good, but during the preheating and direct heating. There is a problem that high-frequency noise is frequently generated in the inside, and a situation in which dissolution of silicon must be stopped frequently occurs. That is, even when the lower limit value of the frequency passed through the induction coil is set to 100 kHz, when heated under reduced pressure, high frequency noise is still generated at this frequency, and this noise becomes a precision instrument for controlling the single crystal growth furnace. It had an effect, disturbed its control and hindered the growth of high quality single crystals.

  As a result of intensive investigations to solve the above problems, the present inventors have exceeded the temperature at which the direct heating of the silicon raw material is started, that is, the temperature at which the preheating mechanism starts to be removed from the periphery of the silicon raw material, exceeding 800 ° C. Knowledge that if the temperature is set, even if the frequency of the alternating current flowing through the induction coil is lowered to less than 100 kHz, the silicon raw material can be efficiently dissolved completely and the frequency of occurrence of high-frequency noise can be further reduced. And reached the present invention.

  An object of the present invention is to provide a silicon melting method and apparatus capable of melting silicon raw materials completely efficiently and further reducing the frequency of occurrence of high frequency noise. Another object of the present invention is to provide a silicon single crystal manufacturing apparatus capable of continuously pulling up a silicon single crystal using this melting apparatus.

  A first aspect of the present invention is a preheating step of preheating the silicon raw material by passing an alternating current through the induction coil in a state of surrounding the outer periphery of the melting container containing the silicon raw material by a cylindrical preheating mechanism. And the silicon raw material that has been preheated by passing an alternating current through the induction coil with the preheating mechanism removed from the periphery of the silicon raw material after the silicon raw material has reached a predetermined temperature by the preheating. And an induction heating process for induction heating of silicon. The characteristic point is that the frequency of the alternating current flowing through the induction coil is 5 kHz or more and less than 100 kHz when the silicon raw material is heated through the preheating mechanism during the preheating and when the preheated silicon raw material is induction heated. The predetermined temperature is set to a temperature exceeding 800 ° C. and less than 1412 ° C.

  A second aspect of the present invention is an invention based on the first aspect, wherein the induction when the silicon raw material is heated via the preheating mechanism during the preheating and when the preheated silicon raw material is induction heated. In this silicon melting method, the frequency of the alternating current flowing in the coil is set to 10 kHz or more and less than 80 kHz, respectively, and the predetermined temperature is set to 1000 ° C. or more and 1200 ° C. or less.

  According to a third aspect of the present invention, there is provided a melting container for containing a silicon raw material, a cylindrical preheating mechanism surrounding the melting container, an induction coil wound around the preheating mechanism, and the induction coil. A power supply device for supplying an alternating current, an attachment / detachment mechanism for attaching / detaching the preliminary heating mechanism, a temperature sensor for detecting the temperature of the silicon raw material, and attachment / detachment of the attachment / detachment mechanism based on a detection output of the temperature sensor. A control circuit, wherein the power supply device is set to flow an alternating current having a frequency of 5 kHz or more and less than 100 kHz to the induction coil, and the control circuit is configured such that the temperature sensor exceeds 800 ° C. and 1412 Until the predetermined temperature of less than 0 ° C. is detected, the preheating mechanism is controlled so as to be disposed at a position surrounding the dissolution vessel, and the temperature sensor is controlled. When the service detects the predetermined temperature, and controlling the detaching mechanism to direct heated directly by the induction coil of the silicon raw material by removing said preheating mechanism from the periphery of the melting vessel.

  A fourth aspect of the present invention is the invention based on the third aspect, wherein the power supply device is set to flow an alternating current having a frequency of 10 kHz or more and less than 80 kHz to the induction coil, and the control circuit is The silicon melting apparatus controls the attaching / detaching mechanism so that the preheating mechanism is arranged at a position surrounding the melting container until the silicon raw material reaches a predetermined temperature of 1000 ° C. or more and 1200 ° C. or less.

  According to a fifth aspect of the present invention, there is provided a pulling mechanism for pulling up a silicon single crystal from a silicon melt in a quartz crucible, a silicon melting apparatus according to the third or fourth aspect, and a silicon melt in a melting container of the melting apparatus. Is a silicon single crystal manufacturing apparatus provided with a supply mechanism for supplying to the quartz crucible.

  A sixth aspect of the present invention is the invention based on the fifth aspect, wherein the supply mechanism can continuously supply the silicon melt continuously to the quartz crucible during the pulling of the silicon single crystal by the pulling mechanism. It is the silicon single crystal manufacturing apparatus comprised in this.

  According to the melting method of the first aspect and the melting apparatus of the third aspect of the present invention, the temperature of the silicon raw material that is a heated object when directly heating is set to 800 ° C. higher than the conventional 700 to 800 ° C. By increasing the temperature to a predetermined temperature exceeding 1412 ° C. by preheating, the resistivity of the object to be heated (silicon raw material) can be significantly reduced. Due to this decrease in resistivity, the penetration depth of the alternating current flowing through the induction coil during direct heating can be reduced even at a frequency of 10 kHz or more and less than 100 kHz, which is lower than the conventional 100 kHz or more. The silicon raw material can be dissolved completely efficiently without reducing the density of the induced current flowing in the skin of the film. In addition, since the frequency during the preheating and the direct heating is lower than the conventional frequency of 10 kHz or more and less than 100 kHz, the risk of the induction coil causing a discharge is further reduced, which adversely affects the precision equipment that controls the single crystal growth furnace. The occurrence frequency of high frequency noise can be further reduced.

  According to the melting method and the fourth melting apparatus of the second aspect of the present invention, the predetermined temperature when starting the direct heating by setting the frequency of the alternating current flowing through the induction coil to 10 kHz or more and less than 80 kHz is 1000 ° C. By setting the temperature to 1200 ° C. or lower, the silicon raw material can be dissolved more completely and efficiently, and the risk of the induction coil causing discharge can be further reduced.

  According to the melting apparatus of the fifth aspect of the present invention, in addition to the conventional pulling mechanism for pulling up the silicon single crystal from the silicon melt in the quartz crucible, the melting apparatus of the third or fourth aspect and the melting apparatus By providing a supply mechanism for supplying the silicon melt in the melting container to the quartz crucible, the conventional pulling mechanism can be a continuous charge CZ furnace (CCZ furnace).

  According to the melting apparatus of the sixth aspect of the present invention, the supply mechanism is configured so that the silicon melt can be additionally supplied continuously to the quartz crucible during the pulling of the silicon single crystal by the pulling mechanism. The single crystal can be continuously pulled up.

It is a mimetic diagram showing the composition of the silicon dissolution device by the embodiment of the present invention. It is a figure which shows the state which removed the preheating mechanism with the attachment / detachment mechanism of the melt | dissolution apparatus. 5 is a flowchart for explaining a silicon melting method according to an embodiment of the present invention. It is a schematic diagram which shows the structure of the silicon single crystal manufacturing apparatus by embodiment of this invention.

  Next, the form for implementing this invention is demonstrated.

  As shown in FIG. 1, the silicon melting apparatus 10 according to the present embodiment includes a melting container 11 in which the silicon raw material 2 is accommodated, an induction coil 12 wound around the melting container 11, and an alternating current in the induction coil 12. , A preheating mechanism 14 for preheating the silicon raw material 2, an attaching / detaching mechanism 15 for attaching / detaching the preheating mechanism 14, a temperature sensor 16 for detecting the temperature of the silicon raw material 2, and a temperature sensor 16 Is provided with a control circuit 17 for controlling the attachment / detachment of the attachment / detachment mechanism 15 based on the detected output.

  The melting container 11 is a container that contains the silicon raw material 2 and holds the silicon melt melted by the preheating by the preheating mechanism 14 and the induction heating by the induction coil 12. The material of the dissolution vessel 11 is not particularly limited as long as it is a material having heat resistance and insulating properties and low reactivity with the silicon melt, but it is particularly preferable to use quartz glass.

  The induction coil 12 is a coil for induction heating the silicon raw material 2 or the preheating mechanism 14 filled in the melting container 11, and is wound around the melting container 11. One end and the other end of the induction coil 12 are connected to the power supply device 13, and induction heating is performed when an alternating current is supplied from the power supply device 13. The power supply device 13 is configured to be able to switch the amount of power to be supplied and the frequency. In the present embodiment, the power supply device 13 is set to supply power to the induction coil 12 in the range of 3 kW to 100 kW, preferably in the range of 5 kW to 40 kW, and in the range of 5 kHz to less than 100 kHz, preferably Is set to flow an alternating current having a frequency in the range of 10 kHz to less than 80 kHz. If the amount of electric power is less than the above lower limit, the raw material temperature will not rise and polysilicon will not dissolve, and if the upper limit is exceeded, the voltage between the coils will increase, creating an environment where discharge is likely to occur between the coils. There is a problem that. When the frequency is less than the lower limit, induction heating by the preheating mechanism and the induction coil to the silicon raw material becomes insufficient, and the heating efficiency is lowered. If the upper limit is exceeded, the number of discharges of the induction coil increases and the frequency of high-frequency noise increases.

  The preheating mechanism 14 is a mechanism for preheating the silicon raw material 2 accommodated in the melting container 11 by radiant heat, and is configured by a cylindrical member surrounding the outer periphery of the melting container 11 in this embodiment. As the material of the cylindrical member, it is necessary to use a material having high heat resistance and conductivity, and a carbon material or a material having conductivity equivalent to carbon is used. If the preheating mechanism 14 is configured by a cylindrical member surrounding the outer periphery of the dissolution vessel 11 as in the present embodiment, the silicon raw material 2 and the preheating mechanism 14 do not directly contact each other, so that impurities mixed into the silicon raw material 2 Can be reduced.

  The preheating mechanism 14 is configured to be detachable from the dissolution container 11 by an attachment / detachment mechanism 15. As shown in FIG. 1, in a state where the preheating mechanism 14 is mounted by the attaching / detaching mechanism 15, the preheating mechanism 14 is positioned between the induction coil 12 and the silicon raw material 2. For this reason, when an alternating current is passed through the induction coil 12 in this state, the preheating mechanism 14 is induction-heated, and the silicon raw material 2 is indirectly heated by the radiant heat generated thereby. That is, the silicon raw material 2 is preheated. On the other hand, as shown in FIG. 2, when the preheating mechanism 14 is removed by the attaching / detaching mechanism 15, the preheating mechanism 14 does not exist between the induction coil 12 and the silicon raw material 2. When an alternating current is passed through the coil 12, the silicon raw material 2 is induction-heated. That is, the silicon raw material 2 is directly heated.

  The temperature sensor 16 detects the temperature of the silicon raw material 2 during preheating and direct heating. Examples of the temperature sensor include a thermocouple of a contact thermometer and a radiation thermometer of a non-contact thermometer. The control circuit 17 controls the attachment / detachment mechanism based on the detection output of the temperature sensor 16. Specifically, the control circuit 17 sets the preheating mechanism 14 until the temperature sensor 16 detects a predetermined temperature of the silicon raw material 2 exceeding 800 ° C. and less than 1412 ° C., preferably 1000 ° C. or more and 1200 ° C. or less. The detachable mechanism 15 is controlled so as to be disposed at a position surrounding the refractor 11, that is, so that the preheating mechanism 14 is mounted. When the temperature sensor 16 detects the predetermined temperature, the control circuit 17 controls the attachment / detachment mechanism 15 so that the preliminary heating mechanism 14 is removed from the periphery of the melting vessel 11 and the silicon raw material 2 is directly induction heated by the induction coil 12. To do. When the temperature is less than the lower limit in the predetermined temperature range, the resistivity of the silicon raw material to be heated cannot be reduced to reduce the current penetration depth, and the frequency of the alternating current of the induction coil is not less than 5 kHz and less than 100 kHz. The silicon raw material cannot be completely efficiently dissolved by direct heating. This is because the upper limit is close to the melting point of silicon and it is almost impossible to exceed this temperature.

  Next, a silicon melting method using the silicon melting apparatus 10 according to the present embodiment will be described.

  As shown in the flowchart of FIG. 3, the melting material 11 is filled with the silicon raw material 2 (step S1). The shape and size of the silicon raw material 2 to be filled are not particularly limited, but the maximum length of each chip raw material is preferably 2 mm or more and less than 100 mm in order to efficiently perform heating in the induction heating in step S5 described later. . This is because if the thickness is less than 2 mm, power does not enter the chip raw material due to the penetration depth of the induced current and high-frequency melting is impossible, and if it is 100 mm or more, there is a possibility that a large thermal stress is generated inside the raw material and breaks. Because.

  After the silicon raw material 2 is filled in the melting container 11, when the temperature sensor 16 detects that the temperature of the silicon raw material 2 is lower than a predetermined temperature, the preheating mechanism 14 is attached by the attaching / detaching mechanism 15. In this state, the power supply device 13 supplies the induction coil 12 with a power amount in the range of 3 kW to 100 kW, and allows an alternating current having a frequency in the range of 5 kHz to less than 100 kHz to flow. As a result, the preheating mechanism 14 is induction-heated, and the silicon raw material 2 is preheated by the radiant heat generated thereby (step S2). The amount of electric power and frequency during preheating are determined from the above range depending on the weight of the silicon raw material 2. For example, if the weight of the silicon raw material 2 is 1.5 kg, it is preferable to set it in the range of 5 kW to 40 kW. The amount of electric power required for induction heating of the silicon raw material 2 becomes smaller as the frequency is lower in the range of 5 kHz or more and less than 100 kHz. Further, when the frequency is increased, a bridge may be formed in the upper part of the dissolution vessel 11, and this may be a problem when the silicon raw material 2 is continuously supplied from the upper part. Considering these points, it is preferable that the frequency at the time of induction heating the silicon raw material 2 is 10 kHz or more and less than 80 kHz.

  When the temperature sensor 16 detects that the silicon raw material 2 has reached a predetermined temperature by preheating (step S3: YES), the control circuit 17 controls the attaching / detaching mechanism 15 to remove the preheating mechanism 14 (step S4). Thereby, the silicon raw material 2 is directly heated by induction and rises to the melting point (step S5). Induction heating has a very high dissolution rate per unit weight as compared with heating by radiant heat, so that the silicon raw material 2 can be efficiently and completely dissolved.

  Through the above process, the silicon raw material 2 in the dissolution vessel 11 is completely dissolved, and a silicon melt can be obtained. As described above, according to the silicon melting method according to the present embodiment, the silicon raw material 2 is first preheated by the radiant heat from the preheating mechanism 14, whereby the silicon raw material 2 is heated to a predetermined temperature and then the silicon raw material 2 is heated. Since direct induction heating is performed, the entire silicon material can be heated. As a result, the silicon material in the form of chips is uniformly reduced, and the material bridge (shelf hanging) phenomenon that has conventionally occurred in the melting process can be avoided. Further, the total amount of electric power required until all the silicon raw materials filled in the melting container are completely melted is reduced. This is because the amount of heat released to the outside is reduced due to the heat-retaining effect of the raw material itself due to the overall heating of the silicon raw material, and a silicon melt can be efficiently generated as compared with local heating only outside the filled raw material. In addition, by making the frequency low, the frequency of occurrence of discharge of the induction coil can be lowered, and by making the frequency less than 100 kHz, the frequency of occurrence can be reduced to 50% or less compared to the conventional case, thereby reducing high frequency noise. The degree of influence on the precision equipment around the melting device can be reduced.

  In addition, since the preheating mechanism 14 is cylindrical, the induction coil 12 and the preheating mechanism 14 can be brought close to each other. For this reason, the preliminary heating mechanism 14 can be efficiently induction-heated. Moreover, since the silicon raw material 2 is preheated from the outer peripheral side, it is possible to perform preheating in a state of high heat retention. Furthermore, in this embodiment, since the preheating mechanism 14 is disposed so as to surround the outer periphery of the melting vessel 11, the silicon raw material 2 and the preheating mechanism 14 do not come into contact with each other, and contamination of the silicon raw material 2 is prevented. can do. In addition, since the preheating mechanism 14 is arranged outside the melting vessel 11, the charge amount of the silicon raw material 2 is not reduced.

  The silicon melting apparatus 10 according to the present embodiment is preferably used in a silicon single crystal manufacturing apparatus capable of pulling up a silicon single crystal by a continuous charge CZ method.

  FIG. 4 is a schematic diagram showing a configuration of a silicon single crystal manufacturing apparatus 20 capable of pulling up a silicon single crystal by a continuous charge CZ method.

  In the silicon single crystal manufacturing apparatus 20 shown in FIG. 4, a quartz crucible 21 for storing the silicon melt 4 is provided inside the chamber 22. The outer peripheral surface and the outer bottom surface of the quartz crucible 21 are held by a graphite susceptor 23. The graphite susceptor 23 is fixed to the upper end of a support shaft 24 parallel to the vertical direction, and is configured to rotate the quartz crucible 21 via the support shaft 24 and to move in the vertical direction.

  The outer peripheral surfaces of the quartz crucible 21 and the graphite susceptor 23 are surrounded by a heater 25, and the heater 25 is further surrounded by a heat insulating cylinder 26. In the raw material melting process in the growth of the silicon single crystal, the high-purity polycrystalline silicon raw material filled in the quartz crucible 21 by the heating of the heater 25 is heated and melted to form the silicon melt 4.

  On the other hand, a lifting mechanism 27 is provided at the upper end of the chamber 22. The pulling mechanism 27 is provided with a wire cable 28 that is suspended toward the rotation center of the quartz crucible 21, and a pulling motor (not shown) that winds or feeds the wire cable 28 is provided. A seed crystal 8 is attached to the lower end of the wire cable 28.

  A cylindrical heat shielding member 29 is provided between the silicon single crystal 6 and the heat insulating cylinder 26 so as to surround the silicon single crystal 6 being grown. The heat shield member 29 includes a cone portion 29a and a flange portion 29b, and the heat shield member 29 is disposed at a predetermined position by attaching the flange portion 29b to the heat retaining cylinder 26.

  The silicon single crystal manufacturing apparatus 20 shown in FIG. 4 further includes the above-described silicon melting apparatus 10, whereby the silicon melt 4 can be additionally supplied to the quartz crucible 21. The silicon melt 4 generated by the silicon melting apparatus 10 is supplied to the quartz crucible 21 via the supply mechanism 30. The supply mechanism 30 can additionally supply the silicon melt 4 to the quartz crucible 21 during the pulling of the silicon single crystal 6 by the pulling mechanism 27, thereby enabling continuous pulling of the silicon single crystal 6. The supply mechanism 30 has a pipe, and the supply of the silicon melt 4 to the pipe can be performed by the vertical movement of a weir provided on the upper part of the dissolution container 11 or the tilting of the dissolution container 11. It can also be performed by connecting a pipe to the bottom of the dissolution vessel 11 and adjusting the pressure of the atmosphere in the sealed chamber 22.

In order to additionally supply the silicon melt 4 in the continuous charge CZ method (CCZ method), it is necessary to dissolve the silicon raw material 2 at a high speed, which is realized by using the silicon melting apparatus 10 according to the present embodiment. It becomes possible.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, these are also included in the present invention.

  For example, in the above-described embodiment, an example of using the silicon melting apparatus 10 as an application of the silicon melt additionally supplied in the continuous charge CZ method is shown as an application of the silicon melting apparatus 10, but the application of the silicon melting apparatus according to the present invention is limited to this. It is not a thing. Therefore, when pulling up the silicon single crystal, the silicon material 2 of the initial charge can be dissolved in advance by the silicon melting apparatus 10 and the obtained silicon melt can be transferred to a quartz crucible. Such an application is considered to be promising as one of the methods for solving the problem of the large charge generated with the recent increase in the size of silicon single crystals and quartz crucibles.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  A silicon melting apparatus having the configuration shown in FIG. 1 was prepared. In the example, a platinum thermocouple (not shown) of the type inserted into the silicon raw material 2 accommodated in the melting container 11 was used as the temperature sensor 16. As the melting container 11, a quartz cylindrical container with a quartz lid having an inner diameter of 120 mm, an outer diameter of 140 mm, and a height of 140 mm was used, and this was placed on a heat-resistant brick. As the preheating mechanism 14, a carbon tubular member (carbon cylinder) having a thickness of 8 mm was used and disposed so as to surround the outer periphery of the dissolution vessel 11.

  Next, 2 kg of chip-shaped polycrystalline silicon raw material 2 having a maximum length of 10 to 30 mm (average 20 mm) was filled in a region surrounded by the carbon cylinder. Furthermore, in order to ensure heat insulation during heating, a heat insulating material (not shown) having a thickness of 35 mm was wound around the entire container. The induction coil 12 has 6 turns. A thermocouple (material: WRe) was inserted as a temperature sensor 16 in the center of the chip-like polycrystalline silicon raw material 2 so that the temperature of the silicon raw material being heated could be directly measured.

  After the above preparation was completed, as shown in FIG. 1, the carbon cylinder was induction-heated by passing an alternating current through the induction coil 12, and the silicon raw material 2 was heated by the radiant heat. The frequency was set so that the frequency of the alternating current passed through the induction coil 12 by the power supply device 13 was switched to 2 kHz, 5 kHz, 10 kHz, 50 kHz, 80 kHz, and 100 kHz. The power was 30 kW. In addition, during the heating of the silicon raw material 2, argon (Ar) gas was always introduced into the dissolution vessel 11, thereby suppressing oxidation of the silicon surface layer.

  Next, alternating currents of the above five frequencies are separately supplied to the induction coil 12, and when the temperature of the silicon raw material 2 heated through the carbon tube reaches 700 ° C., 800 ° C., 1000 ° C., and 1200 ° C., respectively. As shown in FIG. 2, the carbon cylinder was removed from the melting container 11 by the attaching / detaching mechanism 15, and direct heating of the silicon raw material by the induction coil 12 was started. The temperature of the thermocouple inserted in the silicon raw material 2 was measured, and the state of dissolution of silicon by direct heating was investigated. The results are shown in Table 1.

  In Table 1, “good” means that the silicon raw material in the dissolution vessel rises to the silicon melting point and the time until silicon completely dissolves is less than 4 minutes, and “good” indicates the silicon raw material in the dissolution vessel. The temperature rises to the silicon melting point, but the time until the silicon is completely dissolved is longer than 4 minutes, and “impossible” refers to the situation where the temperature of the silicon raw material in the melting container decreases and the silicon does not melt. .

  As is clear from Table 1, in order to completely dissolve the silicon raw material, the frequency of the alternating current flowing through the dielectric coil is set to 5 kHz or more and less than 100 kHz, and the temperature at which direct heating is started is set to 800 ° C. or more and less than 1412 ° C. In addition, it has been found that the frequency of occurrence of discharge can be zero or less than once. Further, it has been found that if the frequency is set to 10 kHz or more and 80 kHz or less and the temperature at which direct heating is started is set to 1000 ° C. or more and 1200 ° C. or less, the frequency of occurrence of discharge becomes zero and a better result can be obtained.

2 Silicon raw material 4 Silicon melt 6 Silicon single crystal 8 Seed crystal 10 Silicon melting device 11 Melting vessel 12 Induction coil 13 Power supply device 14 Preheating mechanism 15 Detachment mechanism 16 Temperature sensor 17 Control circuit 20 Silicon single crystal manufacturing device 21 Quartz crucible 22 Chamber 23 Graphite susceptor 24 Support shaft 25 Heater 26 Thermal insulation cylinder 27 Lifting mechanism 28 Wire cable 29 Heat shield member 29a Cone portion 29b Flange portion 30 Supply mechanism

Claims (6)

A preheating step of preheating the silicon raw material by passing an alternating current through the induction coil in a state of surrounding the outer periphery of the melting container containing the silicon raw material by a cylindrical preheating mechanism, and the silicon raw material by the preheating An induction heating step of inductively heating the preheated silicon material by passing an alternating current through the induction coil in a state where the preheating mechanism is removed from the periphery of the silicon material after the temperature reaches a predetermined temperature. In the silicon melting method provided,
The frequency of the alternating current flowing through the induction coil when heating the silicon raw material through the preheating mechanism during the preheating and when induction heating the preheated silicon raw material is set to 5 kHz or more and less than 100 kHz, respectively. The silicon melting method, wherein the predetermined temperature is set to a temperature exceeding 800 ° C. and less than 1412 ° C.   When the silicon raw material is heated through the preheating mechanism during the preheating and the frequency of the alternating current flowing through the induction coil when the preheated silicon raw material is induction-heated is set to 10 kHz or more and less than 80 kHz, The silicon melting method according to claim 1, wherein the predetermined temperature is set to a temperature of 1000 ° C. or more and 1200 ° C. or less. A melting container containing silicon raw material, a cylindrical preheating mechanism surrounding the melting container, an induction coil wound around the preheating mechanism, and a power supply device for supplying an alternating current to the induction coil, An attachment / detachment mechanism for attaching / detaching the preliminary heating mechanism, a temperature sensor for detecting the temperature of the silicon raw material, and a control circuit for controlling attachment / detachment of the attachment / detachment mechanism based on a detection output of the temperature sensor,
The power supply device is set to flow an alternating current having a frequency of 5 kHz or more and less than 100 kHz to the induction coil,
Until the temperature sensor detects that the temperature of the silicon raw material is a predetermined temperature exceeding 800 ° C. and less than 1412 ° C., the control circuit arranges the preheating mechanism at a position surrounding the melting container. When the predetermined temperature is detected by the temperature sensor, the control circuit removes the preheating mechanism from the periphery of the melting container and directly removes the silicon raw material by the induction coil. A silicon melting apparatus, wherein the attachment / detachment mechanism is controlled to perform induction heating.   The power supply device is set so that an alternating current having a frequency of 10 kHz or more and less than 80 kHz flows through the induction coil, and the control circuit is operated until the temperature of the silicon raw material reaches a predetermined temperature of 1000 ° C. or more and 1200 ° C. or less. 4. The silicon melting apparatus according to claim 3, wherein the attaching / detaching mechanism is controlled so that the preheating mechanism is disposed at a position surrounding the melting container.   A pulling mechanism for pulling up the silicon single crystal from the silicon melt in the quartz crucible, a silicon melting apparatus according to claim 3 or 4, and a supply mechanism for supplying the silicon melt in the melting container of the melting apparatus to the quartz crucible. A silicon single crystal manufacturing apparatus comprising: 6. The silicon single crystal manufacturing apparatus according to claim 5, wherein the supply mechanism is configured to be able to continuously supply the silicon melt continuously to the quartz crucible during the pulling of the silicon single crystal by the pulling mechanism.

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