JP5163386B2 - Silicon melt forming equipment - Google Patents

Description

  The present invention relates to a silicon melt forming apparatus in which a solid silicon raw material is melted in a quartz container by electromagnetic induction, and this silicon melt flows out from an opening provided at the lower end of the quartz container. The present invention relates to a silicon melt forming apparatus suitable as an apparatus for sequentially supplying a silicon melt to a crucible for pulling up a single crystal by growing a silicon single crystal by the “CZ method”.

  A silicon single crystal is a material of a silicon wafer used for a semiconductor device, and a single crystal growing method by a CZ method is widely adopted for its production. Usually, in the growth of a silicon single crystal by the CZ method, a silicon raw material such as polycrystalline silicon filled as an initial charge in a quartz crucible is heated by a heater in a single crystal growth apparatus maintained in an inert gas atmosphere under reduced pressure. Heat to melt. When the silicon melt is formed in the quartz crucible, the seed crystal held on the pulling shaft is lowered above the quartz crucible and immersed in the silicon melt. From this state, while rotating the seed crystal and the quartz crucible in a predetermined direction, the seed crystal is gradually raised, whereby a silicon single crystal is grown and pulled below the seed crystal.

  Since a silicon single crystal is a material of a silicon wafer, electrical characteristics are required as quality characteristics, and specific resistance is defined according to the application. This specific resistance depends on the concentration of a dopant such as B (boron), P (phosphorus), As (arsenic), or Sb (antimony) contained in the silicon single crystal, and decreases as the dopant concentration increases. When growing a silicon single crystal, an appropriate amount of dopant is added to the quartz crucible in the initial charge to adjust the dopant concentration in the silicon melt, thereby adjusting the dopant concentration in the silicon single crystal to be grown. Control the specific resistance.

  However, in the growth of the silicon single crystal, as the growth proceeds, the silicon melt remaining in the crucible decreases and the impurity element between the solid-phase silicon single crystal and the liquid-phase silicon melt. As a result of this segregation phenomenon, the dopant concentration in the silicon melt increases and the dopant concentration in the silicon single crystal also increases, so that there is a problem that the specific resistance of the single crystal gradually decreases.

  As a method for suppressing a decrease in specific resistance of a silicon single crystal, a so-called continuous charge CZ method (hereinafter, referred to as a continuous charge CZ method) in which silicon melt or a solid silicon raw material is sequentially supplied to a crucible for pulling up a single crystal when the silicon single crystal is grown. "CCZ method"). In the CCZ method, since a silicon melt or a solid silicon raw material is supplied to a crucible during single crystal growth, the dopant concentration in the silicon melt in the crucible can be kept almost constant. The dopant concentration in the single crystal becomes almost constant, and the specific resistance of the single crystal can be made uniform.

  Here, when supplying a solid silicon raw material to the crucible, temperature fluctuations are likely to occur in the silicon melt in the crucible, and there is a concern about the quality deterioration of the silicon single crystal to be grown. Is more practical.

  Regarding techniques for growing a silicon single crystal by the CCZ method, Patent Documents 1 and 2 describe a silicon melt forming apparatus for supplying a silicon melt to a crucible for pulling a single crystal. The melt forming apparatus described in this document includes a copper water-cooled crucible divided into a plurality of segments in the circumferential direction, a quartz crucible having an outlet at the bottom disposed inside the water-cooled crucible, a water-cooled crucible and quartz And an induction heating coil surrounding the crucible.

  In Patent Documents 1 and 2, when a solid silicon raw material is supplied to a quartz crucible and an alternating current is applied to an induction heating coil, a magnetic field is formed inside the coil and a vortex is generated in the solid silicon raw material in the quartz crucible. An electric current is generated, and the solid silicon raw material can be melted by Joule heat generated by this eddy current to form a silicon melt. Further, the formed silicon melt is held at that position by the action of electromagnetic force due to the eddy current generated on the inner surface of the water-cooled crucible and the eddy current generated on the surface of the silicon melt, and a new solid silicon raw material is supplied. Thus, an amount of silicon melt corresponding to the supply amount flows out from the outlet at the bottom of the quartz crucible and is supplied to the crucible for pulling up the single crystal.

  In general, the specific resistance of silicon is much higher in the solid state than in the liquid state. In particular, the specific resistance of solid silicon is remarkably high until it exceeds 700 ° C. to 800 ° C. That is, solid silicon has a characteristic that eddy currents caused by electromagnetic induction hardly flow at a temperature as low as about 700 ° C. and hardly generate heat.

  For this reason, in the case of the silicon melt forming apparatus described in Patent Documents 1 and 2, the solid silicon raw material first supplied to the raw material melting quartz crucible in which no silicon melt exists is low in resistivity. Therefore, even if an alternating current is applied to the induction heating coil, practically no eddy current is generated. Therefore, in the melt forming apparatuses described in Patent Documents 1 and 2, it is difficult in the first place to melt the solid silicon raw material first supplied to the quartz crucible, and the silicon melt cannot be formed. is there.

JP-A-5-279166 JP-A-5-18677

  The present invention has been made in view of the above problem, and can be used to grow a silicon single crystal by the CCZ method, by which a solid silicon raw material can be reliably melted by electromagnetic induction to form a silicon melt. An object of the present invention is to provide a silicon melt forming apparatus capable of satisfying the requirements.

  In order to achieve the above object, the present inventors have made extensive studies on the premise that the solid silicon raw material is melted using electromagnetic induction from an induction heating coil. As a result, solid silicon raw materials hardly generate eddy currents due to electromagnetic induction at low temperatures. However, when heated to 700 ° C to 800 ° C or higher, the specific resistance decreases and eddy currents due to electromagnetic induction are effective. It has been found that it generates heat and melts. Furthermore, in order to heat a low-temperature solid silicon raw material, it has been found that it is appropriate to provide a heating element separately from the induction heating coil and use the radiant heat from the heating element.

The present invention has been completed based on such knowledge, and the gist thereof is the following silicon melt forming apparatus. That is, the growth of a silicon single crystal by the CCZ method is used as an apparatus for supplying a silicon melt to a crucible for pulling a single crystal. An apparatus for forming a silicon melt that flows out from an opening provided, comprising: an induction heating coil that surrounds a lower portion of a quartz container; and a carbon product that is disposed so as to surround the quartz container between the quartz container and the induction heating coil . The heating element is arranged separately in the upper part and the lower part of the region between the quartz container and the induction heating coil, and the frequency of the current applied to the induction heating coil is A silicon melt characterized in that it is in a range of 100 kHz or more and less than 300 kHz, and an output when an alternating current is applied to the induction heating coil is in a range of 10 kW to 50 kW. Forming device.

In the melt formation device this, the heating element arranged in the lower portion of the front Symbol regions may be configured to be movable to a position deviated from the region.

  Furthermore, in this melt forming apparatus, it is preferable that the periphery of the quartz container is covered with a heat insulating material, and the heating element is disposed between the quartz container and the heat insulating material.

  According to the silicon melt forming apparatus of the present invention, since the heating element is arranged between the lower part of the quartz container and the induction heating coil surrounding the quartz container, the quartz container is radiated by the radiant heat from the heating element. The low-temperature solid silicon raw material inside can be heated, and the specific resistance of the solid silicon raw material can be reduced. As a result, eddy current is effectively generated in the solid silicon raw material by electromagnetic induction by the induction heating coil, and the solid silicon raw material generates heat, so that the solid silicon raw material can be reliably melted in the quartz container, A silicon melt can be formed.

  If this silicon melt forming apparatus is employed for growing a silicon single crystal by the CCZ method, the silicon melt is allowed to flow out from the lower end of the opening of the quartz container, and the silicon melt is supplied to the crucible for pulling the single crystal. This makes it possible to grow a silicon single crystal of stable quality.

Hereinafter, embodiments of the silicon melt forming apparatus of the present invention will be described in detail.
FIG. 1 is a diagram schematically showing a configuration of a single crystal growth apparatus by a CCZ method provided with a silicon melt forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view showing a main part of the silicon melt forming apparatus according to one embodiment of the present invention. As shown in FIG. 1, the single crystal growing apparatus is configured with a chamber 1 at its outer periphery, and a crucible 2 for pulling up a single crystal is disposed at the center of the chamber 1. The crucible 2 has a double structure, and is composed of an inner quartz crucible 2a and an outer graphite crucible 2b. The crucible 2 is fixed to the upper end portion of the support shaft 3, and can rotate in the circumferential direction and can be lifted and lowered in the axial direction through the rotational drive and lift drive of the support shaft 3.

  A resistance heating heater 4 surrounding the crucible 2 is disposed outside the single crystal pulling crucible 2, and a heat insulating material 5 is disposed along the inner surface of the chamber 1 further outside. The heater 4 melts the solid silicon raw material filled in the crucible 2, whereby a silicon melt 10 is formed in the crucible 2.

  A pulling shaft 6 such as a wire is arranged coaxially with the support shaft 3 above the single crystal pulling crucible 2. The pulling shaft 6 can be moved up and down by rotating by a pulling mechanism (not shown) provided at the upper end of the chamber 1. A seed crystal 7 is attached to the tip of the pulling shaft 6. As the pulling shaft 6 is driven, the seed crystal 7 is immersed in the silicon melt 10 in the crucible 2, and the seed crystal 7 is gradually raised while rotating, whereby a silicon single crystal is formed below the seed crystal 7. 11 is nurtured.

  Further, a cylindrical heat shield 8 surrounding the silicon single crystal 11 being pulled is disposed in the chamber 1. The heat shield 8 serves to block the radiant heat from the silicon melt 10 and the heater 4 in the single crystal pulling crucible 2 and promote the cooling of the silicon single crystal 11 being pulled.

  In addition, a pair of electromagnetic coils 9 facing each other with the single crystal pulling crucible 2 in between are disposed outside the chamber 1. The electromagnetic coil 9 generates a horizontal transverse magnetic field between the electromagnetic coils 9 and applies the transverse magnetic field to the silicon melt 10 in the crucible 2. The application of a transverse magnetic field suppresses natural convection of the silicon melt 10 and suppresses rapid fluctuations in the melt temperature at the crystal growth interface, so that a high-quality silicon single crystal 11 that does not cause dislocation or fluctuation in diameter is generated. Can be nurtured.

  The single crystal growing apparatus shown in FIG. 1 includes a silicon melt forming apparatus 20 for sequentially supplying the silicon melt to the single crystal pulling crucible 2 in the process of growing the silicon single crystal 11. The silicon melt forming apparatus 20 of the present embodiment is configured as follows.

  As shown in FIG. 1 and FIG. 2, a quartz container 21 for melting a raw material is disposed in the chamber 1 above the single crystal pulling crucible 2 at a position off the central axis of the crucible 2. Yes. The quartz container 21 has a substantially cylindrical shape, and its lower part is formed in a funnel shape. That is, the lower part of the quartz container 21 is composed of a reduced diameter portion 21a whose diameter gradually decreases and an outflow pipe portion 21b which protrudes downward from the reduced diameter portion 21a and has a lower end opened.

  An induction heating coil 22 is provided around the quartz container 21 so as to surround the reduced diameter portion 21a and the outflow pipe portion 21b, which are the lower portion of the quartz container 21. FIG. 1 and FIG. 2 show a state in which the number of turns of the induction heating coil 22 is 5 turns around the reduced diameter part 21a and 2 turns around the outflow pipe part 21b. The induction heating coil 22 is connected to a power supply device via a wiring (not shown), and an alternating current is applied from the power supply device.

  Furthermore, in the lower part of the quartz vessel 21, a first cylinder 23A is arranged in a region between the outflow pipe portion 21b and the induction heating coil 22 so as to surround the outer periphery of the outflow pipe portion 21b. In the region between the upper half of the reduced diameter portion 21a and the induction heating coil 22, the second cylinder 23B is arranged so as to surround the outer periphery of the upper half of the reduced diameter portion 21a. Has been. That is, in the area between the lower part of the quartz container 21 and the induction heating coil 22, the second cylinder 23B and the first cylinder 23A are spaced apart from each other by a predetermined distance in the upper and lower parts of the area. Are arranged. These first and second cylinders 23A and 23B are made of carbon having a low specific resistance.

  Further, the quartz container 21 is covered with a heat insulating material 24 such as alumina or glass having low conductivity over the entire periphery thereof together with the first and second cylinders 23A and 23B.

  A quartz material supply pipe 26 is provided above the quartz container 21. The raw material supply pipe 26 passes through the chamber 1, and a raw material feeder (not shown) is connected to the upper end of the raw material supply pipe 26, and the lower end is disposed inside the quartz container 21. A solid silicon raw material is introduced into the raw material supply pipe 26 from the raw material feeder, and the silicon raw material 29 can be supplied to the quartz container 21 through the raw material supply pipe 26.

  Below the quartz container 21, a quartz melt supply pipe 27 is disposed coaxially with the outflow pipe portion 21 b of the quartz container 21. The melt supply pipe 27 opens at its upper end toward the lower open end of the outflow pipe portion 21 b, and its lower end portion closes to the inner side of the side wall of the single crystal pulling crucible 2 to the silicon melt 10 in the crucible 2. Configured to soak.

  In the melt forming apparatus 20 configured as described above, when forming the silicon melt in the quartz container 21, the solid silicon raw material 29 is supplied to the quartz container 21 via the raw material supply pipe 26, and the induction heating coil 22 is supplied. By applying an alternating current, a magnetic field is formed inside the induction heating coil 22. First, an eddy current is generated in the first and second cylinders 23A and 23B having a low specific resistance by the magnetic field, and the first and second cylinders 23A and 23B generate heat by Joule heat generated by the eddy current. .

  At this time, the solid silicon raw material 29 in the quartz container 21 is initially low in temperature and hardly generates eddy currents. However, due to the radiant heat from the generated first and second cylinders 23A and 23B, The solid silicon raw material 29 present in the substrate is gradually heated, and the temperature exceeds 700 ° C. to 800 ° C., and the specific resistance decreases. Then, due to the magnetic field from the induction heating coil 22, an eddy current is effectively generated in the solid silicon material 29 in the quartz container 21, and the solid silicon material 29 generates heat. As a result, the solid silicon raw material 29 can be melted in the quartz container 21 to form the silicon melt 30.

  The silicon melt 30 formed in the quartz container 21 sequentially flows out from the lower end of the opening through the outflow pipe portion 21b below the quartz container 21. At this time, the silicon melt 30 flowing out through the outflow pipe portion 21b is continuously heated by the radiant heat from the first cylindrical body 23A that has generated heat, and thus does not solidify and close the outflow pipe portion 21b. Can be spilled into. The silicon melt 30 that has flowed out is supplied to the crucible 2 for pulling up the single crystal through the melt supply pipe 27.

  At that time, by adjusting the frequency and output of the alternating current applied to the induction heating coil 22, the amount of melting of the solid silicon raw material by electromagnetic induction can be controlled, and the amount of silicon melt flowing out can be controlled.

  The frequency of the current applied to the induction heating coil is preferably in the range of 50 kHz or more and less than 2 MHz, and more preferably in the range of 100 kHz or more and less than 300 kHz. At a frequency of less than 50 kHz, even if the applied output is increased, the solid silicon material cannot be induction heated above the melting point, whereas at a frequency of 2 MHz or more, the solid silicon material can be melted, This is because electric discharges frequently occur in the operation, causing trouble in operation.

  Moreover, it is preferable that the output at the time of applying an alternating current to an induction heating coil shall be in the range of 10 kW-50 kW, More preferably, it shall be in the range of 20 kW-40 kW. This is because the solid silicon raw material cannot be melted at an applied output of less than 10 kW, whereas the applied efficiency exceeding 50 kW saturates the melting efficiency and requires a large-scale power supply device.

  As described above, in the silicon melt forming apparatus of the present embodiment, the first and second cylinders made of carbon having a low specific resistance are disposed between the lower part of the quartz container and the induction heating coil surrounding the quartz container. Therefore, the cylindrical body generates heat by electromagnetic induction by the induction heating coil, and the solid silicon raw material in the quartz container is heated by the radiant heat from the generated cylindrical body, thereby reducing the specific resistance of the solid silicon raw material. be able to. As a result, eddy current is effectively generated in the solid silicon raw material in the quartz container by electromagnetic induction by the induction heating coil, and the solid silicon raw material generates heat, so that the solid silicon raw material can be reliably melted in the quartz container. It is possible to sufficiently form a silicon melt. Furthermore, the silicon melt formed in the quartz container can be smoothly and sequentially flowed out from the lower end of the opening through the outflow pipe portion at the lower part of the quartz container.

  Then, by adopting this silicon melt forming apparatus for the growth of a silicon single crystal by the CCZ method, the silicon melt is supplied so that the position of the silicon melt in the crucible for pulling up the single crystal is constant. This makes it possible to grow a silicon single crystal with stable quality.

  In the melt forming apparatus according to the present embodiment, the second cylinder and the first cylinder are vertically spaced apart from each other at the upper and lower portions of the region between the lower portion of the quartz container and the induction heating coil. Although it is arranged and the cylinder is not present in the range of the predetermined interval, this is due to the following reason. In order to efficiently melt the solid silicon raw material at a high temperature by electromagnetic induction using an induction heating coil, it is desirable that a cylinder does not exist between the quartz container and the induction heating coil. On the other hand, in order to heat a low-temperature solid silicon raw material, it is necessary to dispose a cylinder. For this reason, the cylinder was separated and arranged in the vertical direction so that the heating of the solid silicon raw material and the securing of the melting efficiency can be compatible, and a range in which the cylinder does not exist was provided.

  For this reason, in order to efficiently melt the solid silicon raw material that has once become high temperature by electromagnetic induction, it is desirable that the cylinder does not exist. For example, the above-described first and second cylinders Of these, the first cylindrical body disposed on the lower side may be configured to be slidable to a position deviated downward from the region between the lower portion of the quartz container and the induction heating coil.

  In the melt forming apparatus according to the present embodiment, the first and second cylinders are covered with the heat insulating material together with the quartz container, so that the radiant heat from the generated first and second cylinders is effective for the solid silicon raw material. The solid silicon raw material can be efficiently heated. The heat insulating material is also effective in increasing the heat retention of the quartz container.

  In addition, the melt forming apparatus of the present embodiment is preferably used when pulling and growing a silicon single crystal for a semiconductor device by the CCZ method. In addition, for example, when casting a silicon block for a solar cell. It can also be applied to.

  In order to confirm the effect of the silicon melt forming apparatus of the present invention, the following tests were conducted. As the first example of the present invention, a quartz container having an inner diameter of 200 mm at the upper part and an inner diameter of the outflow pipe part constituting the lower part of 15 mm is used, using the melt forming apparatus shown in FIG. After filling 1.5 kg of silicon, an alternating current having a frequency of 160 kHz was applied to the induction heating coil, and the applied power was gradually increased to 30 kW by gradually increasing the current value. The induction heating coil made of copper having a diameter of 20 mm and having 7 turns around the lower part of the quartz container was used.

  Moreover, as Example 2 of the present invention, a melt forming apparatus that does not include the first cylinder disposed below the first and second cylinders disposed below the quartz container under the same conditions. The test was carried out using Furthermore, for comparison, a test was performed using a melt forming apparatus that does not include both the first and second cylindrical bodies.

  In the tests of Examples 1 and 2 of the present invention and the comparative example, the silicon melt flowing out from the lower end opening of the quartz container was collected with a quartz tray, and its weight was sequentially measured, whereby the outflow amount and average of the silicon melt were measured. The outflow rate was calculated and evaluated. The results are shown in Table 1 below.

  As shown in the table, in Example 1 of the present invention, the silicon melt started to flow out 15 minutes after the start of current application to the induction heating coil, and 1.2 kg of silicon melt corresponding to 80% of the charge amount of the raw material. The liquid could flow out intermittently. The average melt outflow rate was 160 g / min.

  In Inventive Example 2, as in Inventive Example 1, the silicon melt began to flow out 15 minutes after the start of current application, but since the first cylindrical body was not provided, Later, the silicon melt solidified in an icicle shape at the lower end opening of the quartz container, and the outflow of the melt stopped. At this time, the outflow amount of the silicon melt was 100 g, which was less than 10% of the raw material charge amount, and the average outflow rate of the melt was 100 g / min.

  On the other hand, in the comparative example, since neither of the first and second cylindrical bodies was provided, the solid silicon raw material could not be heated, and the silicon melt did not flow out at all.

  From these, it is effective to provide a cylindrical body at the bottom of the quartz container in order to melt the solid silicon raw material, and to provide a lower first cylindrical body to smoothly flow out the molten silicon raw material. It became clear that it was effective.

  According to the silicon melt forming apparatus of the present invention, a heating element is disposed between the lower part of the quartz container and the induction heating coil surrounding the quartz container, so that the quartz container is radiated by the radiant heat from the heating element. The low-temperature solid silicon raw material inside can be heated, and the specific resistance of the solid silicon raw material can be reduced. As a result, eddy currents are effectively generated in the solid silicon raw material by electromagnetic induction by the induction heating coil, so that the solid silicon raw material generates heat, and the solid silicon raw material can be reliably melted in the quartz container, so that the silicon melt can be sufficiently melted. A liquid can be formed.

  This silicon melt forming apparatus is extremely useful for growing a silicon single crystal by the CCZ method because the silicon melt can flow out from the lower end of the opening of the quartz container and can be supplied to the crucible for pulling the single crystal. It is.

It is a figure which shows typically the structure of the single crystal growth apparatus by CCZ method which has arrange | positioned the silicon melt forming apparatus which is one Embodiment of this invention. It is a figure which expands and shows the principal part of the silicon melt formation apparatus which is one Embodiment of this invention.

Explanation of symbols

1: chamber, 2: crucible for pulling single crystal, 2a: quartz crucible,
2b: graphite crucible, 3: support shaft, 4: heater, 5: heat insulating material,
6: Lifting shaft, 7: Seed crystal, 8: Thermal shield, 9: Electromagnetic coil,
10: Raw material melt, 11: Silicon single crystal,
20: Melt forming device, 21: Quartz container,
21a: reduced diameter part, 21b: outflow pipe part, 22: induction heating coil,
23A: 1st cylinder, 23B: 2nd cylinder, 24: Heat insulating material,
26: Raw material supply pipe, 27: Melt supply pipe,
29: Solid silicon raw material, 30: Silicon melt

Claims (3)

In the growth of silicon single crystals by continuous charge Czochralski method, it is used as a device for supplying silicon melt to a crucible for pulling single crystals , melting a solid silicon raw material in a quartz vessel, and using this silicon melt A silicon melt forming apparatus for flowing out from an opening provided at a lower end,
An induction heating coil surrounding the lower part of the quartz container, and a carbon-made cylindrical heating element disposed so as to surround the quartz container between the quartz container and the induction heating coil ,
The heating element is arranged separately in the upper part and the lower part of the region between the quartz container and the induction heating coil,
The frequency of the applied current to the induction heating coil is in the range of 100 kHz or more and less than 300 kHz, and the output when the alternating current is applied to the induction heating coil is in the range of 10 kW to 50 kW. Silicon melt forming equipment. 2. The silicon melt forming apparatus according to claim 1 , wherein the heating element disposed at a lower portion of the region is configured to be movable to a position outside the region. 3. The silicon melt forming apparatus according to claim 1, wherein a periphery of the quartz container is covered with a heat insulating material, and the heating element is disposed between the quartz container and the heat insulating material.

Images