JPS63112489A - Production apparatus for single crystal - Google Patents

Abstract

PURPOSE:To obtain a homogenous high-quality single crystal of e.g. silicon without crystal defects etc. with a small He loss at a low cost, by pulling up a crystal while applying a horizontal magnetic field with a pair of coils dipped in liquid He in a vertically movable cryostat. CONSTITUTION:A melt 1 consisting of a substance having electric conductivity, e.g. silicon is contained in a crucible 3 provided on a frame 2 under a chamber 9 and pulled up at a given speed while being rotated through a seed crystal 6 supported by a pulling up mechanism 5 and heated with a heater 4 to grow a single crystal 8. On the other hand, a cryostat 13 is simultaneously supported by supports 16 around the chamber 9 and set in a vertically movable manner provided through the vertical shafts 14 and a driving machine 15, and a DC horizontal magnetic field is applied to a pair of superconductive coils 11 dipped in liquid He 12 contained in the cryostat 13 through a DC electric power source to product magnetic viscosity in the melt 1. Thereby heat convection 10 in the melt 1 is suppressed to stably grow a crystal. The cryostat 13 is lowered in the cases of taking out the resultant single crystal, exchanging the crucible 3, etc., to readily carry out these operations.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a single crystal manufacturing apparatus for pulling a single crystal under the application of a magnetic field by a superconducting magnet.

(Conventional Technique 4!i) As a conventional manufacturing device for single crystals such as silicon, a device using the CZ method (Czochralski method) is known. This device brings a seed crystal into contact with the surface of a melt, and then slowly pulls up the seed crystal while rotating it to grow a 111 crystal.

In this case, a circulation flow is generated in the melt, such as thermal convection due to heat applied from the side of the melt through the crucible, or forced convection in the centrifugal direction of the surface layer of the melt due to rotation of the seed crystal. This circulating flow causes temperature fluctuations at the interface where the single crystal grows, resulting in adverse effects such as non-uniformity in impurity content, properties, etc., and crystal defects within the grown single crystal.

Therefore, if the melt is a conductive substance such as silicon, applying a magnetic field to the melt in a nearly horizontal direction will generate magnetic viscosity in the melt and increase the v1 reflux of the melt. suppress. As a means for applying this horizontal magnetic field, a superconducting magnet that has been exposed to low drilling temperatures is used from an economic point of view, such as low power consumption.

(Problem to be solved by the invention) A superconducting magnet usually consists of a superconducting coil made of superconducting material and a means (cryostat) for maintaining this coil at an extremely low temperature. Since liquid helium is usually used to maintain the liquid helium at an extremely low temperature, there are problems such as high losses due to evaporation of this liquid helium and high operating costs.

In particular, for each work such as taking out a single crystal and replacing the crucible,
In order to improve the workability, the cryostat is moved, and the current supplied to the superconducting magnet in the cryostat is turned on and off each time the cryostat is moved to demagnetize and demagnetize unnecessary magnetic fields during the work. When a superconducting magnet is switched from an energized state to a demagnetized or demagnetized state or vice versa, it is necessary to heat the thermal switch in the superconducting state at the time of switching, and this heat increases the evaporation loss of liquid helium. There are other problems.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, reduce the amount of liquid helium consumed in a cryostat, and provide a single crystal manufacturing apparatus with low operating costs.

(Means for solving the problems) The above object of the present invention is achieved by the following configuration. That is, a cylindrical crucible, an annular heating means arranged outside the crucible concentrically with the central axis of the crucible and for melting a conductive substance in the crucible, and symmetrical with respect to the central axis. a pair of coils located opposite to each other and applying a horizontal magnetic field to the substance; a container filled with liquid helium and housing the pair of coils immersed in the liquid helium; A cryostat frame, in which the container is suspended with a space between the container and the cryostat frame is movably supported along the central axis; a cylindrical crucible, and a cylindrical crucible arranged concentrically with the central axis of the crucible on the outside of the crucible; an annular heating means for melting a conductive substance in the crucible; a pair of coils located symmetrically opposite to each other with respect to the central axis and applying a horizontal magnetic field to the substance; and a liquid helium inside. The container is suspended inside with a gap between the container filled with the coil and containing the pair of coils immersed in the liquid helium, and the container is moved along the central axis. This single crystal manufacturing apparatus is characterized by comprising a freely supported cryostat frame and a DC power source that applies current to the pair of coils via a switch in order to bring the pair of coils into a superconducting state.

(Specific Example) Hereinafter, one specific example of the apparatus of the present invention shown in the drawings will be described.

Figures 1 and 2 are single crystals produced by the CZ method! FIG. 1 is a vertical cross-sectional view and a partial plan view showing the WI manufacturing equipment. Figures 1 and 2
In the figure, a melt 1 made of a conductive substance such as silicon is filled in a crucible 3 placed on a pedestal 2, and is heated by a heater 4 placed on the side of the crucible 3. It is always kept in a molten state. A seed crystal 6 supported by a pulling drive mechanism 5 is immersed in this melt 1, and a pulling drive 1. When the R structure 5 rotates the seed crystal 6 and pulls it upward at a predetermined speed, a crystal grows in the solid-liquid interface boundary layer 1 and a single crystal 8 is grown. These crucible 3, heater 4, single crystal 8, etc. are housed in a chamber 9.

During crystal growth, thermal convection 10 is induced in the melt 1 by the heating of the heater 4, so in order to suppress this thermal convection 10, a DC parallel magnetic field is applied to the melt 1 by the superconducting coil 11. Make magnetic viscosity raw. A DC power supply 35 (FIG. 4) is connected to this coil 11, and current is supplied to the coil 11 from this DC power supply 35 as appropriate. Further, the coil 11 is immersed in liquid helium 12 so as to constitute a superconducting magnet, and this liquid helium 12 is housed in a cryostat 13. The shape of this cryostat 13 is that chamber 1
It is an integral type having an annular shape surrounding the periphery of 1.

Further, the cryostat 13 is supported by a vertical shaft 14 so as to be movable in the vertical direction, and the cryostat drive machine 1
5 to move as appropriate. Vertical @14 and drive 1
5 is supported by pillars 16, and these structures allow the cryostat 13 to be lowered from a position facing the chamber 9 in order to improve workability during operations such as taking out the single crystal 8 and replacing the crucible 3. 17 in Figure 1
In other words, the cryostat 13 can be moved upward to a position facing the chamber 9 only during single crystal growth.

FIG. 3 is a partial vertical cross-sectional view of a cryostat housing a superconducting coil, and the same parts as in FIG. 1 are given the same reference numerals and their explanations are omitted (the same applies to FIG. 4).Liquid helium 12 is housed in a liquid helium container 20 made of a thin stainless steel plate, and this liquid helium container 20 is thermally insulated by a heat shield plate 21 at 20' and a heat shield plate 22 at 80'. Further, the above-mentioned liquid helium container 20.20'', heat shield plate 21, 80'', and heat shield plate 22 are housed in the cryostat outer frame 23, and these are spaced apart from each other by the support rod 24. It is suspended from the cryostat outer frame 23 by. In addition, the two-stage helium refrigerator 25 placed on the cryostat outer frame 23 is connected to the y heat shield plate 20@ via the heat shield electric heating shaft 26.
Cool 1.

FIG. 4 is an explanatory diagram of the operation of the superconducting coil, and with reference to this diagram, the operation of the superconducting magnet will be explained below by dividing into an excitation process and a demagnetization process.

a) Excitation process While the coil 11 immersed in liquid helium 12 is kept at an extremely low temperature, the heater 32 provided in the thermal switch 31 is energized by the DC power supply 33.
After the thermal switch 31 is turned OFF (normal conduction state) by heating the superconducting wire 34, the coil 11 is turned off by the DC power supply 35, which is necessary for single crystal growth. Excite until it outputs an i field. When the power supply from the DC power source 33 is stopped in this state, the heating of the superconducting wire 34 is stopped.
The thermal switch 31 is turned ON (superconducting state), and the coil 11 enters the persistent current mode. In this model, DC power supply 3
5. Stop the power supply.

b) With the 8'l magnetic process coil 11 in the persistent current mode, first increase the voltage of the DC power supply 35 to the voltage required to excite the coil 11, and then turn on the thermal switch 31 in the same manner as described above. When turned off, the persistent current flowing through the coil 11 flows toward the DC power supply 35. Next, this DC power supply 35
The voltage is finally reduced to 0, and the DC power supply 33 is turned off to complete the demagnetization process.

In the above excitation process and demagnetization process, the amount of evaporation of the liquid helium 12 increases due to the heat generated by the heater 32 in the thermal switch 31. In order to reduce the consumption of such liquid helium 12, single crystal extraction,
Even when moving the cryostat to improve workability during work such as replacing the crucible, the coil 1
It is preferable to hold magnet 1 in an excited state without demagnetizing it.

In this way, when the coil 11 is moved in an excited state, it is preferable that the fixed parts of this device that are exposed to the strong magnetic field of the coil 11 be made of non-ferromagnetic materials, especially the sliding parts and the calendar parts. It is preferable to use a material other than ferromagnetic material for the rotating shaft portion. This is because when a ferromagnetic material is used for the fixed part, the magnetic field creates uneven attractive or repulsive forces between the fixed part and the cryostat.
This is because the operation of the sliding portion of the cryostat, the sliding portion two-rotation bearing portion, etc. is severely hindered by so-called galling. If it is unavoidable to use magnetic materials, for example, non-magnetic materials such as gunmetal, non-magnetic stainless steel, hard graphite, or a combination of hard graphite and soft graphite should be used for ball bearings, and non-magnetic materials such as a combination of hard graphite and soft graphite should be used for ball bearings. It is best to use non-magnetic high strength stainless steel. Also, it is better to replace the electric motor with a hydraulic motor, and even when using an electric motor, if there is a suitable weak magnetic field position where the magnetic field around the motor is about 500 Gauss or less, preferably 300 Gauss or less. , install the electric motor in the weak magnetic field position using an extension shaft, belt, etc., and if there is no suitable weak magnetic field position,
Preferably, the electrically conductive motor is covered by suitable magnetic field interrupting means.

Also, when moving the cryostat 13 up and down,
When a tilt change is applied to the cryostat 13, the support rod 2
4, deformation of the liquid helium container 20, etc., the heat shield plate 21 approaches or comes into contact with the liquid helium containers 20 and 20', and the intrusion of heat into the liquid helium container 20 increases. The result is a loss of liquid helium. The allowable value of the tilt fluctuation of this cryostat 13 is:
Each heat shield 21, 22 is attached to the cryostat outer frame 23.20''K, 80'.It depends on the dimensions of the liquid helium container 20, but normally the distance between the heat shields 21 and the liquid helium containers 20 and 206 is about 10 cm. Since the height of the liquid helium container 20 is about 1 TrL, if the cryostat 13 moves up and down with a tilt change of 0.6°, the distance between the liquid helium containers 20 and 20'' and the heat shield 21 is 1 cI. ! 1, or approximately 10%. According to the experiment, 0.6 in cryostat 13
It has been found that the consumption of liquid helium 1 increases when the tilt is varied by more than 100 degrees when moving up and down.

Therefore, it is preferable that the vertical shaft 14 and the cryostat driver 15, which serve as moving means for the cryostat 13, be configured so as to suppress the tilt fluctuation of the cryostat to 0.6° or less when moving the cryostat 13 up and down. Specifically, by providing three or more vertical shafts 14 that support the cryostand 13, the cryostat 13 is supported at three or more locations, and one drive machine 15 is provided for each vertical shaft 14. It is preferable to provide one. As a matter of course, it is preferable that the working accuracy of the sliding part of the cryostat 13 and the sliding part one rotation bearing part be sufficiently good.

(Effects of the Present Invention) According to the apparatus of the present invention, it is possible to reduce the loss amount of liquid helium in the cryostat and provide a single crystal manufacturing apparatus with low operating costs.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of one specific example of the device of the present invention, FIG. 2 is a partial plan view of one specific example of the device of the present invention, FIG. 3 is a partial vertical cross-sectional view of a cryostat, and FIG. 4 is a superconducting FIG. 3 is an explanatory diagram of the operation of the coil.

Claims (4)

[Claims] (1) a cylindrical crucible; an annular heating means disposed outside the crucible concentrically with the central axis of the crucible for melting a conductive substance within the crucible; Located symmetrically opposite each other,
A pair of coils that apply a horizontal magnetic field to the substance, a container filled with liquid helium, and a container in which the pair of coils are immersed in the liquid helium, and a space provided between the container and the container. the container is suspended therein;
The cryostat frame is supported movably along the central axis, and a moving means moves the cryostat frame along the central axis so that the container and the cryostat frame do not come into contact with each other. Single crystal production equipment. (2) The device according to claim 1, wherein the portion to which the horizontal magnetic field is applied is made of a material that is not ferromagnetic. (3) The device according to claim 1, wherein the portion to which the horizontal magnetic field is applied is covered with means for cutting off the horizontal magnetic field. (4) a cylindrical crucible; an annular heating means disposed outside the crucible concentrically with the central axis of the crucible for melting a conductive substance within the crucible; Located symmetrically opposite each other,
A pair of coils that apply a horizontal magnetic field to the substance, a container filled with liquid helium, and a container in which the pair of coils are immersed in the liquid helium, and a space provided between the container and the container. the container is suspended therein;
The cryostat frame is supported movably along the central axis, and a DC power source applies current to the pair of coils via a switch in order to bring the pair of coils into a superconducting state. Single crystal production equipment.