JPH055796B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a single crystal manufacturing apparatus for manufacturing a single crystal of silicon, gallium arsenide, or the like by applying a magnetic field.

[Technical background of the invention and its problems]

One of the methods for producing single crystals that is commonly used today is the Czyochralski method (CZ method). This is a method in which a raw material melt in a crucible heated to a high temperature is crystallized, and the single crystal to be produced is gradually pulled up and grown while rotating the crucible and the crucible in opposite directions or in the same direction. . This method is characterized by the use of a crucible containing a raw material melt, which is the material for crystals, during crystal growth, and has many advantages, such as the ability to obtain crystals with large diameters.

However, in the single crystal produced by this CZ method,
Since heat is applied from outside the crucible, there is a problem in that slight fluctuations in heat input or disturbances can disturb the upward flow of the melt in the crucible due to natural convection, resulting in temperature fluctuations.

In order to suppress this temperature fluctuation and stabilize the raw material melt that produces single crystals, as well as prevent contamination from the crucible and improve the quality of the single crystals, magnetic field is applied in the direction perpendicular or horizontal to the crucible. It has been proposed to increase the effective viscosity of the melt by applying . As a result, temperature fluctuations were suppressed, but when a perpendicular magnetic field, that is, a longitudinal magnetic field, was applied, a large temperature difference occurred between the temperature of the inner peripheral wall of the crucible and the interface temperature of the single crystal.
In order to produce a single crystal, it is necessary to raise the temperature of the crucible itself to a high temperature, which may cause the crucible to melt.

To deal with this, it has been proposed to apply an equiaxially symmetrical and radial cusp magnetic field to create horizontal lines of magnetic force with respect to the melt surface (Japanese Patent Application Laid-Open No. 1983-1996-
Publication No. 217493).

However, this method requires two magnets, one above the other, and thus requires sufficient space in the height direction. Furthermore, the magnet must be moved to move the center of the magnetic field as the melt level in the crucible decreases. Furthermore, the magnetic lines of force generated by the upper magnet perpendicular to the melt surface leak to the bottom or top of the furnace and generate magnetic flux, which is transmitted to sensors and control equipment installed at the bottom or top of the furnace. There is a risk of adverse effects. Furthermore, since the magnets are arranged in two stages, there is also the problem that manufacturing costs increase.

Furthermore, in the case of applying a conventional transverse magnetic field, there is a drawback that the magnetic field in the circumferential direction of the crucible becomes non-uniform.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned points, and by providing a magnetic shield on the outside of the crucible, the temperature gradient between the crystal interface of the raw material melt and the inner wall surface of the crucible is made gentler, and a large-diameter and It is an object of the present invention to provide a single crystal manufacturing apparatus suitable for manufacturing a single crystal with high purity.

[Summary of the invention]

The inventor of the present invention has realized that by arranging a magnetic shield within the magnetic field generated by a magnetic field generating coil provided on the outside of the crucible, the direction of the magnetic lines of force is aligned approximately horizontally with the surface of the raw material melt. It has been found that by bending the crucible, the temperature distribution of the raw material melt in the crucible can be brought into an optimal state for crystal growth.

The present invention has been made based on the above findings, and more specifically, a single crystal is produced in which a raw material melt in a crucible that is heated to a high temperature is crystallized, and the crystal is gradually pulled out of the crucible while growing. In the manufacturing apparatus, a magnetic field generating coil for generating a magnetic field in the crucible is disposed on the outside of the crucible, and the direction of the magnetic field lines generated from the magnetic field generating coil is at least in the vicinity of the raw material melt surface in the crucible at the liquid level. The device is characterized by being provided with a magnetic shield that bends the lines of magnetic force so as to be oriented substantially horizontally with respect to the magnetic field.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail based on an embodiment shown in the drawings.

In FIG. 1, reference numeral 1 denotes a crucible heated by a heater 2, which is housed in a furnace 3. Further, the crucible 1 contains a raw material melt 4 made of, for example, a silicon melt. A magnetic shield 8 is provided around a rotating shaft 6 for pulling up a single crystal (also simply referred to as a single crystal) 5 and a rotating shaft 7 for rotating the crucible 1, and the shape of the magnetic shield is cylindrical, fence-like, or net-like. Any of these may be used, and the shape and material are selected to be effective in bending the direction of the lines of magnetic force. Also, the position of the magnetic shield is the magnetic field generation coil 9.
The direction of the magnetic lines of force 9a generated by the raw material melt 4
is arranged near the liquid surface so as to be approximately parallel to the liquid surface. So that the direction of the magnetic field lines is optimal,
It is preferable that the crucible 1 or the magnetic shield 8 and/or the coil 9 be formed so as to be movable vertically and horizontally.

When the magnetic field is in the form shown in FIG. 1, the raw material melt in the crucible 1 is caused by rotating the crucible 1 and/or the single crystal 5 with the rotating shafts 7 and/or 6 in both directions or in opposite directions. A circulating flow is generated in the liquid 4 in the direction of the arrow shown in FIG.
That is, in the vicinity of the bottom surface 1a of the crucible 1 or in the vicinity of the interface 5a of the single crystal 5, a radially outward flow is generated due to the centrifugal force due to the rotation of the crucible 1 or the single crystal 5, and also in the vicinity of the side wall surface 1b of the crucible 1. In this case, vertically upward natural convection is generated by the heater 2 . With respect to such a flow, when the magnetic lines of force 9a of the magnetic field generating coil 9 are substantially perpendicular to the flow, the flow of the melt is braked and the flow velocity becomes small.

This can be expressed numerically as follows.

F=-σvB ² F: Electromagnetic force σ: Electrical conductivity v: Melt flow velocity B: Magnetic flux density As described above, according to the present invention, the flow at the melt interface is not significantly affected by the electromagnetic force, and the above The melt interface heated by the heater 2 flows more smoothly than in conventional single crystal pulling means using a vertical magnetic field.
Acts in a direction that does not create large temperature gradients. Furthermore, since the side wall surface 1b of the crucible 1 is exposed to high temperatures, contamination of the crucible wall surface becomes a problem unless a transverse magnetic field is applied, but according to the present invention, the raw material near the side wall surface 1b The melt 4 is decelerated, thereby reducing contamination.

The diagram shown in FIG. 3 shows a typical isotemperature distribution curve in the raw material melt 4 produced by the apparatus of the present invention, and this isotemperature distribution curve 10a
This indicates that the temperature gradient at the interface of the raw material melt 4 of the crucible 1 is small, and there is no need for unnecessary heating from the heater 2.

Further, according to the present invention, since the temperature of the single crystal 5 below the sea surface is approximately the same at any position in the raw material melt 4, there is an effect that crystallization is further promoted.

By the way, the embodiment of the present invention shown in FIG. 1 is formed to have a magnetic flux distribution that makes the magnetic flux density approximately uniform, but in another embodiment shown in FIG. This is an example in which the magnetic shield 8 is arranged upside down. This example has the advantage that a vertical magnetic field effect can be obtained at the center of rotation of the crucible 1, and a transverse magnetic field effect can be obtained at the periphery of the crucible 1.

Since the magnetic shield 8 of the present invention can act as a kind of heat source due to eddy current loss in an alternating magnetic field, it can be applied in place of the heater 2 or as an auxiliary heater thereof. Although not shown in the figure, there are cases where it is better to place the magnetic shield inside the furnace. Furthermore, a magnetic shield with a bottom is another example, and in this case, the heat generating effect is large on a plane that crosses the magnetic flux at a substantially right angle, and is useful as a heat source.

The magnetic field generating coil 9 can be replaced by a normal conductor, a superconductor, or a permanent magnet.
Furthermore, a laminated core may be provided near the coil 9 to improve the magnetic lines of force 9a.

〔Effect of the invention〕

The single crystal manufacturing apparatus of the present invention has a magnetic shield that bends the direction of the magnetic lines of force generated from the magnetic field generating coil in a direction substantially horizontal to the raw material melt surface near the surface of the raw material melt, so that The temperature distribution of the raw material melt can be optimized for crystal growth, making it possible to prevent contamination from the crucible and produce homogeneous, high-purity, large-diameter single crystals. .

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the single crystal production apparatus according to the present invention, FIG. 2 is a diagram showing the flow distribution and magnetic field line distribution of the raw material melt in the crucible of the present invention, and FIG. 3 is a diagram showing the raw material melt of the present invention. FIG. 4, which is a diagram showing the isothermal distribution of the melt, is a sectional view of a single crystal manufacturing apparatus according to another embodiment of the present invention. 1... Crucible, 1a... Crucible bottom, 1b...
Crucible side wall, 2... Heater, 3... Furnace, 4
... Raw material melt, 5 ... Single crystal, 6 ... Single crystal pulling rotation axis, 7 ... Crucible rotation axis, 8 ... Magnetic shield, 9 ... Coil for magnetic field generation, 9a ... Lines of magnetic force, 10a ... ...Isotherms.

Claims (1)

[Claims] 1. In a single crystal manufacturing apparatus that crystallizes a raw material melt in a crucible that is heated to a high temperature and gradually pulls the crystal out of the crucible while growing the crystal, a magnetic field is generated inside the crucible on the outside of the crucible. a magnetic field generating coil, and a magnetic shield that bends the magnetic lines of force generated from the magnetic field generating coil so that the direction of the lines of magnetic force is oriented substantially horizontally to the liquid surface at least in the vicinity of the surface of the raw material melt in the crucible. A single-crystal manufacturing device characterized by being provided with.