JPS6270286A - Apparatus for producting single crystal - Google Patents

Abstract

PURPOSE:To decrease the temperature gradient between the crystal interface of molten raw material and the inner wall surface of a crucible and to enable the production of a single crystal having large diameter and high purity, by applying a magnetic shield to the outer side part of the crucible in the pulling up of the single crystal with a seed crystal from the molten raw material in a crucible. CONSTITUTION:A heater 2 is placed on the inner wall surface of the heating furnace 3 and a crucible 1 is inserted into the heater 2. A raw material 4 for single crystal such as Si, GaAs, etc., is put into the crucible 1 and melted. A single crystal 5 of Si or GaAs is used as a seed crystal and brought into contact with the surface of the molten raw material 4 while generating a magnetic field with the coil 9. The seed crystal is slowly pulled up while rotating the seed crystal 5 and the crucible 1 along the same direction or reverse direction by the magnetic field of the magnetic line of force 9a generated by the coil 9 to effect the growth of a single crystal to the end of the seed crystal. The temperature gradient between the interface 5a of the single crystal 5 in the molten raw material 4 and the inner wall surface 1b of the crucible can be decreased by the magnetic shield 8 applied to the outside of the crucible and a single crystal having large diameter and high purity and free from contamination with the crucible material can be grown by this process.

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 at present is a method called the Czochralski 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 resulting single crystal and the crucible are rotated in opposite directions or in the same direction, and the single crystal is gradually pulled up and grown. . 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 the CZ method, heat is applied from outside the crucible, so slight fluctuations in heat input or disturbances may cause
There is a problem in that the Ueno flow due to natural convection of the melt in the crucible is disturbed and causes 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 (Japanese Patent Publication No. 58-50951). As a result, temperature fluctuations were suppressed, but when applying a vertical Ia field, that is, a longitudinal magnetic field, a large temperature difference occurs 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.

In order to cope with this problem, it has been proposed to apply an equiaxially symmetrical and radial cusp magnetic field to create lines of magnetic force in the horizontal direction with respect to the melt surface (Japanese Patent Laid-Open No. 58-217493).

However, this method requires two magnets, one above the other, and thus requires sufficient space in the height direction. Moreover,
The magnet must be moved to move the center of the magnetic field as the melt level in the crucible decreases. Furthermore, the lines of magnetic 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 has an adverse effect on sensors and control equipment installed at the bottom or top of the furnace. There is a risk of giving. Furthermore, since the magnets are in two stages, there is also the problem that the S4 manufacturing cost increases.

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 An object of the present invention is 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 bends the direction of the magnetic lines of force in a direction substantially horizontal to the surface of the raw material melt by arranging a magnetic shield in the magnetic field generated by a magnetic field generating coil provided on the outside of the crucible. It has been found that the temperature distribution of the raw material melt in the crucible can be brought into the optimum 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 that generates a magnetic field in the crucible is provided on the outside of the crucible, and the direction of the magnetic field lines generated from the magnetic field generating coil is at least at the raw material in the crucible @ near the liquid surface. This sign is characterized by being provided with a magnetic shield that bends the lines of magnetic force so as to be oriented in a substantially horizontal direction.

[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. Either shape and material are selected that are effective in bending the direction of the lines of magnetic force. Moreover, the position of the magnetic shield is arranged so that the direction of the magnetic lines of force 9a generated by the magnetic field generating coil 9 is near the liquid surface of the raw material melt 4 and is substantially parallel to the liquid surface.

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 so that the direction of the magnetic lines of force is optimized.

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 small crystal 5, a radially outward flow is generated due to centrifugal force due to the rotation of the crucible 1 or the single crystal 5, and
In the vicinity of the side wall surface 1b of the crucible 1, 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 is reduced.

This can be expressed numerically as follows.

F-1σ■B2 F: Electromagnetic force σ: Electrical conductivity.

■: Melt flow velocity Beta flux density As described above, according to the present invention, the flow at the melt interface is not so affected by electromagnetic force, and the melt interface heated by the heater 2 is different from the conventional vertical Compared to single crystal pulling means using a magnetic field, it flows more smoothly and acts in a direction that does not create a large temperature gradient. 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. The liquid 4 is decelerated, thereby reducing contamination.

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

Further, according to the present invention, the temperature below the sea surface of the single crystal 5 is approximately the same at any position in the raw material melt 4, so 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 super Ti conductor or a permanent magnet as well as a normal conductor.

In order to roughly improve the magnetic field lines 9a, the laminated iron core is
It can also be provided near.

〔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, and it is possible to prevent contamination from the crucible, make it homogeneous, and produce a single crystal with a high III Iff and a large diameter.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a single crystal manufacturing apparatus according to the present invention, and FIG.
The figure shows the flow distribution and magnetic field line distribution of the raw material melt in the crucible of the present invention, FIG. 3 shows the isothermal line distribution of the raw material melt of the present invention, and FIG. 1 is a sectional view of a single crystal manufacturing apparatus according to an example. DESCRIPTION OF SYMBOLS 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...! 11 Medium coil, 9a... lines of magnetic force,
10a...equal crosstalk. Applicant's agent Mr. Sato Figure 3 Figure 4

Claims (1)

[Claims] In a single crystal manufacturing apparatus 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, a magnetic field is generated in the crucible at 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 magnetic lines of force generated from the magnetic field generating coil is oriented substantially horizontally to the liquid surface at least in the vicinity of the surface of the raw material melt in the crucible. 1. A single crystal manufacturing device, characterized in that: