JPH0478591B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a single crystal production method in which a magnetic field is applied to a single crystal raw material melt.

[Technical background of the invention and its problems] An example of a conventional single crystal production apparatus using the Czyochralski method (CZ method) is one constructed as shown in FIG. That is, single crystal raw material melt 1
A crucible 2 filled with (hereinafter referred to as melt) is heated by a heater 3 so that the single crystal raw material always remains in a molten state. A seed crystal 4 is inserted into this melt,
When the seed crystal 4 is pulled up at a certain constant speed by the pulling drive mechanism 5, the crystal grows in the solid-liquid interface boundary layer 6, and a single crystal 7 is generated.

At this time, fluid movement of the melt induced by the heating of the heating means, for example, the heater 3, that is, thermal convection 8 occurs. The cause of this thermal convection 8 is explained as follows. Thermal convection generally occurs when the balance between the buoyant force due to thermal expansion of the fluid and the viscous force of the fluid is broken. The dimensionless quantity representing the balance between the buoyant force and the viscous force is the Grashof number N _G r.

N _G r=g・α・ΔT・R ³ /ν ^3where , g: Gravitational acceleration α: Coefficient of thermal expansion of the melt ΔT: Temperature difference in the radial direction of the crucible R: Radius of the crucible ν: Coefficient of kinematic viscosity of the melt Generally , Grashof number N _G r exceeds a critical value determined by the geometric dimensions of the melt, thermal boundary conditions, etc., thermal convection occurs within the melt.

Normally, when N _G r > 10 ⁵ , the thermal convection of the melt is in a turbulent state,
When N _G r > 10 ⁹ , a disturbed state occurs. In the case of the current melt conditions for pulling a single crystal with a diameter of 3 to 4 inches, N _G r > 10 ⁹ (according to the above formula for N _G r),
The inside of the melt is in a turbulent state, and the surface of the melt, that is, the solid-liquid interface boundary layer 6, becomes undulating.

When such disturbed thermal convection exists, the temperature fluctuations within the melt, especially at the solid-liquid interface, become large, and the positional and temporal variations of the solid-liquid interface boundary layer are severe, causing microscopic observation of the growing crystal. As a result, dislocation loops, stacking faults, etc. occur in the grown single crystal.

Moreover, these defective areas occur non-uniformly in the single crystal pulling direction due to irregular fluctuations in the solid-liquid interface. Furthermore, due to the chemical reaction between the melt 1 and the crucible 2 on the inner surface of the crucible 2 where the high-temperature melt (for example, about 1500°C) comes into contact, impurities 9 dissolved in the melt from the inner surface of the crucible 2 are transferred to this thermal convection 8. It is transported and dispersed throughout the interior of the melt. This impurity 9
becomes a nucleus, and generates dislocation loops, defects, growth stripes, etc. in the single crystal, deteriorating the quality of the single crystal.

For this reason, when manufacturing integrated circuit (LSI) wafers from such single crystals, wafers containing defective portions have deteriorated electrical characteristics, making them unusable and resulting in poor yields. In the future, the diameter of single crystals will become larger and larger, but as can be seen from the above equation for Grashof's number, as the diameter of the crucible increases, the Grashof's number will increase, and the thermal convection of the melt will become more intense. , the quality of the single crystal will continue to deteriorate.

For this reason, single crystal generation devices that apply a DC magnetic field to the melt have been proposed in order to suppress thermal convection and pull single crystals under growth conditions close to thermal and chemical equilibrium. There is. FIG. 2 schematically shows this configuration, and the same parts as in FIG. 1 are given the same reference numerals and their explanation will be omitted. A magnet 10 is placed around the outer periphery of the crucible 2, and a uniform magnetic field is applied to the melt 1 in the direction of an arrow 11 (magnetic field application direction). A single crystal melt is generally a conductor having an electrical conductivity σ. Therefore, when a fluid having electrical conductivity σ moves due to thermal convection, the fluid moving in a direction not parallel to the magnetic field application direction 11 is subjected to a magnetic resistance force according to Lenz's law. Therefore, the movement of thermal convection is suppressed. In general, the magnetoresistive force when a magnetic field is applied, that is, the magnetorheological coefficient νeff, is νeff = (μHD) ² σ/ρ, where ν: Magnetic permeability of the melt H: Magnetic field strength D: Crucible diameter σ: Electrical conductivity of the melt ρ: Density of the melt, and as the magnetic field strength increases, the magnetorheological coefficient νeff increases, and ν in the formula for the Grashof number shown earlier increases, and the Grashof number suddenly increases. , and the Grashof number can be made smaller than the critical value with a certain magnetic field strength. This completely suppresses thermal convection of the melt. By applying a magnetic field in this way, thermal convection is suppressed, which eliminates the inclusion of impurities in the single crystal, the occurrence of dislocation loops, defects, and growth streaks.
Moreover, single crystals with uniform quality in the pulling direction can be obtained.
Single crystal quality and yield are improved.

Let us now consider the thermal convection pattern in the melt. As shown in FIG. 1, there are two patterns of thermal convection. One is a thermal convection 8 generated by heating the heater 3, and the other is a thermal convection 12 generated by pulling the single crystal 7 while rotating it during single crystal growth. Now, if the diameter of the crucible is D and the height of the melt is H, each thermal convection has a height of H and a width of D/
It is considered that the rotary movement as shown in the figure is occurring within the area indicated by 4. When a magnetic field in 11 directions perpendicular to the pulling direction is applied to this thermal convection as shown in Figure 2, an electromagnetic braking force acts in the height H direction of the thermal convection 8 and 12, suppressing the thermal convection. . Furthermore, when a magnetic field is applied in a direction perpendicular to the direction shown in FIG. 2, that is, in a direction parallel to the pulling direction (not shown), an electromagnetic braking force acts in the width D/4 direction of the thermal convection 8, 12. , the heat convection is suppressed. The electromagnetic braking force is proportional to the distance that the fluid moves, so when H>D/4, that is, when the aspect ratio H/D>1/4, it is better to apply a magnetic field in the direction of 11.
The electromagnetic braking force effect is greater than that when a magnetic field in the direction perpendicular to 1 is applied, that is, the thermal convection suppressing effect is greater. Conversely, H>D/4, that is,
When the aspect ratio H/D>1/4, contrary to the above, applying a magnetic field in a direction perpendicular to the magnetic field direction 11 has a greater thermal convection suppressing effect.

However, when considering the above magnetic field direction and thermal convection suppressing effect, the single crystal generating apparatus equipped with the conventional magnet 10 shown in FIG. 2 has the following drawbacks.

At the time when the single crystal 4 is immersed in the melt 1 and the growth of the single crystal is started, the aspect ratio is usually H/D》
It is 1/4.

In such a state, heat convection is suppressed by applying a magnetic field in the magnetic field direction 11 perpendicular to the pulling direction, and a high-quality single crystal is grown. As the growth of the single crystal progresses, the remaining melt decreases, so at a certain point H/D becomes 1/4, and after that, H/D becomes less than 1/4.
A single crystal will be grown in a state of 4. As mentioned above, in the state where H/D<1/4, thermal convection suppression by applying magnetic fields in 11 directions is not sufficient;
Single crystals grown under these conditions are of low quality, containing impurities, dislocation loops, defects, and growth streaks.

Such products cannot be used as products, resulting in poor yields. Furthermore, in conventional single crystal pulling apparatuses that apply a magnetic field, the amount of melt remaining in the crucible that cannot be grown as a single crystal is large, resulting in poor utilization of the raw material melt.

[Object of the Invention] Therefore, the present invention has been made in order to eliminate the drawbacks of the prior art described above, and it is possible to improve the utilization rate of the raw material melt and to produce single crystals in which all the grown single crystals are of high quality. The purpose is to provide a method.

[Summary of the Invention] In order to achieve the above object, the present invention heats a single crystal raw material in a container with a heating means to create a raw material melt, inserts a seed crystal into this raw material melt, and In a method for producing a single crystal in which a single crystal is produced in a solid-liquid interface boundary layer by pulling the raw material melt using a pulling drive mechanism, under a single crystal pulling situation where the aspect ratio of the raw material melt is large, the raw material melt is When a magnetic field of 2000 Gauss or more is applied perpendicularly to the pulling direction of the single crystal, and in a single crystal pulling situation where the aspect ratio of the raw material melt is small, the raw material melt is applied in the pulling direction of the single crystal. This method applies a magnetic field of about 1000 Gauss parallel to the single crystal.

[Embodiments of the Invention] The present invention will be described below with reference to the drawings. First, an embodiment shown in FIGS. 3a and 3b will be described. The same parts as in FIGS. 1 and 2 are denoted by the same reference numerals, and the explanation thereof will be omitted. That is, the single crystal pulling machine 13. On the outer periphery of the chamber 14, a magnetic field generating means, such as a normal conductive magnet 16, is arranged to apply a magnetic field of about 1000 Gauss in a direction parallel to the pulling direction, that is, in a direction 15 (magnetic field direction). The normal conductive magnet 16 consists of a copper coil 17 wound in the shape of a solenoid and a winding frame 18 for holding the coil. Fixed.

A magnetic field generating means, such as a superconducting magnet 21, is arranged outside the normal conducting magnet 16 to apply a magnetic field of 2000 Gauss or more in a direction perpendicular to the pulling direction, that is, in a direction 11 (magnetic field direction). The superconducting magnet 21 includes a superconducting coil 22 and a cold container 23 for storing the superconducting coil 22 and keeping it at an extremely low temperature (for example, 4.2K).
and rails 24 laid on the floor to support them.
and a drive mechanism 25 that moves them.

Next, the operation of the single crystal generating apparatus configured as above will be explained. Seed crystal 4 is raw material melt 1
(Fig. 1) and the growth of the single crystal 7 is started, since the aspect ratio of the melt is H/D》1/4, the superconducting magnet 21 is immersed in
A magnetic field of Gauss or higher is applied in 11 directions.

In this way, thermal convection of the raw material melt can be suppressed. In this case, if we try to generate a relatively strong magnetic field of 2000 Gauss or more using a normal conducting magnet, the magnet device will be huge compared to the single crystal pulling machine 13, but here we use a superconducting magnet 21. This makes it possible to obtain a strong magnetic field while being lightweight and compact.

Next, as the single crystal 7 grows, the melt height H decreases until the melt aspect ratio H/D becomes 1/4. At this point, raw material melt 1
The magnetic field applied to the superconducting magnet 21 is changed from the superconducting magnet 21 to the normal conducting magnet 16. In this case, since the amount of raw material melt is sufficiently smaller than the initial filling amount, a magnetic field of about 1000 Gauss is applied to the raw material melt. Furthermore, from this point on, the aspect ratio of the melt H/
Since D<1/4, a magnetic field is applied parallel to the pulling direction of the single crystal (direction 15).

In this way, thermal convection of the raw material melt can be suppressed. In this case, a solenoid coil with a thin coil layer wound with a copper coil 17 as shown in FIG. 3 is sufficient as a magnetic field generating means for generating a relatively low magnetic field of about 1000 Gauss. Of course, it is clear that the effect is the same even if a superconducting magnet device is used.

In the region where the aspect ratio H/D of the melt is <1/4, the thermal convection of the melt is suppressed by the magnetic field direction 15 generated by the normal conducting magnet 16, and a high quality single crystal is grown. Therefore, it is possible to effectively use raw material melt 1 having an aspect ratio H/D<1/4, which could not be used in the single crystal generating apparatus equipped with the conventional magnet.

After single crystal growth is completed, chamber 14
It is necessary to clean the crucible 2 that has been decomposed and charge the new raw material melt 1 into the crucible 2. At that time, it is necessary to remove the magnet attached to the single crystal pulling machine 13, but in the apparatus according to the embodiment of the present invention, cleaning and charging operations are simplified as follows. First, the superconducting magnet 21 is moved in a moving direction 26 as shown in FIG. 3 by a rail 24 laid on the floor and a drive mechanism 25, and the superconducting magnet 21 is fixed at a fixed position 27. That is, since the single crystal puller 13 and the superconducting magnet 21 are completely separated, the disassembly work of the chamber 14 is facilitated. Furthermore, since the thin-walled cylindrical normally conducting magnet 16 is fixed to the outer periphery of the chamber 14, when the chamber 14 is disassembled for cleaning the crucible 2, it can be left attached to the chamber.
Therefore, even if the normal conductive magnet 16 is present, there is no problem in disassembling the chamber 14, and the work can be easily carried out.

Next, another embodiment of the present invention will be described with reference to FIG. Components that are the same as those in the embodiment shown in FIG. 3 are given the same reference numerals, and their explanation will be omitted. Third
In place of the normal conducting magnet 16 shown in the figure, a normal conducting magnet 30 consisting of a copper coil 28 and a winding frame 29 is attached to the inner surface of the chamber 14 using a fastener 31. This normally conducting magnet 30 generates a magnetic field in the direction 15.

The operation of the device constructed in this way is the same as the embodiment shown in FIG.

The present invention is not limited to the embodiments described above, but in the normal conductive magnet 30 shown in FIG. 4, the winding frame 29 is not used,
The copper coil 28 may be directly wound along the inner surface of the chamber 14 so that the inner surface of the chamber 14 also serves as a winding frame. The operation in this case is also the same as the embodiment shown in FIG.

As explained above, according to the embodiments of the present invention,
It has the following effects. In areas where the aspect ratio of the melt is large, a strong magnetic field of 2,000 Gauss or more is applied to the melt in a direction perpendicular to the pulling direction, suppressing thermal convection and growing high-quality single crystals. In regions where the aspect ratio of the melt is small, a relatively weak magnetic field of about 1000 Gauss is applied to the melt in a direction parallel to the pulling direction, so thermal convection is suppressed and a high-quality single crystal is grown.

Such a method of applying a magnetic field has the effect of significantly improving the utilization rate of the raw material melt. As a device for applying these magnetic fields, a superconducting magnet 21 is used to generate a magnetic field in a direction perpendicular to the pulling direction, and a normal conducting magnet 16 is used to generate a magnetic field in a direction parallel to the pulling direction. This has the effect of making the entire lifting device more compact. Furthermore, by simultaneously exciting the superconducting magnet 21 and the normal conducting magnet 16, there is an effect that a composite magnetic field in any direction relative to the pulling direction can be applied to the melt.

[Effects of the Invention] According to the present invention described above, it is possible to provide a single crystal production method in which the utilization rate of the raw material melt can be improved and all the grown single crystals are of high quality.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an example of a conventional single crystal generation device, Fig. 2 is a schematic configuration diagram showing another example of a conventional single crystal generation device having a magnet, and Figs. 3 a and b.
4 is a schematic configuration diagram showing a front view and a plan view of one embodiment of the apparatus for carrying out the method for producing a single crystal according to the present invention, and FIG. FIG. 1 is a schematic configuration diagram showing an example. 1... Raw material melt, 2... Crucible, 3... Heater, 4... Seed crystal, 5... Pulling drive mechanism, 6...
solid-liquid interface boundary layer, 7...single crystal, 8...thermal convection,
9... Impurity, 10... Magnet, 11... Magnetic field direction, 12... Heat convection, 13... Single crystal pulling machine, 1
4...Chamber, 15...Magnetic field direction, 16...
Normal conducting magnet, 17... copper coil, 18... winding frame,
19...flange part, 20...stopper, 21...
...Superconducting magnet, 22... Superconducting coil, 23...
Cold storage container, 24...Rail, 25...Drive mechanism,
26...Movement direction, 27...Fixed position, 28...
Copper coil, 29... winding frame, 30... normal conducting magnet,
31...stopper.

Claims (1)

[Claims] 1. A single crystal raw material in a container is heated by a heating means to create a raw material melt, a seed crystal is inserted into this raw material melt, and the seed crystal is pulled up by a pulling drive mechanism to form a solid-liquid interface boundary layer. In a single crystal production method in which a single crystal is produced using A magnetic field is applied, and under a single crystal pulling situation where the aspect ratio of the raw material melt is small, a magnetic field of about 1000 Gauss is applied to the raw material melt parallel to the pulling direction of the single crystal. Single crystal production method.