JP7230781B2 - Single crystal pulling apparatus and single crystal pulling method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a single crystal pulling apparatus and a single crystal pulling method using the same.

Semiconductors such as silicon and gallium arsenide are composed of single crystals and are used for memory devices of small to large computers, and there is a demand for large-capacity, low-cost, and high-quality storage devices.

Conventionally, as one method for pulling a single crystal for producing a single crystal that satisfies these semiconductor requirements, a magnetic field is applied to a molten semiconductor raw material contained in a crucible, thereby generating a magnetic field in the melt. A method (generally referred to as the Czochralski (CZ) method) of suppressing thermal convection to manufacture large-diameter, high-quality semiconductors is known.

An example of a conventional single crystal pulling apparatus using the CZ method will be described with reference to FIG. A single crystal pulling apparatus (conventional example) 100 shown in FIG. A heater 4 for heating and melting the semiconductor raw material in the crucible 3 is provided inside the pulling furnace 2 around the crucible 3, and a pair of superconducting coils 104 (104a, 104b) is provided outside the pulling furnace 2. ) is placed in a refrigerant container (hereinafter referred to as a cylindrical refrigerant container) 6 as a cylindrical container.

In manufacturing a single crystal, semiconductor raw material 11 is placed in crucible 3 and heated by heater 4 to melt semiconductor raw material 11 . A seed crystal (not shown) descends from above the central portion of the crucible 3 and lands in the melt, for example, and is pulled up in a pulling direction 13 at a predetermined speed by a pulling mechanism (not shown). As a result, crystals grow in the solid/liquid boundary layer to produce single crystals. At this time, if a fluid motion of the melt induced by the heating of the heater 4, that is, thermal convection occurs, the melt that is pulled up is disturbed and the yield of single crystal production is reduced.

Therefore, as a countermeasure, the superconducting coil 104 of the superconducting magnet 7 is used. That is, the semiconductor raw material 11 in the melt is subjected to an action restraining force by the magnetic lines of force 10 generated by the energization of the superconducting coil 104, and the growing single crystal is slowly grown as the seed crystal is pulled up without causing convection in the crucible 3. It is pulled upward and becomes manufactured as a solid single crystal 12 . A pulling mechanism (not shown) for pulling the single crystal 12 along the center line 9 is provided above the pulling furnace 2 .

Next, an example of the superconducting magnet 7 used in the single crystal pulling apparatus (conventional example) 100 shown in FIG. 8 will be described with reference to FIG. This superconducting magnet 7 is constructed by housing a superconducting coil 104 (104a, 104b) in a vacuum vessel 8 with a cylindrical refrigerant vessel 6 interposed therebetween. In this superconducting magnet 7, a pair of superconducting coils 104a and 104b facing each other through the central portion in the vacuum vessel 8 are accommodated. These pair of superconducting coils 104a and 104b are Helmholtz type magnetic field coils that generate magnetic fields along the same lateral direction, and as shown in FIG. Axisymmetrical lines of magnetic force 10 are generated (the position of this center line 9 is called the magnetic field center).

8 and 9, the superconducting magnet 7 includes current leads 111 for introducing current to the two superconducting coils 104a and 104b, a first radiation shield 117 housed inside the cylindrical refrigerant container 6, and Equipped with a small helium refrigerator 112 for cooling the second radiation shield 118, a gas discharge pipe 113 for discharging the helium gas in the cylindrical refrigerant container 6, and a service port 114 having a supply port for supplying liquid helium. there is Inside the bore 115 of the superconducting magnet 7, the pulling furnace 2 shown in FIG.

FIG. 10 shows the magnetic field distribution of the conventional superconducting magnet 7 described above. As shown in FIG. 9, in the conventional superconducting magnet 7, since a pair of superconducting coils 104a and 104b facing each other are arranged, in each coil arrangement direction (X direction in FIG. 10), The magnetic field gradually increases, and in the direction perpendicular thereto (the Y direction in FIG. 10), the magnetic field gradually decreases in the vertical direction. In such a conventional configuration, the magnetic field gradient within the bore 115 is too large as shown in FIG. . That is, as shown in FIG. 10 by shaded areas with the same magnetic flux density, the magnetic field uniformity is not good in the area near the central magnetic field (that is, in FIG. 10, it has an elongated cross shape in the vertical and horizontal directions). Therefore, there is a problem that the effect of suppressing heat convection is low, and a high-quality single crystal cannot be pulled.

In Patent Document 1, in order to solve the above problem, as shown in FIGS. 4), and the center of each superconducting coil is arranged on a plane in a cylindrical vessel coaxially provided around the pulling furnace, and each superconducting coil so arranged is placed through the axial center of the cylindrical vessel. The arrangement angle θ (see FIG. 11(b)) at which each pair of superconducting coils adjacent to each other is directed toward the inside of the cylindrical container is set to 100 degrees to 130 degrees. (that is, the central angle α (see FIG. 11(b)) between adjacent coil axes across the X axis is 50 degrees to 80 degrees).

As a result, it is possible to generate a uniform transverse magnetic field with a small magnetic field gradient inside the bore 115, and to generate a concentric or square magnetic field distribution on a plane, thereby significantly increasing the unbalanced electromagnetic force. As a result, the uniform magnetic field region in the pulling direction is improved, the magnetic field in the horizontal magnetic field direction becomes almost horizontal, and the imbalance electromagnetic force is suppressed, resulting in a high-quality single crystal. It is also disclosed that production can be realized and that a high-quality single crystal can be pulled with a high yield according to this single crystal pulling method.

That is, the arrangement angles θ of the superconducting coils 104a, 104b, 104c, and 104d in FIG. 12 to 16, which show the magnetic field distributions in the cases of 100 degrees, 70 degrees, 65 degrees, 60 degrees, and 50 degrees), the central magnetic field is uniformly distributed over a sufficiently wide area. On the other hand, as shown in FIG. 17, when the arrangement angle .theta. is as small as 90 degrees (the central angle .alpha. As shown in 18, when the arrangement angle θ is as large as 140 degrees (the central angle α between the coil axes is 40 degrees), the width of the central magnetic field in the X direction is extremely narrow.

Therefore, in the superconducting magnet 7 of FIG. 11, by setting the arrangement angle θ in the range of 100 degrees to 130 degrees, it is possible to obtain a concentric or square uniformly distributed magnetic field inside the bore 115. .

However, in Patent Document 2, even with a uniform magnetic field distribution as shown in FIGS. It discloses that there is a difference in heat convection in a cross section perpendicular to the axis. This tendency is the same in the technique disclosed in Patent Document 1, which forms a uniform magnetic field distribution with four coils (however, the center angle α between the coil axes is 60 degrees), but the coil axis of the superconducting coil is included. When the direction of the magnetic lines of force on the central axis in the horizontal plane is the X-axis, the magnetic flux density distribution on the X-axis is an upwardly convex distribution, and the magnetic flux density on the central axis in the horizontal plane is the magnetic flux density set value. In this case, the magnetic flux density on the X-axis becomes 80% or less of the magnetic flux density set value on the crucible wall, and at the same time, the magnetic flux density distribution on the Y-axis perpendicular to the X-axis and passing through the central axis in the horizontal plane is The distribution is convex downward, and the magnetic flux density on the crucible wall is 140% or more of the magnetic flux density set value on the crucible wall. The flow velocity of the molten semiconductor raw material can be reduced even in the cross section perpendicular to the X axis, and the flow velocity in the cross section parallel to the X axis of the molten semiconductor raw material and the flow velocity in the cross section perpendicular to the X axis of the molten semiconductor raw material can be balanced with

Even in the cross section perpendicular to the X-axis, by reducing the flow velocity of the melted semiconductor raw material, the time required for oxygen eluted from the quartz crucible wall to reach the single crystal becomes longer, and the free surface of the melted semiconductor raw material By increasing the amount of oxygen evaporated, it is possible to greatly reduce the concentration of oxygen taken into the single crystal, and it is now possible to easily obtain a single crystal of 5 ppma-JEIDA or less.

JP 2004-051475 A Japanese Patent No. 6436031 Japanese Patent No. 5228671

However, high-purity FZ single crystals containing almost no oxygen are used for high-voltage power devices, and in order to obtain this alternative crystal by the CZ method, it is necessary to further reduce the oxygen concentration.

Patent Document 3 describes a method in which a pair of electromagnetic coils are arranged facing each other with a crucible interposed therebetween, and a silicon single crystal is grown from the raw material melt while applying a horizontal magnetic field to the raw material melt in the crucible by the electromagnetic coils. , it is disclosed that the oxygen concentration in the silicon single crystal can be reduced by setting the position of the magnetic field center line of the transverse magnetic field at a position higher than the liquid surface position of the raw material melt. In order to move up and down and turn the chamber of the hoisting machine inside the magnet, it is necessary to connect the arm connected to the hydraulic cylinder from the outside of the magnet to the chamber. become rate-determining. Also, even if the arm and the magnet do not interfere directly, the freezer protrudes from the top of the magnet and may interfere with the bottom of the revolving chamber, so it is not always easy to raise the position of the magnet. There's a problem.

The present invention has been made in view of the above problem, and even if the height of the magnet is not changed, by making the magnetic field distribution equivalent to the case where the height of the magnetic field center is raised by the magnetic shield, the single growing A single crystal pulling apparatus and a single crystal pulling method capable of reducing the oxygen concentration in the crystal are provided.

In order to solve the above problems, the present invention provides a pulling furnace having a central axis in which a heater and a crucible containing a molten semiconductor raw material are arranged, and a magnetic field having a superconducting coil provided around the pulling furnace. and a generating device for applying a horizontal magnetic field to the melted semiconductor raw material by energizing the superconducting coil to suppress convection of the melted semiconductor raw material in the crucible, wherein It has a magnetic shield that can be selectively installed between the pulling furnace and the magnetic field generator, and the height position at which the magnetic shield is installed is adjustable, so that the magnetic field distribution in the central axis direction of the pulling furnace can be changed. A single crystal pulling apparatus is provided.

In this way, a magnetic shield that can be selectively installed is provided between the pulling furnace and the magnetic field generator, and the height position at which the magnetic shield is installed can be adjusted, thereby changing the position of the magnet. By simply changing the magnetic field distribution in the direction of the center axis of the pulling furnace, the oxygen concentration in the single crystal can be controlled.

Further, the magnetic shield has a detachable structure, and the presence or absence of installation of the magnetic shield as well as its shape and installation height can be adjusted.

By doing so, the oxygen concentration in the single crystal can be controlled more easily.

Further, the magnetic shield may have an integral or split cylindrical shape, and may be installed below the central axis of the superconducting coil.

With such a lifting device, when a magnetic shield is installed, the magnetic flux density on the central axis becomes weaker below the superconducting coil, so the magnetic field distribution is the same as when the magnet is relatively raised. It is possible to further reduce the oxygen concentration in the single crystal.

Further, in the magnetic field generator in which the magnetic shield is not inserted, the magnetic flux density distribution on the X-axis is high when the magnetic force line direction on the central axis in the horizontal plane including the coil axis of the superconducting coil is set as the X-axis. When the magnetic flux density on the central axis in the horizontal plane is the magnetic flux density set value, the magnetic flux density on the X axis is 80% or less of the magnetic flux density set value on the crucible wall. In the horizontal plane, the magnetic flux density distribution on the Y-axis perpendicular to the X-axis and passing through the central axis is a downward convex distribution, and the magnetic flux density on the Y-axis is 140% of the magnetic flux density set value on the crucible wall. As described above, the magnetic field distribution is generated, and in the magnetic field generator, two pairs of superconducting coils arranged opposite to each other are provided so that the respective coil axes are included in the same horizontal plane, and the A central angle α between the coil axes sandwiching the X-axis can be set to 100 degrees or more and 120 degrees or less.

With such a magnetic field generator, the single crystal pulling apparatus can stabilize the magnetic field distribution and further reduce the concentration of oxygen taken into the single crystal.

Further, the magnetic field generator without the magnetic shield has four superconducting coils, and the coil axes of the four superconducting coils are all arranged within a single horizontal plane. When the direction of the line of magnetic force on the central axis in the horizontal plane is defined as the X-axis, two each of two The four superconducting coils are arranged in line symmetry with respect to the cross section, and the four superconducting coils all have coil axes in the horizontal plane that are aligned with the X The four superconducting coils are arranged in an angle range of more than -30° and less than 30° with respect to the Y-axis perpendicular to the axis, and the directions of the magnetic lines of force generated by the four superconducting coils are symmetrical with respect to the cross section. In each of the first region and the second region, the two superconducting coils may generate magnetic lines of force in opposite directions.

Such a magnetic field generator can further reduce the concentration of oxygen taken into the single crystal.

Furthermore, a semiconductor single crystal can be pulled using the single crystal pulling apparatus.

As described above, by using the apparatus of the present invention, it is possible to easily grow a semiconductor single crystal in which the concentration of oxygen taken in is greatly reduced.

As described above, the apparatus for pulling a single crystal of the present invention has a magnetic shield that can be selectively installed between the pulling furnace and the magnetic field generator, and the height position at which the magnetic shield is installed is adjustable. The magnetic field distribution can be the same as when the magnet is raised. Furthermore, with the single crystal pulling apparatus of the present invention, it is possible to easily grow a semiconductor single crystal in which the concentration of oxygen taken in is greatly reduced.

1 is a schematic cross-sectional view showing an example of a single crystal pulling apparatus of the present invention; FIG. FIG. 4 is a model diagram showing an example of arranging four superconducting coils when a magnetic shield is inserted; FIG. 3 shows a magnetic flux density distribution (display range: 0 to 1000 Gauss) in a cross section including a central axis parallel to the direction of the magnetic force lines analyzed using the model shown in FIG. FIG. 3 shows the magnetic flux density distribution (display range: 0 to 500 Gauss) in a cross section including the central axis parallel to the direction of the magnetic force lines analyzed using the model shown in FIG. In the model shown in Fig. 2, the maximum magnetic flux density on the central axis is adjusted to 1000 Gauss by multiplying the current flowing through the superconducting coil by 1.845. : 0 to 1000 Gauss). FIG. 4 is a model diagram showing an example of arranging four superconducting coils without inserting a magnetic shield; FIG. 7 shows the magnetic flux density distribution (display range: 0 to 1000 Gauss) in a cross section including the central axis parallel to the direction of the magnetic lines analyzed using the model shown in FIG. It is a schematic sectional view showing an example of a conventional single crystal pulling apparatus by the CZ method. 1 is a schematic perspective view showing an example of a superconducting magnet; FIG. It is a figure which shows the magnetic field distribution of the conventional superconducting magnet. 1A and 1B are a schematic perspective view and a schematic cross-sectional view showing a superconducting magnet of Patent Document 1. FIG. It is a figure which shows magnetic field distribution when arrangement|positioning angle (theta)= 100 degrees. It is a figure which shows magnetic field distribution when arrangement|positioning angle (theta)= 110 degrees. It is a figure which shows magnetic field distribution when arrangement|positioning angle (theta)= 115 degrees. It is a figure which shows magnetic field distribution when arrangement|positioning angle (theta)= 120 degrees. It is a figure which shows magnetic field distribution when arrangement|positioning angle (theta)= 130 degrees. It is a figure which shows magnetic field distribution when arrangement|positioning angle (theta)= 90 degrees. It is a figure which shows magnetic field distribution when arrangement|positioning angle (theta)= 140 degrees. FIG. 4 is a plan view showing an example of arrangement of superconducting coils according to the present invention when using a U-shaped cryostat; FIG. 4 is a plan view showing an example of arrangement of superconducting coils according to the present invention when two cryostats are connected; FIG. 4 is a schematic diagram of the arrangement of superconducting coils according to the present invention at an arrangement angle of 30 degrees with respect to the Y-axis; FIG. 4 is a schematic diagram of the arrangement of the superconducting coils according to the present invention at an arrangement angle of −30 degrees with respect to the Y-axis;

The present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

As described above, in order to obtain crystals for high withstand voltage power devices by the CZ method, it is necessary to further reduce the oxygen concentration.

As described above, in the conventional pulling apparatus, the position of the magnetic field center line of the horizontal magnetic field can be shifted to the liquid surface position of the raw material melt by moving the chamber of the pulling machine up and down and turning and raising the position of the magnet. It has been proposed that the oxygen concentration in the silicon single crystal can be reduced by setting it at a high position, but in reality, due to the structure, it is necessary to move up and down and turn the chamber of the pulling device and to raise the position of the magnet. The problem was that it was not easy.

With regard to the above problems, the present inventors have found that the oxygen concentration in the grown single crystal can be reduced by making the magnetic field distribution equivalent to the case where the height of the magnetic field center is raised without changing the height of the magnet. The present invention was completed as a result of examining the pulling apparatus and the single crystal pulling method.

That is, the present invention comprises a pulling furnace having a central axis in which a heating heater and a crucible containing a melted semiconductor raw material are arranged, and a magnetic field generator having a superconducting coil provided around the pulling furnace, A single crystal pulling apparatus for applying a horizontal magnetic field to the melted semiconductor raw material by energizing the superconducting coil to suppress convection of the melted semiconductor raw material in the crucible, comprising the pulling furnace and the magnetic field generation. It has a magnetic shield that can be selectively installed between apparatuses, the height position of installing the magnetic shield is adjustable, and the magnetic field distribution in the central axis direction of the pulling furnace can be changed. It is a device.

The apparatus for pulling a single crystal of the present invention has a magnetic shield whose installation height can be adjusted, so that the magnetic field distribution can be the same as when the magnet is raised. Furthermore, the apparatus for pulling a single crystal of the present invention can easily grow a semiconductor single crystal in which the concentration of oxygen taken in is greatly reduced.

An example of the single crystal pulling apparatus of the present invention will be described below with reference to FIG. Descriptions of the same components as those of the conventional device will be omitted as appropriate. A single crystal pulling apparatus 1 of the present invention includes a pulling furnace 2 having a central axis in which a heating heater 4 and a crucible 3 containing a melted semiconductor raw material 11 are arranged, and a superconducting coil 5 provided around the pulling furnace 2. and a magnetic field generator that applies a horizontal magnetic field to the melted semiconductor raw material 11 by energizing the superconducting coil 5 to suppress the convection of the melted semiconductor raw material 11 in the crucible 3. It has a magnetic shield 20 that can be selectively installed between the pulling furnace 2 and the magnetic field generator, and the height position at which the magnetic shield 20 is installed is adjustable, and the magnetic field distribution in the central axis direction of the pulling furnace 2 is a single crystal pulling apparatus 1 that can change the

Further, the magnetic shield 20 has a detachable structure, and it is possible to adjust whether or not the magnetic shield 20 is installed, its shape, and the height position at which it is installed. This makes it possible to control the oxygen concentration in the single crystal.

The magnetic shield 20 can be made of ferromagnetic iron. Ferromagnetic materials are divided into hard magnetic materials and soft magnetic materials. Iron is a soft magnetic material and has a small coercive force. It does not emit a magnetic field, can suppress the influence on the human body, and can be easily removed. In the case of the present invention, iron with a thickness of about 25 mm is preferable for the magnetic shield.

The magnetic shield 20 has an integral or split cylindrical shape, and can be installed below the central axis of the superconducting coil 5 .

When the magnet is excited while the magnetic shield 20 is installed between the case of the magnet and the lifting machine, the magnetic shield 20, which is a magnetic material, is drawn toward the magnet. Furthermore, since the magnet is attracted to the superconducting coil 5, which has a high magnetic flux density, an upward force acts on the magnetic shield 20 arranged below the central axis of the superconducting coil 5, and an outward force is applied near the coil. force also acts.

Therefore, the outer diameter of the magnetic shield in the present invention should be matched with the inner diameter of the magnet housing. Also, the shape of the magnetic shield can be a continuous or discontinuous cylindrical shape. Further, when the direction of the line of magnetic force at the central axis is taken as the X axis, it can be arc-shaped so as to be symmetrical with respect to a cross section including the central axis and the X axis.

The height of the magnetic shield should be less than or equal to the radius of the coil. Placing it at least below the central axis of the coil ensures that the magnetic flux density distribution on the central axis is more stable than the coil axis. It can be made to have a peak.

In addition, regarding the method of fixing the magnetic shield, a continuous step is provided at the bottom of the inner surface of the magnet housing, or a plurality of protrusions are provided. A magnetic shield can be installed by installing a fixing jig in the magnet, and the magnetic shield can be removed and set while the magnet is demagnetized.

With such a lifting device, when a magnetic shield is installed, the magnetic flux density on the central axis becomes weaker below the superconducting coil, so the magnetic field distribution is the same as when the magnet is relatively raised. It is possible to reduce the oxygen concentration in the single crystal.

In addition, in the magnetic field generator without the magnetic shield 20 inserted, the magnetic flux density distribution on the X-axis is convex upward when the direction of the magnetic force line on the central axis in the horizontal plane including the coil axis of the superconducting coil 5 is taken as the X-axis. When the magnetic flux density on the central axis in the horizontal plane is taken as the magnetic flux density set value, the magnetic flux density on the X-axis is 80% or less of the magnetic flux density set value on the crucible wall, and at the same time, it is orthogonal to the X-axis in the horizontal plane. However, the magnetic flux density distribution on the Y-axis passing through the central axis is a downward convex distribution, and the magnetic field distribution is generated so that the magnetic flux density on the Y-axis is 140% or more of the magnetic flux density setting value at the crucible wall. In the magnetic field generator, two pairs of superconducting coils are provided so that the respective coil axes are included in the same horizontal plane, and the central angle α between the coil axes sandwiching the X axis is 100 degrees. A single crystal pulling apparatus having a temperature of 120 degrees or less can be obtained.

With such a single crystal pulling apparatus, the convection suppressing force due to the electromagnetic force is sufficient even in the cross section perpendicular to the X-axis, and the flow velocity of the melted semiconductor raw material can be reduced. It is possible to balance the flow velocity in the parallel cross section and the flow velocity in the cross section perpendicular to the X-axis of the melted semiconductor raw material. Even in the cross section perpendicular to the X-axis, by reducing the flow velocity of the melted semiconductor raw material, the time required for oxygen eluted from the crucible wall to reach the single crystal becomes longer, and the oxygen from the free surface of the melted semiconductor raw material is reduced. By increasing the amount of evaporated oxygen, it is possible to provide a single crystal pulling apparatus capable of further reducing the concentration of oxygen taken into the single crystal.

The magnetic field generator without the magnetic shield 20 has four superconducting coils 5, and the coil axes of the four superconducting coils 5 are all arranged in a single horizontal plane. , when the direction of the line of magnetic force on the central axis in the horizontal plane is taken as the X axis, for example, as shown in FIGS. , two superconducting coils 5 are arranged in each region, and the four superconducting coils 5 are arranged line-symmetrically with respect to the cross section. , the coil axes are arranged so that the angle range is more than -30 ° and less than 30 ° with respect to the Y-axis perpendicular to the X-axis in the horizontal plane, and four superconducting coils are generated. The directions of the lines of magnetic force are symmetrical with respect to the cross section, and the two superconducting coils generate magnetic lines of force in opposite directions in each of the first region and the second region. can be done.

With such a single crystal pulling apparatus, the convection suppressing force due to the electromagnetic force is sufficient even in the cross section perpendicular to the X axis, and the flow velocity of the melted semiconductor raw material can be reduced. It is possible to balance the flow velocity in the cross section parallel to the X-axis and the flow velocity in the cross section perpendicular to the X-axis of the melted semiconductor raw material. Even in the cross section perpendicular to the X-axis, by reducing the flow velocity of the melted semiconductor raw material, the time required for oxygen eluted from the crucible wall to reach the single crystal becomes longer, and the oxygen from the free surface of the melted semiconductor raw material is reduced. By increasing the amount of evaporated oxygen, it is possible to provide a single crystal pulling apparatus capable of greatly reducing the concentration of oxygen taken into the single crystal.

Thus, the present invention has a magnetic shield that can be selectively installed between the pulling furnace and the magnetic field generator, and the height position at which the magnetic shield is installed can be adjusted. The magnetic shield also has a removable structure, and the magnetic field distribution in the central axis direction of the pulling furnace can be changed by changing the presence or absence of the magnetic shield, its shape, and the height of installation. It is a single crystal pulling device that can be used. Thereby, the oxygen concentration in the single crystal grown by the single crystal pulling apparatus can be controlled.

EXAMPLES The present invention will be specifically described below using Examples and Comparative Examples, but the present invention is not limited to these.

In Comparative Examples and Examples, magnetic field analysis was performed by ANSY-Maxwell-3D.
(Comparative example)
The number of coil turns×current value was adjusted so that the magnetic flux density at the center of the magnetic field was 1000 Gauss. FIG. 6 is a model diagram of the superconducting coil used for the analysis, and FIG. 7 is the magnetic flux density distribution obtained by the analysis. The magnetic flux density distribution in the cross section including the central axis parallel to the direction of the magnetic lines of force is vertically symmetric with respect to the height of the coil axis, and the coil axis is the strongest magnetic field.

(Example)
A magnetic shield having a thickness of 25 mm, an outer diameter of 800 mm, and a height of 300 mm was placed below the coil axis between the magnet and the pulling machine, as shown in the model diagram of FIG. A magnetic shield was placed at a position 200 to 500 mm below the coil axis. As a result of the magnetic field analysis, as shown in Figs. 3 and 4, the shielding effect of the magnetic shield reduces the maximum magnetic field strength on the central axis by half, but the magnetic flux density below the coil axis is greatly reduced. It can be seen that the center is relatively elevated.

In this case, the magnetic flux density on the central axis is halved, but by increasing the current flowing through the superconducting coil by a factor of 1.845, the maximum magnetic flux density on the central axis can be adjusted to 1000 Gauss as shown in FIG.

In each of the comparative example and the example, the silicon single crystal was pulled under the following conditions, and the oxygen concentration near 40 cm in the straight body was compared.
Crucible used: diameter 800mm
Charge amount of semiconductor raw material: 400kg
Single crystal to grow: diameter 306 mm
Length of straight body part of single crystal: 40 cm
Magnetic flux density: Coil current x number of turns was adjusted so that the maximum magnetic field strength on the central axis was 1000 G Single crystal rotation speed: 6 rpm
Crucible rotation speed: 0.03 rpm

As can be seen from Table 1, the examples of the present invention significantly reduced the concentration of oxygen contained in the crystal compared to the comparative examples. From the above, the single crystal pulling apparatus of the present invention in which a magnetic shield is arranged and the magnetic field distribution in the central axis direction is set high, and the single crystal growing method using the same, the oxygen concentration contained in the grown single crystal can be greatly increased. can be reduced to

It should be noted that the present invention is not limited to the above embodiments. The above-described embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect is the present invention. included in the technical scope of

DESCRIPTION OF SYMBOLS 1... Single-crystal pulling apparatus (example of this application), 2... Pulling furnace, 3... Crucible,
4... heater, 5 (5a, 5b)... superconducting coil, 6... cylindrical refrigerant container,
7 Superconducting magnet 8 Vacuum container 9 Central axis 10 Lines of magnetic force
REFERENCE SIGNS LIST 11: Semiconductor raw material, 12: Single crystal, 13: Pulling direction,
20...Magnetic shield 100...Single crystal pulling apparatus (conventional example)
104 (104a, 104b, 104c, 104d) ... superconducting coils,
111... Current lead, 112... Small helium refrigerator,
113... Gas release pipe, 114... Service port,
115... bore, 117... first radiation shield, 118... second radiation shield.

Claims (5)

A pulling furnace having a central axis in which a heating heater and a crucible containing a melted semiconductor raw material are arranged, and a magnetic field generator provided around the pulling furnace and having a superconducting coil, and energizing the superconducting coil A single crystal pulling apparatus for suppressing convection of the molten semiconductor raw material in the crucible by applying a horizontal magnetic field to the molten semiconductor raw material by
It has a magnetic shield that can be selectively installed between the pulling furnace and the magnetic field generator, and the height position at which the magnetic shield is installed can be adjusted to change the magnetic field distribution in the central axis direction of the pulling furnace. being able to
A single crystal pulling apparatus, wherein the magnetic shield has an integral or split cylindrical shape and is installed below a central axis of the superconducting coil. The magnetic shield further has a detachable structure, and the presence or absence of installation of the magnetic shield, as well as its shape and installation height position can be adjusted, and the oxygen concentration in the single crystal can be controlled. 2. The apparatus for pulling a single crystal according to claim 1, which is capable of pulling a single crystal. In the magnetic field generator in which the magnetic shield is not inserted, the magnetic flux density distribution on the X-axis is convex upward when the direction of the magnetic force line on the central axis in the horizontal plane including the coil axis of the superconducting coil is taken as the X-axis. When the magnetic flux density on the central axis in the horizontal plane is taken as the magnetic flux density set value, the magnetic flux density on the X-axis is 80% or less of the magnetic flux density set value on the crucible wall, and at the same time, the horizontal plane In the crucible wall, the magnetic flux density distribution on the Y-axis perpendicular to the X-axis and passing through the central axis is a downward convex distribution, and the magnetic flux density on the Y-axis is 140% or more of the magnetic flux density set value at the crucible wall. In the magnetic field generator, two pairs of superconducting coils are provided so that the respective coil axes are included in the same horizontal plane, and the coil axes are arranged in the same horizontal plane. 3. The apparatus for pulling a single crystal according to claim 1, wherein a central angle .alpha. The magnetic field generator when the magnetic shield is not inserted has four superconducting coils, and is arranged so that all the coil axes of the four superconducting coils are included in a single horizontal plane, When the direction of the line of magnetic force on the central axis in the horizontal plane is defined as the X-axis, two each of two The superconducting coils are arranged, and the four superconducting coils are arranged axisymmetrically with respect to the cross section. are arranged in an angle range of more than -30° and less than 30° with respect to the vertical Y-axis, and the directions of the magnetic lines of force generated by the four superconducting coils are symmetrical with respect to the cross section; 3. The apparatus for pulling a single crystal according to claim 1, wherein the two superconducting coils generate magnetic lines of force in opposite directions in each of the first region and the second region. 5. A single crystal pulling method, comprising pulling a semiconductor single crystal using the single crystal pulling apparatus according to any one of claims 1 to 4 .

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