JP2021046342A - Apparatus and method for pulling single crystal - Google Patents

Abstract

To provide an apparatus and method for pulling a single crystal, capable of suppressing a growth stripe in a single crystal to be grown to reduce oxygen concentration and obtaining even a single crystal having a high oxygen concentration.SOLUTION: The apparatus for pulling a single crystal comprising a pulling furnace including a crucible storing a semiconductor raw material and heating means for heating and melting the semiconductor raw material and a magnetic field generator including a superconducting coil arranged around the pulling furnace can apply a magnetic field so as to penetrate magnetic field lines into the molten semiconductor raw material in the crucible by energization to the superconducting coil to suppress the convection of the molten semiconductor raw material in the crucible. A magnetic shield can be selectively installed between the pulling furnace and the magnetic field generator, and the magnetic field generator can change a magnetic field line direction and a magnetic field distribution in a horizontal plane including the coil axis of the superconducting coil at the central axis of the pulling furnace by the magnetic shield.SELECTED DRAWING: Figure 1

Description

The present invention relates to a single crystal pulling device and a single crystal pulling method.

For semiconductors such as silicon and gallium arsenide, a single crystal ingod produced with high purity is sliced into a wafer shape, and a highly integrated circuit is formed on this wafer, which is used for computers from small to large size. It is used for memory and the like. By increasing the degree of integration of such a memory, the capacity of the memory is increased, the cost is reduced, and the performance is improved.

The Czochralski (CZ) method, which is conventionally known as one of the single crystal pulling methods for producing a single crystal satisfying the requirements of these semiconductors, will be described with reference to FIG.
The single crystal pulling device 100 of FIG. 3 is provided with a pulling furnace 101 whose upper surface can be opened and closed, and has a configuration in which a crucible 102 is built in the pulling furnace 101. A heater 103 for heating and melting the semiconductor raw material in the pit 102 is provided around the pit 102 inside the pulling furnace 101, and a pair of superconducting magnets is provided outside the pulling furnace 101 as shown in FIG. A superconducting magnet 130 having a coil 104 (104a, 104b) built in a refrigerant container (hereinafter, cylindrical refrigerant container) 105 as a cylindrical container is arranged.
The superconducting magnet 130 generates a magnetic field line 107 that is axisymmetric with respect to the center line 110 of the pulling furnace 101 and the vacuum vessel 119 (the position of the center line 110 is referred to as the magnetic field center).

In the production of a single crystal, the semiconductor raw material 106 is placed in the crucible 102 and heated by the heater 103 to melt the semiconductor raw material 106. A seed crystal (not shown) is lowered into the melt from above the central portion of the crucible 102 to land the liquid, and the seed crystal is pulled up in the pulling direction 108 at a predetermined speed by a pulling mechanism (not shown). As a result, crystals grow in the solid-liquid boundary layer, and single crystals are produced.
At this time, when the fluid motion of the molten liquid induced by the heating of the heater 103, that is, thermal convection occurs, the pulled-up molten liquid is disturbed and the yield of single crystal formation decreases.

Therefore, as a countermeasure, the superconducting coil 104 of the superconducting magnet 130 is used. That is, the semiconductor raw material 106 of the molten liquid receives an operation suppressing force by the magnetic field lines 107 generated by energizing the superconducting coil 104, and the growing single crystal slowly grows as the seed crystal is pulled up without convection in the crucible 102. It is pulled upward and is manufactured as a solid single crystal 109. Although not shown, a pulling mechanism for pulling the single crystal 109 along the crucible center line 110 is provided above the pulling furnace 101.

Next, an example of the superconducting magnet 130 used in the single crystal pulling device 100 shown in FIG. 3 will be described with reference to FIG. The superconducting magnet 130 has a configuration in which superconducting coils 104 (104a, 104b) are housed in a cylindrical vacuum container 119 via a cylindrical refrigerant container. In the superconducting magnet 130, a pair of superconducting coils 104a and 104b facing each other via a central portion in the vacuum vessel 119 are housed. These pairs 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. 3, with respect to the center line 110 of the pulling furnace 101 and the vacuum vessel 119. The axially symmetric magnetic field lines 107 are generated (the position of the center line 110 is referred to as the magnetic field center).

As shown in FIGS. 3 and 4, the superconducting magnet 130 includes a current lead 111 that introduces a current into the two superconducting coils 104a and 104b, a first radiation shield 117 housed inside the cylindrical refrigerant container 105, and the like. A small helium refrigerator 112 for cooling the second radiation shield 118, a gas discharge pipe 113 for discharging helium gas in the cylindrical refrigerant container 105, a service port 114 having a supply port for replenishing liquid helium, and the like are provided. There is. The pulling furnace 101 shown in FIG. 3 is arranged in the bore 115 of such a superconducting magnet 130.

FIG. 5 shows the magnetic field distribution of the conventional superconducting magnet 130 described above. As shown in FIG. 4, in the conventional superconducting magnet 130, since a pair of superconducting coils 104a and 104b facing each other are arranged, they are directed to both sides in each coil arrangement direction (X direction in FIG. 5). The magnetic field gradually increases, and in the direction orthogonal to this (Y direction in FIG. 5), the magnetic field gradually decreases in the vertical direction. In such a conventional configuration, as shown in FIG. 4, the magnetic field gradient in the range within the bore 115 is too large, so that the thermal convection inhibition generated in the molten semiconductor raw material is imbalanced and the magnetic field efficiency is poor. That is, as shown by diagonal lines in the region of the same magnetic flux density in FIG. 5, the magnetic field uniformity is not good in the region near the central magnetic field (that is, in FIG. 5, 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 up.

Therefore, in order to solve the above problems, as shown in FIGS. 6A and 6B, the number of superconducting coils 104 is set to 4 or more (for example, 4 of 104a, 104b, 104c, 104d). , The center of each superconducting coil is arranged on a flat surface in a tubular container coaxially provided around the pulling furnace, and the arranged superconducting coils are oriented so as to face each other via the axis of the tubular container. The arrangement angle θ (see FIG. 6B) in which a pair of superconducting coils adjacent to each other is set and faces the inside of the tubular container is in the range of 100 degrees to 130 degrees (that is, that is). It is disclosed that the center angle α (see FIG. 6B) between the coil axes adjacent to each other across the X axis is set to 50 to 80 degrees (Patent Document 1).
As a result, a lateral magnetic field with a small magnetic field gradient and good uniformity can be generated inside the bore 115, and a concentric or square magnetic field distribution can be generated on a plane, resulting in a large unbalanced electromagnetic force. It is said that it can be suppressed. Further, as a result, the uniform magnetic field region in the pulling direction is improved, the magnetic field in the transverse magnetic field direction becomes substantially horizontal, and the imbalanced electromagnetic force is suppressed, so that a high-quality single crystal can be produced.
Further, it is also disclosed that according to this single crystal pulling method, a high quality single crystal is pulled up with a high yield.

That is, the arrangement angles θ of the superconducting coils 104a, 104b, 104c, and 104d in FIG. 6 are 100 degrees, 110 degrees, 115 degrees, 120 degrees, and 130 degrees, respectively (that is, the center angles α between the coil axes are 80, respectively. In FIGS. 7 to 11 showing the magnetic field distribution in the case of degrees, 70 degrees, 65 degrees, 60 degrees, and 50 degrees), the central magnetic field is uniformly arranged over a sufficiently wide region. On the other hand, as shown in FIG. 12, when the arrangement angle θ is as small as 90 degrees (the center angle α between the coil axes is 90 degrees), the width of the central magnetic field in the Y direction becomes extremely narrow, and FIG. As shown in 13, when the arrangement angle θ is as large as 140 degrees (the center 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 130 of FIG. 6, it is said that a concentric or square evenly distributed magnetic field can be obtained inside the bore 115 by setting the arrangement angle θ in the range of 100 degrees to 130 degrees. ..

However, even if the magnetic field distribution is uniform as shown in FIGS. 7 to 11, in a transverse magnetic field in which the magnetic field lines on the central axis 110 are directed in the X-axis direction, the cross section is parallel to the X-axis and the cross-section is perpendicular to the X-axis. It discloses that there is a difference in heat convection between the inside and the inside (Patent Document 2).
This tendency was the same in the technique disclosed in Patent Document 1 in which a uniform magnetic field distribution was formed by four coils (however, the center angle α between the coil shafts was 60 degrees), but included the coil shafts of the superconducting coils. When the direction of the magnetic field lines 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.

Further, when the magnetic flux density in the central axis in the horizontal plane is set 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 in the wall, and at the same time, the magnetic flux density in the horizontal plane is described. The magnetic flux density distribution on the Y-axis that is orthogonal to the X-axis and passes through the central axis is a downwardly convex distribution, and the magnetic flux density on the Y-axis is 140% or more of the magnetic flux density set value on the wall. I am trying to generate a magnetic field distribution.

According to such a configuration, the flow velocity of the molten semiconductor raw material can be reduced and parallel to the X axis of the molten semiconductor raw material even in a cross section perpendicular to the X axis in which the convection suppression force due to the electromagnetic force is insufficient. The flow velocity in the cross section and the flow velocity in the cross section perpendicular to the X axis of the molten semiconductor raw material can be balanced. Even within the cross section perpendicular to the X-axis, by reducing the flow velocity of the molten semiconductor raw material, it takes longer for oxygen eluted from the quartz wall to reach the single crystal, and from the free surface of the molten semiconductor raw material. By increasing the amount of oxygen evaporated from the single crystal, the oxygen concentration taken into the single crystal can be significantly reduced.

However, such ultra-low oxygen crystals are limited to power device and image sensor applications, and crystals having an oxygen concentration of at least 10 ppma-JEIDA are required for other logic applications such as memory and CPU. Therefore, it is desirable that both ultra-low oxygen crystals and high oxygen crystals can be produced by the same pulling device.

For example, in Patent Document 3, in the magnetic field generator shown in Patent Document 2, an extremely low oxygen crystal can be obtained by making it possible to change the direction of the current flowing through one pair of coils among two pairs of coils. A single crystal pulling device capable of switching between a magnetic field distribution to be generated and a magnetic field distribution to be a high oxygen crystal is disclosed.

However, if the direction of the current flowing through the coil is changed, the direction of the force received by the coil also changes. Therefore, it is necessary to make the structure that restrains the coil correspond to the two types of force directions. Furthermore, in the case of superconducting magnets, it is known that if the superconducting wire moves even slightly, Joule heat is generated due to friction, causing quenching. If the above is switched, the direction of the force received by the superconducting wire is reversed, and the position is likely to shift, which has an adverse effect of easily causing quenching.

Japanese Unexamined Patent Publication No. 2004-051475 Patent No. 6436031 JP-A-2017-206396

The present invention has been made in view of the above-mentioned problems, and is a single crystal pulling device capable of reducing the oxygen concentration in the growing single crystal and suppressing growth fringes in the growing single crystal, and a single crystal pulling device. It is an object of the present invention to provide a crystal pulling method, a single crystal pulling device capable of obtaining a single crystal having a high oxygen concentration by a simple method in the same pulling device, and a single crystal pulling method.

In order to achieve the above object, the present invention comprises a crucible containing a semiconductor raw material, a pulling furnace provided with a heating means for heating and melting the single crystal raw material, and a superconducting coil around the pulling furnace. A magnetic field generator is provided, and by energizing the superconducting coil, a magnetic field is applied so that the magnetic field lines penetrate the molten semiconductor raw material in the crucible, and convection of the molten semiconductor raw material in the crucible. It is a single crystal pulling device that suppresses
A magnetic shield that can be selectively installed is provided between the pulling furnace and the magnetic field generator, and the magnetic field generating device of the pulling furnace in a horizontal plane including the coil shaft of the superconducting coil by the magnetic shield. Provided is a single crystal pulling device characterized in that the direction of magnetic field lines and the magnetic field distribution on the central axis can be changed.

By selectively installing a magnetic shield between the pulling furnace and the magnetic field generator in this way, the magnetic field line direction and the magnetic field distribution in the central axis of the pulling furnace in the horizontal plane including the coil shaft of the superconducting coil can be obtained. It can be changed easily.

Further, the magnetic shield can be changed in shape and arrangement so that the direction of the magnetic field lines and the magnetic field distribution can be changed.

In this way, by changing the shape and arrangement position of the magnetic shield between the pulling furnace and the magnetic field generator, the magnetic field line direction and the magnetic field distribution can be changed more finely.

Further, when the magnetic shield is not installed between the pulling furnace and the magnetic field generating device, the magnetic field line direction in the central axis of the pulling furnace in the horizontal plane including the coil shaft of the superconducting coil. Is assumed to be the X-axis, and the magnetic flux density distribution on the X-axis can be an upwardly convex distribution.

When the magnetic shield is not installed between the pulling furnace and the magnetic field generator in this way, the magnetic flux density distribution as described above can be obtained.

Further, when the magnetic flux density in the central axis of the pulling furnace in the horizontal plane including the coil shaft of the superconducting coil is set as the magnetic flux density set value, the magnetic field generator raises the pulling in the horizontal plane including the coil shaft of the superconducting coil. When the magnetic field line direction on the central axis of the furnace is the X-axis, the magnetic flux density on the X-axis is 80% or less of the magnetic flux density set value on the wall, and at the same time, it is orthogonal to the X-axis in the horizontal plane and the center. It is assumed that the magnetic flux density distribution on the Y-axis passing through the axis is a downwardly convex distribution, and the magnetic flux density on the Y-axis is 140% or more of the magnetic flux density set value on the wall of the wall to generate a magnetic field distribution. be able to.

Anything that generates such a magnetic field distribution can have a more uniform magnetic field distribution.

Further, in the present invention, the magnetic field generator is provided with two pairs of superconducting coils arranged opposite to each other so that the coil shafts are included in the same horizontal plane, and the magnetic field generator is provided in the horizontal plane including the coil shafts of the superconducting coils. When the direction of the magnetic field lines in the central axis of the pulling furnace is the X-axis, it can be assumed that the central angle α sandwiching the X-axis of each coil is 100 degrees or more and 120 degrees or less.

With such a single crystal pulling device, when the magnetic shield is not inserted, the oxygen concentration of the growing single crystal can be significantly reduced, and the growth fringes in the growing single crystal can be suppressed.

At this time, the magnetic shield can be attached and detached between the pulling furnace and the magnetic field generator, and by simply installing the magnetic shield or changing the shape and arrangement of the magnetic shield. It can be assumed that the oxygen concentration in the crystal can be controlled.

In such a single crystal pulling device, when the direction of the magnetic field line is the X-axis, the direction in which the convective inhibition force due to the electromagnetic force in the cross section perpendicular to the X-axis is weakened depending on the installation of the magnetic shield and its shape. It is possible to change to. By weakening the convection suppression force, it becomes difficult to reduce the flow velocity of the molten raw material melt, so that the time it takes for oxygen eluted from the crucible wall to reach a single crystal is shortened, and the molten semiconductor raw material is released from the free surface. By reducing the amount of oxygen evaporation, it is possible to obtain a single crystal pulling device capable of increasing the oxygen concentration taken into the single crystal.

Further, the magnetic shield can be a permalloy having a larger relative magnetic permeability than iron.

In this way, since the effect of the magnetic shield depends on the magnetic permeability, if a permalloy (specific magnetic permeability 80,000) or the like having a specific magnetic permeability larger than Fe (specific magnetic permeability 4,000) is used, the thickness is 2 mm. The same effect can be obtained even with a moderate wall thickness, and the weight can be reduced, so that the material can be easily removed.

Further, the semiconductor single crystal can be pulled up by using the single crystal pulling device.

As described above, by using the apparatus of the present invention, even if the oxygen concentration of the single crystal to be produced is different, the single crystal can be produced by the same production apparatus by selecting whether or not the magnetic shield is installed and the shape of the magnetic shield to be installed. Can be manufactured.

With the single crystal pulling device and the single crystal pulling method of the present invention, it is possible to grow a semiconductor single crystal in which the oxygen concentration taken in is significantly reduced and growth fringes are suppressed, and the semiconductor single crystal is taken in using the same pulling device. A semiconductor single crystal having an increased oxygen concentration can also be easily grown.

It is the schematic sectional drawing which shows an example of the single crystal pulling apparatus of this invention. It is a schematic schematic top view which shows an example of the single crystal pulling apparatus shown in FIG. It is the schematic sectional drawing which shows an example of the conventional single crystal pulling apparatus. It is a schematic perspective view which shows an example of a superconducting magnet. It is a figure which shows the conventional magnetic flux density distribution. It is a schematic perspective view and the schematic cross-sectional view which shows the superconducting magnet of Patent Document 1. FIG. It is a figure which shows the magnetic flux density distribution when the arrangement angle θ = 100 degrees. It is a figure which shows the magnetic flux density distribution when the arrangement angle θ = 110 degrees. It is a figure which shows the magnetic flux density distribution when the arrangement angle θ = 115 degrees. It is a figure which shows the magnetic flux density distribution when the arrangement angle θ = 120 degrees. It is a figure which shows the magnetic flux density distribution when the arrangement angle θ = 130 degrees. It is a figure which shows the magnetic flux density distribution when the arrangement angle θ = 90 degrees. It is a figure which shows the magnetic flux density distribution when the arrangement angle θ = 140 degrees. It is a figure which shows the magnetic flux density distribution when the magnetic shield is not installed between a magnetic field generator and a pulling furnace. FIG. 14A is a diagram showing a magnetic field line vector. It is a figure which shows the magnetic flux density distribution when a magnetic shield is installed between a magnetic field generator and a pulling furnace (Example 1). FIG. 15A is a diagram showing a magnetic field line vector. It is a figure which shows the magnetic flux density distribution when the magnetic shield is installed between the magnetic field generator and the pulling furnace, and the arrangement position is changed (Example 2). FIG. 16A is a diagram showing a magnetic field line vector.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.
As described above, in the single crystal pulling device by the Czochralski method, the fluid motion of the melt of the semiconductor raw material induced by heating of the heater, that is, the melt pulled by heat convection is disturbed, and the yield of single crystal formation is increased. In order to overcome the decrease, superconducting coils are arranged so as to sandwich the furnace, and by energizing the superconducting coils, magnetic field lines that pass through the semiconductor raw material in the furnace are generated, and the semiconductor raw material receives an operation restraining force by these magnetic field lines. , Single crystals that grow with the pulling of seed crystals have come to be produced without convection in the furnace.

However, depending on how the superconducting coils are arranged and the number of arrangements, the magnetic field gradient in the furnace may be too large and the suppression of heat convection generated in the molten single crystal raw material may become unbalanced. By improving the region and suppressing the unbalanced electromagnetic force, it has become possible to produce high-quality single crystals.

Nevertheless, in the magnetic field in the axial direction in which the lines of magnetic force are directed, there is a difference in thermal convection between the cross section parallel to the axis and the cross section perpendicular to the axis, and the magnetic flux density is determined in order to overcome the difference in thermal convection. By setting the magnetic flux density setting value to generate a magnetic field distribution, the flow velocity in the direction in which the convection suppression force by the electromagnetic force was insufficient is adjusted, and the oxygen eluted from the quartz wall reaches the single crystal. By adjusting the time to increase the amount of oxygen evaporated from the free surface of the molten semiconductor raw material, it has become possible to significantly reduce the oxygen concentration taken into the single crystal.

By the way, depending on the application, crystals having different oxygen concentrations of single crystals are required, and it is desirable that both ultra-low oxygen crystals and high oxygen crystals can be produced by the same pulling device. By making it possible to change the direction of the current flowing through a pair of coils in a certain coil, a single crystal that can be generated by switching between a magnetic field distribution in which an extremely low oxygen crystal is obtained and a magnetic field distribution in which a high oxygen crystal is obtained. A pulling device was proposed.

However, if the direction of the current flowing through the coil is changed, the direction of the force received by the superconducting wire is reversed, and the position is likely to shift, so that there is an adverse effect that quenching is likely to occur.

In order to solve the above problems, the present inventor has a single crystal pulling device capable of reducing the oxygen concentration in the growing single crystal and suppressing growth fringes in the growing single crystal, and a single crystal pulling device. The present invention has been completed as a result of studying a single crystal pulling device capable of obtaining a single crystal having a high oxygen concentration by a simple method and a single crystal pulling method in the same pulling device.

That is, the present invention is a pulling furnace provided with a pit containing a semiconductor raw material, a heating means for heating and melting the semiconductor raw material, and a magnetic field generator in which a superconducting coil is arranged around the pulling furnace. A single crystal pulling device that suppresses convection of the molten semiconductor raw material in the pit by applying a magnetic field so that the magnetic field lines penetrate the molten semiconductor raw material in the pit by energizing the superconducting coil. A magnetic shield that can be selectively installed is provided between the pulling furnace and the magnetic field generator, and the magnetic field generator is provided by the magnetic shield in a horizontal plane including the coil shaft of the superconducting coil. It is a single crystal pulling device characterized in that the magnetic field line direction and the magnetic field distribution on the central axis of the pulling furnace can be changed.

FIG. 1 shows an example of the single crystal pulling device 1 of the present invention.
The single crystal pulling device 1 is provided with a pulling furnace 2 whose upper surface can be opened and closed, and has a configuration in which a crucible 3 is built in the pulling furnace 2. A heater 4 for heating and melting the semiconductor raw material 11 in the pit 3 is provided around the pit 3 inside the pulling furnace 2, and a pair of superconducting coils 5 (5a, 5a,) outside the pulling furnace 2. A superconducting magnet 7 having 5b) built in a refrigerant container (hereinafter, cylindrical refrigerant container) 6 as a cylindrical container is arranged. The superconducting magnet 7 generates a magnetic field line 10 that is axisymmetric with respect to the central axis 9 of the pulling furnace 2 and the vacuum vessel 8 (the position of the central axis 9 is referred to as the magnetic field center).

In the production of a single crystal, the semiconductor raw material 11 is placed in the crucible 3 and heated by the heater 4 to melt the semiconductor material 11. A seed crystal (not shown) is lowered into the melt from above the central portion of the crucible 3, for example, to land on the liquid, and the seed crystal is pulled up in the pulling direction 13 at a predetermined speed by a pulling mechanism (not shown). As a result, crystals grow in the solid-liquid boundary layer, and a single crystal 12 is produced.

A magnetic shield 20 that can be selectively installed is provided between the pulling furnace 2 and the superconducting magnet 7 that is the magnetic field generator, and the magnetic field generator is provided with the magnetic shield 20 by the superconducting coil 5. The direction of the magnetic field line and the magnetic field distribution in the central axis of the pulling furnace 2 in the horizontal plane including the coil shaft of the above can be changed.

Here, the shield 20 will be described. For example, iron having a wall thickness of 25 mm is used for the magnetic shield 20, and the magnetic shield 20 has a substantially arcuate cross section along the side surface of the magnet housing. However, the material of the magnetic shield 20 is not limited to iron. For example, permalloy, which has a higher relative magnetic permeability than iron, can be applied to the magnetic shield 20. This is because the effect of the magnetic shield 20 depends on the magnetic permeability, so if a permalloy (specific magnetic permeability 80,000) or the like having a specific magnetic permeability higher than Fe (specific magnetic permeability 4,000) is used, it is about 2 mm. The same effect can be obtained with the same wall thickness, and the weight can be reduced, so that it can be easily removed.
That is, as shown in FIG. 2, the magnetic shield 20 is arranged so as to sandwich the pulling furnace 2 so as to be symmetrical with, for example, the central axis of the pulling furnace 2. In the single crystal pulling device 1 of FIG. 2, four superconducting coils 5 are arranged around the pulling furnace 2, and a pair of superconducting coils 5 adjacent to each other have, for example, a center angle. The structure in which α is in the range of 100 degrees to 130 degrees is shown. Further, the magnetic shield 20 is removable and has a structure in which the arrangement position can be changed around the central axis of the pulling furnace 2.
Further, the shape of the shield 20 can be changed, and for example, a circumferential angle that defines a width dimension, that is, an arc surface length facing the side surface of the magnet inside the housing can be arbitrarily set. Thereby, for example, as is clear from FIG. 14a when the magnetic shield 20 is not installed, the magnetic field lines passing through the quartz crucible in the pulling furnace 2 can be suitably controlled.

When the magnetic shield 20 as described above is arranged, the magnetic field lines passing through the quartz crucible in the pulling furnace 2 change. Due to such a change in the magnetic field lines, the strong restraining force against the vertical natural convection of the melted semiconductor raw material is relaxed even in the cross section perpendicular to the magnetic force lines (see, for example, FIG. 2).
Therefore, the direction of the magnetic field lines and the magnetic field distribution can be controlled by changing the presence / absence, shape, and arrangement of the magnetic shield 20. Therefore, the oxygen concentration in the single crystal grown by the same single crystal pulling device can be freely controlled from low oxygen to high oxygen.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.
(Comparison example)
A magnetic field analysis was performed using the magnetic flux density distribution of Patent Document 2 and the magnetic field line vector ANSYS-Maxwell-3D. The number of coil turns x the current value was adjusted so that the magnetic flux density at the center of the magnetic field was 1000 Gauss.
FIG. 14 (a) shows the magnetic flux density distribution, and FIG. 14 (b) shows the magnetic flux density distribution with the addition of a magnetic field line vector.
In the figure, the circles indicate the outer diameter of the quartz crucible having a diameter of 32 inches (800 mm), and the representative magnetic field lines in the circles are indicated by black arrows.
In the state where the magnetic shield 20 is not inserted between the magnetic field generator and the puller in this way, the magnetic flux density distribution on the X-axis, which is the direction of the magnetic field lines on the central axis, becomes an upwardly convex distribution, and the X in the horizontal plane. The magnetic flux density distribution on the Y-axis that is orthogonal to the axis and passes through the central axis is a downwardly convex distribution.
It can also be seen that the lines of magnetic force are greatly curved near the crucible. Due to such lines of magnetic force, a strong restraining force against natural convection in the vertical direction is generated even in a cross section perpendicular to the lines of magnetic force.

(Example 1)
Magnetic shield 60 degrees x 2 places, Fe (t25mm)
A magnetic shield 20 having a circumferential angle of 60 degrees was placed inside a pair of coils in the lower left and upper right. As a result, the magnetic fields generated by the upper left and lower right coils without a shield became dominant, the magnetic flux density changed asymmetrically, and the X axis, which is the direction of the magnetic field lines on the central axis, changed in the lower right direction. Also, looking at the lines of magnetic force near the crucible, the degree of curvature of the lines of magnetic force is small, especially on the right side of the X-axis, so the force of suppressing natural convection in the cross section perpendicular to the lines of magnetic force is weaker than in the comparative example. Can be seen (FIG. 15 (a), FIG. 15 (b)).
In this embodiment, iron having a wall thickness of 25 mm is used for the magnetic shield 20, the shape is formed along the inner diameter of the housing of the magnet, and the magnetic shield 20 is placed on the support portion at the lower part of the housing by using a hoist crane.
Since the magnetic shield 20 is a ferromagnetic material, it is fixed so as to be attracted to the magnet when a magnetic field is generated, but since the coercive force is not large, it can be removed by a crane if the magnetic field is not generated.

(Example 2)
Magnetic shield 90 degrees x 2 places, Fe (t25mm)
A magnetic shield 20 having a circumferential angle of 90 degrees was also placed inside a pair of coils in the lower left and upper right. The X-axis in the direction of the magnetic field lines on the central axis rotates further to the lower right than in the first embodiment, and the curvature of the magnetic force lines on the right side of the X-axis is further smaller than that in the first embodiment (FIG. 16 (a)). , FIG. 16 (b)).

For each of the above-mentioned Comparative Example and Examples 1 and 2, the silicon single crystal was pulled up under the following conditions, and the oxygen concentration in the vicinity of the straight cylinder 40 cm was compared.

Crucible used: 800 mm in diameter
Charge amount of single crystal material: 400 kg
Single crystal to grow: 306 mm in diameter
Single crystal straight body length: 40 cm
Magnetic flux density: Adjusted to center 1000G without magnetic shield Single crystal rotation speed: 6rpm
Crucible rotation speed: 0.03 rpm

Under the conditions of the comparative example, the magnetic flux density on the central axis is the highest, and the oxygen in the crystal is also the lowest. In Example 1, the central magnetic field decreased to 820 G, but the oxygen concentration tended to increase, and in Example 2, the magnetic flux density was comparable to that of Comparative Example, and the oxygen concentration in the crystal increased to 10 ppma or more.
In this example, a magnetic shield 20 made of Fe having a wall thickness of 25 mm was used, but since the effect of the magnetic shield 20 depends on the magnetic permeability, the relative magnetic permeability is higher than that of Fe (specific magnetic permeability 4,000). If a permalloy (specific magnetic permeability 80,000) or the like having a large magnetic permeability is used, the same effect can be obtained even with a wall thickness of about 2 mm, the weight can be reduced, and the removal can be performed more easily.
In this way, even if the oxygen concentration of the single crystal to be manufactured is different, by selecting the presence or absence of the magnetic shield and the shape of the magnetic shield to be installed, the single crystal having a different oxygen concentration can be manufactured by the same manufacturing apparatus. Is possible.

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

1 ... Single crystal pulling device, 2 ... Pulling furnace, 3 ... 坩 堝, 4 ... Heater, 5 ... Superconducting coil, 6 ... Cylindrical refrigerant container, 7 ... Superconducting magnet, 8 ... Vacuum container, 9 ... Central axis, 10 ... Magnetic line , 11 ... Semiconductor raw material, 12 ... Single crystal, 13 ... Pulling direction, 20 ... Magnetic shield.

Claims (8)

The crucible containing the semiconductor raw material, a pulling furnace provided with a heating means for heating and melting the semiconductor raw material, and a magnetic field generator in which a superconducting coil is arranged around the pulling furnace are provided. A single crystal pulling device that suppresses convection of the molten semiconductor raw material in the crucible by applying a magnetic field so that the magnetic field lines penetrate the molten semiconductor raw material in the crucible by energizing the coil.
A magnetic shield that can be selectively installed is provided between the pulling furnace and the magnetic field generator, and the magnetic field generating device of the pulling furnace in a horizontal plane including the coil shaft of the superconducting coil by the magnetic shield. A single crystal pulling device characterized in that the direction of magnetic field lines and the magnetic field distribution on the central axis can be changed. The single crystal pulling device according to claim 1, wherein the magnetic shield can change the direction of the magnetic field lines and the magnetic field distribution so that the shape and arrangement can be changed. When the magnetic field generator is set so that the magnetic shield is not installed between the pulling furnace and the magnetic field generator, the magnetic field line direction in the central axis of the pulling furnace in the horizontal plane including the coil shaft of the superconducting coil is X. The single crystal pulling device according to claim 1 or 2, wherein the magnetic flux density distribution on the X-axis has an upwardly convex distribution when used as an axis. When the magnetic flux density at the central axis of the pulling furnace in the horizontal plane including the coil shaft of the superconducting coil is set as the magnetic flux density set value, the magnetic field generator of the pulling furnace in the horizontal plane including the coil shaft of the superconducting coil. When the direction of the magnetic field line on the central axis is the X-axis, the magnetic flux density on the X-axis is 80% or less of the magnetic flux density set value on the wall, and at the same time, the central axis is orthogonal to the X-axis in the horizontal plane. The magnetic flux density distribution on the Y-axis passing through is a downwardly convex distribution, and the magnetic flux density on the Y-axis generates a magnetic field distribution that is 140% or more of the magnetic flux density set value at the wall. The single crystal pulling device according to any one of claims 1 to 3, wherein the single crystal pulling device is characterized. The magnetic field generator is provided with two pairs of superconducting coils arranged opposite to each other so that their coil shafts are contained in the same horizontal plane, and the central shaft of the pulling furnace in the horizontal plane including the coil shafts of the superconducting coils. Any of claims 1 to 4, wherein the central angle α of each coil sandwiching the X-axis is 100 degrees or more and 120 degrees or less when the direction of the magnetic field lines in the above is taken as the X-axis. The single crystal pulling device according to item 1. The magnetic shield can be attached and detached between the pulling furnace and the magnetic field generator, and can be formed in a single crystal depending on whether or not the magnetic shield is installed or by changing the shape and arrangement of the magnetic shield. The single crystal pulling device according to any one of claims 1 to 5, wherein the oxygen concentration can be controlled. The single crystal pulling device according to any one of claims 1 to 6, wherein the magnetic shield is a permalloy having a large relative magnetic permeability as compared with iron. A method for pulling a single crystal, which comprises pulling a semiconductor single crystal by using the single crystal pulling device according to any one of claims 1 to 7.

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