WO2017199536A1

WO2017199536A1 - Single crystal pulling device and single crystal pulling method

Info

Publication number: WO2017199536A1
Application number: PCT/JP2017/008434
Authority: WO
Inventors: 清隆高野; 孝世菅原; 友彦太田; 雅彦浦野
Original assignee: 信越半導体株式会社
Priority date: 2016-05-16
Filing date: 2017-03-03
Publication date: 2017-11-23
Also published as: JP2017206396A; JP6620670B2

Abstract

The present invention is a single crystal pulling device that includes: a pulling furnace which has, disposed therein, a heater and a crucible that stores molten single crystal starting material, and has a central axis; and a magnetic field generating device which is provided around the pulling furnace and has a superconductive coil. The single crystal pulling device applies a horizontal magnetic field to the single crystal starting material melted by the energization of the superconductive coil, and suppresses convection in the molten single crystal starting material in the crucible. The magnetic field generating device is capable of generating, in turn, two types of magnetic fields which have different directions of magnetic force lines in the central axis in a horizontal plane that includes a coil axis of the superconductive coil and have different magnetic field distributions. Thus, a single crystal pulling device is provided which is capable of reducing the oxygen concentration in the single crystal to be grown and of suppressing growth striation in the single crystal to be grown, and which is capable of obtaining, with the same pulling device, a single crystal with a high oxygen concentration by a simple method.

Description

Single crystal pulling apparatus and single crystal pulling method

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 a single crystal and are used for memory of computers ranging from small to large, and there is a demand for large capacity, low cost, and high quality storage devices.

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

An example of a conventional single crystal pulling apparatus using the MCZ method will be described with reference to FIG. A single crystal pulling apparatus 100 of FIG. 21 includes a pulling furnace 101 whose upper surface can be opened and closed, and has a structure in which a crucible 102 is built in the pulling furnace 101. A heater 103 for heating and melting the semiconductor raw material 106 in the crucible 102 is provided around the crucible 102 inside the pulling furnace 101, and a pair of superconducting coils 104 (104 a, 104 a, A superconducting magnet 130 in which 104b) is built in a refrigerant container (hereinafter referred to as a cylindrical refrigerant container) 105 as a cylindrical container is disposed.

In manufacturing the single crystal, the semiconductor raw material 106 is put in the crucible 102 and heated by the heater 103 to melt the semiconductor raw material 106. For example, a seed crystal (not shown) descends from the upper part of the center of the crucible 102 into the molten liquid, and the seed crystal is pulled up in a pulling direction 108 at a predetermined speed by a pulling mechanism (not shown). Thereby, a crystal grows in the solid / liquid boundary layer, and a single crystal is generated. At this time, when a fluid motion of the melt induced by the heating of the heater 103, that is, thermal convection occurs, the melt that is pulled up 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 is subjected to an operation deterring force due to the magnetic lines 107 generated by energizing the superconducting coil 104, and the grown single crystal slowly grows as the seed crystal is pulled up without convection in the crucible 102. It is pulled upward and manufactured as a solid single crystal 109. A pulling mechanism for pulling the single crystal 109 along the central axis 110 of the crucible is provided above the pulling furnace 101, although not shown.

Next, an example of the superconducting magnet 130 used in the single crystal pulling apparatus 100 shown in FIG. 21 will be described with reference to FIG. 21 and 22, the same components are denoted by the same reference numerals. In addition, in order to make the drawings easy to see, the constituent elements are appropriately omitted in the respective drawings. The superconducting magnet 130 is configured such that a superconducting coil 104 (104a, 104b) is accommodated in a cylindrical vacuum vessel 119 via a cylindrical refrigerant vessel 105. In this superconducting magnet 130, a pair of

superconducting coils

104 a and 104 b facing each other through the central axis 110 in the vacuum vessel 119 are accommodated. The pair of

superconducting coils

104a and 104b is a Helmholtz type magnetic field coil that generates a magnetic field along the same horizontal direction. As shown in FIG. 21, the pulling furnace 101 and the central axis 110 of the vacuum vessel 119 are arranged. Magnetic field lines 107 that are perpendicular to the horizontal axis are generated (the position of the central axis 110 is referred to as the magnetic field center).

21 and 22, the superconducting magnet 130 includes a current lead 111 for introducing current into the two

superconducting coils

104a and 104b, a first radiation shield 117 housed in the cylindrical refrigerant container 105, and 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 supplying liquid helium, and the like are provided. Yes. The pulling furnace 101 shown in FIG. 21 is disposed in the bore 115 (the inner diameter is D) of the superconducting magnet 130.

FIG. 23 shows the magnetic field distribution of the conventional superconducting magnet 130 described above. As shown in FIG. 22, in the conventional superconducting magnet 130, a pair of

superconducting coils

104 a and 104 b facing each other are arranged, so that each coil arrangement direction (X direction in FIG. 23) faces both sides. The magnetic field gradually increases, and in the direction perpendicular to this (Y direction in FIG. 23), the magnetic field gradually decreases in the vertical direction. In such a conventional configuration, as shown in FIG. 23, since the magnetic field gradient in the bore 115 is too large, the thermal convection suppression generated in the molten single crystal raw material is unbalanced, and the magnetic field efficiency is poor. . That is, as shown by the hatched area in FIG. 23, the magnetic field uniformity is not good in the vicinity of the central magnetic field (that is, in FIG. 23, the cross is elongated in the vertical and horizontal directions). Therefore, there is a problem that the effect of suppressing thermal convection is low and a high quality single crystal cannot be pulled up.

In Patent Document 1, in order to solve the above-described problem, the number of superconducting coils 104 is four or more (for example, 104a, 104b, 104c, 104d, as shown in FIGS. 24 (a) and 24 (b)). 4) and arranged on a plane in a cylindrical vessel coaxially provided around the pulling furnace, and each superconducting coil arranged in the plane is set to face each other through the axis of the cylindrical vessel. In addition, an arrangement angle θ (see FIG. 24B) in which one pair of superconducting coils adjacent to each other faces the inside of the cylindrical container is in the range of 100 degrees to 130 degrees (that is, the X axis is sandwiched) The center angle α between adjacent coil axes (see FIG. 24B) is set to 50 to 80 degrees. As a result, a uniform horizontal magnetic field with a small magnetic field gradient can be generated inside the bore 115, and a concentric or square magnetic field distribution can be generated on the plane, greatly increasing the unbalanced electromagnetic force. As a result, the uniform magnetic field region in the pulling direction is improved, and the magnetic field lines in the transverse magnetic field direction are almost horizontal. It is also disclosed that manufacturing can be realized, and further, according to this single crystal pulling method, a high quality single crystal can be pulled with a good yield. In addition, the same code | symbol was attached | subjected about the component equivalent to the component shown in FIG. 21, 22 among the components in FIG. 24 (a), (b). In FIG. 24B, d is the inner diameter of the coil, and l is the distance between the opposing coils.

That is, the arrangement angles θ of the

superconducting coils

104a, 104b, 104c, and 104d in FIG. 24 are respectively 100 degrees, 110 degrees, 115 degrees, 120 degrees, and 130 degrees (that is, the center angle α between the coil axes is 80 degrees, respectively). In FIG. 25 to FIG. 29 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. 30, when the arrangement angle θ is as small as 90 degrees (the central angle α between the coil axes is 90 degrees), the width of the central magnetic field in the Y direction becomes extremely narrow. As shown in FIG. 31, 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. 24, it is said that a concentric or square uniform magnetic field can be obtained in the bore 115 by setting the arrangement angle θ in the range of 100 degrees to 130 degrees. .

JP 2004-051475 A

However, as a result of the study by the present inventors, even if the magnetic field distribution is uniform as shown in FIGS. 25 to 29, the magnetic field lines in the central axis 110 (that is, the X axis and Y axis shown in FIGS. In a transverse magnetic field in which the magnetic field lines at the intersections of the axes are directed in the X-axis direction, there is a difference in thermal convection between the cross section parallel to the X axis and the cross section perpendicular to the X axis. It became clear by comprehensive heat transfer analysis.

FIG. 19 shows the result of analyzing the state of crystal pulling by the conventional technique using the two coils shown in FIGS. 21 and 22, and the left side in the figure is parallel to the direction of the magnetic force line in the central axis 110 (that is, the X axis). The right side shows the flow velocity distribution in the cross section perpendicular to the X axis (that is, the cross section parallel to the Y axis). Thus, by applying a magnetic field to the raw material melt, convection is suppressed, and in particular, there is almost no flow in the lower half of the raw material melt, but a flow field remains in the upper half. When the conductive fluid moves in a magnetic field, an induced current is generated in the direction perpendicular to the magnetic force line and the velocity component perpendicular to the magnetic force line. However, when an electrically insulating quartz crucible is used, the crucible wall and the raw material fusion are generated. Since the free surface of the liquid becomes an insulating wall, no induced current flows in the direction perpendicular to these. For this reason, the convection suppressing force due to electromagnetic force is weak at the upper part of the raw material melt, and the left side (in the cross section parallel to the X axis) and the right side (in the cross section perpendicular to the X axis) of FIG. It can be seen that the convection is stronger in the cross section perpendicular to the X axis (in the cross section perpendicular to the magnetic field lines) than in the cross section parallel to the X axis (in the cross section parallel to the magnetic force lines).

On the other hand, the single crystal pulling state is analyzed by the technique disclosed in Patent Document 1 in which a uniform magnetic field distribution is formed by the four coils shown in FIG. 24 (however, the central angle α between the coil axes is 60 degrees). In FIG. 20 showing the results, the difference in flow velocity between the left side (in the cross section parallel to the X axis) and the right side (in the cross section perpendicular to the X axis) is slightly smaller than that in FIG. The flow velocity distribution is uneven in the direction.

Here, the analysis results shown in FIGS. 19 and 20 are obtained by simulation analysis of a state where the pulling is performed using the following single crystal pulling conditions using FEMAG-TMF as analysis software.
Used crucible: Diameter 800mm
Single crystal raw material charge: 400kg
Single crystal to grow: Diameter 306mm
Length of straight body of single crystal: 40cm
Magnetic flux density: Adjusted to be 3000 G at the central axis 110 in the horizontal plane including the coil axis. Single crystal rotation speed: 6 rpm
Crucible rotation speed: 0.03 rpm
In addition, the speed displayed in FIGS. 19 and 20 is the speed in the cross section, and the circumferential speed is excluded.

19 and 20, in the prior art and the technique disclosed in Patent Document 1, the flow field from the crucible wall to the growth interface remains in the cross section perpendicular to the X axis. Since the dissolved oxygen reaches the crystal, there is a limit to the effect of lowering the oxygen concentration by applying a horizontal magnetic field, meeting the extremely low oxygen concentration demands of semiconductor crystals for power devices and image sensors, which have recently been increasing in demand. There is a problem that has become difficult. In addition, the presence of a non-uniform flow field in the circumferential direction of the crucible causes growth fringes in a single crystal that is pulled up while rotating the single crystal, and when the cross section parallel to the growth direction is evaluated, Since fluctuations in resistivity and oxygen concentration are observed, there is also a problem that a ring-shaped distribution occurs in the wafer plane sliced perpendicular to the growth direction. However, such ultra-low oxygen crystals are limited to power devices and image sensor applications, and crystals having an oxygen concentration of 10 ppma-JEIDA or higher are required for other memory and CPU logic applications. Therefore, it is desirable that both the extremely low oxygen crystal and the high oxygen crystal can be manufactured with the same pulling apparatus.

The present invention has been made in view of the above problems, and can reduce the oxygen concentration in the single crystal to be grown and can suppress the growth stripes in the single crystal to be grown. An object of the present invention is to provide a single crystal pulling apparatus and a single crystal pulling method capable of obtaining a single crystal having a high oxygen concentration by a simple method.

In order to achieve the above object, in the present invention, a heating furnace and a crucible in which a molten single crystal raw material is accommodated are arranged, a pulling furnace having a central axis, and a magnetic field having a superconducting coil provided around the pulling furnace. A single crystal pulling apparatus that suppresses convection in the crucible by applying a horizontal magnetic field to the molten single crystal raw material by energizing the superconducting coil. The magnetic field generator can switch and generate two types of magnetic fields having different magnetic force line directions in the central axis in a horizontal plane including the coil axis of the superconducting coil and different magnetic field distributions. A single crystal pulling apparatus is provided.

With such a single crystal pulling apparatus, it is possible to reduce the oxygen concentration in the single crystal to be grown and to suppress the growth stripes in the single crystal to be grown. High single crystals can also be obtained.

In addition, it is preferable that the magnetic field generator is capable of switching and generating two types of magnetic fields having different magnetic field distributions in the central axis and having different magnetic field distributions.

If such a magnetic field generator is provided, it is possible to more reliably produce both a single crystal having a low oxygen concentration and a single crystal having a high oxygen concentration by switching between two types of magnetic fields.

Further, the magnetic field generator has a magnetic flux density distribution on the X axis when the magnetic force line direction is the X axis in one of two types of magnetic fields having different magnetic force line directions and different magnetic field distributions. Is a downwardly convex distribution, and when the magnetic flux density at the central axis in the horizontal plane is set as a magnetic flux density setting value, the magnetic flux density on the X axis is a value exceeding the magnetic flux density setting value at the crucible wall. At the same time, the magnetic flux density distribution on the Y axis that is perpendicular to the X axis and passes through the central axis in the horizontal plane is a downwardly convex distribution, and the magnetic flux density on the Y axis is equal to the magnetic flux density setting value at the crucible wall. It is preferable that the magnetic field distribution be 120% or less.

If the magnetic field generating device of the single crystal pulling device generates such a magnetic field distribution, the flow rate of the raw material melt is reduced in the cross section perpendicular to the X axis where the convection suppressing force due to electromagnetic force is insufficient. Because it becomes difficult, the time until oxygen eluted from the crucible wall reaches the single crystal is shortened, and the amount of oxygen evaporated from the free surface of the raw material melt is reduced, increasing the oxygen concentration taken into the single crystal. Can be made. That is, a single crystal having a high oxygen concentration can be manufactured by generating the above magnetic field distribution in one of the two types of magnetic fields.

Further, the magnetic field generator has a magnetic flux density distribution on the Y axis when the magnetic force line direction is the Y axis in one of two types of magnetic fields having different magnetic force line directions and different magnetic field distributions. Is a convex distribution, and when the magnetic flux density at the central axis in the horizontal plane is a magnetic flux density setting value, the magnetic flux density on the Y-axis is 60% or less of the magnetic flux density setting value at the crucible wall. At the same time, the magnetic flux density distribution on the X axis perpendicular to the Y axis and passing through the central axis in the horizontal plane is a downward convex distribution, and the magnetic flux density on the X axis is equal to the magnetic flux density set value at the crucible wall. It is also preferable to generate a magnetic field distribution of 170% or more.

If the magnetic field generator of the single crystal pulling device generates such a magnetic field distribution, the flow rate of the raw material melt is reduced even in a cross section perpendicular to the Y axis where the convection suppression force by electromagnetic force is insufficient. In addition, the flow velocity in the cross section parallel to the Y axis of the raw material melt and the flow velocity in the cross section perpendicular to the Y axis of the raw material melt can be balanced. Even within the cross section perpendicular to the Y-axis, reducing the flow rate of the raw material melt increases the time it takes for oxygen eluted from the crucible wall to reach the single crystal, and evaporates oxygen from the free surface of the raw material melt. By increasing the amount, the oxygen concentration taken into the single crystal can be greatly reduced. Further, by balancing the flow velocity in the cross section parallel to the Y axis of the raw material melt and the flow velocity in the cross section perpendicular to the Y axis of the raw material melt, growth fringes in the single crystal to be grown can be suppressed. That is, by generating the magnetic field distribution as described above in one of the two types of magnetic fields, a single crystal with a very low oxygen concentration and suppressed growth fringes can be manufactured.

In the magnetic field generator, two pairs of superconducting coils opposed to each other are provided so that the respective coil axes are included in the same horizontal plane, and the X axis is sandwiched between the coil axes. The center angle α is preferably 60 degrees or more and 70 degrees or less.

By arranging the superconducting coils of the magnetic field generator in this way, the magnetic field distribution as described above can be generated more reliably.

In the magnetic field generator, two pairs of superconducting coils arranged opposite to each other are provided so that each coil axis is included in the same horizontal plane, and the direction of the current flowing in one pair is switched. It is preferable that the direction of the lines of magnetic force in the central axis can be switched.

Such a magnetic field generator can easily switch between two types of magnetic fields by simply switching the current direction.

Also, the present invention provides a single crystal pulling method for pulling up a semiconductor single crystal using the single crystal pulling apparatus.

With such a single crystal pulling method, it is possible to grow a semiconductor single crystal in which the incorporated oxygen concentration is significantly reduced and the growth fringes are suppressed, and the incorporated oxygen concentration is increased using the same pulling apparatus. A semiconductor single crystal can also be easily grown.

As described above, the single crystal pulling apparatus of the present invention can reduce the oxygen concentration in the single crystal to be grown and can suppress the growth stripes in the single crystal to be grown. The two kinds of magnetic fields can be switched by a simple method such as switching the direction of the flowing current, whereby a single crystal having a high oxygen concentration can be obtained by a simple method in the same pulling apparatus.

It is a schematic sectional drawing which shows an example of the single crystal pulling apparatus of this invention. It is a figure which shows an example of two types of magnetic fields in the single crystal pulling apparatus of this invention. It is a figure which shows arrangement | positioning of the superconducting coil in Example 1, an electric current direction, and a magnetic force line direction. It is a figure which shows arrangement | positioning of the superconducting coil in Example 2, an electric current direction, and a magnetic force line direction. It is a figure which shows arrangement | positioning of the superconducting coil in Example 3, a current direction, and a magnetic force line direction. It is a figure which shows arrangement | positioning of a superconducting coil in the comparative example 1, a current direction, and a magnetic force line direction. It is a figure which shows arrangement | positioning of a superconducting coil in Comparative Example 2, a current direction, and a magnetic force line direction. It is a figure which shows magnetic flux density distribution in the plane containing the coil axis | shaft in Example 1. FIG. It is a figure which shows magnetic flux density distribution in the plane containing the coil axis | shaft in Example 2. FIG. It is a figure which shows magnetic flux density distribution in the plane containing the coil axis | shaft in Example 3. FIG. It is a figure which shows magnetic flux density distribution in the plane containing the coil axis | shaft in the comparative example 1. FIG. It is a figure which shows the flow-velocity distribution in the melt cross section in Example 1. FIG. It is a figure which shows the flow-velocity distribution in the melt cross section in Example 2. FIG. It is a figure which shows the flow-velocity distribution in the melt cross section in Example 3. FIG. It is a figure which shows the flow-velocity distribution in the melt cross section in the comparative example 1. 6 is a graph showing magnetic flux density distributions in the direction of magnetic field lines in Examples 1 to 3 and Comparative Example 1. 6 is a graph showing the magnetic flux density distribution in the direction perpendicular to the magnetic field lines in Examples 1 to 3 and Comparative Example 1. It is a graph which shows the relationship between center angle (alpha) between coil axes | shafts, and oxygen concentration in a single crystal. It is a figure which shows the flow-velocity distribution in the melt cross section at the time of using the 2 coil superconducting magnet of a prior art. It is a figure which shows the flow-velocity distribution in the melt cross section at the time of using the 4 coil superconducting magnet of patent document 1. FIG. It is a 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 the superconducting magnet of 2 coils used for the conventional single crystal pulling apparatus. It is a figure which shows magnetic flux density distribution in the conventional single crystal pulling apparatus. FIG. 2 is a schematic perspective view and a schematic cross-sectional view showing a 4-coil superconducting magnet of Patent Document 1. FIG. It is a figure which shows magnetic flux density distribution when arrangement | positioning angle | corner (theta) = 100 degree | times of a superconducting coil in FIG. It is a figure which shows magnetic flux density distribution when arrangement | positioning angle | corner (theta) = 110 degree | times of a superconducting coil in FIG. It is a figure which shows magnetic flux density distribution when arrangement | positioning angle | corner (theta) = 115 degree | times of a superconducting coil in FIG. It is a figure which shows magnetic flux density distribution when arrangement | positioning angle | corner (theta) = 120 degree | times of a superconducting coil in FIG. It is a figure which shows magnetic flux density distribution when arrangement | positioning angle | corner (theta) = 130 degree | times of a superconducting coil in FIG. It is a figure which shows magnetic flux density distribution when arrangement | positioning angle | corner (theta) = 90 degree | times of a superconducting coil in FIG. It is a figure which shows magnetic flux density distribution when arrangement | positioning angle | corner (theta) = 140 degree | times of a superconducting coil in FIG.

As described above, the oxygen concentration in the single crystal to be grown can be reduced and the growth fringes in the single crystal to be grown can be suppressed, and a single crystal having a high oxygen concentration can be obtained by a simple method in the same pulling apparatus. There has been a demand for the development of a single crystal pulling apparatus and a single crystal pulling method.

As a result of intensive studies on the above problems, the present inventors have pulled a single crystal equipped with a magnetic field generator capable of switching and generating two types of magnetic fields having different magnetic force line directions and different magnetic field distributions. If it is an apparatus, the oxygen concentration in the single crystal to be grown can be reduced, the growth fringes in the single crystal to be grown can be suppressed, and the single crystal having a high oxygen concentration can be obtained in the same pulling apparatus by switching the magnetic field. And the present invention was completed.

That is, the present invention comprises a heating furnace and a pulling furnace having a central axis in which a crucible containing a molten single crystal raw material is placed, and a magnetic field generator having a superconducting coil provided around the pulling furnace, A single crystal pulling device that applies a horizontal magnetic field to the molten single crystal raw material by energizing the superconducting coil and suppresses convection of the molten single crystal raw material in the crucible, wherein the magnetic field generating device comprises: A single crystal pulling apparatus capable of switching and generating two kinds of magnetic fields having different magnetic force line directions in the central axis in a horizontal plane including the coil axis of the superconducting coil and having different magnetic field distributions. .

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

<Single crystal pulling device>
FIG. 1 is a schematic cross-sectional view showing an example of a single crystal pulling apparatus of the present invention. First, an example of an embodiment of the single crystal pulling apparatus of the present invention will be described with reference to FIG. A single crystal pulling apparatus 11 of FIG. 1 includes a heating furnace 3, a pulling furnace 1 having a central shaft 10 in which a crucible 2 in which a molten single crystal raw material (hereinafter referred to as a melt) 6 is accommodated, and a pulling furnace 1 is provided with a magnetic field generator 30 having a superconducting coil 4 provided around 1 and applying a horizontal magnetic field to the melt 6 by energizing the superconducting coil 4 to convect the melt 6 in the crucible 2. The single crystal 9 is pulled up in the pulling direction 8 while being suppressed.

The magnetic field generator 30 can generate two types of magnetic fields by switching the magnetic field lines 7 in the central axis 10 in the horizontal plane 12 including the coil axis of the superconducting coil 4 and having different magnetic field distributions. is there.

Here, two types of magnetic fields generated by the magnetic field generator of the single crystal pulling apparatus of the present invention will be described with reference to FIG. 2 (a) and 2 (b) are diagrams showing examples of two types of magnetic fields in the single crystal pulling apparatus of the present invention. 2 (a) and 2 (b), two pairs of superconducting coils 4 arranged opposite to each other are provided so that the respective coil shafts 13 are included in the same horizontal plane, and have current paths. Each coil pair is wired separately. The arrow on the superconducting coil 4 indicates the direction of the current loop when the coil is viewed from directly above, and the left two coils are right-handed coils, so that the current loop is in the opposite direction to the current direction. The two coils on the right side are left-handed coils, so that a current loop is formed in the same direction as the current direction. In FIG. 2A, the direction of the magnetic force line in the central axis is the X-axis direction, but by reversing the current direction (current polarity) flowing in the lower left and upper right coils as shown in FIG. The current loop formed by the coils of the first and second coils reverses, and the direction of the magnetic field lines in the central axis changes in the Y-axis direction.

It is preferable that the magnetic field generator 30 is capable of generating two types of magnetic fields by switching the direction of the magnetic force lines 7 in the central axis 10 by 90 degrees and having different magnetic field distributions. If it has such a magnetic field generator, both a single crystal with a low oxygen concentration and a single crystal with a high oxygen concentration can be more reliably manufactured by switching between two types of magnetic fields.

Further, the magnetic field generator 30 has the direction of the magnetic force lines 7 in the central axis 10 in the horizontal plane 12 including the coil axis 13 of the superconducting coil 4 in one of two types of magnetic fields having different magnetic force line directions and different magnetic field distributions. , Where the magnetic flux density distribution on the X axis is a downward convex distribution, and the magnetic flux density on the central axis 10 in the horizontal plane 12 is the magnetic flux density setting value, the magnetic flux density on the X axis is At the crucible wall, the value exceeds the set value of the magnetic flux density (preferably more than 100% and 130% or less), and at the same time, the magnetic flux density distribution on the Y axis passing through the central axis 10 perpendicular to the X axis in the horizontal plane 12 is lower. The magnetic flux density on the Y-axis generates a magnetic field distribution that is 120% or less (usually more than 100% and 120% or less) of the magnetic flux density setting value in the crucible wall. Like There.

The magnetic flux density distribution on the X-axis is a downward convex distribution, the magnetic flux density on the X-axis is a value exceeding the magnetic flux density setting value on both sides of the crucible, and at the same time, the magnetic flux density distribution on the Y-axis is If the magnetic flux distribution on the Y-axis is 120% or less of the magnetic flux density setting value on the crucible wall (both sides), the convection suppression force in the cross section perpendicular to the X-axis decreases. Since the flow rate of the raw material melt is less likely to be reduced, the time until the oxygen eluted from the crucible wall reaches the single crystal is shortened, and the amount of oxygen evaporated from the free surface of the raw material melt is reduced. The oxygen concentration taken into the single crystal can be increased. That is, a single crystal having a high oxygen concentration can be produced by generating the magnetic field distribution as described above.

Further, the magnetic field generator 30 has the direction of the magnetic force lines 7 in the central axis 10 in the horizontal plane 12 including the coil axis 13 of the superconducting coil 4 in one of two types of magnetic fields having different magnetic force line directions and different magnetic field distributions. Is the Y-axis, the magnetic flux density distribution on the Y-axis is a convex distribution, and when the magnetic flux density at the central axis 10 in the horizontal plane 12 is the magnetic flux density setting value, the magnetic flux density on the Y-axis is At the crucible wall, the magnetic flux density distribution on the X axis passing through the central axis 10 perpendicular to the Y axis in the horizontal plane 12 is at the same time lower than the magnetic flux density setting value of 60% or less (usually more than 0% and 60% or less). It is also preferable to generate a magnetic field distribution that has a convex distribution and the magnetic flux density on the X-axis is 170% or more (preferably 170% or more and 250% or less) of the magnetic flux density setting value in the crucible wall. .

The magnetic flux density distribution on the Y axis is an upwardly convex distribution, the magnetic flux density on the Y axis is 60% or less of the magnetic flux density setting value on the crucible walls (both sides), and at the same time, the magnetic flux density distribution on the X axis is If the magnetic field distribution is 170% or more of the magnetic flux density setting value on the crucible wall (both sides) on the X axis, the convection suppression force due to electromagnetic force in the cross section perpendicular to the Y axis is sufficient. Thus, the flow rate of the raw material melt is sufficiently reduced, and the flow rate in the cross section parallel to the Y axis of the raw material melt and the flow rate in the cross section perpendicular to the Y axis of the raw material melt can be balanced. Therefore, it takes a long time for oxygen eluted from the crucible wall to reach the single crystal, and the amount of oxygen evaporated from the free surface of the raw material melt increases, thereby greatly reducing the oxygen concentration taken into the single crystal. be able to. Further, by balancing the flow velocity in the cross section parallel to the Y axis of the raw material melt and the flow velocity in the cross section perpendicular to the Y axis of the raw material melt, growth fringes in the single crystal to be grown can be suppressed. That is, by generating the magnetic field distribution as described above, a single crystal having an extremely low oxygen concentration and suppressed growth fringes can be manufactured.

That is, by using a magnetic field generator that can switch and generate two types of magnetic fields that generate a magnetic field distribution as described above, a single crystal with a very low oxygen concentration and suppressed growth fringes, Both single crystals with a high oxygen concentration can be produced with the same single crystal pulling apparatus.

In addition, the magnetic field generator 30 is provided with two pairs of superconducting coils 4 arranged so as to face each other so that the respective coil axes are included in the same horizontal plane, and the center sandwiching the X axis between the coil axes The angle α is preferably not less than 60 degrees and not more than 70 degrees. By arranging the superconducting coils of the magnetic field generator in this way, the magnetic field distribution as described above can be generated more reliably.

When the central angle α sandwiching the X axis between the coil axes is set to 60 degrees or more and 70 degrees or less, the direction of the line of magnetic force changes from the X axis direction to the Y axis direction by switching the direction of the current flowing through one coil pair. At the same time, since the central angle α ′ across the Y axis, which is the direction of the magnetic field, is (180−α) degrees, the central angle between the coil axes including the direction of the magnetic field changes from 110 degrees to 120 degrees.

In addition, the magnetic field generator 30 is provided with two pairs of superconducting coils 4 arranged so as to face each other so that the respective coil axes are included in the same horizontal plane, and the direction of the current flowing in one pair is switched. Thus, it is preferable that the direction of the magnetic force lines 7 in the central axis 10 can be switched. With such a magnetic field generator, two types of magnetic fields can be easily switched by simply switching the current direction.

It should be noted that such switching of the magnetic field distribution can be performed before magnetic field excitation when growing crystals having different required oxygen concentrations. The current flowing in the superconducting coil is supplied from a DC power source for the superconducting magnet. However, the magnetic field distribution can be easily switched by exciting the magnet after changing the polarity inside the power source. In the superconducting state, repulsive force or attractive force acts between the coils, so if the current direction is changed in such a situation, the coil itself moves to cause a quench (collapse of the superconducting state). Therefore, it is necessary to change the polarity before starting excitation.

<Single crystal pulling method>
The present invention also provides a single crystal pulling method for pulling a semiconductor single crystal using the single crystal pulling apparatus of the present invention described above.

Hereinafter, the present invention will be specifically described using examples and comparative examples, but the present invention is not limited thereto.

[Example 1]
In the single crystal pulling apparatus 11 shown in FIG. 1, the arrangement of superconducting coils is the same as that shown in FIG. 3 (the central angle α sandwiching the X-axis between the coil axes is 60 degrees; The semiconductor single crystal was pulled up under the pulling conditions shown below using the wiring).

(Raising conditions)
Used crucible: Diameter 800mm
Single crystal raw material charge: 400kg
Single crystal to grow: Diameter 306mm
Length of straight body of single crystal: 40cm
Magnetic flux density: Adjusted to be 3000 G in the central axis in the horizontal plane including the coil axis. Single crystal rotation speed: 6 rpm
Crucible rotation speed: 0.03 rpm

[Example 2]
In the single crystal pulling apparatus 11 shown in FIG. 1, except that the superconducting coil is arranged as shown in FIG. 4 (center angle α is 70 degrees; two coils are wired separately one by one). In the same manner as in Example 1, the semiconductor single crystal was pulled up.

[Example 3]
In the single crystal pulling apparatus 11 shown in FIG. 1, except that the superconducting coil is arranged as shown in FIG. 5 (center angle α is 80 degrees; two pairs of coils are wired separately). In the same manner as in Example 1, the semiconductor single crystal was pulled up.

[Comparative Example 1]
In the single crystal pulling apparatus 11 shown in FIG. 1, except that the superconducting coil is arranged as shown in FIG. 6 (center angle α is 90 degrees; two pairs of coils are wired separately). In the same manner as in Example 1, the semiconductor single crystal was pulled up.

[Comparative Example 2]
In the single crystal pulling apparatus 11 shown in FIG. 1, the arrangement of superconducting coils is as shown in FIG. 7 (the central angle α sandwiching the X axis between the coil axes is 60 degrees; all two pairs of coils are wired in series) The semiconductor single crystal was pulled up in the same manner as in Example 1 except that the above was used.

When the single crystal pulling apparatus of Examples 1 to 3 and Comparative Example 1 was used, the magnetic flux density distribution in the horizontal plane including the coil axis was measured. The results are shown in FIGS. Here, FIGS. 8A to 11A are magnetic flux density distributions in the horizontal plane including the coil axis when the direction of the magnetic force line is the X-axis direction, and FIGS. 8B to 11B are magnetic field lines. It is magnetic flux density distribution in the horizontal surface containing a coil axis | shaft in case a direction is a Y-axis direction. Table 1 shows the magnetic flux density at the crucible wall when the magnetic force line direction is the X-axis direction and when the magnetic force line direction is the Y-axis direction. FIG. 16 shows a graph showing the magnetic flux density distribution in the direction of the magnetic lines of force, and FIG. 17 shows a graph showing the magnetic flux density distribution in the direction perpendicular to the lines of magnetic force.

Further, the straight body portion of the single crystal in the case where the single crystal is pulled under the pulling conditions described above using the single crystal pulling apparatus of Examples 1 to 3 and Comparative Example 1 using FEMAG-TMF as analysis software The flow velocity distribution in the cross section of the melt (the cross section parallel to the magnetic field lines and the cross section perpendicular to the magnetic field lines) at the time when the length of the film became 40 cm was analyzed by simulation. The analysis results are shown in FIGS. 12 (a) to 15 (a) are flow velocity distributions in a cross section parallel to the magnetic force lines, and FIGS. 12 (b) to 15 (b) are flow velocity distributions in a cross section perpendicular to the magnetic force lines.

Also, the oxygen concentration of the semiconductor single crystals grown in Examples 1 to 3 and Comparative Examples 1 and 2 was examined. The result is shown in FIG.

In Example 1 in which the central angle α sandwiching the X axis between the coil axes is 60 degrees (α ′ is 120 degrees) and two pairs of coils are separately wired one by one, the direction of the magnetic force lines is changed to the X axis by switching the current direction. When switching between the direction and the Y-axis direction, different magnetic field distributions were generated as shown in FIGS. 8A and 8B. Further, as shown in Table 1 and FIGS. 16 and 17, when the magnetic force line direction is the X-axis direction, the magnetic flux density distribution on the X-axis is a downward convex distribution (FIG. 16), and the magnetic flux density on the X-axis. Is a value exceeding the magnetic flux density setting value at the crucible wall, the magnetic flux density distribution on the Y axis is a downward convex distribution (FIG. 17), and the magnetic flux density on the Y axis is the magnetic flux density setting at the crucible wall. It was 120% or less of the value. Further, as shown in Table 1 and FIGS. 16 and 17, when the magnetic field line direction is the Y-axis direction, the magnetic flux density distribution on the Y-axis is an upward convex distribution (FIG. 16), and the magnetic flux density on the Y-axis. Is less than 60% of the magnetic flux density setting value at the crucible wall, the magnetic flux density distribution on the X axis is a downward convex distribution (FIG. 17), and the magnetic flux density on the X axis is the magnetic flux density setting at the crucible wall. It was 170% or more of the value. Further, as shown in FIGS. 12A and 12B, the flow velocity distribution in the cross section of the melt was also different between the cross section parallel to the magnetic force lines and the cross section perpendicular to the magnetic force lines. Further, as shown in FIG. 18, the oxygen concentration of the single crystal pulled up by applying a horizontal magnetic field in which the magnetic force line direction is the X axis direction is about 10 to 15 ppma-JEIDA, and the magnetic force line direction is changed to the Y axis. Since the oxygen concentration of the single crystal pulled up by applying a horizontal magnetic field in the direction is about 3 ppma-JEIDA, it can be seen that single crystals having greatly different oxygen concentrations can be produced by switching the magnetic field. Further, no growth stripes were observed in the grown single crystal having a low oxygen concentration.

In Example 2 in which the center angle α sandwiching the X axis between the coil axes is 70 degrees (α ′ is 110 degrees), and two pairs of coils are separately wired one by one, the direction of the magnetic force lines is changed to the X axis by switching the current direction. When switching between the direction and the Y-axis direction, different magnetic field distributions occurred as shown in FIGS. 9A and 9B. Further, as shown in Table 1 and FIGS. 16 and 17, when the magnetic force line direction is the X-axis direction, the magnetic flux density distribution on the X-axis is a downward convex distribution (FIG. 16), and the magnetic flux density on the X-axis. Is a value exceeding the magnetic flux density setting value at the crucible wall, the magnetic flux density distribution on the Y axis is a downward convex distribution (FIG. 17), and the magnetic flux density on the Y axis is the magnetic flux density setting at the crucible wall. It was 120% or less of the value. Further, as shown in Table 1 and FIGS. 16 and 17, when the magnetic field line direction is the Y-axis direction, the magnetic flux density distribution on the Y-axis is an upward convex distribution (FIG. 16), and the magnetic flux density on the Y-axis. Is less than 60% of the magnetic flux density setting value at the crucible wall, the magnetic flux density distribution on the X axis is a downward convex distribution (FIG. 17), and the magnetic flux density on the X axis is the magnetic flux density setting at the crucible wall. It was 170% or more of the value. Further, as shown in FIGS. 13A and 13B, the flow velocity distribution in the cross section of the melt was also different between the cross section parallel to the magnetic field lines and the cross section perpendicular to the magnetic force lines. Further, as shown in FIG. 18, the oxygen concentration of the single crystal pulled up by applying a horizontal magnetic field in which the magnetic force line direction is the X-axis direction is about 8 to 11 ppma-JEIDA. Since the oxygen concentration of the single crystal pulled up by applying a horizontal magnetic field in the direction is about 3.5 ppma-JEIDA, it can be seen that single crystals having greatly different oxygen concentrations can be produced by switching the magnetic field. Further, no growth stripes were observed in the grown single crystal having a low oxygen concentration.

In Example 3 in which the center angle α sandwiching the X axis between the coil axes is 80 degrees (α ′ is 100 degrees) and two pairs of coils are separately wired one by one, the direction of the magnetic force lines is changed to the X axis by switching the current direction. When the direction and the Y-axis direction are switched, different magnetic field distributions are generated as shown in FIGS. 10 (a) and 10 (b). Further, as shown in Table 1 and FIGS. 16 and 17, when the magnetic field line direction is the X-axis direction, the magnetic flux density distribution on the X-axis is an upward convex distribution (FIG. 16), and the magnetic flux density on the X-axis. Is less than the magnetic flux density setting value at the crucible wall, the magnetic flux density distribution on the Y axis is a downward convex distribution (FIG. 17), and the magnetic flux density on the Y axis is 120, which is the magnetic flux density setting value at the crucible wall. It was a value exceeding%. Further, as shown in Table 1 and FIGS. 16 and 17, when the magnetic field line direction is the Y-axis direction, the magnetic flux density distribution on the Y-axis is an upward convex distribution (FIG. 16), but the magnetic flux on the Y-axis. The density of the crucible wall exceeds 60% of the set value of the magnetic flux density, and the magnetic flux density distribution on the X axis is a downwardly convex distribution (FIG. 17), but the magnetic flux density on the X axis is the crucible wall. Then, it was less than 170% of the magnetic flux density setting value. Further, as shown in FIGS. 14A and 14B, the flow velocity distribution in the cross section of the melt was also different between the cross section parallel to the magnetic field lines and the cross section perpendicular to the magnetic force lines. In addition, as shown in FIG. 18, the oxygen concentration of the single crystal pulled up by applying a horizontal magnetic field in which the magnetic force line direction is the X-axis direction is about 6 to 8 ppma-JEIDA. Since the oxygen concentration of the single crystal pulled up by applying a horizontal magnetic field in the direction is about 4 ppma-JEIDA, it can be seen that single crystals having different oxygen concentrations can be produced by switching the magnetic field. Further, no growth stripes were observed in the grown single crystal having a low oxygen concentration.

On the other hand, in the first comparative example in which the center angle α sandwiching the X axis between the coil axes is 90 degrees (α ′ is also 90 degrees) and two pairs of coils are separately wired one by one, FIG. As shown in (b), even when the direction of the magnetic field is switched between the X-axis direction and the Y-axis direction by switching the current direction, the magnetic field distribution is simply rotated by 90 degrees, and different magnetic field distributions are generated. It wasn't. Further, as shown in Table 1 and FIGS. 16 and 17, when the magnetic field line direction is the X-axis direction, the magnetic flux density distribution on the X-axis is an upward convex distribution (FIG. 16), and the magnetic flux density on the X-axis. Is less than the magnetic flux density setting value at the crucible wall, the magnetic flux density distribution on the Y axis is a downward convex distribution (FIG. 17), and the magnetic flux density on the Y axis is 120, which is the magnetic flux density setting value at the crucible wall. It was a value exceeding%. Further, as shown in Table 1 and FIGS. 16 and 17, the same magnetic flux density distribution except that the magnetic flux density distribution when the magnetic force line direction is the X-axis direction is rotated by 90 degrees even when the magnetic force line direction is the Y-axis direction. It was. Further, as shown in FIGS. 15A and 15B, the flow velocity distribution in the cross section of the melt was also the same in the cross section parallel to the magnetic force lines and the cross section perpendicular to the magnetic force lines. Further, as shown in FIG. 18, a single crystal pulled by applying a horizontal magnetic field whose magnetic force line direction is the X-axis direction and oxygen in the single crystal pulled by applying a horizontal magnetic field whose magnetic force line direction is the Y-axis direction. There is no difference in concentration, and both are about 5 to 6 ppma-JEIDA, so that it is understood that single crystals having different oxygen concentrations cannot be produced even when the magnetic field is switched. Further, no growth stripes were observed in the grown single crystal having a low oxygen concentration.

In Comparative Example 2 in which the center angle α sandwiching the X axis between the coil axes is 60 degrees and all the two pairs of coils are wired in series, the magnetic field lines are different from each other and the magnetic field distributions are different from each other. Therefore, as shown in FIG. 18, the oxygen concentration is as high as that of a single crystal pulled up by applying a horizontal magnetic field in which the direction of the magnetic field is the X-axis direction in Example 1 (10 Only single crystals (about ˜15 ppma-JEIDA) could be produced. Note that growth stripes were observed in the grown single crystal having a high oxygen concentration.

From the above, the single crystal pulling apparatus of the present invention can reduce the oxygen concentration in the single crystal to be grown and can suppress growth fringes in the single crystal to be grown. It was revealed that a single crystal having a high oxygen concentration can be obtained by a simple method. Further, it has been clarified that the difference in oxygen concentration of the single crystal is particularly increased when the magnetic field is switched by setting the central angle α sandwiching the X axis between the coil axes to 60 degrees or more and 70 degrees or less.

Note that the present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Claims

A heating furnace and a crucible in which a molten single crystal raw material is accommodated are arranged, a pulling furnace having a central axis, and a magnetic field generator having a superconducting coil provided around the pulling furnace and energizing the superconducting coil A single crystal pulling device that applies a horizontal magnetic field to the molten single crystal raw material to suppress convection in the crucible of the molten single crystal raw material,
The magnetic field generator is capable of switching and generating two types of magnetic fields having different magnetic force line directions in the central axis in a horizontal plane including the coil axis of the superconducting coil and having different magnetic field distributions. Single crystal pulling device characterized by
2. The magnetic field generation apparatus according to claim 1, wherein the magnetic field lines in the central axis are shifted by 90 degrees, and two types of magnetic fields having different magnetic field distributions can be switched and generated. A single crystal pulling apparatus according to 1.
In the magnetic field generator, the magnetic flux density distribution on the X axis is lower when one of two types of magnetic fields having different magnetic field lines and different magnetic field distributions is used. When the magnetic flux density at the central axis in the horizontal plane is a magnetic flux density setting value, the magnetic flux density on the X-axis is a value exceeding the magnetic flux density setting value at 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 120% of the magnetic flux density setting value at the crucible wall. The single crystal pulling apparatus according to claim 1 or 2, wherein a magnetic field distribution is generated as follows.
In the magnetic field generator, the magnetic flux density distribution on the Y axis is higher when the magnetic force line direction is the Y axis in one of two types of magnetic fields having different magnetic force line directions and different magnetic field distributions. When the magnetic flux density at the central axis in the horizontal plane is a magnetic flux density setting value, the magnetic flux density on the Y axis is 60% or less of the magnetic flux density setting value at the crucible wall, In the horizontal plane, the magnetic flux density distribution on the X axis that is orthogonal to the Y axis and passes through the central axis is a convex downward distribution, and the magnetic flux density on the X axis is 170% of the magnetic flux density setting value at the crucible wall. The single crystal pulling apparatus according to claim 1 or 2, wherein a magnetic field distribution as described above is generated.
In the magnetic field generator, two pairs of superconducting coils arranged opposite to each other are provided so that each coil axis is included in the same horizontal plane, and a central angle sandwiching the X axis between the coil axes The single crystal pulling apparatus according to any one of claims 1 to 4, wherein α is not less than 60 degrees and not more than 70 degrees.
In the magnetic field generator, two pairs of superconducting coils arranged opposite to each other are provided so that each coil axis is included in the same horizontal plane, and the direction of the current flowing in one pair is switched to change the current direction. The single crystal pulling apparatus according to any one of claims 1 to 5, wherein a direction of a line of magnetic force in the central axis can be switched.
A single crystal pulling method comprising pulling up a semiconductor single crystal using the single crystal pulling apparatus according to any one of claims 1 to 6.