JPH10310487A - Apparatus for growing single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the oxygen concn. distribution in a single crystal pulling up direction uniform in CZ pulling up using a cusp magnetic field. SOLUTION: A magnetic field converging member 30 for converging the magnetic field below a crucible 11 along a pedestal 16 is mounted at the pedestal 16 for supporting this crucible 11. The magnetic flux of a sufficient quantity perpendicularly crosses the bottom and peripheral wall part of the crucible 11 and the convection along the inside surface of the crucible 11 is suppressed in the late period of pulling up when the crucible 11 ascends, by which the increase in the oxygen concn. of a raw material melt 12 is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal growing apparatus for pulling a single crystal from a raw material melt in a crucible by a CZ method, and more particularly to a single crystal growing apparatus of the type called MCZ using a magnetic field. .

[0002]

2. Description of the Related Art In pulling a single crystal by the CZ method, as shown in FIG. 6A, a quartz crucible 3 is supported in a main chamber 1 by a pedestal 4, and raw materials generated in the crucible 2 are formed. The single crystal 6 is pulled up from the melt 5 while rotating by the wire 7 and is drawn into the pull chamber 2. At this time, oxygen is dissolved from the quartz crucible 3 into the raw material melt 5 in the crucible 3, and as a result, oxygen is taken into the single crystal 6. If the amount of oxygen in the single crystal 6 is large, it causes various crystal defects and causes deterioration of device characteristics when the device is a semiconductor device. It is an important technical issue.

[0003] As one of the techniques for solving this problem, there is a method called MCZ in which a magnetic field is applied together.
In particular, a method using a cusp magnetic field described in Japanese Patent Publication No. 2-1290 is effective. In this method, an axially symmetric and radial cusp magnetic field is applied to the raw material melt 5 in the crucible 3 by a pair of upper and lower annular magnets 8 as shown in FIG. The feature of this method is that the upper and lower magnetic fields are repelled in the vicinity of the liquid surface of the raw material melt 5 to form an axially symmetric magnetic field that is bent substantially at right angles, thereby reducing the magnetic field component crossing the liquid surface of raw material melt 5 at right angles. In other words, the convection of the raw material melt 5 in the crucible 3 is suppressed by increasing the magnetic field component crossing the peripheral wall and the bottom of the crucible 3 at right angles.

[0004] That is, in the crucible 3, the raw material melt 5 convects along the inner surface of the crucible 3 as indicated by a broken line arrow. Due to this convection, a fresh raw material melt 5 is supplied in the vicinity of the inner surface of the crucible 3, and the dissolution of oxygen from the inner surface is promoted. However, when the magnetic field crosses the peripheral wall and the bottom of the crucible 3, The convection along the inner surface of No. 3 is suppressed, and the dissolution of oxygen from the inner surface of the crucible is suppressed. In order to enhance the suppression effect, it is necessary to reduce the magnetic field component crossing the liquid surface of the raw material melt 5 at right angles and increase the magnetic field component crossing the peripheral wall and bottom of the crucible 3 at right angles. .

[0005]

However, in CZ pulling using a cusp magnetic field, there is a problem specific to this type of pulling in that the oxygen concentration in the single crystal increases with time in the latter stage of pulling. The cause is as follows.

In the pulling of a single crystal by the CZ method, there is a problem that the oxygen concentration in the single crystal decreases with the progress of the pulling regardless of the presence or absence of the application of a magnetic field. That is, while oxygen in the raw material melt in the crucible is supplied from the inner surface of the crucible, it evaporates as SiO from its free surface. The latter evaporation is almost constant during the entire lifting,
The former supply decreases with the lapse of time due to a decrease in the amount of the raw material melt in the crucible as the lifting proceeds and a decrease in the contact area between the two. As a result, the oxygen concentration in the raw material melt decreases with the progress of the pulling, and the oxygen concentration in the single crystal decreases.

Here, when a cusp magnetic field is applied, the convection of the raw material melt is suppressed, so that the oxygen concentration in the raw material melt decreases and the oxygen concentration in the single crystal decreases as a whole. The decrease in the oxygen concentration over time with the progress of the process still remains. In addition, in the latter stage of the withdrawal, the oxygen concentration increases on the contrary for the following reason.

The raw material melt in the crucible is consumed as the single crystal is pulled up, and the melt surface of the raw material melt lowers. In order to prevent this liquid level drop, the crucible is gradually raised, but with the rise of the crucible, the bottom of the crucible rises relatively from the lower cusp magnetic field, and the form of the magnetic field received by the bottom changes. . As a result, in the latter stage of the lifting, as shown in FIG. 6B, the magnetic field component crossing the bottom of the crucible 3 at right angles and the magnetic field component crossing the peripheral wall thereof at right angles are significantly reduced. Therefore, convection along the inner surface of the crucible 3 is not suppressed, and the dissolution of oxygen from the inner surface is promoted.

Apart from this convection, a strong upward flow is generated at the center of the raw material melt 5 by the relative rotation of the single crystal 6 and the raw material melt 5, but the convection along the inner surface of the crucible 3 is generated. By being no longer suppressed, the ascending flow generated in the center of the raw material melt 5 is also relatively promoted, and, together with the decrease in the thickness of the melt, the high oxygen concentration remaining near the bottom of the crucible 3 is reduced. The melt is supplied directly to the interface between the single crystal 6 and the raw material melt 5. As a result, the crucible 3 and the raw material melt 5
Even if the decrease in the amount of dissolved oxygen due to the decrease in the contact surface is subtracted, the oxygen concentration in the single crystal increases with time.

Although the increase in oxygen concentration is limited to the latter stage of the pulling, it is more remarkable than the decrease in the oxygen concentration accompanying the progress of the pulling. Has become.

In order to eliminate non-uniformity of the oxygen concentration distribution in the single crystal pulling direction, in the case of pulling using a cusp magnetic field, for example, one or both of the upper and lower magnets are moved up and down as the pulling proceeds, and the cusp magnetic field is increased. It is considered to actively control the distribution shape of. However, since a large repulsive force acts on the upper and lower magnets for forming the cusp magnetic field, the magnetic field generator including the mount and the like becomes extremely large, and such a magnetic field generator is mechanically moved up and down. To do so is not easy in actual operation. Even if it is possible to raise and lower it, vibrations and the like accompanying the raising and lowering become large, and there is a concern that this may adversely affect the pulling of the single crystal. In any case, it is not realistic to raise and lower the magnetic field generator.

An object of the present invention is to provide a single crystal growing apparatus capable of suppressing an increase in oxygen concentration in the latter stage of pulling by controlling the magnetic field distribution without raising and lowering the magnetic field generator.

[0013]

Means for Solving the Problems A single crystal growing apparatus according to the present invention comprises a growing apparatus main body for pulling a single crystal from a raw material melt in a crucible by a CZ method, and one set of upper and lower units arranged on the outer peripheral side of the growing apparatus main body. Magnetic field generating means for generating a cusp magnetic field by a combination of annular magnets, and a magnetic flux converging member attached to a pedestal supporting a crucible in the growth apparatus main body and for converging a magnetic field below the crucible in a vertical direction along the pedestal. Is what you do.

The magnetic flux converging member can be relatively easily constructed by using, for example, a ferromagnetic material that attracts magnetic flux or a diamagnetic material that does not transmit magnetic flux. Specifically, the ferromagnetic material is preferably provided inside and / or around the pedestal, and the diamagnetic material is preferably provided around the pedestal as a cone member whose diameter gradually decreases upward. The magnetic flux converging member of the ferromagnetic system and the magnetic flux converging member of the diamagnetic system can be shared.

In the method for growing a single crystal of the present invention, FIG.
As shown in (a), it is important that the magnetic flux converging member 30 is attached to the pedestal 16 supporting the crucible 11 in combination with magnetic field generating means 21 and 21 for generating a cusp magnetic field. The magnetic flux converging member 30 includes the pedestal 16.
Is formed of a ferromagnetic material disposed inside and / or around the pedestal, and a cone-shaped diamagnetic material disposed around the pedestal and gradually increasing in diameter downward. The vertical portion of the lower magnetic field can be converged along the pedestal 16.

In the pulling of the single crystal 13, the melt surface of the raw material melt 12 is not lowered by the pulling.
The pedestal 16 is driven upward to raise the crucible 11. When the pedestal 16 is driven upward, the magnetic flux concentrating member 30 attached to the pedestal 16 keeps the distance between the crucible 11 and the crucible 11 constant. Rise with. Therefore, the crucible 11 rises relatively to the lower magnetic field with the lifting, and the magnetic flux converging member 30 also makes this relative rise to the lower magnetic field.

If only the crucible 11 rises with respect to the lower magnetic field, the magnetic field component crossing the bottom of the crucible 11 at right angles and the magnetic field component crossing the peripheral wall thereof at right angles are significantly reduced. As the converging member 30 is raised, the upper end portion of the vertical portion of the lower magnetic field converges, and the radius of curvature of the magnetic flux in the portion where the vertical portion transitions to the horizontal portion is reduced. Therefore, as shown in FIG. 1B, even if the crucible 11 rises with respect to the lower magnetic field, the magnetic field component crossing the bottom of the crucible 11 at right angles and the magnetic field component crossing the peripheral wall at right angles are: Does not decrease much. Therefore, even in the latter stage of the pulling, convection along the inner surface of the raw material melt 12 is effectively suppressed, and an increase in the oxygen concentration in the raw material melt 12 is suppressed.

The ferromagnetic material constituting the magnetic flux converging member 30 is as follows.
By attracting the magnetic flux by the high magnetic permeability, the vertical portion of the lower magnetic field existing below the crucible 1 is converged along the pedestal 16. Examples of the ferromagnetic material include Fe-based materials, Co-based materials, and rare earth-based materials excluding nonmagnetic stainless steel. In order to prevent a decrease in magnetic permeability at a high temperature, it is preferable that these are forcibly cooled with a coolant such as water or liquid nitrogen.

On the other hand, the diamagnetic material does not transmit the magnetic flux, but keeps the magnetic flux away from the diamagnetic material so that the vertical portion of the lower magnetic field existing below the crucible 11 converges along the pedestal 16. Examples of the diamagnetic material include Y-based superconductors, Bi-based superconductors, and N-based superconductors.
Examples thereof include bTi, Nb3Sn, and Nb3Ge. These exhibit a magnetic field shielding function at low temperatures. The refrigerant is Y
Liquid superconductor and Bi superconductor are preferably liquid nitrogen and liquid helium, and NbTi, Nb3Sn, Nb3G
For e, liquid helium is preferred.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIGS. 1 and 2 show Embodiment 1 of the present invention. The single crystal growing apparatus according to the first embodiment is shown in FIG.
As shown in FIG.
3 and a raising device main body 10
Magnetic field generating means 20 provided on the outer peripheral side of the magnetic head and the magnetic flux converging member 3 provided below the crucible 11 in the growth apparatus main body 10
0.

The growing apparatus main body 10 includes a main chamber 14 made of non-magnetic stainless steel or the like and a small-diameter pull chamber 15 superposed thereon, and a quartz crucible 11 is provided in the center of the main chamber 14. The pedestal 16 is supported. Pedestal 1
Numeral 6 is made of non-magnetic stainless steel or the like.
It is driven axially and circumferentially for lifting and lowering and rotation of one. A heater (not shown) and the like are arranged on the outer peripheral side of the crucible 11.

The magnetic field generating means 20 includes the main chamber 14
And a pair of upper and lower annular magnets 21 and 21 for generating a cusp magnetic field, which are provided on the outer peripheral side.

As shown in FIG. 2, the magnetic flux converging member 30
It is a cone-shaped cylinder whose diameter gradually decreases from bottom to top, and is attached to the upper end of the pedestal 16 concentrically with the pedestal 16 by stays 31, 31 made of a non-magnetic material. The cone-shaped magnetic flux converging member 30 is entirely formed of a Y-based superconductor, a Bi-based superconductor, NbTi, Nb3Sn, and Nb3G between the heat insulating materials 32 and 32.
The diamagnetic material 33 has a three-layer structure with a diamagnetic material 33 interposed therebetween, and a refrigerant passage 34 is formed in a meandering shape at the diamagnetic material 33. In order to allow a refrigerant such as liquid nitrogen or liquid helium to pass through the refrigerant passage 34, a refrigerant passage 17 is formed in the pedestal 16, and a refrigerant passage 35 is formed in the stay 31.

In pulling the single crystal 13, a raw material melt 12 is generated in the crucible 11 according to a predetermined procedure. A cusp magnetic field is applied to the raw material melt 12 by passing currents in opposite directions through the annular magnets 21 and 21. In this state, the single crystal 13 is pulled up from the raw material melt 12 by the wire 18. At this time, crucible 11 and single crystal 13 are rotated in opposite directions. In addition, the refrigerant flows through the magnetic flux converging member 30.

As the single crystal 13 is pulled up, the raw material melt 12 in the crucible 11 is consumed. In order to avoid the lowering of the melt surface accompanying this, the pedestal 16 is driven upward to gradually raise the crucible 11. Thereby, the magnetic flux guide member 30 also rises in synchronization with the crucible 11. At this time,
The vertical portion of the lower magnetic field passes through the inside of the magnetic flux concentrating member 30 surrounding the pedestal 16, and the magnetic flux converging member 30 has a cone shape that incorporates the diamagnetic material 33 and reduces its diameter as it goes upward. Therefore, the vertical portion of the lower magnetic field is narrowed down toward the center from the bottom upward, and the vertical portion is converged along the pedestal 16.

In the first stage of the pulling up, as shown in FIG. 1A, the pedestal 16 is located relatively below the lower magnetic field. In this position, the vertical portion of the lower magnetic field is relatively converged along the pedestal 16, so
Although the convergence effect of the magnetic flux convergence member 30 is small, even if the convergence effect of the magnetic flux convergence member 30 is small, the crucible 1
Convection of the raw material melt 12 in the inside 1 along the inner surface of the crucible 11 is effectively suppressed, and the oxygen concentration in the raw material melt 12 is suppressed to a low level.

As the lifting progresses, the crucible 11 and the pedestal 16 rise. If only the crucible 11 and the pedestal 16 rise with respect to the lower magnetic field, the magnetic field component crossing the bottom of the crucible 11 at right angles and the magnetic field component crossing the peripheral wall thereof at right angles are significantly reduced. As the magnetic flux converging member 30 rises, the vertical part of the lower magnetic field, particularly the upper part thereof rises, and the radius of curvature of the magnetic flux in the part where the vertical part transitions to the horizontal part becomes smaller. Therefore, as shown in FIG. 1B, even if the crucible 11 rises with respect to the lower magnetic field, the magnetic field component crossing the bottom of the crucible 11 at right angles and the magnetic field component crossing the peripheral wall at right angles are: Does not decrease much.

Therefore, even in the latter stage of the pulling, the convection along the inner surface of the raw material melt 12 is effectively suppressed, and the increase in the oxygen concentration in the raw material melt 12 is suppressed.

In the magnetic flux converging member 30, the diamagnetic material 33
Are important, the axial height h, the distance d to the crucible 11, the diameter U at the upper end (minimum diameter), and the diameter B at the lower end (maximum diameter). These are preferably in the following ranges.

If the height h is too large, the crucible 11
It is economically disadvantageous because the chamber must be large because it is necessary to secure the vertical movement range. On the other hand, if the chamber is too small, the magnetic flux convergence efficiency is reduced. If the distance d is too large, the magnetic flux spreads at the top of the member, so that the perpendicular component to the bottom of the crucible decreases. If the distance d is too small, cooling becomes difficult, so the distance d is preferably 10 to 100 mm. If the diameter U is too large, the magnetic flux convergence efficiency decreases, and if the diameter U is too small, it becomes difficult to guide the magnetic flux to the outer peripheral portion of the crucible bottom. Therefore, the diameter U is preferably 200 to 600 mm.
If the diameter B is too large, the heater must be increased in size, which is economically disadvantageous. If the diameter B is too small, the magnetic flux convergence efficiency is reduced, so the diameter B is preferably 400 to 800 mm.

(Embodiment 2) FIG. 3 shows Embodiment 2 of the present invention.
Is shown. The single crystal growing apparatus according to the first embodiment is different from the single crystal growing apparatus according to the first embodiment in that the magnetic flux guiding member 30 is formed of an axial ferromagnetic material 36 built in the center of the nonmagnetic pedestal 16. Is different from The ferromagnetic material 36 is forcibly cooled by a coolant such as water or liquid nitrogen flowing through the coolant passage 34. Insulation material 3 between ferromagnetic material 36 and crucible 11
2 are provided.

The magnetic flux converging member 30 is a pedestal 1
The vertical portion of the lower magnetic field is made to converge along the pedestal 16 by the axial ferromagnetic material 36 built in 6. Also,
It moves with the pedestal 16 in the axial direction. for that reason,
As in the case of the single crystal growing apparatus of the first embodiment, an increase in the oxygen concentration in the latter stage of pulling can be suppressed.

In the magnetic flux converging member 30, the ferromagnetic material 36
Height h, distance d to the crucible 11 and diameter U
is important. These are preferably in the following ranges.

If the height h is too large, the crucible support shaft becomes long, which is uneconomical. If the height h is too small, the magnetic flux convergence efficiency decreases, so the height h is preferably 10 to 2500 mm. If the distance d is too large, the magnetic flux spreads at the top of the member, so that the perpendicular component to the bottom of the crucible decreases. If the distance d is too small, cooling becomes difficult, so the distance d is preferably 10 to 100 mm. If the diameter U is too large, the amount of heat for maintaining the melt temperature increases, which is economically disadvantageous. If the diameter U is too small, the magnetic flux induction efficiency decreases.
0 to 500 mm is preferred.

(Embodiment 3) FIG. 4 shows Embodiment 3 of the present invention.
Is shown. The single crystal growing apparatus according to the third embodiment is different from the single crystal growing apparatus according to the first embodiment in that the magnetic flux guiding member 30 is formed of a ring-shaped ferromagnetic material 36 provided concentrically around the upper end of the pedestal 16. , 2 are different from the single crystal growing apparatus. The ring-shaped ferromagnetic material 36 is made of a non-magnetic stay 31,
31 attached to the upper end of the pedestal 16,
The outside is surrounded by a heat insulating material 32 and a refrigerant passage 34 is provided.
Is forcibly cooled from the inside by a coolant such as water or liquid nitrogen flowing through.

The magnetic flux converging member 30 includes a pedestal 1
A ring-shaped ferromagnetic material 3 provided close to the upper end of 6
6 causes the vertical portion of the lower magnetic field to converge along the pedestal 16. It also moves in the axial direction together with the pedestal 10. Therefore, as in the case of the single crystal growing apparatuses of the first and second embodiments, an increase in the oxygen concentration in the latter stage of pulling can be suppressed.

In the magnetic flux converging member 30, the ferromagnetic material 36
Are important in the axial height h, the distance d to the crucible 11, the inner diameter U, and the outer diameter B. These are preferably in the following ranges.

If the height h is too large, unnecessary heat is removed, and the amount of heat required to maintain the melt temperature increases. If the height h is too small, the magnetic flux converging efficiency decreases.
~ 200 mm is preferred. If the distance d is too large, the magnetic flux spreads at the top of the member, and the vertical component to the bottom of the crucible decreases. If the distance d is too small, cooling becomes difficult.
0-100 mm is preferred. If the inner diameter U is too large, it becomes difficult to induce magnetic flux to the central portion of the bottom of the crucible,
If it is too small, it will be difficult to install it structurally.
00 mm is preferred. If the outer diameter B is too large,
If the efficiency of converging magnetic flux to the bottom of the crucible decreases, and if it is too small, it becomes difficult to induce magnetic flux to the outer peripheral portion of the bottom of the crucible.
0 to 700 mm is preferred.

[0040]

Next, an embodiment of the present invention will be described.

An 8-inch single crystal was pulled up using the single crystal growing apparatus of the first, second and third embodiments. Table 1 shows common lifting conditions, and Table 2 shows specifications of the magnetic flux converging members used in each device. The type A is a diamagnetic cone-shaped magnetic flux converging member used in the single crystal growing apparatus of the first embodiment, and the type B is a ferromagnetic type magnetic flux concentrating member used in the single crystal growing apparatus of the second embodiment. The axial magnetic flux converging member and the C type represent ferromagnetic ring magnetic flux converging members used in the single crystal growing apparatus of the third embodiment, respectively. FIG. 5 shows the result of examining the oxygen concentration distribution of the pulled single crystal in the pulling direction.

[0042]

[Table 1]

[0043]

[Table 2]

Comparative Example 1 is a case where the lifting is performed without using the magnetic flux converging member under the application of the cusp magnetic field. Compared to Comparative Example 2 in which no cusp magnetic field was applied, the oxygen concentration was reduced overall, but was extremely noticeable in the latter stage of the pulling, except that the oxygen concentration was reduced due to the decrease in the raw material melt until the middle stage of the pulling. An increase in oxygen concentration occurred.

On the other hand, the first to third embodiments use a diamagnetic (material: YBCO) cone-shaped magnetic flux converging member. In each case, the increase in oxygen concentration in the latter stage of pulling was suppressed as compared with Comparative Example 1, and the oxygen concentration distribution in the single crystal pulling direction was made uniform. Further, although the minimum diameter B of the diamagnetic material is reduced in the order of Examples 1, 2, and 3, the increase in the oxygen concentration in the latter period of the pulling is suppressed accordingly. The concentration was reduced to about the same as the oxygen concentration at the start of pulling, and the oxygen concentration distribution in the single crystal pulling direction was particularly effectively uniformed.

In Examples 4 and 5, a ferromagnetic material (material: Fe-
This is a case where a magnetic flux converging member of Si) is used. Since the outer diameter B of the axial ferromagnetic material and the inner diameter B of the ring-shaped ferromagnetic material were set to be the same as the minimum diameter B of the diamagnetic material in Example 3, the increase in oxygen concentration in the latter stage of pulling was almost the same as in Example 3. Was suppressed until.

[0047]

As described above, the single crystal growing apparatus of the present invention converges the magnetic field along the pedestal by the magnetic flux converging member attached to the pedestal when the CZ is pulled under the application of the cusp magnetic field. Thereby, even when the crucible is raised, a sufficient magnetic field component crossing the bottom and the peripheral wall of the crucible at right angles can be secured. Therefore, an increase in the oxygen concentration in the latter stage of the withdrawal is suppressed,
A high-quality single crystal having a uniform oxygen concentration distribution in the pulling direction can be manufactured. Further, in changing the distribution shape of the magnetic field, a small and static magnetic flux converging member attached to the pedestal is used, so that it is possible to avoid adverse effects such as vibrations which are problematic when operating the magnetic field generating means up and down. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a single crystal growing apparatus according to a first embodiment of the present invention.

FIG. 2 is a structural explanatory view of a magnetic flux converging member used in the single crystal growing apparatus, (a) is a plan view, (b) is an elevation view,
(C) is a longitudinal sectional view.

FIG. 3 is a longitudinal sectional view illustrating a structure of a magnetic flux converging member according to a second embodiment of the present invention.

FIG. 4 is a structural explanatory view of a magnetic flux converging member showing a third embodiment of the present invention, wherein (a) is a plan view and (b) is a longitudinal sectional view.

FIG. 5 is a chart showing the oxygen concentration distribution in the pulling direction for the present invention example and the conventional example.

FIG. 6 is a schematic configuration diagram of a conventional single crystal growing apparatus.

[Explanation of symbols]

 Reference Signs List 10 growth apparatus main body 11 crucible 12 raw material melt 13 single crystal 16 pedestal 20 magnetic field generating means 21 annular magnet for forming cusp magnetic field 30 magnetic flux converging member 33 diamagnetic material 36 ferromagnetic material

Claims (3)

[Claims] 1. A magnetic field generator for generating a cusp magnetic field by a combination of a growth apparatus main body that pulls a single crystal from a raw material melt in a crucible by a CZ method and an upper and lower set of annular magnets arranged on an outer peripheral side of the growth apparatus main body. A single crystal growing apparatus, comprising: means, and a magnetic flux converging member attached to a pedestal supporting a crucible in a growing apparatus main body and for converging a magnetic field below the crucible along the pedestal. 2. The single crystal growing apparatus according to claim 1, wherein the magnetic flux converging member is made of a ferromagnetic material disposed inside and / or around the pedestal. 3. The single crystal according to claim 1, wherein the magnetic flux converging member is provided around the pedestal, and is formed of a cone-shaped diamagnetic material whose diameter gradually decreases upward. Breeding equipment.