JPH0361630B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a single-crystal pulling device for producing a silicon single crystal used as a semiconductor material, for example, and particularly includes a magnet device for applying a magnetic field to a single-crystal raw material melt. This invention relates to a single crystal pulling device.

[Technical Background of the Invention] FIG. 1 shows an example of the configuration of a conventional single crystal pulling apparatus using the CZ method (Cyochralski method). A crucible 2 filled with a single-crystal raw material melt 1 (hereinafter abbreviated as melt) is heated by a heater 3, and the single-crystal raw material always maintains a melt state. When the seed crystal 4 is inserted into the melt 1 and the seed crystal 4 is pulled up at a certain speed by the pulling drive mechanism 5, the solid -
A crystal grows in the liquid interface boundary layer 6, and a single crystal 7 is generated. At this time, fluid movement of the melt 1 induced by heating by the heater 3, that is, thermal convection 8 occurs.

The cause of this thermal convection 8 is explained as follows. That is, the thermal convection 8 generally occurs when the balance between the buoyant force due to thermal expansion of the fluid and the viscous force of the fluid is broken. The dimensionless quantity that represents the balance between this buoyant force and viscous force is the Grashof number N _Gr .

N _Gr = g・α・ΔT・R ³ /ν ³ where, g: Gravitational acceleration α: Coefficient of thermal expansion of melt ΔT: Temperature difference in crucible radial direction R: Crucible radius ν: Coefficient of kinematic viscosity of melt Generally, When the Grashof number N _Gr exceeds a critical value determined by the geometrical dimensions of the melt 1, thermal boundary conditions, etc., thermal convection 8 occurs within the melt 1. Normally, when N _Gr >10 ⁵ the thermal convection 8 of the melt 1 becomes turbulent, and when N _Gr >10 ⁹ it becomes a turbulent state. Under the current melt conditions for pulling a single crystal with a diameter of 3 to 4 inches, N _Gr > 10 ⁹ (according to the formula for N _Gr above), and the inside of the melt 1 is in a disturbed state, and the surface of the melt 1, that is, the solid - The liquid interface boundary layer 6 becomes undulating.

If such a disturbed thermal convection 8 exists,
Temperature fluctuations in the melt 1, especially in the solid-liquid interface boundary layer 6, become intense, and the thickness of the solid-liquid interface boundary layer 6 varies greatly both positionally and temporally, leading to microscopic re-dissolution of crystals during growth. becomes noticeable, and dislocation loops, stacking faults, etc. occur in the grown single crystal 7. Moreover, these defective portions occur non-uniformly in the single crystal pulling direction due to irregular fluctuations of the solid-liquid interface boundary layer 6.

Furthermore, due to the chemical change between the melt 1 and the crucible 2 on the inner surface of the crucible 2 where the high-temperature melt 1 (for example, about 1500°C) contacts, the impurities 9 dissolved in the melt 1 from the inner surface of the crucible 2 are removed by this thermal convection. 8 and was transported to
Dispersed throughout the interior of the melt 1. This impurity 9 becomes a nucleus and causes dislocation loops and defects in the single crystal 7.
Growth stripes and the like occur, deteriorating the quality of the single crystal 7. Therefore, LSI is better than such a single crystal 7.
When manufacturing large scale integration (large scale integrated circuit) wafers, wafers containing defective parts are unusable due to deteriorated electrical characteristics, resulting in poor yield.

In the future, the diameter of the single crystal 7 will become larger and larger, but as can be seen from the equation for the Grashof number mentioned above, as the diameter of the crucible 2 increases, the Grashof number also increases, and the thermal convection 8 of the melt 1 increases. The problem will become even more severe, and the quality of the single crystal 7 will continue to deteriorate.
Therefore, a method has been proposed in which a DC magnetic field is applied to the melt 1 in order to suppress the thermal convection 8 and pull the single crystal under growth conditions close to a thermally and chemically equilibrium state.

FIG. 2 shows an example of a conventional single crystal pulling apparatus using magnetic field application. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals, and their explanations will be omitted. That is, in FIG. 2, the magnet 10 is placed around the outer periphery of the crucible 2 so that a uniform magnetic field is applied to the melt 1 in the direction 11 shown in the figure, which is orthogonal to the single crystal pulling direction.
Place. The melt 1 of the single crystal 7 is generally a conductor having an electrical conductivity σ. Therefore, when a fluid having electrical conductivity moves due to thermal convection 8, the fluid moving in a direction not parallel to the magnetic field application direction 11 is subjected to magnetic resistance according to Lenz's law. Therefore, the movement of thermal convection 8 is prevented. In general, the magnetoresistive force when a magnetic field is applied, that is, the magnetorheological coefficient ν _eff , is ν _eff = (μHD) ² σ/ρ, where μ; magnetic permeability of the melt H; magnetic field strength D; crucible diameter σ; Electrical conductivity of the melt ρ: When the density of the melt increases and the magnetic field strength increases, the magnetorheological coefficient ν _eff increases, and ν in the formula for the Grashof number shown earlier increases, and the Grashof number rapidly decreases. death,
With a certain magnetic field strength, the Grashof number can be made smaller than a critical value. Thereby, thermal convection of the melt 1 is completely suppressed. By applying a magnetic field in this way, thermal convection is suppressed, which eliminates the inclusion of impurities, the generation of dislocation loops, and the generation of defects and growth stripes in the single crystal 7, and moreover, the single crystal is uniform in the pulling direction. A high-quality single crystal 7 is obtained, and the quality and yield of the single crystal 7 are improved.

On the other hand, as a single crystal pulling apparatus by applying a magnetic field exhibiting the above-mentioned characteristics, there is one that employs a superconducting magnet, which has been in the spotlight recently.

Figures 3 and 4 show an example of the configuration of a conventional single crystal pulling apparatus equipped with a superconducting magnet device. 2, the same parts as in FIG. 2 are denoted by the same reference numerals, and the explanation thereof will be omitted.

In FIGS. 3 and 4, 11 is shown in the melt 1.
In order to apply a magnetic field (hereinafter referred to as transverse magnetic field) in the direction of Install it in the location shown.

The superconducting coil 13 is operated at an extremely low temperature (for example, 4.2〓)
It is housed in an inner tank 16 filled with liquid helium 15 and maintained in a superconducting state. Cold storage container 17a, 1 that keeps the superconducting coil 13 in an extremely low temperature state
7b consists of an inner tank 16, an outer tank 18, and a radiation shield plate 19 installed between these to reduce the amount of heat entering from the outside. Small refrigerator 50
a, 50b, 60a, and 60b are directly attached to the cold storage containers 17a and 17b, respectively.

The small refrigerators 50a, 50b have compressor units 52a, 52b that compress the refrigerating medium (for example, helium) 51a, 51b circulating in the small refrigerators 50a, 50b, and the refrigerant medium 51a, 51b compressed by these compressor units 52a, 52b. Expanders 53a and 53b (53b is not shown) that adiabatically expands and cools 51b.
, freezing stages 54a and 54b (54b is not shown) cooled to a radiation shield temperature (for example, 80〓), and a helium liquefaction temperature (for example, 4.2〓).
Helium recondensers 55a and 55b cooled to
(55b is not shown).

The small refrigerators 60a and 20b are the small refrigerators 50
It has the same structure as a and 50b, and the refrigerating medium 61
a, 61b and compressor units 62a, 62b
and expanders 63a, 63b (63b is not shown)
and a freezing stage 64 having a radiation shield temperature.
a, 64b (64b is not shown), and a freezing stage 65a cooled to an extremely low temperature (for example, 20°).
65b (65b is not shown).

The superconducting coils 13 and 14 are heated at room temperature (for example,
300〓) are connected in series by a power lead 20 installed, and an excitation current is supplied from a power source 21. The external heat entering from the power lead 20 is transferred to the freezing stages 64a, 6 of the small refrigerators 60a, 60b.
4b, 65a, and 65b. The helium gas in the inner tank 16 that has evaporated due to the coil excitation is recondensed (liquefied) by the helium recondensers 55a and 55b of the small refrigerators 50a and 50b.
In this way, inside the cold storage containers 17a and 17b,
Always filled with liquid helium, the superconducting coil 13,
14 can continue to maintain the superconducting state.

In general, a single crystal pulling device closes the crucible 2 and the pulling device chamber 1 every time the pulling operation is completed.
It is necessary to clean the inner surface of 2. In a conventional single crystal pulling apparatus equipped with a superconducting magnet device, this cleaning is performed in the following procedure. First, there is a cold container 1 on which the electromagnetic force generated from the superconducting magnet device acts.
The support rod 22 installed to support 7a and 17b is removed. 2 in the horizontal direction 24 on the floor fixed rails 23 installed at the bottom of the frames 19a and 19b holding the respective cold containers 17a and 17b.
5 to the fixed position to completely separate the single crystal pulling device main body and the superconducting magnet device. In this state, the crucible 2 and chamber 12 are cleaned.

[Problems with background technology]

By the way, the conventional single crystal pulling apparatus configured as described above has the following drawbacks. That is, in order to generate a transverse magnetic field, two cylindrical superconducting coils 13 and 14 are used, and are housed in cold containers 17a and 17b, respectively. Therefore, for each cold storage container 17a, 17b, a small refrigerator 60a, 60b that cools the power lead 20,
Small refrigerators 50a and 50b for helium liquefaction are required. Therefore, a total of four small refrigerators are used, which complicates the system and increases manufacturing costs.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and its purpose is to provide a superconducting magnet that applies a transverse magnetic field to a single-crystal raw material melt, and to have a simple configuration and low manufacturing cost. An object of the present invention is to provide a single crystal pulling device.

[Summary of the invention]

The single crystal pulling device according to the present invention includes a single crystal pulling device main body that generates a single crystal by inserting a seed crystal into a single crystal raw material melt filled in a crucible and pulling the seed crystal; a storage container including first and second cold storage containers that face each other and are connected in a U-shape so as to surround the main body of the device; first and second superconducting coils that generate a magnetic field in a direction perpendicular to the pulling direction of the single crystal; , a superconducting crossover cable that connects second superconducting coils in series, and a refrigerator that is attached to the storage container and cools the inside of the container to an extremely low temperature.

According to this configuration, the magnetic field generated in the direction perpendicular to the pulling direction of the single crystal is generated integrally by the first and second superconducting coils, but the superconducting crossover cable that realizes this is Since it is disposed within the first and second cold storage containers that are connected in the U-shape, the intrusion of heat from the room temperature area is significantly reduced. Therefore, only one refrigerator or one with a small capacity is sufficient for cooling the storage container.

In addition, the first and second
The cold storage container is included in the storage container, and the refrigerator is attached to the storage container.
When a stand is used, the storage container including the first and second cold storage containers can be cooled all at once, and effective cooling is achieved despite the simple configuration.

Furthermore, since they are U-shaped and face each other so as to surround the single crystal pulling device main body, it is easy for the storage container to approach or leave the single crystal pulling device main body, which is convenient for cleaning.

[Embodiments of the invention]

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

5 and 6 show an embodiment of a single crystal pulling apparatus according to the present invention, FIG. 5 is a configuration diagram seen from the front direction, and FIG. 6 is a configuration diagram seen from the top direction. , 3 and 4 are designated by the same reference numerals, and their explanation will be omitted. Figures 5 and 7
In the figure, an inner tank 16 housing superconducting coils 13 and 14, a radiation shield 19, and a cold container 17 are shown.
a, 17b as shown in the drawing, the lifting device chamber 1
Connect them in a U shape so as to surround 2. The power lead that connects the superconducting coils 13 and 14 in series is
The superconducting wire 26 is passed through the inner tank 16 filled with liquid helium. Power supply 21 and superconducting coil 1
A small refrigerator 60a that cools the power lead 20 connected to the inner tank 16 and a small refrigerator 50a that recondenses (liquefies) the helium gas evaporated in the inner tank 16 are directly attached to the cold storage container 17a.

Next, the operation and effect of the single crystal pulling apparatus of this embodiment configured as described above will be explained. That is, the superconducting coils 13 and 14, which were conventionally installed at room temperature,
In this embodiment, the crossover cable is configured as a superconducting wire 26 immersed in liquid helium, so heat intrusion from the room temperature section is greatly reduced, and as a result, compared to the conventional Z coil separated type, , inner tank 1
The amount of helium evaporated within 6 is reduced. For this reason,
Only one small refrigerator is needed for helium liquefaction. Also, the power lead connected to the room temperature section is connected to the power supply 2.
1 to the superconducting coil 13, only one small refrigerator is required for cooling the power lead. According to the above, since the cooling system is configured with a small number of refrigerators, the manufacturing cost is about 2/3 of that of the conventional method.

Further, in the conventional example shown in FIGS. 3 and 4, the power lead 20 connecting the superconducting coils 13 and 14 in series is installed at room temperature, so if the persistent current switch is temporarily connected to the superconducting coil 13, 14
The superconducting coils 13 and 14 are connected to the power source 2.
Even if the power lead 20 between the superconducting coils 13 and 14 is removed by the attachment/detachment mechanism and operation is performed in persistent current mode, the power lead 20 extending between the superconducting coils 13 and 14 cannot be removed. Therefore, Joule heat generation occurs, making it impossible to operate in persistent current mode.

On the other hand, in this embodiment, the superconducting coil 13,
Since the crossover cable between 14 and 14 is in a superconducting state, a persistent current switch is installed and the power lead attachment/detachment mechanism connects the power supply 21 to superconducting coil 1.
By removing the power lead 20 between 3 and 3, operation in persistent current mode becomes possible.

Furthermore, in the conventional example shown in FIGS. 3 and 4, support rods 22 are attached to the cold containers 17a, 17b when the superconducting coils 13, 14 are excited in order to support the cold containers 17a, 17b against the action of electromagnetic force. ,
Since it has to be removed when cleaning the crucible 2, these operations have become complicated.

On the other hand, in this embodiment, the superconducting coils 13, 1
4 is a U-shaped cold storage container 17a, 17;
b, the electromagnetic force generated when the coil is excited is supported by the U-shaped cold storage containers 17a and 17b. Therefore,
Since the electromagnetic support rod used in the past is not required, the superconducting magnet device can be easily moved. Therefore, when cleaning the inner surfaces of the crucible 2 and the pulling device chamber 12, the superconducting magnet device is moved in the horizontal direction 24 on the rails 23 fixed to the floor, and the superconducting magnet device becomes a single crystal pulling device. Cleaning is easy because it can be completely separated from the main body.

Furthermore, since the electromagnetic force can be supported by the U-shaped cold storage containers 17a and 17b in addition to being able to be completely separated, the superconducting magnet device can be moved in the persistent current mode and the single crystal magnet device can be pulled while it is fixed at the fixed position 25. Upper device crucible 2 and pulling device chamber 12
It is possible to clean the inner surface of the In this way, single crystal pulling operation and cleaning can be performed in the persistent current mode. Since the cold containers 17a and 17b have a U-shaped configuration, the superconducting magnet device of this embodiment can be attached without any modification to the configuration of the existing single crystal pulling device main body.

Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 7, the same parts as in FIGS. 5 and 6 are given the same reference numerals, and their explanations will be omitted. That is, the U-shaped cold storage container 17a,
A flexible joint 27 and a flexible joint 2 are attached to the connecting portion of 17b.
Attach the length fixing device 28 of 7. The other configurations are the same as the embodiment shown in FIG.

With such a configuration, the length of the flexible joint 27 is adjusted according to the outer diameter dimension of the single crystal pulling device chamber 12, and the length of the flexible joint 27 is adjusted by the length fixing device 28.
7. The length can be fixed, so the superconducting magnet device can be attached to all kinds of existing or new single crystal pulling device bodies. The other operations and effects are the same as those of the embodiment shown in FIGS. 5 and 6, so their explanation will be omitted.

In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

〔Effect of the invention〕

As described above, the present invention provides a single crystal pulling device main body that generates a single crystal by inserting a seed crystal into a single crystal raw material melt filled in a crucible and pulling the seed crystal, and this single crystal pulling device. a storage container including first and second cold storage containers facing each other and connected in a U-shape so as to surround the main body; first and second superconducting coils that generate a magnetic field in a direction perpendicular to the pulling direction of the crystal; The present invention includes a superconducting crossover cable that connects the second superconducting coils in series, and a refrigerator that is attached to the storage container and cools the inside of the container to an extremely low temperature.

According to this configuration, the magnetic field generated in the direction perpendicular to the pulling direction of the single crystal is generated integrally by the first and second superconducting coils, but the superconducting crossover cable that realizes this is Since it is disposed within the first and second cold storage containers that are connected in the U-shape, the intrusion of heat from the room temperature area is significantly reduced. Therefore, only one refrigerator or one with a small capacity is sufficient for cooling the storage container.

In addition, the first and second
The cold storage container is included in the storage container, and the refrigerator is attached to the storage container.
When a stand is used, the storage container including the first and second cold storage containers can be cooled all at once, and effective cooling is achieved despite the simple configuration.

Furthermore, since they are U-shaped and face each other so as to surround the single crystal pulling device main body, it is easy for the storage container to approach or leave the single crystal pulling device main body, which is convenient for cleaning.

Therefore, a practical single crystal pulling device can be provided.

[Brief explanation of drawings]

Figure 1 is a configuration diagram showing an example of a conventional single crystal pulling device, Figure 2 is a configuration diagram explaining the principle of a single crystal pulling device that applies a magnetic field, and Figures 3 and 4 are superconducting magnets. This figure shows an example of a conventional single crystal pulling apparatus equipped with the device. Fig. 3 is a block diagram seen from the front, Fig. 4 is a block diagram seen from the top, and Figs. 5 and 6 are main views. FIG. 5 is a block diagram of the single crystal pulling device according to the present invention as seen from the front, FIG. 6 is a block diagram of the apparatus seen from the top, and FIG. It is a block diagram which shows another Example of an apparatus. 1... Melt, 2... Crucible, 3... Heater, 4
... Seed crystal, 5 ... Pulling drive mechanism, 6 ... Solid -
Liquid interface, 7...Single crystal, 8...Thermal convection, 9...Impurity, 10...Magnet, 11...Magnetic field direction, 12...
...Lifting device chamber, 13, 14...Superconducting coil, 15...Liquid helium, 16...Inner tank, 1
7a, 17b...Cold container, 18...Outer tank, 19
...Radiation shield plate, 20...Power lead, 2
1...Power supply, 22...Support rod, 23...Rail,
24...Horizontal direction, 25...Fixed position, 26...
Superconducting wire, 27... Capable joint, 28... Length fixing device, 29a, 29b... Frame, 50a, 50
b, 60a, 60b...Small refrigerator, 51a, 5
1b, 61a, 61b...refrigeration medium, 52a, 5
2b, 62a, 62b... Compressor unit, 53
a, 53b, 63a, 63b...expander, 54
a, 54b, 64a, 64b, 65a, 65b...
...Freezing stage, 55a, 55b...Helium recondenser.

Claims (1)

[Claims] 1. A single crystal pulling device main body that generates a single crystal by inserting a seed crystal into a single crystal raw material melt filled in a crucible and pulling the seed crystal; a storage container including first and second cold storage containers facing each other and connected in a U-shape so as to surround the storage container; first and second superconducting coils that generate a magnetic field in a direction perpendicular to the pulling direction; A single crystal pulling device comprising: a superconducting crossover cable that connects superconducting coils in series; and a refrigerator that is attached to the storage container and cools the inside of the container to an extremely low temperature.