JPS6036392A - Apparatus for pulling single crystal - Google Patents

Abstract

PURPOSE:To effect the growth of uniform single crystal, and to prevent the breakage of the crucible by thermal stress, by placing a magnet device to apply a magnetic field near the upper and the lower parts of the pulling surface of a single crystal, thereby suppressing the thermal convection at the upper part of the molten liquid and stirring the lower part of the liquid. CONSTITUTION:The objective single crystal pulling apparatus is composed of the main body of the pulling apparatus to pull up the seed crystal immersed in the molten liquid 1 of the raw material of the crystal to form the single crystal, and the magnet device to apply a magnetic field to the molten liquid 1. The magnet device is a superconductive magnet consisting of the magnet 28 to suppress the thermal convection near the boundary layer 6 between the solid and liquid interface of the molten liquid 1 and the magnet 29 to generate the rotary magnetic field to stir the part lower than the boundary layer 6. The magnet 28 is directed to generate the magnetic field perpendicular to the pulling direction of the single crystal, and the magnet 29 is placed to direct the magnetic field parallel to the pulling direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a single crystal pulling apparatus for producing a silicon single crystal used as a semiconductor material, for example, and in particular to a magnet apparatus for applying a magnetic field to a single crystal raw material melt. The present invention relates to a single crystal pulling device equipped with the following.

[Technical background of the invention]

A crucible 2 according to the C2 method (Czochralski method) shown in FIG. 1 is heated by a heater 3, and the single crystal raw material is always kept in a molten state. A seed crystal 4 is inserted into this melt I,
When the glaze crystal 4 is pulled up at a certain speed by the pulling drive mechanism 5, the crystal grows in the solid-liquid interface boundary layer 6,
A single crystal 7 is produced. At this time, fluid movement of the melt 1 spun by the heating of the heater 3, that is, thermal convection 8 occurs.

The cause of this thermal convection 8 is explained as follows. That is,
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 NGr
@Normi J number α・ΔT−R/ν Where, 1: Gravitational acceleration α; Coefficient of thermal expansion of melt ΔT; Ruth 7I? Radial temperature difference R; radius ν; kinematic viscosity coefficient of the melt Generally, when the Grashoff number NcJr exceeds a critical value determined by the geometric dimensions of the melt 1, thermal boundary conditions, etc. Heat convection 8 occurs within 1. Normally, Nor>10
At 5, the thermal convection 8 of the melt 1 is in a turbulent state. r〉10
At 9, the state becomes a disturbance state.

Currently, under the melt conditions for pulling a single crystal with a diameter of 3 to 4 inches, Nor>109 (the above N.

(according to the equation) The interior of the melt 1 is not in a disturbed state, and the surface of the melt 1, that is, the solid-liquid interface boundary layer 6, is in a wavy state.

If such a disturbed thermal convection 8 exists, temperature fluctuations within the melt 1, especially in the solid-liquid interface layer 6, will be severe, and the thickness of the solid-liquid interface layer 6 will change positionally and temporally. The fluctuation is severe, and the microscopic re-dissolution of the crystal during growth is remarkable, and dislocation loops, stacking faults, etc. occur in the grown single crystal 7.

Moreover, this defect area is caused by an irregular solid-liquid interface boundary layer 6.
This occurs non-uniformly with respect to the direction of single crystal pulling due to fluctuations in .

Furthermore, impurities 9 dissolved in the melt 1 from the inner surface of the crucible 2 due to chemical changes between the melt 1 and the crucible 2 on the inner surface of the crucible 2, which are in contact with the high temperature melt 1 (for example, about 1500°C). is carried by this thermal convection 8 and dispersed throughout the interior of the melt 1. These impurities 9 act as nuclei, causing dislocation loops, defects, growth stripes, etc. in the single crystal 7, deteriorating the quality of the single crystal 70. For this reason, such a single crystal7i)
LS I (Large 5cale Integr
When manufacturing wafers for large-scale integrated circuits, wafers containing defective parts cannot be used because their electrical characteristics have deteriorated, resulting in poor yields.

In the future, the single crystal 7 will become increasingly larger in diameter, but the above-mentioned group 2
As can be seen from the formula for the Sukhoff number, as the diameter of the crucible 2 increases, the Grashoff number also increases, the thermal convection 8 of the melt 1 becomes even more intense, and the quality of the single crystal 7 continues to deteriorate. I will follow it. 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(a) shows an example of a conventional single crystal pulling apparatus using magnetic field application. In FIG. 2(a), the same parts as in FIG. 1 are denoted by the same reference numerals, and their explanation will be omitted. That is, the second
In the figure (,), a magnet 1o made of a copper coil is arranged around the outer periphery of the crucible 2 so that a uniform magnetic field is applied to the melt I in the 11 directions shown, which are perpendicular to the single crystal pulling direction. do.

The melt 1 of the single crystal 7 is generally a conductor having an electrical conductivity σ. For this reason, a fluid with electrical conductivity undergoes thermal convection 8
When the fluid moves in a direction that is not parallel to the magnetic field application direction 11, it is subjected to magnetic resistance according to Lenz's law. Therefore, the movement of thermal convection 8 is prevented.

Generally, when a magnetic field is applied, the magnetoresistive force, that is, the magnetorheological coefficient ν87. is, νeff = (μHD)σ/ρ where 1μ; magnetic permeability of the melt H; magnetic field strength D; crucible diameter α; electrical conductivity of the melt ρ: magnetic field strength increases as the density of the melt increases. Then, the magnetorheological coefficient ν8. .

increases, ν in the formula for the Grashof number shown above increases, and the Dallashoff number rapidly decreases, and the Glashof number can be made smaller than the critical value by a certain magnetic field strength. As a result, 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 in the single crystal 7, the generation of loose dislocations, and the generation of defects and growth stripes. A single crystal 7 of uniform quality is obtained in the upward direction, and the single crystal 7
Improved quality and yield.

[Problems with background technology]

By the way, the conventional single-crystal pulling apparatus shown in FIG. 2 (,), which is equipped with a normal-conducting magnet constituted by a copper coil, has the following drawbacks. That is, in a so-called large single crystal pulling apparatus in which the single crystal size to be grown is 4 inches or more, Ruth? 2
The chamber 12 housing the heater 3 is equipped with a magnet 1 installed on the outer periphery of the chamber 12 to apply a required magnetic field strength Bs (for example, 2000 Gauss or more) to the solid-liquid interface N6 in order to suppress direct vibration, for example. If you are trying to get a better result, you will need a very large coil ampere turn, calculated according to the Biot-Savart law. for example,
106 ampere turns or more are required.

In order to achieve such a large ampere turn with a normally conducting magnet, the diameter of the coil must be enormous. yJ? 2 is in the form of being roughly covered by the coil. Therefore, the magnetic field distribution 13 inside the crucible 2 is
As shown in FIG. 2(b), the Grashof number N at the solid-liquid interface boundary layer 6 is generally uniform at about /1 in the height direction of the crucible 2. It will be below C. Here, NG, and N
G2 is the Grashof number of the melt at the bottom of the solid-liquid interface boundary layer 6 and Ruth 2, respectively.

Therefore, Ruth 7+? Heat convection is suppressed everywhere in the melt 1 inside the melt 1, and the melt 1 becomes completely stationary. In this state, there is no heat transfer path due to convective heat transfer, and heat is supplied from the heater 3 to the melt 1 only by thermal conduction.

Now, if the single crystal size is small (2 to 3 inches), the melt 2 is also small (4 to 6 inches), and even if the melt 1 is completely still when a magnetic field is applied, it will not be supplied from the heater 3. The heat is
Since the heat conduction of the melt 1 is sufficiently conducted to the solid-liquid boundary layer 6, the temperature between the solid-liquid boundary layer 6 and the melt? There is almost no temperature difference with the surrounding area of 2. Specifically, the temperature is usually kept within 10-odd degrees Celsius.

On the other hand, in large single crystal pulling equipment where the single crystal size is 4 inches or more, the diameter of the crucible 2 is increased to 10 to 14 inches, so heat conduction alone is no longer enough to keep the crucible at the center of the crucible 2. Heat from the heater 3 is not sufficiently transmitted to the solid-liquid interface boundary layer 6. Therefore, a large temperature difference occurs between the solid-liquid interface boundary layer 6 and the peripheral area of the crucible 2. Specifically, it is usually about several lθ°C.

In order to effectively grow the single crystal 7 in the solid-liquid interface boundary layer 6, a sufficient temperature above a certain level is required. For example, in the case of silicon single crystal, a temperature of 1400° C. or higher is required. Therefore, it is necessary to increase the heater power to overcome the temperature gradient and provide the required temperature to the solid-liquid interface boundary layer 6.

Furthermore, if the temperature gradient is large, a considerable temperature gradient will also occur within the solid-liquid interface boundary layer 6 when the single crystal size is large. In order to grow a homogeneous single crystal 7, i2! Uniformity is also required. Therefore, such a temperature gradient is not preferable for single crystal growth.

Also, if the temperature difference between the center and the periphery of the crucible 2 is too large, the thermal stress acting on the crucible 2 will be excessive, and the crucible will
cracks are more likely to occur.

[Purpose of the invention]

The present invention was made based on the above-mentioned circumstances, and its purpose is to provide a single-crystal pulling device that facilitates the growth of homogeneous single crystals and prevents the crucible from cracking due to thermal stress. It is in.

[Advantage of the invention]

The single crystal pulling apparatus according to the present invention suppresses thermal convection in the vicinity of the solid-liquid interface boundary layer of the single crystal raw material melt in the single crystal pulling apparatus main body and the single crystal raw material melt in the single crystal pulling apparatus main body. It is composed of a magnet device arranged on the main body of the single crystal pulling apparatus so that thermal convection exists near the solid-liquid interface boundary layer of the melt and in the lower part of the single crystal. The crucible filled with the crystal raw material melt has a small temperature difference with the surrounding area, thereby growing a homogeneous single crystal and preventing the crucible from cracking due to thermal stress.

[Embodiments of the invention]

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

No. 311 (a), (b), and (e) show the first embodiment of the single crystal pulling apparatus according to the present invention.
) is a configuration diagram, FIG. 3(b) is a characteristic diagram of magnetic field strength and position, and FIG. 3(c) is a characteristic diagram of Grashof number, position, and 'l+! It's sex i.

The same parts as in 2M(2)ζ帥(C) are given the same reference numerals, and their explanation will be omitted.

The coil center axis X of each superconducting coil 15a, 15b, ~
XI' and X2 to X2' are made to coincide with the extension line of the solid-liquid interface boundary layer 6, and the superconducting coils 15a and 15b are arranged parallel to the single crystal pulling axis 16 with the chamber 12 in between. Due to this coil arrangement, a magnetic field 1 in a direction perpendicular to the single crystal pulling axis 16 is applied to the melt 1 .

The distance Nct' 2 between the superconducting coils 15a and 15b is the chamber diameter Ll and the superconducting coil 15a.

15b cold container x 7h, 17b width T, cold container 17
N L for Ht between a, 17b and chamber 12
Superconducting coils 1'5a arranged at a distance L2 determined as t = L r + 2 t + T,
The inner diameter R1, outer radius R32, width D1, and ampere turns of the magnetic field distribution 18 as shown in FIG.
Select so that

That is, for the solid-quasi-interface boundary layer thickness δ, H(H)
The Grashoff number at the depth position δ) is shown in Figure 3 (c
), set the magnetic field strength at that position to N so that the critical glassphone number N is achieved. Set the magnetic field strength B8 corresponding to C to C. Accordingly, the magnetic field distribution in the height direction of the crucible 2 becomes as shown in 18 in FIG. 3(b), and the corresponding Grashof number distribution becomes as shown in 19 in FIG. 3(c).

Here, B4 is the magnetic field strength in the solid-liquid interface boundary layer 6, and has the relationship B4>Bs, and B,
is the magnetic field strength at the bottom of crucible 2, and! l)B
5 < B a, Na4 is the Grashof number corresponding to B, and pNG4<Noc, No5 is the Grashof 7P corresponding to B, and N
(J5>Noc).

Next, the operation and effect of the single crystal pulling apparatus of this embodiment configured as described above will be explained. Solid-liquid interface boundary rf: From I6 to depth H, the magnetic field strength is B.

Since it is very large, the number of glass holes for melt 1 is NG: No<N
Thermal convection 8 of the melt 1 is suppressed and the melt 1 remains stationary. - 10,000, depth H up to the bottom where the shield is 2, the magnetic field strength is B, so small that the Grashof number N of the melt l. NG)N,c;11 Thermal convection 8 in the melt 1 still exists.

Therefore, the heat from the heater 3 is effectively transferred to the center in this region by convection heat transfer by the heat convection 8. Therefore, the inside of the melt 1 has a fairly uniform temperature distribution.

On the other hand, the depth H'? of the solid-liquid interface boundary layer 6? :
, there is no convective heat transfer. The heat from the heater 3 is transferred to the solid-liquid interface boundary layer 6 by heat conduction from the periphery of the crucible 2 and the uniform temperature melt portion below the depth H. Therefore, since the heat transfer effect to the solid-liquid interface boundary layer 6 is enhanced compared to the conventional type, the temperature difference between the peripheral area of the crucible 2 and the solid-liquid interface boundary layer 6 is small.

Furthermore, since the melt 1 is well stirred by the thermal convection 8 until just below the solid-liquid interface boundary layer 6 where the single crystal 7 is grown, the melt 1 as a homogeneous raw material is grown. supplied to the department.

Next, the second embodiment of the present invention is shown in FIG. 4 (-) (b) (
This will be explained with reference to C).

M4 diagrams (a), (b), and (c) show a second embodiment of the single crystal pulling apparatus according to the present invention, where FIG. 4(a) is a configuration diagram and FIG. 4(b) is a magnetic field The characteristic diagram of intensity and position, Figure 4 (C) is the characteristic diagram of Grashof number and position, and it is in the same part as Figures 1, 2, and 3 (a), (b), and (c). are given the same reference numerals and the explanation thereof will be omitted.
In figure (a), superconducting coil 15a.

A superconducting coil 21 that applies a magnetic field 2o in a direction parallel to the single crystal pulling axis 16 and a cold container 22 that houses the superconducting coil 21 are connected to the wire 15b with the coil center axis Y, %Y,'
is arranged so that it coincides with the solid-liquid interface boundary layer 6.

The parameters of the superconducting coil 21, such as the inner radius, two outer radius widths, ampere turns, etc., are the same as the magnetic field distribution shown in FIG. 4(b) as in the first embodiment shown in FIG. 3(a). 22,
It is determined so that a Grashof number distribution 23 as shown in FIG. 4(c) can be realized.

Note that the operation and effect are the same as those of the first embodiment shown in FIGS. 3(a), 3(b), and 3(c), so the explanation thereof will be omitted.

Next, the third embodiment of the present invention is shown in FIGS.
This will be explained with reference to C).

5(a), 5(b), and 5(c) show a third embodiment of the single crystal pulling apparatus according to the present invention, FIG. 5(-) is a block diagram, and FIG. 5(b) is a block diagram. Figure 5(c) is a characteristic diagram of magnetic field strength and position, and Figure 5(c) is a characteristic diagram of Grashof number and position.
The same parts as in FIGS. 2 and 3 (,) (b) (c) and FIG.

That is, the superconducting coil 25 (Fig. 3 (=) may have any configuration of the embodiment shown in Fig. 4 (, ))
is placed above the solid-liquid interface by a boundary layer 6h.

With such a configuration, the magnetic field distribution 26 shown in FIG. 5(b) and the Grashof number distribution 27 shown in FIG. 5(c), which are similar to the first embodiment shown in FIG. 2 melt 1
When you get it inside, you can do it. In addition, the reason for arranging the coils as described above is because the depth of crucible 2 is shallow, etc.
Even if a superconducting coil is used depending on the shape of the
This is because it may be impossible to obtain the magnetic field distribution as in the first embodiment shown in . In the above case,
By applying the third present embodiment, a desired magnetic field distribution can be obtained.

Incidentally, since the operation and effect are the same as those of the first embodiment shown in FIG.

Next, a fourth embodiment of the present invention will be described with reference to FIG.

FIG. 6 is a configuration diagram showing a fourth embodiment of the single crystal pulling apparatus according to the present invention, and the same parts as in FIGS. do. RIJ, in FIG. 6, in order to increase the stirring effect of the melt 1 at the bottom of the melt 1, a coil 2 for suppressing thermal convection of the melt 1 is installed.
A coil 29 that generates a rotating magnetic field 3θ is disposed below the coil 8 . This coil 29 can be best realized, for example, by using three-phase alternating current and arranging three coils around the outer periphery of the chamber 12 so as to be shifted by 120 degrees around the single crystal pulling axis 16.

By the coil 28, the melt 1 near the solid-liquid interface boundary layer 6
The thermal convection of is stationary, and the melt 1 at the bottom of the crucible 2 is stirred by the coil 29, so that
) The same operation and effect as the first embodiment shown in ) can be obtained.

Next, a fifth embodiment of the present invention will be described with reference to FIG.

FIG. 7 is a configuration diagram showing a fifth embodiment of the single crystal pulling apparatus according to the present invention, and the same parts as in FIGS. do. That is, in FIG. 7, in order to increase the stirring effect of the melt 1 in the lower part of the crucible 2, an ultrasonic wave 32 generated by an ultrasonic generator 32 via a waveguide 31 is applied to the lower part of the crucible 2. is introduced into the melt 1 at the bottom of the crucible 2.

With this configuration, the thermal convection of the melt 1 near the solid-liquid interface boundary layer 6 is stopped by the coil 28, and the ultrasonic wave 3
2, the melt 1 at the bottom of the crucible 2 is stirred, so the third
The same operation and effect as the first embodiment shown in FIGS. (a), (b), and (c) can be obtained.

Note that the present invention is not limited to the above embodiments,
Various modifications can be made without departing from the gist of the invention.

〔Effect of the invention〕

As described above, the single crystal pulling apparatus according to the present invention suppresses thermal convection in the vicinity of the solid-liquid interface boundary layer between the single crystal pulling apparatus main body and the single crystal raw material melt in the single crystal pulling apparatus main body. In addition, it was constructed with a magnet device placed on the main body of the single crystal pulling apparatus so that thermal convection exists near the solid-liquid interface boundary layer of the single crystal raw material melt and at the lower part of the single crystal material melt. exhibits an effect.

In other words, near the solid-liquid interface boundary layer, thermal convection is suppressed and growth conditions close to thermal and chemical equilibrium are satisfied, while at the same time In this region, the melt is well stirred by thermal convection, the melt is homogenized, and the temperature is kept uniform. Therefore, solid -
The heat conduction effect to the liquid interface boundary layer is enhanced, the temperature difference between the surrounding area and the solid-liquid interface boundary layer is small, and the sufficiently stirred melt is supplied to the solid-liquid interface boundary layer. As a result, a homogeneous single crystal is grown. In addition, since the temperature difference between the center and the periphery of the bolt is reduced, cracking of the bolt due to thermal stress is avoided.

[Brief Description of the Drawings] Fig. 1 is a configuration diagram showing an example of a conventional single crystal pulling device, Fig. 2 is a diagram for explaining an example of a conventional single crystal pulling device equipped with a magnet, 3 to 7 are diagrams for explaining first to fifth embodiments of the single crystal pulling apparatus according to the present invention, respectively. 1... Melt, 2... Ruth, 3... Heater, 4.
... Seed crystal, 5... Pulling drive mechanism, 6... Solid-liquid interface boundary layer, 7... Single crystal, 8... Thermal convection, 9...
・Impurity, 10...Magnet, 11.20...Magnetic field direction, 12...Chamber, 13.18.23,26°・
・Magnetic field distribution, 14.19, 24.27... Glassho 7
Number distribution, 15 a, 15 b, 21, 25-
--Superconducting coil, 16--Single crystal pulling shaft, 17 a
*17 b -22・=cold container, 28・thermal convection suppression coil, 29・rotating magnetic field coil, 30・・
- Rotating magnetic field, 31... Waveguide, 32... Ultrasonic generator, 32... Ultrasonic wave. Applicant's agent Patent attorney Takehiko Suzue (8) Figure 5 Figure 7

Claims (6)

[Claims] (1) A single crystal pulling device main body that generates a single crystal by inserting a seed crystal into the single crystal raw material melt filled in Ruth 7Iζ and pulling the seed crystal; It applies a magnetic field, suppresses thermal convection near the solid-liquid interface boundary layer of the single-crystal raw material melt, and suppresses thermal convection near the solid-liquid interface boundary layer of the single-crystal raw material melt below. A single crystal pulling device comprising a magnet device arranged so as to be present. (2) The single crystal pulling device according to claim (1), wherein the magnet device is a superconducting magnet. (3) The magnet device is arranged such that the direction of the magnetic field is perpendicular to the single crystal pulling direction.
) The single crystal pulling device described in item 2. (4) The magnet device is arranged so that the field direction is parallel to the single crystal pulling direction.
) The single crystal pulling device described in item 2. (5) A patented magnet device comprising a first magnet for suppressing thermal convection of the single-crystal raw material melt, and a second magnet for generating a rotating magnetic field for stirring the single-crystal raw material melt. A single crystal pulling apparatus according to claim (1). (6) The single crystal pulling apparatus according to claim 1, wherein the single crystal pulling apparatus main body includes an ultrasonic generator for stirring the single crystal raw material melt.