JPS6153189A - Device for pulling up single crystal - Google Patents

Abstract

PURPOSE:To obtain high-quality single crystal having a desired impurity concentration, by transferring a magnet automatically so that a minimum necessary magnetic field is impressed to a solid-liquid interface. CONSTITUTION:The seed crystal 4 inserted into the melt 1, the center line X of the magnet 10 is made in accord with the solid-liquid interface 6 at the starting of pulling of single crystal, and the maximum magnetic field intensity of the magnet 10 is impressed to the interface 6. Then, the pulling drive mechanism 5 is operated, and the seed crystal 4 is pulled up at a constant velocity to grow the single crystal 7. As the interface 6 is lowered, the lowering amount DELTAh is detected by the detector 16, the position detection signal is inputted to the up and down drive controller 17, the driving gear 14 is operated, the magnet 10 is transferred in an amount corresponding to the lowering amount DELTAh, the center line X of the magnet 10 is made in accord with the interface 6, and the maximum magnetic field intensity of the magnet 10 is impressed to the interface 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a single crystal pulling apparatus comprising a magnet for applying a magnetic field.

[Technical background of the invention and its problems] FIG. 2 shows the configuration of a conventional single crystal pulling apparatus using the C2 method (Czochralski method).

In the figure, a crucible 2 filled with a single-crystal raw material melt 1 (hereinafter simply referred to as melt) is heated by a heater 3 so that the single-crystal raw material always maintains a melt state. When the seed crystal 4 is inserted into the melt 1 and the 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. The heating of the dust remover 3 causes liquid movement of the melt 1, that is, thermal convection 8.

The cause of the occurrence of such thermal convection 80 will be explained as follows. In other words, thermal convection generally occurs when the equilibrium between the buoyant force and the viscous force of the fluid is broken (= due to the thermal expansion of two fluids). N
It is Gr.

NGr = g・α・ΔT, R/υ where, g; Gravitational acceleration α: Coefficient of thermal expansion of the melt ΔT Temperature difference in the radial direction of the Nil crucible R Nil crucible radius υ: Coefficient of kinematic viscosity of the melt Generally, the Glass Hole number NGr When a critical value determined by the liquid's geometric dimensions, thermal boundary conditions, etc. is exceeded, thermal convection occurs within the melt. Normally, the thermal convection of the melt is in a turbulent state at NGr) 105, and is in a turbulent state at NGr) 10. In the case of the current melt conditions for pulling a single crystal with a diameter of 3 to 4 inches, NGr>109 (
According to the above formula of NGr. ), the inside of the melt is in a disturbed state, and the surface of the melt, that is, the boundary layer 6 at the solid-liquid interface, is in a wavy state.0 When such disturbed thermal convection exists, the inside of the melt 1, especially at the solid-liquid interface, becomes undulating. Temperature fluctuations in the solid-liquid interface layer 6 become more intense, positional and temporal changes in the thickness of the solid-liquid interface layer 6 become more intense, microscopic re-dissolution of the crystal during growth becomes remarkable, and dislocation loops, stacking faults, etc. Moreover, these defects occur non-uniformly in the single crystal pulling direction due to irregular fluctuations in the solid-liquid interface 6.Furthermore, when high temperature melt (e.g. about 1500°C) A chemical change occurs between the melt 1 and the crucible 2 on the inner surface of the crucible 2, which are in contact with each other. Then, these impurities 9 act as nuclei in the single crystal (dislocation loops, defects, growth patterns, etc. occur, deteriorating the quality of the single crystal). From L8
When manufacturing wafers I, wafers containing defective parts have deteriorated electrical characteristics, making them unusable and reducing yield.

In the future, single crystals will become increasingly larger in diameter, but as can be seen from the equation for Grashof's number mentioned above, as the diameter of the cell crucible 2 increases, the Grashof number also increases, and the thermal convection 8 of the melt 1 becomes even more intense. Therefore, recently, the above-mentioned thermal convection 8 has been suppressed and the single crystal has been pulled using thermal and chemical growth conditions (growth conditions close to equilibrium). Therefore, a method of applying a DC magnetic field to l!ll:tLl has been proposed.

FIG. 3 shows the configuration of a conventional single crystal pulling apparatus using this a-field application, and the same parts as those in FIG. 2 are given the same reference numerals and their explanations will be omitted. In other words, in FIG. 3, the outer circumference of the crucible 2 (for example, a magnet 10 is arranged to apply a uniform magnetic field in 11 directions shown in the figure) to the melt 1. The melt 1 of the single crystal 7 is generally (Because it is a conductor with electrical conductivity σ, when a fluid with electrical conductivity moves due to thermal convection 8, the fluid is moving in a direction that is not parallel to the magnetic field application direction 1). According to the law of , a magnetic resistance force is applied, which prevents the movement of the thermal convection 8 .

Generally, the magnetoresistance force when a magnetic field is applied, that is, the magnetorheological coefficient ueff, is u ef = (pHD)'2'a /p. Here, μ: Magnetic permeability of the melt H: Magnetic field strength D Nylpot diameter α: Electrical conductivity of the melt ρ: Device of the melt As can be seen from this equation, as the magnetic field strength increases, the magnetorheological coefficient increases. As υeff increases, the value in the Grashof number formula shown above increases, and the Glashov 7 number rapidly decreases, and by increasing the magnetic field strength to a certain extent, the Glashov 7 number can be made smaller than the critical value. . As a result, thermal convection 8 of the melt 1 is completely suppressed. In this way, thermal convection 8 is suppressed by applying a magnetic field, which eliminates the inclusion of impurities in the single crystal 7, the generation of dislocation loops, and the generation of defects and growth structures. A single crystal 7 of uniform quality is obtained, and the quality and yield of the single crystal 7 are improved. FIG. 4 shows the relationship between the magnetic field strength and the impurity concentration contained in the single crystal 7. In Figure 2, the magnetic field strength is H
1 or more ζ; the impurity concentration decreases, and a certain magnetic field strength H
At No. 2, the impurity concentration is the lowest. That is, at this a-field strength H2, the glassho 7 number of the melt 1 becomes less than the critical value,
This is because thermal convection 8 of the melt 1 is suppressed. Even if the magnetic field strength is increased by 82 or more (2), the impurity concentration will not decrease any further because thermal convection has already been suppressed.In other words, increasing the magnetic field strength by 2 or more is meaningless. Regarding the impurity concentration, if it is too high, it causes dislocation loops and defects as mentioned above.Therefore, in order to obtain a high quality single crystal, the impurity concentration needs to be in the hatched region Bl-82 region in Fig. 4. There is.

On the other hand, as the single crystal is pulled up, the melt 1 in the crucible 2 decreases by the amount of the single crystal 7 produced, so the solid-liquid interface 6 decreases. In order to apply a magnetic field of 82 or more to the two-solid-liquid interface 6, a magnet 10 capable of applying a magnetic field of 82 or more is placed throughout the crucible 2 space. In this case,
The on-axis magnetic field strength is maximum at the center of the crucible 2. In order for the entire crucible to be 82 or more, place it in the center of crucible 2)
A magnet capable of applying a magnetic field of a > H2 is required, and the margin for magnetic field strength becomes excessive. Therefore, a relatively large magnet 10 is required, which increases the cost.Also, since the magnet 10 is relatively large, the magnetic field shadow # range also widens.
As a result, the leakage magnetic field of the magnet 10 has an effect on the pulling drive mechanism 5 (2), and has an adverse effect on the motors installed in the pulling drive mechanism 5 (2). The equipment is installed inside the crucible 2 for every 7 single crystals pulled up.
It is necessary to clean and refill the crucible 2 with the single crystal raw material, but in conventional equipment, the magnet 1θ is fixed outside the single crystal pulling device. When cleaning the inside of the crucible 2, it is necessary to remove the magnet 10 from the single crystal pulling device, which is complicated.

[Object of the invention] The present invention was developed in consideration of the above circumstances, and
Summary of the zero-crystal invention, which aims to provide a single crystal pulling device that can automatically move a magnet so as to apply the minimum necessary magnetic field to the solid-liquid interface] Achieving the above object Therefore, in the present invention, a single crystal raw material melt (a kind of crystal) is inserted into a crucible that is heated by a heater, and this seed crystal is pulled up at a constant speed by a pulling drive mechanism to separate the solid-liquid melt. A single crystal puller generates a single crystal at the interface, a magnet is installed outside the crucible to apply a magnetic field of the required strength to the solid-liquid interface of the melt, and this magnet is connected to the crucible (perpendicular to the two). a magnet moving mechanism that moves the magnet in at least the horizontal and vertical directions; a detector that detects the position of the solid-liquid interface of the melt; and the position of the solid-liquid interface detected by this detector and the center of the magnet. and a drive control device that controls the magnet moving mechanism so as to match the magnet movement mechanism.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention shown in FIG. 1 will be described.

Figure 1 shows an example of the configuration of a single crystal pulling apparatus according to the present invention, in which the same parts as in Figures 2 and 3 (: are given the same symbols and their explanations are omitted. Crucible 2 filled with liquid 1. Heater 3 that heats melt 1. Single crystal 7 to be pulled is stored in chamber 11 and placed on pedestal 12.
is installed on top.

Further, a magnet 10 is installed on the outer periphery 1 of this chamber 11 to apply an @ field to the molten t1. The magnet 10 is mechanically connected to a vertical drive shaft 13, and the vertical drive shaft 13 is, for example, a threaded rod, so that the magnet 10 is moved vertically, that is, vertically, by rotation of the drive shaft.

The drive method here is, for example, hydraulic.

Either a pneumatic cylinder or a manual 71-handle method may be used. Furthermore, the vertical drive shaft 13 is connected to a drive 14, for example an electric motor. And these vertical drive shafts 13
．． The vertical drive a Sakaki and magnet lO consisting of the drive machine 14 are
Pillar 15 (supported and fixed by two.

On the other hand, inside the chamber/bar 11 is a detector (for example, a liquid level meter) for detecting the liquid level position of the melt 1.

A laser beam position detector) 16 is installed.
Based on this position detection signal, the driving machine 14 is controlled by the vertical drive control device 17.

An embodiment in which a liquid level meter is used as the detector 16 to control the motor 14 will be described with reference to FIG.

As shown in FIG. 5(2), the electrostatic capacitance itC detected by the liquid level sensor 50 is determined as the composite capacitance of the electrostatic capacitance C1 of the melt and the electrostatic capacitance ffC2 of the space.

That is, since the relative permittivity is significantly different between the lower part of the liquid level (in the melt) and the upper part of the liquid level (space), the detected electrostatic capacitance k' changes when the liquid level position of the melt changes. 5
A comparator 1 compares the current capacitance C with the capacitance CO before the change in the liquid level position to determine the amount of change ΔC in capacitance. As mentioned above, the amount of change Δh in the liquid level position can be expressed as a function of the amount of change ΔC in capacitance, so the amount of change in capacitance ΔC is input to the arithmetic circuit 52 to calculate the amount of change in the liquid level position. Obtain Δh. The magnet 1 is
A motor drive signal is applied from the motor drive circuit 53 to the motor 4 so as to lower the zero.

Next, the operation of this embodiment configured as described above will be explained.

First, at the start of crystal pulling, the liquid level of the melt and the center of the magnet 10 are made to coincide. When the liquid level position decreases by pulling up the crystal 7 and the capacitance C detected by the liquid level sensor 50 changes, the comparator 51 compares the current capacitance C with the capacitance before the change CO. (In this case, this is the capacitance at the start of crystal pulling) and the difference ΔC=lGO−CI is output. The amount of decrease Δh in the liquid level is determined from the amount of change ΔC in capacitance, and the motor 4 is driven so that the magnet IO decreases by Δh.

In this way, the magnet 10 follows the drop in the liquid level.
By lowering the liquid level, the liquid level and the center of the magnet 10 can be made to coincide.

Next, referring to FIG. 6, an embodiment will be described in which the motor 4 is controlled using a laser beam position detector as the detector 16.

In Fig. 6, 60 is a laser emitting and light receiving surface, which emits laser light toward the melt and receives the laser light reflected by the liquid surface. The moving speed of the liquid level is measured from the frequency of the received laser beam, and the moving speed is integrated over time to detect the liquid level position.The comparator 62 calculates the current liquid level position and the liquid level position. The amount of change in the liquid level position Δh is determined by comparing the liquid level level fahO before the change.The amount of change in the liquid level position Δ
The motor drive circuit 53 lowers the magnet 10 by h.
A motor drive signal is given to the motor 14 from.

Even with such a configuration, by moving the magnet 10 in accordance with the drop in the liquid level as in the embodiment shown in FIG. I can do it.

It goes without saying that the amount of change Δh in the liquid level position may be directly detected by the laser measuring device 61.

Note that the number of coil turns and current value are set so that the maximum a-field strength of the melt generated by the magnet 10 is B2 in FIG. 4.

Next, the operation of the single crystal pulling apparatus constructed as described above will be explained in two parts. In FIG. The center line X1 of the magnet 10 is made to coincide with the liquid interface 6. That is, the maximum magnetic field strength H2 of the magnet 10 is applied to the solid-liquid interface 6. Next, the pulling drive mechanism 5 is operated to The crystal 7 is pulled up at a certain speed.As the single crystal 7 is formed, the melt surface, that is, the solid-liquid interface 6, decreases.

If the magnet 10 is fixed at this time, it will move to the bottom of the solid-liquid interface 6 (l-I' magnet center line Xl. Generally, the magnetic field strength decreases as it deviates from the magnet center line, A strong magnetic field with an intensity of H4 in FIG. The single crystal 7 grown from the solid-liquid interface 6 to which a strong magnetic field is applied is of low quality.

Therefore, in this device, the amount of decrease Δh of the melt surface is detected by the detector 16, and the position detection signal is sent to the vertical drive control device 1.
7 and magnet 10 by the amount corresponding to the amount of decrease Δhe.
(2) The vertical drive control device 17 outputs a control signal so that the drive member 14 operates to move the (2) vertical drive control device 17. This will match X1.

Therefore, a strong magnetic field of H2 is always applied to the solid-liquid interface 6, and the single crystal 7 grown from there has an impurity concentration of B.
It falls within the range of 1 to BZ and is of high quality. In this way, during single crystal pulling, the magnet 10 is controlled to be driven up and down to align the solid-liquid interface 6 with the center line X1 of the magnet 10, and a magnetic field with a magnetic field strength H2 is applied to the interface 6. Become.

Next, after the single crystal pulling is finished, the inside of the crucible 2 is cleaned, and the new 7
The case of filling a 'C single crystal raw material will be described. At this time (second step), the current supply to the magnet 10 is stopped and the magnetic field application is stopped.Then, the driver 14 is operated to
is rotated to move the magnet 10 downward at 18 in the figure and fixed at position 19. As a result, the magnet lO moves below the chamber 11 (two times) and is fixed, making disassembly and inspection of the chamber 11 and the crucible 2 easy. This effect can be obtained.

(a) Since the solid-liquid interface 6 of the melt 1 and the center line Xl of the magnet 10 can always be aligned, a magnetic field with a strength that can suppress the thermal convection 8 of the melt 1 and control the impurity concentration to a desired level is generated. can be applied, and a high quality single crystal 7 can be obtained.

(b) Since the solid-liquid interface 6 of the melt 1 and the central leg X1 of the magnet 10 can always be made to coincide, the magnetic field strength to be applied to the melt 1 may be the lowest value to obtain the required degree of impurity. , the number of turns of magnet 10, @.

The flow value is small, making it compact and inexpensive.

(C) Since the magnet 10 can be completely separated from the chamber 11 when cleaning the inside of the crucible 2, the inspection and cleaning work of the crucible 2 becomes extremely easy.

Note that the present invention is not limited to the above embodiments.

FIG. 7 shows another example of the structure of the single crystal pulling apparatus according to the present invention, and the same parts as in FIG. 1 are given the same reference numerals and the explanation thereof will be omitted.

In this embodiment, the magnet 10 is of a split type, and the magnet 10 is of a split type.
This magnet 10 is also designed to be able to apply a magnetic field with an intensity of H2 shown in FIG. 4 to the solid-liquid interface 6. The mechanism for vertically driving the magnet 10 is the same as that shown in FIG. 21 is a moving device that simultaneously moves the magnet lO and the upper and lower wJ mechanisms in the horizontal direction, which allows adjustment of the applied magnetic field distribution and chamber 11. Further work space can be secured when disassembling and inspecting the crucible 2.

FIG. 8 also shows another example of the structure of the single crystal pulling apparatus according to the present invention, and the same parts as in FIG. 7 are given the same reference numerals, and their explanation will be omitted. Note that FIG. 8 shows a plan view of the single crystal pulling apparatus viewed from above. In this embodiment, the magnet 10 has the same configuration as that shown in FIG. 7, so that a transverse magnetic field can be applied to the melt 1. The upper and lower #1 mechanism of the magnet 10 is also the same as the one in FIG. Move it to 2
The magnet 10 is fixed at the position 3 (-).

As a result, the chamber 11 of the pulling device and the magnet 10 are completely separated by two parts, so that a wider crucible cleaning work space can be secured compared to the one shown in FIG. Furthermore, in this case, the magnet IO can be operated in persistent current mode (two times continuously).

[Effects of the Invention] As explained above, according to the present invention, a detector for detecting the amount of decrease in the liquid level of the melt and a drive control device for moving the magnet by the detected amount of decrease in the liquid level are provided. , it is possible to provide a highly reliable fit during pulling of a single crystal, which can be controlled so that the center of the magnet coincides with the solid-liquid interface of the melt.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 3 are block diagrams showing a conventional single crystal pulling apparatus, respectively, and FIG.
The figure shows the relationship between magnetic field strength and impurity concentration in a single crystal.
Fig. 5 is a configuration diagram showing an embodiment in which a driving machine is controlled using a liquid level meter as a detector, and Fig. 6 is a block diagram showing an embodiment in which a driving machine is controlled using a position detector using a laser beam as a detector. The configuration diagrams shown in FIGS. 7 and 8 are configuration diagrams showing other embodiments of the present invention. 1... Melt 2... Crucible 3... Heater 4... Plant crystal 5... Pulling drive mechanism
6...Solid-liquid interface 7...Single crystal 8.
...Thermal convection 9...Impurity lO...Magnet 1
]... Magnetic direction 12... Frame 13... Vertical drive shaft 14... Drive machine 15... Support
16...Detector 17...Vertical drive control device
18...Movement direction 19...Constant position 20.
...Transverse magnetic field direction 21...Movement device 22...
Rail 23... Fixed position 50... Liquid level sensor 60... Laser emitting/receiving surface 61... Laser measuring instrument Fig. 2 Fig. 3 Fig. 4 Fig. 5

Claims (3)

[Claims] (1) A seed crystal is inserted into the single-crystal raw material melt filled in a crucible heated by a heater, and the seed crystal is pulled up at a constant speed by a pulling-up drive mechanism to form a single crystal at the solid-liquid interface of the melt. a single crystal pulling machine for generating crystals; a magnet provided outside the crucible so as to apply a magnetic field of a required strength to the solid-liquid interface of the melt; and a magnet installed in a direction perpendicular to the crucible. , a magnet moving mechanism that moves the magnet in at least the vertical direction in the horizontal direction, a detector that detects the position of the solid-liquid interface of the melt, and a solid that is detected by the detector.
A single crystal pulling apparatus comprising: a drive control device that controls the magnet moving mechanism so that the position of the liquid surface coincides with the center of the magnet. (2) The detector detects the solid state by measuring capacitance.
2. The single crystal pulling device according to claim 1, wherein the device detects the position of a liquid surface. (3) The single crystal pulling apparatus according to claim 1, wherein the detector detects the position of the solid-liquid interface using the optical Doppler effect.