JPS61222984A - Unit for single crystal production - Google Patents

Abstract

PURPOSE:The magnetic field to be applied to the starting melt is made variable in the crucible to optimize the temperature distribution and convection inhibition of the melt to produce a large size of single crystal of high uniformity and high quality with low dislocation. CONSTITUTION:The starting melt 12, a liquid capsule layer 13 are charged in a pyrotic BN crucible 11. The upper magnet 21 which is composed of normally conductive coils and slidably set to the guide 23 parallel to the crucible axis and driven in parallel with the crucible axis by means of a driving mechanism and the lower magnet 22 which is composed of superconductive coils and fixed at the bottom end are arranged so that the same poles opposed to each other. The magnet 21 is allowed to move so that a cusped magnetic field is applied at the same state between the crystal and the liquid surface and the single crystal is pulled up.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a single crystal manufacturing apparatus for pulling and manufacturing a single crystal from a conductive raw material melt by the Czochralski method, and particularly relates to a single crystal manufacturing apparatus for pulling and manufacturing a single crystal from a conductive raw material melt, and in particular, This invention relates to a single crystal manufacturing device that applies a DC magnetic field to a liquid.

(Technical background of the invention and its problems) Conventionally, the Czochralski method has been widely used as a method for producing semiconductor single crystals from a raw material melt.
In this method, when pulling a single crystal from a conductive raw material melt, by applying an external magnetic field to the raw material melt,
It is possible to suppress thermal convection within the melt, reduce contamination from the crucible material, and further control growth streaks and inherent defects. It has been confirmed that high-quality single crystals can be produced using single crystals such as Sl and GaAs.

In conventional magnetic field application methods, there are methods for applying a magnetic field in the horizontal direction as shown in FIG. 3(a), and methods for applying a magnetic field in the vertical direction as shown in FIG. 3(b).

In the figure, 31 is a crucible, 32 is a raw material melt, 33 is a pulled crystal, 34 is a heater, and 35, 351° and 352 are magnets, respectively. However, in the case where a horizontal magnetic field 36 is applied as shown in FIG. 3(a), the temperature distribution 37 is not axially symmetrical as shown in FIG. There are disadvantages such as becoming

Furthermore, in the case of applying a vertical magnetic field 38 as shown in Fig. 3 (1)), since the flow of the melt in the horizontal direction is strongly suppressed, the temperature distribution in the lateral direction becomes large, and the temperature of the crucible wall in particular increases. The contamination of the crucible becomes greater, and as a result, phenomena such as the concentration of residual impurities not being reduced occur.

Recently, as a magnet arrangement to improve these drawbacks, as shown in FIG.
A method has been proposed in which two magnets are placed facing each other and a cusp magnetic field is applied. This type of magnetic field generates an axially symmetrical horizontal magnetic field in the melt inside the crucible, and is the optimal magnet arrangement for pulling high-quality single crystals.

However, even this type of device has the following problems. That is, the optimum conditions for the magnetic field distribution vary depending on the amount of raw materials charged and the amount of residual melt generated during crystal formation. As a result, problems such as initially having an optimal magnetic field distribution deviate from the optimal magnetic field distribution occur as crystals are created. - It was difficult to create it.

(Object of the Invention) The present invention has been made in consideration of the above circumstances, and its purpose is to maintain an optimal cusp magnetic field applied to the raw material melt in the crucible at all times, and to achieve high quality. An object of the present invention is to provide a single crystal manufacturing apparatus capable of pulling and manufacturing a single crystal.

[Summary of the invention]

The gist of the present invention is to make the magnetic field applied to the raw material melt variable in order to optimize the temperature distribution and convection suppression of the raw material melt in the crucible.

The magnitude of the motion restraining force on the raw material melt due to the magnetic field is proportional to the velocity of the conduction fluid and the strength of the magnetic field, and the restraining force is maximum when the direction of the fluid flow and the direction of the magnetic field are perpendicular. When a horizontal magnetic field is applied, a flow parallel to the direction of the magnetic field continues to exist. Therefore, heat exchange with the crucible wall is good, there is little lateral temperature difference, there is little thermal strain during growth, and a low dislocation density crystal can be created.

However, in a simple horizontal magnetic field, there is no axial symmetry on the crucible surface, and non-uniformity occurs between streamlines parallel to the magnetic field and streamlines perpendicular to the magnetic field.

Therefore, by forming a cusp magnetic field using magnets facing the same polarity, an axially symmetrical magnetic field can be formed on the crucible surface, making it possible to solve the above problem. but,
When this cusp magnetic field is used, the melt surface lowers and the melt amount decreases as the crystal is pulled, and the optimum magnetic field distribution changes accordingly. Therefore, it is necessary to vary the magnetic field distribution as the crystal is pulled. In order to vary this magnetic field distribution, the present invention moves the magnet or varies the excitation current of the magnet.

That is, the present invention provides a single crystal manufacturing apparatus that applies a direct current magnetic field to a raw material melt housed in a crucible to pull and manufacture a single crystal using the Czochralski method. The temperature distribution of the raw material melt in the crucible is achieved by moving at least one of these magnets in the vertical direction or by varying the excitation current of at least one of the magnets, which apply an equiaxially symmetric and radial cusp magnetic field. and means for optimizing convection suppression.

〔Effect of the invention〕

According to the present invention, since the cusp magnetic field can be applied optimally, heat exchange from the crucible wall can be performed optimally, and thermal vibration can be effectively suppressed. Furthermore, even if the raw material melt in the crucible decreases due to crystal growth, an optimum cusp magnetic field can always be provided by moving the magnet or varying the excitation current. For this reason, it is large, has low dislocation,
High uniformity.

This makes it possible to create high-quality single crystals.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic diagram showing a semiconductor single crystal manufacturing apparatus according to an embodiment of the present invention. In the figure, reference numeral 11 denotes a pyrotic BN (PBN) crucible, and a raw material melt 12 and a liquid capsule layer 13 are accommodated in this crucible 11, respectively. An upper magnet 21 is arranged above the crucible 11, and a lower magnet 22 is arranged below the crucible 11. These magnets 21 and 22 are arranged to face each other so that the same polarity faces each other. Here, the upper magnet 21 is made of a normally conducting coil, and is slidably attached to a guide body 23 installed parallel to the crucible axis. This magnet 21 is driven by a drive mechanism (not shown).
It is designed to be moved parallel to the crucible axis. Also,
The lower magnet 22 is made of a superconducting coil and is fixed to the fixed end.

In the figure, 14 indicates a pulled single crystal, 15 indicates a seed crystal, and 24 indicates a magnetic field distribution. Further, although not shown in the figure, a heater is arranged around the crucible 11. Furthermore, the crucible 11, the heater, etc. are housed in a pulling furnace (not shown). Further, the magnetic fields generated by the magnets 21 and 22 are equiaxially symmetrical in the vertical direction as shown in FIG. 1, and in the horizontal direction as shown in FIG.

Next, a method for producing a single crystal using the above apparatus will be explained.

First, as raw materials Qa was 4.5[N91, AS was 5[K
g] The crucible 11 was charged, boron oxide was placed on top of the crucible to prevent scattering of As, and GaAS was synthesized at 70 [atl] in an Ar atmosphere. After that, the pressure was increased to 10 [at++
]. After that, the first layer is placed on the surface of the GaAS melt.
To obtain the magnetic field distribution shown in the figure, a cusp magnetic field was formed, and the applied magnetic field strength was adjusted to the surface of the GaAS melt (10511+ from the center).
position) at 2000 [Oe! ] The production of single crystals was started.

Under these conditions, the depth of the melt in the crucible is approximately 100 [am]
In order to always apply a magnetic field in the same state to the crystal and the liquid surface, from the time when the diameter of the pulled crystal reaches, for example, 75 [s+], the upper magnet 21 is gradually adjusted to the lowering rate of the liquid level, for example, 12/hour. It was lowered at [am].

Under the above conditions, the diameter is 75 [am+] and the weight is 9 [K9].
] We succeeded in creating a GaAS single crystal. As a result of measuring the etch bit density of this single crystal, it was found that it had a low dislocation density of 1.5 to 3x103 [cIR''] even though it was additive-free.In a normal pulled crystal, the etch bit density was 5x104. ~2X10'[α4], but by applying a horizontal magnetic field (cusp magnetic field) symmetrical to the pulling axis, a uniform temperature distribution condition was obtained on the surface of the GaAS melt, which showed a tendency to lower dislocations. considered to be a thing.

In addition, there are no growth streaks, and by optimally moving the magnet, it is possible to create large, large-diameter single crystals that are uniform from the head to the tail of the crystal, and the shape of the solid-liquid interface is controlled. Ta. In addition, as a result of investigating the residual impurity concentration in the produced crystal using a cusp magnetic field, it was found that the amount of boron mixed in from the crucible material was 1.
It is believed that the reaction between the GaAS melt and BN is reduced because the magnetic field lines are perpendicular to the crucible wall.This also results in a high purity effect. .

In this way, according to this embodiment, the same-polarity opposing magnets 21, 22
Since the upper magnet 21 is movable in the vertical direction and the cusp magnetic field is formed by the upper magnet 21, the optimal cusp is always maintained for the raw material melt regardless of the lowering of the liquid level and the decrease in the liquid volume of the raw material melt in the crucible 11. A magnetic field can be applied. Therefore, it becomes possible to pull and manufacture a high quality GaAS single crystal.

Note that the present invention is not limited to the embodiments described above. For example, it is not necessary that one of the same polarity opposing magnets be a normal conducting coil and the other a superconducting coil, and both may be normal conducting coils or superconducting coils. Furthermore, the magnet to be moved is not limited to the upper magnet, but may be the lower magnet, or both may be movable. However, although superconducting coils are suitable for obtaining a strong magnetic field, it is not easy to move them. Therefore, as in the above embodiment, one is made up of a normal conducting coil to make it movable, and the other is made of a superconducting coil. It is practical to configure and fix this. Furthermore, instead of moving the magnet, the excitation current of the magnet may be varied. Also in this case, the excitation current of at least one of the same-polarity opposing magnets may be made variable. Furthermore, it goes without saying that the present invention can be applied not only to the pulling of GaAS single crystals but also to the pulling and manufacturing of GaP, InP, and other single crystals. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief Description of the Drawings] Fig. 1 is a schematic configuration diagram showing a semiconductor single crystal manufacturing apparatus according to an embodiment of the present invention, and Fig. 2 shows the horizontal magnetic field distribution and temperature distribution when the above-mentioned apparatus is used. 3(a) and 3(b) are schematic diagrams showing a conventional device, FIG. 4 is a schematic diagram for explaining the problems of the above device, and FIG. 5 is a conventional device using a cusp magnetic field. FIG. 11... Crucible, 12... Raw material melt, 13... Liquid capsule layer, 14... Pulled single crystal, 15... Seed crystal, 21... Upper magnet, 22... Lower magnet , 23
... Guide body, 24 ... Magnetic field distribution, 27 ... Temperature distribution. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 (a) (b)

Claims (5)

[Claims] (1) In a single crystal production device that applies a direct current magnetic field to a raw material melt housed in a crucible to pull and produce a single crystal using the Czochralski method, the devices are arranged oppositely above and below the crucible, and are arranged equilaterally with respect to the crucible axis. Opposed magnets with the same polarity that apply an axisymmetric and radial cusp magnetic field, and moving at least one of these magnets in the vertical direction or varying the excitation current of at least one of them to control the temperature distribution and convection of the raw material melt in the crucible. 1. A single-crystal production apparatus characterized by comprising means for optimizing suppression. (2) One of the magnets is made of a normal conducting coil and is provided to be movable in the vertical direction, and the other is made of a superconducting coil and is fixed. Single crystal production equipment. (3) One of the magnets is made of a normal conducting coil and its excitation current is variable, and the other is made of a superconducting coil and its exciting current is constant. single crystal production equipment. (4) One of the magnets is made of a normal-conducting coil and is provided so as to be movable in the vertical direction, and its excitation current is variable, and the other is made of a superconducting coil and is fixed and its excitation current is constant. An apparatus for producing a single crystal according to claim 1, characterized in that: (5) The optimization means is to form an axially symmetrical horizontal magnetic field with a smaller lateral temperature gradient on the surface of the raw material melt in the crucible than when applying a vertical magnetic field. The apparatus for producing the single crystal described above.