JPS6287480A - Floating zone melting - Google Patents

Abstract

PURPOSE:A part of the rod sample which is held vertically is melted and allowed to move relatively up and down, as the melted part is kept with the surface tension under application of magnetic field to effect high speed of sample purification without break-out and unevenness in the melted part. CONSTITUTION:A rod sample 1 is vertically held in vacuum and melted partially with a high-frequency coil 2 to form the melted part 3. Then, a static magnetic fields over 0.1 stera is applied to the melted part with a superconductive magnet 4 to keep the coil and the magnet 4 in constant positions, as the melted part is supported with its surface tension and the sample is allowed to vertically move up and down, relatively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a method for refining materials, and in particular to an improvement in a floating zone melting method.

[Prior Art] As a refining method for obtaining a single crystal rod-like body and for enhancing the refining effect, there is a method called a floating zone melting method. This floating zone melting method melts a part of a rod-shaped sample held vertically.
According to this method, which moves the molten part in the vertical direction while supporting it by surface tension, the molten part does not come into contact with the crucible or the like. Therefore, it is effective when refining materials that are difficult to support depending on the crucible material, such as high melting point materials, and also when it is desired to prevent contamination from the crucible.

[Problems to be Solved by the Invention] However, this floating zone melting method includes the following problems.

In other words, since the molten part is supported only by surface tension, the support is unstable and breakage occurs there.
・Strict control was required to prevent. Furthermore, materials that can be purified by this method are limited to those with a small diameter that allows sufficient surface tension to work. Furthermore, since the surface of the molten part becomes unstable due to slight vibrations or changes in conditions, the surface smoothness of refined single crystal materials and purified materials is inferior.

It is therefore an object of the present invention to provide an improved floating zone melting process that can overcome the above-mentioned problems.

[Means for Solving the Problems] and [Effects of the Invention] The floating zone melting method according to the present invention melts a part of a rod-shaped sample held vertically, and applies a magnetic field to the melted part. It is characterized in that the molten part is relatively moved in the vertical direction while being supported by surface tension.

By applying a magnetic field to the melt, the apparent viscosity of the melt increases, and therefore the apparent surface tension of the melt increases. Therefore, even if vibrations or the like occur during refining, breakouts and surface irregularities in the molten zone are reduced.

This eliminates the need for strict control over the melting zone as in the past, making refining operations easier. In addition, since the apparent surface tension of the melted zone increases, this method can be applied to materials with a larger diameter than conventional ones, and the surface smoothness of the 1q product is improved. Furthermore, since the apparent viscosity of the melted zone increases, it becomes easier to prevent the occurrence of convection in the melted zone. As a result, the purification effect is improved and it becomes possible to purify at a faster rate.

The magnetic field is applied, for example, by a superconducting magnet. Further, the magnitude of the magnetic field is preferably 0.1 Tesla or more. With this size, the tooling in the melting zone can effectively increase the surface tension. Note that the magnetic field is, for example, a stationary ll field.

This invention, which has the above-mentioned effects, can be applied to metals, semiconductors,
It can be advantageously used when obtaining a single crystal such as a dielectric material or when refining a high melting point material.

[Example] Example 1 FIG. 1 is a diagram schematically showing an example of an apparatus used to carry out the present invention. Using the illustrated apparatus, M.O.
A single crystal rod was obtained. This was done in the following way. First, a rod-shaped sample 1 of polycrystalline MO with a diameter of 1 Q mm was held vertically in a vacuum.

A single crystal seed was placed at the lower end of the rod-shaped sample 1.

Then, a part of the rod-shaped sample 1 was melted by the high-frequency coil 2. A static magnetic field was applied to this melted part 3 by a superconducting magnet 4. The strength of the magnetic field was 0.5 Tesla.

The high-frequency coil 2 and the superconducting magnet 4 were kept at fixed positions, and the bar-shaped sample 1 was moved downward together with its holding mechanism. In this way, the melting section 3 was moved from the lower end of the rod-shaped sample 1 to the upper end.

By the above operation, an MO single crystal rod was easily obtained.

In the above method, a magnetic field was applied to the melted part 3, but for comparison, a method in which no magnetic field was applied to the melted part 3 was also carried out.

Below, the two will be compared and described.

Examples of the present invention: ■ A magnetic field of 0.5 Tesla was applied.

−5= ■ A single crystal rod with a smooth surface was stably obtained.

■ Electrical resistance ratio of the upper 1/10 and lower 1/10 of the sample (
(upper/lower) was 1.3 times as large, indicating a large purification effect.

Comparative example: ■ No magnetic field was applied to the molten part.

■ Breakout was likely to occur in the melted zone, and the surface smoothness of the sample obtained after purification was poor.

■ Electrical resistance ratio of the upper 1/10 and lower 1/10 of the sample (
(upper/lower) was 1.1 times.

Example 2 FIG. 2A is a diagram schematically showing another example of the apparatus used to carry out the present invention. A rod-shaped sample 11 made of polycrystalline Si was held vertically. While rotating this rod-shaped sample 11, a part of it was melted by the infrared heating means 1'2. FIG. 2B is a view of this melting section 13 viewed from above. As shown in the figure, the melting section 13 includes ! The field applying mechanism 14 is designed to apply a horizontal magnetic field of 0.3 Tesla. Then, while keeping the height of the rod-shaped sample 11 constant, the infrared heating device 12 and the magnetic field applying mechanism 14 were moved from the lower end of the rod-shaped sample 11 to the upper end, thereby obtaining a Si single crystal rod.

Conventionally, when attempting to create an St single crystal, a method has often been used in which a sample is melted in a crucible and the sample is pulled up using the Czochralski method. However, this method has a problem in that oxygen is contained from the crucible. Therefore, in order to avoid such problems, floating zone melting methods have been adopted in some cases. However, the conventional floating zone melting method has the problem that the applicable rod-shaped bodies are limited to those with a small diameter, and furthermore, the productivity is poor.

In contrast, the method according to the invention as described above naturally contains less oxygenation than in the Czochralski method. Furthermore, compared to the conventional floating zone melting method, that is, compared to the case where no magnetic field is applied to the melted part 13, the following improvements were observed. That is, compared to the case where no magnetic field is applied to the melting zone 13 using the apparatus shown in FIGS. 2A and 2B, if a magnetic field is applied by the infrared heating device 12, the single crystal growth rate is reduced by 1 for a sample of the same diameter. Stable single crystal growth was obtained even when the temperature was increased 3 times. Also, compared to the case where no magnetic field is applied,
The sample diameter that allows stable crystal growth is set to approximately 1
．． It was possible to increase up to 5ffi.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing an example of an apparatus used to carry out the present invention. FIG. 2A is a diagram schematically showing another example of the apparatus used to carry out the present invention. FIG. 2B is a top view of the melting zone shown in FIG. 2A. In the figure, 1 is a rod-shaped sample, 2 is a high-frequency coil, 3 is a melting part, and 4 is a super N-conducting magnet.

Claims (3)

[Claims] (1) A floating zone melting method in which a part of a rod-shaped sample held vertically is melted, and a magnetic field is applied to the melted part, and the melted part is supported by surface tension and relatively moved in the vertical direction. (2) The floating zone melting method according to claim 1, wherein the magnetic field is a static magnetic field of 0.1 Tesla or more. (3) The floating zone melting method according to claim 1 or 2, wherein the magnetic field is provided by a superconducting magnet.