JP2735752B2 - Single crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for growing a single crystal, and more particularly to a method for growing a single crystal of a high melting point oxide such as sapphire, ruby, YAG, and GGG. Here YAG
Is Yttrium Aluminum Garnet (Y ₃ Al
₅ O ₁₂ ), which has a melting point of 1970 ° C. and GGG is gadolinium gallium garnet (G
d ₃ Ga ₅ O ₁₂ ), which has a melting point of 1710 ° C. Both are used for lasers.

[0002]

2. Description of the Related Art Conventionally, there are various methods for growing a single crystal. Among them, there are the following three types of single crystal growing methods using a solution and not using a crucible (Kyoritsu). Published by KK, Experimental Physics Course No. 13,
"Preparation and processing of samples", pages 135 to 139).

[0003] First, the Bernoulli method is used. In this case, a fine powder sample is dropped in an inverted burner of an oxyhydrogen flame so as to be heated to a semi-molten state, and deposited on a seed crystal or a refractory rod to grow a single crystal. However, it has a drawback such that it cannot be used for a material having a melting point higher than 2300 ° C. or a material having high reactivity.

[0004] Next, there is a floating zone method. In this case, a polycrystalline sample rod is held vertically at both ends, and a part thereof is heated and melted to form a molten zone, which is moved from one end to the other end. Single crystallize. In this method, no crucible is required because the molten zone is held by surface tension. Therefore, this method can be said to be a method suitable for single crystallization of a high melting point material which is active at a high temperature.

Next, there is an immersion arc melting method. In this case,
When a carbon electrode is inserted into the center of the raw material powder packed in the container and a voltage is applied, the material is generated at a high temperature by discharge and the center is melted. A single crystal is obtained by slow cooling with a reduced arc current. This method is used exclusively when the single crystal cannot be obtained by other methods or when the quality is not so important.

[0006] Among these various single crystal growing methods that do not use a crucible, the floating zone method has attracted the most attention. In this method, the molten zone must be locally heated, and three types of heating means are required. Is considered.
In other words, a high frequency heating method, an electron beam heating method, and an arc image method, and a crystal manufacturing apparatus based on an arc image method, that is, an infrared concentrated heating method, has been developed and generally used for more than ten years as being suitable for growing a high melting point oxide. It has become so.

In this infrared concentrated heating method, an infrared light-generating bulb serving as a heat source is placed at one focal point of a spheroid, and light radiated therefrom is reflected on the inner surface of the ellipsoid and collected at another focal point. It utilizes the unique characteristics. Then, the single crystal sample rod is heated while being held vertically so as to pass through the other focal point, but in such an infrared concentrated heating method, only the portion where light (infrared rays) is concentrated is heated, and the other portions are not heated. Therefore, the temperature gradient at the solid-liquid boundary is too large. Therefore, since the molten zone is rapidly cooled, crystals having many defects cannot be obtained. For this reason, the temperature gradient is moderated by slightly blurring the degree of concentration at the focal point, or the in-grown crystal is covered with an alumina pipe to the vicinity of the melting zone and used as an indirectly heated after heater, but this is not sufficient. . Further, the material temperature varies depending on the degree to which the material absorbs light, and also varies depending on the light absorption coefficient of the melting point, and it is difficult to obtain a desired temperature.

As the heating method of the floating zone method, there are a high frequency heating method and an electron beam heating method in addition to the infrared concentrated heating method as described above. In the former case, the high frequency heating device requires expensive and large equipment. In addition, the method of directly applying a high frequency to the sample is not applicable unless the sample is a conductive sample, and the latter case has a problem that the temperature gradient is steep as in the case described above.

In view of such circumstances, the present invention solves the problems of the floating zone method typified by the infrared concentrated heating method, and has a suitable temperature gradient in the melting zone and can easily produce a defect-free crystal. It is an object of the present invention to provide a single crystal growing method by a zone method.

[0010]

Means for Solving the Problems In the single crystal growing method by the floating zone method, the present inventors have developed the above-mentioned heating method of an ultra-high temperature electric resistance furnace provided with a hollow cylindrical zirconia heating element that generates heat by energizing single crystal growth. The present inventors have found that the above problems can be solved by performing the treatment inside the body, and have reached the present invention.

The above-mentioned ultra-high temperature electric resistance furnace suitable for use in the method for growing a single crystal of the present invention has been previously developed and filed for a patent by the present inventors (Japanese Patent Application No. 3-22618).
No. 3), an example of which is described in detail in the specification of the same application, will be described again with reference to the drawings. First, in FIG. 1, reference numeral 1 denotes a hollow cylindrical zirconia heating element used in the present invention. It has a heat-generating portion 2 having a small diameter or small cross-sectional area at the center and a terminal portion 3 having a constant diameter and a larger diameter or large cross-sectional area at both ends thereof. An electric lead wire 4 such as a platinum wire or a platinum-rhodium alloy wire is attached to the terminal portion 3. The heat generating portion 2 and the terminal portion 3 have an inner diameter that is large enough to take a single crystal sample in and out and generate heat inside. This heating element will be described later in detail.

A pipe-like refractory 5 is provided above and below the heating element 1 to support the heating element 1 upright. As the refractory 5, a material having excellent electrical insulation such as alumina or magnesia is used, and the lead wire 4 is disposed inside.
The inner diameter of the refractory 5 is the same as the inner diameter of the heating element 1. When lanthanum chromite, lanthanum manganite, lanthanum cobaltite, or the like is used as the refractory 5, the current-carrying lead wire 4 becomes unnecessary.

Outside these, a preheating device for the heating element and a cylindrical refractory are arranged. First, a zirconia cylindrical refractory 6 and an alumina cylindrical refractory 7 are arranged around the heating element 1 in this order. In order to reduce the thermal load on the refractory 6 and to prevent electrical leakage from the heating element 1, the heating element 1
Some space 8 is provided between and the refractory 6. A preliminary heater 9 is provided on the surface of the alumina refractory 7 to preheat the heating element 1. The alumina refractory 7 prevents electric leakage of the heater 9 and prevents the heater 9 from being affected by the high temperature of the heating element 1. Can be protected. The heater 9 is wound around an alumina refractory. Alumina mortar is used as the spacer and the adhesive.

As the preliminary heater 9, a non-metallic heating element such as silicon carbide or molybdenum disilicide, or a metal heating element such as Fe-Cr-Al or platinum is used. From the viewpoint of thermal efficiency, it is preferable to use a metal heating element wound around the alumina refractory 7. At this time, when zirconia is used as the refractory, a leakage phenomenon occurs to the refractory, so that it is necessary to interpose an alumina refractory.

A ceramic heat insulating material 10 and an outer shell 11 are provided outside the alumina refractory 7. As the heat insulating material 10, an alumina-silica fiber block or bulk is applied. Thereby, the iron shell 11 is protected and insulated. When there is a restriction on the overall size of the furnace, the steel shell 11 can be water-cooled or air-cooled by flowing water or air into the steel shell having a double structure.

A space 12 penetrating vertically is formed inside the hollow cylindrical resistance heating element 1 and the pipe-shaped refractory 5, and the object to be processed is inserted from above or below and the heating section 2 of the heating element 1 is formed.
It can be arranged in the nearby ultra-high temperature heating space 13. The space 13 may be provided with a means for placing or suspending the object to be processed, and the upper or lower part of the space may be sealed with a refractory material (not shown) depending on the purpose.

The refractory disposed around the hollow cylindrical resistance heating element and the pipe-shaped refractory supporting the same may be made of a material that can withstand the heat when the heating element becomes high in temperature. It is necessary, and a zirconia material is used as described above. For example, zirconia hollow spheres or zirconia powder and zirconia fibers can be used (Japanese Patent Application No. 2-242244). As the zirconia fiber, lime,
Zirconia fibers stabilized by adding a stabilizer such as magnesia or yttria are also used. In addition, it has a skin layer composed of zirconia fiber and zirconia powder and having a bulk specific gravity of 2.5 to 5.0 as described in JP-A-3-83856, and has a hollow interior. Or the fiber is entirely or partially zirconia,
Refractories filled with a filler consisting of hollow spheres and fiberboard can also be used.

Referring to FIGS. 2A and 2B, a hollow cylindrical heating element 1 suitable for use in the present invention will be described. Terminal sections 3 are provided at both ends of a heating section 2 having a relatively small sectional area or outer diameter. Is provided. A preferred range of the ratio of the sectional area of the heat generating portion / the sectional area of the terminal portion is 1/3 to 1/10. When the ratio is larger than 1/3, the temperature rise of the terminal portion is large, and when the ratio is smaller than 1/10, the temperature difference between the terminal portion and the heat generating portion becomes large and the terminal portion is easily broken. Note that the heat generating portion 2 can be provided with a hole 14 for observation from outside.

The shape can be adjusted by providing a taper 15 at the boundary between the terminal portion and the heat generating portion according to the desired temperature distribution inside the hollow cylindrical heat generating element.

The length of the heating portion 2 of the heating element 1
The inner diameter and the outer diameter, the structure of the boundary portion between the heat generating portion 2 and the terminal portion 3 and the like are appropriately determined according to the kind of the target single crystal (viscosity of the melt) or the desired temperature gradient between the melt portion and the non-melted portion. Selected.

The hollow cylindrical heating element 1 of such an ultra-high temperature electric resistance furnace is provided with upper and lower shafts 16, 16 'as shown in FIG. The shaft 16 is a jig that can move up and down and rotate. The single crystal samples 17 and 17 'to be grown are formed into a rod shape, inserted into the hollow cylindrical heating element from above and below, and set vertically. In this case, the ends of the upper and lower rod-shaped samples 17, 17 'are brought into contact with each other in the ultra-high temperature heating space 13 near the heat generating portion of the heat generating element. At this time, the lower rod-shaped sample 17 'that comes into contact
It is appropriate to set the upper rod-shaped sample 17 to have a sharp edge by gradually reducing the diameter of the end portion and to set the upper rod-shaped sample 17 while observing it well through the observation hole 14. After the upper and lower rod-shaped single crystal samples are brought into contact with each other in this way, they are heated while being rotated in opposite directions at a constant speed, and while moving the upper and lower samples up and down. The heating temperature is appropriately set according to the type of the single crystal sample. For example, in the case of alumina, the temperature is about 2050 ° C. At this time, the rotation speed of the upper sample is 0.1 to 100 rpm, preferably 1 to 10 rpm, and the rotation speed of the lower sample is 0 to 100 rpm, preferably 0 to 20 rpm.
rpm range. The lowering speed of the upper sample is 1-20.
The range of mm / hr is preferred. Depending on the type of single crystal, rotation of the lower sample is not necessary. The sample is usually lowered, melted and solidified by heating. Raise it only when setting the sample. In FIG. 3, reference numeral 18 denotes a molten zone formed after heating.

In this way, by using an ultra-high temperature electric resistance furnace equipped with a hollow cylindrical zirconia heating element, inserting a single crystal sample into the heating element and heating the same to grow the single crystal sample, it is necessary to increase the temperature between the molten portion and the non-melted portion. The temperature gradient is made slow, and a good single crystal with few defects can be obtained.

[0023]

Example: High purity alumina powder (Al ₂ O ₃ purity ≧ 9)
(9.99%) 100 parts by weight of methyl cellulose 2
The mixture was kneaded and dried, and then molded by a rubber press under a hydrostatic pressure of 2000 kg / cm ² . Then, it is baked in an electric furnace at 1700 ° C. for 2 hours, and is sintered (8)
φ 150 mm). As shown in FIG. 3, these sintered rods (rod-shaped single crystal samples) were placed so that both ends thereof were in contact with the heat generating portion of a hollow cylindrical heating element, and heated to 2050 ° C. to form a molten zone and rotate the upper and lower rods in reverse. Gradually descend, almost 15
After a time, an alumina single crystal was formed.

The height of the ultra-high temperature electric resistance furnace used was 3
The outer diameter was 00 mm and the outer diameter was 300 mm. The composition of the heating element was composed of yttria-stabilized zirconia powder 70 and yttria-stabilized zirconia fibers 30, and the chemical composition was 92% by weight of ZrO _{2 and} 8% by weight of Y ₂ O ₃ . The dimensions of the heating element are as follows: Heating element inner diameter 24mm Heating part length 10mm Terminal part outer diameter 42mm Terminal part length 40mm Sample rotation speed Upper sample 4rpm, Lower sample 10rpm, Sample lowering speed 10
mm / hr The temperature gradient measured at this time was as shown in FIG. 4 and was appropriate. No defects were found in the obtained crystals.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment of an ultra-high temperature electric resistance furnace used in the present invention.

FIG. 2 is a front view of each embodiment of a hollow cylindrical heating element used in the present invention.

FIG. 3 is a sectional view of an essential part of an ultra-high temperature electric resistance furnace used in the present invention.

FIG. 4 is a graph showing a temperature gradient measured in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hollow cylindrical resistance heating element 2 Heating part 3 Terminal part 4 Electric lead wire 5 Pipe-shaped refractory 9 Pre-heater 16, 16 'Shaft 17, 17' Single crystal sample 18 Melting zone

Claims (5)

(57) [Claims] 1. A single crystal growing method according to a floating zone method, wherein the growing is performed inside the heating element of an ultra-high temperature electric resistance furnace having a hollow cylindrical zirconia heating element which generates heat by energization. Crystal growth method. 2. An ultra-high temperature electric resistance furnace, wherein said hollow cylindrical zirconia heating element having a heating part capable of internally heating a single crystal sample and terminals at both ends thereof is supported upright by a pipe-shaped refractory. 2. The method of growing a single crystal according to claim 1, wherein a device for preheating the heating element and a cylindrical refractory for protecting the device are provided outside the heating element. 3. The method of growing a single crystal according to claim 1, wherein said hollow cylindrical zirconia heating element is a zirconia-based resistance heating element containing zirconia fibers. 4. The method of growing a single crystal according to claim 2, wherein a cross-sectional area of said heat generating portion of said hollow cylindrical zirconia heating element is smaller than a cross-sectional area of said terminal portion. 5. The method according to claim 1, wherein the single crystal is grown by inserting a single crystal sample from above and below into the inside of the heating element and heating them while rotatably moving up and down. Single crystal growth method.