JPH0543378A - Apparatus for producing single crystal - Google Patents

Abstract

PURPOSE:To obtain a high quality oxide single crystal free from the defects such as residual void and crack by locally heating a sintered raw material rod to form a floating zone and growing a single crystal from the floating zone in a state to have a slow temperature gradient from the sintered raw material rod to the single crystal. CONSTITUTION:A single crystal 56 is grown by heating and melting a sintered raw material rod 50 by a coil heater 61 formed on the inner wall surface of a cylindrical furnace 60 for holding a sintered raw material rod 50 and by a plane heater 70 to be inserted into a floating zone 51. The coil heater 61 gives a prescribed temperature gradient to the sintered raw material 50 and the single crystal 56 near the floating zone 51 to prevent the abrupt temperature change. The plane heater 70 has a two-dimensional shape formed by folding a filament at plural points. The upper molten liquid flows down through the space between adjacent filaments and is supplied to the side of the solid-liquid interface.

Description

Detailed Description of the Invention

[0001]

The present invention relates to the production of an oxide single crystal from a raw material sintered rod by the floating zone method.
The present invention relates to a single crystal production apparatus used for producing a good quality oxide single crystal body having no defects by controlling the temperature distribution in the longitudinal direction of a raw material sintered rod.

[0002]

2. Description of the Related Art A floating zone method is known as a method for producing an oxide single crystal from a raw material sintered body.
When a single crystal is manufactured by this method, the sintered body of the raw material powder is locally heated by a heating wire or the like to form a melting zone, the melting zone is moved in the longitudinal direction of the sintered body, and the single crystal is precipitated from the melting zone. I am letting you. Impurities, bubbles and the like contained in the raw material sintered body are removed in the course of this melting and precipitation, and a single crystal body of constant quality is obtained.

In the floating zone method using a light source such as a xenon lamp as a heat source, for example, a single crystal manufacturing apparatus having the equipment structure shown in FIG. 1 is used. The heating furnace 10 of this apparatus has an inner surface formed by a spheroidal mirror 11. A light source 12 such as a xenon lamp is arranged as a heat source at one focus of the spheroidal mirror 11, and a raw material sintering rod 20 inserted in a quartz tube 13 is arranged at the other focus.
The heat rays 14 emitted from the light source 12 are spheroidal mirror 11
Is reflected by and is focused on the other focal position.

The raw material sintering rod 20 is heated to a high temperature by the heating wire 14 to form a melting zone 21. In this state, the raw material sintering rod 20 is lowered along the carrying direction A by the upper shaft 30 and the lower shaft 31. Along with the lowering of the raw material sintering rod 20, the local heating position where the heating wire 14 is focused relatively rises. As a result, the melting zone 21 is cooled from the lower end side and a solid phase is deposited to become a single crystal 22.

The process of melting / precipitation is observed through a viewing window 16 through a magnifying lens 15 attached to the side wall of the heating furnace 10. Further, an inert gas 33 such as nitrogen gas is fed into the quartz tube 13 through the gas inlet 32 so that impurities are not taken into the single crystal 22 from the atmospheric gas. The inert gas 33 is discharged out of the system through the exhaust port 34 while being accompanied by the atmospheric gas inside the quartz tube 13.

In order to deposit a solid phase from the melting zone 21 to obtain a single crystal 22 of constant quality, it is necessary to suppress the temperature variation in the radial direction in the melting zone 21 near the solid-liquid interface. In addition, since the precipitated single crystal 22 is rapidly cooled as it moves away from the local heating position, a large thermal stress is generated and a thermal crack is easily generated.

In relation to this, in Japanese Patent Laid-Open No. 62-21788, it is proposed that a flat-plate heater in which filaments are gathered in series in the same plane is arranged as a light source at one focal position of a spheroidal mirror. Has been done. According to this proposal, at the other focal position of the spheroid, heat rays are focused and imaged in the same shape as that of the flat heater, and each section of the raw material sintered rod is heated uniformly. In addition, JP-A-1-18
According to Japanese Patent No. 3497, a plate heater is positioned in the melting zone immediately below the local heating position and auxiliary heating of the melt in the melting zone suppresses a rapid temperature drop.

[0008]

However, when a light source such as a xenon lamp is used as the heat source, the raw material sintering rod can be heated to a high temperature at the position where the heat rays are condensed, but before and after that, the raw material sintering is performed. It is unavoidable that a rapid temperature drop occurs due to heat dissipation through a bond or a grown single crystal. In this respect, the heat rays are condensed in a flat plate shape.
In the method of JP-A-2121788, no measure is taken in the longitudinal direction of the starting crystal ingot or the single crystal. On the other hand,
Positioning a plate heater in the melting zone
According to the method of Japanese Patent Publication No. 7, although the irregular temperature change of the melt near the solid-liquid interface can be suppressed to some extent, a horizontal flow component is imparted to the melt near the solid-liquid interface. The supply state of is different in the radial direction, and it is difficult to uniformly deposit the solid phase over the entire solid-liquid interface.

Further, the raw material sintered body 2 is made to pass through the heating wire 14.
Since the light is focused at 0, the quartz tube 13 is used as a container for housing the raw material sintered body 20 in a protective atmosphere, but the quartz tube 13 causes a devitrification phenomenon and reduces the transmittance of heat rays. This devitrification phenomenon is promoted, for example, by re-precipitating and adhering alumina and the like evaporated from the raw material sintering rod and internal equipment to the inner wall surface of the quartz tube 13. As a result, the utilization efficiency of the heat rays of the quartz tube 13 decreases, and the quartz tube 1
The life of 3 becomes short.

The present invention has been devised to solve such a problem. By combining a tubular furnace in which a heating element is incorporated and a planar heater located in the melting zone, the present invention is provided before and after the floating zone. It is an object of the present invention to provide a single crystal production apparatus capable of controlling a temperature distribution and efficiently using a supplied current for heating a melt.

[0011]

In order to achieve the object, a single crystal production apparatus of the present invention has a tubular furnace body having an internal space into which a raw material sintering rod is inserted, and an inner wall surface of the tubular furnace body. It is characterized in that it is provided with a coil-shaped heater provided and a planar heater positioned in the floating zone forming portion, and the floating zone is formed by heating through the planar heater.

Here, the planar heater is preferably one in which a filament of a non-evaporable heat-resistant material is bent or curved so that the area occupancy in the two-dimensional plane is in the range of 30 to 80%. As the non-evaporable heat resistant material, W, Mo, Ta, Ir, Re, Zr, Ti, Nb or alloys thereof are used. Further, it is preferable that the coiled heater is provided on the inner wall surface of the tubular furnace body from above to below the planar heater, and the coil pitch is increased as the distance from the position facing the floating zone increases.

[0013]

The operation of the present invention will be described in detail below with reference to FIGS. The single crystal production apparatus of the present invention,
As shown in FIG. 2, a tubular furnace body 60 having an internal space into which the raw material sintering rod 50 is inserted, and a floating zone portion 51.
And a planar heater 70 positioned at. The upper end of the raw material sintering rod 50 is supported by the upper support 52, and the lower end is supported by the lower support 54 via the seed crystal 53. The upper support 52 and the lower support 54 descend so that the raw material sintering rod 50 moves in synchronization with the growth rate of the single crystal precipitated from the floating zone portion 51.

The tubular furnace body 60 is made of a material such as stainless steel which has a small amount of evaporating components when heated to a high temperature.
On the inner wall of the tubular furnace body 60, the floating zone portion 51
The coiled heater 61 is embedded from above to below. The raw material sintering rod 50 is heated by radiation heating from the coil heater 61 or high frequency induction heating.
The coiled heater 61 above the floating zone portion 51 preheats the raw material sintering rod 50 and raises the temperature of the portion near the floating zone portion 51 to a temperature suitable for melting. The coil-shaped heater 61 below the floating zone portion 51 heats the floating zone portion 51 or the single crystal formed by depositing a solid phase from the floating zone portion 51, and functions as a post-heating portion that prevents a sudden temperature drop.

Further, in order to secure the maximum temperature in the floating zone portion 51, it is preferable that the coil pitch P of the coiled heater 61 is set to be the smallest in the floating zone portion 51 and set to be larger as the distance from the floating zone portion 51 increases. Thereby, a required temperature distribution can be given along the longitudinal direction of the raw material sintering rod 50.

A planar heater 70 is inserted in the floating zone 51 so as to cross its cross section. As the flat heater 70, as shown in FIGS. 3A and 3B, a filament 7 made of tungsten or the like is used.
The one obtained by bending or curving 1 in a two-dimensional plane is used. Alternatively, as shown in FIG. 3C, a flat heater 70 may be one in which the filament 71 is bent or curved in a plane extending over two or more steps.

The planar heater 70 is inserted into the floating zone portion 51 formed by melting the raw material sintering rod 50 as shown in FIG. Since the planar heater 70 is formed by bending the filament 71, the melt in the upper floating zone 51 passes through the gap between the adjacent filaments 71 as indicated by the arrow and solid-liquid interface 55.
Run down to the side. That is, the melt is supplied as a substantially uniform downward flow over the entire solid-liquid interface 55. At this time, the gap g between the adjacent filaments 71 functions as a kind of orifice and regulates the flow rate of the melt that descends to the solid-liquid interface 55 side.

When the area occupancy of the filaments 71 in the two-dimensional plane is 30 to 80%, the flow rate of the melt passing through the heater 70 becomes constant and the melt flowing between the adjacent filaments 71 is given to the melt. Heat is homogenized,
The melt supplied to the solid-liquid interface 55 side has less variation in temperature distribution with respect to the cross section of the floating zone 51. Therefore, the solid-phase deposition condition over the entire solid-liquid interface 55 is stabilized, and a single crystal 56 having uniform quality in the radial direction can be obtained.

If the area occupancy of the filaments 71 is less than 30%, the gap between the adjacent filaments 71 becomes large, and sufficient heat cannot be given to the melt passing therethrough. On the contrary, the area occupancy of the filament 71 is 8
When it exceeds 0%, the gap between the adjacent filaments 71 becomes small and the flow resistance to the melt becomes large, which is not preferable.

The floating zone portion 51 is formed as follows. First, the upper support 52 and the lower support 54 are moved and adjusted so that the raw material sintered rod 50 and the seed crystal 53 are located directly above and below the planar heater 70, respectively. In this state, the raw material sintering rod 50 is heated to a temperature just below the melting point by the coil heater 61. After that, the upper support 52 and the lower support 54 are brought close to the planar heater 70, the respective tip portions are melted and brought into contact with each other, and the floating zone portion 51 is formed by the surface tension.

[0021]

EXAMPLES Examples will be described below. Particle size 50 to 10
Alumina powder with a purity of 99.99% adjusted to a range of 0 μm was applied at a pressure of 1 ton / cm ^{2 to} a diameter of 60 mm and a length of 80 m
m into a rod-shaped green compact. This rod-shaped green compact is 1700
Sintering was performed by heating for 10 hours in an air atmosphere at 0 ° C., and a raw material sintered rod having a density of 98%, a diameter of 50 mm and a length of 70 mm was prepared.

The raw material sintering rod 50 is inserted into a tubular furnace body 60 having a diameter of 80 mm, and the upper end and the lower end are respectively supported by the upper support 5.
It was charged into the heating furnace while being supported by 2 and the lower support 54. In the tubular furnace body 60, the pitch P = 3 m from 50 mm above to 50 mm below the planar heater 70.
The m-shaped coil heater 61 was used.
Further, as the planar heater 70, the gap g = 3 mm
Then, a tungsten filament bent into the shape shown in FIG.

While supplying nitrogen gas to the tubular furnace body 60 at a flow rate of 5 Nl / min, an electric current is supplied to the coil-shaped heater 61 and the planar heater 70, and the raw material sintering rod 50 is moved in the longitudinal direction 15
A floating zone portion 51 of mm was formed.

Planar heater 70 and coil heater 61
In the example of the present invention in which heating is performed using both of the above, a steep temperature curve in the longitudinal direction of the raw material sintering rod 50 is unlikely to appear, and the floating zone portion 51 is formed in the cross section in which the planar heater 70 is inserted. Simulation of the temperature distribution of shows that the temperature variation across the cross section is ± 30.
It stayed in the range of ℃. That is, it was found that the melt in the floating zone portion 51 near the solid-liquid interface 55 has a substantially uniform temperature distribution in the cross-sectional direction. On the other hand, when an experiment was conducted as a comparative example in which the heating by the coiled heater 61 was not performed, the thickness of the floating zone portion 51 was as thin as 10 mm, and the variation in the temperature of the floating zone portion 51 was also ± 30 ° C. Then, there was a big temperature drop.

The growth rate at which the solid phase is deposited from the floating zone 51 to form the single crystal 22 is set to 30 mm / hour, and the upper support 52 and the lower support 54 are attached to the raw material sintering rod at the same speed as this growth rate. It was moved in the longitudinal direction of 50. In this way, diameter 50mm, length 70mm
An oxide single crystal having a diameter of 50 mm and a length of 60 mm was grown from the raw material sintering rod 50 of.

After cooling, the obtained oxide single crystal was taken out and the internal structure was observed. As a result, it was found that a high-quality oxide single crystal in which bubbles and cracks were not observed at all in a visual field of 1 cm ² at a magnification of 400 times. Further, the residual stress was such a small value that it was not locally concentrated in the cross-sectional direction and could not be detected. On the other hand, in the comparative example in which the oxide single crystal was grown under the same conditions without heating by the coiled heater 61, the obtained single crystal had 5 to 6 cracks in the same field of view. Was detected.

As is clear from this comparison, the heating by both the planar heater 70 and the coil heater 61 makes the temperature distribution and flow state of the melt near the solid-liquid interface 55 suitable for solid phase deposition. It turns out to be effective above. Further, the amount of heat is evenly transferred from the filament 41 to the melt with respect to the cross section of the floating zone portion 51, and the descending flow of the melt has a uniform flow rate distribution. Therefore, even when growing a single crystal having a large diameter. , Solid-liquid interface 5
The temperature distribution and the flow state of the melt in the vicinity of 5 can be made uniform, and the diameter of the manufacturable single crystal can be increased.

[0028]

As described above, according to the present invention, by heating the raw material sintering rod with the flat heater and the coil heater, the single crystal is formed from the floating zone through the solid-liquid interface. Controls sudden temperature drop,
It prevents the generation of large thermal stress that causes thermal cracks. Therefore, the obtained single crystal becomes a high quality product without defects such as residual bubbles and cracks. Further, since the temperature deviation in the central portion and the peripheral portion is reduced by using the planar heater, it is suitable for growing an oxide single crystal rod having a large diameter.

[Brief description of drawings]

FIG. 1 is a schematic view of a conventional condensing heating type single crystal manufacturing apparatus.

FIG. 2 is a schematic diagram for explaining the single crystal production apparatus of the present invention.

FIG. 3 shows some examples of planar heaters used in the present invention.

FIG. 4 is an explanatory diagram showing the flow state of the melt in the floating zone.

[Explanation of symbols]

 50 Raw Material Sintered Rod 51 Floating Zone 60 Tubular Furnace Body 61 Coiled Heater 70 Planar Heater 71 Filament

Claims (3)

[Claims] 1. A tubular furnace body having an internal space into which a raw material sintering rod is inserted, a coil-shaped heater provided on an inner wall surface of the tubular furnace body, and a planar heater positioned in a floating zone forming portion. An apparatus for producing a single crystal, comprising: a floating zone formed by heating through the planar heater. 2. The flat heater according to claim 1, wherein the filament of the non-evaporable heat-resistant material is bent or curved so that the area occupancy in the two-dimensional plane is in the range of 30 to 80%. Characteristic single crystal manufacturing equipment. 3. The single crystal production apparatus according to claim 1, wherein the coiled heater is provided on the inner wall surface of the tubular furnace body from above to below the planar heater.