JPH04367585A - Light-gathering heater type apparatus for production of single crystal - Google Patents

Abstract

PURPOSE:To produce a high-quality product free from a defect such as thermal crack in production of an oxide single crystal from a raw material sintered rod by light-gathering heater method by making the temperature gradient of the oxide single crystal immediately after deposition from the molten zone gentle. CONSTITUTION:A raw material sintered rod 20 placed at a position of one focus of a rotating ellipsoidal mirror 11 is locally heated by heat rays 14 irradiated from a xenon lamp 12 arranged at a position of the other focus to form a molten zone 21. An after heater 40 obtained by winding a filament 41 around a spinel transparent tube 50 and forming it into a coil shape is set to a position directly under the position of formation of the molten zone 21 in a state where the oxide single crystal 22 may be surrounded thereby. The after heater 40 can prevent rapid temperature drop of the oxide single crystal 22 immediately after deposition and generation of thermal cracks can be inhibited therefor.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is equipped with a mechanism for controlling the temperature gradient of the single crystal below the local heating position in order to suppress the occurrence of defects in the single crystal grown from the raw material sintered body. The present invention relates to a condensing heating single crystal manufacturing device.

0002

2. Description of the Related Art A condensing heating device using a spheroidal mirror is used as a method for producing single crystals such as ruby and sapphire. In this method, 1550 to 16
Alumina or the like sintered in an air atmosphere at 50° C. is used as the raw material sintered body. This raw material sintered body is housed inside a quartz tube and placed at one focal point of a spheroidal mirror, and a light source such as a halogen lamp or xenon lamp serving as a heat source is placed at the other focal point. Then, the inside of the spheroidal mirror is maintained in an inert gas atmosphere, and the heat rays from the light source are concentrated on one focal point to heat and melt the raw material sintered rod to a high temperature of 2050° C. or higher.

When the raw material sintered rod is lowered under this heating condition, the local heating position moves continuously in the longitudinal direction of the raw material sintered rod. Along with this, the molten region moves in the longitudinal direction of the raw material sintered rod, and a single crystal grows.

[0004] In the vicinity of the local heating position in this method,
Temperature gradient changes rapidly. In other words, the temperature is extremely low in the part away from the condensing part of the heat ray. This temperature drop is due to the fact that the amount of light condensed in this part is low and that heat is dissipated through the inside of the grown single crystal. In particular, in the case of a material having relatively high thermal conductivity, such as alumina single crystal, the amount of heat dissipated through the single crystal is large, and the added heat is rapidly dissipated to the outside. Therefore, the single crystal that has passed the local heating position is rapidly cooled.

As a result, defects such as thermal cracks occur in the obtained single crystal due to rapid cooling. In order to suppress the occurrence of such defects, it is known to arrange an after-heater near the local heating position, which heats the single crystal past the local heating position to prevent rapid cooling. for example,
"Solid State Physics" Vol. 14, No. 10 (1979) "Single crystal production of high melting point substances using a xenon arc image furnace", a spiral cut is made in an alumina protection tube with a cutter,
A product in which platinum wire wound into a coil is wound along the notch and hardened with alumina cement is introduced.

[0006]

[Problem to be solved by the invention] However, the heat rays emitted from the light source placed at the focal point of the spheroidal mirror are blocked by the alumina protection tube of the afterheater and reach the raw material sintered rod or the grown single crystal. I won't. Therefore,
Thermal efficiency is significantly reduced. In order to prevent this reduction in thermal efficiency, a large alumina protection tube with a diameter of 30 mm or more cannot be used, for example. Since the heater bobbin is inserted into this alumina protection tube, the inner diameter becomes smaller. Therefore, there is a limit to the cross section of the single crystal that can be inserted through the afterheater to prevent rapid cooling, and the size of the single crystal that can be manufactured is restricted.

[0007] Furthermore, the tip of the afterheater is heated to a high temperature by the energy of the focused heat rays and the heat flow generated in the vicinity. Due to this high-temperature heating, evaporated substances such as AlO and Al2O are scattered from the alumina cement and the alumina that is the material of the alumina protection tube and bobbin, and the evaporated substances precipitate and adhere to the inner wall surface of the quartz tube as Al2O3. , the quartz tube becomes devitrified and reduces the light collection efficiency.

Troubles caused by evaporated substances can be avoided by blowing off evaporated substances by flowing a large amount of inert gas inside the quartz tube. However, supplying inert gas complicates the equipment configuration and consumes extra inert gas, which also causes an increase in the manufacturing cost of single crystals.

The present invention was devised to solve these problems, and by using a filament formed into a coil shape as an after-heater placed near the local heating position, the evaporation of alumina can be prevented. It is an object of the present invention to provide a condensing heating type single crystal production apparatus that can produce single crystals with relatively large diameters without causing troubles due to precipitation.

0010

[Means for Solving the Problems] In order to achieve the object, the condensing heating type single crystal production apparatus of the present invention has a rotating system in which a light source is placed at one focal point and a raw material sintered body is placed at the other focal point. an ellipsoidal mirror, an upper shaft and a lower shaft that respectively support the upper and lower ends of the raw material sintered body and lower the raw material sintered body at the same speed as the growth rate of the oxide single crystal, and the raw material sintered body and a coil-shaped afterheater disposed directly under the other focal point surrounding the single crystal rod grown from the crystal rod.

[0011] As the after-heater, W, Mo, Ta
, Ir, Re, Zr, Ti, Nb, etc. filaments formed into a coil shape are used. Since this coil expands at high temperatures, it tends to sag and become deformed. Therefore, in order to prevent the coil from sagging, it is preferable to use a transparent tube or a plurality of alumina rods to maintain the coiled shape.

0012

[Function] By using a heater made of a coiled filament, the inner diameter of the after-heater can be freely expanded, allowing flexibility in the diameter of the single crystal that can be produced. Furthermore, since the heat rays emitted from the light source pass through the gaps between the filaments and reach the surface of the single crystal being grown, the proportion of the heat rays that are blocked by the after-heater is significantly reduced, greatly improving thermal efficiency. Moreover,
Since there is nothing that evaporates or scatters due to the energy of the heat rays and the heat flow in the vicinity, the quartz tube does not suffer from devitrification caused by attached precipitates, and maintains excellent light transmittance over a long period of time.

[0013]

[Example] Hereinafter, an example will be described in which white sapphire was manufactured using a convergent heating type single crystal manufacturing apparatus in which an after-heater made of a tungsten filament formed into a coil shape was placed directly below the local heating position.

As shown in FIG. 1, the single crystal manufacturing apparatus used in this example has a xenon lamp 12 as a heat source at one focal point of a spheroidal mirror 11 forming the inner surface of a heating furnace 10.
was placed. At the other focal point of the spheroidal mirror 11, a raw material sintered rod 20 inserted into the quartz tube 13 was placed. As a result, the heat rays 14 emitted from the xenon lamp 12 are
The light is reflected by the spheroidal mirror 11 and condensed at the other focal point to heat the raw material sintered rod 20 . This heated state is observed through a viewing window 16 through a magnifying lens 15.

Further, an after-heater 40 formed by winding a tungsten filament around a spinel transparent tube 50 and forming it into a coil shape is arranged below the local heating position where the hot wire 14 is concentrated. Although the coil diameter d of the afterheater 40 does not limit the present invention, it was set so that the gap between the afterheater 40 and the raw material sintered rod 20 was 5 mm. Further, although the coil pitch P can be set to the same value in the axial direction, it is preferably set in a range of 2 to 5 mm so that it increases as the distance from the local heating position increases.

A means for preventing the after-heater 40 from sagging is specifically shown in FIGS. 3(a) and 3(b). In Figure 3 (
In a), filament 4 is placed in spinel transparent tube 50.
1 wrapped around it. Further, FIG. 3B shows a state in which the filament 41 is supported by a plurality of alumina rods 51. These spinel transparent tubes 50 or alumina rods 51 have grooves corresponding to the coil pitch P,
Forming a hook or the like to secure the filament 41 at a predetermined position is more effective in preventing drooping. For example, a spiral cut is made on the peripheral surface of the spinel transparent tube 50, and the filament 41 is wound along the cut. Note that from the viewpoint of thermal efficiency, it is preferable to arrange the filament 41 inside the spinel transparent tube 50 or the alumina rod 51.

The raw material sintered rod 20 was supported at its upper and lower ends by an upper shaft 30 and a lower shaft 31, respectively. These shafts 30, 31 are formed by the arrow A as the single crystal grows.
It is possible to descend in the direction. In addition, nitrogen gas was blown in as an inert gas 33 from a gas introduction pipe 32 provided below to prevent impurities from being introduced into the growing single crystal from the atmosphere. After the inert gas 33 rose inside the quartz tube 13, it was discharged to the outside of the system from an exhaust pipe 34 disposed at the top.

The raw material sintered rod 20 was prepared as follows. Particle size is in the range of 50-100μm and purity is 99.99%
Alumina powder of
It was molded into a rod-shaped green compact of m. Then, the rod-shaped powder compact was
The material was sintered by heating in an air atmosphere at 00° C. for 10 hours to obtain a raw material sintered rod having a density of 98%, a diameter of 12 mm, and a length of 70 mm.

This raw material sintered rod 20 was inserted into the quartz tube 13 and heated by condensed light while flowing nitrogen gas at a flow rate of 5 Nl/min. By this heating, a molten zone 21 is formed on the raw material sintered rod 20.
was formed. After passing through the local heating position, the melted zone 21 cools down and becomes an oxide single crystal 22 . At this time, the heating state of the raw material sintered rod 20 could be accurately grasped by observation through the magnifying lens 15.

The heating temperature of the raw material sintered rod 20 can be adjusted by changing the output of the xenon lamp 12. In addition, the molten zone 2 can be measured using a light thermometer or the like through the viewing window 16.
When the temperatures of the melting zone 21 and the afterheater 40 were measured, the temperatures of the melting zone 21 and the afterheater 40 were about 2100°C and about 1500°C, respectively.

When feeding the raw material sintered rod 20 in the conveying direction A,
The heat rays 14 reflected by the spheroidal mirror 11 are the raw material sintered rod 2
In order to focus on a position above 0, the molten zone 21 moves upward. Then, a temperature drop occurs at the lower part of the melting zone 21,
A solid phase is precipitated from the molten zone 21, and an oxide single crystal 22 is grown. In this example, the growth rate of the oxide single crystal 22 is set to 30 mm/hour, and the upper shaft 30 and the lower shaft 31 are moved in the transport direction A at the same speed as this growth rate.
moved along.

[0022] In this way, a diameter of 12 mm and a length of 70
Diameter 12mm, length 60mm from 20mm raw material sintered rod
An oxide single crystal 22 was grown. After cooling, the oxide single crystal 22 was taken out from the heating furnace 10 and its internal structure was observed. As a result, it was found to be a high quality oxide single crystal with no bubbles or cracks observed in a field of view of 1 cm2 at 400x magnification. This is achieved by using an afterheater 40 that is made by winding a tungsten filament around a spinel transparent tube and forming it into a coil shape.
1 and the rapid cooling of the oxide single crystal 22 immediately after precipitation is avoided,
This shows that bubbles contained in the melted zone 21 have been removed and the occurrence of thermal cracks has been suppressed.

On the other hand, when the molten zone 21 and the oxide single crystal 22 immediately after precipitation are heated by a conventional afterheater using a heater embedded around the alumina protection tube, the hot wire 14 passes through the alumina protection tube. In order to compensate for the lack of heat blocked by
% increase was necessary.

In the above example, as the afterheater 40, a tungsten filament 41 is wound around a transparent spinel tube 50 and formed into a coil shape with the coil pitch P changed along the axial direction, as shown in FIG. used. That is, the coil pitch on the upper side near the local heating position is made relatively small, and the coil pitch is gradually increased toward the lower side. As a result, the molten zone 21
Alternatively, the amount of heat applied to the oxide single crystal 22 immediately after precipitation increases as it approaches the local heating position, thereby suppressing rapid fluctuations in the temperature gradient. As a result, it is possible to reduce the thermal stress generated in the oxide single crystal 22.

Further, the coil diameter d is preferably maintained at (d-D)/2≦5 mm, where D is the diameter of the oxide single crystal 22. As a result, the filament 41 comes close to the peripheral surface of the oxide single crystal 22, and the radiant heat from the filament 41 is efficiently transmitted to the oxide single crystal 22. In addition, the heat transferred to the oxide single crystal 22 from the filament 41 diffuses into the inside of the single crystal and raises the temperature of the oxide single crystal 22 evenly in the axial direction.

The material of the filament 41 is W, Mo, Ta, Ir, Re, etc., which have excellent heat resistance and do not generate evaporated substances even at high temperatures in an inert atmosphere.
Zr, Ti, Nb, etc. are suitable. Since the filament made of this material is used as the afterheater 40 as it is, there is no deposit or adhesion on the inner wall surface of the quartz tube 13, and defects such as devitrification do not occur. It also has a long lifespan.

[0027]

[Effects of the Invention] As explained above, in the oxide single crystal production apparatus of the present invention, a filament wound around a transparent spinel tube and formed into a coil shape is placed as an after-heater directly below the local heating position. Therefore, the degree of freedom regarding the inner diameter of the afterheater increases, and the diameter of the oxide single crystal that can be manufactured can be increased. Moreover, since the hot wire passes between the filaments wound into a coil shape and reaches the surface of the oxide single crystal immediately after precipitation, thermal efficiency is improved. In addition, since there is nothing to evaporate from the afterheater due to the energy of the heat ray passing near the tip of the afterheater and the heat flow generated in the vicinity, the flow rate of the inert gas that was sent into the quartz tube to blow away the flying debris can be saved. In this way, according to the present invention, a high quality oxide single crystal free of defects such as bubbles and cracks can be produced with good productivity.

[Brief explanation of the drawing]

FIG. 1 shows an outline of a condensed heating type oxide single crystal manufacturing apparatus used in Examples of the present invention.

FIG. 2 shows an example of an after-heater.

FIG. 3 shows an after-heater with a coil sag prevention function.

[Explanation of symbols]

10 heating furnace, 11 spheroidal mirror, 12
Xenon lamp (light source) 20 Raw material sintered rod, 21 Melting zone, 2
2 Oxide single crystal (single crystal rod) 30 Upper shaft, 31 Lower shaft, 40 After heater, 41
Filament 50 spinel transparent tube,
51 Alumina rod

Claims (3)

[Claims] 1. A spheroidal mirror having a light source disposed at one focal point and a raw material sintered body disposed at the other focal point, supporting the upper and lower ends of the raw material sintered body, respectively, and supporting an oxide single crystal. an upper shaft and a lower shaft that lower the raw material sintered body at the same speed as the growth speed; and a coil-shaped afterheater that surrounds the single crystal rod grown from the raw material sintered body and is placed directly under the other focal point. A condensed heating single crystal production device characterized by comprising: [Claim 2] The after-heater according to Claim 1 comprises W,
1. A condensed heating type single crystal production apparatus characterized in that a filament of Mo, Ta, Ir, Re, Zr, Ti, Nb, etc. is formed into a coil shape. 3. A condensed heating type single crystal manufacturing apparatus, wherein the afterheater according to claim 1 is supported by a transparent tube or a plurality of alumina rods so as to maintain a coiled shape.