JPH07277869A - Apparatus and process for producing single crystal - Google Patents

Abstract

PURPOSE:To improve a single crystallization rate and to enable growth of a non- dislocation crystal by installing a heat insulating section of a prescribed length between the high-temp. sections and low-temp. section of a heating mechanism. CONSTITUTION:A seed crystal 1 is housed in the bottom of a crucible 5 having a bore 80mm of the apparatus for producing the single crystal by a perpendicular Bridgman method and a GaAs melt doped with about 2000g Si is housed as a raw material 3 in the upper part thereof. The heat insulating part 7 is formed to a bore 100m, outside diameter 200mm, thickness 50mm, length 100m (above 1/3 the diameter of the crucible 5 and below 3 times this diameter) and the spacing <=20mm from the crucible 5 and is composed of a molding of ceramic wool or carbon felt. The heating mechanisms 81, 82 are formed as high-temp. sections and 83 is formed as a low-temp. section. A furnace body 11 is composed of these sections and a heat insulating material 10. The descending speed (crystal growth speed) of the crucible 5 is set at 5mm/H and the temps. of the heating mechanisms 81, 82, 83 are regulated in such a manner that the temp. of the crucible is higher than the temp. of the grown crystal 2 measured at temp. measuring hole 9 existing on the high-temp. side of the heat insulating section 7, by which the single crystal of the non-dislocation crystal of the grown crystal 2 is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal manufacturing apparatus and method using a vertical Bridgman method (hereinafter referred to as VB method), and more particularly to a compound semiconductor single crystal,
It is suitable for the production of oxide single crystals.

[0002]

2. Description of the Related Art As shown in FIG. 2 (FIG. 2 of Japanese Patent Application Laid-Open No. 1-212291), a conventional single crystal manufacturing apparatus using the VB method has a crucible 5 containing a seed crystal 1 at the bottom thereof.
Is covered with a carbon crucible holder 6, and the crucible holder 6
A temperature distribution is given to the surface of the 5 heaters 8 ₁ to 8 ₅ to divide it into a high temperature portion and a low temperature portion, the melting point is near the boundary portion, and the temperature in the crucible holder 6 is controlled by the thermocouples 9 _{1 to} 9 ₅ . Measure the temperature at 5 points, estimate the temperature distribution in the melt from the measured temperature with a computer, and make each heater 8 ₁ to 8 ₅ so that the shape of the solid-liquid interface 12 is convex upward.
The power applied to is adjusted. However, since the diameters of the heaters 8 ₁ to 8 ₅ are larger than the diameter of the crucible holder 6, the heat flow rate due to the radiation passing outside the crucible holder 6 is equal to the heat flow rate passing through the solid-liquid interface 12, or more than that. As a result, the heat flow rate passing through the solid-liquid interface 12 cannot be sufficiently controlled.
It is extremely difficult to make the shape of 2 convex as shown in FIG. In the figure, 2 is a crystal, 3 is a melt, and 4 is a liquid sealant.

Besides, Suzuki, Okano,
Hoshikawa, Fukuda J. Crystal
Growth vol. 128 P435-438 (1
993) proposes a means for controlling the solid-liquid interface. In this proposal, as shown in FIG. 3, in the same furnace, the crucible 5 is covered with double carbon crucible holders 6a and 6b, and 6 pairs of thermocouples 9 are embedded near the inside of the outer crucible holder 6b.
The temperature distribution in the axial direction is monitored. The outer crucible holder 6b is provided with a heat insulating material 7 portion between the crucible holder 6b in order to freely set the temperature difference between the high temperature portion and the low temperature portion of the furnace. This heat insulating material 7 is for giving a temperature difference to the heater portion 8 and is not for controlling the heat flow. This is also apparent from the fact that the crucible holder 6a is further provided inside. In this structure, when carbon felt is used for the heat insulating material 7 and the temperature gradient of the heater portion 8 is increased to 75 ° C./cm, the calculated temperature gradient in the crystal is about 25 ° C./cm. No convex solid-liquid interface shape has been obtained, and there is no report that an upwardly convex solid-liquid interface shape crystal was actually obtained.

[0004]

When the solid-liquid interface shape is concave upward, the following two problems occur. (1) Polycrystallization from the peripheral portion: Since the heat flow control and the temperature control were not sufficiently performed in the conventional technique as described above, the solid-liquid interface shape becomes concave upward. The fact that the solid-liquid interface is concave upward means that the peripheral part of the crystal growth precedes the central part, and further that the temperature of the crucible wall is lower. Shows. Therefore, there is a probability that crystals will grow from the crucible wall, and the orientation of the crystals growing there may be unrelated to the seed crystal, resulting in the problem of polycrystallization. (2) Dislocation generation: The fact that the solid-liquid interface is concave upward indicates that the isothermal surface is concave upward in the solid to some extent from the solid-liquid interface. There is also a temperature distribution in the cross section of the crystal, indicating that the periphery is the low temperature part and the center is the high temperature. In the case of such a temperature distribution, compressive stress is applied from the periphery to generate dislocations. Further, dislocations that have entered once are difficult to come out to the outer peripheral portion because the solid-liquid interface faces inward. In such a conventional technique, the single crystallization rate is not high, and it is difficult to form a low dislocation crystal.

[0005]

The present invention has been proposed in view of the above, and a seed crystal is contained in the bottom of a crucible for growing a single crystal, and a raw material is contained in the upper part of the crucible. From the heating mechanism, the temperature of the seed crystal accommodating portion is low, the temperature of the raw material accommodating portion is heated to a temperature gradient such that the temperature rises, and the raw material is heated to become a melt, the temperature gradient The crucible, so that it moves upward as it is,
Alternatively, in the single crystal manufacturing apparatus by the VB method in which the single crystal growth operation is performed by moving the heating mechanism relatively, a heat insulating part having a predetermined length is provided between the high temperature part and the low temperature part of the heating mechanism. The present invention relates to a single crystal production apparatus characterized by the above.

That is, in the single crystal production apparatus by the VB method, by installing a heat insulating part of a predetermined length between the high temperature part and the low temperature part of the heating mechanism, the heat flow from the high temperature part to the low temperature part of the heating mechanism. Mainly flows in the raw material, and the heat flow is controlled so that the raw material serves as a heat inlet in a high temperature portion and serves as a heat outlet in a low temperature portion. At this time, the isothermal surface is convex above the center of the heat insulating part and is concave above the center of the heat insulating part. That is, if the heating temperature is lowered to bring the solid-liquid interface above the center of the heat insulating section, the solid-liquid interface becomes convex, and if the heating temperature is raised to bring the solid-liquid interface below the center of the heat insulating section, the solid-liquid interface becomes It becomes concave upwards. Therefore, if the position of the solid-liquid interface is estimated from the temperature and temperature gradient of each part of the heat insulating part and the heating temperature is adjusted so that the solid-liquid interface is located above the center of the heat insulating part, the solid-liquid interface becomes convex upward. Can grow a single crystal.

Further, since the heat insulating portion of the present invention is intended to reduce the heat flow rate from the high temperature portion to the low temperature portion outside the crucible as much as possible, the heat insulating portion of the heat insulating portion is reduced so as to reduce the leakage of radiation outside the crucible. 20m clearance between inner diameter and outer diameter of crucible
It is desirable that the number be m or less and as small as possible.

Further, when the length of the heat insulating portion is given, the isothermal surface of the raw material approaches a flat surface in the heat insulating portion region, and becomes nearly uniform in the radial direction. Although the temperature gradient in the axial direction remains, the temperature gradient in the axial direction is determined by the temperature difference between the high temperature portion and the low temperature portion divided by the length of the heat insulating portion. Therefore, the dislocation-free crystal can be grown by lengthening the heat insulating portion to reduce the temperature gradient in the crystal so that the stress based on the temperature distribution is equal to or lower than the critical stress for dislocation generation. The length of such a heat insulating part is
Although it depends on the thermal conductivity of the crystal material and the critical stress value for dislocation generation, generally one third or more of the crucible diameter is required, and three times the crucible diameter is required to achieve a practical growth rate. Must be within.

The heat insulating portion is made of ceramic wool such as alumina wool (thermal conductivity 0.3 W / (m · K)), silica wool (thermal conductivity 0.27 W / (m · K)) or carbon felt ( Thermal conductivity 0.09W / (m ・
K)) or its molded product has a thermal conductivity of 0.5 W /
It is composed of heat insulating material of (m · K) or less. Also tantalum,
It is also possible to make a heat shield by stacking a number of thin plates of refractory metal such as molybdenum concentrically. Further, two heat shields having the above-described configurations having different diameters may be produced, and the heat insulating portion length may be made variable by forming a slide structure in which the heat shields are intricately engaged with each other.

Further, it is preferable to provide a plurality of temperature side fixed points provided in the heat insulating portion so that the temperature gradient in the heat insulating portion can be measured. In the case of compound semiconductor crystal growth, the crystal container is enclosed in a quartz ampoule, and the purpose of temperature measurement is to estimate the solid-liquid interface, so the surface of the crystal container is measured with a radiation thermometer. If the quartz is cloudy and the radiation thermometer measurement is inaccurate, measure outside the ampoule with a thermocouple. In any case, since the measurement temperature is different from the crystal temperature by the crucible, it is necessary to calibrate the measurement temperature and the solid-liquid interface position.

[0011]

According to the present invention having the above structure, it is possible to grow the solid-liquid interface so as to be convex upward, whereby a high single crystal yield can be obtained. Further, the length of the heat insulating material portion is set to a length at which the crystal internal stress based on the temperature gradient is equal to or less than the critical value for generating dislocations, whereby a dislocation-free crystal can be grown.

[0012]

1 is a conceptual diagram showing the gist of the present invention. In the figure, 9 ₁ , 9 ₂ and 9 ₃ are heat insulating parts 7 according to the present invention.
3 shows temperature measuring holes for radiation thermometers at three locations for detecting temperatures at a plurality of locations on the outer circumference of the crucible 5 in FIG. The temperature can be measured using a thermocouple, but in the case of a thermocouple, since the temperature outside the quartz ampoule that houses the crucible is measured, there is a large deviation from the raw material surface temperature.

[Embodiment 1] FIG. 1 is a schematic view showing a crystal growth furnace according to an embodiment of the present invention, in which pB having an inner diameter of 80 mm is used.
Ga in which the seed crystal 1 was housed in the bottom of the N crucible 5 and about 2000 g of Si was doped as the raw material 3 in the upper part thereof
The As melt was housed. About 200 g of B is included in the liquid sealing material 4.
₂ O ₃ was used. The pBN crucible 5 was held in a transparent quartz ampoule 6 having an outer diameter of 90 mm. Thermal insulation 7 is 100m inside diameter
m, outer diameter 200 mm, thickness 50 mm, and length 100 mm. The heat insulating portion 7 is a carbon felt molded body (density: 0.
16 g / cm ³ , thermal conductivity 0.09 W / (m · K) at
1000 ° C.), the heaters 8 ₁ , 8 ₂ and 8 ₃ are made of graphite, 8 ₁ and 8 ₂ are the high temperature part, 8 ₃ is the low temperature part, and the furnace body 11 is composed of the heat insulating material 10. (Note that the diameters of the crucible 5, the quartz ampoule 6 and the heat insulating portion 7 in this furnace body are shown in FIG. 4). The descent rate (= crystal growth rate) of the pBN crucible 5 was constant at 5 mm / H.
The heaters 8 ₁ and 8 were adjusted so that the surface temperature of the pBN crucible 5 measured by the radiation thermometer at the temperature measuring hole 9 ₁ was 1238 ° C.
_When the temperatures of ₂ and 8 ₃ were adjusted, the solid-liquid interface position was about 6 mm above the temperature measuring hole 9 ₁ . This is a pBN crucible 5
Axial thermal conductivity of 30W / (mK) and GaAs of 1
Higher than 5W / (m · K), in the vicinity of measuring Yutakaana 9 ₁ because the direction of pBN crucible 5 than the growing crystal 2 it becomes hot. When the growth fringes of the obtained GaAs single crystal were observed by etching, the solid-liquid interface shape was convex upward, and dislocation-free crystals were obtained over the entire straight body portion of the growth crystal 2.

[Embodiment 2] A thickness of 0.2 as shown in FIG.
Insulation with a structure in which two sets of heat shields of 8-fold cylinders (the diameter of each cylinder increases at intervals of 8 mm) are made with mm thin tantalum plates 71 and 72, and the diameters of each set are offset by 4 mm, and interlock with each other in a non-contact manner. Part 7 was prepared. The length of the two heat shields was 90 mm for each of the two sets, and they were combined to form an 8-fold cylindrical structure. A carbon felt molded body 13 having a length of 10 mm was placed on the upper portion, and a temperature measuring hole 9 ₁ for a radiation thermometer was installed. In the heat insulating portion 7 having the eight-fold cylindrical structure, the length can be made variable, and the thermal conductivity is 0.09 W / (m · K) at1000.
Adiabatic performance of ℃ was obtained. Example 1 using this device
A GaAs single crystal was grown under the same conditions as above. The obtained single crystal had a solid-liquid interface shape that was convex upward, and the straight body portion was dislocation-free over the entire region.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-mentioned embodiments, and may be carried out in any manner as long as the configuration described in the claims is not changed. You can

[0016]

As described above, according to the apparatus and method for producing a single crystal of the present invention, a heat insulating unit having a predetermined length is installed between the high temperature portion and the low temperature portion of the heating mechanism to increase the temperature of the heating mechanism. Since the heat flow from the part to the low temperature part is controlled so as to mainly flow in the raw material, the position of the solid-liquid interface is estimated from the temperature of the heat insulating part, and the temperature is adjusted so that this solid-liquid interface is located above the center of the heat insulating part. Can be grown so that the solid-liquid interface has a convex shape, and a high single crystal yield can be obtained.

Further, if the length of the heat insulating portion is not less than one-third and not more than three times the crucible diameter, the crystal internal stress due to the temperature gradient is set to a length not more than the critical value for dislocation generation. Therefore, a dislocation-free crystal can be grown without generating dislocations.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing the configuration of an apparatus of the present invention.

FIG. 2 is a diagram showing an example of a conventional VB method apparatus.

FIG. 3 is a diagram showing another example of a conventional VB method apparatus.

FIG. 4 is an enlarged cross-sectional view showing the diameters of a crucible, a quartz ampoule, and a heat insulating portion of Example 1.

FIG. 5 is an enlarged cross-sectional view showing a heat insulating portion of the second embodiment.

[Explanation of symbols]

1 seed crystal 3 raw material (melt) 5 crucible 7 adiabatic part 8 ₁ , 8 ₂ , 8 ₃ heating mechanism

Claims (7)

[Claims] 1. A seed crystal is contained in a bottom portion of a crucible for growing a single crystal, and a raw material is contained in an upper portion of the crucible. A heating mechanism is provided from the outside of the crucible so that a temperature of the seed crystal accommodating portion is low, Heating to a temperature gradient such that the temperature of the raw material containing portion becomes high, and raising the temperature so that the raw material becomes a melt, the crucible so as to move the temperature gradient upward as it is,
Alternatively, in a single crystal manufacturing apparatus by the vertical Bridgman method for performing a single crystal growth operation by relatively moving the heating mechanism, a heat insulating unit having a predetermined length is provided between a high temperature portion and a low temperature portion of the heating mechanism. A single crystal manufacturing device characterized by being installed. 2. The apparatus for producing a single crystal according to claim 1, wherein the length of the heat insulating portion is not less than ⅓ and not more than three times the diameter of the crucible. 3. The apparatus for producing a single crystal according to claim 1, wherein the gap between the heat insulating portion and the crucible is 20 mm or less. 4. The heat insulating part is made of ceramics wool such as alumina or silica, carbon felt, or a molded body thereof, and is characterized in that:
Or the single crystal manufacturing apparatus according to 3. 5. The single crystal production apparatus according to claim 1, wherein a temperature measuring point is provided on the high temperature side of the heat insulating section. 6. The heat insulating portion has a slide structure in which thin plates of tantalum or molybdenum are displaced in diameter from each other, and a large number of concentric circles are superposed on each other so as to interlock with each other. Or the single crystal manufacturing apparatus according to 5. 7. A method for producing a single crystal by the vertical Bridgman method, wherein a heat insulating part having a predetermined length is installed between a high temperature part and a low temperature part of a heating mechanism, and the position of the solid-liquid interface is determined from the temperature of the heat insulating part. A method for producing a single crystal, which is characterized by adjusting the temperature so that the solid-liquid interface is located above the center of the heat insulating portion, and making the shape of the solid-liquid interface convex upward to grow a single crystal.