JPH07138090A - Method for growing mixed crystal in liquid phase and apparatus therefor - Google Patents

Abstract

PURPOSE:To grow a mixed single crystal at a high speed by transporting a solute according to the heat convection. CONSTITUTION:This method for growing a mixed crystal in the liquid phase is to heat a melt 30 contained in a double cylindrical container 20 through an outer cylindrical part 21 with a high-frequency heating coil 11, cool the melt from the lower side with a movable bed 23, produce the heat convection 33 in the melt 30, transport a microcrystal present in the upper layer part to the side of a seed crystal wafer 31, crystallize the microcrystal as a mixed single crystal 34, rapidly move a solute from a source part to a seed part and increase the growth rate of the mixed single crystal 34 capable of being sliced into plural mixed crystal substrates due to a relatively larger thickness of the resultant mixed single crystal 34 than that of a conventional mixed crystal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for liquid phase growing a mixed crystal used as a compound semiconductor such as a mixed crystal for a light emitting device.

[0002]

2. Description of the Related Art In a mixed crystal formed between a plurality of types of semiconductors, the band structure takes an intermediate form of each component simple substance, and the crystal lattice constant also takes an intermediate value in accordance with Vegard's law. Utilizing this characteristic, it is widely used for wavelength control and formation of a heterojunction in a direct transition type band structure region in a light emitting device. Most of the mixed crystals formed by the conventional method are in the form of a thin film epitaxially grown on a single substrate crystal, and thick wafer-shaped mixed crystals are rare. Mixed crystals on thick wafers are useful as light transmissive substrates for light emitting diodes.
For example, after a Ga _1-x Al _x As-based mixed crystal is epitaxially grown thickly on a GaAs substrate crystal without segregation, the substrate GaAs is polished and removed, and only the mixed crystal portion is used as a secondary substrate. At this time, if the light transmissive substrate portion is processed into a hemispherical shape, total reflection at the interface with air is prevented.

Various methods have been proposed for growing a Ga _1-x Al _x As-based mixed crystal thick without segregation under the condition that the AlAs component is kept substantially constant. For example, in JP-A-51-20081, a temperature gradient is provided between the melt and the substrate to crystallize a mixed crystal from a large amount of melt at a constant temperature. In this method, a cooling mechanism is provided at the substrate holding position portion of the growth reaction tube in order to effectively establish a temperature gradient between the melt and the substrate. In addition, in the Journal of Applied Physics, "Applied Physics", Vol. 44, No. 9 (1975), pp. 971-978 "Growth of Ga _1-x Al _x As thick films by liquid phase epitaxial method", raw materials prepared in advance are used. In order to float on the surface of the melt, the solution mixed with an excessive amount of undissolved GaAs solid is once held at a high temperature and then cooled to a predetermined temperature to crystallize and float the raw material mixed crystal on the liquid surface. A temperature gradient is applied to the melt in which the raw material mixed crystal floats on the liquid surface, and the solute is diffuse-transported onto the substrate by utilizing the change in solubility according to the temperature gradient. Thereby, a mixed crystal having a predetermined composition is crystallized. Also, a method of controlling the composition of the growth layer is disclosed.

[0004]

In the conventional mixed crystal growth method, the solute contained in the melt is supplied to the seed crystal side by diffusion. Therefore, the growth of the mixed crystal is limited by the diffusion rate, and it is difficult to obtain a thick crystallized layer at a high growth rate. Specifically, the growth rate at which a good epitaxial growth layer is obtained is an extremely slow rate of 1 μm / min or less. When the supersaturation degree of the melt near the surface of the seed crystal substrate is kept high, the growth rate can be increased. To obtain a high degree of supersaturation, JP-A-50-105
As disclosed in Japanese Patent No. 374, it is necessary to provide a steep temperature gradient from the substrate surface toward the inside of the melt. However, it is difficult to maintain a steep temperature gradient under stable conditions. The degree of supersaturation is described in JP-A-49-110.
As disclosed in Japanese Patent No. 578, it is possible to raise the temperature of the melt to some extent by continuing the growth while lowering the temperature of the melt. In this case, there is a drawback that the components of the mixed crystal are segregated due to the decrease of the crystallization temperature, and the composition of the growth layer changes in the thickness direction. Moreover, if the temperature drop rate is too high, the melt is likely to be overcooled, and the growth layer has a disadvantage that it has a cellular mosaic structure.

As a result, the mixed crystal layer that can be grown on the substrate crystal is 1.4 even when grown for about 24 hours.
It has a thickness of about mm. Due to the restriction caused by this thickness, the number of mixed crystal wafers obtained from the mixed crystal layer obtained by polishing and removing the substrate portion is at most one, and a plurality of mixed crystal wafers cannot be cut out. Further, when the growth is continuously performed for several tens of hours or more, the influence of the composition change due to the evaporation of the melt component, especially As and the like becomes significant, and the quality stability of the obtained mixed crystal wafer deteriorates. The present invention has been devised in order to solve such a problem, and forcibly generates thermal convection in a melt in which microcrystals serving as a mixed crystal source are suspended in the upper layer, and fine convection is generated by the thermal convection. By transporting the crystal to the seed crystal side, it is intended to grow a thick mixed crystal on the seed crystal surface at a high growth rate.

[0006]

In order to achieve the object of the liquid phase growth method of the present invention, an inner cylinder portion having a side wall having a through hole is arranged in the outer cylinder portion forming the outer shell of the container. The melt is housed in a heavy-cylindrical container, the mixed crystal source is crystallized and suspended in the upper layer of the melt as fine crystals, and the seed crystal wafer is placed on the movable bed inserted from below into the inner cylinder. Holding in the vicinity of the bottom of the double cylindrical container, heat convection that rises outside the inner cylinder part and descends inside by heating through the outer cylinder part and cooling through the movable floor is generated, The microcrystals in the upper layer of the melt are transported to the seed crystal side by the thermal convection and crystallized as a mixed crystal on the seed crystal. Further, the liquid phase growth apparatus is a double cylinder in which an inner cylinder part having a height smaller than that of the outer cylinder part and having a through hole formed in a side wall is arranged inside the outer cylinder part forming the outer shell of the container. A container, a movable bed that is provided inside the inner tubular part, and holds a seed crystal at a position near the bottom of the double tubular container, and the melt contained in the double tubular container with the outer tubular part. Heating means for heating via the heating means, and by the heating by the heating means and the cooling by the movable floor, heat convection that rises outside the inner cylindrical portion and descends inside is generated in the melt. To do.
The movable bed is vertically rotatably and rotatably inserted into the inner cylindrical portion from below and has a seed crystal holding portion formed on the top surface.

The liquid phase growth apparatus according to the present invention has, for example, the structure shown in FIG. 1, and a graphite double tube-shaped melt holder 20 is arranged in a reaction tube 10 made of quartz glass.
The reaction tube 10 is surrounded by a heating means such as a high-frequency heating coil 11 and a resistance heating body, and a silica gas introduction tube 12 is arranged inside. From the gas introduction pipe 12,
A reducing gas such as a hydrogen stream or an inert gas is fed into the reaction tube 10. The melt holder 20 has an outer cylinder portion 21.
The inner cylindrical portion 22 is disposed inside the inner cylindrical portion 22, and a cylindrical movable floor 23 is provided inside the inner cylindrical portion 22. The outer tube portion 21 is a melt 30.
Which constitutes the outer shell of the container for housing the bottom of the container and is supported by the cylindrical support 24 made of silica. The inner tubular portion 22 is lower than the outer tubular portion 21 so as to function as an overflow weir, and is integrated with the bottom wall of the outer tubular portion 21. A circulation hole 25 is formed in the side surface of the inner tubular portion 22 at a position corresponding to the lower portion of the outer tubular portion 21.
The tubular leg portion 26 of the inner tubular portion 22 includes the outer tubular portion 21 and the movable floor 23.
It functions as a guide for the movable floor 23 by being inserted into the annular gap between the and.

Since the movable floor 23 acts as a heat sink, a graphite sintered body material having good thermal conductivity,
In particular, it is made of a material such as heat-resistant steel coated with B-free graphite or glassy carbon that is used as a neutron absorber for nuclear reactors having a low impurity concentration. Moreover, you may incorporate the cooling mechanism which circulates an appropriate refrigerant | coolant. The movable floor 23 has a piston-shaped or spindle-shaped structure, and holds the seed crystal wafer 31 on its top surface. The movable floor 23 is inserted from a shaft hole provided at the bottom of the container, and is connected to an appropriate drive means (not shown) so as to move up and down and rotate. Melt holder 20
The temperature of the melt 30 stored in is increased by heating with the high-frequency heating coil 11. The melt 30 is prepared by heating to a high temperature region with an excess of solute. At this time, the movable bed 23 is raised to maintain the seed crystal wafer 31 above the liquid surface of the melt 30. During the process of lowering the temperature of the melt 30 in which the components have been prepared, the supersaturated portion of the mixed crystal is crystallized as fine crystals 32. The crystallized microcrystals 32 float as microcrystal aggregates or polycrystals in the upper layer of the melt 30 due to the difference in specific gravity, or adhere to the inner wall surface of the outer cylinder 21. Movable floor 2 in this state
3, the seed crystal wafer 31 is positioned near the bottom of the outer cylinder 21. The seed crystal wafer 31 has its growth surface always maintained at an optimum position by adjusting the amount of elevation of the movable floor 23. Also, by rotating the movable floor 31,
The temperature of the melt 30 in the vicinity of the seed crystal wafer 31 is made uniform.

The melt 30 is heated from the outer surface of the outer cylinder portion 21 by the high frequency heating coil 11 and cooled from below by the movable floor 23 which functions as a heat sink. The tubular leg portion 26 of the inner tubular portion 22 also acts as a heat sink. Therefore, the melt 30 has a temperature gradient in which the upper layer is high and the lower layer is low. Further, in the melt 30, as shown by an arrow, a thermal convection 33 is generated, which is an ascending flow along the inner wall of the outer tubular portion 21 and a downward flow in the inner tubular portion 22. The microcrystals 32 floating in the upper layer portion of the melt 30 are dissolved in the melt 30 by the thermal convection 33 and are carried to the lower layer portion,
Crystallized on the surface of the seed crystal wafer 31 and grown mixed crystal single crystal 34
Becomes The melt 30 having a low concentration by crystallizing the mixed crystal single crystal 34 flows out to the outer cylinder part 21 through the flow hole 25 and becomes an upward flow to flow to the upper layer part of the melt 30. The rising melt 30 melts the fine crystals 32 in the upper layer into a high-concentration melt, and then descends toward the seed crystal wafer 31. Due to this circulating flow, in the upper layer portion of the melt 30, the fine crystals 3
3, the mixed crystal single crystal 34 crystallizes out in the lower layer.

[0010]

Operation: The melt 30 between the outer cylinder portion 21 and the inner cylinder portion 22
Is heated by the high frequency heating coil 11 to a high temperature that melts a sufficient amount of the source mixed crystal to the saturated state. On the other hand, the melt 30 inside the inner tubular portion 22 is cooled to a temperature at which the melted solute is crystallized by the movable floor 23 and the tubular leg portion 26 that function as heat sinks. As a result, the melt 30
The solute is rapidly transported from the source part in the upper layer part to the seed part in the lower layer part. Due to the thermal convection 33 caused by the temperature difference of the melt 30 inside and outside the inner tubular portion 22, a sufficient transport amount is secured even if the distance from the source portion to the seed portion becomes long. Increasing the distance from the source part to the seed part increases the capacity of the melt 30 to increase the production capacity, and of course allows a larger temperature difference to be provided between the source part and the seed part. As a result, the mixed crystal single crystal 34 grows at a growth rate 10 times faster than that of the conventional method. The movable floor 23 holding the seed crystal wafer 31 is
The temperature condition around the crystal growth interface is made uniform by rotating and / or descending. Therefore, the outer shape of the mixed crystal single crystal 34 is controlled symmetrically, and the growth can be continued while keeping the position of the solid-liquid interface at an optimum level. Therefore, a high-quality and large-sized thick mixed crystal can be obtained.

[0011]

EXAMPLE GaAs having a plane orientation (100) was used as a seed crystal wafer 31 and was fixed to the top surface of a piston-shaped movable floor 23 made of graphite and having a diameter of 25 mm. 1200g metal Ga, 7
7 g of GaAs, 2.3 g of metallic Al, and 0.7 g of metallic Zn as a dopant are added to the outer cylindrical portion 2 having an inner diameter of 150 mm.
1 and a melt holder 2 having an inner tube portion 22 having an inner diameter of 40 mm
Charged 0. Then, the inside of the reaction tube 10 was replaced with a hydrogen flow containing 10% Ar. After completely replacing the inside of the reaction tube 10 with an Ar-containing hydrogen stream, a small current was supplied to the high-frequency heating coil 11 to melt Ga. When the current supplied to the high frequency heating coil 11 was gradually increased, Al and Zn were completely dissolved in the Ga melt, and then GaAs was also gradually dissolved. During this temperature raising process, when the temperature of the melt 30 did not rise above 300 ° C., the movable bed 23 was raised so that the seed crystal wafer 31 was located above the liquid surface of the melt 30.

Next, the melt 30 was heated to 890 ° C. and kept at that temperature for 30 minutes. By maintaining high temperature, G
Most solutes including aAs were dissolved in the melt 30. 840 the prepared melt 30 at a temperature decreasing rate of 2 to 3 ° C. per minute.
Cooled to ° C. By this cooling, Ga _1-x Al _x As
The supersaturated portion of the mixed crystal becomes crystallites 32 and crystallizes, and the melt 30
Floated in the upper layer. Therefore, the movable floor 23 was lowered until the seed crystal wafer 31 was positioned near the bottom of the melt holder 20. Further, the movable bed 23 was rotated at 5 to 6 revolutions per minute to make the temperature condition around the seed crystal wafer 31 uniform.
In this state, the melt 30 had an upper layer temperature of 840 ° C and a lower layer temperature of 705 ° C.
That is, a temperature gradient with a temperature difference of 135 ° C. is generated in the vertical direction, and the heat convection 3 rises outside the inner tubular portion 22 and falls inside the inner tubular portion 22.
3 was constantly generated in the melt holder 20. The convection velocity inferred from the result of the model experiment in which the movement of the floating crystallites 32 was observed from above the furnace was high, reaching 15 cycles per minute.

Mixed crystal single crystal 3 on seed crystal wafer 31
The growth rate of No. 4 was an average of 500 μm / hour in terms of the increasing rate of thickness. Movable floor 23 at a rate of 1 mm every 2-3 hours
Was moved downward and held for 48 hours while adjusting the solid-liquid interface position of the growth part. Shut off the power supply to the furnace,
The movable bed 23 is moved upward so that the grown crystal 23 melts 30
Out of the liquid surface. After the whole furnace is cooled, the grown crystal 23
Was taken out of the furnace. The grown Ga _1-x Al _x As mixed crystal single crystal 34 had a bell shape with a sharp upper end, and the total height was about 15 mm. Mixed crystal single crystal 34
Was sliced to obtain 7 mixed crystal wafers having a thickness of 500 μm. The mixed crystal ratio x showed a value of 0.4, which was almost uniform in the plane of the wafer and between the wafers, and could be used as an epitaxial substrate for a light emitting device.

In the above embodiment, the melt 30
The case of high-frequency heating was explained. However, the present invention is not limited to this, and other heating means including resistance heating can be adopted as long as the outer cylindrical portion of the double cylindrical container is heated from the outside. . Further, the mixed crystal to be grown is not limited to GaAs-AlAs. For example, GaAs-InAs system, GaP
Other mixed crystals having a group V element as a common element in the periodic table such as —InP system can be similarly grown according to the present invention.

[0015]

As described above, in the present invention, the solute is transported from the source portion to the seed portion by the thermal convection forcefully generated in the melt, and the mixed crystal is formed on the seed crystal substrate. Growing fast. The thermal convection enables the seed portion to be largely separated from the source portion, and also enables a gradual temperature gradient in the vicinity of the solid-liquid interface of the crystal growth portion, in other words, a concentration gradient. As a result, an extremely large mixed crystal single crystal easily grows as compared with the conventional method. Moreover, since the temperature uniformity near the solid-liquid interface and an appropriate interface position are ensured by rotating and moving the movable bed, the shape can be controlled even when growing a large crystal. Since the obtained mixed crystal single crystal is thicker than the conventional mixed crystal, it can be cut into several mixed crystal substrates, and the productivity is improved.

[Brief description of drawings]

FIG. 1 is a liquid phase growth apparatus used in Examples of the present invention.

[Explanation of symbols]

10: Reaction tube 11: High frequency heating coil (heating means)
20: Melt holder (double cylinder container) 21: Outer cylinder part 22: Inner cylinder part 23: Movable floor 25: Flow hole 30: Melt 31: Seed crystal wafer 32: Microcrystal 33: Thermal convection 34: Growth Mixed crystal single crystal

Claims (4)

[Claims] 1. A melt is contained in a double cylindrical container in which an inner cylinder having a side wall with a through hole is arranged in an outer cylinder forming an outer shell of the container, and a mixed crystal is contained in an upper layer of the melt. The source is crystallized and suspended as fine crystals, and the seed crystal wafer is held at a position near the bottom of the double cylindrical container by a movable bed inserted from below into the inner cylindrical portion, and the outer cylindrical portion is interposed therebetween. By the heating and cooling through the movable bed, thermal convection that rises outside and descends inside of the inner tubular portion is generated, and the microcrystals in the upper layer portion of the melt are heated by the convection to the seed crystal side. And a liquid crystal growth method of crystallizing as a mixed crystal on the seed crystal. 2. The liquid phase growth method according to claim 1, wherein the movable bed according to claim 1 is provided so as to be vertically movable and rotatable and holds a seed crystal on a top surface thereof. 3. A double cylindrical container in which an inner cylinder portion having a height smaller than that of the outer cylinder portion and having a side wall formed with a through hole is disposed inside an outer cylinder portion forming an outer shell of the container, A movable bed that is provided inside the inner tubular part and holds a seed crystal at a position near the bottom of the double tubular container, and a melt contained in the double tubular container through the outer tubular part. A liquid phase growth apparatus comprising: heating means for heating, and by the heating by the heating means and the cooling by the movable bed, thermal convection that rises outside the inner cylindrical portion and descends inside is generated in the melt. 4. The liquid phase growth apparatus according to claim 3, wherein the movable bed is vertically rotatably and rotatably inserted into the inner cylindrical portion from below and a seed crystal holding portion is formed on the top surface.