JP2004250237A - Method for manufacturing gallium arsenide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a GaAs single crystal by an LEC method, by which a GaAs single crystal wafer with few square pits can be obtained. <P>SOLUTION: In the method for manufacturing the compound semiconductor single crystal by the LEC method comprising accommodating a gallium arsenide melt being a raw material melt and a boron trioxide melt as a liquid encapsulating agent in a crucible 5 which is accommodated in a pressure-resistant vessel filled with an inert gas and heated, and growing the compound semiconductor single crystal by relatively moving a seed crystal and the crucible while bringing the seed crystal into contact with the raw material melt, a gallium arsenide polycrystal 6 is used as the raw material, and the inside of the pressure-resistant vessel 1 is kept at a reduced pressure until the temperature is raised to a temperature at which the boron trioxide 7 softens in a temperature raising step for melting the gallium arsenide polycrystal 6 and the boron trioxide 7. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a compound semiconductor single crystal by an LEC method suitable for growing a GaAs single crystal.
[0002]
[Prior art]
Compound semiconductors have been widely used in high-speed integrated circuits, opto-electronic integrated circuits, and other electronic devices due to the high quality of single crystals. In particular, gallium arsenide, which is a III-V compound semiconductor, has a feature that electron mobility is faster than that of silicon and that a wafer having a specific resistance of 10 ⁷ Ω · cm or more can be easily manufactured. At present, the GaAs single crystal is mainly manufactured by a liquid-encapsulated Czochralski method (hereinafter, referred to as an “LEC method”).
[0003]
A production example of gallium arsenide (hereinafter, referred to as “GaAs”), which is a kind of compound semiconductor single crystal, by the LEC method will be described with reference to FIG. 1 according to an embodiment of the present invention.
[0004]
In the drawing, reference numeral 1 denotes a pressure vessel of a high temperature furnace for crystal growth. A lower shaft 2 is inserted into the pressure vessel 1 from below, and a susceptor 4 is supported at the tip of the lower shaft 2 via a pedestal 3. I have. A crucible 5 made of pyrolytic boron nitride (PBN) is arranged in the susceptor 4. A heater 8 is provided around the susceptor 4 so that the PBN crucible 5 can be heated from the periphery through the susceptor 4. The lower shaft 2 is connected to a rotating / elevating mechanism (not shown) and is rotatable / elevable. A pull-up shaft 9 is inserted coaxially with the lower shaft 2 from above the container 1, and a seed crystal 11 having a desired orientation is placed in a seed crystal holder 10 provided at the lower end thereof (usually (100 ) Is used. The pulling shaft 9 is rotatable and vertically movable coaxially with the PBN crucible 5 by a rotating / elevating mechanism (not shown). A weight sensor 12 is provided in the middle of the pulling shaft 9 so that the weight of the crystal during the growth process can be detected.
[0005]
At the time of crystal growth, first, 24,000 g of the GaAs polycrystalline raw material 6 and boron trioxide (B) as a liquid sealant 7 for preventing volatilization of As were placed in a PBN crucible 5 having a diameter of 280 mm. _2, O ₃ ) is put into the pressure vessel 1 of the growth furnace.
[0006]
The inside of the pressure vessel 1 is evacuated to vacuum, and then an inert gas such as nitrogen or argon is sealed, adjusted, and held so that the pressure inside the pressure vessel becomes about 8 atm. The main heater 8 is energized to raise the temperature inside the PBN crucible 5. At about 500 ° C., the liquid sealant (B ₂ O ₃ ) 7 softens and melts to cover the GaAs polycrystalline raw material 6. Then, the temperature inside the PBN crucible 5 is raised to 1,238 ° C. or higher to melt the polycrystalline raw material 6.
[0007]
Next, the seed crystal 11 is lowered, and its tip is immersed in the raw material melt to perform seeding. Thereafter, while lowering the temperature of the main heater 8, the pulling shaft 9 is pulled up at a speed of 9 to 12 mm / hr while rotating the pulling shaft 9 and the lower shaft 2 relatively, and the weight of the crystal is detected by the weight sensor 12. While detecting, the output of the main heater 8 is controlled to grow, for example, a GaAs single crystal of φ105 mm.
[0008]
The single crystal is cut and polished into a wafer, and a cavity defect (hereinafter, referred to as “square pit”) having a square shape of up to about 10 μm is often observed on a mirror-finished wafer surface. The generation ratio of the square pits reached about 10% of the number of GaAs single crystal wafers with a diameter of 105 mm.
[0009]
2. Description of the Related Art Conventionally, a technique for growing a compound semiconductor crystal in an environment with small thermal strain while maintaining an elemental atmosphere having a high vapor pressure is known. For example, when the entire crucible as a crystal growing container is covered with a highly airtight container (pressure-resistant container), it is difficult to control the As gas pressure inside the airtight container, and various adverse effects occur due to the pressure difference between the inside and outside pressures of the airtight container. In view of the above problem, a pressure buffer passage is provided in the hermetic container, and the path from the pressure buffer passage to the diffusion of the element gas such as As to the outside of the hermetic container is lengthened or bent. This is a technique for suppressing the external diffusion of element gases such as As and As (see Patent Document 1).
[0010]
[Patent Document 1]
Japanese Patent No. 2576239
[Problems to be solved by the invention]
However, Patent Literature 1 or another conventional technique does not focus on reducing the rate of occurrence of square pits, and uses boron trioxide (B ₂ O ₃ ) as a liquid sealant under the pressure of an inert gas. Is softened and melted.
[0012]
For this reason, as described in the above-mentioned prior art manufacturing example, the GaAs single crystal wafer often has square pits, which are defects of a rectangular cavity having a maximum shape of about 10 μm. The unevenness of the surface of the wafer in which the angular pits occurred was a major cause of a decrease in the yield at the time of fine processing of the device. In addition, when the number of square pits is large, there has been a problem that fine processing becomes impossible.
[0013]
Therefore, an object of the present invention is to provide a method of manufacturing a GaAs single crystal by the LEC method, which can solve the above-mentioned problems of the conventional technique in a GaAs single crystal wafer and can obtain a GaAs single crystal wafer having few square pits. It is in.
[0014]
[Means for Solving the Problems]
The gist of the present invention is to obtain a GaAs single crystal by the LEC method with few corner pits, and the method is as follows.
[0015]
The method for producing a gallium arsenide single crystal according to the first aspect of the present invention is characterized in that a gallium arsenide melt as a raw material melt and a liquid sealing agent are housed in a pressure-resistant container filled with an inert gas and heated in a crucible. A method for producing a compound semiconductor single crystal by the LEC method of growing a compound semiconductor single crystal by containing a boron trioxide melt and relatively moving the seed crystal and the crucible while contacting the seed crystal with the raw material melt Wherein gallium arsenide polycrystal is used as a raw material, and the pressure inside the pressure vessel is reduced to a temperature at which boron trioxide is softened in a temperature rising process of melting the gallium arsenide polycrystal and boron trioxide.
[0016]
According to a second aspect of the present invention, in the method for producing a gallium arsenide single crystal according to the first aspect, in the temperature increasing process for melting the gallium arsenide polycrystal and boron trioxide, the pressure-resistant container is heated to a temperature at which boron trioxide is softened. Is maintained at 13.3 Pa or less.
[0017]
According to a third aspect of the present invention, in the method for producing a gallium arsenide single crystal according to the first or second aspect, when the boron trioxide is softened and melted, an inert gas is sealed in a pressure vessel and pressurized (for example, The pressure is increased to about 8 atm), the temperature is raised to prepare a gallium arsenide melt, and seeding is performed with a seed crystal.
[0018]
<The gist of the invention>
The present invention has been made based on the following findings of the inventors.
[0019]
It was confirmed that the square pits of the GaAs wafer were filled with an atmosphere gas for crystal growth. The investigation also revealed that the square pits were distributed along the solid-liquid interface at some point during growth.
[0020]
Regarding the frequency of occurrence of angular pits, it does not occur in all crystals or in all wafers. Therefore, it is presumed that the square pits are generated during growth under certain conditions.
[0021]
From the above, the following models can be considered as a mechanism for generating the square pit.
[0022]
In the heating process of melting the boron trioxide and the GaAs polycrystal in the PBN crucible housed in the pressure-resistant container filled with the inert gas, the inert gas is melted at the lower portion of the boron trioxide melt when the boron trioxide is melted. It remains or is taken in on the GaAs polycrystal side). It is considered that the inert gas remains on the GaAs melt side even when the GaAs polycrystal becomes a melt and floats between the interfaces of the GaAs melt and the boron trioxide melt.
[0023]
In the GaAs single crystal growth process, the inert gas is considered to be on the solid-liquid interface which is the interface between the grown GaAs single crystal and the GaAs melt, but in the normal growth process, the inert gas is incorporated into the GaAs single crystal. Will not be. It is considered that the inert gas is taken into the GaAs single crystal only when the GaAs melt enters a supercooled state due to some situation and the subcooled portion becomes single crystallized at a higher speed than the normal growth rate.
[0024]
The above model can clearly explain the results of gas analysis in the square pits, the frequency of occurrence of the square pits, and the like.
[0025]
Therefore, as in the present invention, in the heating process for melting the raw material and boron trioxide, the pressure inside the pressure vessel is reduced to the boron trioxide softening temperature, so that the inert gas becomes trioxidized when the boron trioxide is melted. The ratio of remaining or being taken in the lower portion (the GaAs polycrystal side) of the boron melt becomes extremely small.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the illustrated examples.
[0027]
[Example]
The growth furnace of FIG. 1 having the configuration described above was used. In the same manner as in the production example of the prior art, at the time of crystal growth, first, 24,000 g of the GaAs polycrystalline raw material 6 was placed in a PBN crucible 5 having a diameter of 280 mm, and a liquid sealant for preventing volatilization of As was used. 1,500 g of boron trioxide (B ₂ O ₃ ) as No. 7 is put into the pressure vessel 1 of the growth furnace.
[0028]
Then, the inside of the pressure vessel 1 was evacuated, and the inside of the pressure vessel was adjusted and maintained at 0.1 Torr (about 13.3 Pa) or less.
[0029]
Next, the heater 8 is energized to raise the temperature inside the PBN crucible 5. At about 500 ° C., boron trioxide (B ₂ O ₃ ) of the liquid sealant 7 softens and melts, and covers the GaAs polycrystalline raw material 6. The pressure inside the pressure vessel 1 was kept at a reduced pressure until the temperature at which the boron trioxide was softened. Then, when the boron trioxide was melted, an inert gas was sealed in a pressure-resistant container and adjusted to 8 atm and maintained.
[0030]
Further, the temperature inside the PBN crucible 5 is increased to 1,238 ° C. or higher by heating by the heater 8 to melt the polycrystalline raw material 6.
[0031]
After preparing the gallium arsenide melt, the seed crystal 11 attached to the tip of the pulling shaft 9 is lowered, and the tip is immersed in the raw material melt for seeding. After seeding with a seed crystal, the crystal was grown by slowly raising the pulling shaft 9 while rotating the pulling shaft 9, thereby growing a GaAs single crystal having a diameter of 105 mm.
[0032]
When the single crystal was cut into a wafer and polished to obtain a mirror-finished wafer, no square pits were observed. A single crystal was grown 50 times by the same method, and all the crystals were cut into a wafer and polished to obtain a mirror-finished wafer. The occurrence rate of square pits was 2%.
[0033]
In the above embodiment, the method of manufacturing a GaAs single crystal has been described. However, the method of manufacturing other compound semiconductor single crystals such as InP, GaP, and InAs can be directly applied, and similar effects can be expected.
[0034]
The GaAs single crystal wafer obtained by the manufacturing method according to the present invention has significantly less square pits than the conventional method. Therefore, when device elements such as FETs, HEMTs, and HBTs are manufactured using a GaAs single crystal wafer obtained by the manufacturing method of the present invention, it is possible to prevent a decrease in element yield due to square pits. Therefore, there is a great economic effect in industrial production.
[0035]
【The invention's effect】
As described above, according to the present invention, in a method for producing a GaAs single crystal in the LEC method, gallium arsenide polycrystal is used as a raw material, and boron trioxide is softened in a temperature rising process for melting boron trioxide with the raw material. Since the inside of the pressure vessel is kept at a reduced pressure up to the temperature, a GaAs single crystal wafer having few square pits can be manufactured.
[Brief description of the drawings]
FIG. 1 is a view showing a configuration of a growth furnace used in a method for producing a gallium arsenide single crystal according to the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 pressure vessel 2 lower shaft 3 pedestal 4 susceptor 5 crucible made of PBN 6 polycrystalline raw material 7 liquid sealant (B ₂ O ₃ )
Reference Signs List 8 heater 9 pulling shaft 10 seed crystal holder 11 seed crystal 12 weight sensor

Claims (3)

A gallium arsenide melt, which is a raw material melt, and a boron trioxide melt, which is a liquid sealant, are housed in a pressure-resistant container filled with an inert gas and heated. In the method for producing a compound semiconductor single crystal by the LEC method in which the seed crystal and the crucible are relatively moved while being brought into contact with each other to grow the compound semiconductor single crystal,
Gallium arsenide single crystal, characterized in that gallium arsenide polycrystal is used as a raw material, and the pressure in the pressure vessel is reduced to a temperature at which boron trioxide is softened in a temperature increasing process of melting the gallium arsenide polycrystal and boron trioxide. Manufacturing method. The method for producing a gallium arsenide single crystal according to claim 1,
A method for producing a single crystal of gallium arsenide, characterized in that in the heating process for melting the polycrystalline gallium arsenide and boron trioxide, the inside of the pressure vessel is kept at 13.3 Pa or less until the temperature at which boron trioxide is softened. The method for producing a gallium arsenide single crystal according to claim 1 or 2,
When the boron trioxide is softened and melted, an inert gas is sealed in a pressure-resistant container, pressurized, heated to produce a gallium arsenide melt, and seeded with a seed crystal. A method for producing a gallium single crystal.

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