JP2008270401A - Method for producing al-based iii nitride crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide Al-based III nitride crystal of high purity. <P>SOLUTION: (1) An Al-based III nitride producing method is the method for allowing an Al raw material containing a halogen gas to act with a nitrogen raw material containing ammonia, on a crystal surface. (2) The Al-based III nitride producing method described in (1) is the method where the halogen gas is chlorine. (3) The Al-based III nitride producing method described in (1) or (2) is the method where the Al raw material is AlCl<SB>3</SB>. (4) The Al-based III nitride producing method described in (1), (2), or (3) is the method where the Al-based III nitride is AlN. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing an Al-based group III nitride crystal.

  Group III nitride crystals such as AlN, GaN, InN, AlGaN, GaInN, AlInN, and AlInGaN are expected and used as materials for forming light emitting elements such as LEDs and electronic elements such as HEMTs. Of these, only GaN is in the range of practical use for manufacturing large crystals at the substrate level, and is mainly manufactured by the hydride vapor phase epitaxy (HVPE) method. GaN growth methods include metalorganic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE), and pulsed laser deposition (PLD), but HVPE grows faster than other methods. Therefore, a crystal having a thickness that can be used as a substrate can be manufactured at a low cost (Patent Document 1).

  As a method for producing an Al-based group III nitride crystal, a sublimation method and the like have been proposed in addition to the HVPE method, MOVPE method, MBE method, and PLD method described above. Compared with the sublimation method, the HVPE method, the MOVPE method, the MBE method, and the PLD method have many advantages such as easy acquisition of high-purity raw materials. Further, the point that the HVPE method can increase the growth rate as compared with other methods is the same as in the case of GaN. However, even with the HVPE method, the growth rate of the Al-based group III nitride is significantly slower than that of GaN, and has not been put into practical use.

  The sublimation method does not have a high growth rate compared with the other methods described above, but since the apparatus is inexpensive, it has been considered that it is possible to produce an Al-based group III nitride crystal at a low cost as a result. . However, Al metal can be used in the HVPE method and MBE method, and an organic metal can be used in the MOVPE method, whereas an Al-based group III nitride material is required in the sublimation method.

Japanese Patent Laid-Open No. 11-1399

Since Al-based Group III nitride materials conventionally contain a large amount of impurities such as oxygen, crystals obtained by the sublimation method are also colored with low purity. The colored crystal absorbs light and thus is not suitable as a material for a light emitting element, and has a drawback that the lattice constant is changed.
The present invention has been made to solve the above problems, and an object of the present invention is to provide an Al-based group III nitride crystal having high purity at a low cost.

  As a result of intensive studies to solve the above problems, the present inventors have reached the present invention.

That is, the present invention relates to [1] a method for producing an Al-based group III nitride in which an Al raw material containing a halogen gas and a nitrogen raw material containing ammonia are reacted on the crystal surface.
The present invention also provides [2] a method for producing an Al-based group III nitride according to [1], wherein the halogen gas is chlorine,
[3] The method for producing an Al-based group III nitride according to [1] or [2], wherein the Al raw material is AlCl ₃ ;
[4] The method for producing an Al group III nitride according to any one of [1] to [3], wherein the Al group III nitride is AlN,
[5] The Al group III nitride according to any one of [1] to [4], wherein the temperature of the crystal surface for reacting the Al source containing halogen gas with the nitrogen source containing ammonia is controlled to 1300 ° C to 2300 ° C. Manufacturing method,
[6] Al-based group III nitride obtained by the method for producing an Al-based group III nitride according to any one of [1] to [5],
It is related to.

  According to the method for producing an Al-based group III nitride of the present invention, the crystal surface can be locally heated by the reaction heat of halogen gas and ammonia. As a result, an Al-based group III nitride crystal with few impurities and crystal defects can be produced at a high growth rate, which is extremely useful industrially.

  In the method for producing an Al-based group III nitride according to the present invention, an Al raw material containing a halogen gas and a nitrogen raw material containing ammonia are reacted on the crystal surface. In this method, since the surface of the crystal can be locally raised by the reaction heat of halogen gas and ammonia, a crystal with few impurities and crystal defects can be produced at a high growth rate.

  Examples of the halogen gas include one or more selected from the group consisting of chlorine, bromine and iodine, preferably one or more selected from the group consisting of chlorine and bromine, and more preferably chlorine.

Examples of the Al raw material include one or more selected from the group consisting of chloride, bromide, iodide, and organic metal, and chloride is preferred. Examples of the chloride include one or more selected from the group consisting of AlCl, AlCl ₂ and AlCl ₃ , with AlCl ₃ being preferred.

  Examples of the Al group III nitride include AlN, AlGaN, AlInN, and AlGaInN. Since nitride containing In has a high vapor pressure and has a strong tendency to volatilize at high temperatures, AlN and AlGaN are preferable, and AlN is most preferable.

  The temperature of the crystal surface at which the Al source containing halogen gas reacts with the nitrogen source containing ammonia affects the crystallinity and purity of the Al group III nitride. If the temperature is lower than 1300 ° C., the crystallinity deteriorates, so the growth rate cannot be increased. If the temperature exceeds 2300 ° C., the growth rate is sufficient, but impurities are likely to be mixed from the apparatus members, and crystal defects such as nitrogen vacancies are likely to occur. Therefore, the substrate temperature is preferably 1300 ° C to 2300 ° C, more preferably 1400 ° C to 2250 ° C.

Next, a preferred embodiment of the method for producing an Al-based group III nitride of the present invention will be described with reference to the drawings.
A seed crystal 10 is placed on the susceptor 9 shown in FIG. The seed crystal is stable at a high temperature of 1300 ° C. or higher, and the seed crystal must have a lattice constant close to that of the Al-based group III nitride produced. For example, when manufacturing an AlN crystal, AlN is most preferable, but SiC or the like can also be used. Since ammonia gas is used, sapphire has a limit of up to about 1400 ° C., which is not preferable because it decomposes at higher temperatures. The susceptor is provided with a pulling mechanism 7 in addition to the rotating mechanism 8, and the solid-gas interface can always be kept constant.

  Heating of the reaction furnace is locally performed by a reaction between chlorine and ammonia, but is assisted by a heater 4 attached to the outside. About 1000 ° C. is sufficient for heating by the heater, and general methods such as high-frequency induction heating, resistance heating, and lamp heating are used. Although there is no problem even in the hot wall method in which the reaction vessel wall becomes high in temperature, a cold wall is preferable in order to prevent deposition of deposits on the vessel wall. The temperature of the crystal surface is measured by a radiation thermometer 12 attached to the reaction vessel 1.

Examples of the Al raw material include chloride, bromide, iodide, and organic metal. Any raw material can be used, but chloride, particularly AlCl ₃ is preferable. AlCl ₃ is relatively stable among chlorides, and it is easy to obtain a high purity and is inexpensive. Further, as in the HVPE method, HCl gas may be reacted with metal Al at about 500 ° C. and supplied. The Al raw material is mixed with a halogen gas and supplied to the crystal surface. The Al raw material supply pipe 2 is preferably kept at about 200 ° C. in order to prevent condensation of AlCl ₃ .

  Examples of the halogen gas include chlorine, bromine and iodine. Considering reactivity with ammonia, chlorine is easier to handle than bromine and iodine. Considering the side reaction, if the Al raw material is chloride, chlorine is preferable, and bromide is preferable to be bromine.

  The temperature of the crystal surface is controlled by the reaction heat of the halogen gas and ammonia in addition to the heating of the heater. Therefore, the halogen gas flow rate must be determined depending on how much the crystal surface temperature is to be controlled, and must be adjusted according to the temperature change. The growth rate is controlled by the supply amount of the Al raw material.

Referring to FIG. 1, for example, an AlN single crystal can be produced as follows. The AlN seed crystal 10 is placed on the susceptor 9 in the reaction vessel 1 and heated by the heater 4 while flowing ammonia from the ammonia gas inlet 13a and nitrogen from the Al raw material inlet 13b. When the seed crystal reaches a predetermined temperature, supply of chlorine is started from the Al raw material inlet. Simultaneously with the start of supply of chlorine, the seed crystal surface temperature starts to rise due to the reaction heat of chlorine and ammonia. When a temperature sufficient for AlN growth is reached, the growth is started by supplying a mixed gas obtained by adding AlCl ₃ to chlorine. Growth is performed while maintaining the crystal surface temperature at, for example, 1900 ° C. by adjusting the supply amount of chlorine and the output of the heater. As AlN crystal growth proceeds, the AlN crystal surface position (solid-gas interface) moves upward and the distance from the Al raw material ejection port changes, so the susceptor is pulled down by the pull-down mechanism 7 and the solid-gas interface is changed. Keep growing at a certain position.

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples with reference to FIGS. 1 to 3, but the present invention is not limited to the examples.

Example 1
With reference to FIG. 1, a method of manufacturing an AlN single crystal according to the present invention will be described. The surface of the AlN seed crystal (0001) having a diameter of 2 inches cut out from the AlN single crystal is subjected to surface polishing and the damaged layer is removed by etching, and then placed on the susceptor 9 in the reaction vessel 1 and the susceptor is rotated. Heating of the seed crystal is started by the lamp heater 4 while flowing ammonia at 1 slm from the ammonia gas inlet 13a and nitrogen at 1 slm from the Al raw material inlet 13b. When the seed crystal temperature measured by the radiation thermometer 12 reaches 1000 ° C., the introduction of nitrogen from the Al raw material inlet 13b is stopped and the supply of chlorine is started instead. Simultaneously with the start of chlorine supply, the seed crystal temperature begins to rise due to the reaction heat with ammonia. Since a reaction occurs explosively when a large amount of chlorine is supplied, the supply amount is gradually increased while confirming the seed crystal temperature with the radiation thermometer 12. When the seed crystal temperature reaches 1900 ° C., growth is started by supplying a mixed gas obtained by adding AlCl ₃ gas to chlorine at 8.2 × 10 ⁻³ mol / min. As the AlN crystal growth proceeds, the crystal surface position (solid-gas interface) moves upward, and the distance from the Al raw material ejection port changes. Therefore, the susceptor is pulled down at 0.15 cm / hour by the pulling mechanism 7. Then, the solid-gas interface is maintained at a fixed position for growth. After growing the AlN crystal for about 20 hours under the above growth conditions, the supply of AlCl ₃ is stopped and the growth is terminated. Further, the crystal is gradually cooled by decreasing the supply amount of chlorine, and the supply of chlorine is stopped at about 1000 ° C. Thereafter, the crystal is cooled to room temperature over about 5 hours while gradually decreasing the power of the heater. After cooling, an AlN single crystal having a diameter of 2 inches and a length of 3 cm can be obtained. The growth rate is 0.15 cm / hour.

Comparative Example 1
A method for producing an AlN single crystal using the conventional HVPE apparatus shown in FIG. 2 will be described.
After polishing the surface of the AlN seed crystal (0001) having a diameter of 2 inches cut out from the AlN single crystal and removing the damaged layer by etching, the AlN seed crystal 26 is placed on the susceptor 25 in the reaction vessel 21, and the susceptor Rotate-. While heating ammonia through the ammonia gas inlet 22b at 1 slm and nitrogen through the hydrogen chloride inlet 22c at 1 slm, heating of the seed crystals is started by the resistance heaters 23 and 24. The seed crystal temperature is measured with a susceptor, and the Al raw material boat temperature is measured with a thermocouple attached to the raw material boat 28, respectively. When the seed crystal temperature reaches 1200 ° C. and the Al material boat temperature reaches 500 ° C., the amount of nitrogen introduced from the hydrogen chloride inlet is set to 0.8 slm, and hydrogen chloride supply is started at 0.2 slm at the same time. After growing the AlN crystal for about 10 hours under the above growth conditions, the supply of hydrogen chloride is stopped and the growth is terminated. Thereafter, the crystal is cooled to room temperature over about 5 hours while gradually decreasing the power of the heater. After cooling, an AlN polycrystal having a diameter of 2 inches and a length of 0.3 cm is obtained. Compared with Example 1, the growth rate is remarkably slow at 0.03 cm / hour, the crystal is a cluster of fine particles, and Al droplets are also observed in some places.

Comparative Example 2
An AlN crystal is produced in the same manner as in Comparative Example 1 except that the supply amount of hydrogen chloride is 0.02 slm. An AlN single crystal thin film having a diameter of 2 inches and a thickness of 0.03 cm is obtained. Compared with Example 1, the growth rate is remarkably slow at 0.003 cm / hour.

Comparative Example 3
A method for producing an AlN single crystal using the conventional sublimation apparatus shown in FIG. 3 will be described.
After polishing the surface of the AlN seed crystal (0001) having a diameter of 2 inches cut out from the AlN single crystal and removing the damaged layer by etching, the AlN seed crystal 33 is placed in the crystal growth vessel 35 in the reaction vessel 31. An AlN powder is stored as an AlN raw material 34 in the lower portion of the growth vessel. Nitrogen is introduced into the reaction vessel through the nitrogen gas inlet 40a and exhausted through the nitrogen gas outlet 40b. The temperature is raised by the high frequency heating coil 37, the AlN seed crystal part is set at 2150 ° C., the AlN raw material part is set at 2200 ° C., and the growth of the AlN crystal is started. After 50 hours of crystal growth, the reaction vessel is gradually cooled to room temperature over about 5 hours to obtain an AlN single crystal having a diameter of 2 inches and a thickness of 1.5 cm. Compared to Example 1, the growth rate is remarkably slow at 0.03 cm / hour. The crystals are brown.

An example of an apparatus used in the method for producing an Al-based group III nitride of the present invention Hydride vapor phase epitaxy (HVPE) equipment Sublimation method equipment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction container 2 Al raw material supply pipe 3 Reaction container stand 4 Heater 5 Reflector 6 Crystal rotating shaft 7 Pulling-down mechanism 8 Rotating mechanism 9 Susceptor
10 seed crystal 11 Al group III nitride crystal 12 radiation thermometer 13a ammonia gas inlet 13b Al raw material inlet 13c reactive gas outlet 21 reaction vessel 22a nitrogen gas inlet 22b ammonia gas inlet 22c hydrogen chloride inlet 22d nitrogen Gas exhaust port 22e Reaction gas exhaust port 23, 24 Heater 25 Susceptor
26 Seed crystal 27 AlN crystal 28 Raw material boat 31 Reaction vessel 32 AlN crystal 33 Seed crystal 34 AlN raw material 35 Crystal growth vessel 36 Seed crystal holding jig 37 High-frequency heating coil 38 Heating material 39 Radiation thermometer 40a Nitrogen gas inlet 40b Nitrogen gas exhaust port

Claims (6)

  A method for producing an Al-based group III nitride, comprising reacting an Al raw material containing a halogen gas and a nitrogen raw material containing ammonia on the crystal surface.   The method for producing an Al-based group III nitride according to claim 1, wherein the halogen gas is chlorine. _{3. The} method for producing an Al-based group III nitride according to claim 1, wherein the Al raw material is AlCl ₃ .   The method for producing an Al-based group III nitride according to any one of claims 1 to 3, wherein the Al-based group III nitride is AlN.   The Al group III nitride according to any one of claims 1 to 4, wherein the temperature of the crystal surface for reacting the Al raw material containing halogen gas and the nitrogen raw material containing ammonia is controlled to 1300 ° C to 2300 ° C. Manufacturing method.   An Al group III nitride obtained by the method for producing an Al group III nitride according to any one of claims 1 to 5.

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