KR20080109030A - Single crystal of nitride of group iii element and method of growing the same - Google Patents

Abstract

A method of growing a good-quality single crystal of a Group III element nitride with satisfactory reproducibility; and a single crystal of a Group III element nitride obtained by the growth method. The method comprises growing a single crystal (3) of a Group III element nitride in a crystal growth vessel (11), and is characterized in that a porous object which is made of a metal carbide and has a porosity of 0.1-70% is used as at least part of the crystal growth vessel (11). Due to the use of this crystal growth vessel (11), 1-50% of a raw-material gas (4) present in the crystal growth vessel (11) can be discharged from the crystal growth vessel (11) through pores of the porous object. ® KIPO & WIPO 2009

Description

Group II nitride single crystal and its growth method {SINGLE CRYSTAL OF NITRIDE OF GROUP III ELEMENT AND METHOD OF GROWING THE SAME}

The present invention relates to a large, high quality group III nitride crystal and its growth method inside a crystal growth vessel.

In general, growth of group III nitride crystals is performed by a gas phase method such as a sublimation method or a liquid phase method such as flux growth. For example, when growing AlN single crystal which is one of group III nitride crystals by sublimation method, crystal growth temperature of 1900 degreeC or more is required (for example, refer patent document 1 thru | or patent document 3). For this reason, as a crystal growth container used for the sublimation method, carbon members, such as graphite and pyrolytic graphite, and high melting metals, such as W (tungsten) and Ta (tantalum), are known.

However, when the carbon member is used as the crystal growth container, there is a problem that C (carbon) in the carbon member is mixed into the AlN single crystal as an impurity, thereby degrading the quality of the crystal. When a high melting point metal is used as the crystal growth container, the high melting point metal member as the crystal growth container is consumed by nitriding or carbonizing the high melting point metal, or the reproducibility of single crystal growth is impaired by the material change as the crystal growth container. There was a problem.

In addition, in a gas phase method such as a sublimation method, the composition ratio and impurities of Al (Group III element) and N (nitrogen) in the source gas (hereinafter referred to as source gas for growing Group III nitride single crystals) in the crystal growth container. It is necessary to constantly control the gas concentration, and for this reason, it is necessary to form a special exhaust structure in the crystal growth container for discharging a part of the source gas and the impurity gas inside the crystal growth chamber to the outside of the crystal growth container.

[Patent Document 1] US Patent No. 5858086

[Patent Document 2] US Patent No. 6001748

[Patent Document 3] US Patent No. 6296956

An object of the present invention is to provide a method for growing a Group III nitride single crystal having good reproducibility, large size, and good quality, and a Group III nitride crystal obtained by the growth method.

The present invention provides a method of growing a group III nitride single crystal in a crystal growth container, wherein at least a portion of the crystal growth container uses a porous body having a porosity of 0.1% or more and 70% or less, which is formed of metal carbide. Nitride single crystal growth method.

In the method for growing a group III nitride single crystal according to the present invention, (metal) :( carbon), which is an elemental composition ratio of metal and carbon in metal carbide, may be 9: 1 to 4: 6. In addition, the metal carbide can be a composite carbide containing TaC or TaC. In addition, the impurity content of the metal carbide can be 500 ppm or less. Moreover, 1% or more and 50% or less of the source gas in the crystal growth container can be discharged to the outside of the crystal growth container through the pores of the porous body. In addition, the crystal growth container may be coated with at least a part of the surface of the porous body having a porosity of 0.1% or more and 70% or less with a coating layer having a porosity of less than 0.1% of the metal carbide. have.

The present invention is a group III nitride single crystal obtained by the method for growing a group III nitride single crystal, which is a group III nitride single crystal having a diameter of 2.5 cm or more and a thickness of 200 m or more.

[Effects of the Invention]

According to the present invention, it is possible to provide a method for growing a Group III nitride single crystal having good reproducibility and large quality, and a Group III nitride crystal obtained by the growth method.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows an example of the growth method of group III nitride single crystal which concerns on this invention.

<Explanation of symbols for the main parts of the drawings>

1: seed crystal 2: raw material

3: group III nitride single crystal 4: source gas

5: exhaust gas 10: crystal growth apparatus

11: crystal growth vessel 12: reaction vessel

13: heater 13a: first heater

13b: second heater

The present invention is a method of growing a group III nitride single crystal 3 inside the crystal growth container 11 with reference to FIG. 1, wherein a porosity of metal carbide formed in at least a part of the crystal growth container 11 is 0.1. It is a growth method of group III nitride single crystal characterized by using the porous body which is 20% or more and 70% or less.

Here, the group III nitride single crystal refers to a single crystal of a compound formed from a group III element and nitrogen, for example, Al _x Ga _y In _1-xy N (0 ≦ 1, 0 ≦ y, x + y ≦ 1) single crystal or the like. Is displayed. Representative Group III nitride single crystals include, for example, AlN single crystals and GaN single crystals.

In addition, the porosity of a porous body means the percentage of the volume of a pore with respect to the volume of a porous body, and is a following formula (1)

Porosity (%) = 100 × (volume of pores) / (volume of porous body)... (One)

Is displayed.

Metal carbides are superior in stability at high temperatures (reaction resistance and heat resistance) as compared with carbon members and high melting point metals. For this reason, by using metal carbide as at least a part of the material of the crystal growth container 11, deterioration of the crystal growth container is suppressed, and the incorporation of impurities into the group III nitride single crystal from the crystal growth container is reduced, thereby improving the quality. Good Group III nitride single crystals can be grown reproducibly and stably.

However, the dense bodies formed of such metal carbides generally have poor workability and are difficult to process into the shape and size of a crystal growth container suitable for the growth of large single crystals. In addition, since it is difficult to form an exhaust structure for controlling the source gas and the impurity gas in the crystal growth container constantly, stable growth of the group III nitride single crystal cannot be expected.

On the other hand, by making the material formed from metal carbide into the porous body which has a some pore, it becomes possible to improve the workability of a metal carbide material, and to form the crystal growth container of a desired shape and size. For this reason, the main structure of a crystal growth container can be made into the bulk material of the metal carbide porous body whose thickness is 200 micrometers or more, for example. In addition, since the source gas and the impurity gas inside the crystal growth container are discharged to the outside of the crystal growth container through the pores of the porous body, the source gas and the impurities inside the crystal growth container without providing a special exhaust structure in the crystal growth container. It is possible to control the gas constantly, and to grow a high quality Group III nitride single crystal with reproducibility and stability.

Here, the porosity of the porous body formed of metal carbide is 0.1% or more and 70% or less. If the porosity is less than 0.1%, the workability of the porous body and the exhaustability of the source gas and the impurity gas from the pores of the porous body are reduced. On the other hand, when the porosity exceeds 70%, the exhaust amount of the source gas from the pores of the porous body becomes too large, and the crystal growth rate of the group III nitride single crystal decreases. From such a viewpoint, the porosity of the porous body is preferably 0.5% or more and 40% or less, and more preferably 5% or more and 30% or less.

The pore diameter of the porous body formed of metal carbide is not particularly limited, but is preferably 0.1 µm or more and 100 µm or less. If the pore diameter is less than 0.1 µm, the exhaustability of the source gas and the impurity gas from the pores of the porous body is lowered. On the other hand, when the pore diameter exceeds 100 µm, the exhaust amount of the source gas from the pores of the porous body becomes too large, and the crystal growth rate of the group III nitride single crystal decreases. From such a viewpoint, it is more preferable that the pore diameter of a porous body is 1 micrometer or more and 20 micrometers or less.

In the present invention, with reference to Fig. 1, by adjusting the porosity of the porous body formed of metal carbide, the porous pores of 1% or more and 50% or less of the source gas 4 inside the crystal growth container 11 Through, it is preferable to discharge to the outside of the crystal growth container (11). The impurity gas in the crystal growth container is discharged to the outside of the crystal growth container together with the source gas in the crystal container, and it becomes possible to constantly control the source gas and the impurity gas in the crystal growth container. Here, if less than 1% of source gas is discharge | released, the exhaustability of source gas and impurity gas will fall. On the other hand, if the discharge exceeds 50% of the source gas, the exhaust volume of the crystal source gas is too large, and the crystal growth rate of the group III nitride single crystal is lowered.

In the present invention, in order to control the amount of the source gas and the impurity gas discharged from the pores of the porous body in the crystal growth container 11, the porosity formed of the metal carbide in the crystal growth container is 0.1% or more and 70. It is also preferable to coat at least a part of the surface of the porous body which is% or less with a coating layer having a porosity formed of metal carbide of less than 0.1%. Although the thickness of a coating layer does not have a restriction | limiting in particular here, It is preferable that it is 30 micrometers or more from a viewpoint of improving the adjustment effect of the exhaust amount of source gas and impurity gas.

In addition, instead of the coating layer of the metal carbide, a coating layer of a high melting point metal such as W or Ta may be formed. Here, although the coating layer of this high melting point metal is nitrided or carbonized during single crystal growth, the reproducibility of single crystal growth is not impaired because the volume of the coating layer is small.

Moreover, there is no restriction | limiting in particular as a metal carbide used for this invention, TiC, ZrC, NbC, MoC, TaC, WC and the composite carbide containing two or more of these metal carbides are mentioned. From the viewpoint of high stability at high temperature, the metal carbide is preferably a composite carbide containing TaC or TaC.

Moreover, it is preferable that the impurity content of a metal carbide is 500 ppm or less. This is from the viewpoint of reducing the impurity gas inside the crystal growth container and suppressing deterioration of the crystal growth container.

Moreover, it is preferable that (metal) :( carbon) which is an elemental composition ratio of metal and carbon in metal carbide is 9: 1-4: 6. Here, the metal carbide is composed of at least one phase of a metal carbide phase, at least one phase of a metal phase, and at least one phase of a metal carbide phase. Deterioration of the crystal growth vessel formed using a metal carbide having a metal component larger than 9: 1 increases, and the mechanical growth decreases in a crystal growth vessel formed using a metal carbide having a carbon component larger than 4: 6. From this point of view, the (metal) :( carbon) is more preferably 8: 2 to 5: 5.

There is no restriction | limiting in particular as a method of forming the above-mentioned porous body or coating layer of a metal carbide, The gas-phase method, the press baking method of metal carbide powder, the reaction baking method, etc. are mentioned.

Here, the reaction baking method is a method of producing metal carbide by baking the mixed powder of metal and carbon of a predetermined elemental composition ratio. Since the reaction firing method does not use a binder which is a low melting point impurity, it is advantageous for the high purity of the metal carbide, and since the particles are strongly bound to each other even at high porosity, a material having high mechanical strength and high impact resistance can be obtained. In view of the above, it is particularly suitable for forming the porous body or the coating layer of the metal carbide used in the present invention.

The present invention is not particularly limited as long as it is a method of growing single crystals in a crystal growth vessel, and a gas phase method and a liquid phase method can be widely applied. Examples of the vapor phase method to which the present invention is applied include various vapor phase methods such as the sublimation method, the HVPE (hydride vapor phase epitaxial) method, the MBE (molecular beam epitaxial) method, and the MOCVD (organic metal chemical vapor deposition) method. The present invention is particularly preferably applied to a sublimation method in which group III nitride single crystals such as AlN single crystals are grown at high temperatures because of the properties of metal carbides in which the metal carbides are stable compounds at high temperatures. Moreover, as a liquid phase method to which this invention is applied, various liquid phase methods, such as a flux method and a melting method, are mentioned.

Here, the case where the method of growing the group III nitride single crystal according to the present invention is applied to the sublimation method will be described in detail with reference to FIG. 1. The sublimation furnace which is the crystal growth apparatus 10 is a crystal growth apparatus provided in the reaction vessel 12, the crystal growth vessel 11 provided in the inside of the reaction vessel 12, and the reaction vessel 12. A heater 13 for heating the vessel 11. Here, a porous body having a porosity of 0.1% or more and 70% or less is used in at least a part of the crystal growth container 11. In addition, the heater 13 is a raw material for growing the first heater 13a for heating the seed crystal 1 side of the crystal growth container 11 and the raw material (Group III nitride single crystal) of the crystal growth container 11. And a second heater for heating (2) side.

First, for example, group III nitride seed crystals are disposed on one side of the crystal growth vessel 11 (upper in FIG. 1) as seed crystals 1, and raw materials are placed on the other side (lower portion in FIG. 1) of the crystal growth vessel 11. As (2), for example, group III nitride powder or group III nitride polycrystal is disposed.

Subsequently, the inside of the crystal growth vessel 11 is heated up using the first heater 13a and the second heater 13b while flowing nitrogen gas, for example, as the exhaust gas 5 into the reaction vessel 12. By controlling the heating amounts of the first heater 13a and the second heater 13b, the temperature of the raw material 2 side of the crystal growth container 11 is maintained higher than the temperature of the seed crystal 1 side, thereby obtaining the raw material ( The group III nitride is sublimed from 2) to the source gas 4, and the source gas 4 is solidified again on the seed crystal 1 to grow the group III nitride single crystal 3. As the exhaust gas, an inert gas such as nitrogen gas or argon gas is preferably used.

In this group III nitride crystal growth step, since at least a part of the crystal growth container is a porous body having a porosity of 0.1% or more and 70% or less, the incorporation of impurities into the group III nitride single crystal is reduced, and the porous material is By the pores, the source gas and the impurity gas in the crystal growth container are constantly controlled to enable stable growth of the group III nitride single crystal.

In addition, by raising the temperature of the seed crystal 1 side of the crystal growth container higher than the temperature of the raw material 2 side during the temperature increase inside the crystal growth container 11, the surface of the seed crystal 1 is cleaned by etching. Since the impurity gas in the crystal growth container 11 is discharged from the pores of the porous body to the outside of the crystal growth container 11, and the discharge of the impurity gas is promoted by the exhaust gas 5, Group III nitride Impurity incorporation into the single crystal is further reduced.

By using the group III nitride single crystal growth method, it is possible to stably grow a group III nitride single crystal with high crystal quality, so that a large, high quality group III nitride single crystal having a diameter of 2.5 cm or more and a thickness of 200 µm or more can be obtained. You can get it.

In addition, the Group III nitride single crystal substrate obtained by processing such a large, high quality Group III nitride single crystal is large in size and high in crystal quality. Electronic devices such as high electron mobility transistors, semiconductor sensors such as temperature sensors, pressure sensors, radiation sensors, acceleration sensors, visible-ultraviolet light detectors, surface acoustic wave (SAW) devices, microelectromechanical system (MEMS) components, It can be widely applied to piezoelectric vibrators, resonators, piezo actuators and the like.

EXAMPLE

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated further more concretely based on an Example.

(Production of crystal growth container)

As the crystal growth container 11 of FIG. 1, the crucible of the porous body formed from TaC was produced as follows. That is, Ta powder having a purity of 99.99% by mass and C powder having a purity of 99.99% by mass are mixed so as to have an elemental composition ratio Ta: C of 1: 1, and molded, and then fired in a carbon crucible to have an inner diameter of 6 cm. And a crucible of a porous body formed from TaC having a hollow cylindrical shape having an inner height of 8 cm and a thickness of 5 mm. The impurity content of this porous TaC crucible was 150 ppm as measured by SIMS (secondary ion mass spectrometry). In addition, the porosity and pore diameter of this porous TaC crucible were 15% and 1 micrometer-20 micrometers, respectively, when measured with the mercury porosimeter.

(Example 1)

Referring to Fig. 1, AlN single crystal [Group III nitride single crystal 3] was grown by sublimation using the porous TaC crucible as the crystal growth vessel 11. First, AlN seed crystals were placed as seed crystals 1 on top of the porous TaC crucible (crystal growth vessel 11), and AlN powder was placed as raw material 2 on the bottom of the porous TaC crucible. Next, the inside of the porous TaC crucible (crystal growth vessel 11) is heated using the first heater 13a and the second heater 13b while flowing nitrogen gas as the exhaust gas through the reaction vessel 12, The AlN single crystal [Group III nitride single crystal (3)] on the AlN seed crystal [seed crystal (1)] was maintained by keeping the temperature of the AlN seed crystal in the porous TaC crucible at 2200 ° C. and the temperature of the AlN powder at 2300 ° C. for 24 hours. ]. After crystal growth, after naturally cooling, AlN single crystal was extracted.

The AlN single crystal obtained as mentioned above was 5.08 cm in diameter and 3.5 mm in thickness. In addition, the impurity content of this AlN single crystal was very small at 10 ppm as measured by SIMS. Moreover, the half width of the (0002) peak in the X-ray diffraction of this AlN single crystal was 82 arsec, which had good crystal quality. In this AlN crystal growth, no damage or defect was observed in the porous TaC crucible, and when AlN crystal growth was carried out nine times under the same conditions using the same porous TaC crucible, the AlN single crystal obtained in each AlN crystal growth was It had the same shape, size and quality as the AlN single crystal obtained in the first crystal growth.

(Example 2)

GaN single crystal was grown by Na-flux method using the porous TaC crucible as a crystal growth vessel. First, a GaN seed crystal produced by MOCVD as a seed crystal, a metal Ga as a Ga raw material, and a metal Na (Ga: Na = 64: 36 in molar ratio) were disposed in a porous TaC crucible. Next, the inside of the crystal growth container was vacuumed (0.3 kPa), heated to 300 ° C, and held for 0.5 hour to remove moisture from the GaN seed crystal, the Ga-Na melt, and the porous TaC crucible. Next, a GaN single crystal was grown on a GaN seed crystal by introducing an N ₂ gas serving as an N raw material into the crystal growth container, holding the inside of the crystal growth container at an internal pressure of 5 MPa to 800 ° C. for 100 hours. The porous TaC crucible used as the crystal growth vessel had a porosity of 15% and a pore diameter of 1 µm to 20 µm (100 µm or less), and no leakage of Ga-Na melt was observed in the growth of the GaN single crystal.

The GaN single crystal obtained as described above was 2.5 cm in diameter and 510 µm in thickness. In addition, SIMS analysis of this GaN single crystal revealed that 380 ppm of Al was included as a main impurity in the GaN single crystal. Moreover, the half width of the (0002) peak in the X-ray diffraction of this GaN single crystal was 60 arsec, and had good crystal quality.

In addition, when the inside of the porous TaC crucible was observed, a few particles were seen at the interface between the crucible and the Ga-Na melt. 0.6 g of these particles were collected. Moreover, when these particles were analyzed by X-ray diffraction, it turned out that it is GaN polycrystal.

(Comparative Example)

A GaN single crystal was grown in the same manner as in Example 2 except that an Al ₂ O ₃ crucible was used as the crystal growth vessel. The obtained GaN single crystal was 1.8 cm in diameter and 350 µm in thickness. In addition, SIMS analysis of the GaN single crystal revealed that Ga630 single crystal contained 630 ppm of Al as a main impurity. The half width of the (0002) peak in the X-ray diffraction of this GaN single crystal was 180 arsec.

In addition, when the inside of the Al ₂ O ₃ crucible was observed, many particles were seen at the interface between the crucible and the Ga-Na melt. 1.5 g of these particles were collected. Moreover, when these particles were analyzed by X-ray diffraction, it turned out that it is GaN polycrystal.

In comparison with Comparative Example and Example 2, in the Na-flux method, by using a porous TaC crucible instead of an Al ₂ O ₃ crucible as the crystal growth vessel, the Al impurity content in the GaN single crystal was reduced from 630 ppm to 380 ppm. , The half width of the (0002) peak in X-ray diffraction was reduced from 180 arsec to 60 arsec, and it was found that the crystal quality was improved. In the Al ₂ O ₃ crucible, Al is eluted during growth of the single crystal and mixed into the single crystal that grows. However, since the porous TaC crucible has high stability at high temperature, it is thought that a high quality single crystal can be obtained with high purity.

In contrast to Comparative Example and Example 2, in the Na-flux method, by using a porous TaC crucible instead of an Al ₂ O ₃ crucible as the crystal growth vessel, production of polycrystalline particles can be suppressed from 1.5 g to 0.6 g. I knew you could. This is considered to be because the porous TaC crucible is less wettable on the crucible surface and the Ga-Na melt compared to the Al ₂ O ₃ crucible.

It should be thought that embodiment and the Example which were disclosed this time are an illustration and restrictive at no points. The scope of the present invention is defined not by the above description but by the scope of the claims, and is intended to include all modifications within the meaning and range equivalent to the scope of the claims.

Claims (7)

A method of growing a group III nitride single crystal inside a crystal growth vessel, A method for growing a group III nitride single crystal, characterized in that a porous body having a porosity of 0.1% or more and 70% or less is used for at least part of the crystal growth container. The method of growing a group III nitride single crystal according to claim 1, wherein (metal) :( carbon), which is an elemental composition ratio of metal and carbon in the metal carbide, is from 9: 1 to 4: 6. The method of growing a group III nitride single crystal according to claim 1 or 2, wherein the metal carbide is a complex carbide including TaC or TaC. The method of growing a group III nitride single crystal according to any one of claims 1 to 3, wherein the impurity content of the metal carbide is 500 ppm or less. The method according to any one of claims 1 to 4, wherein 1% or more and 50% or less of the source gas in the crystal growth container is discharged to the outside of the crystal growth container through the pores of the porous body. Method for growing group III nitride single crystals. The crystal growth container according to any one of claims 1 to 5, wherein the crystal growth container is formed of the metal carbide on at least a part of the surface of the porous body having a porosity of 0.1% or more and 70% or less. A method for growing a group III nitride single crystal in which a coating layer having a porosity of less than 0.1% is coated. As a group III nitride single crystal obtained by the method for growing a group III nitride single crystal according to any one of claims 1 to 6, A group III nitride single crystal having a diameter of 2.5 cm or more and a thickness of 200 m or more.

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