JP4678212B2 - Group III nitride single crystal growth method - Google Patents

Description

The present invention includes an internal large and good group III nitride sintered method of growing crystals about the quality of the crystal growth vessel.

  In general, group III nitride crystals are grown by a vapor phase method such as a sublimation method or a liquid phase method such as a flux method. For example, when an AlN single crystal that is one of group III nitride crystals is grown by a sublimation method, a crystal growth temperature of 1900 ° C. or higher is required (for example, see Patent Document 1 to Patent Document 3). ). For this reason, carbon members such as graphite and pyrolytic graphite, and refractory metals such as W (tungsten) and Ta (tantalum) are known as crystal growth containers used in the sublimation method.

  However, when a carbon member is used as a crystal growth container, there is a problem that C (carbon) in the carbon member is mixed as an impurity in the AlN single crystal, thereby reducing the quality of the crystal. In addition, when a refractory metal is used as a crystal growth vessel, the refractory metal member as the crystal growth vessel is consumed due to nitridation or carbonization of the refractory metal, or single crystal growth occurs due to changes in the material as the crystal growth vessel. There was a problem that the reproducibility was impaired.

In a vapor phase method such as a sublimation method, Al (group III element) and N in a source gas (referred to as a source gas for growing a group III nitride single crystal, hereinafter the same) inside the crystal growth vessel. Therefore, it is necessary to control the composition ratio with (nitrogen) and the impurity gas concentration to a certain level. It was necessary to form a special exhaust structure for discharging to the outside.
US Pat. No. 5,858,086 US Pat. No. 6,0017,481 US Pat. No. 6,296,956

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

The present invention is a method for growing a group III nitride single crystal in a crystal growth vessel by a sublimation method, wherein the porosity formed of metal carbide in at least a part of the crystal growth vessel is 0.1%. A porous body having a porosity of 70% or less is used, and at least a part of the surface of the porous body is coated with a coating layer made of metal carbide and having a porosity of less than 0.1%. This is a method for growing a group III nitride single crystal.

In the group III nitride single crystal growth method according to the present invention, the porous body can be formed by a press firing method or a reaction firing method of metal carbide powder. Moreover, (metal) :( carbon) which is an elemental composition ratio of the metal and carbon in a metal carbide can be set to 9: 1 to 4: 6. Further, the metal carbide can be TaC or a composite carbide containing TaC. Moreover, the impurity content of the metal carbide can be set to 500 ppm or less. Further, 1% or more and 50% or less of the raw material gas inside the crystal growth vessel can be discharged to the outside of the crystal growth vessel through the pores of the porous body. Moreover, the pore diameter of the porous body can be set to 0.1 μm or more and 100 μm or less. The coating layer can be formed by press firing or reaction firing of metal carbide powder.

According to the present invention, it is possible to provide a way of growing a good III nitride single crystal quality in good reproducibility large.

  The present invention is a method for growing a group III nitride single crystal 3 inside a crystal growth vessel 11 with reference to FIG. 1, wherein at least a part of the crystal growth vessel 11 is formed of a metal carbide. It is a group III nitride single crystal growth method characterized by using a porous body having a porosity of 0.1% to 70%.

Here, the group III nitride single crystal refers to a single crystal of a compound formed of a group III element and nitrogen. For example, Al _x Ga _y In _1-xy N (0 ≦ 1, 0 ≦ y, x + y ≦ 1) It is expressed as a single crystal. Typical group III nitride single crystals include, for example, AlN single crystals and GaN single crystals.

Moreover, 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 the following formula | equation (1)
Porosity (%) = 100 × (pore volume) / (porous body volume) (1)
It is represented by

  Metal carbide is superior in stability (reaction resistance, heat resistance) at high temperatures as compared with carbon members and refractory metals. Therefore, by using metal carbide as at least a part of the material of the crystal growth vessel 11, the deterioration of the crystal growth vessel is suppressed, and the contamination of impurities from the crystal growth vessel to the group III nitride single crystal is reduced. By doing so, a high-quality group III nitride single crystal can be stably grown with good reproducibility.

  However, a dense body formed of such a metal carbide generally has poor processability and is difficult to process into a crystal growth vessel shape and size suitable for growing a large single crystal. In addition, it is difficult to form an exhaust structure for controlling the source gas and impurity gas inside the crystal growth vessel to be constant, and stable growth of the group III nitride single crystal cannot be expected.

  On the other hand, by forming the material formed from the metal carbide into a porous body having a plurality of pores, it is possible to improve the workability of the metal carbide material and form a crystal growth vessel having a desired shape and size. It becomes possible. For this reason, the main structure of the crystal growth vessel can be a bulk material of a porous metal carbide body having a thickness of 200 μm or more, for example. In addition, since the source gas and impurity gas inside the crystal growth vessel are discharged to the outside of the crystal growth vessel through the pores of the porous body, the crystal growth can be performed without providing a special exhaust structure in the crystal growth vessel. The source gas and impurity gas inside the container can be controlled to be constant, and a high-quality group III nitride single crystal can be stably grown with good reproducibility.

  Here, the porosity of the porous body formed of metal carbide is 0.1% or more and 70% or less. When the porosity is less than 0.1%, the workability of the porous body and the exhaustability of the source gas and impurity gas from the pores of the porous body are lowered. On the other hand, when the porosity exceeds 70%, the exhaust amount of the raw material 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 this 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.

  Moreover, 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. When the pore diameter is less than 0.1 μm, the exhaustability of the raw material gas and impurity gas from the pores of the porous body is lowered. On the other hand, if 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 is lowered. From this viewpoint, the pore diameter of the porous body is more preferably 1 μm or more and 20 μm or less.

  In the present invention, referring to FIG. 1, by adjusting the porosity of the porous body formed of metal carbide, 1% or more and 50% or less of the raw material gas 4 inside the crystal growth vessel 11 is It is preferable to discharge to the outside of the crystal growth vessel 11 through the pores of the porous body. The impurity gas inside the crystal growth vessel is discharged to the outside of the crystal growth vessel together with the source gas inside the crystal vessel, and the source gas and impurity gas inside the crystal growth vessel can be controlled to be constant. Here, if the discharge is less than 1% of the source gas, the exhaustability of the source gas and the impurity gas is lowered. On the other hand, if the discharge exceeds 50% of the source gas, the amount of crystal source gas exhausted becomes too large, and the crystal growth rate of the group III nitride single crystal decreases.

  Further, in the present invention, in order to adjust the amount of the source gas and the impurity gas inside the crystal growth vessel 11 discharged from the pores of the porous body, the porosity formed of the metal carbide in the crystal growth vessel is It is also preferable to cover at least a part of the surface of the porous body of 0.1% or more and 70% or less with a coating layer made of metal carbide and having a porosity of less than 0.1%. Here, the thickness of the coating layer is not particularly limited, but is preferably 30 μm or more from the viewpoint of enhancing the effect of adjusting the exhaust amount of the source gas and the impurity gas.

  Instead of the metal carbide coating layer, a coating layer of a refractory metal such as W or Ta may be formed. The refractory metal coating layer is nitrided or carbonized during single crystal growth. However, since the volume of the coating layer is small, the reproducibility of single crystal growth is not impaired.

  In addition, the metal carbide used in the present invention is not particularly limited, and examples thereof include TiC, ZrC, NbC, MoC, TaC, WC, and composite carbide containing two or more of these metal carbides. From the viewpoint of high stability at high temperatures, the metal carbide is preferably TaC or a composite carbide containing TaC.

  The impurity content of the metal carbide is preferably 500 ppm or less. This is from the viewpoint of reducing impurity gas inside the crystal growth vessel and suppressing deterioration of the crystal growth vessel.

  Moreover, it is preferable that (metal) :( carbon) which is an elemental composition ratio of the metal and carbon in a metal carbide is 9: 1 to 4: 6. Here, the metal carbide is composed of one or more metal carbide phases, one or more metal phases, and one or more metal carbide phases. The crystal growth vessel formed using a metal carbide having a metal component larger than 9: 1 is greatly deteriorated, and the crystal growth vessel formed using a metal carbide having a carbon component larger than 4: 6 is mechanical strength. Decreases. From this viewpoint, (metal) :( carbon) is more preferably 8: 2 to 5: 5.

  The method for forming the metal carbide porous body or the coating layer as described above is not particularly limited, and examples thereof include a gas phase method, a metal carbide powder press firing method, and a reaction firing method. Here, the reactive firing method is a method in which a metal carbide is generated by firing a mixed powder of metal and carbon having a predetermined elemental composition ratio. Such a reaction firing method is advantageous in increasing the purity of the metal carbide because it does not use a binder that is an impurity having a low melting point, and has high mechanical strength because the particles are strongly bonded to each other even at a high porosity. From the viewpoint of obtaining a material having high impact resistance, it is particularly suitable for forming a porous body or coating layer of metal carbide used in the present invention.

  The present invention is not particularly limited as long as it is a method for growing a single crystal inside a crystal growth vessel, and can be widely applied to a gas phase method and a liquid phase method. Examples of the vapor phase method to which the present invention is applied include various vapor phase methods such as a sublimation method, HVPE (hydride vapor phase epitaxy) method, MBE (molecular beam epitaxy) method, and MOCVD (metal organic chemical vapor deposition) method. It is done. The present invention is particularly preferably applied to a sublimation method in which a group III nitride single crystal such as an AlN single crystal is grown at a high temperature because of the characteristics of the metal carbide, which is a stable compound at a high temperature. Examples of the liquid phase method to which the present invention is applied include various liquid phase methods such as a flux method and a melting method.

  Here, the case where the growth method of the group III nitride single crystal according to the present invention is applied to the sublimation method will be specifically described with reference to FIG. The sublimation furnace as the crystal growth apparatus 10 includes a reaction vessel 12, a crystal growth vessel 11 installed inside the reaction vessel 12, a heater 13 installed outside the reaction vessel 12 and for heating the crystal growth vessel 11. including. Here, a porous body having a porosity of 0.1% or more and 70% or less formed of metal carbide is used in at least a part of the crystal growth vessel 11. The heater 13 includes a first heater 13a for heating the seed crystal 1 side of the crystal growth vessel 11 and a raw material for the crystal growth vessel 11 (a raw material for growing a group III nitride single crystal, the same applies hereinafter) 2 And a second heater for heating the side.

  First, for example, a group III nitride seed crystal is arranged as a seed crystal 1 on one side (upper part in FIG. 1) of the crystal growth vessel 11, and a source group 2 is given, for example, group III on the other side (lower side in FIG. 1). Nitride powder or Group III nitride polycrystal is disposed.

  Next, the inside of the crystal growth vessel 11 is heated using the first heater 13a and the second heater 13b while flowing, for example, nitrogen gas as the exhaust gas 5 inside the reaction vessel 12, and the first heater 13a and the first heater 13b are heated. The temperature of the raw material 2 side of the crystal growth vessel 11 is kept higher than the temperature of the seed crystal 1 side by adjusting the heating amount of the crystal growth vessel 11 to sublimate the group III nitride from the raw material 2 to obtain the raw material gas 4. 4 is solidified again on the seed crystal 1 to grow a 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 stage, at least a part of the crystal growth vessel is a porous body made of metal carbide and having a porosity of 0.1% to 70%. Impurities are reduced and the source gas and impurity gas inside the crystal growth vessel are controlled to be constant by the pores of the porous body, and the group III nitride single crystal can be stably grown.

  During the temperature increase inside the crystal growth vessel 11, the surface of the seed crystal 1 is cleaned by etching by making the temperature on the seed crystal 1 side of the crystal growth vessel higher than the temperature on the raw material 2 side, Since the impurity gas inside the crystal growth vessel 11 is discharged from the pores of the porous body to the outside of the crystal growth vessel 11 and the exhaust gas 5 facilitates the discharge of the impurity gas, the group III nitride single crystal is obtained. The contamination of impurities is further reduced.

  By using the group III nitride single crystal growth method described above, a group III nitride single crystal having high crystal quality can be stably grown. Therefore, the diameter is 2.5 cm or more and the thickness is 200 μm or more. A large Group III nitride single crystal of good quality can be obtained.

  Furthermore, since the group III nitride single crystal substrate obtained by processing such a large and high-quality group III nitride single crystal is large and has a high crystal quality, a light emitting element such as a light emitting diode or a laser diode. , Rectifiers, bipolar transistors, field effect transistors, electronic devices such as HEMT (High Electron Mobility Transistor), temperature sensors, pressure sensors, radiation sensors, acceleration sensors, semiconductor sensors such as visible-ultraviolet light detectors, SAW (surface elasticity) Wave) devices, MEMS (micro electro mechanical system) parts, piezoelectric vibrators, resonators, piezoelectric actuators, and the like.

  Hereinafter, based on an Example, this invention is demonstrated further more concretely.

(Production of crystal growth vessel)
As the crystal growth vessel 11 in FIG. 1, a porous crucible formed of 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 and molded so that the elemental composition ratio Ta: C is 1: 1, and then fired in a carbon crucible. Thus, a porous crucible made of hollow cylindrical TaC having an inner diameter of 6 cm, an inner height of 8 cm, and a thickness of 5 mm was obtained. The impurity content of this porous TaC crucible was 150 ppm as measured by SIMS (secondary ion mass spectrometry). The porosity and pore diameter of this porous TaC crucible were 15% and 1 μm to 20 μm, respectively, as measured with a mercury porosimeter.

Example 1
Referring to FIG. 1, using the porous TaC crucible as the crystal growth vessel 11, an AlN single crystal (Group III nitride single crystal 3) was grown by a sublimation method. First, an AlN seed crystal was disposed as the seed crystal 1 on the upper portion of the porous TaC crucible (crystal growth vessel 11), and an AlN powder was disposed as the raw material 2 on the lower portion 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 exhaust gas through the reaction vessel 12, and the porous TaC crucible is heated. The AlN seed crystal (group III nitride single crystal 3) is grown on the AlN seed crystal (seed crystal 1) by maintaining the temperature of the AlN seed crystal at 2200 ° C. and the temperature of the AlN powder at 2300 ° C. for 24 hours. I let you. After crystal growth and after natural cooling, the AlN single crystal was taken out.

  The AlN single crystal obtained as described above had a diameter of 5.08 cm and a thickness of 3.5 mm. Further, the impurity content of the AlN single crystal was as extremely low as 10 ppm as measured by SIMS. Further, the half width of the (0002) peak in the X-ray diffraction of this AlN single crystal was as good as 82 asec. Moreover, in this AlN crystal growth, damage and a defect | deletion were not recognized by the porous TaC crucible. Furthermore, when AlN crystal growth was performed nine times under the same conditions using the same porous TaC crucible, the AlN single crystal obtained in each AlN crystal growth was equivalent to the AlN single crystal obtained in the first crystal growth. Had the shape, size and quality.

( Reference example )
Using the above porous TaC crucible as a crystal growth vessel, a GaN single crystal was grown by the Na-flux method. First, in a porous TaC crucible, a GaN seed crystal produced by MOCVD method as a seed crystal, metal Ga as a Ga raw material, and metal Na as a flux raw material (Ga: Na = 64: 36 in molar ratio) are arranged. did. Next, the inside of the crystal growth vessel was evacuated (0.3 Pa), heated to 300 ° C. and held for 0.5 hour to remove moisture from the GaN seed crystal, Ga—Na melt, and porous TaC crucible. . Next, N ₂ gas as an N raw material is introduced into the crystal growth vessel, and the inside of the crystal growth vessel is heated to 800 ° C. at an internal pressure of 5 MPa and held for 100 hours, whereby GaN is deposited on the GaN seed crystal. Single crystals were grown. The porous TaC crucible used as a crystal growth vessel has a porosity of 15% and a pore diameter of 1 μm to 20 μm (100 μm or less). In the growth of the GaN single crystal, leakage of Ga—Na melt does not occur. I was not able to admit.

  The GaN single crystal obtained as described above had a diameter of 2.5 cm and a thickness of 510 μm. Further, when this GaN single crystal was analyzed by SIMS, the GaN single crystal contained 380 ppm of Al as a main impurity. Moreover, the half-width of the (0002) peak in the X-ray diffraction of this GaN single crystal was as good as 60 asec.

  When the inside of the porous TaC crucible was observed, a small number of particles were observed at the interface between the crucible and the Ga—Na melt. When these particles were collected, it was 0.6 g. Further, when these particles were analyzed by X-ray diffraction, it was found to be GaN polycrystal.

(Comparative example)
A GaN single crystal was grown by the Na-flux method in the same manner as in the reference example except that an Al ₂ O ₃ crucible was used as the crystal growth vessel. The obtained GaN single crystal had a diameter of 1.8 cm and a thickness of 350 μm. Further, when the GaN single crystal was analyzed by SIMS, the GaN 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 asec.

When the inside of the Al ₂ O ₃ crucible was observed, a large number of particles were observed at the interface between the crucible and the Ga—Na melt. When these particles were collected, it was 1.5 g. Further, when these particles were analyzed by X-ray diffraction, it was found to be GaN polycrystal.

When the comparative example and the reference example are compared, in the Na-flux method, the Al Ta content in the GaN single crystal is changed from 630 ppm to 380 ppm by using a porous TaC crucible instead of the Al ₂ O ₃ crucible as the crystal growth vessel. It can be seen that the half width of the (0002) peak in X-ray diffraction was reduced from 180 to 60 asec, and the crystal quality was improved. This is because, in the Al ₂ O ₃ crucible, Al elutes during single crystal growth and is mixed into the single crystal that grows. However, since the porous TaC crucible has high stability at high temperatures, a single crystal with high purity and quality can be obtained. It is considered to be obtained.

Further, when the comparative example and the reference example are compared, in the Na-flux method, by using a porous TaC crucible instead of the Al ₂ O ₃ crucible as the crystal growth vessel, the production of polycrystalline particles is reduced from 1.5 g to 0 g. It can be seen that it can be suppressed to 0.6 g. This is presumably because the porous TaC crucible reduces the wettability between the crucible surface and the Ga—Na melt compared to the Al ₂ O ₃ crucible.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a cross-sectional schematic diagram which shows an example of the growth method of the group III nitride single crystal concerning this invention.

Explanation of symbols

  1 seed crystal, 2 raw materials, 3 group III nitride single crystal, 4 raw material gas, 5 exhaust gas, 10 crystal growth apparatus, 11 crystal growth vessel, 12 reaction vessel, 13 heater, 13a first heater, 13b second heater.

Claims (8)

A method of growing a group III nitride single crystal inside a crystal growth vessel by a sublimation method ,
A porous body made of metal carbide having a porosity of 0.1% to 70% is used for at least a part of the crystal growth vessel, and the metal is formed on at least a part of the surface of the porous body. A method for growing a group III nitride single crystal, wherein a coating layer made of carbide and having a porosity of less than 0.1% is coated.   2. The method for growing a group III nitride single crystal according to claim 1, wherein the porous body is formed by a reaction firing method or a press firing method of metal carbide powder.   3. The group III nitride single crystal growth according to claim 1, wherein (metal) :( carbon), which is an elemental composition ratio of metal to carbon in the metal carbide, is 9: 1 to 4: 6. Method.   The method for growing a group III nitride single crystal according to any one of claims 1 to 3, wherein the metal carbide is TaC or a composite carbide containing TaC.   The method for growing a group III nitride single crystal according to any one of claims 1 to 4, wherein an impurity content of the metal carbide is 500 ppm or less.   6. The method according to claim 1, wherein 1% or more and 50% or less of the raw material gas inside the crystal growth vessel is discharged to the outside of the crystal growth vessel through the pores of the porous body. A method for growing a group III nitride single crystal according to claim 1.   The method for growing a group III nitride single crystal according to any one of claims 1 to 6, wherein a pore size of the porous body is 0.1 µm or more and 100 µm or less.   The method for growing a group III nitride single crystal according to any one of claims 1 to 7, wherein the coating layer is formed by a reactive firing method or a press firing method of a metal carbide powder.

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