JP2011001211A - Method for growing group iii nitride crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for growing a group III nitride crystal which reduces the dislocation density of the whole of the crystal to be grown.SOLUTION: In the method for growing a group III nitride crystal 10, where a solution 6, obtained by dissolving a nitrogen raw material gas 5 into a melt 3 including a group III metal and an alkali metal, is brought into contact with a group III nitride seed crystal 1, thus a group III nitride crystal 10 is grown from the group III nitride seed crystal 1, the group III nitride seed crystal 1 has an upper face as a (000-1)N atom surface 1n, and a lower face arranged so as to be brought into contact with the inside surface 23i of a crystal growth vessel 23, and the group III nitride crystal 10 is grown substantially on the side surface 1s of the group III nitride seed crystal 1 to a direction parallel to the (000-1)N atom surfaces 1n, 10n.

Description

  The present invention relates to a method for growing a group III nitride crystal by a liquid phase method, particularly a flux method.

  Group III nitride crystals are widely used for substrates of various semiconductor devices. In recent years, a group III nitride crystal having a low dislocation density has been demanded in order to produce various semiconductor devices having high characteristics.

  As a method for growing a group III nitride crystal, a gas phase method such as HVPE (hydride vapor phase epitaxy) method, MOCVD (metal organic chemical vapor deposition) method, a liquid phase method such as high nitrogen pressure solution method, flux method, etc. and so on. Here, the liquid phase method is superior to the gas phase method in terms of environmental protection because no toxic gas is used in crystal growth.

  As a method for growing a group III nitride crystal having a low dislocation density in such a liquid phase method, for example, Japanese Patent Laid-Open No. 2005-350291 (Patent Document 1) includes a step of preparing a seed crystal and a liquid phase method such as a flux method. And growing a first group III nitride crystal on the seed crystal by the step, wherein the first group III nitride crystal is grown in parallel to the (0001) Ga atom surface that is the main surface of the seed crystal. Disclosed is a method for growing a group III nitride crystal, characterized in that the crystal growth rate in any direction is greater than the crystal growth rate in the direction perpendicular to the (0001) Ga atom surface.

JP-A-2005-350291

  However, in the growth method disclosed in Japanese Patent Laid-Open No. 2005-350291 (Patent Document 1), the dislocation density of a crystal growing in a direction parallel to the (0001) Ga atom surface, which is the main surface of the seed crystal, is reduced. However, it has been difficult to reduce the dislocation density of crystals growing in a direction perpendicular to the (0001) Ga atom surface. In addition, the crystal growth rate in the direction parallel to the (0001) Ga surface was low. For this reason, in the method for growing a group III nitride crystal disclosed in Japanese Patent Application Laid-Open No. 2005-350291 (Patent Document 1), the range and degree of reduction in the dislocation density of the crystal is limited. .

  An object of the present invention is to provide a method for growing a group III nitride crystal in which the dislocation density of the entire crystal to be grown is reduced.

  The present invention grows a group III nitride crystal from a group III nitride seed crystal by bringing a solution in which a nitrogen source gas is dissolved in a melt containing a group III metal and an alkali metal into contact with the group III nitride seed crystal. A method for growing a group III nitride crystal, wherein the group III nitride seed crystal has an upper surface that is a (000-1) N atom surface, and a lower surface disposed to contact the inner surface of the crystal growth vessel A method for growing a group III nitride crystal, comprising growing a group III nitride crystal in a direction parallel to the (000-1) N atom surface substantially on a side surface of the group III nitride seed crystal. .

  In the group III nitride crystal growth method according to the present invention, the alkali metal may contain at least one of Na and Li. The group III nitride crystal to be grown can be a GaN crystal.

  ADVANTAGE OF THE INVENTION According to this invention, the growth method of the group III nitride crystal which can reduce the dislocation density of the whole crystal to grow can be provided.

It is a schematic sectional drawing which shows an example of the crystal growth apparatus used for the growth of a group III nitride crystal. It is a schematic sectional drawing which shows an example of the growth method of the group III nitride crystal concerning this invention. It is a schematic sectional drawing which shows an example of the growth method of the conventional group III nitride crystal. It is a chart which shows an example of the sequence control in the growth of a group III nitride crystal.

  Referring to FIGS. 1 and 2, one embodiment of the method for growing a group III nitride crystal according to the present invention is a solution 6 in which a nitrogen source gas 5 is dissolved in a melt 3 containing a group III metal and an alkali metal. Is a group III nitride crystal growth method in which a group III nitride crystal 10 is grown from a group III nitride seed crystal 1 by bringing the group III nitride seed crystal 1 into contact with the group III nitride seed crystal 1. 000-1) has an upper surface that is an N atom surface 1n, has a lower surface arranged to contact the inner surface 23i of the crystal growth vessel 23, and is substantially on the side surface 1s of the group III nitride seed crystal 1 (000-1) A Group III nitride crystal growth method characterized in that a Group III nitride crystal 10 is grown in a direction parallel to the N atom surface 1n.

  The present inventors have made contact with a group III nitride seed crystal 1 by bringing a solution 6 in which a nitrogen source gas 5 is dissolved in a melt 3 containing a group III metal and an alkali metal into the group III nitride seed crystal 1. In the flux method for growing the crystal 10, the group III nitride seed crystal 1 is arranged so that its upper surface is a (000-1) N atomic surface and its lower surface is in contact with the inner surface 23 i of the crystal growth vessel 23, It has been found that the group III nitride crystal 10 hardly grows on the (000-1) N atom surface 1n of the group III nitride seed crystal 1 and that the group III nitride crystal 10 substantially grows on the side surface 1s. The present invention has been completed.

<Crystal growth equipment>
Referring to FIGS. 1 and 2, the crystal growth apparatus used in the method for growing a group III nitride crystal of the present embodiment includes, for example, an outer container 29, a heat insulating material 27 arranged inside the outer container 29, A heater 25 disposed inside the heat insulating material 27 and an inner container 21 disposed inside the heater 25 are provided. In the inner vessel 21, a crystal growth vessel 23 for growing the group III nitride crystal 10 is disposed. Further, the opening of the crystal growth vessel 23 may be covered with a lid 24.

Here, the material of the crystal growth vessel 23 and the lid 24 is not particularly limited as long as it does not react with the melt 3 and the nitrogen raw material gas 5 and has high mechanical strength and heat resistance, but pNB (pyrolytic nitriding) Boron) and Al ₂ O ₃ (also referred to as aluminum oxide or alumina) are preferable. The material of the inner container 21 is not particularly limited as long as it has high mechanical strength and heat resistance, but stainless steel, heat resistant steel, and the like are preferable. The material of the outer container 29 is not particularly limited as long as it has high mechanical strength and heat resistance, but stainless steel is preferable. The material of the heat insulating material 27 is not particularly limited as long as it has high mechanical strength, heat resistance, and heat insulating properties, but wool-like graphite or the like is preferable.

  In addition, the crystal growth apparatus used in the present embodiment includes a nitrogen source gas supply device 31 connected to the inner container 21 by the first pipe 41 and an additional container connected to the outer container 29 by the second pipe 43. A pressure gas supply device 33 and a vacuum exhaust device 35 connected to the outer container 29 by a third pipe 45 are provided. Here, a valve 41v for adjusting the supply flow rate of the nitrogen source gas 5 is provided in the first pipe 41, and a first pressure gauge 41p is provided in a portion 41a on the inner container 21 side from the valve 41v. ing. The second pipe 43 is provided with a valve 43v for adjusting the supply flow rate of the pressurizing gas 7, and a second pressure gauge 43p is provided at a portion 43a on the outer container 29 side from the valve 43v. Yes. The third pipe 45 is provided with a valve 45v for adjusting the exhaust flow rate.

  Furthermore, a fourth pipe 47 is provided that connects a portion 41 a closer to the inner container 21 than the valve 41 v of the first pipe 41 and a portion 45 a closer to the outer container 29 than the valve 45 v of the third pipe 45. The fourth pipe 47 is provided with a valve 47v. In FIG. 1, for reference, a portion 41 b on the nitrogen source gas supply device 31 side from the valve 41 v of the first pipe 41, and a portion 43 b on the pressurization gas supply device 33 side from the valve 43 v of the second pipe 43. The portion 45b on the side of the vacuum exhaust device 35 from the valve 45v of the third pipe 45 is also illustrated.

<Crystal growth method>
The method for growing a group III nitride crystal of the present embodiment is not particularly limited. For example, a step of preparing a group III nitride seed crystal 1 in which one of the surfaces is a (000-1) N atom surface 1n; A step of disposing the nitride seed crystal 1 so that its upper surface is a (000-1) N atomic surface 1n and its lower surface is in contact with the inner surface 23i of the crystal growth vessel 23, and a fusion containing a group III metal and an alkali metal By bringing the solution 6 in which the nitrogen source gas 5 is dissolved in the liquid 3 into contact with the group III nitride seed crystal 1, the (000-1) N atom surface is substantially parallel to the side surface 1s of the group III nitride seed crystal. Growing a group III nitride crystal 10 in any direction.

<Step of preparing group III nitride seed crystal>
Referring to FIG. 2, the method for growing a group III nitride crystal of this embodiment includes a step of preparing group III nitride seed crystal 1 in which one of the surfaces is (000-1) N atom surface 1n. Such a group III nitride seed crystal 1 is prepared, and a group III nitride crystal 10 is formed on the seed crystal in a direction parallel to the (000-1) N atom surface 1n of the group III nitride seed crystal 1 using a flux method. , The group III nitride crystal 10 having a low dislocation density of the entire crystal can be obtained. The measurement of the crystal dislocation density is not particularly limited, but can be performed by CL (cathode luminescence) method, EPD (etch pit density) method, or the like.

  Here, the prepared group III nitride seed crystal 1 is not particularly limited as long as it has (000-1) N atom surface 1n, but one of the surfaces is (000-1) N atom surface 1n. The opposite surface is a (0001) Ga atom surface 1g, and there is a side plane 1s that connects the surfaces. Here, the side surface 1s may not be perpendicular to the (000-1) N atom surface 1n. Further, from the viewpoint of further reducing the dislocation density of the group III nitride crystal 10 by matching the crystal lattice and lattice constant with the group III nitride crystal 10 to be grown, the same chemical composition as the group III nitride crystal 10 is obtained. It is preferable to have. The same chemical composition as the group III nitride crystal means that the types and ratios of atoms constituting the crystal are the same.

<Step of arranging group III nitride seed crystal>
Referring to FIG. 2, in the method for growing a group III nitride crystal of this embodiment, the upper surface of group III nitride seed crystal 1 is (000-1) N atom surface 1n, and the lower surface thereof is crystal growth vessel 23. The process arrange | positions so that the inner surface 23i may be contacted. Through this process, the group III nitride seed crystal 1 is arranged in the crystal growth vessel 23 such that the upper surface is the (000-1) N atomic surface 1n and the lower surface is in contact with the inner surface 23i of the crystal growth vessel 23. The

  Here, since the upper surface of the group III nitride seed crystal 1 is a (000-1) N atom surface, the lower surface of the group III nitride seed crystal 1 is usually a (0001) Ga atom surface. That is, since the (0001) Ga atom surface is in contact with the inner surface 23i of the crystal growth vessel 23, the nitrogen source gas is added to the melt 3 containing the group III metal and the alkali metal disposed in the crystal growth vessel 23. 5 cannot be contacted with the solution 6 in which the group 5 is dissolved, and the group III nitride crystal 10 cannot be grown thereon. Further, even if the (000-1) N atom surface is brought into contact with a solution 6 in which a nitrogen source gas 5 is dissolved in a melt 3 containing a group III metal and an alkali metal, a group III nitride crystal 10 is formed thereon. Hardly grows up. Accordingly, by disposing the group III nitride seed crystal 1 as described above, the group III nitride is substantially parallel to the (000-1) N atom surface on the side surface 1 s of the group III nitride seed crystal 1. The nitride crystal 10 can be grown.

<Step of growing group III nitride crystal>
Referring to FIG. 2, in the method for growing a group III nitride crystal of this embodiment, a solution 6 in which a nitrogen source gas 5 is dissolved in a melt 3 containing a group III metal and an alkali metal is used as a group III nitride seed crystal. 1, the group III nitride crystal 10 is grown on the side surface 1s of the group III nitride seed crystal substantially in a direction parallel to the (000-1) N atom surface.

  In the flux method, since the group III nitride crystal 10 hardly grows on the (000-1) N atom surface 1n for the group III nitride seed crystal 1, substantially only on the side surface 1s by the above process. Group III nitride crystal 10 grows in a direction parallel to (000-1) N atomic surface 1n. At this time, the dislocation of the group III nitride crystal 10 propagates in the crystal growth direction, that is, in a direction parallel to the (000-1) N atomic surfaces 1n and 10n. Therefore, the group III nitride crystal 10 has a low dislocation density at the (000-1) N atom surface 10n and the (0001) Ga atom surface 10g. In this way, a group III nitride crystal 10 having a low dislocation density is obtained.

  Here, the side surface 1s is grown on the group III nitride crystal 10 in a direction parallel to the (000-1) N atom surface, whereby (000-1) N atoms of the group III nitride crystal 10 are grown. From the viewpoint of reducing the dislocation density on the surface and the (0001) Ga atom surface, it is not necessary to be parallel to the (000-1) N atom surface 1n, and may not be perpendicular. However, from the viewpoint of effectively reducing the dislocation density, the side surface 1s is preferably perpendicular to the (000-1) N atom surface 1n.

  In the step of growing the group III nitride crystal of the present embodiment, a melt 3 containing a group III metal and an alkali metal is used. Since the melt 3 contains an alkali metal in addition to the group III metal, the alkali metal is contained above the impurity concentration (for example, a concentration of less than 1 mol% with respect to the entire melt). The crystal growth temperature and / or the crystal growth pressure of the group III nitride crystal can be reduced as compared to the melt without the melt. This is considered because the alkali metal contained in the melt 3 promotes the dissolution of the nitrogen source gas 5 in the melt 3.

  The alkali metal is not particularly limited, but preferably contains at least one of Na and Li from the viewpoint of a large effect of reducing the crystal growth temperature and / or the crystal growth pressure of the group III nitride crystal 10, More preferably, it is at least one of Li.

The molar ratio of the group _III metal M _III and the alkali metal M _A contained in the melt 3 reduces the crystal growth temperature and / or the crystal growth pressure of the group III nitride crystal, suppresses dislocation growth, and dislocation density. From the viewpoint of achieving a crystal growth rate suitable for growing a low group III nitride crystal (for example, 0.1 μm / hr or more and 2 μm / hr or less), for example, M _III : M _A = 90: 10 to 10: 90 is preferable, and M _III : M _A = 50: 50 to 20:80 is more preferable. Even if the molar ratio of the group III metal M _III is larger than M _III : M _A = 90: 10 or the molar ratio of the alkali metal M _A is larger than M _III : M _A = 10: 90, the crystal growth rate decreases. Too much.

  Further, from the viewpoint of easily obtaining the temperature and pressure necessary for crystal growth, the group III nitride crystal 10 to be grown is preferably a GaN crystal.

  The process for growing the group III nitride crystal of the present embodiment is not particularly limited, but can include, for example, the following plurality of sub-processes.

(Melt material arrangement sub-process)
Next, referring to FIG. 2, a group III metal and an alkali metal are placed in the crystal growth vessel 23 as a melt raw material placement sub-step. From the viewpoint of growing the high purity group III nitride crystal 10, the purity of the group III metal is preferably 99 mol% or more, and more preferably 99.999 mol% or more. From the same viewpoint, the purity of the alkali metal is preferably 99 mol% or more, and more preferably 99.99% or more.

  Here, the amount of the melt raw material (group III metal and alkali metal) is not particularly limited, but the depth of the melt 3 when liquefied is the (000-1) N atom surface of the group III nitride seed crystal 1 It is preferable that it is 1 mm or more and 50 mm or less. If the depth is less than 1 mm, the melt 3 may not cover the entire exposed surface of the group III nitride seed crystal 1 ((000-1) N atom surface 1n and side surface 1s) due to the surface tension of the melt 3. If it is larger than 50 mm, the supply of the nitrogen source gas 5 from the liquid surface of the melt 3 is insufficient.

(Temperature raising sub-process)
Next, referring to FIGS. 2 and 4, as temperature raising sub-step S1, nitrogen source gas 5 is placed in crystal growth vessel 23 in which a group III nitride seed crystal and a melt source (group III metal and alkali metal) are arranged. , The atmospheric pressure is set to the predetermined pressure P ₁ , and the atmospheric temperature is raised from the room temperature T ₀ to the predetermined temperature T using the heater 25 over a predetermined time H ₁ . In the temperature raising sub-step, the melt raw material is melted to form a melt 3 containing a group III metal and an alkali metal, and further, a solution 6 in which the nitrogen raw material gas 5 is dissolved in the melt 3 is formed. . Such a solution 6 contacts the (000-1) N atom surface 1n and the side surface 1s (the side surface 1s is preferably perpendicular to the (000-1) N atom surface 1n) of the group III nitride seed crystal 1.

In the heated sub-step, ambient pressure and ambient temperature (a predetermined pressure P ₁ and the predetermined temperature T) is a condition is satisfied that the group III nitride crystal does not grow.

  During the temperature raising sub-process, the supply amount of the nitrogen raw material gas 5 to the inner container 21 and the supply flow rate of the pressurizing gas 7 to the outer container 29 are adjusted so that the inner pressure of the inner container 21 becomes the inner pressure of the outer container 29. It is preferable to increase it in the range of 0.01 MPa or more and 0.1 MPa or less. That is, it is preferable that 0.01 MPa ≦ {(internal pressure of the inner container) − (internal pressure of the outer container)} ≦ 0.1 MPa. This is because the pressurizing gas 7 in the outer container 29 is prevented from being mixed into the inner container 21 and the purity of nitrogen in the inner container 21 is kept high.

  Here, the nitrogen source gas 5 supplied into the inner vessel 21 is particularly suitable as long as it can be dissolved in the melt 3 containing a group III metal and an alkali metal to grow the group III nitride crystal 10. There is no limitation, and nitrogen gas, ammonia gas, etc. are used. In addition, from the viewpoint of growing the high-purity group III nitride crystal 10, the purity of the nitrogen source gas is preferably 99.999 mol% or more, and more preferably 99.9999 mol% or more. On the other hand, the pressurizing gas 7 supplied to the outer container 29 is used for maintaining the pressure in the outer container 29 and is not used for growing a group III nitride crystal. Good. However, since the heater 25 is disposed in the outer container 29, an inert gas that does not react with the heater 25, such as nitrogen gas or argon gas, is preferably used for the pressurizing gas 7.

(Crystal growth preparation sub-process)
Next, referring to FIG. 2 and FIG. 4, as the crystal growth preparation sub-step S <b> 2, the supply flow rate of the nitrogen source gas 5 to the crystal growth vessel 23 is adjusted, and the atmospheric pressure in the crystal growth vessel 23 is set to a predetermined pressure. P ₂ and the atmospheric temperature are maintained at a predetermined temperature T for a predetermined time H ₂ . Here, the predetermined pressure P ₂ is higher than the predetermined pressure P ₁ . Thereby, the state of the group III nitride seed crystal 1 and the solution 6 in which the nitrogen source gas 5 is dissolved in the melt 3 can be made constant, and the initial conditions for starting the crystal can be made constant.

It is assumed that the atmospheric pressure (predetermined pressure P ₂ ) and the atmospheric temperature (predetermined temperature T) in this crystal growth preparation sub-step satisfy the condition that the group III nitride crystal 10 does not grow.

  Even during the crystal growth preparation sub-process, the supply flow rate of the nitrogen raw material gas 5 to the inner vessel 21 and the supply flow rate of the pressurizing gas 7 to the outer vessel 29 are adjusted so that the inner pressure of the inner vessel 21 becomes the outer vessel 29. It is preferable to increase the pressure in the range of 0.01 MPa or more and 0.1 MPa or less compared to the internal pressure. That is, it is preferable that 0.01 MPa ≦ {(internal pressure of the inner container) − (internal pressure of the outer container)} ≦ 0.1 MPa. This is because the pressurizing gas 7 in the outer container 29 is prevented from being mixed into the inner container 21 and the purity of nitrogen in the inner container 21 is kept high.

(Crystal growth sub-process)
Next, referring to FIGS. 2 and 4, as the crystal growth sub-step S3, the supply flow rate of the nitrogen source gas 5 to the crystal growth vessel 23 is adjusted, and the atmospheric pressure in the crystal growth vessel 23 is set to a predetermined pressure P _3. Further, the group III nitride crystal 10 is grown while maintaining the atmospheric temperature at the predetermined temperature T for a predetermined time H ₃ . Here, the predetermined pressure P ₃ is higher than the predetermined pressure P ₂ .

  In such a crystal growth sub-step, the solution 6 in which the nitrogen source gas 5 is dissolved in the melt 3 containing a group III metal and an alkali metal is used as the (000-1) N atom surface 1n and side of the group III nitride seed crystal 1. It is in contact with the surface 1s (the side surface 1 is preferably perpendicular to the (000-1) N atomic surface 1n). However, the group III nitride crystal 10 hardly grows on the (000-1) N atom surface 1n. For this reason, the group III nitride crystal 10 grows substantially on the side surface 1s of the group III nitride seed crystal 1 in a direction parallel to the (000-1) N atom surface 1n. At this time, the dislocation of the group III nitride crystal 10 propagates in the crystal growth direction, that is, in a direction parallel to the (000-1) N atomic surfaces 1n and 10n. Therefore, the group III nitride crystal 10 has a low dislocation density at the (000-1) N atom surface 10n and the (0001) Ga atom surface 10g. In this way, a group III nitride crystal 10 having a low dislocation density is obtained.

  Even during the crystal growth sub-process, the supply amount of the nitrogen source gas 5 to the inner vessel 21 and the supply amount of the pressurizing gas 7 to the outer vessel 29 are adjusted so that the inner pressure of the inner vessel 21 becomes the same as that of the outer vessel 29. It is preferable to increase the pressure in the range of 0.01 MPa or more and 0.1 MPa or less compared to the internal pressure. That is, it is preferable that 0.01 MPa ≦ {(internal pressure of the inner container) − (internal pressure of the outer container)} ≦ 0.1 MPa. This is because the pressurizing gas 7 in the outer container 29 is prevented from being mixed into the inner container 21 and the purity of nitrogen in the inner container 21 is kept high.

(Cooling sub-process)
Next, referring to FIGS. 2 and 4, as a temperature lowering sub-step S4, the amount of heating by the heater 25 to the crystal growth vessel 23 is adjusted, and the atmospheric pressure in the crystal growth vessel 23 is maintained at a predetermined pressure P ₃ . At the same time, the ambient temperature is lowered from the predetermined temperature T to the room temperature T ₀ over a predetermined time H ₄ .

  Even during the temperature lowering sub-process, the supply flow rate of the nitrogen source gas 5 to the inner vessel 21 and the supply flow rate of the pressurizing gas 7 to the outer vessel 29 are adjusted so that the inner pressure of the inner vessel 21 becomes the inner pressure of the outer vessel 29. It is preferable to increase it in the range of 0.01 MPa or more and 0.1 MPa or less. That is, it is preferable that 0.01 MPa ≦ {(internal pressure of the inner container) − (internal pressure of the outer container)} ≦ 0.1 MPa. This is because the pressurizing gas 7 in the outer container 29 is prevented from being mixed into the inner container 21 and the purity of nitrogen in the inner container 21 is kept high.

Furthermore, it is possible to depressurize the crystal-growth vessel 23 from the predetermined pressure P ₃ to the atmospheric pressure, take out the III nitride crystal 10 grown group III nitride seed crystal first side surface 1s.

Example 1
1. Preparation of Group III Nitride Seed Crystal Referring to FIG. 1 and FIG. 2, (0001) Ga atom surfaces 1 g and (000-1) having principal surfaces parallel to each other, produced by HVPE method as group III nitride seed crystal 1 A GaN seed crystal having a diameter of 3 mm and a thickness of 0.4 mm having a side surface 1s perpendicular to the (000-1) N atom surface 1n was prepared. The dislocation density in the 1 g of (0001) Ga atom surface of the GaN seed crystal (Group III nitride seed crystal 1) was 5 × 10 ⁵ cm ^{−2 as} measured by the CL (cathode luminescence) method.

2. Arrangement of Group III Nitride Seed Crystal Referring to FIG. 2, a GaN seed crystal (Group III nitride seed crystal 1) has an inner diameter of 30 mm and a depth of 20 mm with its (000-1) N atom surface 1n facing upward. It was arranged at the bottom of an Al ₂ O ₃ crucible (crystal growth vessel 23). At this time, the (0001) Ga atom surface of the GaN seed crystal was in contact with the bottom surface (inner surface) of the crucible, and the (000-1) N atom surface and the side surface were exposed.

3. Group III nitride crystal growth (disposition of melt raw material)
Referring to FIG. 2, in a crucible made of Al ₂ O ₃ (crystal growth vessel 23), metal Ga having a purity of 99.9999 mol% and metal Na having a purity of 99.99 mol% (melt raw material) are mixed with metal. The molar ratio of Ga (group III metal M _III ) to metal Na (alkali metal M _A ) is a ratio of M _III : M _A = 3: 7, and the depth from the surface of the melt 3 when melted to the bottom of the crucible The amount of 5 mm was added.

Next, an Al ₂ O ₃ crucible (crystal growth vessel 23) containing GaN seed crystal (Group III nitride seed crystal 1) and metal Ga and metal Na (melt raw material) was placed in the inner vessel 21. Next, an Al ₂ O ₃ lid 24 was placed on the Al ₂ O ₃ crucible (crystal growth vessel 23). Here, the Al ₂ O ₃ crucible (crystal growth vessel 23) is secured to the inner vessel 21, and the atmospheric pressure in the Al ₂ O ₃ crucible (crystal growth vessel 23) is the inner vessel 21. It becomes equal to the atmospheric pressure inside. Further, since the Al ₂ O ₃ crucible (crystal growth vessel 23) is disposed in the inner vessel 21, the ambient temperature in the Al ₂ O ₃ crucible (crystal growth vessel 23) is set in the inner vessel 21. It becomes equal to the ambient temperature.

(Evacuation)
Next, referring to FIG. 1, the inside of the inner container 21 and the outer container 29 was evacuated using a vacuum pump (evacuation apparatus 35). The degree of vacuum of the inner container 21 and the outer container 29 after evacuation was 1 × 10 ⁻³ Pa.

(Temperature raising sub-process)
Next, referring to FIG. 1, FIG. 2 and FIG. 4, the atmospheric pressures in the inner container 21 and the outer container 29 are 1 MPa (predetermined pressure P ₁ ) and 0.95 MPa in the inner container 21 and the outer container 29, respectively. The nitrogen source gas 5 and the pressurizing gas 7 were supplied so that the atmospheric pressure in the crucible made of Al ₂ O ₃ (crystal growth vessel 23) was 1 MPa (predetermined pressure P ₁ ). High purity nitrogen gas having a purity of 99.99999 mol% was used as the nitrogen source gas 5 supplied into the inner vessel 21. On the other hand, nitrogen gas having a purity of 99.9999 mol% was used as the pressurizing gas 7 supplied to the outer container 29. Next, referring to FIGS. 1, 2, and 4, the inside of the inner container 21 and the outer container 29 is heated for 2 hours (predetermined time H ₁ ) using the resistance heating type heater 25, and the inner container 21. The ambient temperature was raised from 30 ° C. (room temperature T ₀ ) to 865 ° C. (predetermined temperature T) (temperature raising sub-step S1).

In the temperature raising sub-step S1, a Ga—Na melt (melt 3) in which metal Ga and metal Na are melted is formed, and high purity nitrogen gas (nitrogen raw material) is formed in the Ga—Na melt (melt 3). A solution 6 in which the gas 5) is dissolved is formed, and the solution 6 contacts the (000-1) N atom surface 1n of the GaN seed crystal and the side surface 1s perpendicular to the (000-1) N atom surface 1n. . Here, the conditions under which the atmospheric pressure is 1 MPa (predetermined pressure P ₁ ) and the atmospheric temperature is 865 ° C. (predetermined temperature T) are conditions in which crystal growth does not occur.

(Crystal growth preparation sub-process)
Next, referring to FIG. 1, FIG. 2, and FIG. 4, the atmospheric pressures in the inner container 21 and the outer container 29 are 2 MPa (predetermined pressure P ₂ ) and 1.95 MPa in the inner container 21 and the outer container 29, respectively. The nitrogen source gas 5 and the pressurizing gas 7 are supplied so that the atmospheric pressure in the crucible made of Al ₂ O ₃ (crystal growth vessel 23) is 2 MPa (predetermined pressure P ₂ ) and the atmospheric temperature is 865. ° C. (predetermined temperature T) in 50 hours (a predetermined time H ₂₎ and held (crystal growth preparation substep S2). Here, the conditions under which the atmospheric pressure is 2 MPa (predetermined pressure P ₂ ) and the atmospheric temperature is 865 ° C. (predetermined temperature T) are conditions in which crystal growth does not occur.

(Crystal growth sub-process)
Next, referring to FIG. 1, FIG. 2 and FIG. 4, the (000-1) N atom surface 1n and the (000-1) N atom surface of the GaN seed crystal of the GaN seed crystal (Group III nitride seed crystal 1) With the solution 6 in contact with the side surface 1s perpendicular to 1n, the atmospheric pressure in the inner container 21 and the outer container 29 is 3 MPa (predetermined pressure P ₃ ) and 2 in the inner container 21 and the outer container 29, respectively. Each of the nitrogen source gas 5 and the pressurizing gas 7 is supplied so as to be .95 MPa, the atmospheric pressure in the Al ₂ O ₃ crucible (crystal growth vessel 23) is 3 MPa (predetermined pressure P ₃ ), and the atmospheric temperature. Was held at 865 ° C. (predetermined temperature T) for 200 hours (predetermined time H ₃ ) to grow a GaN crystal (Group III nitride crystal 10) (crystal growth sub-step S3).

(Cooling sub-process)
Next, referring to FIG. 1, FIG. 2 and FIG. 4, the heating by the heater 25 is stopped, and the atmospheric pressure in the Al ₂ O ₃ crucible (crystal growth vessel 23) is set to 3 MPa (predetermined pressure P ₃ ). While maintaining the temperature, the temperature was lowered from 865 ° C. (predetermined temperature T) to 30 ° C. (room temperature T ₀ ) over 8 hours (predetermined time H ₄ ) (temperature-decreasing sub-step S4). Subsequently, the atmospheric pressure in the Al ₂ O ₃ crucible (crystal growth vessel 23) in the inner vessel 21 is reduced from ₃ MPa (predetermined pressure P ₃ ) to atmospheric pressure, and a GaN seed crystal (Group III nitride seed crystal 1) is obtained. ) A GaN crystal (Group III nitride crystal 10) grown thereon was taken out. At this time, the atmospheric pressure in the outer container 29 was adjusted to be 0 to 0.05 MPa lower than the atmospheric pressure in the inner container 21.

(GaN crystal)
The extracted GaN crystal (Group III nitride crystal 10) was 9 mm in diameter and 0.4 mm in thickness including the GaN seed crystal (Group III nitride seed crystal 1). That is, the GaN crystal hardly grows in the direction perpendicular to the (000-1) N atom surface 1n on the (000-1) N atom surface 1n of the GaN seed crystal, and is substantially only on the side surface 1s. (000-1) N atoms were grown to a thickness of 3 mm in the direction parallel to the surface 1n. The dislocation density on the surface 10c appearing as the (0001) Ga surface in the grown GaN crystal after polishing from the (0001) Ga atom surfaces 10g and 1g of the GaN crystal and the GaN seed crystal to a surface 10c having a depth of 0.1 mm. When measured by the CL method, it was as low as 1 × 10 ⁵ cm ⁻² .

(Comparative Example 1)
Referring to FIGS. 1, 3 and 4, a GaN seed crystal (Group III nitride seed crystal 1) similar to that in Example 1 was prepared by using a (000-1) N atom surface 1g made of Al ₂ O ₃ . A GaN crystal was grown in the same manner as in Example 1 except that the (0001) Ga atom surface 1g and the side surface 1s were placed in contact with the bottom surface of the (crystal growth vessel 23). .

The obtained GaN crystal (Group III nitride crystal 10) was 5 mm in diameter and 1.4 mm in thickness including the GaN seed crystal (Group III nitride seed crystal 1). That is, the GaN crystal grows 1 mm in a direction perpendicular to the (0001) Ga atom surface 1g on the (0001) Ga atom surface 1g of the GaN seed crystal, and is parallel to the (0001) Ga atom surface 1g on the side surface 1s. It grew 1 mm in the direction. Such a GaN crystal is polished from a (0001) Ga atom surface 10g to a surface 10a having a depth of 0.1 mm and a surface 10b having a depth of 1.1 mm, and appears as a (0001) Ga surface in the grown GaN crystal. The dislocation densities on the surface 10a and the surface 10b were 8 × 10 ⁶ cm ⁻² and 1 × 10 ⁵ cm ⁻² , respectively, as measured by the CL method.

  As is clear from comparison between Example 1 and Comparative Example 1, in Example 1, substantially all of the GaN crystal (Group III nitride crystal 10) is on the side of the GaN seed crystal (Group III nitride seed crystal 1). By growing only on the surface 1s, the dislocation density of the entire crystal could be reduced. On the other hand, in Comparative Example 1, since the GaN crystal was grown on the (0001) Ga atom surface 1g and the side surface 1s of the GaN seed crystal, the crystal portion grown on the (0001) Ga atom surface 1g The dislocation density was not reduced, and the dislocation density of the entire crystal could not be reduced.

(Example 2)
As melt raw materials, metal Ga having a purity of 99.9999 mol%, metal Na having a purity of 99.99 mol%, and metal Li having a purity of 99.99 mol%, metal Ga (group _III metal MIII), and metal Na (alkali The molar ratio of metal M _A ) is M _III : M _A = 3: 7, and the molar ratio of metal Na (Na metal M _Na ) to metal Li (Li metal M _Li ) is M _Na : M _Li = 97: 3. GaN crystal (Group III nitridation) in the same manner as in Example 1 except that it was placed in a crucible (crystal growth vessel) and the atmosphere temperature (predetermined temperature T) in the crystal growth preparation step and crystal growth step was 875 ° C. A product crystal 10) was grown.

The obtained GaN crystal (Group III nitride crystal 10) was 10 mm in diameter and 0.4 mm in thickness including the GaN seed crystal (Group III nitride seed crystal 1). That is, the GaN crystal hardly grows in the direction perpendicular to the (000-1) N atom surface 1n on the (000-1) N atom surface 1n of the GaN seed crystal, and is substantially only on the side surface 1s. (000-1) N atoms were grown to a thickness of 3.5 mm in a direction parallel to the surface 1n. The dislocation density on the surface 10c appearing as the (0001) Ga surface in the grown GaN crystal by polishing from the (0001) Ga atom surface 10g, 1g of the GaN crystal and the GaN seed crystal to the surface 10c having a depth of 0.1 mm. When measured by the CL method, it was as low as 2 × 10 ⁵ cm ⁻² .

(Comparative Example 2)
As melt raw materials, metal Ga having a purity of 99.9999 mol%, metal Na having a purity of 99.99 mol%, and metal Li having a purity of 99.99 mol%, metal Ga (group _III metal MIII), and metal Na (alkali The molar ratio of metal M _A ) is M _III : M _A = 3: 7, and the molar ratio of metal Na (Na metal M _Na ) to metal Li (Li metal M _Li ) is M _Na : M _Li = 97: 3. GaN crystal (Group III nitridation) in the same manner as in Example 2 except that it was placed in a crucible (crystal growth vessel) and the atmosphere temperature (predetermined temperature T) in the crystal growth preparation step and crystal growth step was 875 ° C. A product crystal 10) was grown.

The obtained GaN crystal (Group III nitride crystal 10) was 5.4 mm in diameter and 1.6 mm in thickness including the GaN seed crystal (Group III nitride seed crystal 1). That is, the GaN crystal grows 1.2 mm on the (0001) Ga atom surface 1g of the GaN seed crystal in the direction perpendicular to the (0001) Ga atom surface 1g, and on the (0001) Ga atom surface 1g on the side surface 1s. It grew 1.2 mm in the parallel direction. Polishing from the (0001) Ga atom surface 10g of the GaN crystal to the surface 10a having a depth of 0.1 mm and the surface 10b having a depth of 1.3 mm, appears as a (0001) Ga surface in the grown GaN crystal. The dislocation densities on the surface 10a and the surface 10b were 7 × 10 ⁶ cm ⁻² and 2 × 10 ⁵ cm ⁻² , respectively, as measured by the CL method.

  As is clear from comparison between Example 2 and Comparative Example 2, in Example 2, substantially all of the GaN crystal (Group III nitride crystal 10) is on the side of the GaN seed crystal (Group III nitride seed crystal 1). By growing only on the surface 1s, the dislocation density of the entire crystal could be reduced. On the other hand, in Comparative Example 2, since the GaN crystal was grown on the (0001) Ga atom surface 1g and the side surface 1s of the GaN seed crystal, the crystal portion grown on the (0001) Ga atom surface 1g The dislocation density was not reduced, and the dislocation density of the entire crystal could not be reduced.

  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.

  A group III nitride crystal obtained by the growth method according to the present invention and a group III nitride crystal obtained by another growth method using this crystal as a substrate are light emitting elements such as light emitting diodes and laser diodes, rectifiers, bipolar transistors, Electronic devices such as field effect transistors and HEMTs (high electron mobility transistors), micro electron sources (emitters), temperature sensors, pressure sensors, radiation sensors, semiconductor sensors such as visible-ultraviolet light detectors, SAW (surface acoustic waves) It is widely used as a substrate for devices such as devices, vibrators, resonators, oscillators, MEMS (Micro Electro Mechanical System) parts, and piezoelectric actuators.

  1 Group III nitride seed crystal, 1 g, 10 g (0001) Ga atom surface, 1 n, 10 n (000-1) N atom surface, 1 s side surface, 3 melt, 5 nitrogen source gas, 6 solution, 7 pressurizing gas, 10 Group III nitride crystal, 10a, 10b, 10c plane, 21 inner vessel, 23 crystal growth vessel, 24 lid, 25 heater, 27 heat insulating material, 29 outer vessel, 31 nitrogen source gas supply device, 33 pressurization gas supply device , 35 Vacuum exhaust device, 41 1st piping, 41a valve inner part side, 41b valve nitrogen source gas supply side part, 41p, 43p pressure gauge, 41v, 43v, 45v, 47v valve, 43 2 piping, 43a, 45a The portion on the outer container side from the valve, 43b The portion on the pressure gas supply device side from the valve, 45 Third piping, 45b A part on the side of the vacuum exhaust device from Lub, 47 4th piping.

Claims (3)

A group III nitride crystal is grown from a group III nitride seed crystal by contacting a group III nitride seed crystal with a solution in which a nitrogen source gas is dissolved in a melt containing a group III metal and an alkali metal. A method for growing a physical crystal,
The group III nitride seed crystal has a top surface that is a (000-1) N atom surface, and a bottom surface that is arranged to contact the inner surface of the crystal growth vessel,
A method for growing a group III nitride crystal comprising growing the group III nitride crystal in a direction parallel to the surface of the (000-1) N atom substantially on a side surface of the group III nitride seed crystal .   The group III nitride crystal growth method according to claim 1, wherein the alkali metal contains at least one of Na and Li.   The method for growing a group III nitride crystal according to claim 1 or 2, wherein the group III nitride crystal is a GaN crystal.

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