JP2010024124A - Method for growing group iii nitride crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a group III nitride crystal, in which an increase in dislocation is suppressed during growing a crystal by a liquid phase method. <P>SOLUTION: The method for growing a group III nitride crystal includes a step of preparing a base substrate 1 and a step of growing a group III nitride crystal 10 on the major surface of the base substrate 1 by bringing the major surface 1m into contact with a solution prepared by dissolving a nitrogen-containing gas 5 into a solvent 3 containing a group III metal, an alkali metal and a metal that reduces the crystal growth rate of the group III nitride crystal. The crystal growth rate of the group III nitride crystal is less than the critical growth rate of the crystal where dislocation of the group III nitride crystal starts to increase. The alkali metal contains at least either Na or Li. The metal that decreases the crystal growth rate of the group III nitride crystal contains at least one metal selected from a group consisting of transition metals, Ge, Sn, Pb and Bi. <P>COPYRIGHT: (C)2010,JPO&INPIT

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, in order to efficiently manufacture various semiconductor devices, a large group III nitride crystal having a low dislocation density has been demanded.

  As a method for growing a group III nitride crystal, there are 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 pressure solution method and flux method. is there. 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.

For example, H. Yamane and three others, “Preparation of GaN Single Crystals Using a Na Flux”, Chem. Mater., Vol. 9, No. 2, (1997), p.413-416 (Non-Patent Document 1) discloses a method for growing GaN crystals by the Na flux method. Japanese Patent Laying-Open No. 2003-206198 (Patent Document 1) discloses a method for growing a group III nitride crystal by a Na flux method using a plate-like group III nitride seed crystal. Also, F. Kawamura and 7 others, “Growth of a Two-Inch GaN Single Crystal Substrate Using the Na Flux Method”, Japanese Journal of Applied Physics, Vol. 45, No. 43, (2006), p.L1136- L1138 (non-Patent Document 2), by growing the GaN crystal dislocation density is 10 ⁸ cm ^-2 order of GaN on a substrate by Na flux method, 2.3 × 10 ⁵ cm ^-2 order of dislocation density of GaN Disclose that crystals are obtained.

However, the growth method disclosed in Non-Patent Document 1 has a low crystal growth rate and does not use a seed crystal, so it is difficult to grow a large crystal. Patent Document 1 does not describe or suggest the dislocation density of the seed crystal and the grown crystal. In addition, regarding the Na flux method disclosed in Non-Patent Document 2, there is a description of the dislocation density of the seed crystal and the grown crystal, but the evaluation of the dislocation density of the grown crystal was partial.
JP 2003-206198 A H. Yamane and 3 others, “Preparation of GaN Single Crystals Using a Na Flux”, Chem. Mater., Vol.9, No.2, (1997), p.413-416 F. Kawamura and 7 others, “Growth of a Two-Inch GaN Single Crystal Substrate Using the Na Flux Method”, Japanese Journal of Applied Physics, Vol. 45, No. 43, (2006), p.L1136-L1138

As described above, in Non-Patent Document 2, a GaN crystal having a dislocation density of 2.3 × 10 ⁵ cm ⁻² is grown on a GaN substrate having a dislocation density of the order of 10 ⁸ cm ⁻² by the Na flux method. It is described. The present inventors examined the Na flux method disclosed in Non-Patent Document 2 in detail. As a result, the GaN crystal grown by the Na flux method has a region where the dislocation density greatly exceeds 1 × 10 ⁶ cm ⁻² in addition to the region where the dislocation density is 1 × 10 ⁶ cm ⁻² or less as described above. The average dislocation density of the whole crystal exceeds 1 × 10 ⁶ cm ⁻² , which is a dislocation density comparable to that of a commercially available GaN crystal grown by the HVPE (hydride vapor phase epitaxy) method. It was.

Furthermore, the inventors have grown a GaN crystal on a GaN substrate having a dislocation density of 1 × 10 ⁶ cm ⁻² or less by the Na flux method. The dislocation density of the GaN crystal was measured by the number of pits per unit area (etch pit density) that appeared by etching the crystal surface with HCl gas at 750 ° C. Similarly, it has a region where the dislocation density is 1 × 10 ⁶ cm ⁻² or less and a region where the dislocation density greatly exceeds 1 × 10 ⁶ cm ^−2, and the average dislocation density of the entire crystal is 1 × 10 ⁶ cm. ^It was higher than ^-2 .

  This is because when a group III nitride crystal such as a GaN crystal is grown by the Na flux method, the group III nitride crystal not only takes over the dislocation of the substrate, but also the dislocation is propagated during the crystal growth. Means.

  Therefore, the present inventors examined the Na flux method in detail for the purpose of providing a growth method in which the growth of dislocations during crystal growth is suppressed in the liquid phase method. The crystal growth rate of the group III nitride crystal is sufficiently reduced by bringing a solution in which a nitrogen-containing gas is dissolved in a solvent containing a metal that reduces the crystal growth rate of the group III nitride crystal into contact with the main surface of the base substrate. As a result, it was found that the growth of dislocations during crystal growth was suppressed, and the present invention was completed.

  The present invention is a method for growing a group III nitride crystal by a liquid phase method, comprising the steps of preparing a base substrate, and crystal growth of a group III metal, an alkali metal, and a group III nitride crystal on the main surface of the base substrate And a step of growing a group III nitride crystal on a main surface by contacting a solution in which a nitrogen-containing gas is dissolved in a solvent containing a metal for reducing the speed. .

  In the method for growing a group III nitride crystal according to the present invention, the crystal growth rate of the group III nitride crystal can be less than the critical crystal growth rate at which the dislocation of the group III nitride crystal starts to grow. The alkali metal can contain at least one of Na and Li. The group III nitride crystal can be a GaN crystal. In addition, the metal that reduces the crystal growth rate of the group III nitride crystal may include at least one metal selected from the group consisting of transition metals, Ge, Sn, Pb, and Bi. The metal that reduces the crystal growth rate of the group III nitride crystal can include In. Further, the crystal growth rate of the group III nitride crystal can be 0.05 μm / hr or more and 2 μm / hr or less.

  According to the present invention, in a group III nitride crystal by a liquid phase method, the growth of dislocations during crystal growth is suppressed and the average dislocation density is reduced by stably reducing the crystal growth rate of the group III nitride crystal. Low group III nitride crystals are obtained.

  1 and 2, the method for growing a group III nitride crystal according to an embodiment of the present invention is a method for growing a group III nitride crystal 10 by a liquid phase method, and a base substrate 1 is prepared. The step is brought into contact with a main surface 1m of the base substrate 1 with a solution in which a nitrogen-containing gas 5 is dissolved in a solvent 3 containing a group III metal, an alkali metal, and a metal that reduces the crystal growth rate of a group III nitride crystal. And growing a group III nitride crystal 10 on the main surface 1m.

  According to the Group III nitride crystal growth method of this embodiment, in addition to a Group III metal and an alkali metal, a Group III nitride is obtained by including in the solvent a metal that reduces the crystal growth rate of the Group III nitride crystal. The crystal growth rate of the product crystal can be stably reduced, and the growth of dislocations during crystal growth is suppressed, and a group III nitride crystal having a low average dislocation density is obtained.

(Crystal growth equipment)
Referring to FIGS. 1 and 2, the crystal growth apparatus used in the group III nitride crystal growth method of the present embodiment includes, for example, an outer container 29, and a heat insulating material 27 disposed inside the outer container 29. The heater 25 disposed inside the heat insulating material 27 and the 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 solvent 3 and the nitrogen-containing gas 5 and has high mechanical strength and heat resistance, but Al ₂ O ₃ (oxidation) Aluminum and alumina) are preferred. 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-containing gas supply device 31 connected to the inner container 21 by the first pipe 41 and an additive 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-containing 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-containing 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.

(Process for preparing the base substrate)
Referring to FIGS. 1 and 2, the group III nitride crystal growth method of this embodiment includes a step of preparing base substrate 1. Here, the prepared base substrate 1 is not particularly limited as long as the group III nitride crystal 10 can be grown on the main surface 1 m, but the group III nitride crystal 10 to be grown and the base substrate are grown. Group III nitride seed crystal 1a having one main surface 1m is preferably included, and group III nitride crystal 10 and group III nitride seed crystal to be grown are preferable. More preferably, 1a has the same chemical composition. Here, having the same chemical composition as the group III nitride crystal means that the types and ratios of atoms constituting the crystal are the same.

Here, the base substrate 1 including the group III nitride seed crystal 1a having one main surface 1m is, for example, a template substrate in which the group III nitride seed crystal 1a is formed on the base substrate 1b, and the group III nitride seed as a whole. For example, a free-standing substrate formed of the crystal 1a can be used. When an Al _x Ga _y In _1-xy N crystal (0 ≦ x, 0 ≦ y, x + y ≦ 1) is homoepitaxially grown as the group III nitride crystal 10, the group III nitride seed crystal 1a of the base substrate 1 is used. Al _x Ga _y In _1-xy N seed crystal (0 ≦ x, 0 ≦ y, x + y ≦ 1) is used.

  Here, the main surface 1m of the base substrate 1 is not particularly limited, but is preferably a (0001) group III metal atom surface from the viewpoint of easily obtaining a high-quality and large base substrate.

In addition, the average dislocation density in the main surface 1 m of the base substrate 1 is not particularly limited, but is preferably 1 × 10 ⁷ cm ⁻² or less, and more preferably 1 × 10 ⁶ cm ⁻² or less. By reducing the average dislocation density on the main surface 1m of the base substrate 1, the dislocations inherited by the group III nitride crystal 10 grown on the main surface 1m can be reduced. Here, the dislocation in the main surface 1m refers to a dislocation penetrating the main surface 1m, and appears in a dot shape on the main surface 1m. Moreover, the average dislocation density in 1 m of main surfaces means the average of the dislocation density in 1 m of main surfaces. The average dislocation density on the main surface 1 m of the base substrate 1 is measured by using a differential interference microscope to measure the number of pits per unit area (etch pit density) that appears when the main surface 1 m of the base substrate 1 is etched with HCl gas. it can.

Further, the area of the main surface 1 m of the base substrate 1 is not particularly limited, but is preferably 1 cm ² or more, and more preferably 10 cm ² or more. In crystal growth by the growth method of this embodiment, a large group III nitride crystal having a low average dislocation density on the crystal growth surface 10g is obtained by using a base substrate having a large area of the main surface.

  The base substrate 1 prepared in the present embodiment may be grown by any method such as a gas phase method such as HVPE method or MOCVD method, a liquid phase method such as solution method or flux method.

(Step of growing group III nitride crystal)
Referring to FIGS. 1 and 2, in the method for growing a group III nitride crystal of this embodiment, the crystal growth rate of a group III metal, an alkali metal, and a group III nitride crystal is applied to main surface 1m of base substrate 1. A step of bringing a group 3 nitride crystal 10 to grow on the main surface 1 m by bringing a solution containing the nitrogen-containing gas 5 into contact with the solvent 3 containing the metal to be reduced is provided.

  In the growth process of the group III nitride crystal in the present embodiment, a solvent 3 containing a group III metal, an alkali metal, and a metal that reduces the crystal growth rate of the group III nitride crystal is used. Since the solvent 3 contains an alkali metal in addition to the group III metal, the solvent contains a group III metal and does not contain an alkali metal at an impurity concentration (for example, a concentration of less than 1 mol% with respect to the whole solvent). As compared with the above, the crystal growth temperature and / or the crystal growth pressure of the group III nitride crystal can be reduced. This is presumably because the alkali metal contained in the solvent 3 promotes the dissolution of the nitrogen-containing gas 5 in the solvent 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.

Molar ratio reduces the crystal growth temperature and / or crystal growth pressure of the group III nitride crystal, the average dislocation density to inhibit the growth of dislocation between the Group III metal M _III an alkali metal M _A contained in the solvent 3 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.

  In addition, the solvent 3 contains a metal that reduces the crystal growth rate of the group III nitride crystal in addition to the group III metal and the alkali metal, so that the crystal growth rate of the group III nitride crystal is stably reduced. can do. Here, the metal that reduces the crystal growth rate of the group III nitride crystal is not particularly limited, but from the viewpoint of a large effect of reducing the crystal growth rate of the group III nitride crystal, transition metal, Ge, Sn, Pb And at least one metal selected from the group consisting of Bi. Furthermore, when a GaN crystal is grown as a group III nitride crystal, the metal that reduces the crystal growth of the GaN crystal preferably contains In from the viewpoint of a large effect of reducing the crystal growth rate of the GaN crystal.

Here, in the solvent 3, the percentage of the number of moles of the metal M _M that reduces the crystal growth rate of the group III nitride crystal with respect to the total number of moles of the group III metal M _III and the alkali metal M _A is 10 mol% or less. Is preferable, and it is more preferable that it is 1 mol% or more and 5 mol% or less. III-nitride mole percentage is greater than 10 mol% and the crystal growth rate of the metal M _M to reduce the crystal growth rate of the crystal is too low. Moreover, the effect of the molar percentage of metal M _M to reduce the crystal growth rate of the Group III nitride crystal is reduced crystal growth rate of 0.1 mole% less than the III-nitride crystal is reduced.

  In the Group III nitride crystal growth method of the present embodiment, the solvent 3 is formed from the viewpoint that crystal growth is preferably performed at about 700 ° C. to 900 ° C. using the liquefied solvent 3 (melt). The melting point of the mixture of the group III metal, the alkali metal, and the metal that reduces the crystal growth rate of the group III nitride crystal is preferably 800 ° C. or less, and more preferably 700 ° C. or less. Further, from the viewpoint of reducing damage to the base substrate 1, the melting point of the mixture of the group III metal forming the solvent 3, the alkali metal, and the metal reducing the crystal growth rate of the group III nitride crystal is 500 ° C. or less. preferable. Therefore, the crystal growth rate of the group III nitride crystal in which the melting point of the mixture of the group III metal forming the solvent 3, the alkali metal, and the metal that reduces the crystal growth rate of the group III nitride crystal is 800 ° C. or less is reduced. It is preferable to use a metal.

  Further, the crystal growth rate of the group III nitride crystal 10 is less than the critical crystal growth rate at which the dislocation of the group III nitride crystal starts to grow from the viewpoint of growing the group III nitride crystal 10 having a low average dislocation density. Is preferred. The critical crystal growth rate may vary somewhat depending on the crystal growth conditions such as the chemical composition of the solvent, the crystal growth temperature, and the crystal growth pressure, but is approximately 2 μm / hr. From such a viewpoint, the crystal growth rate of the group III nitride crystal is preferably 2 μm / hr or less, and more preferably 1 μm or less. On the other hand, as the crystal growth rate becomes smaller (lower), a longer time is required for crystal growth and the productivity is lowered. From the viewpoint of increasing productivity, the crystal growth rate is preferably 0.05 μm / hr or more, and more preferably 0.1 μm / hr or more.

Referring to FIGS. 1 and 2, the group III nitride crystal growth step of the present embodiment is performed, for example, by the following plurality of sub-steps. First, the base substrate 1 is placed on the bottom of the crystal growth vessel 23 with its main surface 1m facing up (base substrate placement sub-step). The crystal growth vessel 23 is not particularly limited, from the viewpoint of heat resistance, such as made of Al ₂ O ₃ crucible is preferably used. When a GaN crystal is grown as a group III nitride crystal, a GaN substrate is preferably used as the base substrate.

  Next, the solvent 3 containing a group III metal, an alkali metal, and a metal that reduces the crystal growth rate of the group III nitride crystal is placed in the crystal growth vessel 23 in which the base substrate 1 is arranged (solvent arrangement sub-step). This solvent 3 is solid at room temperature (about 25 ° C.), but is liquefied by subsequent heating.

  Although there is no restriction | limiting in the solvent 3 containing the group III metal, an alkali metal, and the metal which reduces the crystal growth rate of a group III nitride crystal, From a viewpoint of growing a high purity group III nitride crystal, group III nitridation It is preferable that the metal, the group III metal, and the alkali metal that reduce the crystal growth rate of the physical crystal have high purity. Moreover, as a metal which reduces the crystal growth rate of a group III nitride crystal, at least 1 type of metal chosen from the group which consists of a transition metal, Ge, Sn, Pb, and Bi is preferable. For example, in order to grow a high-purity GaN crystal, a high-purity metal Ga, a high-purity metal Na, and a high-purity metal that reduces the crystal growth rate of the GaN crystal (for example, transition metals, Ge, Sn, Pb And at least one metal selected from the group consisting of Bi and In). In this case, the purity of the metal Ga is preferably 99 mol% or more, and more preferably 99.999 mol% or more. The purity of metal Na is preferably 99 mol% or more, and more preferably 99.99 mol% or more. Further, the purity of the metal that reduces the crystal growth rate of the group III nitride crystal is preferably 99.9 mol% or more, and more preferably 99.99 mol% or more.

  Here, the amount of the solvent 3 containing the group III metal, the alkali metal, and the metal that reduces the crystal growth rate of the group III nitride crystal is not particularly limited, but the depth of the liquefied solvent 3 (melt) is not limited. It is preferable that it is 1 mm or more and 50 mm or less from the main surface 1 m of the base substrate 1. If the depth is less than 1 mm, the surface of the base substrate 1 may not be covered with the solvent 3 (melt) due to the surface tension of the solvent 3 (melt). This is because the supply of nitrogen from the surface is insufficient.

  Next, the crystal growth vessel 23 containing the solvent 3 containing the group III metal, the alkali metal, and the metal for reducing the crystal growth rate of the group III nitride crystal and the base substrate 1 is placed in the inner vessel 21 (crystals). Growth vessel placement sub-process). Here, it is preferable to cover the opening of the crystal growth vessel 23 with the lid 24 from the viewpoint of suppressing evaporation of the alkali metal in the solvent 3.

  Next, the inside of the inner container 21 and the outer container 29 is evacuated using the evacuation apparatus 35 (evacuation sub-process). This is for removing impurities inside the inner container 21 and the outer container 29. At this time, the valves 41v and 43v are closed, and the valves 47v and 45v are opened. The degree of vacuum of the inner container 21 and the outer container 29 after evacuation is not particularly limited, but is preferably 1 Pa or less from the viewpoint of reducing residual impurities.

  Next, the nitrogen-containing gas 5 and the pressurizing gas 7 are supplied into the inner container 21 and the outer container 29 so that the internal pressure of each container is 0.5 MPa or more and 5 MPa or less (nitrogen-containing gas supply sub-process). . Here, even if the lid 24 is disposed on the crystal growth vessel 23, the lid 24 is not in close contact with the crystal growth vessel 23, so that the nitrogen-containing gas 5 supplied into the inner vessel 21 is supplied to the crystal growth vessel 23. Then, the liquid is supplied into the solvent 3 in the crystal growth vessel 23 through a gap between the lid 24 and the lid 24. At this time, the nitrogen-containing gas 5 supplied into the inner vessel 21 is not particularly limited, but it is preferable that the purity of nitrogen is high from the viewpoint of growing a high-purity group III nitride crystal. From this viewpoint, the nitrogen-containing gas 5 is preferably nitrogen gas having a purity of 99.999 mol% or more. On the other hand, the pressurizing gas 7 supplied to the outer container 29 is not used for growing a group III nitride crystal because it is used for maintaining the pressure in the outer container 29 and is not necessarily a nitrogen-containing gas. 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.

  Next, the inside of the inner container 21 and the outer container 29 is heated using the heater 25, and the temperature inside the inner container 21 is set to 700 ° C. or higher and 900 ° C. or lower (heating sub-step). By such heating, the solvent 3 containing the group III metal, the alkali metal, and the metal that reduces the crystal growth rate of the group III nitride crystal disposed in the inner container 21 is changed from a solid to a liquid (melt). The main surface 1m is covered, and the nitrogen-containing gas 5 is dissolved in the solvent 3 (melt). In this way, a solution in which the nitrogen-containing gas 5 is dissolved in the solvent 3 containing the group III metal, the alkali metal, and the metal that reduces the crystal growth rate of the group III nitride crystal on the main surface 1m of the base substrate 1 is obtained. Can be contacted. Here, the heater 25 is not particularly limited as long as it is suitable for heating the inside of the inner container 21 and the outer container 29. However, from the viewpoint of easy control of the temperature distribution inside the inner container and the outer container, the heater 25 is resistant. A heating system is preferably used.

  During the heating sub-process, the nitrogen-containing gas 5 is further supplied to the inner container 21 so that the inner pressure of the inner container 21 becomes larger than the inner pressure of the outer container 29 in the range of 0.01 MPa to 0.1 MPa. . That is, 0.01 MPa ≦ {(inner pressure of inner container) − (inner pressure of 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.

  Next, the supply amount and heating amount of the nitrogen-containing gas 5 to the inner container 21 are adjusted, and the temperature of the entire inner container 21 is maintained at 700 ° C. or higher and 900 ° C. or lower (crystal growth temperature). The group III nitride crystal 10 is grown for a predetermined time on the main surface 10 m of the base substrate 1 at an internal pressure of 0.5 MPa to 5 MPa (crystal growth pressure) (crystal growth sub-step). At this time, the supply amount of the pressurizing gas 7 to the outer container 29 is adjusted so that the inner pressure of the outer container 29 becomes smaller than the inner pressure of the inner container 21 in the range of 0.01 MPa to 0.1 MPa. . That is, during the crystal growth, as in the heating, 0.01 MPa ≦ {(internal pressure of the inner container) − (internal pressure of the outer container)} ≦ 0.1 MPa.

  Next, while maintaining the relationship of 0.01 MPa ≦ {(inner pressure of inner container) − (inner pressure of outer container)} ≦ 0.1 MPa, the inside of each of inner container 21 and outer container 29 is cooled and reduced in pressure. Then, the group III nitride crystal 10 grown on the base substrate 1 is taken out from the crystal growth vessel 23 of the inner vessel 21 (crystal removal sub-step).

  The group III nitride crystal obtained by the growth method of this embodiment can be processed and used as a semiconductor device substrate. However, the growth method of this embodiment is not advantageous for obtaining a thick group III nitride crystal because the growth rate of the crystal is low. Therefore, the thickness obtained by using a growth method (for example, HVPE method) having a high crystal growth rate on the group III nitride crystal substrate obtained by processing the group III nitride crystal obtained by the growth method of the present embodiment. It is advantageous to process a thick group III nitride crystal to produce a large number of semiconductor device substrates.

Example 1
1. Preparation of GaN Substrate Referring to FIGS. 1 to 2, as a base substrate 1, a main surface 1 m produced by the HVPE method has a (0001) Ga atom surface, a diameter of 2 inches (50.8 mm), and a self-supporting thickness of 500 μm. GaN substrate was prepared (substrate preparation step). The average dislocation density at 1 m of the main surface of the GaN substrate was determined by measuring the number of pits (etch pit density) per unit area that appeared when the main surface of the substrate was etched with HCl gas using a differential interference microscope. × 10 ⁵ cm ^-2 Here, in the measurement of the average dislocation density, the dislocation density in a 100 μm × 100 μm square area of the main surface 1 m of the GaN substrate was measured at 81 locations on a lattice point with a pitch of 5 mm, and the average was calculated. Such a measurement method of the average dislocation density is also called an EPD (etch pit density) measurement method.

2. 2. Growth of GaN crystal Referring to FIG. 2, each of the above GaN substrates (underlying substrate 1) is an alumina crucible (crystal growth vessel 23 having an inner diameter of 60 mm and a depth of 20 mm with its flat main surface 1 m facing upward. (Substrate placement sub-process). Next, in a crucible (crystal growth vessel 23) made of Al ₂ O ₃ on which a GaN substrate (underlying substrate 1) is disposed, metal Ga having a purity of 99.9999 mol%, metal Na having a purity of 99.99 mol%, A metal Au (solvent 3) having a purity of 99.99 mol% is obtained, and the molar ratio of metal Ga (group III metal M _III ) to metal Na (alkali metal M _A ) is M _III : M _A = 3: 7 Ratio in which the percentage of the number of moles of metal Au (metal M _M that reduces the crystal growth rate) is 5 mol% with respect to the total number of moles of Ga (group III metal M _III ) and metal Na (alkali metal M _A ) The amount of the depth from the surface of the solvent 3 (Ga—Na—Au melt) when melted to the main surface 1 m of the GaN substrate (underlying substrate 1) was 5 mm.

Next, a GaN substrate (underlying substrate 1) and an Al ₂ O ₃ crucible (crystal growth vessel 23) containing metal Ga, metal Na and metal Au (solvent 3) were placed in the inner vessel 21. An Al ₂ O ₃ lid 24 was placed on the Al ₂ O ₃ crucible (crystal growth vessel 23) (crystal growth vessel placement sub-step).

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

  Next, the nitrogen-containing gas 5 and the pressurizing gas 7 were supplied into the inner container 21 and the outer container 29 so that the inner pressure of each container was 1 MPa (nitrogen-containing gas supply sub-step). At this time, high purity nitrogen gas having a purity of 99.99999 mol% was used as the nitrogen-containing 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, the inside of the inner container 21 and the outer container 29 was heated using the resistance heating type heater 25, and the temperature inside the inner container 21 was set to 850 ° C. (heating sub-process). By this heating, the metal Ga, metal Na, and metal Au (solvent 3) disposed in the inner container 21 are liquefied to cover the main surface 1m of the GaN substrate (underlying substrate 1), and this liquefied metal Ga, metal Na And high purity nitrogen gas (nitrogen-containing gas 5) dissolves in metal Au, that is, Ga—Na—Au melt (solvent 3). In this way, the main surface 1m of the GaN substrate (underlying substrate 1) is brought into contact with a solution in which a high-purity nitrogen gas (nitrogen-containing gas 5) is dissolved in a Ga—Na—Au melt (solvent 3). I was able to. During heating, high-purity nitrogen gas (nitrogen-containing gas 5) is further supplied to the inner container 21 so that the inner pressure of the inner container 21 is in the range of 0.01 MPa to 0.1 MPa as compared with the inner pressure of the outer container 29. I tried to get bigger. That is, 0.01 MPa ≦ {(internal pressure of the inner container) − (internal pressure of the outer container)} ≦ 0.1 MPa.

  Next, the supply amount and heating amount of the nitrogen-containing gas 5 to the inner container 21 are adjusted, and the inner pressure of the inner container 21 is set to 3 MPa (3 MPa) while maintaining the temperature inside the inner container 21 at 850 ° C. (crystal growth temperature). As the crystal growth pressure, a GaN crystal (Group III nitride crystal 10) was grown on the main surface 10m of the GaN substrate (underlying substrate 1) for 360 hours (crystal growth sub-step). At this time, the supply amount of nitrogen gas (pressurizing gas 7) to the outer container 29 is adjusted so that the internal pressure of the outer container 29 is smaller than the internal pressure of the inner container 21 in the range of 0.01 MPa to 0.1 MPa. It was made to become. That is, during the crystal growth, as in the heating, 0.01 MPa ≦ {(inner pressure in the inner container) − (inner pressure in the outer container)} ≦ 0.1 MPa.

  Next, while maintaining the relationship of 0.01 MPa ≦ {(inner pressure of inner container) − (inner pressure of outer container)} ≦ 0.1 MPa, the inside of each of inner container 21 and outer container 29 is cooled and reduced in pressure. The GaN crystal (Group III) grown on the GaN substrate (underlying substrate 1) from the Ga—Na—Au melt (solvent 3) in the BN crucible (crystal growth vessel 23) of the inner vessel 21 cooled to 30 ° C. The nitride crystal 10) was taken out with tweezers (crystal removal sub-step). The thickness of the obtained GaN crystal was 180 μm. That is, the growth rate of the GaN crystal was 0.5 μm / hr.

The average dislocation density in the plane 10t having a crystal growth thickness T of 100 μm of the GaN crystal (Group III nitride crystal 10) obtained as described above was measured by the same EPD measurement method as described above, and was 5 × 10 5. a ⁵ cm ^-2, this value is equivalent to the average dislocation density of ⁵ × 10 5 cm ^-2 in the main surface of the substrate, the growth of the dislocation is suppressed during growth of a group III nitride crystal. The results are summarized in Table 1.

(Comparative Example 1)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 1 except that the solvent 3 did not contain a metal that reduces the crystal growth rate. The thickness of the obtained GaN crystal was 1800 μm. That is, the growth rate of the GaN crystal was 5.0 μm / hr. The average dislocation density in the plane 10t of the GaN crystal (group III nitride crystal 10) having a crystal growth thickness T of 100 μm is 8 × 10 ⁶ cm ⁻² , and this value is the average dislocation density 5 × in the main surface of the substrate. Much larger than 10 ⁵ cm ⁻² , dislocations grew in the group III nitride crystals.

(Example 2)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 1 except that metal Ag was used as the metal for reducing the crystal growth rate. The thickness of the obtained GaN crystal was 144 μm. That is, the growth rate of the GaN crystal was 0.4 μm / hr. The average dislocation density in the plane 10t of the GaN crystal (group III nitride crystal 10) having a crystal growth thickness T of 100 μm is 5 × 10 ⁵ cm ⁻² , and this value is the average dislocation density 5 × in the main surface of the substrate. This is equivalent to 10 ⁵ cm ^−2, and the growth of dislocations was suppressed during the growth of the group III nitride crystal. The results are summarized in Table 1.

(Example 3)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 1 except that metal Cu was used as the metal for reducing the crystal growth rate. The thickness of the obtained GaN crystal was 108 μm. That is, the growth rate of the GaN crystal was 0.3 μm / hr. The average dislocation density in the plane 10t of the GaN crystal (group III nitride crystal 10) having a crystal growth thickness T of 100 μm is 5 × 10 ⁵ cm ⁻² , and this value is the average dislocation density 5 × in the main surface of the substrate. This is equivalent to 10 ⁵ cm ^−2, and the growth of dislocations was suppressed during the growth of the group III nitride crystal. The results are summarized in Table 1.

Example 4
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 1 except that metal Pt was used as the metal for reducing the crystal growth rate. The thickness of the obtained GaN crystal was 180 μm. That is, the growth rate of the GaN crystal was 0.5 μm / hr. The average dislocation density in the plane 10t of the GaN crystal (group III nitride crystal 10) having a crystal growth thickness T of 100 μm is 5 × 10 ⁵ cm ⁻² , and this value is the average dislocation density 5 × in the main surface of the substrate. This is equivalent to 10 ⁵ cm ^−2, and the growth of dislocations was suppressed during the growth of the group III nitride crystal. The results are summarized in Table 1.

(Example 5)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 1 except that metal In was used as the metal for reducing the crystal growth rate. The thickness of the obtained GaN crystal was 72 μm. That is, the growth rate of the GaN crystal was 0.2 μm / hr. The average dislocation density in the plane 10t of the GaN crystal (group III nitride crystal 10) having a crystal growth thickness T of 50 μm is 5 × 10 ⁵ cm ⁻² , and this value is the average dislocation density 5 × in the main surface of the substrate. This is equivalent to 10 ⁵ cm ^−2, and the growth of dislocations was suppressed during the growth of the group III nitride crystal. The results are summarized in Table 1.

(Example 6)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 1 except that metal Sn was used as the metal for reducing the crystal growth rate. The thickness of the obtained GaN crystal was 180 μm. That is, the growth rate of the GaN crystal was 0.5 μm / hr. The average dislocation density in the plane 10t of the GaN crystal (group III nitride crystal 10) having a crystal growth thickness T of 100 μm is 8 × 10 ⁵ cm ⁻² , and this value is the average dislocation density 5 × in the main surface of the substrate. Although it increased slightly compared with 10 ⁵ cm ⁻² , the growth of dislocations was considerably suppressed during the growth of the group III nitride crystal. The results are summarized in Table 1.

(Example 7)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 1 except that metal Pb was used as the metal for reducing the crystal growth rate. The thickness of the obtained GaN crystal was 180 μm. That is, the growth rate of the GaN crystal was 0.5 μm / hr. The average dislocation density in the plane 10t of the GaN crystal (group III nitride crystal 10) having a crystal growth thickness T of 100 μm is 9 × 10 ⁵ cm ⁻² , and this value is the average dislocation density 5 × in the main surface of the substrate. Although it increased slightly compared with 10 ⁵ cm ⁻² , the growth of dislocations was considerably suppressed during the growth of the group III nitride crystal. The results are summarized in Table 1.

(Example 8)
A GaN crystal (Group III nitride crystal 10) was grown in the same manner as in Example 1 except that metal Bi was used as the metal for reducing the crystal growth rate. The thickness of the obtained GaN crystal was 144 μm. That is, the growth rate of the GaN crystal was 0.4 μm / hr. The average dislocation density in the plane 10t of the GaN crystal (group III nitride crystal 10) having a crystal growth thickness T of 100 μm is 7 × 10 ⁵ cm ⁻² , and this value is the average dislocation density 5 × in the main surface of the substrate. Although it increased slightly compared with 10 ⁵ cm ⁻² , the growth of dislocations was considerably suppressed during the growth of the group III nitride crystal. The results are summarized in Table 1.

  Referring to Table 1, the main surface of the base substrate is brought into contact with a solution in which a nitrogen-containing gas is dissolved in a solvent containing a group III metal, an alkali metal, and a metal that reduces the crystal growth rate of the group III nitride crystal. Thus, by growing a group III nitride crystal on the main surface, it becomes possible to grow a group III nitride crystal while suppressing the growth of dislocations, and a group III nitride crystal having a low average dislocation density is obtained. It was.

  In addition, the GaN crystals obtained in Examples 6 to 8 were slightly uneven as compared to the GaN crystals obtained in Examples 1 to 5, and the flatness was impaired. It was. The difference in the morphology of the crystal growth surface may have influenced the difference in the average dislocation density.

  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.

It is a schematic sectional drawing which shows one Embodiment of the growth method and growth apparatus of the group III nitride crystal concerning this invention. It is the schematic sectional drawing to which the II part of FIG. 1 was expanded.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Base substrate, 1a Group III nitride seed crystal, 1b Base substrate, 1m main surface, 3 Solvent, 5 Nitrogen-containing gas, 7 Gas for pressurization, 10 Group III nitride crystal, 10 g Crystal growth surface, 10t plane, 21 inner container , 23 Crystal growth vessel, 24 lid, 25 heater, 27 heat insulating material, 29 outer vessel, 31 nitrogen-containing gas supply device, 33 pressurization gas supply device, 35 vacuum exhaust device, 41 first piping, 41a inner vessel from valve Side part, 41b valve side nitrogen-containing gas supply side part, 41p, 43p pressure gauge, 41v, 43v, 45v, 47v valve, 43 second piping, 43a, 45a valve side part, outer container side part, 43b valve A portion closer to the pressurizing gas supply device, 45 third piping, a portion closer to the vacuum exhaust device than the 45b valve, 47 a fourth piping.

Claims (7)

A method for growing a group III nitride crystal by a liquid phase method,
Preparing a base substrate;
Contacting the main surface of the base substrate with a solution in which a nitrogen-containing gas is dissolved in a solvent containing a group III metal, an alkali metal, and a metal that reduces the crystal growth rate of the group III nitride crystal; Growing a group III nitride crystal thereon, a method for growing a group III nitride crystal.   2. The method for growing a group III nitride crystal according to claim 1, wherein a crystal growth rate of the group III nitride crystal is less than a critical crystal growth rate at which dislocations of the group III nitride crystal start to grow.   The method for growing a group III nitride crystal according to claim 1 or 2, wherein the alkali metal includes at least one of Na and Li.   The method for growing a group III nitride crystal according to any one of claims 1 to 3, wherein the group III nitride crystal is a GaN crystal.   The metal for reducing the crystal growth rate of the group III nitride crystal includes at least one metal selected from the group consisting of transition metals, Ge, Sn, Pb, and Bi. 3. A method for growing a group III nitride crystal according to 1.   The method for growing a group III nitride crystal according to claim 4, wherein the metal that reduces the crystal growth rate of the GaN crystal contains In.   The method for growing a group III nitride crystal according to any one of claims 1 to 6, wherein a crystal growth rate of the group III nitride crystal is 0.05 µm / hr or more and 2 µm / hr or less.

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