JP5333374B2 - GaN crystal manufacturing method, GaN crystal substrate, and group III nitride semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a group III nitride crystal, a group III nitride crystal substrate and a group III nitride semiconductor device with low dislocation density and low impurity concentration. <P>SOLUTION: The method for manufacturing the group III nitride crystal includes steps of: growing a first group III nitride crystal 10 by a liquid phase method using a liquid 2 for crystal growth, the liquid containing a group III element and a solvent containing at least one kind of metal element; heat-treating the first group III nitride crystal 10 in a liquid 4 for crystal treatment containing at least one kind of metal element; and growing a second group III nitride crystal 20 by a vapor phase method on the heat-treated first group III nitride crystal 10. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

The present invention relates to a GaN crystal manufacturing method, a GaN crystal substrate, and a group III nitride semiconductor device. Such GaN crystals, GaN crystal substrates, and group III nitride semiconductor devices are preferably used for various semiconductor devices such as light-emitting elements, electronic elements, and semiconductor sensors.

  In order to obtain a group III nitride crystal substrate having a low dislocation density and a low production cost, in Japanese Patent Application Laid-Open No. 2005-236261 (hereinafter referred to as Patent Document 1), a first group III is formed on a base substrate by a liquid phase method. A method for producing a group III nitride crystal comprising a step of growing a nitride crystal and a step of growing a second group III nitride crystal on the first group III nitride crystal by a vapor phase method is proposed. Yes.

  According to the manufacturing method according to Patent Document 1, whether the dislocation density of the group III nitride crystal grown by the vapor phase method is low and the surface becomes flat (in the case of growth by metal organic chemical vapor deposition method). ) Or the crystal growth rate is high (in the case of growth by hydride vapor phase epitaxy), a low dislocation density group III nitride crystal can be produced at low cost.

JP 2005-236261 A

  However, irregularities may exist in the crystal or the crystal surface of the first group III nitride crystal grown by a liquid phase method such as a flux method, and impurities incorporated during crystal growth (for example, Li Etc.) may exist. When the second group III nitride crystal is grown on the first group III nitride crystal by a vapor phase method, the second group III nitride crystal may be significantly warped or impurities may be generated. Or spread. A group III nitride crystal substrate useful for various semiconductor devices cannot be produced from a group III nitride crystal in which significant warpage has occurred. Depending on the type of impurities, the impurities contained in the group III nitride crystal may deteriorate the optical, electrical and / or mechanical properties of the group III nitride crystal and the substrate obtained by processing the group III nitride crystal. Let

Accordingly, the present invention is to solve the above problems, the dislocation density is low, warping is small, and a method for producing a concentration of the impurity is low GaN crystal, to provide a GaN crystal substrate and the Group III nitride semiconductor device With the goal.

The present invention includes a step of growing a first GaN crystal by a liquid phase method, a step of processing the surface of the first GaN crystal so that the surface roughness Ra is 5 nm or less and the curvature radius of warpage is 2 m or more. a method for producing a GaN crystal and a step of growing a second GaN crystal by a vapor phase method on the first GaN on the crystal machining is.

The present invention also provides a GaN crystal substrate including the first or second GaN crystal obtained by the above manufacturing method.

The present invention is also a group III nitride semiconductor device including the above GaN crystal substrate, wherein at least one group III nitride semiconductor layer is formed on the GaN crystal substrate. is there.

According to the present invention, dislocation density is low, warping is small, and a method for producing a concentration of the impurity is low a GaN crystal, it is possible to provide a GaN crystal substrate and the Group III nitride semiconductor device.

It is a schematic sectional drawing which shows one form used as a reference regarding the manufacturing method of the group III nitride crystal concerning this invention. Here, (a) is a step of growing a first group III nitride crystal by a liquid phase method, (b) is a step of heat-treating the first group III nitride crystal, and (c) is a vapor phase method. (D) shows a step of producing a group III nitride crystal substrate. It is a schematic sectional drawing which shows one Embodiment of the manufacturing method of the group III nitride crystal concerning this invention. Here, (a) shows the step of growing the first group III nitride crystal by the liquid phase method, (b) shows the step of processing the surface of the first group III nitride crystal, and (c) shows the step of processing. (D) shows the process of producing a group III nitride crystal substrate, the process of growing the 2nd group III nitride crystal by a phase method. It is a schematic sectional drawing which shows other embodiment of the manufacturing method of the group III nitride crystal concerning this invention. Here, (a) is a step of growing a first group III nitride crystal by a liquid phase method, and (b) is a step of removing at least a part of the surface side region of the first group III nitride crystal. (C) shows a step of growing a second group III nitride crystal by a vapor phase method, and (d) shows a step of producing a group III nitride crystal substrate. It is a schematic sectional drawing which shows other embodiment of the manufacturing method of the group III nitride crystal concerning this invention. Here, (a) is a step of growing a first group III nitride crystal by a liquid phase method, (b) is a step of growing a second group III nitride crystal by a vapor phase method, (c) Indicates a step of producing a group III nitride crystal substrate. It is a schematic sectional drawing which shows other embodiment of the manufacturing method of the group III nitride crystal concerning this invention. Here, (a) is a step of growing a first group III nitride crystal by a liquid phase method, (b) is a step of growing a second group III nitride crystal by a vapor phase method, (c) Is a step of removing at least part of the surface side region of the second group III nitride crystal, (d) is a step of growing a third group III nitride crystal by a vapor phase method, and (e) is a step of growing III The process of producing a group nitride crystal substrate is shown. It is a schematic sectional drawing which shows other embodiment of the manufacturing method of the group III nitride crystal concerning this invention. Here, (a) is a step of growing a first group III nitride crystal by a liquid phase method, (b) is a step of slicing the first group III nitride crystal, (c1) and (c2) Shows a step of growing a second group III nitride crystal, and (d1) and (d2) show a step of producing a group III nitride crystal substrate. It is a schematic sectional drawing which shows one Embodiment of the base substrate used in this invention. It is a schematic sectional drawing which shows other embodiment of the manufacturing method of the group III nitride crystal concerning this invention. Here, (a) is a step of growing a first group III nitride crystal by a liquid phase method, (b) is a step of growing a second group III nitride crystal by a vapor phase method, (c) Indicates a step of producing a group III nitride crystal substrate. It is a schematic sectional drawing which shows one Embodiment of the semiconductor device concerning this invention. In Comparative Example 2, it is a schematic cross-sectional view showing a strain region generated in a group III nitride crystal. Here, (a) is a step of growing a first group III nitride crystal by a liquid phase method, and (b) to (d) are steps of growing a second group III nitride crystal by a vapor phase method. Show. In Example 11, it is a top view which shows the mask layer formed on the GaAs substrate. In Example 11, it is a top view which shows the mode of the GaN crystal layer which grows on the GaAs substrate in which the mask layer was formed. In Example 11, it is a top view which shows the mode of the GaN layer grown on the whole surface on the GaAs substrate in which the mask layer was formed. In Example 11, it is a schematic sectional drawing which shows the method of manufacturing a GaN crystal base substrate. Here, (a) is a step of forming a mask layer on a GaAs substrate, (b) is a step of forming a GaN buffer layer, (c) and (d) are steps of growing a GaN crystal, (e ) Shows a step of forming a GaN crystal base substrate. In Example 12, it is a schematic sectional drawing which shows the method of manufacturing a GaN crystal base substrate. Here, (a) and (b) are a step of forming a GaN layer on a sapphire substrate, (c) is a step of forming a mask on the GaN layer, (d) is a step of growing a GaN crystal, (E) shows the process of producing a GaN crystal base substrate.

(Reference form 1)
Referring to FIG. 1, one embodiment which is a reference regarding the method for producing a group III nitride crystal according to the present invention is a solvent containing at least one metal element by a liquid phase method as shown in FIG. And a step of growing the first group III nitride crystal 10 using the crystal growth liquid 2 containing a group III element and at least one of the above metal elements as shown in FIG. A step of heat-treating the first group III nitride crystal 10 in the crystal processing liquid 4 and a vapor phase method on the first group III nitride crystal 10 that has been heat-treated as shown in FIG. Growing a second group III nitride crystal 20.

  The liquid phase method used in Reference Form 1 is not particularly limited as long as it is a liquid phase method using a solvent, and Ga in the Ga melt using a Ga melt (group III element melt) as a main solvent. A solution growth method in which a group III element) and N (nitrogen) dissolved in a Ga melt are reacted, and a melt in which a GaN (group III nitride) raw material is melted at high temperature and high pressure and then cooled to grow a crystal. Compared with the growth method, using a melt containing at least one kind of metal element as a group III element and its solvent, a group III element in the melt and N (nitrogen) dissolved in the melt at high temperature and high pressure Is preferable from the viewpoint that a group III nitride crystal having a low dislocation density can be grown at a relatively high speed in the liquid phase method, that is, can be produced at a relatively low cost. Here, the solvent used in the flux method is called a flux. In such a flux method, a crystal growth melt containing a group III element that is a raw material of a group III nitride crystal and at least one metal element that is a flux thereof is used as the crystal growth liquid.

  When the flux method is used as the liquid phase method, as shown in FIG. 1 (a), the Group III nitride crystal manufacturing method of the present embodiment has at least one group III element and a flux of the Group III element. A step of growing a first group III nitride crystal 10 by a liquid phase method using a crystal growth melt (crystal growth liquid 2) containing a metal element of the above, as shown in FIG. A step of heat-treating the first group III nitride crystal 10 in a crystal-treating melt (crystal-treating liquid 4) containing at least one of the above metal elements, and heat treatment as shown in FIG. And growing a second group III nitride crystal 20 on the first group III nitride crystal 10 by a vapor phase method.

  Here, with reference to FIG. 1A, the flux method refers to at least one group III element and flux at a temperature of about 600 ° C. to 1400 ° C. and a pressure of about 0.1 MPa to 10 MPa. The first group III nitride crystal 10 is grown by dissolving the nitrogen-containing gas 3 in a crystal growth melt (crystal growth liquid 2) containing a metal element. As the flux, at least one metal element is not particularly limited, but is preferably at least one metal element selected from the group consisting of alkali metal elements, alkaline earth metals, and transition metal elements. For example, when the group III element is Ga, alkali metal elements such as Na (sodium) and Li (lithium), such as alkaline earth metal elements such as Ca (calcium), are preferably used. When the group III element is Al, transition metal elements such as Cu (copper), Ti (titanium), Fe (iron), Mn (manganese), and Cr (chromium) are preferably used.

  Heat-treating the first group III nitride crystal 10 having a large amount of impurities grown in the crystal growth melt (crystal growth liquid 2) by the liquid phase method (for example, flux method) in the crystal processing liquid 4 Thus, impurities in the first group III nitride crystal 10 and on the surface are released into the crystal processing liquid 4 and removed. Here, in the flux method, as the crystal processing liquid 4, a crystal processing melt containing at least one metal element contained in the crystal growth melt is used. Thus, the first group III nitride crystal having a low impurity concentration is obtained. By growing the second group III nitride crystal by the vapor phase method on the first group III nitride crystal with the reduced impurity concentration, the dislocation density is low, the warp is small, and the impurity concentration Is obtained (ie, high purity) second group III nitride crystal.

  Here, in the heat treatment of the first group III nitride crystal, the nitrogen-containing gas 3 is supplied to the crystal processing melt (crystal processing liquid 4) in order to suppress the decomposition and breakage of the crystal. preferable. The partial pressure of the nitrogen-containing gas 3 (that is, the heat treatment pressure of the crystal) is preferably 0.1 MPa or more. If it is lower than 0.1 MPa, the decomposition and / or breakage of the first group III nitride crystal tends to proceed.

  The heat treatment temperature of the first group III nitride crystal is preferably 600 ° C. or higher and 1600 ° C. or lower. When the temperature is lower than 600 ° C., the diffusion of impurities is slow, and it is difficult to remove the impurities from the first group III nitride crystal. When the temperature is higher than 1600 ° C., the decomposition and / or breakage of the first group III nitride crystal is difficult. Is easy to proceed. The heat treatment time for the first group III nitride crystal is preferably 5 hours or more and 500 hours or less. If it is shorter than 5 hours, it is difficult to remove impurities from the first group III nitride crystal, and if it is longer than 500 hours, the first group III nitride crystal is likely to be decomposed and / or broken.

  Further, when a GaN crystal is grown as the first group III nitride crystal 10 by the flux method, Na and Li are used as the flux of the crystal growth melt (crystal growth liquid 2) from the viewpoint of promoting crystal growth. Is included. Such Na and Li are taken into the first GaN crystal and the surface together with other impurities. Of the impurities incorporated into the first GaN crystal, Li in particular tends to diffuse into the crystal, causing a problem of reducing the electrical characteristics of the GaN crystal. Here, by heat-treating the first GaN crystal in the crystal processing liquid 4 that does not contain Li and contains Na in the flux used in the first GaN crystal growth step, Li in the crystal and on the surface is reduced. Can be removed. That is, in the liquid phase method (for example, flux method), the first group III nitridation in which the crystal growth liquid is grown in the crystal growth liquid (crystal growth melt) containing Li as a solvent (for example, flux) By subjecting the product crystal to heat treatment in a crystal processing liquid not containing Li (crystal processing melt), Li in the crystal and on the surface can be removed.

(Reference form 2)
Referring to FIG. 1, another embodiment to be referred to for the method for producing a group III nitride crystal according to the present invention contains at least one metal element by a liquid phase method as shown in FIG. A step of growing a first group III nitride crystal 10 using a crystal growth liquid 2 containing a solvent and a group III element, and at least one of the above metal elements as shown in FIG. A step of heat-treating the first group III nitride crystal 10 in the crystal processing liquid 4 containing a group III element, and the first group III nitride crystal 10 that has been heat-treated as shown in FIG. And a step of growing the second group III nitride crystal 20 thereon by a vapor phase method. The liquid phase method used in the present embodiment is not particularly limited as long as it is a liquid phase method using a solvent, but a group III nitride crystal having a low dislocation density is grown at a relatively high speed in the liquid phase method. It is preferable to use the flux method from the viewpoint that it can be manufactured, that is, manufactured at a relatively low cost.

  When the flux method is used as the liquid phase method, as shown in FIG. 1 (a), the Group III nitride crystal manufacturing method of the present embodiment has at least one group III element and a flux of the Group III element. A step of growing a first group III nitride crystal 10 by a liquid phase method using a crystal growth melt (crystal growth liquid 2) containing a metal element of the above, as shown in FIG. A step of heat-treating the first group III nitride crystal 10 in a crystal processing melt (crystal processing liquid 4) containing at least one of the above metal elements and a group III element, as shown in FIG. Growing the second group III nitride crystal 20 by the vapor phase method on the first group III nitride crystal 10 that has been heat-treated in this manner.

  That is, the crystal processing liquid (crystal processing melt) used in Reference Embodiment 1 includes at least one metal element contained in the solvent (flux) of the crystal growth liquid (crystal growth melt). On the other hand, the crystal processing liquid (crystal processing melt) used in Reference Embodiment 2 includes at least one metal element contained in the solvent (flux) of the crystal growth liquid (crystal growth melt). It is characterized by the inclusion of group III elements in addition to the types.

  In Reference Form 2, since the crystal processing liquid 4 (crystal processing melt) contains at least one metal element and group III element contained in the crystal growth liquid, the first group III The nitride crystal can be heat-treated in an environment close to thermochemical equilibrium, and the decomposition and / or breakage of the crystal during the heat treatment can be further suppressed.

  As in the case of Reference Mode 1, it is preferable to supply the nitrogen-containing gas 3 to the crystal processing liquid 4 during the heat treatment of the first group III nitride crystal, and the partial pressure of the nitrogen-containing gas 3 is The heat treatment temperature of the first group III nitride crystal is preferably 600 ° C. to 1600 ° C., and the heat treatment time of the first group III nitride crystal is 5 It is preferable that the time is not less than 500 hours.

  For example, when a GaN crystal is grown as the first group III nitride crystal 10 by the flux method, from the viewpoint of promoting crystal growth, the crystal growth liquid 2 is composed of a flux containing Na and Li and a group III element. A crystal growth melt containing Ga is used. Such Na and Li are taken into the first GaN crystal and the surface together with other impurities. Of the impurities incorporated into the first GaN crystal, especially Li has a problem of deteriorating the electrical characteristics of the GaN crystal. Here, the first GaN crystal is heat-treated in a crystal processing melt (crystal processing liquid 4) containing Ga, which is a group III element, in addition to a flux that does not contain Li and contains Na. While suppressing decomposition and / or breakage of Li, Li in the crystal and on the surface can be removed. That is, in a liquid phase method (eg, flux method), a first group III nitride crystal grown in a crystal growth liquid (crystal growth melt) containing Li as a solvent (eg, flux) is converted into Li Li in the crystal and on the surface can be removed by heat treatment in a crystal processing liquid that does not contain (a crystal processing melt).

(Embodiment 1)
Referring to FIG. 2, in one embodiment of the method for producing a group III nitride crystal according to the present invention, a first group III nitride crystal 10 is grown by a liquid phase method as shown in FIG. A step of processing the surface of the first group III nitride crystal 10 as shown in FIG. 2B so that the surface roughness Ra is 5 nm or less and the curvature radius of warpage is 2 m or more; 2 (c), growing a second group III nitride crystal by a vapor phase method on the first group III nitride crystal processed.

  The liquid phase method in the present embodiment is not particularly limited, and a Ga melt (group III element melt) is used as a main solvent and dissolved in Ga (group III element) and the Ga melt. In addition, a solution growth method in which N (nitrogen) is reacted, a melt growth method in which a GaN (Group III nitride) raw material is melted at a high temperature and a high pressure and then cooled to grow a crystal, and Ga (Group III) in supercritical ammonia. Elemental) or Ga (Group III element) compound may be present, and an athermal synthesis method for growing GaN (Group III nitride crystal) may be used. However, compared to these methods, a group III element and a melt containing at least one metal element as its solvent are used, and a group III element in the melt and N (nitrogen) dissolved in the melt are used. Is preferable from the viewpoint that a group III nitride crystal having a low dislocation density can be grown at a relatively high speed in the liquid phase method, that is, can be produced at a relatively low cost.

  In the growth of the first group III nitride crystal by the liquid phase method such as the flux method, it is difficult to grow the crystal while maintaining the thermodynamic quasi-equilibrium state completely. Large irregularities may remain on the surface. When large irregularities exist on the surface, the growth of the second group III nitride crystal by the vapor phase method takes over the growth of the first group III nitride crystal, and crystal growth planes with various plane orientations appear. It's easy to do. Due to this difference in plane orientation, the impurity incorporation efficiency differs, so that the impurity distribution in the crystal and on the crystal surface tends to be nonuniform in the growth of the second group III nitride crystal. Further, when the second group III nitride crystal is grown on the first group III nitride crystal having large irregularities on the surface by a vapor phase method, the irregularities on the surface of the first group III nitride crystal are obtained. As a result, crystal growth surfaces with various plane orientations appear and problems such as loss of crystal homogeneity arise.

In the present embodiment, as shown in FIG. 2B, the surface of the first group III nitride crystal is processed so that the surface roughness Ra is 5 nm or less and the curvature radius of warpage is 2 m or more. By including the impurities on the crystal surface and / or impurities segregated in the surface side region can be removed. Thus, the first group III nitride crystal having a low impurity concentration is obtained. Here, the surface roughness Ra is a reference area extracted from the roughness curved surface in the direction of the average surface, and the total distance (absolute value of deviation) from the average surface of the extracted portion to the measurement curved surface is a reference area. The average value is used, and can be measured by an AFM (atomic force microscope) or the like. In the present application, the reference area is 10 μm × 10 μm. When the surface roughness Ra is larger than 5 nm or the curvature radius of warpage is less than 2 m, the unevenness of the surface of the first group III nitride crystal becomes large, and the above-mentioned problems are likely to occur. From this viewpoint, the surface roughness Ra is preferably 5 nm or less, and more preferably 3 nm or less. The curvature radius R of the warp is defined as R = D ² / 8H, assuming that at two points separated by a distance D in the substrate, the other point is higher than the other point by the height H. Is done. The curvature radius R of the warp is preferably 2 m or more, and more preferably 3 m or more.

  Here, the method of processing the surface of the first group III nitride crystal so that the surface roughness Ra is 5 nm or less and the curvature radius of curvature is 2 m or more is not particularly limited, but the surface of the crystal is flattened. It is preferable to combine a method such as grinding or polishing, which is a method for forming a film, and a method such as etching which is a method for removing a work-affected layer formed in the surface side region of the crystal by grinding and / or polishing. Here, as an etching method, a gas phase such as RIE (reactive ion etching) using chlorine gas or the like, etching using a mixed gas of hydrogen chloride gas and hydrogen gas or a mixed gas of ammonia gas and hydrogen gas, or the like. Etching is preferably used.

(Embodiment 2)
Referring to FIG. 3, in another embodiment of the method for producing a group III nitride crystal according to the present invention, a first group III nitride crystal 10 is grown by a liquid phase method as shown in FIG. A step of removing at least part of the surface-side region 10a of the first group III nitride crystal 10 as shown in FIG. 3B, and a surface-side region 10a as shown in FIG. Growing a second group III nitride crystal on the first group III nitride crystal 10 from which at least a part of the first group III nitride crystal 10 has been removed by a vapor phase method. The liquid phase method used in this embodiment is not particularly limited, but a group III nitride crystal having a low dislocation density can be grown at a relatively high speed in the liquid phase method, that is, manufactured at a relatively low cost. From the viewpoint of possible, it is preferable to use the flux method.

  In the present embodiment, as shown in FIG. 3B, at least a part of the surface-side region 10a of the first group III nitride crystal 10 is removed to segregate on the crystal surface and / or the surface-side region. Impurities can be removed. Thus, the first group III nitride crystal having a low impurity concentration is obtained.

  The method for removing at least a part of the surface-side region 10a of the first group III nitride crystal 10 is not particularly limited, but RIE (reaction using chlorine gas or the like from the viewpoint that the crystal is hardly distorted). Gas phase etching such as etching using a mixed gas of hydrogen chloride gas and hydrogen gas or a mixed gas of ammonia gas and hydrogen gas is preferably used.

(Embodiment 3)
Referring to FIG. 4, in another embodiment of the method for producing a group III nitride crystal according to the present invention, a first group III nitride crystal 10 is formed by a liquid phase method as shown in FIG. And a step of growing the second group III nitride crystal 20 to be thicker than 3500 μm on the first group III nitride crystal 10 by a vapor phase method as shown in FIG. 4B. The liquid phase method used in this embodiment is not particularly limited, but a group III nitride crystal having a low dislocation density can be grown at a relatively high speed in the liquid phase method, that is, manufactured at a relatively low cost. From the viewpoint of possible, it is preferable to use the flux method.

In the present embodiment, the first nitride crystal is grown to be thicker than 3500 μm by the vapor phase method on the first group III nitride crystal grown by the liquid phase method, for example, the flux method. The quantity per unit volume of impurities diffused from the group III nitride crystal to the second group III nitride crystal (that is, the impurity concentration, the unit is cm ⁻³ ) can be reduced, and the second impurity concentration is low. Group III nitride crystals can be grown.

(Embodiment 4)
Referring to FIG. 5, in another embodiment of the method for producing a group III nitride crystal according to the present invention, a first group III nitride crystal 10 is formed by a liquid phase method as shown in FIG. A step of growing, a step of growing the second group III nitride crystal 20 on the first group III nitride crystal 10 by a vapor phase method as shown in FIG. 5B, and FIG. A step of removing at least part of the surface-side region 20a of the second group III nitride crystal 20 as shown in FIG. 5; and a second step in which at least part of the surface-side region 20a is removed as shown in FIG. And 30 growing a third group III nitride crystal on the group III nitride crystal 20 by a vapor phase method. The liquid phase method used in the present embodiment is not particularly limited, but the flux method is preferably used from the viewpoint of producing a group III having a low dislocation density at low cost.

  When the second group III nitride crystal is grown by the vapor phase method on the first group III nitride crystal grown by the liquid phase method, for example, the flux method, the second group III nitride crystal is grown from the first group III nitride crystal. It was confirmed by SIMS (secondary ion mass spectrometry) that impurities diffused in the group III nitride crystal segregate on the surface of the second group III nitride crystal and the surface side region in the vicinity thereof. Therefore, in the present embodiment, at least a part of the surface-side region 20a of the second group III nitride crystal 20 is removed, and the second group III nitride crystal 20 after the removal is formed by a vapor phase method. By growing the third group III nitride crystal, a third group III nitride crystal having a further reduced impurity concentration can be obtained.

(Embodiment 5)
Referring to FIG. 4, in another embodiment of the method for producing a group III nitride crystal according to the present invention, a first group III nitride crystal is grown by a liquid phase method as shown in FIG. And a step of growing a second group III nitride crystal 20 on the first group III nitride crystal 10 by a vapor phase method as shown in FIG. 4B. In the method, the step of growing the second group III nitride crystal 20 includes a sub-step of growing the crystal at the first crystal growth temperature and a sub-step of growing the crystal at the second crystal growth temperature. The crystal growth temperature of 1 is lower than the second crystal growth temperature. The liquid phase method used in this embodiment is not particularly limited, but a group III nitride crystal having a low dislocation density can be grown at a relatively high speed in the liquid phase method, that is, manufactured at a relatively low cost. From the viewpoint of possible, it is preferable to use the flux method.

  When the second group III nitride crystal is grown by the vapor phase method on the first group III nitride crystal grown by the liquid phase method, for example, the flux method, the second group III nitride crystal is grown from the first group III nitride crystal. Impurities diffuse into the group III nitride crystal. In the present embodiment, by lowering the initial crystal growth temperature of the second group III nitride crystal, the impurity diffusion rate can be lowered, and the second group III nitride having a low impurity concentration. Crystals are obtained.

  Here, the first crystal growth temperature for growing the second group III nitride crystal is a temperature at which the diffusion rate of impurities can be made lower than the initial crystal growth rate of the second group III nitride crystal. If it is, there will be no restriction | limiting in particular, However, It is preferable that it is 50 degreeC or more lower than the 2nd crystal growth temperature, and it is more preferable that it is 100 degreeC or more lower. The first crystal growth temperature is preferably 800 ° C. or higher and 1100 ° C. or lower. When the first crystal growth temperature is lower than 800 ° C., the crystallinity of the growing group III nitride crystal is deteriorated. When the first crystal growth temperature is higher than 1100 ° C., the group III nitride crystal is easily decomposed during the crystal growth.

(Embodiment 6)
Referring to FIG. 4, in another embodiment of the method for producing a group III nitride crystal according to the present invention, a first group III nitride crystal 10 is formed by a liquid phase method as shown in FIG. And a step of growing a second group III nitride crystal 20 by a vapor phase method on the first group III nitride crystal 10 as shown in FIG. 4B. In the manufacturing method, the step of growing the second group III nitride crystal 20 includes a sub-step of growing the crystal at the first crystal growth rate and a sub-step of growing the crystal at the second crystal growth rate, The first crystal growth rate is higher than the second crystal growth rate. The liquid phase method used in this embodiment is not particularly limited, but a group III nitride crystal having a low dislocation density can be grown at a relatively high speed in the liquid phase method, that is, manufactured at a relatively low cost. From the viewpoint of possible, it is preferable to use the flux method.

  When the second group III nitride crystal is grown by the vapor phase method on the first group III nitride crystal grown by the liquid phase method, for example, the flux method, the second group III nitride crystal is grown from the first group III nitride crystal. Impurities diffuse into the group III nitride crystal. In the present embodiment, the second group III nitride crystal having a low impurity concentration is obtained by increasing the initial crystal growth rate of the second group III nitride crystal.

  Here, when growing the second group III nitride crystal, the first crystal growth rate is not particularly limited as long as the crystal growth rate can be sufficiently higher than the impurity diffusion rate. However, it is preferably 1.5 times or more, more preferably 2 or more times as large as the second crystal growth rate. Further, the first crystal growth rate is preferably 100 μm / hr or more and 1000 μm / hr or less. If the first crystal growth rate is less than 100 μm / hr, the effect of suppressing the diffusion of impurities is reduced, and if it is greater than 1000 μm / hr, abnormal crystal growth such as polycrystallization tends to occur.

  The method for increasing the growth rate of the group III nitride crystal is not particularly limited, and examples thereof include a method for increasing the partial pressure of the group III element-containing gas and / or the nitrogen-containing gas, and a method for increasing the crystal growth temperature. From the viewpoint of increasing the crystal growth rate without increasing the impurity diffusion rate, a method of increasing the partial pressure of the group III element-containing gas and / or nitrogen-containing gas is preferable.

(Embodiment 7)
Referring to FIG. 6, in another embodiment of the method for producing a group III nitride crystal according to the present invention, a first group III nitride crystal 10 is formed by a liquid phase method as shown in FIG. A group III including a step of growing, and a step of growing the second group III nitride crystal 20 on the first group III nitride crystal 10 by a vapor phase method as shown in FIG. 6 (c1) or (c2) In the method of manufacturing a nitride crystal, in the step of growing the second group III nitride crystal 20, the group III nitride crystal including the first group III nitride crystal 10 is brought into contact with the susceptor 9, 1 is characterized by diffusing impurities in the group III nitride crystal 10 into the susceptor 9. The liquid phase method used in this embodiment is not particularly limited, but a group III nitride crystal having a low dislocation density can be grown at a relatively high speed in the liquid phase method, that is, manufactured at a relatively low cost. From the viewpoint of possible, it is preferable to use the flux method.

  When the second group III nitride crystal is grown by the vapor phase method on the first group III nitride crystal grown by the liquid phase method, for example, the flux method, the III group containing the first group III nitride crystal is included. By bringing the group nitride crystal into contact with the susceptor and diffusing the impurities in the first group III nitride crystal into the susceptor, the diffusion of impurities into the second group III nitride crystal is reduced, and the impurity concentration A low second group III nitride crystal.

  6 (c1) and 6 (c2), the susceptor is a group III nitride crystal including a first group III nitride crystal for growing a second group III nitride crystal. A table to be placed. Further, the group III nitride crystal including the first group III nitride crystal includes the first group III nitride crystal 10 in addition to the first group III nitride crystal itself (see FIG. 6C2). When the base substrate 1 used for the growth of the substrate is formed of a group III nitride crystal, the base substrate 1 of the group III nitride crystal (hereinafter referred to as group III nitride) on which the first group III nitride crystal 10 is grown is used. (Also referred to as a crystal base substrate) (see FIG. 6C1). When a group III nitride crystal substrate on which a first group III nitride crystal is grown (that is, a group III nitride crystal including the first group III nitride crystal) is brought into contact with the susceptor, the first group III nitride is obtained. Impurities in the crystal and the group III nitride crystal base substrate can be diffused into the susceptor, and the impurities in the first group III nitride crystal can be reduced. Thus, the first group III nitride crystal having a low impurity concentration is obtained.

  The material of the susceptor 9 is not particularly limited as long as it has a property of diffusing impurities in the first group III nitride crystal into the susceptor. However, the material of the susceptor 9 has high heat resistance and high chemical stability. Quartz, carbon, nitride, etc. are preferable from the viewpoint of increasing the diffusion of the above, and nitride is more preferable among these. From the viewpoint of increasing the diffusion of impurities into the susceptor, the susceptor 9 is nitrided in a region in contact with the group III nitride crystal including at least the first group III nitride crystal (hereinafter referred to as crystal contact region 9c). It is preferable that it is formed of a product.

  In the method for producing a group III nitride crystal of the present embodiment, the first group III nitride crystal 10 is grown thin or thick by, for example, a flux method (see FIG. 6A).

  Next, when the first group III nitride crystal is grown thin, the first group III nitride crystal 10 is predetermined from the interface with the group III nitride crystal base substrate 1 when grown thick. The first GaN crystal (first group III nitride crystal 10) grown on the base substrate 1 is obtained by slicing in parallel with the main surface of the base substrate 1 at a plane at a distance of 6 (b)). In addition, the first GaN crystal serving as a free-standing substrate can be obtained by slicing the first group III nitride crystal grown thickly (see FIG. 6B).

  Next, the group III nitride crystal base substrate 1 (see FIG. 6 (c1)) on which the first group III nitride crystal 10 is grown or the first group III nitride crystal (see FIG. 6 (c2)) is used. ) Is brought into contact with the susceptor 9, and the second group III nitride crystal 20 is grown by the vapor phase method. By this manufacturing method, a second group III nitride crystal having a low impurity concentration can be obtained.

  In the first to seventh embodiments and the first to second embodiments, when the first group III nitride crystal is grown by the liquid phase method, the base substrate 1 is used from the viewpoint of easily obtaining a large area crystal. It is preferable. The base substrate 1 is not particularly limited as long as the first group III nitride crystal can be grown thereon, but the viewpoint of facilitating the growth of the first group III nitride crystal by the flux method. Therefore, a so-called template substrate, SiC base substrate, group III nitride crystal base substrate, etc. in which a thin group III nitride crystal is formed on a different base substrate such as a sapphire base substrate is preferable. A crystal base substrate is particularly preferred.

  Therefore, in the step of growing the first Group III nitride crystal in Embodiments 1 to 7 and Reference Embodiments 1 and 2, referring to FIG. 7, at least part of crystal growth surface side region 1g is Group III. It is preferable to use the base substrate 1 formed of a nitride crystal. By using such a base substrate, the growth of the first group III nitride crystal by the liquid phase method is facilitated.

  Further, in the step of growing the first group III nitride crystal in the first to seventh embodiments and the first and second embodiments, the group III nitride crystal is grown on the GaAs substrate by a vapor phase method. It is preferable to use a base substrate (group III nitride crystal base substrate). Such a group III nitride crystal base substrate has a small difference in thermal expansion coefficient from that of the GaAs substrate, so that the strain and dislocation density in the crystal are low, the warp is small, the quality is high, and the first group III by the liquid phase method is used. It is suitable as a base substrate for nitride crystal growth. Further, in the step of growing the second group III nitride crystal by the vapor phase method on the first group III nitride crystal grown by the liquid phase method, the impurities in the first group III nitride crystal are changed to III. Diffusion into the group nitride crystal base substrate can reduce the diffusion of impurities from the first group III nitride into the second group III nitride crystal.

Here, the dislocation density of the group III nitride crystal base substrate grown on the GaAs substrate by a vapor phase method is 5 × 10 ⁶ cm ⁻ from the viewpoint of growing the first group III nitride crystal having a low dislocation density. It is preferably ² or less. The dislocation density can be obtained by TEM (transmission electron microscope) analysis or etch pit density (hereinafter referred to as EPD) measurement. Compared to TEM analysis, dislocation density can be observed over a wide range using an optical microscope. In the present application, the dislocation density means a dislocation density by EPD measurement unless otherwise specified.

  In addition, in the method for producing a group III nitride crystal in Embodiments 1 to 7 and Reference Embodiments 1 and 2, referring to FIG. 8, it is grown on a GaAs substrate by a vapor phase method as shown in FIG. The base substrate 1 formed of the group III nitride crystal has a low dislocation density region 1k and a high dislocation density region 1h. In the step of growing the first group III nitride crystal 10, a low dislocation density is obtained. The growth rate of the first group III nitride crystal 10 in which the first region 10k having a high growth rate of the first group III nitride crystal 10 growing on the region 1k grows on the high dislocation density region 1h. The second region 10h having a small size is covered.

  A low dislocation density region 1k (the crystal surface of that region is a Ga surface) on a GaAs substrate by a vapor phase method such as a facet growth method, and a high dislocation density region 1h (a crystal surface of that region) having a different plane orientation compared to that region Can be produced, and when the first group III nitride crystal 10 is grown on the group III nitride crystal base substrate 1 by a flux method, A first region 10k having a low dislocation density grows on the low dislocation density region 1k, and a second region 10h having a high dislocation density grows on the high dislocation density region 1h. Here, since the first region 10k has a higher crystal growth rate than the second region 10h, the first region 10k covers the second region 10h as shown in FIG. A first group III nitride crystal 10 having a low density is obtained. For this reason, referring to FIG. 8B, the second group III nitride crystal 20 is grown on the first group III nitride crystal 10 having such a low dislocation density by the vapor phase method. Is obtained.

In the above method for producing a group III nitride crystal, the dislocation density of the low dislocation density region 1k in the base substrate 1 is 5 × 10 ⁶ cm ⁻² or less, and the first group III nitride crystal 10 has the first dislocation density. One region 10k can take over the low dislocations of the low dislocation density region 1k. As a result, a first group III nitride crystal having a low dislocation density is obtained.

  Here, in Embodiments 1 to 7 and Reference Embodiments 1 and 2, the description has been given using the flux method as a liquid phase method mainly for growing the first group III nitride crystal. However, the liquid phase method for growing the first group III nitride crystal is not particularly limited as long as it is a liquid phase method using a solvent in Reference Embodiments 1 and 2. In Embodiments 1 to 7, there is no particular limitation as long as it is a liquid phase method, and a flux method, a solution growth method using Ga as a main solvent, a melt growth method, a thermal synthesis method, and the like can be used. Further, in the first to seventh embodiments and the reference embodiments 1 and 2, the vapor phase method for growing the second group III nitride crystal 20 on the first group III nitride crystal 10 is not particularly limited. From the viewpoint of allowing epitaxial growth of crystals having a low dislocation density, it is preferable to use a hydride vapor phase epitaxy method (hereinafter referred to as HVPE method) or a metal organic chemical vapor deposition method (hereinafter referred to as MOCVD method).

(Embodiment 8)
One embodiment of the group III nitride crystal substrate according to the present invention is a substrate including the first, second, or third group III nitride crystal obtained by the manufacturing method of the first to seventh embodiments. Referring to FIGS. 2 (d), 3 (d), 4 (c), 5 (e), 6 (d1) and (d2) and 8 (c), such a group III nitride crystal The substrates U1, V1 to V11, and W1 to W5 are obtained by processing the first, second, or third group III nitride crystals 10, 20, and 30 formed on the base substrate 1 into a flat plate shape. Here, the processing into a flat plate shape means that the first, second, or third group III nitride crystal is cut in parallel with, for example, the base substrate, and the main surface thereof is ground and / or polished. Further, group III nitride crystal substrate U1 includes a first group III nitride crystal 10, group III nitride crystal substrates V1 to V11 each include a second group III nitride crystal 20, and group III nitride. Crystal substrates W1 to W5 each include a third group III nitride crystal 30. More specifically, group III nitride crystal substrate U1 is formed of first group III nitride crystal 10 or first group III nitride crystal 10 and underlying substrate 1, and group III nitride crystal substrate V1. -V11 are all formed of the second group III nitride crystal 20, and the group III nitride crystal substrates W1-W5 are all formed of the third group III nitride crystal 30.

In the group III nitride crystal substrate of the present embodiment, the atomic concentration of the alkali metal element is 5 × 10 ¹⁶ cm ⁻³ or less from the viewpoint of making the substrate suitable for producing a semiconductor device having good characteristics. Is preferred.

  Moreover, in the group III nitride crystal substrate of this embodiment, it is preferable that a diameter is 45 mm or more. According to the group III nitride crystal manufacturing method of the first to seventh embodiments, a group III nitride crystal substrate having a substrate diameter of 45 mm or more can be easily obtained, and the cost for manufacturing the substrate can be reduced.

(Embodiment 9)
One embodiment of a group III nitride semiconductor device according to the present invention is a group III nitride semiconductor device 900 including a group III nitride crystal substrate 90 of embodiment 8, with reference to FIG. At least one group III nitride semiconductor layer 99 is formed on physical crystal substrate 90.

  Since the semiconductor device of this embodiment has a III nitride semiconductor having a low impurity concentration and a low dislocation density and a low dislocation density formed on a group III nitride crystal substrate with a low warp, the characteristics thereof are low. high.

Referring to FIG. 9, group III nitride semiconductor device 900 of the present embodiment has the following structure, for example. That is, an n-type GaN layer 91, an Al _0.3 Ga _0.7 N layer 92, Al is formed as at least one group III nitride semiconductor layer 99 on one main surface of the GaN crystal substrate (Group III nitride crystal substrate 90). _{A 0.04} Ga _0.96 N layer 93, an Al _0.08 Ga _0.92 N layer 94, an Al _0.3 Ga _0.7 N layer 95, and a p-type GaN layer 96 are formed. A p-side electrode 97 is formed on a part of the p-type GaN layer 96. An n-side electrode 98 is formed on the other main surface of the GaN crystal substrate (Group III nitride crystal substrate 90).

  Referring to FIG. 9, the manufacturing method of the semiconductor device of the present embodiment includes the first group III nitride crystal grown by the liquid phase method or the second or third group III nitride grown by the vapor phase method. Forming a group III nitride crystal substrate 90 by processing a physical crystal, and forming at least one group III nitride semiconductor layer 99 on the group III nitride crystal substrate 90 by a vapor phase method. Including.

  The second or third group III nitride crystal obtained by the vapor phase method in the first to seventh embodiments can be suitably used as a substrate for a semiconductor device because the impurity concentration and the dislocation density are low and the warpage is small. In addition, the first group III nitride crystal has a low dislocation density, and heat treatment as in Reference Embodiment 1 or 2 or removal of at least a part of the surface side region as in Embodiment 2 Thus, or by contacting the susceptor as in Embodiment 7, the crystal surface and the impurity concentration in the crystal can be reduced, so that it can be suitably used as a substrate of a semiconductor device.

  Here, referring to FIG. 1C, the second group III nitride is formed on the first group III nitride crystal whose impurity concentration is reduced in the same manner as in reference embodiment 1 or 2 by a vapor phase method. At least one group III nitride semiconductor layer can also be formed as a crystal. Further, referring to FIGS. 6 (c1) and (c2), the impurity concentration is reduced by the contact of the group III nitride crystal including the first group III nitride crystal with the susceptor in the same manner as in the seventh embodiment. Further, at least one group III nitride semiconductor layer can be formed as a second group III nitride crystal on the first group III nitride crystal by a vapor phase method.

  The vapor phase method for forming at least one group III nitride semiconductor layer on the group III nitride crystal substrate is not particularly limited, but the crystal growth rate can be easily controlled, and the impurity concentration and dislocation density can be reduced. The MOCVD method, the MBE (molecular beam epitaxy) method and the like are preferable from the viewpoint of easy growth of a low semiconductor layer.

(Reference Example 1)
1. Growth of First Group III Nitride Crystal by Flux Method Referring to FIG. 1, first, as base substrate 1, a crystal growth surface having a diameter of 50 mm and a thickness of 300 μm manufactured by HVPE method is a (0001) plane. A wurtzite GaN crystal base substrate was prepared. Next, as shown in FIG. 1A, a first GaN crystal (first group III nitride crystal 10) was grown on the GaN crystal base substrate 1 to a thickness of 100 μm by a flux method. Specifically, the GaN crystal base substrate 1 was placed with its (0001) surface facing upward at the bottom of a BN (boron nitride) crucible which is the reaction vessel 7. Next, 20 g of metal Ga, 10 g of metal Na, and 1 g of metal Li are placed in the reaction vessel 7 and heated to 875 ° C. in the chamber to form Ga—Na— that becomes the crystal growth liquid 2. Li melt was formed. By supplying nitrogen gas (nitrogen-containing gas 3) having a gas partial pressure of 3.0 MPa for 30 hours into this Ga—Na—Li melt (crystal growth liquid 2), a first GaN crystal base substrate 1 is coated with the first gas. A GaN crystal (first group III nitride crystal 10) was grown.

About this 1st GaN crystal, the dislocation density by the analysis using TEM (dislocation density by the TEM analysis) was 1 × 10 ⁷ cm ⁻² or less. In order to measure the dislocation density with higher accuracy, the first GaN crystal was immersed in a mixed solution of phosphoric acid and sulfuric acid at 250 ° C. for 1 hour to generate etch pits corresponding to the dislocation. The dislocation density (dislocation density by EPD measurement) with high accuracy measured by the density of this etch pit (EPD) was 3.7 × 10 ⁶ cm ⁻² . On the other hand, the dislocation density of the base substrate 1 was 2.0 × 10 ⁷ cm ⁻² . From these facts, it was found that the dislocation density of the first GaN crystal was lower than that of the base substrate. Furthermore, the impurities contained in the first GaN crystal were evaluated by SIMS (secondary ion mass spectrometry). As a result, the first GaN crystal contained Li atoms at a high concentration of 2.0 × 10 ¹⁸ cm ⁻³ as impurities.

2. Next, as shown in FIG. 1 (b), the grown first GaN crystal (first group III nitride crystal 10) and 10 g of metal Na are reacted in a reaction vessel. 7 and heated to 875 ° C. to form a Na melt, which is a crystal processing liquid 4 brought into contact with the first GaN crystal. That is, the crystal processing liquid 4 contains Na but not Li among the fluxes of Na and Li contained in the crystal growth liquid 2. By supplying nitrogen gas (nitrogen-containing gas 3) having a gas partial pressure of 2.7 MPa to this Na melt (crystal treatment liquid 4) for 250 hours, the first GaN crystal (first group III nitride crystal) is supplied. The heat treatment of 10) was performed. As a result, the surface of the crystal is roughened, and the thickness of the first GaN crystal grown by the flux method is reduced by 20 μm and the thickness of the GaN crystal base substrate 1 is reduced by 15 μm. There wasn't. The impurity concentration in the first heat-treated GaN crystal was evaluated by SIMS, and the Li atom concentration was significantly reduced to 3.0 × 10 ¹⁶ cm ⁻³ .

3. Growth of second group III nitride crystal by vapor phase method Next, the first heat-treated GaN crystal is etched with hydrochloric acid, washed with pure water, and then subjected to ultrasonic cleaning in isopropanol solution for 5 minutes. It was washed 3 times and dried.

Next, as shown in FIG. 1C, the second GaN crystal (second group III) is formed on the heat-treated first GaN crystal (first group III nitride crystal 10) by the HVPE method. Nitride crystals 20) were grown. Specifically, GaCl gas, NH ₃ gas, and H ₂ gas (carrier gas) are mixed at a molar ratio of 120: 1000: 7000 under the crystal growth conditions of 1030 ° C. and 101 kPa on the first GaN crystal. By supplying at 8120 sccm for 30 hours, a second GaN crystal was grown. The thickness of the second GaN crystal was 3.0 mm at the thickest part and 2.9 mm at the thinnest part.

4). Production of Group III Nitride Crystal Substrate Next, as shown in FIGS. 1C and 1D, a first GaN crystal (first group III nitride crystal 10) and a first GaN crystal are formed on a GaN crystal base substrate 1. A group III nitride crystal formed by integrating two GaN crystals (second group III nitride crystal 20) is sliced parallel to the (0001) plane, and the surface is polished to obtain a thickness. Six GaN crystal substrates having a thickness of 300 μm and a surface roughness Ra of 0.01 μm were obtained. These GaN crystal substrates are referred to as GaN crystal substrates U1 _(A) , V1 _(A) , V2 _(A) , V3 _(A) , V4 _(A), and V5 _(A) from the base substrate 1 side. Here, the substrate U1 _(A) is formed of the first GaN crystal and the base substrate 1, and the substrates V1 _(A) , V2 _(A) , V3 _(A) , V4 _(A), and V5 _(A) are the first, respectively. 2 GaN crystals (second group III nitride crystals 20). Impurities contained in these GaN crystal substrates (in the first GaN crystal for the substrate U1 _(A) ) were evaluated by SIMS. The results are summarized in Table 1.

5. Production of Group III Nitride Semiconductor Device Next, referring to FIG. 9, after cleaning each of the above GaN crystal substrates (Group III nitride crystal substrate 90), on one main surface thereof, by MOCVD method, As the group III nitride semiconductor layer 99, an n-type GaN layer 91 having a thickness of 1 μm, an Al _0.3 Ga _0.7 N layer 92 having a thickness of 10 nm, an Al _0.04 Ga _0.96 N layer 93 having a thickness of 3 nm, and Al _0.08 Ga _{0.92 having} a thickness of 3 nm. An N layer 94, an Al _0.3 Ga _0.7 N layer 95 having a thickness of 10 nm, and a p-type GaN layer 96 having a thickness of 10 μm were sequentially epitaxially grown. Next, a p-side electrode 97 having a diameter of 80 μm and a stacked structure of a Pd layer (thickness 5 nm) and an Au layer (thickness 5 nm) was formed on a part of the p-type GaN layer 96. Further, an n-side electrode 98 having a laminated structure of an Al layer (thickness 10 nm) and an Au layer (thickness 10 nm) is formed on the other main surface of each GaN crystal substrate (group III nitride crystal substrate 90). Thus, an LED device was obtained. The emission peak intensity at a wavelength of 360 nm of these LED devices is measured, and the relative emission peak intensity of each LED device when the emission peak intensity of the LED device including the GaN crystal substrate V1 _(A) is 1.00 is shown in Table 2. Summarized.

(Reference Example 2)
In the same manner as in Reference Example 1, a first GaN crystal was grown by a flux method. Next, the first GaN crystal was heat-treated in the same manner as in Reference Example 1 except that a Ga—Na melt formed of 20 g of metal Ga and 10 g of metal Na was used as the crystal processing liquid. As a result, the reduction in crystal thickness as seen in Reference Example 1 was not observed. The impurity concentration in the heat-treated first GaN crystal was evaluated by SIMS. As in the case of Reference Example 1, the Li atom concentration was significantly reduced to 3.0 × 10 ¹⁶ cm ^−3. It was.

Next, in the same manner as in Reference Example 1, the first GaN crystal was washed, and then a second GaN crystal was grown thereon by the HVPE method. The thickness of the obtained second GaN crystal was 3.0 mm at the thickest part and 2.9 mm at the thinnest part. Next, a group III nitride crystal in which the first GaN crystal and the second GaN crystal are integrally formed on the GaN crystal base substrate 1 is formed on the (0001) plane in the same manner as in Reference Example 1. Slicing was performed in parallel, and the surface was polished to obtain six GaN crystal substrates having a thickness of 300 μm and a surface roughness Ra of 0.01 μm. These GaN crystal substrates are referred to as GaN crystal substrates U1 _(B) , V1 _(B) , V2 _(B) , V3 _(B) , V4 _(B), and V5 _(B) from the base substrate 1 side. Here, the substrate U1 _(B) is formed of the first GaN crystal (first group III nitride crystal 10) and the base substrate 1, and the substrates V1 _(B) , V2 _(B) , V3 _(B) , V4. _(B) and V5 _(B) are each formed of a second GaN crystal (second group III nitride crystal 20). Impurities contained in these GaN crystal substrates (for the substrate U1 _(B) in the first GaN crystal) were evaluated by SIMS. The results are summarized in Table 1.

Next, a group III nitride semiconductor layer was sequentially epitaxially grown on one main surface of each GaN crystal substrate in the same manner as in Reference Example 1 to produce an LED device. The emission peak intensity at a wavelength of 360 nm of these LED devices is measured, and the relative emission peak intensity of each LED device when the emission peak intensity of the LED device including the GaN crystal substrate V1 _(A) in Reference Example 1 is 1.00. Are summarized in Table 2.

(Comparative Example 1)
In the same manner as in Reference Example 1, a first GaN crystal was grown by a flux method. Next, the obtained first GaN crystal is washed by the same method as in Reference Example 1 without performing the above heat treatment, and then the second GaN crystal is formed thereon by HVPE as in Reference Example 1. Grown up. The thickness of the obtained second GaN crystal was 3.0 mm at the thickest part and 2.9 mm at the thinnest part. Next, a group III nitride crystal in which the first GaN crystal and the second GaN crystal are integrally formed on the GaN crystal base substrate 1 is formed on the (0001) plane in the same manner as in Reference Example 1. Slicing was performed in parallel, and the surface was polished to obtain six GaN crystal substrates having a thickness of 300 μm and a surface roughness Ra of 0.01 μm. These GaN crystal substrates are referred to as GaN crystal substrates U1 _(C) , V1 _(C) , V2 _(C) , V3 _(C) , V4 _(C), and V5 _(C) from the base substrate 1 side. Here, the substrate U1 _(C) is formed of the first GaN crystal (first group III nitride crystal 10) and the base substrate 1, and the substrates V1 _(C) , V2 _(C) , V3 _(C) , V4. _(C) and V5 _(C) are each formed of a second GaN crystal (second group III nitride crystal 20). Impurities contained in these GaN crystal substrates (in the first GaN crystal for the substrate U1 _(C) ) were evaluated by SIMS. The results are summarized in Table 1.

Next, a group III nitride semiconductor layer was sequentially epitaxially grown on one main surface of each GaN crystal substrate in the same manner as in Reference Example 1 to produce an LED device. The emission peak intensity at a wavelength of 360 nm of these LED devices is measured, and the relative emission peak intensity of each LED device when the emission peak intensity of the LED device including the GaN crystal substrate V1 _(A) in Reference Example 1 is 1.00. Are summarized in Table 2.

  As is apparent from Table 1, among group III elements contained in the crystal growth liquid and elements contained in the flux, at least one element contained in the flux, more preferably at least one element contained in the flux And heat treatment of the first group III nitride crystal grown by the flux method in a crystal processing liquid containing a group III element and a group III element, thereby significantly reducing the impurity concentration in the first group III nitride crystal and on the surface. We were able to. Further, by growing the second group III nitride crystal by the vapor phase method on the first group III nitride crystal with the reduced impurity concentration, the dislocation density is low, the warp is small, and the impurity concentration is low. A second group III nitride crystal is obtained. As is apparent from Table 2, a semiconductor device obtained by forming at least one group III nitride semiconductor layer on a group III nitride crystal substrate obtained from the second group III nitride crystal ( For example, LED devices have higher characteristics (for example, emission intensity).

Example 1
1. Growth of first GaN crystal by flux method Referring to FIG. 2 (a), as crystal growth liquid 2, Ga formed from 20 g of metal Ga, 10 g of metal Na, and 0.5 g of metal Li. The first GaN crystal was grown to a thickness of about 500 μm in the same manner as in Reference Example 1 except that the —Na—Li melt was used and the crystal growth time was 150 hours. On the surface of the obtained first GaN crystal, the concentration of Li atoms as impurities was as low as 5.0 × 10 ¹⁶ cm ⁻³ , but large irregularities were observed, and the thickness of the first GaN crystal was the thickest. The thickness of the portion was 550 μm, the thickness of the thinnest portion was 350 μm, and the height difference reached 200 μm.

2. Next, referring to FIG. 2B, the surface of the first GaN crystal is polished by using diamond abrasive grains so that the surface roughness Ra is 5 nm or less. processed. Next, the surface of the first GaN crystal whose surface has been polished is etched by about 3 μm by RIE (reactive ion etching) using chlorine gas, so that the work-affected layer introduced by the polishing process using the diamond abrasive grains is performed. Completely removed.

  The warpage of the first GaN crystal after the surface treatment was measured by scanning over a diameter of 50 mm using a stylus type step shape from the back side not subjected to surface processing, and was convex downward, and its curvature radius was 2 .2 m.

3. Growth of Second Group III Nitride Crystal by Vapor Phase Method Referring to FIG. 2C, the first GaN crystal (first group III nitride crystal 10) is cleaned in the same manner as in Reference Example 1. Then, a second GaN crystal (second group III nitride crystal 20) was grown thereon by HVPE. Specifically, GaCl gas, NH ₃ gas, and H ₂ gas (carrier gas) in a molar ratio of 120: 1000: 7000 and a total gas amount of 8120 sccm on the first GaN crystal under crystal growth conditions of 1030 ° C. and 101 kPa. For 30 hours to grow a second GaN crystal. The thickness of the second GaN crystal was 3.0 mm, and the surface was flat. The warpage of the second GaN crystal was convex downward, and the radius of curvature was 5.5 m. Further, this second GaN crystal had a dislocation density of 1 × 10 ⁷ cm ⁻² or less by TEM analysis and a dislocation density of 3.7 × 10 ⁶ cm ⁻² by EPD measurement. Further, no distortion of the crystal was observed in the second GaN crystal by Raman spectroscopy.

(Comparative Example 2)
In the same manner as in Example 1, the first GaN crystal was grown to a thickness of about 500 μm by the flux method. On the surface of the obtained first GaN crystal, as in Example 1, the Li concentration as an impurity was as low as 5.0 × 10 ¹⁶ cm ⁻³ , but large irregularities were observed, and the first GaN crystal was observed. In the crystal, the thickness of the thickest part was 550 μm, and the thickness of the thinnest part was 350 μm.

  Next, the first GaN crystal was washed in the same manner as in Example 1 without performing surface processing. A second GaN crystal was grown on the cleaned first GaN crystal by the HVPE method in the same manner as in Example 1. The thickness of the second GaN crystal was 3.0 mm at the thickest part and 2.5 mm at the thinnest part. In addition, the second GaN crystal had a large convex warp with a radius of curvature of 1.5 m. This indicates that when the second GaN crystal is sliced, the group III nitride semiconductor crystal substrate has a large crystal orientation distribution that cannot be practically used.

In the second GaN crystal, it was observed using Raman spectroscopy and X-ray diffraction that stress was generated due to the distribution of impurities. Further, this second GaN crystal had a dislocation density of 1 × 10 ⁷ cm ⁻² or less by TEM analysis and a dislocation density of 3.7 × 10 ⁶ cm ⁻² by EPD measurement.

  In this comparative example, it is considered that the distortion occurs in the second GaN crystal (second group III nitride crystal) for the following reason with reference to FIG. Referring to FIG. 10A, when a group III nitride crystal is grown thickly on the base substrate 1 by a flux method, the first group III nitride crystal (first group III nitride crystal 10) is formed. Unevenness is generated on the surface, and a c-plane 10 c parallel to the main surface of the base substrate 1 and a facet 10 f that is not parallel appear.

  Referring to FIGS. 10B to 10D, a second group III nitride crystal 20 is formed on the first group III nitride crystal 10 having c-plane 10c and facet 10f on the crystal surface by a vapor phase method. When grown, a high carbon concentration containing region 20c having a high carbon atom concentration is formed on the c-plane 10c, and a high oxygen concentration containing region 20d having a high oxygen atom concentration is formed on the facet 10f. Here, the high carbon concentration region 20c and the high oxygen concentration region 20d have different lattice constants and thermal expansion coefficients, so that internal stress is generated and a strain region 12h is generated in the crystal.

(Example 2)
Referring to FIG. 3A, the first GaN crystal (first group III nitride crystal 10) is thickened by the flux method in the same manner as in Reference Example 1 except that the crystal growth time is 60 hours. The film was grown to 180 μm. The first GaN crystal had no irregularities on the surface, but was colored black brown in the vicinity of the surface. When SIMS analysis was performed in the depth direction from the surface, the concentration of Li atoms as impurities on the surface was as high as 1.0 × 10 ¹⁸ cm ⁻³ , but the depth from the surface was 20 μm. In this case, the concentration of Li atoms was reduced to 6.0 × 10 ¹⁶ cm ⁻³ .

Next, the first GaN crystal was washed in the same manner as in Reference Example 1. Next, referring to FIG. 3B, the cleaned first GaN crystal (first group III nitride crystal 10) is placed in the crystal growth vessel of the HVPE apparatus, and the first GaN crystal (first The surface-side region 10a of the first group III nitride crystal 10) was removed by gas phase etching. Specifically, at 1030 ° C. and 101 kPa, a mixed gas of HCl gas and H ₂ gas (carrier gas) (molar ratio is 1000: 7000) is supplied for 1 hour at a total gas flow rate of 8000 sccm, then 1030 ° C., By supplying a mixed gas (molar ratio 1000: 7000) of NH ₃ gas and H ₂ gas (carrier gas) at 101 kPa at a total gas flow rate of 8000 sccm for 30 minutes, 20 μm from the surface of the first GaN crystal. The surface side region 10a up to the depth was removed by etching.

Next, referring to FIG. 3 (c), on the first GaN crystal (first group III nitride crystal 10) subjected to the above-mentioned vapor phase etching, in the same manner as in Reference Example 1, the HVPE method is used. A second GaN crystal (second group III nitride crystal 20) was grown. Specifically, GaCl gas, NH ₃ gas, and H ₂ gas (carrier gas) are mixed at a molar ratio of 120: 1000: 7000 under the crystal growth conditions of 1030 ° C. and 101 kPa on the first GaN crystal. By supplying at 8120 sccm for 30 hours, a second GaN crystal was grown. The thickness of the second GaN crystal was 3.0 mm at the thickest part and 2.9 mm at the thinnest part.

Next, referring to FIGS. 3C and 3D, a first GaN crystal (first group III nitride crystal 10) and a second GaN crystal (second The second GaN crystal portion of the group III nitride crystal formed integrally with the group III nitride crystal 20) is sliced in parallel to the (0001) plane in the same manner as in Reference Example 1, and further the surface. The five GaN crystal substrates having a thickness of 300 μm and a surface roughness Ra of 0.01 μm were obtained. These GaN crystal substrates are referred to as GaN crystal substrates V1 _(D) , V2 _(D) , V3 _(D) , V4 _(D), and V5 _(D) from the side closer to the base substrate 1. Impurities contained in these GaN crystal substrates were evaluated by SIMS. The results are shown in Table 3 together with the results of Comparative Example 1.

  As apparent from Table 3, after removing at least a part of the surface side region of the first group III nitride crystal grown by the flux method, the HVPE method or the like is formed on the first group III nitride crystal. By growing the second group III nitride crystal by a vapor phase method, a second group III nitride crystal having a low impurity concentration can be obtained.

(Example 3)
4A, in the same manner as in Reference Example 1, a first GaN crystal (first group III nitride crystal 10) was grown to a thickness of 100 μm by the flux method.

Next, the first GaN crystal was washed in the same manner as in Reference Example 1. Next, referring to FIG. 4B, the same procedure as in Reference Example 1 is performed except that the crystal growth time is set to 60 hours on the cleaned first GaN crystal (first group III nitride crystal 10). Then, the second GaN crystal (second group III nitride crystal 20) was grown by the HVPE method. Specifically, GaCl gas, NH ₃ gas, and H ₂ gas (carrier gas) are mixed at a molar ratio of 120: 1000: 7000 under the crystal growth conditions of 1030 ° C. and 101 kPa on the first GaN crystal. By supplying at 8120 sccm for 60 hours, a second GaN crystal having a thickness of about 6.5 mm was obtained.

4B and 4C, the first GaN crystal (first group III nitride crystal 10) and the second GaN crystal (second GaN crystal) are formed on the GaN crystal base substrate 1. The second GaN crystal portion of the group III nitride crystal formed integrally with the group III nitride crystal 20) is sliced in parallel to the (0001) plane in the same manner as in Reference Example 1, and further the surface. Then, eleven GaN crystal substrates having a thickness of 300 μm and a surface roughness Ra of 0.01 μm were obtained. From these GaN crystal substrates, the GaN crystal substrates V1 _(E) , V2 _(E) , V3 _(E) , V4 _(E) , V5 _(E) , V6 _(E) , V7 _{( E)} , V8 _(E) , V9 _(E) , V10 _(E) and V11 _(E) . Impurities contained in these GaN crystal substrates were evaluated by SIMS. The results are summarized in Table 4. Here, the GaN crystal substrate V7 _(E) is located at a distance larger than 3.5 mm (3500 μm) from the crystal growth start surface of the second GaN crystal.

Next, after each GaN crystal substrate was washed, each LED device including each GaN crystal substrate was fabricated in the same manner as in Reference Example 1. The emission peak intensity at a wavelength of 360 nm of each LED device is measured, and the relative emission peak intensity of each LED device when the emission peak intensity of the LED device including the GaN crystal substrate V1 _(A) in Reference Example 1 is set to 1.00. Table 5 summarizes.

In Table 4, Li which is an impurity in the GaN crystal substrates V7 _{(E) to} V11 _(E) located at a distance larger than 3500 μm from the crystal growth start surface of the second GaN crystal (second group III nitride crystal) Since no atoms were detected, the second group III nitride crystal is grown to a thickness of more than 3500 μm on the first group III nitride crystal grown by the flux method by a vapor phase method such as the HVPE method. Thus, it can be seen that a second group III nitride crystal having a low impurity concentration can be obtained. Also, from Tables 4 and 5, it can be seen that the LED using the group III nitride crystal substrate having a low impurity concentration has higher emission intensity than other LEDs.

Example 4
Referring to FIG. 5A, in the same manner as in Reference Example 1, a first GaN crystal (first group III nitride crystal 10) was grown to a thickness of 100 μm by a flux method.

Next, the first GaN crystal was washed in the same manner as in Reference Example 1. Next, referring to FIG. 5B, the same as in Reference Example 1 except that the crystal growth time was set to 2 hours on the cleaned first GaN crystal (first group III nitride crystal 10). Then, the second GaN crystal (second group III nitride crystal 20) was grown by the HVPE method. Specifically, GaCl gas, NH ₃ gas, and H ₂ gas (carrier gas) are mixed at a molar ratio of 120: 1000: 7000 under the crystal growth conditions of 1030 ° C. and 101 kPa on the first GaN crystal. By supplying at 8120 sccm for 2 hours, a second GaN crystal having a thickness of about 200 μm was obtained.

  Next, referring to FIG. 5C, the second GaN crystal (second group III nitride crystal 20) is taken out of the crystal growth furnace, and the second GaN crystal (second group III nitride) is taken out. The surface of the crystal 20) was mechanically polished with diamond abrasive grains to remove the surface side region 20a up to a distance of 50 μm from the crystal surface.

  Next, referring to FIG. 5D, a third GaN crystal (third group III nitride) is formed on the surface-polished second GaN crystal (second group III nitride crystal 20) by HVPE. A crystal 30) was grown. Here, the crystal growth conditions were the same as the growth conditions of the second GaN crystal in this example except that the crystal growth time was 30 hours. The thickness of the obtained third GaN crystal was 3.0 mm at the thickest part and 2.9 mm at the thinnest part.

Next, referring to FIGS. 5D and 5E, the first GaN crystal (first group III nitride crystal 10) and the second GaN crystal (second The third GaN crystal portion of the group III nitride crystal formed by integrating the group III nitride crystal 20) and the third GaN crystal (third group III nitride crystal 30) is represented by its (0001) Slicing was performed in parallel to the surface, and the surface was further polished to obtain five GaN crystal substrates having a thickness of 300 μm and a surface roughness Ra of 0.01 μm. These GaN crystal substrates are referred to as GaN crystal substrates W1 _(F) , W2 _(F) , W3 _(F) , W4 _(F), and W5 _(F) from the side closer to the base substrate 1. Impurities contained in these GaN crystal substrates were evaluated by SIMS. The results are shown in Table 6 together with the results of Comparative Example 1.

Next, after each GaN crystal substrate was washed, each LED device including each GaN crystal substrate was fabricated in the same manner as in Reference Example 1. The emission peak intensity at a wavelength of 360 nm of each LED device is measured, and the relative emission peak intensity of each LED device when the emission peak intensity of the LED device including the GaN crystal substrate V1 _(A) in Reference Example 1 is set to 1.00. The relative emission peak intensities in Comparative Example 1 are summarized in Table 7.

  As is apparent from Table 6, a second group III nitride crystal is grown on the first group III nitride crystal grown by the flux method by a vapor phase method such as the HVPE method. Removing at least a part of the surface side region of the nitride crystal and growing a third group III nitride crystal on the second group III nitride crystal thus removed by a vapor phase method such as an HVPE method; As a result, a third group III nitride crystal having a low impurity concentration is obtained. Further, as is clear from Tables 6 and 7, the LED using the group III nitride crystal substrate having a low impurity concentration has a higher emission intensity than other LEDs.

(Example 5)
4A, in the same manner as in Reference Example 1, a first GaN crystal (first group III nitride crystal 10) was grown to a thickness of 100 μm by the flux method.

  Next, the first GaN crystal was washed in the same manner as in Reference Example 1. Next, referring to FIG. 4B, a second GaN crystal (second group III nitride) is formed on the cleaned first GaN crystal (first group III nitride crystal 10) by the HVPE method. Crystals 20) were grown.

In the growth of the second GaN crystal, first, at 930 ° C. (first crystal growth temperature) and 101 kPa, GaCl gas, NH ₃ gas and H ₂ gas (carrier gas) are in a molar ratio of 120: 1000: 7000, By supplying a total gas amount of 8120 sccm for 3 hours, a GaN crystal having a thickness of about 200 μm (referred to as GaN crystal II-A in Example 5) was grown. Next, at 1030 ° C. (second crystal growth temperature) and 101 kPa, GaCl gas, NH ₃ gas and H ₂ gas (carrier gas) are supplied at a molar ratio of 120: 1000: 7000 for a total gas amount of 8120 sccm for 30 hours. Thus, a GaN crystal (GaN crystal II-B, the same as in Example 5) having a thickness of 3.0 mm at the thickest portion and 2.9 mm at the thinnest portion was grown.

Next, referring to FIGS. 4B and 4C, the first GaN crystal (first group III nitride crystal 10) and the second GaN crystal (GaN crystal II) are formed on the GaN crystal base substrate 1. -A and the GaN crystal II-B, the second group III nitride crystal 20) are integrally formed, and the portion of the GaN crystal II-B of the group III nitride crystal formed in the same manner as in Reference Example 1, Slicing was performed in parallel to the (0001) plane, and the surface was further polished to obtain five GaN crystal substrates having a thickness of 300 μm and a surface roughness Ra of 0.01 μm. These GaN crystal substrates are referred to as GaN crystal substrates V1 _(G , V2 _(G) , V3 _(G) , V4 _(G), and V5 _(G) from the side closer to the base substrate 1. In these GaN crystal substrates The impurities contained in were evaluated by SIMS, and the results are summarized in Table 8.

(Example 6)
4A, in the same manner as in Reference Example 1, a first GaN crystal (first group III nitride crystal 10) was grown to a thickness of 100 μm by the flux method.

  Next, the first GaN crystal was washed in the same manner as in Reference Example 1. Next, referring to FIG. 4B, a second GaN crystal (second group III nitride) is formed on the cleaned first GaN crystal (first group III nitride crystal 10) by the HVPE method. Crystals 20) were grown.

In the second GaN crystal growth, first, GaCl gas, NH ₃ gas and H ₂ gas (carrier gas) are supplied at a molar ratio of 240: 1000: 7000 and a total gas amount of 8240 sccm for 1 hour at 1030 ° C. and 101 kPa. As a result, a GaN crystal having a thickness of about 200 μm (referred to as GaN crystal II-C in Example 6) was grown. That is, the crystal growth rate (first crystal growth rate) at this time was about 200 μm / hr.

Next, at 1030 ° C. and 101 kPa, GaCl gas, NH ₃ gas, and H ₂ gas (carrier gas) are supplied at a molar ratio of 120: 1000: 7000 at a total gas amount of 8120 sccm for 30 hours, whereby 3. A GaN crystal (GaN crystal II-D, the same as in Example 6) having a thickness of 0 mm and a thickness of 2.9 mm at the thinnest part was grown. That is, the crystal growth rate (second crystal growth rate) at this time was about 100 μm / hr.

Next, referring to FIGS. 4B and 4C, the first GaN crystal (first group III nitride crystal 10) and the second GaN crystal (GaN crystal II) are formed on the GaN crystal base substrate 1. -C and the GaN crystal II-D, the second group III nitride crystal 20) is formed integrally with the portion of the GaN crystal II-D of the group III nitride crystal formed in the same manner as in Reference Example 1, Slicing was performed in parallel to the (0001) plane, and the surface was further polished to obtain five GaN crystal substrates having a thickness of 300 μm and a surface roughness Ra of 0.01 μm. These GaN crystal substrates are referred to as GaN crystal substrates V1 _(H) , V2 _(H) , V3 _(H) , V4 _(H), and V5 _(H) from the side closer to the base substrate 1. Impurities contained in these GaN crystal substrates were evaluated by the SIMS method. The results are summarized in Table 8.

  As apparent from Table 8, the step of growing the second group III nitride crystal by the vapor phase method such as the HVPE method on the first group III nitride crystal grown by the flux method, As the two changed steps, the second group III nitride crystal having a low impurity concentration can be obtained by lowering the first crystal growth temperature in the first step or increasing the first crystal growth rate in the first step. Is obtained.

(Example 7)
Referring to FIG. 6A, in the same manner as in Reference Example 1, a first GaN crystal (first Group III nitride crystal 10) was grown to a thickness of 100 μm by a flux method.

  Next, referring to FIG. 6C1, the first GaN crystal is washed in the same manner as in Reference Example 1, and then the first GaN crystal (first Group III nitride crystal 10) having a thickness of 100 μm is obtained. A GaN crystal base substrate 1 on which is formed (this corresponds to a group III nitride crystal including a first group III nitride crystal, the same applies hereinafter) to a carbon susceptor 9 having a thickness of 1 mm, A second GaN crystal (second group III nitride crystal 20) was grown on the first GaN crystal (first group III nitride crystal 10) by the HVPE method. The crystal growth conditions were the same as in Reference Example 1. The thickness of the obtained second GaN crystal was 3.0 mm at the thickest part and 2.9 mm at the thinnest part.

Next, referring to FIGS. 6 (c1) and (d1), a first GaN crystal (first group III nitride crystal 10) and a second GaN crystal (second The second GaN crystal portion of the group III nitride crystal formed integrally with the group III nitride crystal 20) is sliced parallel to the (0001) plane, and the surface is polished to obtain a thickness. 5 GaN crystal substrates having a surface roughness Ra of 0.01 μm and a surface roughness Ra of 300 μm were obtained. These GaN crystal substrates are referred to as GaN crystal substrates V1 _(I) , V2 _(I) , V3 _(I) , V4 _(I), and V5 _(I) from the side closer to the base substrate 1. Impurities contained in the GaN crystal substrate were evaluated by the SIMS method. The results are summarized in Table 9.

(Example 8)
Referring to FIG. 6A, the first GaN crystal (first group III nitride crystal 10) is thickened by the flux method in the same manner as in Reference Example 1 except that the crystal growth time is 130 hours. The film was grown to 450 μm.

  Next, referring to FIG. 6B, the distance of 100 μm from the interface between the GaN crystal base substrate 1 and the first GaN crystal (first group III nitride crystal 10) into the first GaN crystal. The first GaN crystal is sliced by a slicer with a cutting margin of 100 μm parallel to the (0001) plane on a certain surface, and the first GaN crystal with a thickness of 50 μm formed on the base substrate 1 and the thickness A 300 μm first GaN crystal was obtained. After polishing the slice surface of these first GaN crystals (first group III nitride crystals), the first GaN crystals were washed in the same manner as in Reference Example 1.

  Next, referring to FIG. 6 (c1) or (c2), on each of the two first GaN crystals (first group III nitride crystal 10) obtained as described above, In this manner, the second GaN crystal (second group III nitride crystal 20) was grown by the HVPE method. Hereinafter, as Example 8-1 in which a second GaN crystal is grown on a first GaN crystal having a thickness of 50 μm formed on the base substrate 1, the first GaN crystal having a thickness of 300 μm is formed on the first GaN crystal. An example of growing 2 GaN crystals will be described as Example 8-2.

(Example 8-1)
Referring to FIG. 6 (c1), the GaN crystal base substrate 1 on which the first GaN crystal (first group III nitride crystal 10) having a thickness of 50 μm is formed is contacted with the region (crystal contact). The region 9c) is brought into contact with a 1 mm thick carbon susceptor 9 coated with pBN (pyrolytic boron nitride) so as to have a flat surface, and the first GaN crystal (first group III nitride) A second GaN crystal (second group III nitride crystal 20) was grown on the crystal 10) by HVPE. The crystal growth conditions were the same as in Reference Example 1. The thickness of the obtained second GaN crystal was 3.0 mm at the thickest part and 2.9 mm at the thinnest part.

Next, referring to FIGS. 6 (c1) and (d1), a first GaN crystal (first group III nitride crystal 10) and a second GaN crystal (second The second GaN crystal portion of the group III nitride crystal formed integrally with the group III nitride crystal 20) is sliced parallel to the (0001) plane, and the surface is polished to obtain a thickness. 5 GaN crystal substrates having a surface roughness Ra of 0.01 μm and a surface roughness Ra of 300 μm were obtained. These GaN crystal substrates are referred to as GaN crystal substrates V1 _(J) , V2 _(J) , V3 _(J) , V4 _(J), and V5 _(J) from the side closer to the base substrate. Impurities contained in the GaN crystal substrate were evaluated by SIMS. The results are summarized in Table 9.

(Example 8-2)
Referring to FIG. 6 (c2), the first GaN crystal (first group III nitride crystal 10) having a thickness of 300 μm has a region (crystal contact region 9c) in contact with the crystal of pBN (pyrolytic boron nitride). ) In contact with a susceptor 9 made of carbon having a thickness of 1 mm and coated so that the surface thereof is flat, and then the second HVPE method is applied on the first GaN crystal (first group III nitride crystal 10). GaN crystal (second group III nitride crystal 20) was grown. The crystal growth conditions were the same as in Reference Example 1. The thickness of the obtained second GaN crystal was 3.0 mm at the thickest part and 2.9 mm at the thinnest part.

Next, referring to FIGS. 6 (c2) and (d2), the first GaN crystal (first group III nitride crystal 10) and the second GaN crystal (second group III nitride crystal 20). The second GaN crystal portion of the group III nitride crystal formed integrally is sliced parallel to the (0001) plane, and the surface is further polished to a thickness of 300 μm and a surface roughness. Five GaN crystal substrates having Ra of 0.01 μm were obtained. From these GaN crystal substrates, the GaN crystal substrates V1 _(K) , V2 _(K) , V3 _(K) , V4 _(K) from the side closer to the first GaN crystal (first group III nitride crystal 10 _). And V5 _(K) . Impurities contained in the GaN crystal substrate were evaluated by SIMS. The results are summarized in Table 9.

  As apparent from Table 9, when the second group III nitride crystal is grown by the vapor phase method on the first group III nitride crystal grown by the flux method, the first group III nitride crystal is grown. Is brought into contact with the susceptor to diffuse the impurities in the first group III nitride crystal into the susceptor, thereby obtaining the second group III nitride crystal and group III nitride substrate having a low impurity concentration. With reference to FIG. 6C, in particular, by using a susceptor 9 in which at least a region (crystal contact region 9c) in contact with the first group III nitride crystal 10 is formed of nitride, The impurity concentration of the second group III nitride crystal and the group III nitride substrate can be further reduced.

Example 9
Referring to FIG. 6A, in the same manner as in Reference Example 1, a first GaN crystal (first group III nitride crystal 10) was grown to a thickness of 450 μm by a flux method.

  Next, referring to FIG. 6B, the distance of 100 μm from the interface between the GaN crystal base substrate 1 and the first GaN crystal (first group III nitride crystal 10) into the first GaN crystal. The first GaN crystal is sliced in parallel with the (0001) plane on a certain surface to obtain a first GaN crystal having a thickness of 50 μm and a first GaN crystal having a thickness of 300 μm formed on the base substrate 1. It was. After polishing the slice surface of these first GaN crystals (first group III nitride crystals), the first GaN crystals were washed in the same manner as in Reference Example 1.

  Next, referring to FIG. 6 (c1) or (c2), on each of the two first GaN crystals (first group III nitride crystal 10) obtained as described above, In this manner, the second GaN crystal (second group III nitride crystal 20) was grown by the MOCVD method. Hereinafter, as Example 9-1 in which a second GaN crystal is grown on a first GaN crystal having a thickness of 50 μm formed on the base substrate 1, a first GaN crystal having a thickness of 300 μm is formed on the first GaN crystal. An example of growing 2 GaN crystals will be described as Example 9-2.

(Example 9-1)
Referring to FIG. 6 (c1), the GaN crystal base substrate 1 on which the first GaN crystal (first group III nitride crystal 10) having a thickness of 50 μm is formed is contacted with the region (crystal contact). The region 9c) is brought into contact with a 1 mm thick carbon susceptor 9 coated with pBN (pyrolytic boron nitride) so as to have a flat surface, and the first GaN crystal (first group III nitride) A second GaN crystal (second group III nitride crystal 20) was grown on the crystal 10) by MOCVD. Specifically, TMG (trimethylgallium) gas, NH ₃ gas, H ₂ gas (carrier gas), and N ₂ gas (carrier gas) are grown on the first GaN crystal under crystal growth conditions of 1100 ° C. and 101 kPa. A second GaN crystal having a thickness of 6 μm was obtained by supplying the gas in a molar ratio of 1: 2000: 7000: 9000 at a total gas amount of 40000 sccm for 2 hours. Impurity concentrations on the susceptor surface before and after the growth of the first GaN crystal, the second GaN crystal, and the second Ga crystal were evaluated by SIMS. The results are summarized in Table 10.

(Example 9-2)
Referring to FIG. 6 (c2), the first GaN crystal (first group III nitride crystal 10) having a thickness of 300 μm has a region (crystal contact region 9c) in contact with the crystal of pBN (pyrolytic boron nitride). In this example, the surface of the first GaN crystal (first group III nitride crystal 10) is contacted with a susceptor 9 made of carbon having a thickness of 1 mm and coated so as to have a flat surface. A second GaN crystal (second group III nitride crystal 20) was grown in the same manner as in 9-1. As a result, a second GaN crystal having a thickness of 6 μm was obtained. Impurity concentrations on the susceptor surface before and after the growth of the first GaN crystal, the second GaN crystal, and the second GaN crystal were evaluated by SIMS. The results are summarized in Table 10.

As shown in Table 10, when the second group III nitride crystal is grown by the vapor phase method on the first group III nitride crystal grown by the flux method, the first group III nitride crystal is When the containing group III nitride crystal was brought into contact with the susceptor, the impurity concentration on the susceptor surface was not detected as Li atoms as impurities before the second GaN crystal growth, but the second GaN crystal (second III After the growth of the group nitride crystal), the concentration of Li atoms increased to 3.0 × 10 ¹⁷ cm ⁻³ or 2.0 × 10 ¹⁷ cm ⁻³ . In addition, it was found that a second GaN crystal with a reduced impurity concentration was obtained compared to the first GaN crystal.

(Example 10)
Instead of a wurtzite type GaN crystal base substrate having a diameter of 50 mm × thickness of 300 μm and a crystal growth surface of (0001) manufactured by the HVPE method, the ground substrate 1 is a polished sapphire substrate having a diameter of 50 mm ( A GaN crystal substrate and an LED were produced in the same manner as in Examples 1 to 9 except that a substrate on which a GaN crystal thin film was grown by 3 μm on the (0001) surface by MOCVD was used. Results were obtained.

(Example 11)
As the base substrate 1, a vapor phase method was used in the same manner as in Examples 1 to 9, except that a GaN crystal base substrate produced on a GaAs substrate by the method described in paragraphs 0051 to 0056 of the following Patent No. 3788041 was used. When a GaN crystal substrate was produced from the second or third GaN crystal grown by the above method, the dislocation density by EPD measurement of this substrate was 1 × 10 ⁶ cm ⁻² on average, and the GaN crystals of Examples 1 to 9 The crystallinity was further improved as compared with the substrate. Here, the base substrate used in this example was specifically manufactured by the following method with reference to FIGS.

(1) Formation of mask layer First, referring to FIGS. 11 and 14, a plasma CVD apparatus is used to make a GaAs (111) A substrate having a diameter of 30 mm (the main surface used for crystal growth is the (111) A plane). A SiN layer having a thickness of 0.1 μm was formed as a mask layer 142 on a GaAs substrate cut out in FIG. Next, windows 142w having a regular distribution in the mask layer 142 were opened by photolithography. The window 142w is a staggered dot window shown in FIG. 11 (this window is arranged on a straight line parallel to GaAs <11-2> and adjacent window groups are shifted by a half pitch. Here, the width W of the window is 2 μm square, The window pitch P was 4 μm, and the window row pitch d was 3.5 μm.

(2) Formation of GaN buffer layer Next, referring to FIG. 14 (a), the GaAs substrate 140 covered with the mask layer 142 having the periodic window 142w is put into the HVPE apparatus by using the HVPE apparatus. Arranged. The GaAs substrate 140 was heated to about 500 ° C. in the HVPE apparatus. A mixed gas of H ₂ gas and HCl gas was introduced from the source gas inlet, and was brought into contact with the Ga melt in the Ga reservoir heated to 850 ° C. to synthesize GaCl gas. A mixed gas of H ₂ and NH ₃ is introduced from another source gas inlet, and a reaction of GaCl + NH ₃ → GaN is caused in the vicinity of the GaAs substrate 140 heated to 500 ° C. to deposit GaN on the GaAs substrate 140. It was. Thus, referring to FIG. 14B, a GaN buffer layer 143b having a thickness of about 70 nm was formed on the GaAs substrate 140. The SiN layer has a GaN growth suppressing action, and GaN is not deposited on the SiN layer. Here, the thickness of the GaN buffer layer 143b is 70 nm, and the thickness of the mask layer 142 is smaller than 100 nm. Therefore, the GaN buffer layer 143b is formed only on the portion of the GaAs substrate 140 serving as the window 142w.

(3) Formation of GaN crystal Next, the introduction of HCl was stopped, and the substrate temperature was raised from 500 ° C. to about 1000 ° C. Again, by introducing HCl gas into the Ga reservoir, GaCl gas is synthesized in the same manner as described above. A mixed gas of H ₂ and NH ₃ is introduced from another source gas inlet, and a reaction of GaCl + NH ₃ → GaN is caused in the vicinity of the GaAs substrate 140 heated to about 1000 ° C. to deposit GaN on the GaAs substrate 140. I let you. Such GaN is epitaxially grown on the GaN buffer layer 143b in the window 142w. The formed GaN buffer layer 143b is also crystallized by being heated to about 1000 ° C. Therefore, the GaN crystal 143 grows on the GaAs substrate 140 in the window 142w.

  Referring to FIGS. 12 and 14C, when the thickness of the GaN crystal 143 is larger than the thickness (100 nm) of the mask layer 142, the GaN crystal 143 spreads in a regular hexagonal shape on the mask layer 142. Here, since the window is located at the apex of the regular triangle, referring to FIG. 13, the GaN crystal 143 that spreads from a certain window to a regular hexagonal shape contacts the crystal that has spread from the adjacent window to a regular hexagonal shape. . Since the growth rate of the GaN crystal 143 extending from each window is the same, the regular hexagonal pyramid crystals were in good contact. After the GaN crystal 143 completely covered the upper surface of the mask layer 142, the GaN crystal 143 grew upward with reference to FIG. The growth rate of the GaN crystal 143 was 50 μm / hr. Thus, a GaN crystal 143 having a thickness of about 350 μm was grown. As described above, since nucleation is independently generated from countless small windows and crystal growth (lateral growth) is performed, internal stress in the GaN crystal 143 can be greatly reduced. The surface was frosted glass.

(4) Removal of GaAs Substrate Next, referring to FIGS. 14D and 14E, the GaAs substrate 140 on which the GaN crystal 143 is grown is placed in an etching apparatus, and about 10 using aqua regia. Etched for hours. Thereby, the GaAs substrate 140 was completely removed, and a GaN crystal 143 was obtained. The main surfaces on both sides of the GaN crystal 143 were polished to obtain a GaN crystal base substrate used in this example. This was a free-standing substrate.

Regarding the GaN crystal substrate obtained as described above, the relationship between the angle of the substrate surface and the GaN (0001) plane was measured by an X-ray diffractometer. The angle formed with the line was 2.5 ° within the substrate. Further, the variation of the normal line of the GaN (0001) plane was 3.2 ° within the substrate. Further, the warpage of the substrate after polishing was about 25 μm in height H when the length D was 1 inch (about 25 mm). The curvature radius R of the warp of the substrate is defined by R = D ² / 8H and is 3125 mm. Such a warp is a warp capable of pattern drawing by photolithography. In this way, a GaN crystal substrate with less warpage, that is, with less internal stress and distortion of the crystal was used as the base substrate.

(Example 12)
As a base substrate, a low dislocation density region having a dislocation density of 1 × 10 ⁴ cm ⁻² and a dislocation density of 1 × 10 ⁸ cm produced by the HVPE method as described in paragraphs 0221 to 0271 of JP2003-183100A. ^Using a GaN crystal base substrate having a high dislocation density region of ^-2, a first GaN crystal was grown on the GaN crystal base substrate by a flux method in the same manner as in Examples 1-9. The dislocation density measured by EPD on the crystal growth surface of the first GaN crystal was 1 × 10 ⁶ cm ⁻² on average. A second or third GaN crystal grown by a vapor phase method was grown on the first GaN crystal. When a GaN crystal substrate was fabricated from the second or third GaN crystal, the dislocation density of the substrate measured by EPD was 5 × 10 ⁵ cm ⁻² on average, which was found in the GaN crystal substrates of Examples 1-9. In comparison, the crystallinity was further improved.

  In this example, referring to FIG. 8A, when a cross section of the first GaN crystal having a thickness of 300 μm grown by the flux method is observed with a fluorescence microscope, the low dislocation density region 1k of the GaN crystal base substrate 1 is observed. The first region 10 k formed on the upper surface covered the second region 10 h formed on the high dislocation density region 1 h of the GaN crystal base substrate 1. Here, this is considered to be due to the fact that the first region 10k has a higher crystal growth rate than the second region 10h. For this reason, in the first GaN crystal, the dislocation density on the entire crystal growth surface is reduced.

  Here, the base substrate used in this example was specifically manufactured by the following method with reference to FIG.

(1) Formation of GaN layer Referring to FIG. 15A, as a substrate for growing a GaN crystal base substrate, for example, a sapphire c-plane substrate having a diameter of 50 mm (the principal surface used for crystal growth is c-plane ({ Sapphire substrate 150 cut out so as to be 0001} plane, and so on). Here, the sapphire crystal is hexagonal and belongs to the same crystal system as the GaN crystal.

  First, referring to FIG. 15B, a GaN layer 151 having a thickness of about 2 μm was epitaxially grown on the sapphire substrate 150 by MOCVD. Here, the crystal growth surface of the GaN layer was the c-plane of the GaN crystal.

(2) Formation of Mask Next, referring to FIG. 15C, an SiO ₂ layer having a thickness of 100 nm was formed on the GaN layer 151 by a thermal CVD method. Next, a mask pattern in which stripe-like masks 152 were arranged at equal intervals was formed by photolithography. In the mask pattern, the longitudinal direction of the mask 152 was the <1-100> direction of the GaN layer 151 (that is, parallel to the a-plane ({11-20} plane) of the GaN layer). The width of the mask 152 (stripe width, the same applies hereinafter) M, the exposed portion width N of the GaN layer 151, and the pitch P of the mask 152 were M = 50 μm, N = 350 μm, and P = 400 μm, respectively. These have a relationship of P = M + N.

(3) Formation of GaN Crystal Next, referring to FIG. 15D, a GaN crystal 153 was grown on the GaN layer 151 on which the mask 152 was formed by the HVPE method. The growth conditions of the GaN crystal are as follows: growth temperature (specifically, sapphire substrate temperature) is 1050 ° C., NH ₃ gas partial pressure is 30 kPa (0.3 atm), HCl gas partial pressure (this corresponds to GaCl gas partial pressure) ) Was 2 kPa (0.02 atm), the temperature of the Ga reservoir was 800 ° C. or higher, and the growth time was 10 hours. Thus, a GaN crystal 153 having a thickness of about 1250 μm was grown.

  Referring to FIG. 15D, in the growth of the GaN crystal 153, a plurality of c-planes 153c and facets 153f are formed on the crystal growth surface, and a V-groove 153p is formed by two opposing facets. It was. Many of the facets forming the V-groove 153p have {11-22} faces. In this example, since the stripe having the longitudinal direction in the <1-100> direction (direction parallel to the {11-22} plane) is formed, it can be seen that the facet is parallel to the longitudinal direction of the stripe.

  When the cross section of the GaN crystal 153 is observed with a fluorescence microscope, three regions are seen due to the difference in brightness. One is a region extending in the c-axis direction from the groove bottom 153v of the V-groove 153p while capturing dislocations in the interior thereof at a high density, and this will be defined later as a high dislocation density region 153h. That is, the high dislocation density region 153h is formed in the c-axis direction from the groove bottom 153v of the V groove 153p to the inside of the crystal. One is a facet growth region 153j extending in the c-axis direction while sweeping dislocations from the facet 153f to the groove bottom 153v. That is, the facet growth region 153j is formed in the c-axis direction from the facet 153f to the inside of the crystal. One is a c-plane growth region 153i extending in the c-axis direction while sweeping dislocations from the c-plane 153c to the groove bottom 153v. That is, the c-plane growth region 153i is formed in the c-axis direction from the c-plane 153c to the inside of the crystal.

  In this embodiment, when the c-plane 153c, facet 153f and V-groove 153p are maintained and the GaN crystal 153 grows, crystal growth and dislocation progress in a direction perpendicular to the crystal growth plane. The dislocations in the facet growth region 153j gather in a region extending in the c-axis direction from the groove bottom 153v of the V-groove 153p to the inside of the crystal, and the dislocation density in this region increases. To do. On the other hand, for this high dislocation density region 153h, the c-plane growth region 153i and the facet growth region 153j are defined as a low dislocation density region 153k. In this way, by forming a GaN crystal having the high dislocation density region 153h and the low dislocation density region 153k, a GaN crystal 153 having a low dislocation density is partially obtained. Note that the high dislocation density region 153h and the low dislocation density region 153k of the GaN crystal 153 in FIG. 15 correspond to the high dislocation density region 1h and the low dislocation density region 1k of the GaN crystal base substrate 1 in FIG. 8, respectively.

  Referring to FIGS. 15D and 15E, after cutting the GaN crystal 153 along a plane parallel to the main surface of the sapphire substrate 150, the main surface is polished to use the GaN crystal base substrate used in this embodiment. It was.

  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.

1 ground substrate, 10c, 153c c-plane, 10f, 153f facet, 1g crystal growth surface side region, 1h, 153h high dislocation density region, 1k, 153k low dislocation density region, 2 crystal growth liquid, 3 nitrogen-containing gas, 4 Crystal processing liquid, 7 reaction vessel, 9 susceptor, 9c crystal contact region, 10 first group III nitride crystal, 10a, 20a surface side region, 10h second region, 10k first region, 12h strain region, 20 second group III nitride crystal, 20c high carbon concentration region, 20d high oxygen concentration region, 30 third group III nitride crystal, 90 group III nitride crystal substrate, 91 n-type GaN layer, 92 Al _0.3 Ga _0.7 n layer, 93 Al _0.04 Ga _0.96 n layer, 94 Al _0.08 Ga _0.92 n layer, 95 Al _0.3 Ga _0.7 n layer, 96 p-type GaN layer, 97 p-side electrode, 98 n-side Pole, 99 Group III nitride semiconductor layer, 140 GaAs substrate, 142 mask layer, 142w window, 143,153 GaN crystal, 143b GaN buffer layer, 150 sapphire substrate, 151 GaN layer, 152 mask, 153 ic surface growth region, 153j Facet growth region, 153p V-groove, 153v groove bottom, 900 Group III nitride semiconductor device, U1, V1, V2, V3, V4, V5, V6, V7, V8, V9, V10, V11, W1, W2, W3 W4, W5 Group III nitride crystal substrate.

Claims (3)

A step of growing a first GaN crystal by a liquid phase method, a step of processing the surface of the first GaN crystal so that a surface roughness Ra is 5 nm or less and a curvature radius of warpage is 2 m or more, method for producing a GaN crystal and a step of growing a second GaN crystal by a vapor phase method processing have been the first GaN on the crystal, the. A GaN crystal substrate comprising the first or second GaN crystal obtained by the manufacturing method according to claim 1 . A group III nitride semiconductor device comprising the GaN crystal substrate of claim 2 ,
A group III nitride semiconductor device in which at least one group III nitride semiconductor layer is formed on the GaN crystal substrate.

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