JP7236655B2 - RAMO4 substrate, manufacturing method thereof, and manufacturing method of group III nitride crystal. - Google Patents

Description

The present invention relates to a _RAMO4 substrate, its manufacturing method, and a manufacturing method of group III-nitride crystals.

In recent years, a single crystal substrate represented by the general formula _RAMO4 has attracted attention as a substrate for growing GaN crystals. wherein R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanides, and A represents the group consisting of Fe(III), Ga, and Al. represents one or more trivalent elements selected from Mg, Mn, Fe(II), Co, Cu, Zn, and Cd. represents a valence element.

In particular, the ScAlMgO ₄ single crystal (also referred to as “SCAMO crystal”), which is an example of RAMO ₄ described in Patent Document 1, has a (111) face ScO ₂ layer with a rock salt structure and a hexagonal (0001 ) are alternately stacked with planar AlMgO ₂ layers. The hexagonal (0001) plane two layers are planar compared to the wurtzite structure, and compared to the in-plane bond, the bond between the upper and lower layers is about 0.03 nm longer, and the bond strength is is weak. Therefore, the _ScAlMgO4 single crystal can be cleaved at the (0001) plane.

Further, the a-axis lattice constant of the hexagonal (0001) AlMgO ₂ layer is 3.23 Å (32.3 nm), the a-axis lattice constant of GaN is 3.18 Å (31.8 nm), The lattice mismatch between the two is about 1.5%. On the other hand, since the lattice mismatch between the sapphire single crystal and GaN is 16%, it can be expected that the SCAM crystal can be used as a growth substrate to obtain a higher quality GaN crystal than the sapphire crystal.

Also, the thermal expansion coefficient of ScAlMgO ₄ crystal is 6.6×10 ⁻⁶ /K, which is larger than 5.5×10 ⁻⁶ /K of GaN. Therefore, after growing a thick GaN crystal of more than 200 μm on the ScAlMgO ₄ crystal, by utilizing the above-mentioned c-plane cleavage and the stress difference during thermal contraction during the cooling process after crystal growth, c It is expected that it will be possible to peel off the surface and make it self-supporting.

However, when a GaN thin film of about several μm is formed on an actual cleaved ScAlMgO ₄ single crystal, the dislocation density is about 5×10 ⁷ cm ⁻² to 1×10 ⁸ cm ⁻² . rice field. The dislocation density of the GaN thin film on the sapphire substrate was about 1×10 ⁸ cm ⁻² to 1×10 ⁹ cm ⁻² , and there was an improvement trend. Considering that the dislocation density is ⁶ cm ⁻² , the dislocation density cannot be sufficiently reduced according to the recent requirements of GaN devices. In addition, when a thick GaN crystal exceeding 400 μm is grown on a cleaved ScAlMgO ₄ single crystal, an attempt was made to make it self-sustaining by utilizing the c-plane exfoliation of ScAlMgO ₄ , but the adhesion was strong and natural exfoliation was difficult. Met. Occasionally, either the ScAlMgO ₄ crystal or the GaN crystal is cracked, and the expected characteristics cannot be fully utilized.

When forming a GaN crystal on a sapphire substrate, in order to reduce the pit density and dislocation density of the GaN crystal after crystal growth, an uneven pattern is formed on the sapphire substrate, and GaN is crystal-grown on the pattern substrate. It is known that such a method is effective.
For example, Patent Document 2 discloses that pit density and dislocation density can be reduced by forming a GaN crystal on a sapphire substrate having conical or pyramidal projections arranged in a lattice pattern on the surface. It is disclosed that there is

In addition, as a method for reducing the dislocation density, Patent Document 3 discloses a method for reducing the dislocation density by crystal-growing GaN on a pattern in which stripe-shaped grooves are formed.

JP 2015-178448 A JP 2016-060659 A JP 2006-114829 A

However, the methods according to Patent Documents 1 to 3 are not sufficient to reduce the dislocation density, and a method for producing a _RAMO4 substrate capable of obtaining a Group III nitride crystal with a lower dislocation density has been a problem.

An object of the present disclosure is to provide a _RAMO4 substrate that solves the above problems.

In order to achieve the above object, the RAMO ₄ substrate according to the present invention is a single crystal represented by the general formula RAMO ₄ (in the general formula, R is from the group consisting of Sc, In, Y, and lanthanide elements represents one or more selected trivalent elements, A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al; M represents Mg , Mn, Fe(II), Co, Cu, Zn, and _Cd . and
Having a truncated triangular pyramid formed by covering the +c plane with a plurality of V-grooves,
When one of the triangular vertex directions of the truncated triangular pyramid is defined as the [-1100] direction of the hexagonal crystal system and the crystal plane orientation,
The slope of the V-groove is composed of a {11-2Z} plane, a (01-1Z) plane, a (-101Z) plane, or a (1-10Z) plane (where Z is a positive integer). .

A method for manufacturing a RAMO ₄ substrate according to the present invention is a single crystal represented by the general formula RAMO ₄ (wherein R is one selected from the group consisting of Sc, In, Y, and lanthanoid elements). or multiple trivalent elements, A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al; M represents Mg, Mn, Fe ( II), representing one or more divalent elements selected from the group consisting of Co, Cu, Zn, and Cd), providing a RAMO ₄ substrate having a +c-plane as a major surface;
In forming a truncated triangular pyramid surrounded by a V-groove by masking and wet-etching the +c plane,
When one of the triangular vertex directions of the truncated triangular pyramid is defined as the [−1100] direction of the hexagonal system and the crystal plane orientation,
The slope of the V-groove is the {11-2Z} plane, or the (01-1Z) plane, (-101Z) plane, or (1-10Z) plane (where Z is a positive integer). The wet etching is performed.

According to the present disclosure, superior RAMO ₄ substrates and low dislocation density group III-nitride crystals can be produced.

(a): Top view of the m-plane proximity pattern of the triangular epitaxial region on the _RAMO4 substrate with unevenness according to the fourth embodiment, (b): Cross-sectional view of the RAMO4 substrate with unevenness according to the _fourth embodiment, (c) ): Plan view of the a-plane proximity pattern of the triangular epitaxial region on the _RAMO4 substrate according to the fourth embodiment. Plan view of m-plane proximity pattern of hexagonal epitaxial regions on RAMO4 substrate according to embodiment ₄ Plan view of the a-plane proximity pattern of the hexagonal epitaxial region on the _RAMO4 substrate according to the fourth embodiment Crystal lattice of _ScAlMgO (normal view) Crystal lattice of _ScAlMgO4 (rotated 60° from the normal view) Crystal lattice of _ScAlMgO4 (120° rotation from the normal view) Definition diagram of the crystal orientation of the _ScAlMgO4 crystal Definition of m-plane orientation of hexagonal crystal Definition of the a-plane orientation of a hexagonal crystal (a): Surface micrograph after wet etching of ScAlMgO substrate, (b): Surface _electron micrograph of GaN thin film formed on uneven _ScAlMgO substrate, (c): GaN on _uneven ScAlMgO substrate Surface electron micrograph of a thick film formed, (d): cross-sectional micrograph of crystal abnormally grown on the V-groove sidewall ([-1100] direction), (e): on the V-groove sidewall ([11-20] direction) Cross-sectional micrograph of abnormally grown crystal Wet etching process flow of _RAMO4 substrate Pattern formed on _ScAlMgO4 substrate Surface electron micrograph of GaN crystal growth on a pattern formed on a _ScAlMgO4 substrate Crystal growth flow on _ScAlMgO4 substrate Crystal growth flow on _ScAlMgO4 substrate Crystal growth flow on _ScAlMgO4 substrate Crystal growth flow on _ScAlMgO4 substrate Surface electron micrograph of a GaN crystal formed on a textured _ScAlMgO4 substrate Surface electron micrograph of a GaN crystal formed on a textured _ScAlMgO4 substrate Surface electron micrograph of a GaN crystal formed on a textured _ScAlMgO4 substrate Optical micrograph of a GaN crystal surface formed on a triangular epitaxial region on a ScAlMgO ₄ substrate with unevenness defined in Embodiment 4. CL image (500x) of the GaN crystal surface formed on the triangular epi region on the uneven ScAlMgO ₄ substrate defined in Embodiment 4. CL image of the GaN crystal surface formed on the unevenness-free _ScAlMgO4 substrate (2000x) CL image of GaN crystal surface formed on uneven _ScAlMgO4 substrate (2000x)

The RAMO ₄ substrate according to the first aspect is a single crystal represented by the general formula RAMO ₄ (wherein R is one selected from the group consisting of Sc, In, Y, and lanthanide elements or represents a plurality of trivalent elements, A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al; M represents Mg, Mn, Fe(II ), representing one or more divalent elements selected from the group consisting of Co, Cu, Zn _, and Cd.
Having a truncated triangular pyramid formed by covering the +c plane with a plurality of V-grooves,
When one of the triangular vertex directions of the truncated triangular pyramid is defined as the [-1100] direction of the hexagonal crystal system and the crystal plane orientation,
The slope of the V-groove is composed of a {11-2Z} plane, a (01-1Z) plane, a (-101Z) plane, or a (1-10Z) plane (where Z is a positive integer). .

In the RAMO ₄ substrate according to the second aspect, in the first aspect, the V-groove slope may be composed of a {11-2Z} plane (where Z is a positive integer).

In the RAMO ₄ substrate according to the third aspect, in the first or second aspect, a group III nitride crystal may be formed on the +C plane.

A method for manufacturing a RAMO ₄ substrate according to the fourth aspect is a single crystal represented by the general formula RAMO ₄ (wherein R is selected from the group consisting of Sc, In, Y, and lanthanoid elements represents one or more trivalent elements, A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al; M represents Mg, Mn, providing a RAMO ₄ substrate having a +c-plane as a major surface composed of Fe(II), Co, Cu, Zn, and Cd representing one or more divalent elements selected from the group consisting of Fe(II), Co, Cu, Zn, and Cd;
In forming a truncated triangular pyramid surrounded by a V-groove by masking and wet-etching the +c plane,
When one of the triangular vertex directions of the truncated triangular pyramid is defined as the [−1100] direction of the hexagonal system and the crystal plane orientation,
The slope of the V-groove is the {11-2Z} plane, or the (01-1Z) plane, (-101Z) plane, or (1-10Z) plane (where Z is a positive integer). The wet etching is performed.

A method for producing a group III nitride crystal according to a fifth aspect comprises preparing the _RAMO4 substrate of the first aspect,
growing a III-nitride crystal on the _RAMO4 substrate;
The III-nitride and the _RAMO4 substrate are spontaneously exfoliated.

Hereinafter, a _RAMO4 substrate, a method for manufacturing the same, and a method for manufacturing a Group III nitride crystal according to embodiments will be described with reference to the accompanying drawings. In addition, the same code|symbol is attached|subjected about the substantially same member in drawing.

A GaN crystal, which is a type of group III nitride crystal with a low dislocation density, is formed on a _ScAlMgO4 substrate, which is a type of _RAMO4 substrate. explain.

First, the physical properties of the ScAlMgO ₄ crystal will be explained. The crystal lattice of the ScAlMgO ₄ single crystal (also called “SCAMO crystal”) is shown in FIG. Atomic rock salt type structure (111) consisting of Sc (scandium) atoms (11) and O (oxygen) atoms (12). Surface ScO ₂ layer, aluminum (Al) atoms and magnesium (Mg) atoms enter the same site. AlMg sites (13) and hexagonal (0001) plane AlMgO layers consisting of O (oxygen) atoms (12) atoms are alternately stacked, and the _two hexagonal (0001) plane layers are laminated. is planar compared to the wurtzite structure, and the bond between the upper and lower layers is about 0.03 nm longer and weaker than the in-plane bond. Therefore, the ScAlMgO ₄ single crystal has the property of being easily cleaved on the (0001) plane as described above. This ScAlMgO ₄ single crystal structure has three-fold symmetry as a unique feature. Looking at the arrangement of atoms, it looks like a hexagonal crystal at first glance, but if you pay attention to the bonding of atoms, you can see that it has three-fold symmetry in a strict sense. The arrangement of the crystal group shown in FIG. 3B, which is obtained by rotating the atomic group of the crystal shown in FIG. Furthermore, it can be seen that the arrangement of the crystals in FIG. 3(c) obtained by rotating the crystal group in FIG. 3(b) by 60° about the c-axis coincides with that in FIG. . For example, when focusing only on the arrangement of scandium (Sc) atoms (11), it has six-fold symmetry, but when focusing on the bonds between scandium (Sc) atoms and oxygen atoms (O), it can have three-fold symmetry. Recognize. In addition, such a view is also seen with respect to the AlMg site. Therefore, from this atomic arrangement, the ScAlMgO ₄ single crystal is expected to possess both three-fold and six-fold symmetry properties.

In fact, when the ScAlMgO ₄ single crystal was examined using XRD (X-ray diffraction method) for evaluating the arrangement of atoms, it was confirmed that it had the property of 6-fold symmetry of the (11-29) plane.

Further, as shown in FIG. 5(a), when a ScAlMgO ₄ single crystal is used as a substrate of ScAlMgO ₄ and a mask is applied and wet etching is performed, three-fold symmetrical pyramid-shaped protrusions appear. It can be said that this result is caused by the bond symmetry of the crystal. The orientation of the ScAlMgO ₄ crystal can be defined from the shape of this triangular pyramid.

The three-fold symmetry of the ScAlMgO ₄ crystal cannot be detected at all by the XRD method described above, and at present cannot be investigated without using the wet etching method described above. This is because the properties are derived from the bonding state of the atoms rather than from the arrangement of atoms in the ScAlMgO ₄ crystal.

A 0.5 μm GaN crystal was grown on such a ScAlMgO ₄ substrate with unevenness by MOCVD, and the result of observing the substrate surface with an electron microscope is shown in FIG. 5(b). It can be seen that a hexagonal GaN crystal is grown on the c-plane at the vertex of the triangular pyramid. According to the XRD (X-ray diffraction method) evaluation, the apex direction of the triangular pyramid-shaped protrusions coincides with the [-1100], [10-10], and [0-110] directions of the ScAlMgO ₄ crystal and the GaN crystal, respectively. It was confirmed that

From these results, the planes appearing in the [-1100], [10-10], [0-110] directions of the ScAlMgO ₄ crystal and [01-10], [1-100], [-1010] It can be said that the faces appearing in the directions are different faces. In the case of the plane corresponding to the m-plane of the GaN crystal, it was fine to regard it as an equivalent plane in the GaN crystal, but the situation is different in the ScAlMgO ₄ crystal.

Here, for the sake of clarity in the following description, the crystal direction and crystal plane of the ScAlMgO ₄ crystal are defined as follows.

FIG. 3(d) shows a convex shape (14) appearing by applying a mask to the ScAlMgO ₄ substrate and performing wet etching. 10] and [0-110] orientations.

When the crystal orientation is defined using the hexagonal Miller index, the crystal plane of the ScAlMgO ₄ crystal is defined as shown in FIG. When the Miller indexes of the a1-axis, a2-axis, a3-axis, and c-axis are represented by k, l, m, and Z, the plane is represented as a (klmZ) plane.
The slopes of the m-plane direction of the hexagonal crystal are the [-1100] direction slopes (21) (-110Z), the [10-10] direction slopes (25) (10-1Z), and the [0-110] direction. is (23)(0-11Z), [01-10] direction is (26)(01-1Z), [1-100] direction is (24)(1-10Z), [ −1010] direction is defined by (22)(−101Z) (where Z is a positive integer). FIG. 4(a) shows a surface when Z=2 as an example.

The slopes in the a-plane direction of the hexagonal crystal are the slopes in the [11-20] direction (31) (11-2Z), the slopes in the [-12-10] direction (35) (-12-1Z), [- 2110] direction slope is (33)(-211Z), [-1-120] direction slope is (32)(-1-12Z), [1-210] direction slope is (36)(1- 21Z), and the slope in the [2-1-10] direction is defined by (34)(2-1-1Z) (where Z is a positive integer). FIG. 4(b) shows a surface when Z=2 as an example.

(Embodiment 1)
The structure of the uneven RAMO ₄ substrate according to the first embodiment is a single crystal represented by the general formula RAMO ₄ (in the general formula, R is selected from the group consisting of Sc, In, Y, and lanthanoid elements. A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al; M represents Mg, Mn , representing one or more divalent elements selected from the group consisting of Fe(II), Co, Cu, Zn, and Cd) with a c-plane surfaced _RAMO4 substrate, one major surface of is the epitaxial plane, which is defined as the +c plane for convenience. It has a V-groove with respect to the +c plane, and is constructed by arranging a Group III nitride crystal on a RAMO ₄ substrate with unevenness. The protrusions of the _RAMO4 substrate with protrusions and the group III nitride are in contact with each other, and the recesses of the _RAMO4 substrate with protrusions and recesses have cavities.

The method for manufacturing this uneven RAMO ₄ substrate is a single crystal represented by the general formula RAMO ₄ (wherein R is one selected from the group consisting of Sc, In, Y, and lanthanide elements or represents a plurality of trivalent elements, A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al; M represents Mg, Mn, Fe(II ), representing one or more divalent elements selected from the group consisting of Co, Cu, Zn, and Cd), with one major surface being the _epitaxial plane. It is processed to the epiready state as. For example, the c-plane is peeled to a predetermined substrate thickness, the off-angle is formed to a predetermined off-angle, and the epitaxial surface is subjected to CMP processing so that Ra is about 0.2 nm. smoothing is performed on the surface and completed with a final wash. The epitaxial plane thus obtained is defined as +c plane for convenience. A hard mask is patterned against the +c plane, the RAMO ₄ substrate is etched to form V-grooves, and finally the hard mask is removed. A group III nitride crystal is grown on the thus completed RAMO ₄ substrate with unevenness.

When a GaN crystal, which is a type of group III nitride crystal with a low dislocation density, is grown on a ScAlMgO4 substrate, which is a type of _RAMO4 substrate, a hexagonal (0001) plane _, which is a cleavage plane of the _ScAlMgO4 substrate, is grown. The a-axis lattice constant of the simple _AlMgO2 layer is 3.23 Å, and the a-axis lattice constant of GaN is 3.18 Å, which are very close. In contrast, the slope of the V-groove of ScAlMgO ₄ does not match the lattice constant of GaN at all. Due to the difference in these physical properties, when a GaN crystal is grown on an uneven ScAlMgO ₄ substrate having V-grooves, selectivity of the crystal growth occurs. The strength of selectivity has a relationship of: c-plane of convex portion on ScAlMgO ₄ substrate>c-plane of concave portion on ScAlMgO ₄ substrate>slant surface of V-groove on ScAlMgO ₄ substrate.

As a result, if the c-plane area of the protrusions on the _ScAlMgO4 substrate is set to be larger than the area of the c-planes of the recesses on the _ScAlMgO4 substrate, the protrusions on the _ScAlMgO4 substrate are most selectively GaN grows, and the growth of GaN on the sides and bottom of the V-groove is suppressed. Therefore, the V-groove is made hollow by connecting the GaN grown on the convex portions by lateral growth. It becomes possible to reduce the dislocation density.

(Embodiment 2)
(Progress leading to the present invention)
The ScAlMgO ₄ single crystal has a hexagonal (0001) AlMgO ₂ plane on the c-plane, which is the c-plane, and its a-axis lattice constant is 0.323 nm (3.23 Å). On the other hand, the a-axis lattice constant of GaN crystal is 0.318 nm (3.18 Å). The a-axis lattice constants of both are very close, and it is possible to grow a high-quality GaN crystal with a low dislocation density on the peeled surface of the ScAlMgO ₄ substrate.

The lattice mismatch between the ScAlMgO ₄ crystal and the GaN crystal is about 1.5%, and the lattice mismatch between the sapphire single crystal and the GaN crystal is 16%. Comparing the respective lattice mismatches, it can be seen that the ScAlMgO ₄ crystal is more suitable as a substrate for growth than the sapphire crystal. Actually, when GaN crystals with a thickness of about 10 μm were grown on each crystal, the dislocation density in the crystal was about 5×10 ⁸ cm ⁻² on the sapphire substrate, whereas it was about 5×10 8 cm −2 on the ScAlMgO ₄ substrate. In , it was greatly reduced to 8×10 ⁷ cm ⁻² .

However, the above dislocation density is not yet sufficient as required by device specifications. For this reason, it is necessary to further reduce the dislocations in the GaN crystal even on the ScAlMgO ₄ substrate, and a selective crystal growth technique is required. The required dislocation density specification is about 5×10 ⁶ cm ⁻² for the current _commercially available self-supporting GaN substrate. If it can be realized, it will be advantageous in terms of cost when compared with a self-supporting GaN substrate, and the market value will increase. In addition, a selective crystal growth structure on ScAlMgO ₄ is also required to promote spontaneous exfoliation of the GaN crystal on ScAlMgO ₄ .

However, the selective crystal growth technique of GaN on _ScAlMgO4 is significantly different from the selective crystal growth technique on sapphire substrate. In the selective crystal ^growth technique on the sapphire substrate, GaN is crystal-grown on the entire surface of the ^uneven sapphire substrate ^. Because of the large size, the size of the uneven pattern is as small as several micrometers, resulting in uniform GaN crystal growth over the entire surface. The target dislocation density is also about 1×10 ⁸ cm ⁻² . On the other hand, using ScAlMgO ₄ whose dislocation density contained in the buffer layer is an order of magnitude lower than that of the sapphire substrate, the pattern size of the crystal growth surface for achieving a low dislocation density of the order of 1×10 ⁶ cm ⁻² is About 5 μm to 100 μm is preferable. This is a guideline for the pattern dimension obtained by selective crystal growth on ScAlMgO ₄ and aiming for a low dislocation density on the order of 1×10 ⁶ cm ⁻² with a thickness of about 10 μm to 100 μm. The dimension of the pattern here may be considered as the dimension of the repetition period. At that time, the deposition of crystals on the sidewalls of the pattern became a big problem.

As for the crystal growth mode of pattern epitaxy, there is a method in which crystals grow from the bottom of the pattern, and a seed crystal is grown three-dimensionally on the upper surface of the pattern and bonded in the lateral direction to promote the bonding of dislocations through slant crystal growth, thereby reducing the dislocation density. There is a method that can be implemented. In the former, the reduction rate of the dislocation density is the area of the bottom of the pattern divided by the total area, and the reduction rate of the dislocation density is about 1/10 at maximum. The latter method uses the principle of dislocation bonding by three-dimensional growth, so that the reduction rate of dislocation density can be reduced to 1/100 or 1/1000, which is very effective. Therefore, the latter epi method is adopted this time.

The inventors of the present invention have discovered a method that enables selective crystal growth of GaN crystals on _ScAlMgO4 by forming pattern grooves in the _ScAlMgO4 substrate in the first embodiment. Efforts have been made to achieve dense GaN crystals. The problem with this approach was the abnormal growth of crystals, which is harmful to the sidewalls of the pattern. As a result of diligent studies by the present inventors, they have found that it is possible to realize a structure in which crystals are not deposited on the side walls of pattern grooves, leading to the present invention. Specifically, it was found that on the RAMO ₄ substrate, there is a plane that is selectively easily crystallized in a certain crystal plane orientation.

In Embodiment 2, a single crystal represented by the general formula RAMO ₄ (in the general formula, R is one or more trivalent selected from the group consisting of Sc, In, Y, and lanthanide elements) represents the elements, A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al, M represents Mg, Mn, Fe(II), Co, Cu , Zn, and Cd representing one or more divalent elements selected from the group consisting of Zn, and Cd) as a major surface for a _RAMO4 substrate having a c-plane as a major surface, one major surface being configured as an epitaxial plane. This is defined by the +c plane, and one of the triangular apex directions of the truncated triangular pyramid that has a V groove on the +c plane and that appears by applying a mask to the epitaxial plane and etching it is a hexagonal [− 1100] direction and the crystal plane orientation, the slope of the V-groove is the {11-2Z} plane, or the (01-1Z) plane, the (-101Z) plane, or the (1-10Z) plane (however, Z is a _positive integer).
By limiting the orientation of the slope of the V-groove in this way, it is possible to suppress harmful GaN crystal growth that occurs on the slope of the V-groove.

(Embodiment 3)
A method of forming a RAMO ₄ substrate with unevenness in order to realize the configuration of the third embodiment will be described below. First, a single crystal represented by the general formula RAMO ₄ (in the general formula, R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanide elements, A represents one or more trivalent elements selected from the group consisting of Fe(III), Ga, and Al; M represents Mg, Mn, Fe(II), Co, Cu, Zn, and A RAMO ₄ substrate having a c-plane as a major surface made of Cd (representing one or more divalent elements selected from the group consisting of Cd) is prepared. Subsequently, one main surface is processed as an epitaxial plane and this plane is defined as the +c plane. Subsequently, one of the triangular vertex directions of the truncated triangular pyramid appearing by applying a mask to the +c plane and performing wet etching is defined as the [-1100] direction of the hexagonal crystal system and the crystal plane orientation. Subsequently, with respect to the +c plane, the slope of the V groove is the {11-2Z} plane, or the (01-1Z) plane, the (-101Z) plane, or the (1-10Z) plane (where Z is a positive A RAMO ₄ substrate with unevenness is completed by processing to form a V-groove so as to be an integer).

(Embodiment 4)
As a fourth embodiment of the present disclosure, FIGS. 1(a) and 1(c) show a region where a GaN crystal is selectively grown on a _RAMO4 substrate and a region where it is not grown. The concept will be described in detail below.
As described above, the ScAlMgO ₄ crystal is a crystal with 3-fold symmetry, and the GaN crystal is a crystal with 6-fold symmetry.

In FIG _. 5(a), a _SiO2 film was deposited _to a thickness of 200 nm to form a perfect circular mask pattern with a pitch of 10 μm and a diameter of 2 μm. The results of observation with an optical microscope of the surface of the substrate on which unevenness appeared by etching are shown. A triangular pattern appears, which is a result of the three-fold symmetry property of the ScAlMgO ₄ single crystal. SiO ₂ as a mask is in a state after being removed by hydrofluoric acid treatment. Although the mask pattern was a perfect circle, the shape of the pattern that appeared was substantially triangular. It can be seen that the ScAlMgO ₄ crystal has an anisotropy of the wet etch rate. After removing the SiO ₂ , there is an area where the +c plane is exposed at the top of the triangular pyramid, and the +c plane is also exposed on the same base as the bottom plane of the triangular pyramid.

FIG. 5(b) is an electron microscope observation of the surface of the patterned ScAlMgO ₄ substrate having the irregularities formed in this way and growing a GaN crystal to a thickness of 0.5 μm by MOCVD. It can be seen that hexagonal GaN crystals are grown on the +c planes of the apexes of the triangular pyramids, and GaN is also grown on the bottoms of the triangular pyramids that are flush with the bottoms of the triangular pyramids. On the other hand, no GaN crystal has grown on the side walls.

Next, FIG. 5(c) shows the result of growing a crystal corresponding to a film thickness of 20 μm on a non-patterned GaN substrate by the HVPE method on the substrate of FIG. 5(b). Abnormal GaN crystals are grown on the (-110Z), (10-1Z), and (0-11Z) planes (Z is a positive integer), which are sidewall slopes of the ScAlMgO ₄ crystal. If crystal growth continues in this state, the GaN crystal on the side wall will grow larger, making it impossible to obtain a flat GaN crystal, and the crystal growth will fail. Therefore, it has been found that the GaN crystals formed on the sidewalls are harmful and that countermeasures for suppressing their generation are necessary.

This phenomenon occurs even if the pattern shape is not a dot but a stripe shape. FIG. 5(d) shows selective crystal growth on the (-110Z) plane (Z is a positive integer) of the striped V-groove. A similar phenomenon occurs in the (10-1Z) and (0-11Z) planes (Z is a positive integer) in the striped V-groove. It was also confirmed that there was no abnormal growth of GaN crystals on the (1-10Z), (-101Z), and (01-1Z) planes (Z is a positive integer) in the opposite direction.

FIG. 5(e) shows a cross section of the stripe structure of the {11-2Z} plane (Z is a positive integer) of the ScAlMgO ₄ substrate. It was confirmed that the {11-2Z} plane (where Z is a positive integer) tends to grow GaN crystals in the lateral direction, and that GaN crystals do not form on the side walls at all.
From these results, it is preferable to expose the (−110Z), (0−11Z), and (10−1Z) planes (where Z is a positive integer) in order to achieve selective crystal growth on the ScAlO ₄ substrate. result in no.

Conversely, it is preferable to expose (01-1Z), (1-10Z), (-101Z) (Z is a positive integer), or {11-2Z} (Z is a positive integer). Become.
From these results, the patterning configuration of the _epi region is shown in FIGS.

FIG. 1(a) is a preferable pattern that can be arranged so that the seed crystal region is most filled in the m-axis direction of the GaN crystal. The epitaxial region (1) is the region where crystal growth starts, and the surrounding area is the non-epitaxial region. FIG. 1(b) shows a cross-sectional view taken along line XX' in FIG. 1(a). A V-groove (4) is formed on the ScAlO ₄ substrate (3).

Amorphous regions other than the epitaxial regions (1) are etched to form non-epitaxial regions that form grooves. The <11-2Z> plane is formed around the epi region (1). Therefore, it quickly grows laterally to become the seed crystal region (2). Since (-110Z), (10-1Z), and (0-11Z) (where Z is an integer) where GaN tends to grow on the sidewall do not exist, a GaN crystal with high crystal quality can be obtained.

FIG. 1(c) shows an arrangement pattern of the epitaxial region that can be refilled with the seed crystal region in the a-axis direction of the GaN crystal. The epitaxial region (5) is the region where crystal growth starts, and the surrounding area is the non-epitaxial region.
Amorphous regions other than the epitaxial region (5) are etched to form non-epitaxial regions that form V-grooves. A {11-2Z} plane (Z is a positive integer) is formed around the epi region (5) . Therefore, it quickly grows laterally to become the seed crystal region (6) . Since slopes (-110Z), (0-11Z), and (10-1Z) (Z is an integer) on which GaN tends to grow do not exist on the sidewall, a GaN crystal with high crystal quality can be obtained.

FIGS. 2(a) and 2(b) are arrangements for avoiding GaN deposition on sidewalls when realizing hexagonal seed regions of GaN crystals.

FIG. 2(a) is a preferable pattern that can be arranged so that the seed crystal region is most filled in the m-axis direction of the GaN seed crystal. The epitaxial region (7) is the region where crystal growth starts, and the surrounding area is the non-epitaxial region. As explained above, to avoid (-110Z), (0-11Z), (10-1Z) (Z is a positive integer ), we It is avoided by inserting a notch. For example, if the cut is composed of {11-2Z} planes (where Z is a positive integer), sidewall deposition can be avoided and crystal quality can be improved. Since the notch portion is composed of {11-2Z} planes (where Z is a positive integer), the epitaxial region (7) rapidly grows laterally to become the seed crystal region (8). FIG. 2(b) is a preferable pattern that can be arranged so that the seed crystal region is most filled in the a-axis direction of the GaN seed crystal. The epitaxial region (9) is the region where crystal growth starts, and the surrounding area is the non-epitaxial region.

In the pattern formation method described in Embodiment 3, when it is composed of triangles or hexagons consisting only of {11-2Z} planes (Z is a positive integer) described in Embodiment 4, ScAlMgO There is no need to worry about the difference in the m-plane of GaN peculiar to the three-fold symmetry of _{the four-} substrate, and the step of investigating the orientation of the _ScAlMgO4 crystals need not be included.

(Embodiment 5)
The non-epi regions consist of V-grooves that are easily formed by wet etching. FIG. 6 shows the formation flow of the V-grooves. First, in step (a) of FIG. 6, a ScAlMgO ₄ substrate having a c-plane surface is prepared. Subsequently, in step (b) of FIG. 6, a hard mask (51) resistant to chemicals containing at least sulfuric acid and hydrogen peroxide is deposited on the ScAlMgO ₄ substrate (50). For example, a silicon dioxide film can be formed by plasma CVD or sputtering.

(1) Subsequently, in step (c) of FIG. 6, a resist mask (52) is formed on the hard mask (51), exposed and patterned.
(2) Subsequently, in step (d) of FIG. 6, the resist mask (52) is used to pattern the hard mask (51). For example, wet etching using a chemical solution containing hydrofluoric acid or a dry etching process can be used to facilitate this process. The resist mask (52) is removed after patterning the hard mask (51). Through such a process it is possible to form a patterned hard mask (53).
(3) Next, while forming a patterned hard mask (53) on _{the ScAlMgO4} substrate (50), sulfuric acid represented by the _chemical formula _H2SO4 and _H2O2 represented by the chemical formula chemically react with the ScAlMgO ₄ crystals in a chemical solution containing at least a hydrogen peroxide solution. As for the temperature of this chemical, it is possible to etch the ScAlMgO ₄ substrate at a practically acceptable etching rate by etching in a high temperature state of 35° C. or higher. The ScAlMgO ₄ substrate (50) is etched by being immersed in a chemical mixture of at least sulfuric acid and hydrogen peroxide. Since the temperature rises to nearly 100° C. due to reaction heat immediately after mixing sulfuric acid and peroxide water, etching may be performed with such a chemical solution. The temperature is adjusted to 95° C., which is lower than the boiling point of water when boiling a chemical solution in which sulfuric acid and hydrogen peroxide are mixed at a ratio of 3:1. A ScAlMgO ₄ substrate (50) having a patterned hard mask as described above may be soaked in this chemical. Here, the temperature of the chemical solution is desirably set in the range of 35°C to 290°C, more preferably in the range of 50°C to 150°C. The higher the temperature, the higher the etching rate, but the more difficult it becomes to control the shape of the V-groove (pattern groove).

More preferably, the temperature of the chemical is in the range of 75° C. to 95° C., and the concentration of sulfuric acid is adjusted to 75% to 95% with a mixed chemical of sulfuric acid and hydrogen peroxide. Under such conditions, it becomes possible to form a V-groove with a smooth slope at an etching rate exceeding 20 μm/hr.

The V-shaped grooves shown in FIGS. 5(d) and 5(e) show cross-sectional shapes etched for 60 minutes with sulfuric acid hydrogen peroxide having a temperature of 95° C. and a sulfuric acid concentration of 90%. The inclination angle of the V-groove slope in the a-axis direction is 45°, and the inclination angle of the V-groove slope in the m-axis direction is 48° for the [-1100] direction slope and 60° for the [1-100] direction slope. ° had a slope. Here, the V groove is defined as follows. A V-groove is defined when the slope of the slope with respect to the horizontal is in the range of 40° to 70° and the area ratio of the bottom of the concave portion of the unevenness is 50% or less of the groove portion. By setting in this way, the area ratio of the bottom of the ScAlMgO ₄ substrate concave portion can be suppressed with respect to the area of the convex portion. will be

(Embodiment 6)
A ScAlMgO ₄ /GaN composite with unevenness in which 0.5 μm GaN is epitaxially grown by MOCVD on the ScAlMgO ₄ with the triangular pattern described in the fourth embodiment will be described below as a sixth embodiment.
FIG. 7(a) is a micrograph of the surface after V-grooves were formed in ScAlMgO ₄ . Each side of the triangle, which is the epitaxial region, is designed to be 10 μm and the pitch is 12 μm. Regions (61) and (64) correspond to epitaxial regions surrounded by {11-2Z} planes (Z is a positive integer) described in the fourth embodiment. Regions (62) and (63) are m planes (-110Z), (0-11Z), (10-1Z), (01-1Z), (1-10Z), (-101Z) (Z is positive (integer of ). FIG. 7(b) corresponds to a photograph of the substrate surface observed with an electron microscope as a result of epitaxial growth of 0.5 μm by MOCVD on the ScAlMgO ₄ substrate having the pattern. It can be seen that the seed crystal grows in a hexagonal shape in the region (65) and the region (68) surrounded by the a-plane <11-2Z> plane (Z is an integer). Seed crystals are formed without bonding in the regions arranged in the m-plane closest arrangement. In the region (69) arranged in the a-plane closest arrangement, the crystals coalesce to form one island, and a void is formed in the lower portion between them. With such a configuration, the influence of takeover from the ScAlMgO ₄ substrate on the lower surface can be suppressed, so a low dislocation density can be realized. On the other hand, in the regions (66) and (67), lateral growth is suppressed in the regions surrounded by the m-planes, so it is found that these regions are not suitable for seed crystal placement.
Here, the process for realizing a seed crystal of 0.5 μm by MOCVD will be described. GaN growth on ScAlMgO ₄ requires a buffer layer due to the heterogeneous growth. Here, after forming a low-temperature buffer layer with a film thickness of 20 nm at a temperature of 600° C. to 700° C., the temperature is increased to over 1100° C. to recrystallize, and then crystal growth is started. It is possible to obtain seed crystals with a uniform grain size.

(Embodiment 7)
Hereinafter, as Embodiment 7, a crystal growth process for obtaining a GaN crystal with a low dislocation density on a hexagonal seed crystal formed on ScAlMgO ₄ with triangular-patterned unevenness explained in Embodiment 6 is shown in FIG. shown in A hexagonal seed crystal (72) is formed on a ScAlMgO ₄ substrate (70) having a V-groove (71) formed thereon by the method described in Embodiment 6 with reference to FIG. 8(a). An electron micrograph of the surface is shown in FIG. 8(e). Subsequently, in FIG. 8B, HVPE is used to grow GaN three-dimensionally to obtain a pyramidal GaN crystal (73). An electron micrograph of the surface is shown in FIG. 8(f). Subsequently, in FIG. 8C, a flat film (74) is two-dimensionally grown using the HVPE method. Finally, a high-quality GaN crystal (75) is crystal-grown to obtain a GaN crystal with a low dislocation density. An electron microscope photograph of the surface is shown in FIG. 8(g). FIG. 9(a) shows a surface optical micrograph of a chip crystal-grown through this process. In this case, the triangular pattern had a dimension of 20 um and a pitch of 24 um. It can be seen that there is a region (76) where a clean smooth film is formed, although there are regions where pits are formed. FIG. 9(b) shows the result of observing the dislocation density of the surface by a CL (cathode luminescence) method at a magnification of 500 times. It can be confirmed that dislocation convergence occurs due to variations in dislocation density. FIG. 10(b) shows the result of magnifying a part of it and observing it at a magnification of 2000 times. The dislocation density in the take-over region (76) from the seed crystal is on the order of 6.0×10 ⁷ cm ⁻² . The dislocation density in the laterally grown region is on the order of 1.2×10 ⁷ cm ⁻² . The dislocation density at the triple point region where crystals from the epi region join is on the order of 1.3×10 ⁸ cm ⁻² . FIG. 10(a) shows the result of observation at a magnification of 2000 times for a sample in which a 3 μm crystal was grown directly on a ScAlMgO ₄ substrate by MOCVD without using selective crystal growth. It can be seen that the dislocation density can be reduced by about one order of magnitude from 1.3×10 ⁸ cm ⁻² to 1.2×10 ⁷ cm ⁻² by using selective epitaxial growth. The seed transfer region (76) has a slightly higher dislocation density. An increase in dislocation density is observed at the triple point, which is the joint of the seed crystal, but this can be suppressed by finely adjusting the arrangement and finely adjusting the crystal growth conditions. It was shown that the dislocation density can be greatly suppressed by pursuing an epistructure that promotes dislocation pair annihilation.
By using the triangular pattern in this manner, the contact area between the GaN crystal and the ScAlMgO ₄ crystal can be reduced, so that the dislocation density can be reduced and, in addition, natural exfoliation can be promoted.

(Embodiment 8)
This time, a seed crystal was formed by MOCVD, and an attempt was made to thicken the film by HVPE. However, it is also possible to directly form the buffer layer by the HVPE method, and a series of processes can be realized by either MOCVD alone or HVPE equipment alone.
Furthermore, if a film thickness of 200 μm or more is deposited by the HVPE method, it is possible to make the GaN crystal self-sustaining by natural peeling from the ScAlMgO ₄ substrate.

It should be noted that the present disclosure includes appropriate combinations of any of the various embodiments and / or examples described above, and each embodiment and / or The effects of the embodiment can be obtained.

The _RAMO4 substrate according to the present invention can be used in a method for manufacturing group III nitride crystals.

1 Triangular Epitaxial Region 2 on ScAlMgO ₄ Substrate in Fourth Embodiment Seed Crystal Growth Region 3 on ScAlMgO ₄ Substrate in Fourth Embodiment ScAlMgO 4 Substrate 4 with V Groove Formed V Groove 5 on ScAlMgO 4 Substrate Fourth Embodiment Seed crystal growth region 7 on ScAlMgO ₄ substrate in Embodiment 4 Epi region 8 on ScAlMgO ₄ substrate in Embodiment 4 Seed crystal growth region on ScAlMgO ₄ substrate in Embodiment ₄ 9 Triangular epitaxial regions on ScAlMgO ₄ substrate in Embodiment 4 11 Scandium (Sc) atoms 12 Oxygen (O) atoms 13 Al—Mg sites 14 ScAlMgO ₄ etching shape 21 (−110Z) plane of hexagonal crystal (Z= 2)
22 (-101Z) plane of hexagonal crystal (when Z = 2)
23 (0-11Z) plane of hexagonal crystal (when Z=2)
24 (1-10Z) plane of hexagonal crystal (when Z = 2)
25 (10-1Z) plane of hexagonal crystal (when Z = 2)
26 (01-1Z) plane of hexagonal crystal (when Z = 2)
31 (11-2Z) plane of hexagonal crystal (when Z = 2)
32 (-1-12Z) plane of hexagonal crystal (when Z = 2)
33 (-211Z) plane of hexagonal crystal (when Z = 2)
34 (2-1-1Z) plane of hexagonal crystal (when Z = 2)
35 (-12-1Z) plane of hexagonal crystal (when Z = 2)
36 (1-21Z) plane of hexagonal crystal (when Z = 2)
50 ScAlMgO ₄ substrate 51 Hard mask 52 Thick film resist mask 53 Patterned hard mask 54 Patterned V-groove 55 Patterned ScAlMgO ₄ substrate 61 Pattern 62 in which the epitaxial region is surrounded by a planes The epitaxial region is m planes A pattern 63 surrounded by a pattern 64 having an epitaxial region surrounded by an a-plane A pattern 65 having an epitaxial region surrounded by an m-plane A region 66 in which GaN is crystal-grown in region 31 A region 67 in which GaN is crystal-grown in region 32 Region 33 GaN crystal-grown region 68 GaN crystal-grown region 69 GaN a-plane closely arranged GaN crystal 70 on patterned ScAlMgO ₄ substrate 71 Patterned on ScAlMgO ₄ substrate Formed V-grooves 72 GaN seed crystals 73 formed on patterned _ScAlMgO4 substrates Pyramidal GaN crystals 74 on GaN seed crystals _formed on patterned ScAlMgO4 substrates Pyramidal GaN crystals Grown smooth GaN crystal 75 High-quality GaN crystal 76 GaN crystal 77 on ScAlMgO ₄ substrate GaN crystal 77 inherited from ScAlMgO ₄ substrate GaN crystal 78 connected by lateral growth GaN crystal 78 on ScAlMgO ₄ substrate GaN crystal region

Claims (5)

A single crystal represented by the general formula RAMO ₄ (wherein R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanide elements, and A represents , Fe(III), Ga, and Al, and M represents one or more trivalent elements selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd. representing one or more divalent elements selected _from the group consisting of:
Having a truncated triangular pyramid formed by covering the +c plane with a plurality of V-grooves,
In the V-groove, the inclination of the slope with respect to the horizontal is in the range of 40° to 70°, and the area ratio of the bottom of the recess of the unevenness is 50% or less of the groove,
When one of the triangular vertex directions of the truncated triangular pyramid is defined as the [-1100] direction of the hexagonal crystal system and the crystal plane orientation,
The slope of the V-groove is composed of a {11-2Z} plane, a (01-1Z) plane, a (-101Z) plane, or a (1-10Z) plane (where Z is a positive integer). , RAMO ₄ substrate. 2. The RAMO ₄ substrate of claim 1, wherein the V-groove slope is composed of {11-2Z} planes (where Z is a positive integer). 3. The _RAMO4 substrate of claim 1 or 2, wherein a III-nitride crystal is formed on the + c- plane. A single crystal represented by the general formula RAMO ₄ (wherein R represents one or more trivalent elements selected from the group consisting of Sc, In, Y, and lanthanide elements, and A represents , Fe(III), Ga, and Al, and M represents one or more trivalent elements selected from the group consisting of Mg, Mn, Fe(II), Co, Cu, Zn, and Cd. preparing a _RAMO4 substrate having a +c-plane as a major surface composed of one or more divalent elements selected from the group consisting of
In forming a truncated triangular pyramid surrounded by a V-groove by masking and wet-etching the +c plane,
When one of the triangular vertex directions of the truncated triangular pyramid is defined as the [−1100] direction of the hexagonal system and the crystal plane orientation,
The slope of the V-groove is the {11-2Z} plane, or the (01-1Z) plane, (-101Z) plane, or (1-10Z) plane (where Z is a positive integer). A method for manufacturing a _RAMO4 substrate, wherein the wet etching is performed. providing a _RAMO4 substrate according to claim 1;
growing a III-nitride crystal on the _RAMO4 substrate;
A method for producing a group III nitride crystal, wherein the group III nitride and the _RAMO4 substrate are spontaneously exfoliated.

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