JP7598113B2 - Crystalline film growth method and crystalline oxide film - Google Patents

Description

The present invention relates to a method for growing a high-quality crystal film with reduced in-plane rotation domains, a crystalline oxide film, and applications using the same.

Gallium oxide has been reported to have five crystal structures, α, β, δ, ε and γ, as well as κ crystal structure. κ-Ga ₂ O ₃ , like β-Ga ₂ O ₃ and α-Ga ₂ O ₃ , has a large band gap of 4.9 eV and is considered to be a promising material for next-generation power semiconductor materials with high voltage resistance and low power consumption (see, for example, Non-Patent Document 1). According to Non-Patent Document 1, since κ-Ga ₂ O ₃ has spontaneous polarization, it has been pointed out that a high concentration of two-dimensional electron gas can be formed at the heterointerface such as κ-Ga ₂ O ₃ / (Al _x Ga _1-x ) ₂ O ₃ , and it is expected that a high-performance power device using this gas will be realized.

Epi-growth technology must be established for the application of κ-Ga ₂ O ₃ to devices. However, since κ-Ga ₂ O ₃ is a metastable phase, there are no single-crystal κ-Ga ₂ O ₃ substrates. Therefore, attempts have been made mainly to grow heteroepi-growth on heterogeneous substrates (see, for example, Non-Patent Documents 2-4). However, Non-Patent Documents 2-4 report that, whether grown by MOCVD, mist CVD, or HVPE, the epi-grown film of κ-Ga ₂ O ₃ consists of three types of domains rotated by 120° in the (001) plane, and these domains are mixed together on the nanoscale (5-10 nm).

When such domains are mixed, the domain boundaries may scatter electrons, reducing mobility or causing current leakage, lowering the breakdown voltage of power devices. Therefore, it is desirable to reduce such rotational domains and realize a single crystal film that preferably has a single in-plane orientation.

Sung Beom Cho et al., Appl. Phys. Lett. , 112, 162101, 2018 Ildiko Cora et al., CrystEngComm, 2017, 19, 1509 Hiroyuki Nishinaka et al., Jpn. J. Appl. Phys. ,57,115601,2018 Masaka Higashiwaki et al., eds., Springer Series in Materials Science 293, Gallium Oxide, p. 223, section 11.3.1

In view of the above, the object of the present invention is to provide a method for growing a high-quality crystal film with reduced in-plane rotation domains, a crystalline oxide film, and uses thereof.

As a result of intensive research to achieve the above object, the inventors have discovered that by using a crystal film growth method using ELO with a specific mask pattern, they have succeeded in creating a crystal film and/or a crystalline oxide film that has a rectangular crystal structure and has fewer in-plane rotation domains than conventional methods, and that the crystallinity and other qualities of the resulting crystal film and/or crystalline oxide film are excellent. They have also discovered that such a crystal film growth method can solve the above-mentioned conventional problems in one fell swoop.

After obtaining the above findings, the inventors conducted further research and completed the present invention.

[1] A method for growing a crystalline film by supplying a raw material to a substrate provided with a mask having a plurality of windows, the crystalline film having a plurality of in-plane rotational domain groups, the plurality of windows being arranged linearly and having a striped shape, the method comprising forming the mask on the substrate and growing the crystalline film such that a growth rate along the linear direction of the window of one of the plurality of in-plane rotational domain groups is greater than a growth rate along the linear direction of the other in-plane rotational domain groups.
[2] The method according to [1] above, wherein the crystalline film comprises a material selected from the group consisting of oxides, nitrides, and oxynitrides.
[3] The method according to _[ 2] above, wherein the oxide is selected from the group consisting of κ-( _{AlxInyGa1 -xy ) 2O3} , _β- ( _AlxInyGa1 - _xy ) _2O3 , and γ-( _{AlxInyGa1 -xy ) 2O3} (wherein x, y, and z satisfy 0≦x≦1, 0≦y≦1, 0≦ _{x +} y≦1).
[4] The method according to any one of [1] to [3] above, wherein a method selected from the group consisting of HVPE, mist CVD and MOCVD is used for growing the crystal film.
[5] The method according to any one of [1] to [4] above, wherein the width of the window is within the range of 0.1 μm to 20 μm.
[6] The method according to any one of [1] to [5] above, wherein the width of the mask is within the range of 5 μm to 500 μm.
[7] The method according to any one of [1] to [6], wherein the width of the window is smaller than the width of the mask.
[8] A method for growing a crystal film by supplying a raw material to a substrate provided with a mask having a plurality of windows, the crystal film having a plurality of in-plane rotational domain groups, the plurality of windows being arranged linearly and having a dot-like shape, the method including forming the mask on the substrate and growing the crystal film such that a growth rate along the linear direction of the window of one of the plurality of in-plane rotational domain groups is greater than a growth rate along the linear direction of the window of another in-plane rotational domain group, the method further including the step of: when a center-to-center distance between two adjacent dots in the linear direction of the window is p, a center-to-center distance between two adjacent dots in a direction perpendicular to the linear direction of the window satisfies p×2/√3 or more and 500 μm or less.
[9] The method according to [8], wherein each of the plurality of windows has a circular and/or polygonal shape.
[10] The method according to [9], wherein the circles and/or polygons are approximately perfect circles and/or approximately regular polygons, and when a center-to-center distance of the approximately perfect circles and/or the approximately regular polygons in a direction parallel to the linear direction of the windows is p, a center-to-center distance of the approximately perfect circles and/or the approximately regular polygons in a direction perpendicular to the linear direction of the windows satisfies p×2/√3 or more and 500 μm or less.
[11] The method according to [10], wherein a diameter of the approximately perfect circle and/or the approximately regular polygon is within a range of 0.1 μm or more and 10 μm or less, and a center-to-center distance of the approximately perfect circle and/or the approximately regular polygon in a direction parallel to the linear direction of the window is within a range of 0.3 μm or more and 25 μm or less.
[12] The method according to any one of [1] to [11] above, wherein the mask comprises a material selected from the group consisting of oxides, nitrides, oxynitrides, and metals.
[13] The method according to any one of [1] to [12] above, wherein the mask is made of an amorphous material.
[14] The method according to any one of [1] to [13], wherein the substrate further comprises a buffer layer between the mask and the substrate.
[15] The method according to [14], further comprising growing the crystalline film on the buffer layer.
[16] The method according to any of [1] to [15], comprising forming the mask as a first mask on the substrate and growing the crystal film as a first crystal film, followed by forming a second mask on the first crystal film and further growing a second crystal film, wherein the second mask has a plurality of windows arranged linearly, and the second mask is formed on the first crystal film such that the plurality of windows of the second mask do not overlap with the plurality of windows of the first mask.
[17] The crystal film is κ-(Al _x In _y Ga _1-xy ) ₂ O ₃ (wherein x, y, and z satisfy 0≦x≦1, 0≦y≦1, 0≦x+y≦1),
the substrate is selected from the group consisting of a sapphire substrate, a GaN substrate, an AlN substrate, a 6H—SiC substrate, and a 4H—SiC substrate;
The method according to any one of claims 1 to 16, wherein the mask is formed such that an angle between the linear direction of the window and a [11-20] direction of the substrate is between -5° and 5°.
[18] The method according to [17] above, wherein the surface index of the substrate is a (0001) surface.
[19] A crystalline oxide film having a rectangular crystal structure and containing at least one or more metals selected from aluminum, gallium and indium, wherein the content of rotational domains in the crystalline oxide film is 30% or less.
[20] The crystalline oxide film according to [19], wherein a main component of the crystalline oxide film is κ-(Al _x In _y Ga _1-xy ) ₂ O ₃ (wherein x, y, and z satisfy 0≦x≦1, 0≦y≦1, 0≦x+y≦1) oriented in the (001) plane.
[21] A semiconductor device comprising the crystalline oxide film according to claim 19 or 20.
[22] A semiconductor element comprising at least a semiconductor layer provided on a crystal substrate having a crystal structure including a [11-20] axis or a [10-10] axis, and a first electrode and a second electrode each disposed on a first surface side of the semiconductor layer, wherein a current flows in the semiconductor layer in a first direction from the first electrode to the second electrode, wherein the semiconductor layer has a crystal structure different from that of the crystal substrate, and the first direction is parallel to the [11-20] axis or the [10-10] axis of the crystal substrate.
[23] The semiconductor device according to [22], wherein the crystal substrate has a corundum structure.
[24] The semiconductor element according to any one of [21] to [23], wherein the semiconductor element is selected from the group consisting of a diode, an ultraviolet detection element, and a transistor.
[25] The semiconductor device according to [23] or [24] above, which is a high electron mobility transistor (HEMT).

The crystal film growth method of the present invention allows for preferential growth of only a single group of in-plane rotation domains. As a result, it is possible to provide a high-quality crystal film and/or crystalline oxide film with reduced in-plane rotation domains.

FIG. 2 is a flow chart showing a method for growing a crystalline film according to an embodiment of the present invention. FIG. 2 is a flow chart showing a method for growing a crystalline film according to an embodiment of the present invention. 2A to 2C are diagrams illustrating steps of forming a buffer layer and a mask on a substrate according to an embodiment of the present invention. 1 is a schematic diagram showing a crystal film having a plurality of in-plane rotation domains to which a crystal film growth method according to an embodiment of the present invention is applied. FIG. FIG. 2 is a schematic diagram for explaining the difference in crystal films obtained by different growth rates of a plurality of in-plane rotation domain groups in an embodiment of the present invention. 1 is a schematic diagram illustrating an exemplary mask in a growth method according to an embodiment of the present invention. 1 is a schematic diagram showing a transistor including a crystal film according to an embodiment of the present invention; 1 is a schematic diagram showing an ultraviolet detection element including a crystal film according to an embodiment of the present invention. FIG. 1 is a schematic diagram showing a high electron mobility transistor (HEMT) including a crystalline film according to an embodiment of the present invention. FIG. 1 is a diagram illustrating a halide vapor phase epitaxy (HVPE) apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a substrate on which a mask is formed via a buffer layer in an embodiment of the present invention. FIG. 2 is a diagram illustrating a substrate on which a mask is formed via a buffer layer in an embodiment of the present invention. FIG. 11 is a diagram illustrating a substrate on which a mask is formed via a buffer layer in Comparative Example 2. FIG. 2 is a diagram showing the results of SEM observation after film formation in Example 1. 15A and 15B are diagrams showing observation results after film formation in Example 1. Fig. 15A is a TEM image, and Fig. 15B and Fig. 15C are diagrams showing selected area electron diffraction (SAED) patterns. FIG. 1 shows the results of an XRD122 diffraction φ scan in Example 1. FIG. 2 is a diagram showing the results of EBSD (Electron Back Scatter Diffraction Patterns) analysis in Example 1. FIG. 13 is a diagram showing the results of SEM observation after film formation in Comparative Example 1. FIG. 1 shows the results of an XRD122 diffraction φ scan in Comparative Example 1. FIG. 1 is a diagram showing the results of EBSD (Electron Back Scatter Diffraction Patterns) analysis in Comparative Example 1. 13 is a diagram showing the results of SEM observation in Example 2. (a) shows a bird's-eye view after 5 minutes, (b) shows a bird's-eye view after 15 minutes, and (c) shows a bird's-eye view after 2 hours. FIG. 13 shows the results of an XRD122 diffraction φ scan in Example 2. FIG. 11 is a diagram showing the results of EBSD (Electron Back Scatter Diffraction Patterns) analysis in Example 2. FIG. 13 is a diagram showing the results of SEM observation after film formation in Comparative Example 2. FIG. 13 is a diagram showing the results of EBSD (Electron Back Scatter Diffraction Patterns) analysis in Comparative Example 2. FIG. 13 is a diagram showing the results of an XRD122 diffraction φ scan in Comparative Example 3.

A method for growing a crystal film in an embodiment of the present invention is a method for supplying raw material onto a substrate having a mask with multiple windows and growing a crystal film, the crystal film having multiple in-plane rotational domain groups, the multiple windows being arranged linearly and having a stripe shape, and the method is characterized in that it includes forming the mask on the substrate and growing the crystal film such that the growth rate along the linear direction of the window of one of the multiple in-plane rotational domain groups is greater than the growth rate along the linear direction of the other in-plane rotational domain groups. In addition, a method for growing a crystal film in an embodiment of the present invention is a method for growing a crystal film by supplying a raw material to a substrate equipped with a mask having multiple windows, the crystal film having multiple in-plane rotational domain groups, the multiple windows being arranged linearly and having a dot-like shape, and the mask is formed on the substrate and the crystal film is grown so that the growth rate along the linear direction of the window of one of the multiple in-plane rotational domain groups is greater than the growth rate along the linear direction of the other in-plane rotational domain groups, and further characterized in that, when the center-to-center distance between two adjacent dots in the linear direction of the multiple windows is p, the center-to-center distance between two adjacent dots in a direction perpendicular to the linear direction of the multiple windows satisfies p×2/√3 or more and 500 μm or less.

The following describes an embodiment of the present invention with reference to the drawings. It is of course possible to combine multiple embodiments of the present invention, or to apply some of the components to other embodiments, and such combinations also belong to the embodiments of the present invention.

Figure 1 is a diagram showing an example of a flow chart for growing a crystal film in an embodiment of the present invention. In step S110, a buffer layer is formed on a substrate. In an embodiment of the present invention, a mask may be formed directly on the substrate (without a buffer layer) and then the crystal film may be grown, or a mask may be formed on the substrate via a buffer layer and then the crystal film may be grown. In an embodiment of the present invention, as shown in step S110 of Figure 1, it is preferable to form the mask on the substrate via a buffer layer and then grow the crystal film on the buffer layer.

(Buffer layer)
The constituent material of the buffer layer is not particularly limited and may be a known material. Examples of the constituent material of the buffer layer include oxides, nitrides, and oxynitrides. Examples of the oxides include metal oxides containing one or more metals selected from aluminum (Al), gallium (Ga), indium (In), iron (Fe), chromium (Cr), vanadium (V), titanium (Ti), rhodium (Rh), iridium (Ir), cobalt (Co), zinc (Zn), tin (Sn), zirconium (Zr), silicon (Si), tungsten (W), tantalum (Ta), hafnium (Hf), scandium (Sc), and yttrium (Y). Examples of the nitrides include nitrides containing one or more metals selected from aluminum (Al), gallium (Ga), and indium (In). More specifically, examples of the nitrides include gallium nitride (GaN), indium nitride (InN), aluminum nitride (AlN), and mixed crystals thereof. Examples of the oxynitride include SiON, AlON, and TiON. In an embodiment of the present invention, the buffer layer preferably contains an oxide, and more preferably contains titanium oxide. By using such a preferable buffer layer, the crystal film having a rectangular crystal structure (e.g., a κ-type crystal structure) with excellent crystal quality can be grown better. The method for forming the buffer layer is not particularly limited and may be a known method. Examples of the method for forming the buffer layer include a vacuum deposition method, a CVD method, and a sputtering method.

Next, in step S120, a mask having a number of windows arranged in a line is formed on the substrate obtained in step S110, on whose surface a buffer layer has been formed, and a crystal film is formed on the obtained substrate.

(substrate)
The substrate is not particularly limited as long as it is provided with a mask having a plurality of windows and serves as a support for the crystal film. Examples of the substrate include a substrate selected from the group consisting of a sapphire substrate, a GaN substrate, an AlN substrate, a 6H-SiC substrate, and a 4H-SiC substrate. In an embodiment of the present invention, the substrate is preferably a crystal substrate. The crystal substrate is not particularly limited as long as it is a substrate containing a crystal as a main component, and may be a known substrate. It may be an insulating substrate, a conductive substrate, or a semiconductor substrate. It may be a single crystal substrate or a polycrystalline substrate. Examples of the crystal substrate include a substrate containing a crystal having a corundum structure as a main component, a substrate containing a crystal having a β-gallia structure as a main component, and a substrate containing a crystal having a hexagonal structure as a main component. In an embodiment of the present invention, the crystal substrate preferably has a crystal structure including a [11-20] axis (a-axis) or a [10-10] axis (m-axis). Examples of crystal structures including a [11-20] axis (a-axis) or a [10-10] axis (m-axis) include corundum structures and hexagonal structures (e.g., ε-type structure, wurtzite-type structure, etc.). The term "main component" refers to a substrate that contains 50% or more of the crystalline matter, preferably 70% or more, and more preferably 90% or more, in terms of composition ratio in the substrate. The plane index of the main surface of the substrate is not particularly limited, but in an embodiment of the present invention, it is preferably the (0001) plane (c-plane).

Examples of the substrate containing a crystal having a corundum structure as a main component include a sapphire substrate and an α-type gallium oxide substrate. Examples of the substrate containing a crystal having a β-gallium structure as a main component include a β-Ga ₂ O ₃ substrate, or a mixed crystal substrate containing β-Ga ₂ O ₃ and Al ₂ O _3. A suitable example of the mixed crystal substrate containing β-Ga ₂ O ₃ and Al ₂ O ₃ is a mixed crystal substrate containing Al ₂ O ₃ in an atomic ratio of more than 0% and 60% or less. Examples of the substrate having a hexagonal crystal structure include a SiC substrate, a ZnO substrate, a GaN substrate, or an AlN substrate. Examples of other crystal substrates include a Si substrate.

In an embodiment of the present invention, the crystal substrate is preferably a sapphire substrate. Examples of the sapphire substrate include a c-plane sapphire substrate, an m-plane sapphire substrate, and an a-plane sapphire substrate. The sapphire substrate may have an off-angle. The off-angle is not particularly limited, but is preferably 0° to 15°. The thickness of the crystal substrate is not particularly limited, but is preferably 50 to 2000 μm, and more preferably 200 to 800 μm.

The mask is not particularly limited as long as it has a plurality of windows and the plurality of windows are arranged in a line. The material of the mask is not particularly limited and may be a known material. It may be an insulating material, a conductive material, or a semiconductor material. The material may be amorphous, single crystal, or polycrystalline. Examples of the material of the convex portion include oxides, nitrides, or carbides of Si, Ge, Ti, Zr, Hf, Ta, Sn, Al, carbon, diamond, metals, and mixtures thereof. More specifically, Si-containing compounds containing SiO ₂ , SiN, or polycrystalline silicon as a main component, and metals having a melting point higher than the crystal growth temperature of the crystalline oxide semiconductor (e.g., noble metals such as platinum, gold, silver, palladium, rhodium, iridium, and ruthenium) may be mentioned. In an embodiment of the present invention, the material of the mask is preferably at least one selected from oxides, nitrides, oxynitrides, and metals. In an embodiment of the present invention, the material of the mask may be an amorphous material. Examples of the oxide, nitride, or oxynitride include oxides, nitrides, or oxynitrides of Si, Ge, Ti, Zr, Hf, Ta, Sn, etc. Examples of the metal include precious metals such as platinum, gold, silver, palladium, rhodium, iridium, and ruthenium.

The shape of the plurality of windows arranged in a line is not particularly limited, and may be stripe-shaped or dot-shaped. In an embodiment of the present invention, when the shape of the plurality of windows is dot-shaped, the center-to-center distance between two adjacent dots in the linear direction of the plurality of windows is usually p, and the center-to-center distance between two adjacent dots in the direction perpendicular to the linear direction of the plurality of windows is q, which satisfies the condition of p×2/√3 or more and 500 μm or less. When the shape of the plurality of windows is dot-shaped, such an arrangement of dimensions allows a domain with a single in-plane orientation to grow preferentially. The surface shape of the dot is also not particularly limited, and may be circular or polygonal (e.g., triangular, rectangular, pentagonal, hexagonal, etc.). In an embodiment of the present invention, it is preferable that the shape of the plurality of windows is stripe-shaped, because a crystal film with a single in-plane orientation can be obtained better and more easily. In an embodiment of the present invention, when the shape of the plurality of windows is dot-shaped, it is preferable that the shape of the plurality of windows is approximately a perfect circle and/or approximately a regular polygon. In this case, if the center-to-center distance between adjacent nearly perfect circles and/or adjacent nearly regular polygons in a direction parallel to the linear direction of the windows is p, the center-to-center distance q between adjacent nearly perfect circles and/or adjacent nearly regular polygons in a direction perpendicular to the linear direction of the windows satisfies p×2/√3 or more and 500 μm or less. Furthermore, in an embodiment of the present invention, it is preferable that the diameter of the nearly perfect circle and/or the nearly regular polygon is in the range of 0.1 μm to 10 μm, and the center-to-center distance between the nearly perfect circle and/or the nearly regular polygon in a direction parallel to the linear direction of the windows is in the range of 0.3 μm to 25 μm. Figure 6 shows a top view of a mask and windows as an example of a mask in which a plurality of windows are arranged linearly. Figure 6(A) shows a stripe shape, Figure 6(B) shows a dot shape (circle shape), Figure 6(C) shows a dot shape (triangle shape), and Figure 6(D) shows a dot shape (square shape).

The mask may be formed by any known method, such as photolithography, electron beam lithography, laser patterning, and subsequent etching (e.g., dry etching or wet etching). The pitch of the pattern shape is not particularly limited, but in the embodiment of the present invention, it is preferably 100 μm or less, more preferably 0.5 μm to 50 μm, and most preferably 0.5 μm to 10 μm.

Figure 3 is a schematic diagram showing a manufacturing process for forming a mask on a substrate via a buffer layer in an embodiment of the present invention. Figure 3(a) shows a substrate 1. A buffer layer 2 is formed on the substrate 1 of Figure 3(a) using a known method to obtain a laminate of Figure 3(b). Next, a mask layer is formed on the obtained laminate (b) using a known film formation method (e.g., vacuum deposition method, CVD method or sputtering method), and then a mask 3 arranged in a line is formed by processing using a known patterning processing method to obtain a laminate of Figure 3(c). Examples of the patterning processing method include known patterning processing methods such as photolithography, electron beam lithography, laser patterning, and subsequent etching (e.g., dry etching or wet etching, etc.).

Figure 11 is a perspective view showing a substrate on which a mask is formed via a buffer layer. The substrate 1 in Figure 11 has a mask 3 having a plurality of striped windows formed on its surface via a buffer layer 2, and the plurality of windows 4 of the mask are arranged linearly. In an embodiment of the present invention, when forming a crystal film having, for example, a rectangular crystal structure (for example, a κ-type crystal structure) as the crystal film, for example, a c-plane sapphire substrate is used as the substrate, and the mask is formed so that the linear direction d1 of the plurality of windows 4 is parallel to the [11-20] axis (a-axis) direction of the sapphire substrate, so that the growth rate along the linear direction of the windows of one of the plurality of in-plane rotational domain groups of the crystal film can be made larger than the growth rate along the linear direction of the other in-plane rotational domain groups. In addition, in an embodiment of the present invention, when the substrate is a substrate selected from the group consisting of a sapphire substrate, a GaN substrate, an AlN substrate, a 6H-SiC substrate, and a 4H-SiC substrate, the angle between the linear direction d1 of the window 4 and the [11-20] direction of the substrate is preferably within the range of -5° to 5°.

The width D _W of the window is not particularly limited as long as it does not impede the object of the present invention. In an embodiment of the present invention, the width of the window is preferably in the range of 0.1 μm to 20 μm, more preferably in the range of 1 μm to 15 μm, and most preferably in the range of 3 μm to 7 μm. The width D _M of the mask is not particularly limited as long as it does not impede the object of the present invention. In an embodiment of the present invention, the width D _M of the mask is preferably in the range of 5 μm to 500 μm, more preferably in the range of 5 μm to 200 μm, and most preferably in the range of 10 μm to 50 μm. The width D _W of the window is preferably smaller than the width D _M of the mask. By setting the width of the window and the width of the mask to values within such preferred ranges, the quality of the crystal film can be improved.

Figure 12 is a schematic perspective view of a substrate having a mask formed on its surface via a buffer layer in another embodiment of the present invention. The substrate 1 in Figure 12 has a mask 3 having a plurality of dot-shaped (circular) windows formed on its surface via a buffer layer 2, and the plurality of windows 4 of the mask are arranged linearly. In an embodiment of the present invention, when forming a crystal film having, for example, a rectangular crystal structure (for example, a κ-type crystal structure) as the crystal film, for example, a c-plane sapphire substrate is used as the substrate, and the mask is formed so that the linear direction of the plurality of windows 4 is parallel to the [11-20] axis (a-axis) direction of the sapphire substrate, so that the growth rate along the linear direction of the windows of one of the plurality of in-plane rotational domain groups of the crystal film can be made larger than the growth rate along the linear direction of the other in-plane rotational domain groups. In an embodiment of the present invention, when the center-to-center distance in a direction parallel to the linear direction of the window 4 is p, the center-to-center distance q in a direction perpendicular to the linear direction of the window 4 satisfies "p x 2/√3 ≤ q ≤ 500 μm". In addition, in an embodiment of the present invention, it is preferable that the diameter R of the window 4 is in the range of 0.1 μm to 10 μm, and the center-to-center distance p in the direction parallel to the linear direction of the window 4 is in the range of 0.3 μm to 25 μm. By setting the width of the window and the width of the mask within such a preferable range, the quality of the crystal film can be improved.

(Crystalline film)
The crystal film is not particularly limited as long as it has a plurality of in-plane rotation domain groups. Here, the in-plane rotation domain group refers to, for example, three types of domains rotated by 120° in the (001) plane when the crystal film is (001) plane κ-Ga ₂ O _3. In an embodiment of the present invention, the crystal film preferably contains at least one selected from the group consisting of oxides, nitrides, and oxynitrides as a main component. Examples of the oxide include metal oxides containing one or more metals selected from aluminum (Al), gallium (Ga), indium (In), iron (Fe), chromium (Cr), vanadium (V), titanium (Ti), rhodium (Rh), iridium (Ir), cobalt (Co), zinc (Zn), tin (Sn), zirconium (Zr), silicon (Si), tungsten (W), tantalum (Ta), hafnium (Hf), scandium (Sc), and yttrium (Y). Examples of the nitride include nitrides containing one or more metals selected from aluminum (Al), gallium (Ga), and indium (In). More specifically, examples of the nitride include gallium nitride (GaN), indium nitride (InN), aluminum nitride (AlN), or mixed crystals thereof. Examples of the oxynitride include SiON, AlON, TiON, and the like.

In an embodiment of the present invention, the crystal film preferably contains an oxide. In addition, in an embodiment of the present invention, the oxide is preferably at least one selected from the group consisting of κ-(Al _x In _y Ga _1-x-y ) ₂ O ₃ , β-(Al _x In _y Ga _1-x-y ) ₂ O ₃ , and γ-(Al _x In _y Ga _1-x-y ) ₂ O ₃ (wherein x, y, and z satisfy 0≦x≦1, 0≦y≦1, 0≦x+y≦1). The crystal structure of the oxide is not particularly limited as long as it does not impede the object of the present invention. Examples of the crystal structure of the oxide include a corundum structure, a β-gallia structure, a hexagonal structure (e.g., an ε-type structure), an orthorhombic structure (e.g., a κ-type structure), a cubic structure, and a tetragonal structure. In an embodiment of the present invention, the crystal structure of the oxide is preferably a corundum structure, a hexagonal structure or an orthorhombic structure, more preferably an orthorhombic structure, and most preferably a κ-type structure.

The crystal film may contain a dopant. The dopant is not particularly limited and may be a known one, and may be an n-type dopant or a p-type dopant. Examples of the n-type dopant include tin, germanium, silicon, titanium, zirconium, vanadium, niobium, or two or more of these elements. Examples of the p-type dopant include Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Ti, Pb, N, P, or two or more of these elements. The content of the dopant in the second crystal layer is not particularly limited, but is preferably 0.00001 atomic % or more, more preferably 0.00001 atomic % to 20 atomic %, and most preferably 0.00001 atomic % to 10 atomic %.

(Raw materials)
The raw material is not particularly limited as long as it contains a substance that is a material for the crystal film, and may contain an inorganic material or an organic material. In an embodiment of the present invention, it is preferable that the raw material contains a metal. Examples of the metal include one or more metals selected from gallium (Ga), iridium (Ir), indium (In), rhodium (Rh), aluminum (Al), gold (Au), silver (Ag), platinum (Pt), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), palladium (Pd), cobalt (Co), ruthenium (Ru), chromium (Cr), molybdenum (Mo), tungsten (W), tantalum (Ta), zinc (Zn), lead (Pb), rhenium (Re), titanium (Ti), tin (Sn), gallium (Ga), magnesium (Mg), calcium (Ca), and zirconium (Zr).

The method for growing the crystal film is not particularly limited and may be a known method. Examples of the method for growing the crystal film include the HVPE method, the mist CVD method, and the MOCVD method. In an embodiment of the present invention, it is preferable to grow the crystal film using the HVPE method.

Hereinafter, the embodiment of the present invention will be described in more detail, taking as an example a case where the HVPE method is used as a method for growing the crystal film and κ-Ga ₂ O ₃ is grown as the crystal film. Specifically, the HVPE method is preferably carried out by gasifying a metal source containing a metal to form a metal halide gas, and then supplying the metal halide gas and an oxygen-containing source gas to the crystal substrate in a reaction chamber to form a film. In addition, in the embodiment of the present invention, it is also preferable to supply a reactive gas onto the crystal substrate and perform the film formation under the flow of the reactive gas.

(Metal Source)
The metal source is not particularly limited as long as it contains a metal and can be gasified, and may be a metal element or a metal compound. Examples of the metal include one or more metals selected from gallium, aluminum, indium, iron, chromium, vanadium, titanium, rhodium, nickel, cobalt, and iridium. In an embodiment of the present invention, the metal is preferably one or more metals selected from gallium, aluminum, and indium, more preferably gallium, and the metal source is most preferably gallium element. The metal source may be gas, liquid, or solid, but in an embodiment of the present invention, for example, when gallium is used as the metal, the metal source is preferably liquid.

The gasification means is not particularly limited and may be a known means as long as it does not impede the object of the present invention. In an embodiment of the present invention, it is preferable that the gasification means is performed by halogenating the metal source. The halogenating agent used for the halogenation is not particularly limited and may be a known halogenating agent as long as it can halogenate the metal source. Examples of the halogenating agent include halogen and hydrogen halide. Examples of the halogen include fluorine, chlorine, bromine, and iodine. Examples of the hydrogen halide include hydrogen fluoride, hydrogen chloride, hydrogen bromide, and hydrogen iodide. In an embodiment of the present invention, it is preferable to use hydrogen halide for the halogenation, and more preferably hydrogen chloride. In an embodiment of the present invention, it is preferable to perform the gasification by supplying a halogen or hydrogen halide as a halogenating agent to the metal source and reacting the metal source with the halogen or hydrogen halide at a temperature equal to or higher than the vaporization temperature of the metal halide to form a metal halide. The halogenation reaction temperature is not particularly limited, but in an embodiment of the present invention, for example, when the metal source is gallium and the halogenating agent is HCl, the temperature is preferably 900°C or less, more preferably 700°C or less, and most preferably 400°C to 700°C. The metal halide gas is not particularly limited as long as it is a gas containing a halide of the metal source. Examples of the metal halide gas include halides of the metal (fluorides, chlorides, bromides, iodides, etc.).

In an embodiment of the present invention, a metal source containing a metal is gasified to form a metal halide gas, and then the metal halide gas and the oxygen-containing source gas are supplied onto the substrate in the reaction chamber. In an embodiment of the present invention, a reactive gas is supplied onto the substrate. The temperature for forming the crystal layer is not particularly limited, but in an embodiment of the present invention, for example, when the metal source is gallium and the halogenating agent is HCl, the temperature is preferably 900° C. or less, more preferably 700° C. or less, and most preferably 400° C. to 700° C. The oxygen-containing source gas is, for example, one or more gases selected from O ₂ gas, CO ₂ gas, NO gas, NO ₂ gas, N ₂ O gas, H ₂ O gas, or O ₃ gas. In an embodiment of the present invention, the oxygen-containing source gas is preferably one or more gases selected from the group consisting of O ₂ , H ₂ O, and N ₂ O, and more preferably contains O ₂ . The reactive gas is usually a gas having a different reactivity from the metal halide gas and the oxygen-containing source gas, and does not include an inert gas. The reactive gas is not particularly limited, but may be, for example, an etching gas. The etching gas is not particularly limited as long as it does not impede the object of the present invention, and may be a known etching gas. In an embodiment of the present invention, the reactive gas is preferably a halogen gas (e.g., fluorine gas, chlorine gas, bromine gas, or iodine gas), a hydrogen halide gas (e.g., hydrofluoric acid gas, hydrochloric acid gas, hydrogen bromide gas, or hydrogen iodide gas), hydrogen gas, or a mixed gas of two or more of these, and preferably contains a hydrogen halide gas, and most preferably contains hydrogen chloride. The metal halide gas, the oxygen-containing source gas, and the reactive gas may contain a carrier gas. Examples of the carrier gas include an inert gas such as nitrogen or argon. The partial pressure of the metal halide gas is not particularly limited, but in an embodiment of the present invention, it is preferably 0.5 Pa to 1 kPa, and more preferably 5 Pa to 0.5 kPa. The partial pressure of the oxygen-containing source gas is not particularly limited, but in an embodiment of the present invention, it is preferably 0.5 to 100 times the partial pressure of the metal halide gas, and more preferably 1 to 20 times. The partial pressure of the reactive gas is also not particularly limited, but in an embodiment of the present invention, it is preferably 0.1 to 5 times the partial pressure of the metal halide gas, and more preferably 0.2 to 3 times.

In an embodiment of the present invention, it is also preferable to supply a dopant-containing source gas to the substrate. The dopant-containing source gas is not particularly limited as long as it contains a dopant. The dopant is also not particularly limited, but in an embodiment of the present invention, the dopant preferably contains one or more elements selected from germanium, silicon, titanium, zirconium, vanadium, niobium and tin, more preferably germanium, silicon or tin, and most preferably germanium. By using the dopant-containing source gas in this way, the conductivity of the resulting film can be easily controlled. The dopant-containing source gas preferably contains the dopant in the form of a compound (e.g., a halide, an oxide, etc.), more preferably in the form of a halide. The partial pressure of the dopant-containing source gas is not particularly limited, but in an embodiment of the present invention, it is preferably 1×10 ⁻⁷ to 0.1 times, and more preferably 2.5×10 ⁻⁶ to 7.5×10 ⁻² times, the partial pressure of the metal-containing source gas. In addition, in an embodiment of the present invention, it is preferable to supply the dopant-containing source gas onto the substrate together with the reactive gas.

In an embodiment of the present invention, it is also preferable to form the mask as a first mask on the substrate, grow the crystal film as a first crystal film, and then, as step S130, form a second mask on the first crystal film and further grow the second crystal film. By further growing the second crystal film in this manner, a second crystal film having an in-plane rotation domain further reduced than that of the first crystal film can be obtained. In this case, the second mask has a plurality of windows arranged linearly like the first mask, and is preferably formed so that the plurality of windows of the second mask and the plurality of windows of the first mask do not overlap.

Figure 2 is a diagram showing another preferred example of a flow chart for growing a crystal film in an embodiment of the present invention. The growth method shown in Figure 2 differs from the growth method shown in Figure 1 in that it includes a step S210 between steps S110 and S120, in which a flat film is grown on the buffer layer. The material of the flat film is not particularly limited, but in an embodiment of the present invention, it is preferably the same as the material of the crystal film. The method of forming the flat film may also be the same as the method of forming the crystal film.

In an embodiment of the present invention, the crystal film has a plurality of in-plane rotational domain groups, and the mask is formed on the substrate so that the growth rate of the window in one of the plurality of in-plane rotational domain groups along the linear direction is greater than the growth rate of the other in-plane rotational domain groups along the linear direction. The method of forming a mask and growing the crystal film in this manner will be described in more detail below with reference to the drawings.

Figure 4 is a surface diagram showing a crystal film having multiple in-plane rotation domains to which the crystal film growth method of the embodiment of the present invention is applied. Figure 4 shows a schematic diagram of the crystal film grown from the window 310 growing laterally on the mask when the crystal film is grown on a substrate having a striped mask. For simplicity, the crystal film growing on the window 310 is not shown. When the crystal film is grown using ELO, as shown in Figure 4, it usually contains multiple in-plane rotation domains 320a, 320b, and 320c when it grows laterally from the window 310. For convenience, Figure 4 shows the multiple in-plane rotation domains 320a, 320b, and 320c growing evenly in a specific order, but the crystal film obtained by the conventional crystal film growth method usually has these three types of in-plane rotation domains distributed in random sizes and orders.

5 is a schematic diagram for explaining the difference in the crystal film obtained by the difference in the growth rate of the multiple in-plane rotational domain groups in the embodiment of the present invention. FIG. 5(A) shows the case where the growth rate of the in-plane rotational domain 320b along the linear direction of the mask (hereinafter also simply referred to as "growth rate") is greater than that of the in-plane rotational domain 320c, and the growth rate of the in-plane rotational domain 320a is greater than that of the in-plane rotational domain 320b. FIG. 5(B) shows the case where the growth rates of the in-plane rotational domain 320b and the in-plane rotational domain 320c are equal, and the growth rate of the in-plane rotational domain 320a is greater than that of the in-plane rotational domains 320b and 320c. As shown in FIG. 5(A) and FIG. 5(B), when the growth rate of one of the multiple in-plane rotational domain groups is greater than that of the other in-plane rotational domain groups, a crystal film having a single in-plane orientation in the lateral growth portion can be obtained. This is a finding that the present inventors first obtained through actual experiments, as shown in the examples described below. On the other hand, FIG. 5(C) shows a case where the growth rates of the in-plane rotational domains 320a, 320b, and 320c are all equal. FIG. 5(D) shows a case where the growth rate of the in-plane rotational domain 320b is greater than the growth rate of the in-plane rotational domain 320a, and the growth rate of the in-plane rotational domain 320b is equal to the growth rate of the in-plane rotational domain 320c. In the cases of FIG. 5(C) and FIG. 5(D), it is difficult to obtain a crystal film having a single in-plane orientation.

According to the growth method of the embodiment of the present invention described above, for example, a crystalline film (hereinafter also referred to as a "crystalline oxide film") having a rectangular crystal structure and containing at least one or more metals selected from aluminum, gallium and indium, characterized in that the content of rotation domains in the crystalline oxide film is 30% or less, can be obtained. Also, according to the preferred growth method described above, a crystalline oxide film having a content of the rotation domains of 20% or less can be obtained. Here, the content of the rotation domains can be calculated, for example, from an image of the result of EBSD (Electron Backscattered Diffraction) measured from the surface side of the crystalline film. In an embodiment of the present invention, the main component of the crystalline oxide film is preferably a crystalline oxide having a rectangular crystal structure, and more preferably κ-(Al _x In _y Ga _1-x-y ) ₂ O ₃ (wherein x, y, and z satisfy 0≦x≦1, 0≦y≦1, 0≦x+y≦1) oriented in the (001) plane. Here, the term "main component" means that, for example, when the crystalline oxide film contains κ-Ga ₂ O ₃ as a main component, κ-Ga ₂ O ₃ is preferably contained in an atomic ratio of 50% or more, more preferably 70% or more, and even more preferably 90% or more of the total components of the crystalline film, and may be 100%.

In addition, the crystalline oxide film can be suitably used as the semiconductor layer in a semiconductor element having a crystal structure different from that of the crystal substrate, the semiconductor layer having at least a semiconductor layer provided on a crystal substrate having a crystal structure including an [11-20] axis (a-axis) or a [10-10] axis (m-axis), a first electrode and a second electrode respectively disposed on the first surface side of the semiconductor layer, and a current flows in the semiconductor layer in a first direction from the first electrode to the second electrode, the semiconductor layer having a crystal structure different from that of the crystal substrate, and the first direction is parallel to the a-axis direction or the m-axis direction of the crystal substrate, and the semiconductor element thus obtained is also included in one of the embodiments of the present invention. In an embodiment of the present invention, it is preferable that the crystal substrate has a corundum structure. Note that here, being parallel to the [11-20] axis (a-axis) or the [10-10] axis (m-axis) means that it does not have to be completely parallel, but may be slightly deviated from that (for example, the angle between the first direction and the a-axis or the m-axis may be greater than 0° and less than or equal to 10°).

The crystalline film or crystalline oxide film according to the embodiment of the present invention can be particularly suitably used in semiconductor elements, and is particularly useful in power devices. Examples of semiconductor elements formed using the crystalline film or crystalline oxide film include semiconductor elements selected from the group consisting of diodes, ultraviolet detection elements, and transistors, and more specifically, examples of such elements include transistors and TFTs such as MIS, HEMT, and MOS, Schottky barrier diodes using semiconductor-metal junctions, PN or PIN diodes combined with other P layers, and light-receiving and emitting elements. In the embodiment of the present invention, it is preferable that the semiconductor element is a HEMT. In the embodiment of the present invention, the crystalline film or crystalline oxide film may be used as it is in a semiconductor element, or the substrate and/or the mask may be peeled off using known means and then applied to the semiconductor element.

Figure 7 is a schematic diagram showing a transistor including a crystal film or a crystalline oxide film (hereinafter, simply referred to as a "crystal film") according to an embodiment of the present invention. The transistor 900 includes at least a crystal film 910 according to an embodiment of the present invention, a source 920 formed on a portion of one main surface of the crystal film 910, a drain 930 formed opposite the source 920, a channel 940 formed between the source 920 and the drain 930, an insulating film 950 formed on the channel 940, and a gate electrode 960 formed on the insulating film 950.

The crystal film 910 is preferably a single crystal film including κ-Ga ₂ O ₃ or a mixed crystal thereof according to an embodiment of the present invention. In the embodiment of the present invention, the crystal film 910 preferably exhibits n-type conductivity. The thickness of the crystal film is, for example, 0.1 μm or more and 10 μm or less.

The source 920 includes an n+ type region 970a in which a dopant element is implanted at a high concentration into a part of the crystal film 910, and an electrode 980a formed on the n+ type region 970a. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, niobium, or two or more of these elements. The carrier concentration of the n+ type region 970a is, for example, in the range of 1×10 ¹⁵ /cm ³ to 1×10 ²⁰ /cm ^3. The n+ type region 970a may be formed not only by implantation, but also by using, for example, a known patterning method and a known film formation method. Examples of the electrode 980a include metal materials selected from the group consisting of Al, Ti, Pt, Ru, Au, and alloys thereof.

The drain 430 includes an n+ type region 970b in which a dopant element is implanted at a high concentration into a part of the crystal film 910, and an electrode 980b formed on the n+ type region 970b. As with the n+ type region 970a, the dopant may be, for example, an n-type dopant such as tin, germanium, silicon, titanium, zirconium, vanadium, niobium, or two or more elements thereof. The carrier concentration of the n+ type region 970b is, for example, in the range of 1×10 ¹⁵ /cm ³ to 1×10 ²⁰ /cm ^3. The n+ type region 970b may be formed not only by implantation, but also by using, for example, a known patterning method and a known film formation method. The electrode 980b may be, for example, a metal material selected from the group consisting of Al, Ti, Pt, Ru, Au, and alloys thereof.

_The insulating film 950 is made of an insulating material selected from the group consisting of _Al2O3 , _SiO2 , _HfO2 , SiN, and SiON. The gate electrode 906 is made of a metal material selected from the group consisting of Al, Ti, Pt, Ru, Au, and alloys thereof. The insulating film 950 has a thickness of, for example, 1 nm or more and 100 nm or less.

A method for manufacturing such a transistor 900 will be described. The transistor 900 is manufactured by an existing LSI manufacturing process. For example, the transistor 900 is manufactured by forming n+ regions 970a and 970b by ion implantation using a photolithography technique on the α-Ga ₂ O ₃ single crystal 910 obtained in the first embodiment, then forming an insulating film 950 using an existing growth technique such as vapor phase epitaxial growth, liquid phase epitaxial growth, halide vapor phase growth, or metal organic chemical vapor deposition (MOCVD), and then forming electrodes 980a and 980b and a gate electrode 460 by an existing electrode formation technique such as vacuum deposition or sputtering.

Although not shown, a pn junction (which may be a heterojunction) can be formed by using a crystal film according to an embodiment of the present invention as an n-type semiconductor to manufacture a diode.

Figure 8 is a schematic diagram showing an ultraviolet detection element equipped with a crystal film according to an embodiment of the present invention.

As shown in Figures 8(A) and (B), the ultraviolet detection elements 1000a and 1000b include at least the crystal film 1010 of the present invention, a Schottky electrode 1020 formed on the crystal film 1010, and an ohmic electrode 1030 formed on the crystal film 1010. In detail, according to the ultraviolet detection element 1000a of Figure 8(A), the Schottky electrode 1020 is formed on one main surface of the α-Ga ₂ O ₃ single crystal 1010, and the ohmic electrode 1030 is formed on the other main surface (the back surface in Figure 8) of the crystal film 1010. On the other hand, according to the ultraviolet detection element 1000b of Figure 8(B), as described later, the crystal film 1010 is located on a substrate (e.g., a sapphire substrate, etc.) 1040, so that the Schottky electrode 1020 and the ohmic electrode 1030 are both formed on the same main surface of the crystal film 1010.

The crystal film 1010 is preferably a single crystal film including κ-Ga ₂ O ₃ or a mixed crystal thereof according to an embodiment of the present invention. In the embodiment of the present invention, the crystal film 910 preferably exhibits n-type conductivity. The thickness of the crystal film is, for example, 0.1 μm or more and 10 μm or less.

The Schottky electrode 1020 may be a metal material selected from the group consisting of Ni, Pt, Au, and alloys thereof. The Ohmic electrode 1030 may be a metal material selected from the group consisting of Ti, In, and alloys thereof.

A method for manufacturing such an ultraviolet detection element 1000 will be described. The ultraviolet detection element 1000 is manufactured by an existing large-scale integrated circuit (LSI) manufacturing process. For example, the ultraviolet detection element 1000 is manufactured by forming a Schottky electrode 1020 and an ohmic electrode 1030 on the main surface and back surface of the crystal film 1010 in the embodiment of the present invention by using existing metal film deposition techniques such as vacuum deposition and sputtering and photolithography. Similarly, the ultraviolet detection element 1000b may be manufactured by forming a Schottky electrode 1020 and an ohmic electrode 1030 on the main surface of an α-Ga ₂ O ₃ single crystal 1010 formed on a substrate (e.g., a sapphire substrate, etc.) 1040 by using the above-mentioned metal film deposition technique and photolithography.

Figure 9 shows an example of a high electron mobility transistor (HEMT) according to the present invention. The HEMT in Figure 9 includes a wide bandgap n-type semiconductor layer 121a, a narrow bandgap n-type semiconductor layer 121b, an n+ type semiconductor layer 121c, a semi-insulator layer 124, a buffer layer 128, a gate electrode 125a, a source electrode 125b, and a drain electrode 125c.

The material of each electrode may be a known electrode material, and examples of the electrode material include metals such as Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, Ta, Ti, Au, Pt, V, Mn, Ni, Cu, Hf, W, Ir, Zn, In, Pd, Nd, and Ag, or alloys thereof; metal oxide conductive films such as tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); organic conductive compounds such as polyaniline, polythiophene, and polypyrrole, or mixtures and laminates thereof. The electrodes can be formed by known means such as vacuum deposition or sputtering.

The n+ type semiconductor layer is not particularly limited, but it is preferable that the main component of the n+ type semiconductor layer is the same as or similar to the main component of the wide band gap n-type semiconductor layer 121a or the narrow band gap n-type semiconductor layer 121b.

The crystal film can be used for the n-type semiconductor layer 121a with a wide band gap and the n-type semiconductor layer 121b with a narrow band gap. By using it in this way, a semiconductor device can be realized that has excellent high-temperature and high-frequency characteristics and further has excellent semiconductor characteristics such as high-temperature and high-voltage resistance.

The following describes examples of the present invention, but the present invention is not limited to these.

Example 1
1. Formation of a buffer layer and a mask A TiO _x film (thickness 2 nm) was formed as a buffer layer on a (0001) sapphire substrate by RF sputtering. A SiO _x mask was formed on the obtained titanium oxide film by RF sputtering and photolithography. The mask pattern was as shown in FIG. 11, and was formed so that the [11-20] axis direction of the sapphire and the linear direction of the multiple windows 4 (the direction of d1 in FIG. 11) were parallel. In this case, the direction of d2 in FIG. 11 is the [10-10] direction of the sapphire. The width D _W of the window was 5 μm, and the width D _M of the mask was 20 μm.

2. Growth of Crystal Film 2-1. HVPE Apparatus The halide vapor phase epitaxy (HVPE) apparatus 50 used in this embodiment will be described with reference to FIG. 10. The HVPE apparatus 50 includes a reaction chamber 51, a heater 52a for heating a metal source 57, and a heater 52b for heating a substrate fixed to a substrate holder 56. The reaction chamber 51 further includes an oxygen-containing source gas supply pipe 55b, a reactive gas supply pipe 54b, and a substrate holder 56 for placing a substrate. The reactive gas supply pipe 54b includes a metal-containing source gas supply pipe 53b, forming a double-pipe structure. The oxygen-containing source gas supply pipe 55b is connected to an oxygen-containing source gas supply source 55a, and forms a flow path for the oxygen-containing source gas so that the oxygen-containing source gas can be supplied from the oxygen-containing source gas supply source 55a through the oxygen-containing source gas supply pipe 55b to the substrate fixed to the substrate holder 56. The reactive gas supply pipe 54b forms a flow path for the reactive gas so that the reactive gas can be supplied to the substrate fixed to the substrate holder 56. The metal-containing source gas supply pipe 53b is connected to the halogen-containing source gas supply pipe 53a, and the halogen-containing source gas is supplied to the metal source to become a metal-containing source gas, and a metal-containing source gas exhaust part 59 is provided.

A gallium (Ga) metal source 57 (with a purity of 99.99999% or more) was placed inside the metal-containing source gas supply pipe 53b, and the sapphire substrate with the buffer layer and mask obtained in 1 above was placed as a substrate on the substrate holder 56 inside the reaction chamber 51. Thereafter, the heaters 52a and 52b were operated to raise the temperature inside the reaction chamber 51 to 540°C.

Hydrogen chloride (HCl) gas (purity 99.999% or more) was supplied from the halogen-containing source gas supply source 53a to the gallium (Ga) metal 57 arranged inside the metal-containing source gas supply pipe 53b. Gallium chloride (GaCl/GaCl ₃ ) was generated by a chemical reaction between the Ga metal and the hydrogen chloride (HCl) gas. The obtained gallium chloride (GaCl/GaCl ₃ ) and O ₂ gas (purity 99.99995% or more) supplied from the oxygen-containing source gas supply source 55a were supplied to the substrate through the metal-containing source supply pipe 53b and the oxygen-containing source gas supply pipe 55b, respectively. Then, the gallium chloride (GaCl/GaCl ₃ ) and the O ₂ gas were reacted on the substrate at atmospheric pressure and 540° C. to form a film on the substrate. The film formation time was 25 minutes. Here, the partial pressure of the HCl gas supplied from the halogen-containing raw material gas supply source 53a was maintained at 0.125 kPa, and the partial pressure of the _O2 gas supplied from the oxygen-containing raw material gas supply source 55 was maintained at 1.25 kPa. The obtained film was identified by performing 2θ/ω scanning at angles of 15 degrees to ₉₅ degrees using a thin film XRD diffractometer. The measurement was performed using CuKα radiation. As a result, the obtained film was κ- _Ga2O3 . A bird's-eye SEM image of the obtained crystal film is shown in FIG.

(evaluation)
A cross-sectional TEM image of the obtained crystal film is shown in FIG. 15(A), and selective area electron diffraction (SAED) patterns observed from the [11-20] direction in the window and lateral growth parts are shown in FIG. 15(B) and (C), respectively. As is clear from FIG. 15(A), in the lateral growth part, no streaky contrast due to dislocations or domain boundaries associated with domain mixing is observed, and it can be seen that a clean crystal is obtained. Also, as is clear from the SAED pattern of the lateral growth part in FIG. 15(B), single crystal κ-Ga ₂ O ₃ was obtained in the lateral growth part. Also, FIG. 16 shows the result of φ scan of κ-Ga ₂ O ₃ 122 diffraction by XRD. As is clear from FIG. 16, it can be seen that a crystal film with reduced rotation domains has been obtained, with the four peak intensities being overwhelmingly larger than the other eight peak intensities. FIG. 17 shows the results of EBSD (Electron Backscattered Diffraction) measurement of the obtained crystal film from the surface side. As is clear from FIG. 17, one rotation domain A occupies a large area compared to the other rotation domains B and C. As shown in FIG. 17, the rotation domain A is a domain whose [010] direction is perpendicular to the [11-20] direction of the sapphire substrate. In addition, it can be seen that a κ-Ga ₂ O ₃ single crystal having a single in-plane orientation is obtained in the lateral growth portion.

(Comparative Example 1)
The crystal film was grown in the same manner as in Example 1, except that the mask was formed on the substrate in the mask pattern shown in FIG. 11, and the [10-10] axis direction of the sapphire was parallel to the linear direction of the windows 4 (the direction of d1 in FIG. 11). The obtained film was identified by performing 2θ/ω scanning at angles of 15 degrees to 95 degrees using a thin film XRD diffractometer. The measurement was performed using CuKα radiation. As a result, the obtained film was κ-Ga ₂ O _3. A bird's-eye SEM image of the obtained crystal film is shown in FIG. 18. FIG. 19 shows the results of φ scanning of κ-Ga ₂ O ₃ 122 diffraction by XRD. As is clear from FIG. 19, eight strong peaks and four weak peaks are observed, and it is understood that there are multiple in-plane rotation domains. FIG. 20 shows the results of EBSD measurement. As is clear from FIG. 20, it is found that two types of in-plane rotation domains are mixed in the laterally grown portion.

Example 2
The crystal film was grown in the same manner as in Example 1, except that the mask pattern on the substrate was as shown in FIG. 12, the window width (diameter) _DW was 5 μm, the center-to-center distance q in the direction d2 perpendicular to the linear direction in the multiple windows 4 was 50 μm, and the center-to-center distance p in the direction parallel to the linear direction d1 was 20 μm. The crystal growth was observed by SEM 5 minutes, 15 minutes, and 2 hours after the start of the crystal film growth. The results are shown in FIG. 21. As is clear from FIG. 21, hexagonal κ-Ga ₂ O ₃ islands were formed from each window of the dot pattern (FIG. 21(a)). These κ-Ga ₂ O ₃ islands eventually met in the short-period direction of the mask to form κ-Ga ₂ O ₃ stripes with sawtooth sides (FIG. 21(b)). When the growth was continued, the κ-Ga ₂ O ₃ stripes met to form a continuous film (c). FIG. 22 shows the results of φ scan of κ-Ga ₂ O ₃ 122 diffraction by XRD of the obtained crystal film. As is clear from FIG. 22, the four peak intensities are overwhelmingly larger than the other eight peak intensities, and it can be seen that a crystal film with reduced rotation domains has been obtained. In addition, the results of EBSD (Electron Backscattered Diffraction) measured from the surface side of the obtained crystal film are shown in FIG. 23. As is clear from FIG. 23, it can be seen that one rotation domain A occupies the majority of the area compared to the other rotation domains B and C. Note that the rotation domain A is a domain in which the [010] direction is perpendicular to the [11-20] direction of the sapphire substrate, as shown in FIG. 23. It can also be seen that in the lateral growth portion, a κ-Ga ₂ O ₃ single crystal having a single in-plane orientation has been obtained.

(Comparative Example 2)
The crystal film was grown in the same manner as in Example 1, except that the mask on the substrate was formed in a regular triangular lattice pattern as shown in FIG. 13, and the [11-20] axis direction of the sapphire was parallel to the linear direction of the windows 4 (the direction of d1 in FIG. 13). The obtained film was identified by performing 2θ/ω scanning at angles of 15 degrees to 95 degrees using a thin film XRD diffractometer. The measurement was performed using CuKα radiation. As a result, the obtained film was κ-Ga ₂ O _3. A bird's-eye SEM image of the obtained crystal film is shown in FIG. 24. The measurement result of EBSD is also shown in FIG. 25. As is clear from FIG. 25, it can be seen that three types of in-plane rotation domains are mixed in the lateral growth portion. This is because, although the stripes are arranged so that the growth rate in the direction parallel to the stripes is the fastest for the domain group shown in red, the condition "center-to-center distance q is p×2/√3 or more" is not satisfied, and a sufficient lateral growth distance (d2 direction) for the red domain group to select the blue and green domain groups is not secured.

(Comparative Example 3)
A crystal film was grown in the same manner as in Example 1, except that the same TiOx buffer layer as in Example 1 was formed on the sapphire substrate, and the crystal film was formed without forming a mask. For the obtained crystal film, φ-scan measurement of κ-Ga ₂ O ₃ 122 diffraction by XRD was performed. The results are shown in Figure 26. As is clear from Figure 26, 12 peaks of similar intensity were observed, and it can be seen that three types of in-plane rotation domains are mixed in the same ratio.

(Evaluation of Rotational Domain Content)
The content of rotation domains was measured for the crystal films obtained in Examples 1 and 2 and Comparative Examples 1 to 3 using the results of EBSD. Specifically, the content of rotation domains was calculated by calculating the ratio of the area of the in-plane rotation domains in a 150 μm square range from the image of the result of measurement from the surface side of the obtained crystal film. For example, in the image of FIG. 17, the content of rotation domains was calculated by calculating the ratio of the total area of the two in-plane rotation domains B and C to the total area of the three in-plane rotation domains A, B, and C in a 160 μm square range. The results are shown in Table 1. As is clear from Table 1, it can be seen that the rotation domains are significantly reduced in the crystal films obtained in Examples 1 and 2.

By employing the manufacturing method of the present invention, a high-quality crystal film having a single in-plane orientation, particularly a κ-Ga ₂ O ₃ crystal film having a (001) plane orientation, can be obtained. Such a crystal film can be applied to various semiconductor elements such as diodes, transistors (particularly HEMTs), and ultraviolet detection elements. Furthermore, due to its large band gap and excellent light transmittance, the κ-Ga ₂ O ₃ crystal film is effective for light-emitting elements and power applications among semiconductor elements.

1. Substrate (crystal substrate)
2 Buffer layer 3 Mask 4 Window 50 Halide vapor phase epitaxy (HVPE) apparatus 51 Reaction chamber 52a Heater 52b Heater 53a Halogen-containing source gas supply source 53b Metal-containing source gas (metal halide gas) supply pipe 54a Reactive gas supply source 54b Reactive gas supply pipe 55a Oxygen-containing source gas supply source 55b Oxygen-containing source gas supply pipe 56 Substrate holder 57 Metal source 59 Gas exhaust section 121a Wide band gap n-type semiconductor layer 121b Narrow band gap n-type semiconductor layer 121c N+ type semiconductor layer 124 Semi-insulating layer 125a Gate electrode 125b Source electrode 125c Drain electrode 128 Buffer layer 900 Transistor 920 Source 930 Drain 940 Channel 950 Insulating film 960 Gate electrode 970a N+ region 970b N+ region 980a Electrode 980b Electrode 1000a UV detection element 1000b UV detection element 1010 Crystal film (crystalline oxide film)
1020 Schottky electrode 1030 Ohmic electrode 1040 Substrate (sapphire substrate)

Claims (15)

A method for growing a crystalline film by supplying a source material to a substrate having a mask with a plurality of windows, the crystalline film being κ-(Al _x In _y Ga _1-x-y ) ₂ O ₃ (wherein x, y, and z satisfy 0≦x≦1, 0≦y≦1, 0≦x+y≦1), the substrate has a plurality of in-plane rotational domain groups, the substrate is a substrate selected from the group consisting of a sapphire substrate, a GaN substrate, an AlN substrate, a 6H—SiC substrate, and a 4H—SiC substrate, the plurality of windows are linearly arranged and have a stripe shape, and the method includes forming the mask on the substrate and growing the crystal film such that a growth rate along the linear direction of the window of one in-plane rotational domain group among the plurality of in-plane rotational domain groups is greater than a growth rate along the linear direction of the other in-plane rotational domain groups, and an angle between the linear direction of the window and a [11-20] direction of the substrate is -5° or more and 5° or less . 2. The method according to claim 1, wherein the crystal film is grown by a method selected from the group consisting of HVPE, mist CVD and MOCVD. The method of claim 1 or claim 2 , wherein the width of the window is in the range of 0.1 μm to 20 μm. The method according to any one of claims 1 to 3 , wherein the width of the mask is in the range of 5 µm to 500 µm. The method according to any one of claims 1 to 4 , wherein the width of the window is smaller than the width of the mask. A method for growing a crystal film by supplying a source material to a substrate provided with a mask having a plurality of windows, the crystal film being κ-(Al _x In _y Ga _1-x-y ) ₂ O ₃ (wherein x, y, and z satisfy 0≦x≦1, 0≦y≦1, 0≦x+y≦1) and having a plurality of in-plane rotational domain groups, the substrate being a substrate selected from the group consisting of a sapphire substrate, a GaN substrate, an AlN substrate, a 6H—SiC substrate, and a 4H—SiC substrate, the plurality of windows being linearly arranged and having a dot-like shape, and a growth rate along the linear direction of the window of one in-plane rotational domain group among the plurality of in-plane rotational domain groups is higher than that of other in-plane rotational domains. forming the mask on the substrate and growing the crystal film so that the growth rate of the mask is greater than the growth rate of the dots along the linear direction of the window and such that an angle between the linear direction of the window and a [11-20] direction of the substrate is between -5° and 5°, and further wherein, when a center-to-center distance between two adjacent dots in the linear direction of the window is p, a center-to-center distance between two adjacent dots in a direction perpendicular to the linear direction of the window satisfies p×2/√3 or more and 500 μm or less. The method of claim 6 , wherein each of the plurality of windows is circular and/or polygonal in shape. 8. The method according to claim 7, wherein the circles and/or polygons are approximately perfect circles and/or approximately regular polygons, and when a center-to-center distance of the approximately perfect circles and/or the approximately regular polygons in a direction parallel to the linear direction of the windows is defined as p, a center-to-center distance of the approximately perfect circles and/or the approximately regular polygons in a direction perpendicular to the linear direction of the windows satisfies p×2/√3 or more and 500 μm or less. 9. The method according to claim 8, wherein a diameter of the approximately perfect circle and/or the approximately regular polygon is within a range of 0.1 μm or more and 10 μm or less, and a center-to-center distance of the approximately perfect circle and/or the approximately regular polygon in a direction parallel to the linear direction of the window is within a range of 0.3 μm or more and 25 μm or less. The method of any one of claims 1 to 9 , wherein the mask comprises a material selected from the group consisting of oxides, nitrides, oxynitrides, and metals. The method according to any one of claims 1 to 10 , wherein the mask is made of an amorphous material. The method according to any one of claims 1 to 11 , wherein the substrate further comprises a buffer layer between the mask and the substrate. The method of claim 12 further comprising growing the crystalline film on the buffer layer. 14. The method according to claim 1, further comprising forming a second mask on the first crystal film and further growing a second crystal film, following forming the mask as a first mask on the substrate and growing the crystal film as a first crystal film, the second mask having a plurality of windows arranged in a line, and the second mask being formed on the first crystal film such that the plurality of windows of the second mask do not overlap with the plurality of windows of the first mask. The method according to any one of claims 1 to 14 , wherein the surface index of the substrate is a (0001) surface.