Method for producing β-type gallium oxide film and substrate with β-type gallium oxide film

Abstract

The present invention relates to a method for producing a β-type gallium oxide film, said method comprising: converting a mixed gas that includes oxygen and ozone into plasma to dissociate the ozone into oxygen constituent particles, and supplying the oxygen constituent particles to a reaction chamber under reduced pressure; supplying elemental gallium to the reaction chamber; and epitaxially growing the β-type gallium oxide film on a β-type gallium oxide substrate inside the reaction chamber. A β-type gallium oxide substrate that has an off-angle is used as the β-type gallium oxide substrate.

Description

Method for producing β-type gallium oxide film and substrate with β-type gallium oxide film

[0001] The present invention relates to a method for producing a β-type gallium oxide film and a substrate with a β-type gallium oxide film.

[0002] Gallium oxide (Ga ２ O ３ ) has various crystal structures such as α-type, β-type, γ-type, δ-type, and ε-type. Among these, β-type gallium oxide (β-type Ga ２ O ３ ) is a stable phase at low temperatures and atmospheric pressures. The band gap of β-type gallium oxide is approximately 4.5 eV to 4.9 eV, which is larger than the band gaps of 4H—SiC (3.26 eV) and GaN (3.39 eV). For this reason, β-type gallium oxide is expected to be a semiconductor material with high dielectric breakdown strength.

[0003] Various methods have been attempted to grow the β-type gallium oxide on a substrate of β-type gallium oxide. ２ O ３ It is made of β-Ga single crystal ２ O ３ A β-Ga single crystal is formed on a semiconductor substrate having a principal surface parallel to the

[100] axis. ２ O ３ Furthermore, Patent Document 2 discloses a semiconductor substrate as a β-type gallium oxide substrate, which is made of a single crystal of a gallium oxide-based semiconductor, has a growth base surface which is a (001) plane, and in a continuous region of 70 area% or more of the growth base surface, the misorientation angle with respect to the

[010] direction is in the range of more than −0.3° and less than −0.01°, or in the range of more than 0.01° and less than 0.3°, and in the region of the growth base surface, the misorientation angle with respect to the

[001] direction is in the range of more than −1° and less than 1°, and has a diameter of 2 inches or more.

[0004] Japanese Patent Publication No. 2017-109902 Japanese Patent Publication No. 2023-023898

[0005] However, as described in Patent Documents 1 and 2, the epitaxial growth of a β-type gallium oxide film on a β-type gallium oxide substrate is performed using the HVPE method, with the growth temperature being as high as 900°C or higher and the growth rate being slow. Furthermore, the resulting β-type gallium oxide film has extremely poor surface morphology and must be polished before use as a semiconductor material. The reason for this phenomenon is that there are many microscopic irregularities at the interface between the resulting β-type gallium oxide film and the substrate, raising concerns about the presence of heterogeneous crystal planes with crystal orientations other than the specific crystal plane.

[0006] Therefore, an object of the present invention is to provide a method for producing a β-type gallium oxide film that has small unevenness at the interface between the β-type gallium oxide film and the β-type gallium oxide substrate and good surface morphology without slowing down the growth rate, and to provide a substrate with a β-type gallium oxide film that has small unevenness at the interface between the β-type gallium oxide film and the β-type gallium oxide substrate.

[0007] As a result of extensive research into the above-mentioned problems, the present inventors have discovered that a mixed gas of oxygen and ozone is converted into plasma, and Ga and triplet oxygen atoms O( ３ The present inventors have found that by forming a β-type gallium oxide film by a reaction with β-type gallium oxide (P), it is possible to epitaxially grow a β-type gallium oxide film having excellent crystallinity and flatness without slowing down the growth rate. Furthermore, they have conceived that by using a β-type gallium oxide substrate having an off-angle, it is possible to reduce unevenness at the interface between the β-type gallium oxide film and the β-type gallium oxide substrate, and have completed the present invention.

[0008] That is, the gist of the present invention is as follows. [1] A method for producing a β-type gallium oxide film, comprising: generating plasma from a mixed gas containing oxygen and ozone, thereby dissociating the ozone into oxygen-constituent particles and supplying the ozone to a reaction chamber under reduced pressure; and supplying elemental gallium to the reaction chamber; and epitaxially growing a β-type gallium oxide film on a β-type gallium oxide substrate inside the reaction chamber, wherein the β-type gallium oxide substrate is an off-angle β-type gallium oxide substrate. [2] A method for producing a β-type gallium oxide film according to [1] above, wherein a concentration of the ozone relative to the total of the oxygen and the ozone in the mixed gas is 5% by volume or more. [3] A method for producing a β-type gallium oxide film according to [1] above, wherein the temperature of the β-type gallium oxide substrate is set to 0°C or more and 700°C or less to epitaxially grow the β-type gallium oxide film. [4] The method for producing a β-type gallium oxide film according to any one of [1] to [3], wherein the surface of the β-type gallium oxide substrate having an off-angle has the (001) plane tilted at an angle of more than 1° and not more than 10° toward the

[010] axis. [5] The method for producing a β-type gallium oxide film according to any one of [1] to [4], wherein the surface of the β-type gallium oxide substrate having an off-angle has the (001) plane tilted at an angle of 3° to 8° toward the

[010] axis. [6] The method for producing a β-type gallium oxide film according to any one of [1] to [3], wherein the surface of the β-type gallium oxide substrate having an off-angle has the (001) plane tilted at an angle of more than 1° and not more than 10° toward the

[100] axis.

[0009] [7] A substrate with a β-type gallium oxide film, comprising a β-type gallium oxide film on an off-angled β-type gallium oxide substrate, wherein the surface of the off-angled β-type gallium oxide substrate has a (001) plane tilted at an angle of more than 1° and not more than 10° toward the

[010] axis. [8] A substrate with a β-type gallium oxide film on an off-angled β-type gallium oxide substrate, wherein the β-type gallium oxide film has a (001) plane orientation. [9] A substrate with a β-type gallium oxide film on an off-angled β-type gallium oxide substrate, wherein the surface of the off-angled β-type gallium oxide substrate has a (001) plane tilted at an angle of more than 1° and not more than 10° toward the

[100] axis.

[10] The gallium oxide film according to [7], wherein the β-type gallium oxide film has a (001) plane orientation.

[11] The β-type gallium oxide film-included substrate according to any one of [7] to

[10] , wherein the β-type gallium oxide film has a thickness of 0.5 μm or more.

[12] The β-type gallium oxide film-included substrate according to

[11] , wherein the β-type gallium oxide film has a thickness of 50 μm or less.

[13] The β-type gallium oxide film-included substrate according to any one of [7] to

[12] , wherein the off-angled β-type gallium oxide substrate has a surface in which the (001) plane is inclined at an angle of 3° to 8° toward the

[010] axis.

[14] The β-type gallium oxide film-included substrate according to any one of [7] to

[13] , wherein the β-type gallium oxide film has a breakdown voltage of 80 V / μm or more.

[15] The β-type gallium oxide film-included substrate according to any one of [7] to

[14] , wherein the surface roughness (Ra) of the β-type gallium oxide film is 0.1 nm to 2.0 nm.

[0010] According to the manufacturing method of the present invention, a β-type gallium oxide film can be manufactured on a β-type gallium oxide substrate without slowing down the growth rate and with small unevenness at the interface between the β-type gallium oxide film and the β-type gallium oxide substrate. Furthermore, the β-type gallium oxide film-coated substrate of the present invention has small unevenness at the interface between the β-type gallium oxide film and the β-type gallium oxide substrate. This means that the growth of a β-type gallium oxide film with a heterogeneous crystal plane having a crystal orientation other than the specific crystal plane on the β-type gallium oxide substrate can be suppressed. Furthermore, since the growth rate in epitaxial growth is fast and a low growth temperature can be used, industrialization at lower costs than conventional methods is expected.

[0011] FIG. 1 is a schematic diagram showing the structure of a β-type gallium oxide film-attached substrate 100 according to this embodiment. FIG. 2 is a schematic diagram showing the structure of a manufacturing apparatus 1000 that can be used in the manufacturing method according to this embodiment. FIG. 3 is a TEM image of the β-type gallium oxide film-attached substrate obtained in Example 1. FIG. 4 is a TEM image of the β-type gallium oxide film-attached substrate obtained in Example 2. FIG. 5 is a TEM image of the β-type gallium oxide film-attached substrate obtained in Example 3. FIG. 6 is a TEM image of the β-type gallium oxide film-attached substrate obtained in Example 4.

[0012] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified as desired within the scope of the present invention. In this specification, a single-crystal substrate refers to a substrate in which the entire substrate is single crystal. In this specification, uniaxial orientation refers to the presence of a large number of crystal grains in which the direction of at least one of the crystal axes is aligned, and refers to a state in which a large number of crystal grains rotated around this single axis are present. The uniaxial orientation of a gallium oxide film can be confirmed, for example, by symmetric X-ray diffraction (symmetric XRD). In this specification, oxygen-component particles refer to oxygen atoms containing singlet oxygen atoms and triplet oxygen atoms, oxygen molecules, ozone, or particles containing these in an excited state. In this specification, the symbol "to" indicating a numerical range is used to mean that the numerical values ​​before and after it are included as the lower and upper limits.

[0013] 1 is a schematic diagram showing the structure of a β-type gallium oxide film-attached substrate 100 obtained by the manufacturing method according to this embodiment. The β-type gallium oxide film-attached substrate 100 includes a β-type gallium oxide substrate 110 and a β-type gallium oxide film 120 formed on a first main surface 110a of the β-type gallium oxide substrate 110.

[0014] One aspect of the β-type gallium oxide film-attached substrate 100 according to this embodiment has a β-type gallium oxide film 120 on a β-type gallium oxide substrate 110 having an off-angle, and the surface of the β-type gallium oxide substrate 110 having an off-angle has the (001) plane tilted at an angle of more than 1° and not more than 10° toward the

[010] axis.

[0015] Another aspect of the β-type gallium oxide film-attached substrate 100 according to this embodiment has a β-type gallium oxide film 120 on a β-type gallium oxide substrate 110 having an off-angle, and the β-type gallium oxide film 120 has a (001) plane orientation.

[0016] One aspect of the β-type gallium oxide film-attached substrate 100 according to this embodiment has a β-type gallium oxide film 120 on an off-angled β-type gallium oxide substrate 110, and the (001) plane of the off-angled β-type gallium oxide substrate 110 is tilted at an angle of more than 1° and not more than 10° toward the

[100] axis. The above aspect will be collectively described in detail below.

[0017] <β-Type Gallium Oxide Substrate> The β-type gallium oxide substrate 110 in this embodiment has an off-angle. The off-angled β-type gallium oxide substrate 110 is, for example, a substrate oriented in the (001) plane. By having the off-angled β-type gallium oxide substrate 110, it is possible to reduce the unevenness at the interface between the first main surface 110a of the β-type gallium oxide substrate 110 and the β-type gallium oxide film 120 formed thereon. In other words, it is possible to suppress the growth of a β-type gallium oxide film on a heterogeneous crystal plane having a crystal orientation other than the specific crystal plane.

[0018] The β-type gallium oxide substrate in this embodiment may be a bulk β-type gallium oxide substrate 110 as shown in Fig. 1, or may be a template in which a β-type gallium oxide film is grown on a substrate other than β-type gallium oxide. In other words, the β-type gallium oxide substrate may be a substrate whose first main surface is made of β-type gallium oxide having an off-angle. In other words, the β-type gallium oxide substrate in this embodiment is a substrate whose first main surface is a single crystal or a crystal close to a single crystal of β-type gallium oxide.

[0019] In this embodiment, from the viewpoints of achieving a high epitaxial growth rate and reducing unevenness at the interface, the first main surface 110a of the off-angled β-type gallium oxide substrate 110 is (001)-oriented, and this (001) plane is preferably tilted by more than 1° and not more than 10° toward the

[010] axial direction or the

[100] axial direction, and more preferably tilted by more than 1° and not more than 10° toward the

[010] axial direction. Furthermore, from the viewpoint of forming a β-type gallium oxide film 120 that is also oriented in the (001) axial direction, the first main surface 110a of the off-angled β-type gallium oxide substrate 110 is (001)-oriented, and this (001) plane is more preferably tilted by 3° to 8° toward the

[010] axial direction or the

[100] axial direction, and even more preferably tilted by 3° to 8° toward the

[010] axial direction. The off-angle is more preferably 5° to 7°.

[0020] A β-type gallium oxide film is likely to grow three-dimensionally when crystals grow on the terrace surfaces of the substrate. That is, heterogeneous crystal planes having crystal orientations other than the specific crystal plane also tend to grow. In contrast, if the first main surface 110a of the β-type gallium oxide substrate 110 has an off-angle, the number or area of ​​steps per unit area increases, increasing the probability that gallium and oxygen will react at the steps, thereby suppressing the growth of heterogeneous crystal planes.

[0021] Furthermore, in this embodiment, although the details will be described later, a mixed gas of oxygen and ozone is turned into plasma, and Ga and triplet oxygen atoms O( ３In this case, the bonding strength between gallium and oxygen is presumably stronger than when conventional HVPE methods are used, and the growth of the heterocrystalline planes is further suppressed, resulting in smaller irregularities at the interface.

[0022] From the above viewpoints, the off-angle of the first main surface 110a of the β-type gallium oxide substrate 110 is preferably more than 1°, more preferably 3° or more, and even more preferably 5° or more. Moreover, if the off-angle is too large, the crystal plane orientation such as the (001) plane changes, so the off-angle is preferably 10° or less, more preferably 8° or less, and even more preferably 7° or less.

[0023] The β-type gallium oxide substrate 110 having an off-angle can be manufactured by a conventionally known method, such as a method of polishing a bulk β-type gallium oxide substrate to have a desired off-angle, or a method of growing a crystal using a substrate having a desired off-angle as a seed crystal.

[0024] <β-Type Gallium Oxide Film> The β-type gallium oxide film 120 in this embodiment is provided on the first main surface 110a of the β-type gallium oxide substrate 110 having an off-angle, preferably on the first main surface 110a oriented in the (001) plane.

[0025] From the viewpoint of crystallinity, the β-type gallium oxide film 120 is preferably uniaxially oriented.

[0026] The β-type gallium oxide film 120 may be single crystal or polycrystalline. However, from the viewpoint of the yield and characteristics of semiconductor devices, a single crystal or a crystal close to a single crystal is preferred, and a single crystal is more preferred. Furthermore, when a small amount of impurities is mixed to grow an n-type or p-type gallium oxide semiconductor, the gallium oxide film may contain these impurities. Note that, in this specification, the crystal structure of a β-type gallium oxide film and whether it is a single crystal film or not can be measured, for example, by a crystal X-ray diffraction (XRD) device using CuKα radiation as a radiation source. Each of the α-type to ε-type crystal structures has a unique XRD pattern. Furthermore, if they are single crystals, an XRD pattern specific to the single crystal can be obtained.

[0027] When the β-type gallium oxide film 120 is single crystal, the plane orientation of the β-type gallium oxide film 120 is preferably (001), and it is more preferable that a β-type gallium oxide film with a (001) plane orientation is provided on the first main surface 110a of the β-type gallium oxide substrate 110 having an off-angle.

[0028] For the β-type gallium oxide film 120 in this embodiment, the presence or absence of a peak by symmetrical X-ray diffraction can be used as an index of the crystallinity of the single crystal film. For example, for a β-type gallium oxide film, the presence or absence of a peak of β-type gallium oxide attributed to the (001) plane can be used. Examples of the peak of β-type gallium oxide attributed to the (001) plane include peaks of the (002) plane, the (003) plane, the (004) plane, etc.

[0029] Symmetric X-ray diffraction measurement is performed, for example, by using CuKα radiation as a radiation source, irradiating the surface of the β-type gallium oxide substrate with an incident angle of X-rays at a Bragg diffraction angle θ, and rotating the detector to measure the diffracted X-rays at θ-2θ. ２ O ３ The (002) plane is at a Bragg diffraction angle 2θ = 31.7° ± 0.5°, and Ga ２ O ３ The (003) plane is located at a Bragg diffraction angle 2θ=48.4°, and Ga ２ O ３ The (004) plane has a diffraction peak at a Bragg diffraction angle 2θ=66.2°±0.5°. Therefore, if a diffraction peak is obtained at the above Bragg diffraction angle, it can be attributed to the peak of the (001) plane of β-type gallium oxide.

[0030] When a small amount of impurities is mixed in to grow an n-type or p-type gallium oxide semiconductor, the β-type gallium oxide film 120 may contain the impurities. Furthermore, the β-type gallium oxide film 120 is not limited to a (001) plane orientation, and may be a film with a plane orientation in which the (010) axis is the crystal zone axis, such as a (40-1) plane orientation film or a (100) plane orientation film.

[0031] The arithmetic mean surface roughness Ra of the β-type gallium oxide film in this embodiment is preferably 0.1 nm or more and 2.0 nm or less. Here, from the viewpoint of improving the flatness of the β-type gallium oxide film and realizing higher pressure resistance, the arithmetic mean surface roughness Ra is preferably 2.0 nm or less, more preferably 1.5 nm or less, and even more preferably 1.0 nm or less. The smaller the better, but it is usually 0.1 nm or more. The arithmetic mean surface roughness Ra of the β-type gallium oxide film in this specification can be measured using an atomic force microscope (AFM).

[0032] The thickness of the β-type gallium oxide film in this embodiment is preferably 0.5 μm or more, more preferably 0.5 to 50 μm, even more preferably 0.8 to 30 μm, and particularly preferably 1 to 20 μm. From the viewpoint of application to power devices and the like, the thickness is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1 μm or more. In addition, although there are no particular upper limits, from the viewpoint of film formation rate and film quality, the thickness is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. The thickness can be measured by using a scanning electron microscope (SEM) or the like on a cross section of the substrate with the β-type gallium oxide film.

[0033] In this embodiment, the breakdown voltage of the β-type gallium oxide film is preferably 80 V / μm or more, more preferably 80 to 400 V / μm, even more preferably 100 to 250 V / μm, and even more preferably 105 to 200 V / μm. Here, the breakdown voltage of the β-type gallium oxide film is preferably 80 V / μm or more, more preferably 100 V / μm or more, and even more preferably 105 V / μm or more. The upper limit of the breakdown voltage of the β-type gallium oxide film is not particularly limited, but may be, for example, 400 V / μm or less, 250 V / μm or less, or 200 V / μm or less. The breakdown voltage of the β-type gallium oxide film can be measured using a curve tracer.

[0034] The half-width in X-ray diffraction of the β-type gallium oxide film in this embodiment is calculated, for example, from the diffraction peak attributable to the (002) plane of the diffraction peak attributable to β-type gallium oxide. In this specification, the half-width is also referred to as FWHM. The half-width of the β-type gallium oxide film can be measured using a crystal X-ray diffractometer (CuKα radiation). The FWHM of the β-type gallium oxide film is preferably 15 to 80 arcsec, more preferably 15 to 70 arcsec, and even more preferably 15 to 60 arcsec. Here, the upper limit of the FWHM is preferably 80 arcsec or less, more preferably 70 arcsec or less, and even more preferably 60 arcsec or less. The lower limit of the FWHM is not particularly limited, but is preferably 15 arcsec or more.

[0035] <Other Optional Layers> The β-type gallium oxide film-coated substrate according to this embodiment exhibits the effects of the present invention only with the β-type gallium oxide substrate and the β-type gallium oxide film, but does not exclude embodiments in which other optional layers are included. Examples of other optional layers include a buffer layer, a nucleation layer, and a surface modification layer.

[0036] The buffer layer is a layer inserted mainly for the purpose of alleviating lattice constant mismatch, and is, for example, a single crystal film of the material of interest with a predetermined thickness, a layer formed by gradually changing the composition of a mixed crystal of the material and a different material, or a layer grown with a superlattice structure of the material of interest and a different material, etc. The buffer layer usually has a thickness of 20 nm or more.

[0037] The nucleation layer and the surface modification layer are layers provided for the purpose of promoting the crystallization of β-type gallium oxide, and differ from the buffer layer in terms of crystallinity.

[0038] The nucleation layer refers to a thin film having a lattice constant different from that of the adsorption layer or the material. The thickness of the nucleation layer is, for example, less than 20 nm, preferably less than 10 nm, and more preferably less than 5 nm. The nucleation layer may be a continuous layer or a discontinuous layer. The presence of the nucleation layer can be determined from the difference in atomic arrangement by cross-sectional TEM (transmission electron microscope) observation. If no change in atomic arrangement is observed, it can be determined that the β-type gallium oxide substrate and the β-type gallium oxide film are in direct contact.

[0039] Examples of the surface-modified layer include a layer containing an element different from that of the substrate, or a layer formed by modifying the surface of a substrate, etc. In other words, the surface-modified layer is a layer formed by modifying the surface of a substrate such as a single crystal substrate, and has a lattice constant different from that of the substrate material.

[0040] The rate of lattice constant mismatch between the β-type gallium oxide substrate and the β-type gallium oxide film is preferably 15% or less, more preferably 12% or less, and even more preferably 8% or less. The lower the rate, the better, but it is usually above 0%. The rate of lattice constant mismatch is determined by analyzing the epitaxial relationship of the β-type gallium oxide film on the β-type gallium oxide substrate from the results of symmetric X-ray diffraction measurement and in-plane X-ray diffraction measurement. Note that the lattice constant mismatch is the ratio of the difference in lattice constant of the β-type gallium oxide film in the same direction to the lattice constant of the β-type gallium oxide substrate, and can be calculated, for example, from the ratio between the lattice constant of the β-type gallium oxide substrate and the lattice constant of the β-type gallium oxide single crystal film projected in a certain direction onto the β-type gallium oxide substrate.

[0041] <<Method for Producing a β-Type Gallium Oxide Film>> In the method for producing a β-type gallium oxide film according to this embodiment, a mixed gas containing oxygen and ozone is converted into plasma, dissociating the ozone into oxygen-constituent particles and supplying the ozone to a reaction chamber under reduced pressure, while supplying elemental gallium to the reaction chamber. This causes a β-type gallium oxide film to be epitaxially grown on a β-type gallium oxide substrate inside the reaction chamber. The β-type gallium oxide substrate used here has an off-angle.

[0042] Prior to describing specific steps, one embodiment of the manufacturing apparatus to be used will be described with reference to Fig. 2. Note that the manufacturing apparatus to be used in the manufacturing method according to this embodiment is not limited to the following.

[0043] <Manufacturing Apparatus> The manufacturing method according to this embodiment can use, for example, a manufacturing apparatus 1000 shown in the schematic configuration diagram of Fig. 2. The manufacturing apparatus 1000 is an apparatus for epitaxially growing a β-type gallium oxide film 120 on a β-type gallium oxide substrate 110.

[0044] The manufacturing apparatus 1000 includes a reaction chamber 1100 , a substrate placement unit 1200 , a gallium element supply unit 1300 , an oxygen element supply unit 1400 , and a heating unit 1220 .

[0045] The reaction chamber 1100 is a place where a β-type gallium oxide film 120 is epitaxially grown on a β-type gallium oxide substrate 110. The reaction chamber 1100 is provided with a substrate placement part 1200 and a susceptor 1210 inside, and the β-type gallium oxide substrate 110 is placed on the substrate placement part 1200 and supported by the susceptor 1210.

[0046] The substrate placement section 1200 in the reaction chamber 1100 can be heated by a heating device 1220, allowing the β-type gallium oxide substrate 110 to be set to a desired temperature. The heating device can set the temperature of the substrate placement section 1200 to 0°C or higher, preferably room temperature or higher. There is no particular upper limit to the heating temperature, but it is sufficient to be able to heat up to, for example, 700°C. That is, it is preferable to set the temperature of the β-type gallium oxide substrate to 0°C or higher and 700°C or lower, and then epitaxially grow the subsequent β-type gallium oxide film, and the temperature is more preferably room temperature or higher and 700°C or lower.

[0047] Gallium element (Ga) is supplied to the placed β-type gallium oxide substrate 110 by a gallium element supply device 1300. The gallium element supply device 1300 is not particularly limited as long as it can supply gallium element, and an example thereof is a Knudsen cell. In the case of a Knudsen cell, the gallium element supply device 1300 has a shutter 1310, which connects or disconnects the gallium element supply device 1300 and the reaction chamber 1100. The gallium element supply device 1300 may have a heating device or a cooling device.

[0048] Gallium element is supplied to the β-type gallium oxide substrate 110 as described above, and oxygen constituent particles are supplied by an oxygen element supply device 1400. This oxygen element supply device 1400 has a plasma generation unit 1450 and, if necessary, a shutter 1410. The shutter 1410 connects or disconnects the oxygen element supply device 1400 from the reaction chamber 1100. The oxygen element supply device 1400 may have a heating device or a cooling device.

[0049] The oxygen constituent particles supplied to the β-type gallium oxide substrate by the oxygen element supply device 1400 are formed by dissociating ozone when a mixed gas containing oxygen and ozone is turned into plasma by the plasma generation unit 1450. This allows a β-type gallium oxide film 130 to be grown on the surface of the β-type gallium oxide substrate.

[0050] Specifically, oxygen gas is supplied from an oxygen gas supply unit 1500 toward the oxygen element supply device 1400. The oxygen gas passes through an oxygen gas supply pipe 1810 and flows into the ozonizer 1700 while the flow rate is adjusted by a mass flow controller 1820.

[0051] The oxygen gas flowing into the ozonizer 1700 is partially ozonized to produce a mixed gas containing oxygen and ozone. An example of such an ozonizer 1700 is a first plasma generator that converts oxygen gas into plasma. The mixed gas generated by the ozonizer 1700 preferably has an ozone concentration of 5% by volume or more relative to the total of oxygen and ozone, more preferably 10% by volume or more, even more preferably 20% by volume or more, and even more preferably 25% by volume or more. The upper limit of the ozone concentration is not particularly limited, but is typically 50% by volume or less.

[0052] The mixed gas containing oxygen and ozone generated by the ozonizer 1700 flows into the oxygen element supply device 1400 through an ozone-oxygen mixed gas supply pipe 1830 while the flow rate is adjusted by a mass flow controller 1840. The ozonizer 1700 and the oxygen element supply device 1400 may be directly connected, in which case the ozone-oxygen mixed gas supply pipe 1830 and the mass flow controller 1840 are not necessary.

[0053] In addition to the mixed gas containing oxygen and ozone, an inert gas is supplied to the oxygen element supply device 1400 from an inert gas supply unit 1600. Examples of the inert gas include rare gases such as Ar gas and He gas. However, as long as there is a mixed gas containing oxygen and ozone, the plasma generation described below is possible even without the inert gas, and therefore the supply of the inert gas is optional.

[0054] The inert gas flows from the inert gas supply unit 1600 through the inert gas supply pipe 1850 and into the oxygen element supply device 1400 while the flow rate is adjusted by the mass flow controller 1860 .

[0055] The mixed gas containing oxygen and ozone and the inert gas may flow separately into the oxygen element supply device 1400, or as shown in Fig. 2, both gases may flow into a mixed gas supply pipe 1870 and be supplied in a mixed state to the oxygen element supply device 1400. In other words, the mixed gas supply pipe 1870 is a pipe for supplying a gas in which the mixed gas containing oxygen and ozone and the inert gas are mixed to the oxygen element supply device 1400 for generating plasma.

[0056] If the mixed gas for generating plasma does not contain an inert gas, the inert gas supply unit 1600, the inert gas supply pipe 1850, and the mass flow controller 1860 are not necessary.

[0057] In addition to the above, the manufacturing apparatus 1000 may also include an impurity element supply unit (not shown) that supplies impurities. The impurity element supply unit supplies impurity elements to grow n-type β-type gallium oxide or p-type β-type gallium oxide.

[0058] <Procedure for Producing a β-Type Gallium Oxide Film> First, a β-type gallium oxide substrate 110 having an off-angle is attached to a susceptor 1210. The first main surface 110a of the β-type gallium oxide substrate 110 having an off-angle is such that the (001) plane is preferably tilted by more than 1° and not more than 10° toward the

[010] axial direction or the

[100] axial direction, and more preferably tilted by more than 1° and not more than 10° toward the

[010] axial direction. Furthermore, the tilt is more preferably 3° or more and not more than 8°. Other preferred aspects of the β-type gallium oxide substrate 110 are the same as the preferred aspects of the β-type gallium oxide substrate in the above <<Substrate with a β-Type Gallium Oxide Film>>.

[0059] The β-type gallium oxide substrate 110 having the off-angle is heated by a heater. At this time, the temperature of the β-type gallium oxide substrate 110 is preferably set to a temperature of 0° C. or higher and 700° C. or lower, and more preferably to a temperature of room temperature or higher and 700° C. or lower. Then, the pressure in the reaction chamber 1100 is reduced.

[0060] Oxygen gas is supplied to ozonizer 1700 by oxygen gas supply unit 1500. The oxygen gas is subjected to plasma treatment by the first plasma generated by ozonizer 1700. As a result, a mixed gas of oxygen and ozone is generated in ozonizer 1700. Meanwhile, Ar gas is supplied from inert gas supply unit 1600 to mixed gas supply pipe 1870. The mixed gas of oxygen and ozone and Ar gas are mixed inside mixed gas supply pipe 1870 to form a mixed gas containing oxygen, ozone, and Ar gas.

[0061] The plasma generating unit 1450 generates a second plasma inside the oxygen element supply device 1400. The mixed gas for generating the plasma is a mixed gas containing oxygen, ozone, and Ar gas. As a result, mainly the ozone is decomposed to generate oxygen molecules and singlet oxygen atoms O( １ It is believed that oxygen radicals with strong oxidizing power containing a large amount of D) are generated.

[0062] In the mixed gas, the concentration of ozone relative to the total of oxygen and ozone is preferably 5% by volume or more, more preferably 10% by volume or more, even more preferably 20% by volume or more, and even more preferably 25% by volume or more. The upper limit of the ozone concentration is not particularly limited, but is usually 50% by volume or less.

[0063] Here, the oxygen radical is a singlet oxygen atom O( １ D) and triplet oxygen atom O( ３ P) and singlet oxygen atom O( １ D) converts triplet oxygen atoms O( ３ These oxygen constituent particles are supplied to the β-type gallium oxide substrate 110.

[0064] The mixed gas supplied to the oxygen element supply device 1400 via the mixed gas supply pipe 1870 is mainly decomposed into ozone by the second plasma generated by the plasma generation unit 1450 in the oxygen element supply device 1400, and the decomposition is converted into oxygen molecules and singlet oxygen atoms O( １ It is believed that oxygen radicals with strong oxidizing power containing a large amount of singlet oxygen atoms O( １ D) and triplet oxygen atom O( ３ P) and singlet oxygen atom O( １ D) converts triplet oxygen atoms O( ３ P).

[0065] Ozone dissociated into oxygen molecules and oxygen radicals in this way is called oxygen-constituting particles, and is supplied to the reduced pressure reaction chamber 1100. Note that this does not exclude the possibility of supplying not only oxygen-constituting particles but also a mixed gas containing non-plasmaized oxygen and ozone to the reduced pressure reaction chamber 1100.

[0066] Meanwhile, elemental gallium (Ga) is supplied from a gallium element supply device 1300 to the β-type gallium oxide substrate 110. That is, elemental gallium (Ga) is supplied from the gallium element supply device 1300 to the reaction chamber 1100 under reduced pressure. As a result, the supplied Ga reacts with the oxygen radicals and the like provided above on the first main surface 110a of the β-type gallium oxide substrate 110, preferably in one of the steps, to epitaxially grow a flat β-type gallium oxide film.

[0067] Specifically, on the first main surface 110a of the β-type gallium oxide substrate 110, Ga and singlet oxygen atoms or singlet oxygen atoms O( １ D) transitioned to triplet oxygen atom O( ３ P) reacts with the β-type gallium oxide film to grow. １ D) transitioned to triplet oxygen atom O( ３ When the β-type gallium oxide film reaches the surface, a β-type gallium oxide film having excellent crystallinity and flatness is grown.

[0068] In epitaxially growing the β-type gallium oxide film, the β-type gallium oxide substrate 110 has an off-angle, so that the β-type gallium oxide film can be grown with small unevenness at the interface between the growing β-type gallium oxide film and the β-type gallium oxide substrate. This is because, as described above, by relatively narrowing the terrace surfaces and widening the steps, the probability of gallium and oxygen reacting at the steps to produce gallium oxide is increased, and as a result, three-dimensional growth can be suppressed and the growth of heterocrystalline planes can be suppressed.

[0069] In addition to the above, the deposition rate of the β-type gallium oxide film is faster than the deposition rate of the β-type gallium oxide film when using conventional manufacturing equipment.

[0070] The gas pressure of O supplied from the oxygen element supply device 1400 containing oxygen constituent particles is 1.0×10 －５ ~1.0 x 10 －１ Pa is preferred, and 1.0 x 10 －４ ~1.0 x 10 －１ Pa is more preferable, and 1.0 × 10 －３ ~1.0 x 10 －２From the viewpoint of supplying a sufficient amount of oxygen radicals, the gas pressure is preferably 1.0×10 Pa. －５ Pa or more is preferable, and 1.0 × 10 －４ Pa or more is more preferable, and 1.0 × 10 －３ From the viewpoint of generating sufficient oxygen radicals, the gas pressure is more preferably 1.0×10 Pa or more. －１ Pa or less, and 1.0 × 10 －２ Pa or less is more preferable.

[0071] The gas pressure of Ga supplied from the gallium element supply device 1300 is 1.0×10 －５ ~1.0 x 10 －２ Pa is preferred, 5.0 × 10 －５ ~1.0 x 10 －２ Pa is more preferable, and 1.0 × 10 －４ ~1.0 x 10 －３ From the viewpoint of supplying a sufficient amount of Ga element, the gas pressure is more preferably 1.0×10 Pa. －５ Pa or more is preferable, and 5.0 × 10 －５ Pa or more is more preferable, and 1.0 × 10 －４ In order to prevent the Ga deposition rate from becoming too high and becoming uncontrollable, the gas pressure is preferably 1.0×10 Pa or more. －２ Pa or less, and 1.0 × 10 －３ Pa or less is more preferable.

[0072] The internal pressure of the reaction chamber 1100 is preferably 0.001 to 0.01 Pa, and more preferably 0.006 to 0.009 Pa. From the viewpoint of the exhaust capacity of the apparatus, the internal pressure is preferably 0.001 Pa or more, and more preferably 0.006 Pa or more. Furthermore, from the viewpoint of the mean free path of oxygen radicals and gallium, the internal pressure is preferably 0.01 Pa or less, and more preferably 0.009 Pa or less.

[0073] The temperature of the β-type gallium oxide substrate 110 is, for example, 0°C or higher and 700°C or lower, preferably 0°C or higher and 500°C or lower, more preferably 0°C or higher and 450°C or lower, even more preferably 0°C or higher and 400°C or lower, even more preferably 0°C or higher and 350°C or lower, particularly preferably 10°C or higher and 350°C or lower, particularly preferably 100°C or higher and 350°C or lower, and most preferably 200°C or higher and 350°C or lower. Here, the temperature of the β-type gallium oxide substrate 110 is, for example, 0°C or higher, preferably 10°C or higher, or may be 20°C or higher, which is about room temperature, 100°C or higher, or 200°C or higher. Furthermore, the temperature of the β-type gallium oxide substrate 110 is preferably 700°C or lower, preferably 500°C or lower, more preferably 450°C or lower, even more preferably 400°C or lower, and even more preferably 350°C or lower.

[0074] The concentration of ozone in the total volume of oxygen and ozone in the mixed gas supplied to the oxygen element supply device 1400 is, for example, preferably 10% by volume or more, more preferably 20% by volume or more, and even more preferably 25% by volume or more. The upper limit of this volume is not particularly limited, but is usually 50% by volume or less.

[0075] <<Modifications>> Instead of the β-type gallium oxide substrate 110, other substrates such as an α-type gallium oxide substrate may be used. The crystal orientation may also be selected depending on the application. The other substrates are substrates for epitaxially growing a gallium oxide film. Therefore, the substrate has a single crystal or a crystal close to a single crystal of gallium oxide on the surface.

[0076] The ozonizer may generate plasma by a method other than dielectric barrier discharge. Alternatively, ozone may be generated by a method other than plasma. For example, ozone may be generated by irradiating oxygen with ultraviolet light.

[0077] When oxygen gas is converted into a mixed gas of oxygen and ozone by the ozonizer 1700, the mixed gas may contain excited ozone.

[0078] The plasma generating unit 1450 may dissociate oxygen molecules into oxygen radicals.

[0079] The oxygen element supply device 1400 may generate plasma inside the plasma generation chamber by a method other than an ICP antenna.

[0080] In addition to Ar, rare gases such as He and Ne may be used as the inert gas for generating plasma. Depending on the growth conditions, it may not be necessary to supply an inert gas. That is, in this case, the manufacturing apparatus does not have the inert gas supply unit 1600. In this case, the mixed gas supply pipe 1870 supplies a mixed gas of oxygen and ozone to the inside of the oxygen element supply device 1400. In this case, the inert gas supply pipe 1850 and the like are not required.

[0081] The manufacturing apparatus 1000 may have an impurity element supply unit that supplies impurities. The impurity element supply unit supplies impurity elements to grow n-type β-type gallium oxide or p-type β-type gallium oxide.

[0082] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Example 1 is a reference example, and Examples 2 to 5 are working examples.

[0083] Examples 1 to 4: Production of substrate with β-type gallium oxide film Using the production apparatus 1000 shown in FIG. 2, a β-type gallium film was epitaxially grown on a β-type gallium oxide substrate by the following procedure, thereby obtaining a substrate with a gallium oxide film.

[0084] First, for the β-type gallium oxide substrate, Example 1 used a substrate in which the first main surface was oriented in the (001) plane and had an off-angle of 0°, i.e., no off-angle. Furthermore, Examples 2 to 4 used substrates in which the first main surface was oriented in the (001) plane and the (001) plane was tilted toward the

[010] axis by 0.15° (Example 2), 0.7° (Example 3), or 1° (Example 4), respectively. Note that the β-type gallium oxide substrates in Examples 2 to 4 were all prepared by polishing β-type gallium oxide substrates oriented in the (001) plane and not having an off-angle, to obtain substrates with an off-angle.

[0085] Next, the β-type gallium oxide substrate was placed on the substrate placement unit 1200 with the (001) plane facing up, and was supported by a susceptor 1210. The temperature of the β-type gallium oxide substrate was heated to 300°C at a heating rate of 10°C / min, and while maintaining this state, the pressure inside the reaction chamber 1100 was reduced to 5×10 －８ The pressure was reduced to 100 Pa.

[0086] On the other hand, an ozonizer 1700 was used to supply oxygen gas supplied from the oxygen gas supply unit, and a mixed gas containing oxygen and ozone, with the ozone concentration relative to the total of oxygen and ozone being 28% by volume, was supplied into the oxygen element supply device 1400. At the same time, Ar gas was also supplied from the inert gas supply unit 1600 into the oxygen element supply device 1400. The ratio of the mixed gas containing oxygen and ozone to Ar gas was 1:4.

[0087] After that, O ２ and O ３ at a flow rate of 8 sccm O ２ +O ３ The oxygen element supply device 1400 supplied Ga to the reaction chamber 1100 under reduced pressure. At the same time, the plasma output was set to 1000 W, and Ga was supplied to a pressure of 1.13×10 －４ Pa was further supplied from the gallium element supply device 1300 to the reaction chamber 1100, and a gallium oxide film was grown for 60 minutes. In this way, a substrate with a gallium oxide film was obtained.

[0088] Example 5 Production of a Substrate with a β-Type Gallium Oxide Film A gallium oxide film-coated substrate is obtained in the same manner as in Examples 1 to 4 above, except that a β-type gallium oxide substrate is used in which the first main surface is (001)-oriented and the (001) plane is inclined at an angle of 6° toward the

[010] axis, i.e., the substrate has an off-angle.

[0089] <Evaluation> <β-Gallium Oxide Film> Observation with an atomic force microscope (AFM) and a transmission electron microscope (TEM) was performed on the surfaces of the β-gallium oxide film side of the β-gallium oxide film-coated substrates of Examples 1 to 4 obtained above. Furthermore, as a result of XRD measurement, it was confirmed that the plane orientation of the β-gallium oxide films of Examples 1 to 4 was (40-1).

[0090] AFM Observation The β-type gallium oxide films obtained above in Examples 1 to 4 were observed by AFM at room temperature, and the arithmetic mean surface roughness Ra of the surface was measured. The results are shown in Table 1.

[0091] <β-Type Gallium Oxide Substrate | β-Type Gallium Oxide Film Interface> For the β-type gallium oxide film-attached substrates of Examples 1 to 4 obtained above, the interface between the β-type gallium oxide film and the β-type gallium oxide substrate was observed with a transmission electron microscope (TEM). From the obtained TEM images, the film thickness of the β-type gallium oxide film was measured, and the unevenness at the interface between the β-type gallium oxide substrate and the β-type gallium oxide film was observed. TEM images of Examples 1 to 4 are shown in Figures 3 to 6.

[0092] <Breakdown voltage> A substrate with a β-type gallium oxide film is immersed in Fluorinert, a fluorine-based inert liquid with pressure resistance, and Al foil is attached to the backside. A tungsten (W) needle is then brought into contact with the surface to measure the breakdown voltage.

[0093]

[0094] From the above TEM images, it was confirmed that, compared to Example 1, in Examples 2 to 4 having an off-angle, the unevenness at the interface between the β-type gallium oxide film and the β-type gallium oxide substrate was reduced. This also suggested that the growth of heterocrystalline planes other than the (40-1) plane in the β-type gallium oxide film could be suppressed, and the surface morphology was also good. Furthermore, in Examples 1 to 4, the β-type gallium oxide film formed on the (001) plane of the β-type gallium oxide substrate had a crystal rotation about the 010 axis, and epitaxial growth occurred in the (40-1) plane orientation. On the other hand, in Example 5, in which the (001) plane of the β-type gallium oxide substrate was tilted 6° toward the

[010] axis, it is believed that the β-type gallium oxide film did not undergo crystal rotation about the 010 axis, and epitaxial growth occurred in the (001) plane orientation.

[0095] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2023-159113) filed on September 22, 2023, the contents of which are incorporated herein by reference.

[0096] REFERENCE SIGNS LIST 100 β-type gallium oxide film-attached substrate 110 β-type gallium oxide substrate 110a First main surface 120 β-type gallium oxide film 1000 Manufacturing apparatus 1100 Reaction chamber 1200 Substrate placement unit 1210 Susceptor 1220 Heating device 1300 Gallium element supply device 1310, 1410 Shutter 1400 Oxygen element supply device 1450 Plasma generation unit 1500 Oxygen gas supply unit 1600 Inert gas supply unit 1700 Ozonizer 1810 Oxygen gas supply pipe 1820, 1840, 1860 Mass flow controller 1830 Ozone-oxygen mixed gas supply pipe 1850 Inert gas supply pipe 1870 Mixed gas supply pipe

Claims

1. A method for producing a β-type gallium oxide film, comprising: generating plasma from a mixed gas containing oxygen and ozone, thereby dissociating the ozone into oxygen-constituting particles and supplying the ozone to a reaction chamber under reduced pressure; supplying elemental gallium to the reaction chamber; and epitaxially growing a β-type gallium oxide film on a β-type gallium oxide substrate inside the reaction chamber, wherein the β-type gallium oxide substrate is an off-angle β-type gallium oxide substrate.

2. The method for producing a β-type gallium oxide film according to claim 1, wherein the concentration of the ozone in the mixed gas relative to the total of the oxygen and the ozone is 5 volume % or more.

3. A method for producing a β-type gallium oxide film according to claim 1 or 2, wherein the temperature of the β-type gallium oxide substrate is set to 0°C or higher and 700°C or lower to epitaxially grow the β-type gallium oxide film.

4. A method for producing a β-type gallium oxide film according to claim 1 or 2, wherein the surface of the β-type gallium oxide substrate having an off-angle has a (001) plane inclined at an angle of more than 1° and not more than 10° toward the [010] axis.

5. A method for producing a β-type gallium oxide film as described in claim 1 or 2, wherein the surface of the β-type gallium oxide substrate having an off-angle has a (001) plane inclined at an angle of 3° to 8° toward the [010] axis.

6. A method for producing a β-type gallium oxide film according to claim 1 or 2, wherein the surface of the β-type gallium oxide substrate having an off-angle has a (001) plane inclined at an angle of more than 1° and not more than 10° toward the [100] axis.

7. A substrate with a β-type gallium oxide film, comprising a β-type gallium oxide substrate having an off-angle, the surface of which has a (001) plane tilted by more than 1° and not more than 10° toward the [010] axis.

8. A substrate with a β-type gallium oxide film, comprising a β-type gallium oxide substrate having an off-angle and a β-type gallium oxide film, the β-type gallium oxide film being oriented in the (001) plane.

9. A substrate with a β-type gallium oxide film, comprising a β-type gallium oxide substrate having an off-angle, the surface of which has a (001) plane tilted at an angle greater than 1° and less than 10° toward the [100] axis.

10. The gallium oxide film according to claim 7, wherein the β-type gallium oxide film has a (001) plane orientation.

11. The β-type gallium oxide film-attached substrate according to claim 7 or 8, wherein the β-type gallium oxide film has a thickness of 0.5 μm or more.

12. The β-type gallium oxide film-attached substrate according to claim 11, wherein the β-type gallium oxide film has a thickness of 50 μm or less.

13. A substrate with a β-type gallium oxide film according to claim 7 or 8, wherein the surface of the β-type gallium oxide substrate having an off-angle has a (001) plane inclined at an angle of 3° to 8° toward the [010] axis.

14. The β-type gallium oxide film-attached substrate according to claim 7 or 8, wherein the β-type gallium oxide film has a dielectric breakdown voltage of 80 V / μm or more.

15. The β-type gallium oxide film-attached substrate according to claim 7 or 8, wherein the surface roughness (Ra) of the β-type gallium oxide film is 0.1 nm or more and 2.0 nm or less.

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