Iii-nitride semiconductor epitaxial wafer and electronic device

Abstract

Provided are a Group III nitride semiconductor epitaxial wafer and an electronic device. The Group III nitride semiconductor epitaxial wafer has a Group III nitride semiconductor film that is epitaxially grown on a Group III nitride semiconductor substrate obtained by an OVPE method, and a topmost surface that is flat. A Group III nitride semiconductor epitaxial wafer has a Group III nitride semiconductor film that is epitaxially grown on a Group III nitride semiconductor substrate obtained by an OVPE method, and a topmost surface that is flat. The Group III nitride semiconductor film has a carrier concentration of 10 20 cm ‑3 The above Group III nitride semiconductor substrate; a first Group III nitride semiconductor film that contains Al and Ga as Group III elements and is epitaxially grown on the Group III nitride semiconductor substrate; and a second Group III nitride semiconductor film that is epitaxially grown on the first Group III nitride semiconductor film.

Description

Technical Field

[0001] This disclosure relates to a group III nitride semiconductor epitaxial wafer having a group III nitride semiconductor substrate, a first group III nitride semiconductor film epitaxially grown thereon, and a second group III nitride semiconductor film epitaxially grown on the first group III nitride semiconductor film, and an electronic device using the group III nitride semiconductor epitaxial wafer. Background Technology

[0002] Group III nitride semiconductors are used in optical devices such as semiconductor lasers and light-emitting diodes, as well as in high-frequency or high-output electronic devices. These semiconductors have attracted particular attention in recent years because they are expected to reduce conversion losses during power conversion compared to silicon-based devices. To fabricate high-frequency or high-output electronic devices, it is necessary to fabricate the devices on high-quality group III nitride semiconductor substrates that can suppress crystal defects generated in the device layer.

[0003] Methods for manufacturing group III nitride crystals include, for example, hydride vapor phase growth (hereinafter also known as HVPE), ammonothermal method, sodium flux method, and oxide vapor phase growth (hereinafter also known as OVPE).

[0004] The most commonly used method for substrate fabrication, HVPE, involves introducing hydrogen halide gas into elemental Group III raw materials to generate halide gas, which is then used as the raw material gas for crystal growth. For example, in the growth of gallium nitride crystals, HCl gas is introduced into Ga metal to generate gallium chloride (e.g., GaCl2) gas, and high-speed growth of over 1 mm / h is achieved by using gallium chloride-containing gas as a Group III source. It is known that HVPE primarily involves adding silicon to Group III nitride crystals to obtain Group III nitride crystals with N-type conductivity.

[0005] The OVPE method manufactures group III nitride crystals by adding a high concentration of oxygen to them using an oxide feedstock gas (see, for example, Patent Document 1). This method involves reacting a group III oxide gas with a nitrogen-containing gas to produce group III nitride crystals. The resulting substrate has a dislocation density of 10-1. 4 cm -2 With its low dislocation density, the OVPE method is one of the means to obtain high-quality group III nitride crystals.

[0006] Existing technical documents Patent documents Patent Document 1: WO2015 / 053341A1 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, the inventors have discovered that although the group III nitride semiconductor substrates obtained by the OVPE method have 10 20 cm -3 The above-mentioned high carrier concentration, but the group III nitride semiconductor film obtained by direct epitaxial growth on it, such as Figures 7A-7C As shown, there is a problem of not being able to obtain sufficient flatness. Figure 7A It is an AFM image of a surface with a diameter of 1 μm × 1 μm. Figure 7B It is an AFM image of a surface measuring 10 μm × 10 μm. Figure 7C This is an AFM image of the surface at 90μm × 90μm. Regarding their respective root mean square heights (Rq: JIS B0601). Figure 7A The value is Rq = 0.377 nm (1 μm square). Figure 7B The value is 0.793 nm (10 μm square). Figure 7C The value is 9.66 nm (30 μm square). It can be seen that although it is low in a narrow range, it is high in a large range, resulting in a ridge structure on the surface and failing to achieve sufficient flatness.

[0009] Therefore, the purpose of this disclosure is to provide a group III nitride semiconductor epitaxial wafer with a group III nitride semiconductor film epitaxially grown on a group III nitride semiconductor substrate obtained by the OVPE method, and with the outermost surface being flat.

[0010] means for solving problems

[0011] The group III nitride semiconductor epitaxial wafer disclosed herein possesses: n-type conductivity and a carrier concentration of 10-1. 20 cm -3 The above-mentioned group III nitride semiconductor substrate; a first group III nitride semiconductor film containing Al and Ga as group III elements, obtained by epitaxial growth on the group III nitride semiconductor substrate; and a second group III nitride semiconductor film obtained by epitaxial growth on the first group III nitride semiconductor film.

[0012] The electronic device disclosed herein uses the aforementioned group III nitride semiconductor epitaxial wafer.

[0013] The method for manufacturing a group III nitride semiconductor epitaxial wafer disclosed herein includes the following steps: forming an n-type conductive wafer with a carrier concentration of 10 by OVPE method. 20 cm -3The above-described process for a group III nitride semiconductor substrate includes: a process for epitaxially growing a first group III nitride semiconductor film containing Al and Ga as group III elements on a group III nitride semiconductor substrate; and a process for epitaxially growing a second group III nitride semiconductor film on the first group III nitride semiconductor film.

[0014] Invention Effects

[0015] The group III nitride semiconductor epitaxial wafer disclosed herein comprises a first group III nitride semiconductor film containing Al and Ga as group III elements, epitaxially grown on a group III nitride semiconductor substrate, and a second group III nitride semiconductor film epitaxially grown on the first group III nitride semiconductor film. By providing the first group III nitride semiconductor film containing Al and Ga as group III elements as an intermediate layer, the flatness of the second group III nitride semiconductor film on the uppermost surface can be ensured. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view showing the cross-sectional structure of the group III nitride semiconductor epitaxial wafer of Embodiment 1.

[0017] Figure 2 This is a flowchart of a method for manufacturing a group III nitride semiconductor substrate constituting a group III nitride semiconductor epitaxial wafer according to Embodiment 1.

[0018] Figure 3 This is a schematic cross-sectional view showing the cross-sectional structure of a manufacturing apparatus for a group III nitride semiconductor substrate constituting a group III nitride semiconductor epitaxial wafer of Embodiment 1.

[0019] Figure 4A Table 1 shows the manufacturing conditions of the group III nitride semiconductor epitaxial wafer of Example 1.

[0020] Figure 4B Table 2 shows the manufacturing conditions of the group III nitride semiconductor epitaxial wafer of Example 2.

[0021] Figure 4C Table 3 shows the manufacturing conditions of the group III nitride semiconductor epitaxial wafer of Example 3.

[0022] Figure 5 Table 4 shows the composition of each layer of the group III nitride semiconductor epitaxial wafers of Examples 1-3.

[0023] Figure 6Table 5 shows AFM images of the surface of the group III nitride semiconductor epitaxial wafers of Examples 1-3 and the values ​​of the root mean square roughness (RMS) of the surface at 30 μm square.

[0024] Figure 7A This is an AFM image of the surface of a group III nitride semiconductor film, measuring 1 μm × 1 μm, obtained by direct epitaxial growth on a group III nitride semiconductor substrate obtained by the OVPE method.

[0025] Figure 7B This is an AFM image of the surface of a group III nitride semiconductor film, measuring 10 μm × 10 μm, obtained by direct epitaxial growth on a group III nitride semiconductor substrate obtained by the OVPE method.

[0026] Figure 7C This is an AFM image of the surface of a group III nitride semiconductor film, measuring 90 μm × 90 μm, obtained by direct epitaxial growth on a group III nitride semiconductor substrate obtained by the OVPE method.

[0027] Figure 8 Table 6 shows the composition of each layer of the group III nitride semiconductor epitaxial wafers of Examples 3 and 4-7 and the Al composition ratio in the first group III nitride semiconductor film.

[0028] Figure 9 Table 7 shows the AFM images of the surface of the group III nitride semiconductor epitaxial wafers of Examples 3 and 4-7, as well as the values ​​of the root mean square roughness (RMS) of the surface at 30 μm square.

[0029] Symbol Explanation 2. Group III nitride semiconductor substrates 4 Group III Nitride Semiconductor Films 6 Group III Nitride Semiconductor Films 10 Group III nitride semiconductor epitaxial wafer 100 Raw Material Room 101 Raw Material Reaction Chamber 102 First Carrier Gas Supply Port 103 Reactive gas supply pipe 104 Raw Material Boat 105 Initial Group III Elemental Source 106 First Heater 107 Group III element oxide gas exhaust outlet 108 Gas Exhaust Port 109 Connecting pipe 110 Third Heater 111 Cultivation Room 112 Third Carrier Gas Supply Port 113 Nitrogen-containing gas supply port 114 Second Carrier Gas Supply Port 115 Second Heater 116 types of substrates 117 Substrate base 118 Gas supply port 119 Exhaust port Detailed Implementation

[0030] The first type of group III nitride semiconductor epitaxial wafer exhibits: n-type conductivity and a carrier concentration of 10. 20 cm -3 The above-mentioned group III nitride semiconductor substrate; a first group III nitride semiconductor film containing Al and Ga as group III elements, obtained by epitaxial growth on the group III nitride semiconductor substrate; and a second group III nitride semiconductor film obtained by epitaxial growth on the first group III nitride semiconductor film.

[0031] The second type of group III nitride semiconductor epitaxial wafer can be, in the first type described above, where the root mean square roughness (RMS) of the surface of the second group III nitride semiconductor film on the uppermost surface is less than 1 nm (30 μm square).

[0032] The third type of group III nitride semiconductor epitaxial wafer may be, in the first or second type described above, a gallium nitride substrate.

[0033] The fourth type of group III nitride semiconductor epitaxial wafer may be, in any of the first to third types above, a second group III nitride semiconductor film formed above the first group III nitride semiconductor film, comprising a group III nitride semiconductor film with an Al composition ratio less than that of the first group III nitride semiconductor film.

[0034] The fifth type of group III nitride semiconductor epitaxial wafer can be, in any of the first to fourth types described above, a second group III nitride semiconductor film formed above the first group III nitride semiconductor film, containing a carrier concentration of 10. 17 cm -3 The following are group III nitride semiconductor films.

[0035] The group III nitride semiconductor epitaxial wafer of the sixth embodiment can be, in any of the embodiments of the first to fifth embodiments above, wherein the doping element of the group III nitride semiconductor substrate is oxygen.

[0036] According to a seventh aspect, the group III nitride semiconductor epitaxial wafer may have, in any one of the first to sixth aspects described above, an Al composition ratio of 0.001 or more and 0.3 or less when the total of the composition ratios of group III elements in the first group III nitride semiconductor film is set to 1.

[0037] According to an eighth aspect, the group III nitride semiconductor epitaxial wafer may have, in any one of the first to seventh aspects described above, a thickness of the first group III nitride semiconductor film of 0.02 μm or more and 1 μm or less.

[0038] According to a ninth aspect, an electronic device uses the group III nitride semiconductor epitaxial wafer according to any one of the first to eighth aspects described above.

[0039] According to a tenth aspect, a method for manufacturing a group III nitride semiconductor epitaxial wafer comprises the following steps: forming a group III nitride semiconductor substrate that exhibits n-type conductivity and has a carrier concentration of 10 20 cm -3 or more; epitaxially growing a first group III nitride semiconductor film containing Al and Ga as group III elements on the group III nitride semiconductor substrate; and epitaxially growing a second group III nitride semiconductor film on the first group III nitride semiconductor film.

[0040] Hereinafter, a group III nitride semiconductor epitaxial wafer and a method for manufacturing the same according to an embodiment of the present disclosure will be described with reference to the accompanying drawings.

[0041] (Embodiment 1)

[0042] <Group III Nitride Semiconductor Epitaxial Wafer>

[0043] Figure 1 is a schematic cross-sectional view schematically showing an example of the nitride semiconductor epitaxial wafer 10 of Embodiment 1.

[0044] The group III nitride semiconductor epitaxial wafer 10 of the present disclosure includes at least three layers, namely a group III nitride semiconductor substrate 2, a first group III nitride semiconductor film 4 including an epitaxial layer obtained by epitaxial growth on the substrate, and a second group III nitride semiconductor film 6 obtained by epitaxial growth on the first group III nitride semiconductor film 4. The group III nitride semiconductor substrate 2 exhibits n-type conductivity and has a carrier concentration of 10 20 cm -3 or more.

[0045] Hereinafter, each member constituting the group III nitride semiconductor epitaxial wafer 10 will be described.

[0046] <Group III nitride semiconductor substrate> In order to reduce on-resistance during operation, the Group III nitride semiconductor substrate 2 is doped with impurities that form an n-type dopant, exhibits n-type conductivity, and has a carrier concentration of 10 20 cm -3 or higher.

[0047] The n-type doping element of the Group III nitride semiconductor substrate 2 may, for example, include at least one selected from the group consisting of silicon, germanium and oxygen.

[0048] As the n-type doping element of the Group III nitride semiconductor substrate, oxygen is more preferred. In this case, particularly when producing a Group III nitride semiconductor substrate used for a substrate by the OVPE method, oxygen can be easily added to the Group III nitride semiconductor substrate.

[0049] When oxygen constitutes the main element among the n-type doping elements of the Group III nitride semiconductor substrate, oxygen is added, for example, at a composition level of 10 20 atoms·cm -3 or higher. Thereby, the carrier concentration of the Group III nitride semiconductor substrate can easily be set to 10 20 cm -3 or higher.

[0050] The Group III nitride semiconductor substrate may be GaN obtained by the OVPE method.

[0051] <First Group III nitride semiconductor film>

[0052] The first Group III nitride semiconductor film 4 is a Group III nitride semiconductor film obtained by epitaxial growth on the Group III nitride semiconductor substrate 2, containing Al and Ga as Group III elements. When the total composition ratio of Group III elements in the first Group III nitride semiconductor film is set to 1, the Al composition ratio may, for example, be 0.001 or more and 0.3 or less.

[0053] The epitaxial layer constituting the first Group III nitride semiconductor film may be a single layer, or may have a structure of two or more layers.

[0054] The thickness of the first Group III nitride semiconductor film may, for example, be 0.02μm or more and 1μm or less.

[0055] The thickness of the first Group III nitride semiconductor film is preferably 0.02μm or more. When the Group III nitride semiconductor film is thinner than 0.02μm, a stable surface cannot be sufficiently formed during epitaxial layer growth on the substrate, and sufficient flatness cannot be obtained.

[0056] The thickness of the first group III nitride semiconductor film is preferably 1 μm or less. If the thickness is greater than 1 μm, the influence of lattice mismatch with the second group III nitride semiconductor film epitaxially grown thereon may occur in some cases.

[0057] <Second Group III Nitride Semiconductor Film>

[0058] The second group III nitride semiconductor film is a group III nitride semiconductor film obtained by epitaxial growth on a group III nitride semiconductor substrate. The thickness of the second group III nitride semiconductor film may be, for example, 1 μm or more and 30 μm or less. By setting the thickness of the second group III nitride semiconductor film to 1 μm or more, a stable surface can be sufficiently formed when an epitaxial layer is formed on the substrate, allowing a device to be formed on the uppermost surface. In addition, when the thickness is 30 μm or less, the flatness of the epitaxial layer is easily maintained.

[0059] The thickness of the second group III nitride semiconductor film is more preferably 1 μm or more and 8 μm or less. When the thickness is 1 μm or more and 8 μm or less, a film with a stable surface can be sufficiently formed, and flatness can be sufficiently maintained even when the lattice mismatch between the substrate and the epitaxial layer is large.

[0060] The epitaxial layer constituting the second group III nitride semiconductor film may have a structure of one layer or two or more layers.

[0061] For example, the root mean square roughness (RMS) of the second group III nitride semiconductor film measured in a 30 μm square area is 1 nm or less, which means it has sufficient flatness.

[0062] In addition, compared with the first group III nitride semiconductor film, the Al composition ratio of the second group III nitride semiconductor film in the entire group III elements can be lower. In the case where the epitaxial layer constituting the second group III nitride semiconductor film has two or more layers, the Al composition ratio can decrease as the layer goes from the film closer to the first group III nitride semiconductor film to the upper layers.

[0063] Furthermore, when used in electronic devices, a device with low operating resistance and low leakage current can be achieved.

[0064] <Electronic Device>

[0065] In an electronic device, the above-mentioned group III nitride semiconductor epitaxial wafer can be used. Thereby, a device with a flat surface, low operating resistance and low leakage current can be achieved.

[0066] <Method for Manufacturing Group III Nitride Semiconductor Epitaxial Wafer>

[0067] The method for manufacturing a group III nitride semiconductor epitaxial wafer according to Embodiment 1 comprises the following steps.

[0068] (1) Forming a group III nitride semiconductor substrate exhibiting n-type conductivity and having a carrier concentration of 10 20 cm -3 or higher by an OVPE method. It should be noted that the method for manufacturing a group III nitride semiconductor substrate based on the OVPE method will be described later.

[0069] (2) Epitaxially growing a first group III nitride semiconductor film containing Al and Ga as group III elements on the group III nitride semiconductor substrate. The first group III nitride semiconductor film is AlGaN, for example. More specifically, when the chemical formula of the first group III nitride semiconductor film is denoted as (Al x Ga 1-x )N, the Al composition ratio x is, for example, 0.001 or more and 0.3 or less. By setting the Al composition ratio x within the above range, sufficient flatness can be obtained for the first group III nitride semiconductor film, and lattice distortion occurring between the first group III nitride semiconductor film and the underlying group III nitride semiconductor substrate can be suppressed.

[0070] (3) Epitaxially growing a second group III nitride semiconductor film on the first group III nitride semiconductor film. Since the first group III nitride semiconductor film has sufficient flatness, the second group III nitride semiconductor film can obtain sufficient flatness with a root mean square roughness RMS value of 1 nm or less on a 30 μm square surface, for example. Accordingly, the second group III nitride semiconductor film has sufficient flatness as the outermost surface.

[0071] As described above, the group III nitride semiconductor epitaxial wafer according to Embodiment 1 can be obtained.

[0072] <Outline of Method for Manufacturing Group III Nitride Semiconductor Substrate>

[0073] Reference is made to Figure 2 the flow chart and Figure 3 the following describes an outline of a method for manufacturing the group III nitride semiconductor substrate constituting the group III nitride semiconductor epitaxial wafer according to Embodiment 1 based on the OVPE method. Figure 2 (a) of shows a time-sequential flow chart of the manufacturing method. Figure 2 (b) of is a diagram illustrating functional units from upstream to downstream in a manufacturing apparatus used in the present manufacturing method as steps.

[0074] In the seed substrate preparation step of preparing a seed substrate 116, the seed substrate 116 is placed on a substrate susceptor 117.

[0075] The heating process involves heating the incubation chamber 111 to above 100°C but below 500°C in an inert gas atmosphere.

[0076] In the decomposition protection heating process 1, the incubation chamber 111 is heated to above 500°C but below 1100°C in an NH3 gas atmosphere.

[0077] In the decomposition protection heating process 2, the incubation chamber 111 is heated to above 1100℃ but below 1500℃ in an atmosphere of NH3 gas and Ga2O gas.

[0078] In the growth process of growing a group III nitride semiconductor substrate on the seed substrate 116, a group III element oxide gas is generated in the raw material chamber 100 and supplied to the cultivation chamber 111, and a nitrogen-containing gas is supplied to the cultivation chamber 111 to grow the group III nitride semiconductor substrate on the seed substrate 116.

[0079] The growth process also includes a reactive gas supply process, a group III element oxide gas generation process, a group III element oxide gas supply process, a nitrogen-containing gas supply process, a group III nitride semiconductor substrate formation process, and a residual gas removal process. It should be noted that all the steps included in the growth process can be performed simultaneously within the group III nitride semiconductor substrate manufacturing apparatus.

[0080] The reactive gas supply process supplies reactive gas to the raw material reaction chamber.

[0081] The process for generating group III element oxide gases involves reacting a starting group III element source with a reactive gas (a reducing gas if the starting group III element source is an oxide, and an oxidizing gas if the starting group III element source is a metal) to generate group III element oxide gases.

[0082] The Group III element oxide gas supply process supplies the Group III element oxide gas produced in the Group III element oxide gas generation process to the incubation chamber.

[0083] The nitrogen-containing gas supply process supplies nitrogen-containing gas to the cultivation chamber.

[0084] The group III nitride semiconductor substrate formation process involves reacting the group III element oxide gas supplied to the growth chamber in the group III element oxide gas supply process with the nitrogen-containing gas supplied to the growth chamber in the nitrogen-containing gas supply process, thereby growing the group III nitride semiconductor substrate on the seed substrate.

[0085] The residual gas venting process removes unreacted gases that do not contribute to the formation of group III nitride semiconductor substrates to the outside.

[0086] In the decomposition-protection temperature lowering step, in order to suppress the decomposition of the group III nitride semiconductor substrate grown on the seed substrate 116, the temperatures of the raw material chamber 100 and the growth chamber 111 are lowered to 500°C while supplying NH₃ gas.

[0087] In the temperature lowering step, the temperatures of the raw material chamber 100 and the growth chamber 111 are lowered to below 100°C under an inert gas atmosphere.

[0088] In the taking-out step, the seed substrate 116 with the grown group III nitride substrate is taken out from the growth chamber 111.

[0089] <Outline of Manufacturing Apparatus for Group III Nitride Semiconductor Substrate>

[0090] Refer to Figure 3 An outline of the manufacturing apparatus used in the method for manufacturing a group III nitride semiconductor substrate that constitutes the group III nitride semiconductor epitaxial wafer of the present embodiment 1 will be described. Figure 3 is a schematic sectional view of the manufacturing apparatus for a group III nitride semiconductor substrate that constitutes the group III nitride semiconductor epitaxial wafer according to Embodiment 1.

[0091] In Figure 3 , the size and ratio of each constituent member may differ from those in practice. In the manufacturing apparatus for a group III nitride semiconductor substrate, a raw material reaction chamber 101 is arranged in a raw material chamber 100, and a raw material boat 104 carrying a starting group III element source 105 is arranged in the raw material reaction chamber 101. The raw material reaction chamber 101 is connected with a reactive gas supply pipe 103 for supplying a gas that reacts with the starting group III element source 105. The raw material reaction chamber 101 is provided with a group III element oxide gas discharge port 107 for discharging the generated group III element oxide gas. When the starting group III source is an oxide, a reducing gas is used as the reactive gas. When the starting group III source is a metal, an oxidizing gas is used as the reactive gas. In addition, the raw material chamber 100 is connected with a first carrier gas supply port 102 for supplying a first carrier gas. The first carrier gas supplied from the first carrier gas supply port 102 and the group III element oxide gas discharged from the group III element oxide gas discharge port 107 flow from the gas discharge port 108 into the growth chamber 111 via the connecting pipe 109, and are supplied into the growth chamber 111 from the gas supply port 118 connected to the growth chamber 111. The growth chamber 111 is provided with a gas supply port 118, a third carrier gas supply port 112, a nitrogen-containing gas supply port 113, a second carrier gas supply port 114 and an exhaust port 119. The growth chamber 111 is provided with a substrate susceptor 117 for arranging the seed substrate 116 thereon.

[0092] <Details of Manufacturing Method and Manufacturing Apparatus>

[0093] Refer to Figure 2 and Figure 3 The manufacturing method of the group III nitride semiconductor substrate of Embodiment 1 will be described in detail.

[0094] In this embodiment 1, Ga metal is used as the starting group III element source 105, but it is not limited to this; for example, Al or In can be used.

[0095] First, a seed substrate 116 is prepared. For example, gallium nitride, gallium arsenide, silicon, sapphire, silicon carbide, zinc oxide, gallium oxide, or ScAlMgO4 can be used as the seed substrate 116. In this embodiment 1, gallium nitride is used as the seed substrate 116.

[0096] based on Figure 2 Explain (a).

[0097] The heating process involves heating the incubation chamber in an inert gas atmosphere until the seed substrate 116 reaches a temperature at which it does not decompose. In the manufacture of group III nitride semiconductor substrates based on the OVPE method, heating is carried out in an inert gas atmosphere (e.g., N2 gas) until approximately 500°C.

[0098] The decomposition protection heating process 1 involves heating in a nitrogen-containing gas atmosphere while suppressing the decomposition of the seed substrate 116. In the manufacture of Group III nitride semiconductor substrates based on the OVPE method, heating is performed at temperatures above 500°C and below 1100°C in an atmosphere mixed with an inert gas and a nitrogen-containing gas (NH3). The reason for mixing NH3 is to prevent the decomposition of the seed substrate 116 due to the removal of N atoms. Furthermore, heating can be performed with an additional mixture of H2 gas.

[0099] The decomposition protection heating step 2 involves heating in an atmosphere of Group III oxide gas and nitrogen-containing gas to suppress the decomposition of the seed substrate 116. In the manufacture of Group III nitride semiconductor substrates based on the OVPE method, heating is performed at temperatures above 1100°C and below 1500°C in an atmosphere containing a mixture of H2 gas, an inert gas, Group III oxide gas, and nitrogen-containing NH3 gas. The reason for mixing Group III oxide gas is that decomposition cannot be suppressed by nitrogen-containing gas alone. By providing a driving force for the growth of the Group III nitride semiconductor substrate, decomposition can be suppressed.

[0100] The growth process generates Group III element oxide gas in the raw material chamber 100 and supplies it to the cultivation chamber 111. Nitrogen-containing gas is also supplied to the cultivation chamber 111 to generate a Group III nitride semiconductor substrate on the seed substrate 116. Specifically, the growth process includes a reactive gas supply process, a Group III element oxide gas generation process, a Group III element oxide gas supply process, a nitrogen-containing gas supply process, a Group III nitride semiconductor substrate generation process, and a residual gas removal process.

[0101] Next, based on Figure 2 (b) will be explained.

[0102] The reactive gas supply process supplies reactive gas from the reactive gas supply pipe 103 to the raw material reaction chamber 101 within the raw material chamber 100. As described above, either a reducing gas or an oxidizing gas can be used as the reactive gas, depending on the need. In this embodiment 1, since metallic Ga is used as the Group III element source 105, H2O gas is used as the reactive gas.

[0103] The Group III element oxide gas generation process involves reacting the reactive gas supplied to the raw material reaction chamber 101 in the reactive gas supply process with Ga, which serves as the starting Group III element source 105, to generate Ga₂O gas, which is a Group III element oxide gas. The generated Ga₂O gas is discharged from the raw material reaction chamber 101 to the raw material chamber 100 via the Group III element oxide gas outlet 107. The discharged Ga₂O gas is mixed with the first carrier gas supplied to the raw material chamber from the first carrier gas supply port 102 and supplied to the gas outlet 108. In this embodiment 1, the raw material chamber 100 is heated by the first heater 106. When heating the raw material chamber 100, from the perspective of the boiling point of Ga₂O gas, it is preferable that the temperature of the raw material chamber 100 is 800°C or higher. Furthermore, it is preferable that the temperature of the raw material chamber 100 is lower than that of the incubation chamber 111. When heating the incubation chamber by the second heater 115 as described later, it is preferable that the temperature of the raw material chamber 100 is, for example, lower than 1800°C. The starting group III element source 105 is placed in a feed boat 104 disposed within the feed reaction chamber 101. The feed boat 104 is preferably shaped to allow for a large contact area between the reactive gas and the starting group III element source. For example, to prevent the starting group III element source 105 from passing through the feed reaction chamber 101 without contact with the reactive gas, the feed boat 104 is preferably a multi-stage vessel shape.

[0104] It should be noted that the methods for generating Group III element oxide gases can be broadly categorized into methods of reducing the starting Group III element source 105 and methods of oxidizing the starting Group III element source 105. For example, in the reduction method, an 105 oxide (e.g., Ga₂O₃) is used as the starting Group III element source, and a reducing gas (e.g., H₂, CO, CH₄, C₂H₆, H₂S, SO₂) is used as the reactive gas. On the other hand, in the oxidation method, a non-oxide (e.g., liquid Ga) is used as the starting Group III element source 105, and an oxidizing gas (e.g., H₂O, O₂, CO, CO₂, NO, N₂O, NO₂) is used as the reactive gas. Furthermore, in addition to the starting Group III element source 105, In and Al sources can also be used as starting Group III elements. As the first carrier gas, inert gases such as H₂ can be used.

[0105] The Group III oxide gas supply process supplies Ga₂O gas generated in the Group III oxide gas generation process to the incubation chamber 111 via gas outlet 108, connecting pipe 109, and gas supply port 118. If the temperature of the connecting pipe 109 connecting the raw material chamber 100 and the incubation chamber 111 is lower than the temperature of the raw material chamber 100, a reverse reaction of the Group III oxide gas generation reaction will occur, and the initial Ga source 105 will precipitate within the connecting pipe 109. Therefore, the connecting pipe 109 is preferably heated to a higher temperature than the first heater 106 by the third heater 110 so that it does not decrease compared to the temperature of the raw material chamber 100.

[0106] The nitrogen-containing gas supply process supplies nitrogen-containing gas from nitrogen-containing gas supply port 113 to the cultivation chamber 111. Examples of nitrogen-containing gases include NH3 gas, NO gas, NO2 gas, N2O gas, N2H2 gas, and N2H4 gas.

[0107] The group III nitride semiconductor substrate formation process involves reacting the raw material gases supplied to the cultivation chamber via each feeding process to grow the group III nitride semiconductor substrate on the seed substrate 116. The cultivation chamber 111 is preferably heated to the temperature at which the group III element oxide gas and the nitrogen-containing gas react, via the second heater 115. At this time, to prevent the reverse reaction that generates group III element oxide gas, the temperature of the cultivation chamber 111 is preferably controlled so that it does not decrease compared to the temperature of the raw material chamber 100. The temperature of the cultivation chamber 111 heated by the second heater 115 is preferably 1000°C or higher and 1800°C or lower. Furthermore, to suppress temperature fluctuations in the cultivation chamber 111 caused by the Ga2O gas generated in the raw material chamber 100 and the first carrier gas, it is ideal to make the temperatures of the second heater 115 and the third heater 111 the same.

[0108] By mixing the Group III element oxide gas supplied to the growth chamber 111 via the Group III element oxide supply process and the nitrogen-containing gas supplied to the growth chamber 111 via the nitrogen-containing gas supply process upstream of the seed substrate 116, the growth of a Group III nitride semiconductor substrate can be performed on the seed substrate 116.

[0109] It should be noted that the reactive gas supply process, the group III element oxide gas generation process, the group III element oxide gas supply process, the nitrogen-containing gas supply process, the group III nitride semiconductor substrate generation process, and the residual gas removal process included in the growth process can be carried out simultaneously.

[0110] As the second carrier gas, an inert gas or H2 gas can be used.

[0111] The residual gas discharge process discharges unreacted Group III element oxide gases and nitrogen-containing element gases, as well as the first carrier gas, the second carrier gas, and the third carrier gas, from the exhaust port 119.

[0112] The decomposition protection cooling process involves cooling the substrate while suppressing its decomposition under a nitrogen-containing gas atmosphere. In the manufacturing of group III nitride semiconductor substrates based on the OVPE method, cooling is performed to below 500°C in a mixture of inert gas and nitrogen-containing gas (NH3).

[0113] The cooling process is carried out in an inert gas atmosphere to cool the group III nitride semiconductor substrate to a temperature at which it can be removed from the growth chamber.

[0114] In this embodiment 1, after a cooling process, the seed substrate 116 on which the group III nitride semiconductor substrate is grown is taken out from the cultivation chamber 111.

[0115] From the above, a group III nitride semiconductor substrate can be obtained.

[0116] <Group III Nitride Semiconductor Films>

[0117] The first group III nitride semiconductor film is obtained by epitaxially growing a group III nitride semiconductor film containing Al and Ga as group III elements on a group III nitride semiconductor substrate. The aforementioned epitaxial growth process of the first group III nitride semiconductor film can be performed by replacing the seed substrate with a group III nitride semiconductor substrate and the starting group III element source with a substance containing Al and Ga in the aforementioned group III nitride semiconductor substrate manufacturing apparatus and manufacturing method, thereby manufacturing based on the OVPE method. Therefore, after manufacturing the group III nitride semiconductor substrate, it is not necessary to remove it from the growth chamber, and the first group III nitride semiconductor film can be continuously epitaxially grown on the group III nitride semiconductor substrate. It should be noted that the manufacturing of the first group III nitride semiconductor film is not limited to the aforementioned OVPE-based manufacturing method.

[0118] <Group III Nitride Semiconductor Films>

[0119] The second group III nitride semiconductor film is obtained by epitaxially growing a group III nitride semiconductor film on a first group III nitride semiconductor film. The aforementioned process of epitaxially growing the second group III nitride semiconductor film can be performed by replacing the seed substrate with the first group III nitride semiconductor substrate in the aforementioned group III nitride semiconductor substrate manufacturing apparatus and method, thereby manufacturing based on the OVPE method. Therefore, after manufacturing the first group III nitride semiconductor film, it is not necessary to remove it from the growth chamber, and the second group III nitride semiconductor film can be continuously epitaxially grown on the first group III nitride semiconductor film. It should be noted that the manufacturing of the second group III nitride semiconductor film is not limited to the aforementioned OVPE-based manufacturing method.

[0120] From the above, we can obtain a group III nitride semiconductor epitaxial wafer.

[0121] (Example 1)

[0122] Figure 4A Table 1 shows the manufacturing conditions of the group III nitride semiconductor epitaxial wafer of Example 1. Table 1 shows the manufacturing conditions of the group III nitride semiconductor epitaxial wafer formed by stacking four layers with film thicknesses of 0.02 μm, 0.3 μm, 0.7 μm and 7.2 μm on a group III nitride semiconductor substrate obtained by OVPE method.

[0123] Figure 5Table 4 shows the composition of each layer of the group III nitride semiconductor epitaxial wafers of Examples 1-3. Figure 5 As shown in the composition of each layer of Example 1, the group III nitride semiconductor substrate is GaN based on the OVPE method, the lower layer is a first group III nitride semiconductor film containing Al and Ga as group III elements, and the upper three layers are second group III nitride semiconductor films. Figure 5 As shown, the Al composition ratio in group III elements decreases from the lower to the upper layers.

[0124] (Example 2)

[0125] Figure 4B Table 2 shows the manufacturing conditions of the group III nitride semiconductor epitaxial wafer of Example 2. Table 2 shows the manufacturing conditions of the group III nitride semiconductor epitaxial wafer formed by stacking three layers with film thicknesses of 0.3 μm, 0.7 μm, and 7.2 μm on a group III nitride semiconductor substrate obtained by OVPE method.

[0126] like Figure 5 As shown in the composition of each layer of Example 2, the group III nitride semiconductor substrate is GaN based on the OVPE method, the lower layer 1 is a first group III nitride semiconductor film containing Al and Ga as group III elements, and the upper layer 2 is a second group III nitride semiconductor film.

[0127] (Example 3)

[0128] Figure 4C Table 3 shows the manufacturing conditions of the group III nitride semiconductor epitaxial wafer of Example 3. Table 3 shows the manufacturing conditions of the group III nitride semiconductor epitaxial wafer formed by stacking two layers with film thicknesses of 1 μm and 7.2 μm on a group III nitride semiconductor substrate obtained by OVPE method.

[0129] like Figure 5 As shown in the composition of each layer of Example 3, the group III nitride semiconductor substrate is GaN based on the OVPE method, the lower layer is a first group III nitride semiconductor film containing Al and Ga as group III elements, and the upper layer is a second group III nitride semiconductor film. Compared with Example 2, Example 3 changes the structure of the lower layer of the second group III nitride semiconductor film, which was originally a two-layer structure, to a thickness of 1 μm and is used as the first group III nitride semiconductor film. That is, from the early stage of growth on the substrate, a 1 μm layer of AlGaN with an Al composition ratio of 0.3% is formed at 1130°C and serves as the first group III nitride semiconductor film.

[0130] Figure 6Table 5 shows AFM images of the surface of the group III nitride semiconductor epitaxial wafers of Examples 1-3 and the values ​​of the root mean square roughness (RMS) of the surface at 30 μm square.

[0131] exist Figure 6 Atomic steps were observed in the AFM images. The root mean square roughness (RMS) values ​​of the 30 μm × 30 μm region were 0.422 nm and 0.372 nm in Examples 1 and 2, respectively, which are below 1 nm, indicating sufficient flatness. Furthermore, the value was also 1.04 nm in Example 3, showing relatively good flatness.

[0132] As described above, by setting a first group III nitride semiconductor film containing Al and Ga as group III elements as an intermediate layer, the flatness of the second group III nitride semiconductor film on the uppermost surface can be ensured.

[0133] (Example 3 and Experimental Examples 4-7)

[0134] Figure 8 Table 6 shows the composition of each layer of the group III nitride semiconductor epitaxial wafers of Examples 3 and 4-7 and the Al composition ratio in the first group III nitride semiconductor film. Figure 9 Table 7 shows the AFM images of the surface of the group III nitride semiconductor epitaxial wafers of Examples 3 and 4-7, as well as the values ​​of the root mean square roughness (RMS) of the surface at 30 μm square.

[0135] Comparing Experimental Examples 4-7 with Example 3, the difference lies in the altered Al composition ratio in the Group III nitride semiconductor film. Experimental Examples 4-7, as... Figure 8 As shown in Table 6, when the Al composition ratio in the group III nitride semiconductor film is 0.1% (Experimental Example 4), 3% (Experimental Example 5), and 5% (Experimental Example 6), as... Figure 9 As shown in Table 7, atomic steps were observed on the surface at a 30 μm square. Furthermore, the root mean square roughness (RMS) of the 30 μm square surface was 0.280 nm, 0.238 nm, and 0.592 nm, respectively, all below 1 nm, indicating sufficient flatness. On the other hand, when the Al content in the group III nitride semiconductor film was 30% (Experimental Example 7), the RMS of the 30 μm square surface was 17.4 nm, greater than 1 nm, indicating a rough surface.

[0136] Industrial availability

[0137] According to the group III nitride semiconductor epitaxial wafer disclosed herein, by providing a first group III nitride semiconductor film containing Al and Ga as group III elements as an intermediate layer, the flatness of the second group III nitride semiconductor film on the uppermost surface can be ensured.

Claims

1. A group III nitride semiconductor epitaxial wafer, comprising: This indicates the conductivity of the n-type and a carrier concentration of 10. 20 cm -3 The above are group III nitride semiconductor substrates; A first group III nitride semiconductor film containing Al and Ga as group III elements, epitaxially grown on the group III nitride semiconductor substrate; and The second group III nitride semiconductor film is obtained by epitaxial growth on the first group III nitride semiconductor film.

2. The group III nitride semiconductor epitaxial wafer according to claim 1, wherein, The root mean square roughness (RMS) of the surface of the second group III nitride semiconductor film on the uppermost surface is less than 1 nm (30 μm square).

3. The group III nitride semiconductor epitaxial wafer according to claim 1, wherein, The group III nitride semiconductor substrate is a gallium nitride substrate.

4. The group III nitride semiconductor epitaxial wafer according to claim 1, wherein, The second group III nitride semiconductor film formed above the first group III nitride semiconductor film comprises a group III nitride semiconductor film with an Al composition ratio less than that of the first group III nitride semiconductor film.

5. The group III nitride semiconductor epitaxial wafer according to claim 1, wherein, The second group III nitride semiconductor film formed above the first group III nitride semiconductor film contains a carrier concentration of 10. 17 cm -3 The following are group III nitride semiconductor films.

6. The group III nitride semiconductor epitaxial wafer according to claim 1, wherein, The doping element of the group III nitride semiconductor substrate is oxygen.

7. The group III nitride semiconductor epitaxial wafer according to claim 1, wherein, When the total composition ratio of group III elements in the first group III nitride semiconductor film is set to 1, the Al composition ratio is 0.001 or higher and 0.3 or lower.

8. The group III nitride semiconductor epitaxial wafer according to claim 1, wherein, The thickness of the first group III nitride semiconductor film is greater than 0.02 μm and less than 1 μm.

9. An electronic device that uses the group III nitride semiconductor epitaxial wafer as described in any one of claims 1 to 8.

10. A method for manufacturing a group III nitride semiconductor epitaxial wafer, comprising the following steps: An n-type conductive structure with a carrier concentration of 10 was formed using the OVPE method. 20 cm -3 The above are the processes for group III nitride semiconductor substrates; The process of epitaxially growing a first group III nitride semiconductor film containing Al and Ga as group III elements on the group III nitride semiconductor substrate; and The process of epitaxially growing a second group III nitride semiconductor film on the first group III nitride semiconductor film.

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