Method for manufacturing epitaxial substrate and epitaxial substrate

Abstract

The method for manufacturing the epitaxial substrate includes: a step of epitaxially growing a group III nitride semiconductor layer on a substrate; a step of taking the substrate out of a growth furnace; a step of irradiating the surface of the group III nitride semiconductor layer with ultraviolet light while exposing it to an oxygen-containing atmosphere; and a step of measuring the sheet resistance value of the group III nitride semiconductor layer.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an epitaxial substrate and the epitaxial substrate.

[0002] This application claims the priority based on Japanese Application No. 2019-200738 filed on November 5, 2019, and cites all the contents described in the Japanese Application. Background Art

[0003] Patent document 1 discloses a method for activating a p-type layer included in a gallium nitride compound semiconductor device. In this method, the p-type layer is irradiated with light having a wavelength in the range of ultraviolet light to visible light at a temperature of 200°C to 500°C. As a result, hydrogen bonded to a p-type dopant included in the p-type layer is separated and removed, and activation of the p-type dopant as an acceptor is promoted.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2000-306854

[0007] Patent Document 2: International Publication No. 2006 / 013846 Summary of the invention

[0008] A method for manufacturing an epitaxial substrate according to one embodiment of the present disclosure comprises: a step of epitaxially growing a group III nitride semiconductor layer on a substrate; a step of taking the substrate out of a growth furnace; a step of irradiating the surface of the group III nitride semiconductor layer with ultraviolet light while exposing it to an oxygen-containing atmosphere; and a step of measuring the sheet resistance value of the group III nitride semiconductor layer.

[0009] An epitaxial substrate of one embodiment of the present disclosure includes a channel layer, a barrier layer, and a cap layer. The channel layer is provided on the main surface of the substrate. The barrier layer is provided on the channel layer, and the composition of the barrier layer is Al y Ga 1-y N(0<y<0.4). The cap layer is provided on the barrier layer. In the epitaxial substrate, the sheet resistance value of the III-nitride semiconductor layer composed of the channel layer, the barrier layer and the cap layer is 300 (Ω / sq.) or more and 800 (Ω / sq.) or less. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a diagram showing the cross-sectional structure of a substrate product including a nitride semiconductor layer for measuring the sheet resistance value.

[0011] Figure 2 1 is a flowchart showing a manufacturing method according to one embodiment.

[0012] Figure 3A This is a diagram showing one process of the manufacturing method.

[0013] Figure 3B This is a diagram showing one process of the manufacturing method.

[0014] Figure 3C This is a diagram showing one process of the manufacturing method.

[0015] Figure 3D This is a diagram showing one process of the manufacturing method.

[0016] Figure 4A This is a diagram showing one process of the manufacturing method.

[0017] Figure 4B This is a diagram showing one process of the manufacturing method.

[0018] Figure 4C This is a diagram showing one process of the manufacturing method.

[0019] Figure 5 This is a diagram showing a structural example of a He—Cd laser.

[0020] Figure 6 This is a graph showing an example of a change in the sheet resistance value of the group III nitride semiconductor layer with time when the substrate is taken out of the growth furnace after the group III nitride semiconductor layer is grown and left as it is.

[0021] Fig. 7A This is a schematic diagram (band diagram) of the potential of the Group III nitride semiconductor layer obtained by simulation.

[0022] Figure 7B yes Fig. 7A A partial enlarged view of area A is shown.

[0023] Fig. 8A This is the result of analyzing and counting the negative ions present on the surface of the Group III nitride semiconductor layer.

[0024] Figure 8B This is the result of analyzing and counting the negative ions present on the surface of the Group III nitride semiconductor layer.

[0025] Figure 8C This is a result obtained by analyzing and counting the positive ions present on the surface of the Group III nitride semiconductor layer.

[0026] Fig. 9A This is a diagram for explaining the reason why oxidation of the surface of the Group III nitride semiconductor layer is accelerated by irradiation with ultraviolet light UV.

[0027] Fig. 9B This is a diagram for explaining the reason why oxidation of the surface of the Group III nitride semiconductor layer is accelerated by irradiation with ultraviolet light UV.

[0028] Fig. 9C This is a diagram for explaining the reason why oxidation of the surface of the Group III nitride semiconductor layer is accelerated by irradiation with ultraviolet light UV.

[0029] Fig.9D This is a diagram for explaining the reason why oxidation of the surface of the Group III nitride semiconductor layer is accelerated by irradiation with ultraviolet light UV.

[0030] Fig.10 This is a graph showing the ratio of the sheet resistance value based on the sheet resistance value 48 hours after the substrate on which the group III nitride semiconductor layer was formed was taken out of the growth furnace (100%). DETAILED DESCRIPTION

[0031] [Problems to be Solved by the Present Disclosure]

[0032] Most semiconductor elements of group III nitrides have a semiconductor layer epitaxially grown on a substrate. In order to grasp the performance of the semiconductor layer, it is effective to measure the sheet resistance of the semiconductor layer. This is because the sheet resistance has a high correlation with the operating characteristics of the semiconductor element (such as the maximum forward drain current Ifmax, etc.). The determination of the sheet resistance is performed, for example, by the eddy current method. In order to accurately grasp the performance of the semiconductor element, it is ideal to measure the sheet resistance with good accuracy. However, when the semiconductor layer is grown and the substrate is taken out of the growth furnace, various substances contained in the environment outside the growth furnace will bond with group III atoms (such as Ga). These substances gradually leave the group III atoms, and instead, oxygen atoms bond with group III atoms. Therefore, the degree of oxidation on the surface of the semiconductor layer is initially low and gradually increases over time. The sheet resistance depends on the degree of oxidation on the surface of the semiconductor layer. Therefore, in order to accurately measure the sheet resistance of the semiconductor layer, it is necessary to place the semiconductor layer for a long time (about 48 hours according to experience) after taking the substrate with the semiconductor layer grown out of the growth furnace, and measure it after the oxidation is fully progressed and the sheet resistance value is stable. This will lead to a longer production lead time, which is a major cause of reduced production efficiency.

[0033] [Effects of the present disclosure]

[0034] According to the present disclosure, the sheet resistance value of the epitaxial substrate can be stabilized in a shorter time.

[0035] [Description of Embodiments of the Present Disclosure]

[0036] First, the embodiments of the present disclosure are listed for explanation. A method for manufacturing an epitaxial substrate in one embodiment of the present disclosure comprises: a step of epitaxially growing a group III nitride semiconductor layer on a substrate; a step of taking the substrate out of a growth furnace; a step of irradiating the surface of the group III nitride semiconductor layer with ultraviolet light while exposing the surface of the group III nitride semiconductor layer to an oxygen-containing atmosphere; and a step of measuring the sheet resistance value of the group III nitride semiconductor layer.

[0037] When ultraviolet light is irradiated on the surface of the group III nitride semiconductor layer while the surface of the group III nitride semiconductor layer is exposed to an oxygen-containing atmosphere, the oxidation of the surface of the group III nitride semiconductor layer is promoted compared to the case where it is left as it is. This is considered to be due to the following effects. When ultraviolet light is irradiated on the surface of the group III nitride semiconductor layer, the surface of the group III nitride semiconductor layer generates heat. The bonds between various substances contained in the environment outside the growth furnace and the group III atoms are released due to the heat. Alternatively, various substances are oxidized and become low-density substances. Due to these effects, various substances are separated from the group III nitride semiconductor layer. Afterwards, the oxygen atoms in the atmosphere immediately bond with the group III atoms on the surface of the group III nitride semiconductor layer, thereby oxidizing the group III atoms. In this way, the oxidation of the surface of the group III nitride semiconductor layer is promoted, and the sheet resistance value can be stabilized in a shorter time. Therefore, the production lead time can be shortened and the production efficiency can be improved.

[0038] In the above-mentioned manufacturing method, the III-nitride semiconductor layer may contain Ga on the surface. In this case, when ultraviolet light is irradiated on the surface of the III-nitride semiconductor layer, oxygen atoms are bonded to Ga atoms to form GaO. x Therefore, oxidation of the surface of the Group III nitride semiconductor layer is promoted, and the sheet resistance value can be stabilized in a shorter time.

[0039] In the above-mentioned manufacturing method, after irradiating the surface of the group III nitride semiconductor layer with ultraviolet light having a central wavelength of not less than 320 nm and not more than 330 nm, the GaO intensity I obtained when the Ga3d peak of the surface obtained by X-ray photoelectron spectroscopy is fitted by a Gaussian function may be obtained. GaO GaN intensity I GaN The ratio (I GaO / I GaN ) is 0.15 or more. According to the experience of the inventors, when the substrate is taken out of the growth furnace and left to stand after the epitaxial growth of the III-nitride semiconductor layer on the substrate, the sheet resistance value stabilizes in about 48 hours. The above ratio (I GaO / I GaN) is about 0.15. According to the above-mentioned measuring method, the oxidation degree of the group III nitride semiconductor layer can be promoted to the same degree or more in a short time.

[0040] In the above manufacturing method, the sheet resistance value of the group III nitride semiconductor layer may be measured within 0.2 hours after the substrate is taken out of the growth furnace. Thus, according to the above measurement method, the sheet resistance value of the group III nitride semiconductor layer can be measured in a very short time after the substrate is taken out of the growth furnace, which can help improve production efficiency.

[0041] In the above-mentioned manufacturing method, the central wavelength of the ultraviolet light may be less than 441.6 nm. In this case, the strong energy of the ultraviolet light releases the bonds between various substances and the group III atoms earlier, and the oxidation of the surface of the group III nitride semiconductor layer can be more effectively promoted. In addition, the ultraviolet light may be, for example, a He-Cd laser. In this case, ultraviolet light UV can be irradiated in a range of a central wavelength of more than 190 nm and less than 441.6 nm.

[0042] In the above-mentioned manufacturing method, in the step of irradiating the surface with ultraviolet light, the irradiation energy density which is the product of the intensity of the ultraviolet light and the irradiation time may be 2.4 W·s / m 2 In this case, the oxidation of the surface of the Group III nitride semiconductor layer can be further promoted, and the sheet resistance value can be stabilized in a shorter time.

[0043] The above-mentioned manufacturing method may further include a step of forming an insulating film on the Ga surface of the group III nitride semiconductor layer. In this case, the Ga surface is stabilized and the sheet resistance can be stabilized as soon as possible.

[0044] An epitaxial substrate of one embodiment of the present disclosure includes a channel layer, a barrier layer, and a cap layer. The channel layer is provided on the main surface of the substrate. The barrier layer is provided on the channel layer, and the composition of the barrier layer is Al y Ga 1- y N(0<y<0.4). The cap layer is provided on the barrier layer. In the epitaxial substrate, the sheet resistance value of the III-nitride semiconductor layer composed of the channel layer, the barrier layer and the cap layer is 300 (Ω / sq.) or more and 800 (Ω / sq.) or less.

[0045] In the above-mentioned epitaxial substrate, the GaO intensity I at the surface of the group III nitride semiconductor layer, when the Ga3d peak of the surface obtained by X-ray photoelectron spectroscopy is fitted with a Gaussian function, may be GaO GaN intensity I GaNThe ratio (I GaO / I GaN ) is greater than 0.15.

[0046] [Details of the embodiments of the present disclosure]

[0047] Hereinafter, a specific example of the method for manufacturing an epitaxial substrate disclosed in the present invention will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited to these examples, but is shown by the claims, and is intended to include all changes within the meaning and scope equivalent to the claims. In the following description, the same elements are marked with the same reference numerals in the description of the drawings and repeated descriptions are omitted.

[0048] Figure 1 1 is a diagram showing the cross-sectional structure of an epitaxial substrate 10 including a group III nitride semiconductor layer 12 for measuring the sheet resistance value. The epitaxial substrate 10 is, for example, an epitaxial wafer used in the manufacture of a high electron mobility transistor (HEMT). As an example, the epitaxial substrate 10 includes: a substrate 11 having a flat primary surface 11a; and a group III nitride semiconductor layer 12 epitaxially grown on the primary surface 11a of the substrate 11. The material of the substrate 11 can be any material as long as the lattice constant is close to that of the group III nitride semiconductor, such as SiC. The primary surface 11a is a c-plane, but may also have some deviation angle. The group III nitride semiconductor layer 12 includes: a GaN channel layer 13 epitaxially grown on the primary surface 11a; an AlGaN barrier layer 14 epitaxially grown on the GaN channel layer 13; and a GaN cap layer 15 epitaxially grown on the AlGaN barrier layer 14. It should be noted that the GaN channel layer 13 also functions as a buffer layer for improving the crystallinity of the AlGaN barrier layer 14. In addition, an InGaN barrier layer may be provided instead of the AlGaN barrier layer 14. The thickness of the GaN channel layer 13 is, for example, greater than 200 nm and less than 1000 nm. The thickness of the AlGaN barrier layer 14 is, for example, greater than 10 nm and less than 30 nm. The thickness of the GaN cap layer 15 is, for example, greater than 1 nm and less than 10 nm.

[0049] Figure 2 1 is a flow chart showing the manufacturing method of this embodiment. First, as step S1, a group III nitride semiconductor layer 12 is epitaxially grown on a substrate 11. Specifically, Figure 3A As shown in FIG. 1 , the substrate 11 is placed in the growth furnace GR. Then, after controlling the temperature and pressure in the growth furnace GR, trimethyl gallium (TMG) gas and ammonia (NH 3 ) gas are supplied into the growth furnace GR. Figure 3BAs shown in FIG. 1 , a GaN channel layer 13 is epitaxially grown on a substrate 11. Next, after changing the temperature and pressure in the growth furnace GR, TMG gas, trimethylaluminum (TMA) gas, and NH3 gas are supplied into the growth furnace GR. Figure 3C As shown in FIG. 1 , an AlGaN barrier layer 14 is epitaxially grown on the substrate 11. It should be noted that, when an InGaN barrier layer is formed instead of the AlGaN barrier layer 14, it is better to supply trimethylindium (TMI) gas instead of TMA gas. Next, after changing the temperature and pressure in the growth furnace GR again, TMG gas and NH3 gas are supplied into the growth furnace GR. Thus, as shown in FIG. Figure 3D As shown, a GaN cap layer 15 is epitaxially grown on the substrate 11 . In this way, a group III nitride semiconductor layer 12 including a GaN channel layer 13 , an AlGaN barrier layer 14 and a GaN cap layer 15 is formed on the substrate 11 .

[0050] Next, as step S2, Figure 4A As shown, the substrate 11 on which the group III nitride semiconductor layer 12 is formed is taken out from the growth furnace GR. At this time, the surface 12a of the group III nitride semiconductor layer 12 is exposed to the oxygen-containing atmosphere.

[0051] Next, as step S3, Figure 4B As shown, while the surface 12a of the group III nitride semiconductor layer 12 is exposed to the atmosphere, the surface 12a is irradiated with ultraviolet light UV at room temperature and atmospheric pressure. It should be noted that, when the substrate 11 is thin enough to transmit the ultraviolet light UV, the surface 12a of the group III nitride semiconductor layer 12 may be irradiated with ultraviolet light UV from the back side of the substrate 11.

[0052] The ultraviolet light UV is, for example, a single wavelength laser, and the entire surface 12a is uniformly scanned (also referred to as swept) with a beam of ultraviolet light UV. The central wavelength of the ultraviolet light is, for example, greater than 200 nm, and may also be greater than 320 nm and less than 330 nm, and as an example, less than 325 nm. As a source of ultraviolet light UV, for example, a helium-cadmium (He-Cd) laser may be used. Figure 5 This is a diagram showing an example of the structure of a He-Cd laser. Figure 5In the He-Cd laser 50 shown, He and Cd are sealed in a gas tube 51, and an anode 55 and a cathode 56 are provided on the side wall of the gas tube 51 to be separated from each other. The inside of the gas tube 51 is heated to above 250°C, and He and Cd are vaporized and become atomic. In this state, a voltage from a power supply 57 is applied between the anode 55 and the cathode 56, thereby generating a discharge in the gas tube 51. At this time, the atomic Cd collides with He, becomes an excited state, and then returns to the ground state. At this time, light La is generated. The generated light La oscillates between a pair of reflectors 52 and 53 provided at both ends of the gas tube 51. A portion of the oscillated light is taken out from a laser transmission port 54 formed in one reflector 52 and output as laser Lb. It should be noted that the following is an example of the irradiation conditions of ultraviolet light UV, but it is not limited to this. For example, the irradiation energy density, which is the product of the intensity of the ultraviolet light and the irradiation time, can also be 2.4W·s / m 2 above.

[0053] Wavelength: 325nm

[0054] Output power: 2.7mW

[0055] Irradiation time: 90 seconds

[0056] Irradiation beam diameter: 1mm

[0057] Irradiation energy density: 2.4W·s / m 2

[0058] By irradiating the ultraviolet light UV, the sheet resistance value of the group III nitride semiconductor layer 12 is stabilized. Next, as step S4, Figure 4C As shown, the sheet resistance value of the III-nitride semiconductor layer 12 is measured by a non-contact measurement method (such as an eddy current method). For example, the sheet resistance value is measured within 0.2 hours after the substrate 11 is taken out of the growth furnace GR. Specifically, a probe P with a built-in electromagnet is brought close to the surface 12a of the III-nitride semiconductor layer 12 to generate an alternating magnetic field that penetrates the III-nitride semiconductor layer 12. As a result, eddy currents are generated inside the III-nitride semiconductor layer 12, generating a demagnetizing field. Due to the influence of the demagnetizing field, a current is generated in the coil inside the probe P, and the magnitude of the current is measured. Thus, the magnitude of the eddy current can be measured, and the sheet resistance value of the III-nitride semiconductor layer 12 can be calculated by a prescribed relationship. It should be noted that the method for measuring the sheet resistance value is not limited to this, and other methods can also be used.

[0059] The effects obtained by the manufacturing method of the present embodiment described above will be described. Figure 61 is a graph showing an example of a change in the sheet resistance value of the group III nitride semiconductor layer 12 over time when the substrate 11 is taken out of the growth furnace GR after the group III nitride semiconductor layer 12 is grown and left as it is. Figure 6 In FIG. 1 , the horizontal axis represents the elapsed time (unit: time), and the vertical axis represents the ratio of the sheet resistance value when the sheet resistance value immediately after being taken out of the growth furnace GR is set as 100% (unit: %). Figure 6 As shown in FIG. 1 , after the substrate 11 is taken out of the growth furnace GR, the sheet resistance value of the group III nitride semiconductor layer 12 gradually decreases with the passage of time. Then, after about 48 hours, the sheet resistance value stabilizes. Such a change in the sheet resistance value is related to the degree of oxidation of the surface 12a of the group III nitride semiconductor layer 12.

[0060] Here, the reason why the sheet resistance value changes depending on the degree of oxidation of the surface 12 a of the group III nitride semiconductor layer 12 will be described. Fig. 7A This is a schematic diagram (band diagram) of the potential of the group III nitride semiconductor layer 12 obtained by simulation. Fig. 7A In the embodiment, range B1 corresponds to the GaN channel layer 13, range B2 corresponds to the AlGaN barrier layer 14, range B3 corresponds to the GaN cap layer 15, and range B4 corresponds to the surface oxide layer (GaO x ) corresponds. In addition, graph G11 represents the potential of the surface 12a before oxidation, and graph G12 represents the potential of the surface 12a after sufficient oxidation. Figure 7B yes Fig. 7A A partial enlarged view of part A.

[0061] like Fig. 7A As shown in the graph G12, compared with the surface 12a before oxidation (just after the formation of the group III nitride semiconductor layer 12, graph G11), the more the oxidation of the surface 12a progresses (the thickness of the surface oxide film increases), the lower the conduction band potential of the group III nitride semiconductor layer 12 as a whole. Figure 7B As shown in FIG. 1 , the valley of the conduction band potential at the boundary between the AlGaN barrier layer 14 and the GaN channel layer 13 becomes deeper. As a result, the carrier density of the two-dimensional electron gas generated near the interface between the GaN channel layer 13 and the AlGaN barrier layer 14 increases, and the sheet resistance value decreases. For this reason, the more the oxidation of the surface 12a progresses, the lower the sheet resistance value.

[0062] In addition, it can be considered that the oxidation of the surface 12a takes time based on the following reasons. When the substrate 11 is taken out of the growth furnace GR after the formation of the III-nitride semiconductor layer 12, the surface 12a is exposed to the atmospheric atmosphere, and various substances contained in the atmosphere (such as hydrocarbons, halogens, sulfur oxides, nitrogen carbonides, etc.) are physically adsorbed on the surface 12a. At this time, these substances bond with the III-group atoms (Ga) on the surface 12a, hindering the bonding between the III-group atoms (Ga) and the oxygen atoms. It should be noted that Fig. 8A and Figure 8B is the result obtained by analyzing / counting the negative ions present on the surface 12a. Figure 8C It is the result obtained by analyzing / counting the positive ions present on the surface 12a. FIG. 8A to FIG. 8C In the graph, the vertical axis represents the number of ions, and the horizontal axis represents the atomic weight or molecular weight. It can be considered that the bonding between these substances and group III atoms is mainly based on intermolecular forces, which is less stable than the covalent bonding between group III atoms and oxygen, so these substances are gradually replaced by oxygen atoms. Due to such a process, the oxidation of the surface 12a takes a long time.

[0063] In the conventional measurement method, after the substrate 11 is taken out of the growth furnace GR, the substrate 11 is placed in the atmosphere as it is, and the above-mentioned substances are replaced by oxygen atoms, and the sheet resistance value is measured after the surface 12a is fully oxidized. However, in this method, since a long time (for example, about 48 hours) is required before the surface 12a is fully oxidized, the production lead time is prolonged and the production efficiency is reduced. In addition, the sheet resistance value needs to be measured multiple times before the sheet resistance value stabilizes, which will increase the manufacturing man-hours.

[0064] With regard to this problem, in the present embodiment, after the substrate 11 on which the group III nitride semiconductor layer 12 is formed is taken out of the growth furnace GR, the surface 12a of the group III nitride semiconductor layer 12 is exposed to the atmosphere while being irradiated with ultraviolet light UV. According to the findings of the present inventors, when the surface 12a of the group III nitride semiconductor layer 12 is exposed to the atmosphere while being irradiated with ultraviolet light UV, the oxidation of the surface 12a is significantly promoted compared to the case where the surface 12a is left exposed to the atmosphere.

[0065] 9A to 9D This is a diagram for explaining the reason why oxidation of the surface 12 a is accelerated by irradiation with ultraviolet light UV. Fig. 9A This shows the state immediately after the formation of the Group III nitride semiconductor layer 12. Fig. 9A1 and 12 show the GaN cap layer 15 as the uppermost layer of the Group III nitride semiconductor layer 12 and the surface of the GaN cap layer 15 (i.e., the surface 12a of the Group III nitride semiconductor layer 12). Fig. 9B As shown, various substances 61 such as hydrocarbons, halogens, sulfur oxides, and carbonized nitrogen are bonded to the Group III atoms (Ga atoms in this example) 60 on the surface 12a, thereby hindering the bonding between the Group III atoms 60 and the oxygen atoms 62. Fig. 9C As shown in FIG. 1 , when ultraviolet light UV is irradiated to the surface 12a, the surface 12a generates heat. The bonding between each substance 61 and the group III atom 60 is released by the heat. Alternatively, each substance 61 is oxidized and becomes a low-density substance. Due to these effects, each substance 61 is separated from the group III nitride semiconductor layer 12. Then, the oxygen atoms 62 in the atmosphere immediately bond with the group III atom 60 on the surface 12a, thereby oxidizing the group III atom 60 ( Fig.9D ). In this way, the oxidation of the surface 12a is promoted, and the thin film resistance value can be stabilized in a shorter time. Therefore, according to this embodiment, the production lead time can be shortened and the production efficiency can be improved. It should be noted that, thereafter, the fluctuation of the stabilized thin film resistance value can be suppressed by growing an insulating film on the surface of Ga. The insulating film can be grown by CVD (Chemical Vapor Deposition). For example, the insulating film can be any of a silicon nitride film, a silicon oxide film, and a silicon oxynitride film formed by a growth method of P-CVD (Plasma CVD), ALD-CVD (Atomic Layer Deposition CVD), thermal CVD (Thermal CVD), or LP-CVD (Low Pressure CVD).

[0066] Fig.10 This is a graph showing the ratio of the sheet resistance value based on the sheet resistance value 48 hours after the substrate 11 on which the group III nitride semiconductor layer 12 is formed is taken out of the growth furnace GR (100%). Fig.10 Graph G21 shows the sheet resistance value just after being taken out of the growth furnace GR and before being irradiated with ultraviolet light UV. Graph G22 shows the sheet resistance value after being irradiated with ultraviolet light UV. It should be noted that the irradiation conditions are wavelength: 325nm, output power: 2.7mW, irradiation time: 90 seconds, irradiation beam diameter: 1mm, irradiation energy density: 2.4W·s / m 2 . Reference Fig.10, the sheet resistance value just after being taken out of the growth furnace GR and before being irradiated with ultraviolet light UV exceeded 104%. In contrast, it can be seen that the sheet resistance value after irradiation with ultraviolet light UV becomes extremely close to 100%, and there is almost no change in the sheet resistance value after 48 hours (that is, the state after oxidation has fully progressed). Based on the experimental results, the above-mentioned effect is confirmed. It should be noted that it can be considered that: when irradiated with ultraviolet light UV with a higher energy center wavelength of less than 325nm, the same or higher effect can be obtained. In addition, it can be considered that: even if it is below 441.6nm, which is the wavelength of He-Cd laser, the same effect can be obtained.

[0067] After the above experiment, the sample of the III-nitride semiconductor layer 12 whose sheet resistance value had stabilized (after 48 hours) was analyzed by X-ray photoelectron spectroscopy (XPS), and the Ga3d peak obtained was fitted with a Gaussian function. As a result, the GaO intensity I GaO GaN intensity I GaN The ratio (I GaO / I GaN ) is 0.15. Therefore, in order to stabilize the sheet resistance value, it is ideal that the surface oxide layer (GaO x ) GaO / I GaN ) is 0.15 or more. According to the measurement method of this embodiment, the degree of oxidation of the group III nitride semiconductor layer 12 (I GaO / I GaN ) was promoted to the same extent (0.15) or above.

[0068] As described above, the Group III nitride semiconductor layer 12 may contain Ga on the surface 12a. In this case, when the surface 12a is irradiated with ultraviolet light UV, oxygen atoms are bonded to Ga atoms to form GaO. x Therefore, the oxidation of the surface 12a is promoted, and the sheet resistance value can be stabilized in a shorter time.

[0069] As described above, the sheet resistance value of the group III nitride semiconductor layer 12 may be measured within 0.2 hours after the substrate 11 is taken out of the growth furnace GR. According to this embodiment, the sheet resistance value can be measured in such a short time after the substrate 11 is taken out of the growth furnace GR, which can contribute to the improvement of production efficiency.

[0070] As described above, the central wavelength of the ultraviolet light UV may be less than 325 nm. In this case, the bonds between the various substances 61 and the group III atoms 60 are released earlier by the strong energy of the ultraviolet light UV, and the oxidation of the surface 12a of the group III nitride semiconductor layer 12 can be more effectively promoted. In addition, the ultraviolet light may be, for example, a He-Cd laser. In this case, the ultraviolet light UV can be irradiated in a range of a central wavelength of more than 190 nm and less than 441.6 nm. In this way, it can be considered that, as far as the ultraviolet light UV is concerned, even if it is less than 441.6 nm, which is the wavelength of the He-Cd laser, the same effect can be obtained.

[0071] Alternatively, the sheet resistance value of the group III nitride semiconductor layer 12 after the sheet resistance value is stabilized may be, for example, 300 (Ω / sq.) or more and 800 (Ω / sq.) or less.

[0072] The method for manufacturing an epitaxial substrate disclosed in the present invention is not limited to the above-mentioned embodiment, and various modifications can be made. For example, in the above-mentioned embodiment, the method disclosed in the present invention is applied to a substrate product used in the manufacture of a GaN-based HEMT, but the method disclosed in the present invention is not limited thereto, and can also be applied to substrate products having a group III nitride semiconductor layer for various purposes and structures. In addition, in the above-mentioned embodiment, the group III nitride semiconductor layer is exposed to the atmospheric atmosphere when irradiating ultraviolet light, but it can also be exposed to other atmospheres as long as it is an atmosphere containing oxygen. In addition, in the above-mentioned embodiment, the group III nitride semiconductor layer whose surface is GaN is irradiated with ultraviolet light, but the surface of the group III nitride semiconductor layer can also be composed of other group III nitride semiconductors such as AlGaN and InGaN.

[0073] Description of Reference Numerals

[0074] 10: Epitaxial substrate

[0075] 11: Substrate

[0076] 11a: Main side

[0077] 12: Group III nitride semiconductor layer

[0078] 12a: Surface

[0079] 13: GaN channel layer

[0080] 14: AlGaN barrier layer

[0081] 15: GaN cap layer

[0082] 50: He-Cd laser

[0083] 51: Gas pipe

[0084] 52, 53: Reflector

[0085] 54: Laser transmission port

[0086] 55: Anode

[0087] 56: Cathode

[0088] 57: Power supply

[0089] 60: Group III atoms

[0090] 61: Matter

[0091] 62: Oxygen atom

[0092] B1, B2, B3, B4: Range

[0093] GR: Growth furnace

[0094] La: light

[0095] Lb: Laser

[0096] P: Probe

[0097] UV: ultraviolet light.

Claims

1. A method for manufacturing an epitaxial substrate, comprising: A step of epitaxially growing a group III nitride semiconductor layer on a substrate; The step of taking the substrate out of the growth furnace; a step of irradiating the surface of the group III nitride semiconductor layer with ultraviolet light while exposing the surface to an atmosphere containing oxygen; and a step of measuring the sheet resistance value of the group III nitride semiconductor layer, in, The group III nitride semiconductor layer contains Ga on the surface, and wherein, after irradiating the surface of the group III nitride semiconductor layer with ultraviolet light having a central wavelength of not less than 320 nm and not more than 330 nm, the GaO intensity I when the Ga3d peak of the surface obtained by X-ray photoelectron spectroscopy is fitted by a Gaussian function is obtained. GaO GaN intensity I GaN Ratio I GaO / I GaN It is above 0.

15.

2. A method for manufacturing an epitaxial substrate, comprising: A step of epitaxially growing a group III nitride semiconductor layer on a substrate; The step of taking the substrate out of the growth furnace; a step of irradiating the surface of the group III nitride semiconductor layer with ultraviolet light while exposing the surface to an atmosphere containing oxygen; and a step of measuring the sheet resistance value of the group III nitride semiconductor layer, in, The group III nitride semiconductor layer contains Ga on the surface, and wherein, after irradiating the surface of the group III nitride semiconductor layer with ultraviolet light having a central wavelength of not less than 320 nm and not more than 441.6 nm, the GaO intensity I when the Ga3d peak of the surface obtained by X-ray photoelectron spectroscopy is fitted by a Gaussian function is GaO GaN intensity I GaN Ratio I GaO / I GaN It is above 0.

15.

3. The method for manufacturing an epitaxial substrate according to claim 1 or 2, wherein: The sheet resistance value of the Group III nitride semiconductor layer is measured within 0.2 hours after the substrate is taken out of the growth furnace.

4. The method for manufacturing an epitaxial substrate according to claim 1 or 2, wherein: The ultraviolet light is He-Cd laser.

5. The method for manufacturing an epitaxial substrate according to claim 1 or 2, wherein: In the step of irradiating the surface with the ultraviolet light, the irradiation energy density, which is the product of the intensity of the ultraviolet light and the irradiation time, is 2.4 W·s / m 2 above.

6. The method for manufacturing an epitaxial substrate according to claim 1 or 2, The method further comprises forming an insulating film on a Ga surface of the group III nitride semiconductor layer.

7. An epitaxial substrate comprising: A channel layer is provided on the main surface of the substrate; A barrier layer is provided on the channel layer, wherein the barrier layer is composed of Al y Ga 1-y N, where 0＜y＜0.4； as well as a cap layer, disposed on the barrier layer, The sheet resistance value of the group III nitride semiconductor layer composed of the channel layer, the barrier layer, and the cap layer is 300 (Ω / sq.) or more and 800 (Ω / sq.) or less, The GaO intensity I at the surface of the Group III nitride semiconductor layer is obtained by fitting the Ga3d peak of the surface obtained by X-ray photoelectron spectroscopy using a Gaussian function. GaO GaN intensity I GaN Ratio I GaO / I GaN It is above 0.15.

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