Method for manufacturing a gallium nitride multilayer substrate, gallium nitride multilayer substrate, and gallium nitride single crystal substrate

Abstract

This technology provides a way to suppress the degradation of current conduction in GaN devices having a pn junction, such as pn diodes. [Solution] A method for manufacturing a gallium nitride laminated substrate for fabricating a device having a pn junction comprises the steps of: preparing an n-type gallium nitride single crystal substrate with a diameter of 50 mm or more, in which the lowest index crystal plane closest to the main plane is the (0001) plane; growing an n-type gallium nitride single crystal layer on the substrate; subjecting the laminated substrate on which the n-type gallium nitride single crystal layer has been grown to a hydrogen desorption treatment; growing a p-type gallium nitride single crystal layer on the laminated substrate that has been subjected to the hydrogen desorption treatment; and further subjecting the laminated substrate on which the p-type gallium nitride single crystal layer has been grown to a hydrogen desorption treatment.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a gallium nitride multilayer substrate, a gallium nitride multilayer substrate, and a gallium nitride single crystal substrate. [Background technology]

[0002] p-type gallium nitride (GaN) is generally produced by growing magnesium (Mg)-doped GaN crystals and then subjecting them to a dehydrogenation treatment. Mg-doped GaN crystals readily incorporate hydrogen (protons), and since these hydrogens bind to Mg and deactivate its function as an acceptor, a dehydrogenation treatment is necessary (see, for example, Patent Document 1).

[0003] GaN-based pn diodes used as power devices have a problem in that their diode characteristics deteriorate when a large current is passed through them during forward bias testing. Furthermore, slight deterioration of diode characteristics is also observed when reverse bias testing is performed (see, for example, Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-183189 [Non-Patent Document 1] T. Narita et al., Scientific Reports 12, 1458 (2022) [Overview of the project] [Problems that the invention aims to solve]

[0005] One objective of the present invention is to provide a technology for suppressing the degradation of current conduction in GaN devices having a pn junction, such as pn diodes. [Means for solving the problem]

[0006] According to one aspect of the present invention, A step to prepare an n-type gallium nitride single crystal substrate with a diameter of 50 mm or more, in which the lowest index crystal plane closest to the main plane is the (0001) plane, The process involves growing an n-type gallium nitride single crystal layer on the aforementioned substrate, The process involves subjecting the laminated substrate, on which the n-type gallium nitride single crystal layer has been grown, to a hydrogen dehydrogenation treatment. The process involves growing a p-type gallium nitride single crystal layer on a laminated substrate that has undergone the hydrogen removal treatment, The process involves further subjecting the laminated substrate, on which the p-type gallium nitride single crystal layer has been grown, to a hydrogen removal treatment. A method for manufacturing a gallium nitride multilayer substrate for fabricating a device having a pn junction. It will be provided.

[0007] According to another aspect of the present invention, The structure has an n-type gallium nitride single crystal substrate with a diameter of 50 mm or more, where the lowest index crystal plane closest to the main plane is the (0001) plane, and at least an n-type gallium nitride single crystal layer and a p-type gallium nitride single crystal layer are stacked in this order. At a minimum, the hydrogen concentration in the region within a thickness of 50 μm from the main surface of the n-type gallium nitride single crystal substrate and in the n-type gallium nitride single crystal layer is 5 × 10 16 cm -3 Less than, Gallium nitride laminated substrate for fabricating devices with pn junctions It will be provided.

[0008] According to yet another aspect of the present invention, An n-type gallium nitride single crystal substrate having a diameter of 50 mm or more, a thickness of 300 μm or more, and in which the lowest index crystal plane closest to the main plane is the (0001) plane, The hydrogen concentration in the gallium nitride single crystal has a gradient distribution that gradually increases from the main surface toward the thickness direction of the substrate. The hydrogen concentration in the region with a thickness of 50 μm or less from the main surface is 5 × 10 16 cm -3 Less than, Gallium nitride single crystal substrate It will be provided. [Effects of the Invention]

[0009] A technology is provided to suppress the electrical degradation of GaN devices having a pn junction. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view showing a laminated substrate 100 according to an embodiment of the present invention. [Figure 2] Figure 2 is a timing chart showing a first example of a method for manufacturing a laminated substrate 100 according to an embodiment. [Figure 3] Figure 3 is a timing chart showing a second example of a method for manufacturing the laminated substrate 100 according to the embodiment. [Figure 4] Figure 4 is a timing chart showing a third example of the method for manufacturing the laminated substrate 100 according to the embodiment. [Figure 5] Figure 5 is a graph illustrating an example of how the characteristics of a GaN-based pn diode with degraded characteristics can be restored by performing a hydrogen desorption treatment again. [Modes for carrying out the invention]

[0011] Before describing embodiments of the present invention, we will first explain the findings obtained by the present inventors. As mentioned above, in gallium nitride (GaN) pn diodes (hereinafter also simply referred to as diodes), the diode characteristics deteriorate due to forward current flow, etc. As a result of diligent research, the present inventors have found that if a diode with deteriorated characteristics is subjected to hydrogen desorption treatment again, the deteriorated characteristics are restored.

[0012] Figure 5 is a graph of experimental results illustrating an example of the phenomenon. The experiment was conducted as follows: A silicon (Si) concentration of 2 × 10⁻¹⁶ was applied to an n-type GaN single crystal substrate. 18 cm -3 A 2 μm thick n-type GaN single crystal layer and a Si concentration of 2 × 10 16 cm-3 an n-type GaN single crystal layer with a thickness of 9 μm and a magnesium (Mg) concentration of 1×10 18 cm -3 and a p-type GaN single crystal layer with a thickness of 500 nm were laminated in this order to produce a laminated substrate. After performing a hydrogen removal treatment on the laminated substrate, a p-side electrode was formed on the upper side of the p-type GaN single crystal layer, an n-side electrode was formed on the lower side of the n-type GaN single crystal substrate, and an insulating film was appropriately formed, thereby producing a diode.

[0013] After conducting an energization test of 1A for 1 hour on the diode, the p-side electrode, n-side electrode and insulating film were removed, and the laminated substrate from which the electrodes and other components had been removed was subjected to heat treatment at 850° C. for 30 minutes in a nitrogen gas atmosphere (that is, a second hydrogen removal treatment). Electrodes and other components were re-formed on the laminated substrate that had been subjected to the second hydrogen removal treatment, thereby re-fabricating the diode.

[0014] Electrical characteristic evaluation was performed on the diode three times: before the energization test, after the energization test, and after re-fabrication (after the second hydrogen removal treatment). The energization test was performed under the condition that a current of 1A was passed through a device with an electrode diameter of Φ400μm for 1 hour. As electrical characteristic evaluation, forward I-V measurement and reverse I-V measurement were performed. FIG. 5 shows the results of the reverse I-V measurement obtained in these three measurements. The solid line shows the result before the energization test, the broken line shows the result after the energization test, and the one-dot chain line shows the result after re-fabrication.

[0015] In the measurement before the energization test, the current density of the reverse leakage current from an applied voltage of 0V to about -900V is 10 -6 A / cm 2 and is suppressed below this level, and breakdown occurs at about -900V. In contrast, in the measurement after the energization test, a significant increase in reverse leakage current is observed. The current density of the reverse leakage current reaches 10 -6 A / cm 2 at an applied voltage of about -300V, and reaches 10 -4 A / cm 2 and exceeds this value at about -800V. That is, degradation of diode characteristics occurs due to forward energization. It has also been found that slight degradation of diode characteristics can also be observed in reverse bias tests.

[0016] However, in measurements taken after remanufacturing, that is, on diodes that had undergone hydrogen dehydrogenation treatment again after degradation, the current density of the reverse leakage current was 10 from the applied voltage of 0V to approximately -900V, just as before the energization test. -6 A / cm 2 The voltage was kept below the specified level, with breakdown occurring at around -900V. Thus, it was found that the diode characteristics could be restored by performing the hydrogen dehydrogenation treatment again.

[0017] Based on this phenomenon, the inventors of the present invention investigated the mechanism of current-conducting degradation of diodes and found that the cause is hydrogen diffusion from the n-type GaN single crystal layer, which is the underlayment for the p-type GaN single crystal layer. Specifically, they found that as the device temperature rises during current flow, hydrogen in the n-type GaN single crystal layer or the n-type GaN single crystal substrate penetrates into the p-type GaN single crystal through anomalous diffusion via dislocation cores, and deactivates the p-type layer by bonding with Mg.

[0018] Almost all of the GaN single crystal substrates on the market are grown using the HVPE method. Furthermore, the MOCVD method is generally used to grow n-type GaN single crystal layers on these substrates. In these growth methods, ammonia is used as the nitrogen source, and (conventional) n-type GaN crystals contain 5 × 10⁻¹⁶ hydrogen atoms derived from ammonia, though not to the same extent as in p-type GaN crystals. 16 cm -3 The above is included.

[0019] In pn junctions, such as those used in currently widespread light-emitting devices, hydrogen in the substrate or n-type GaN layer did not degrade the device characteristics. However, the inventors of this invention have discovered for the first time that hydrogen in the substrate or n-type GaN layer degrades the device characteristics in devices that use high voltage and carry large currents, such as GaN power devices.

[0020] Based on these findings, the following describes an embodiment of the present invention: a technique for suppressing hydrogen diffusion into the p-type GaN single crystal layer by reducing the hydrogen concentration on the n-type GaN single crystal layer that serves as the underlay for the p-type GaN single crystal layer.

[0021] A GaN multilayer substrate 100 (hereinafter also simply referred to as "multilayer substrate 100") according to an embodiment of the present invention will be described. Figure 1 is a schematic cross-sectional view showing the multilayer substrate 100. The multilayer substrate 100 has a structure in which at least an n-type GaN single crystal layer 20 (hereinafter also simply referred to as "n-type layer 20") and a p-type GaN single crystal layer 30 (hereinafter also simply referred to as "p-type layer 30") are stacked in this order on an n-type GaN single crystal substrate 10 (hereinafter also simply referred to as "substrate 10"), and is used as a material for manufacturing a device having a pn junction, preferably a power device.

[0022] The substrate 10 is composed of a GaN single crystal doped with Si or germanium (Ge) as an n-type impurity, has a diameter of 50 mm or more and a thickness of 300 μm or more, and has a main surface 11 that serves as the base for the growth of the n-type layer 20. The lowest index crystal plane closest to the main surface 11 is the (0001) plane. The n-type impurity concentration (total concentration of Si and Ge) in the substrate 10 is, for example, 1 × 10⁻⁶ 18 cm -3 The above 3 x 10 19 cm -3 The following applies:

[0023] The n-type layer 20 is composed of a GaN single crystal doped with Si or Ge as an n-type impurity, epitaxially grown on the substrate 10 (on the main surface 11). By stacking the n-type layer 20 on the substrate 10, a GaN laminated substrate 50 (which is an intermediate structure of the laminated substrate 100) is formed. The thickness of the n-type layer 20 is, for example, 4 μm or more and 30 μm or less. The n-type layer 20 may be composed of a stack of multiple layers with different n-type impurity concentrations. Specifically, as in the experiment described above, a layer with a relatively high Si concentration (e.g., 2 × 10⁻⁶) may be used. 18 cm -3 The lower layer (the layer on the substrate 10 side) and the layer with a relatively low Si concentration (for example, 2 × 10 16 cm -3An example is shown of an n-type layer 20 formed by stacking the upper layer (the layer on the p-type layer 30 side) and the other layers.

[0024] The n-type layer 20 has at least a layer with a relatively low concentration of n-type impurities, located directly beneath the p-type layer 30, in order to increase the breakdown voltage of the pn junction. The n-type impurity concentration (total concentration of Si and Ge) in the layer with a relatively low concentration of n-type impurities in the n-type layer 20 is, for example, 4 × 10⁻⁶ 15 cm -3 The above 2 x 10 16 cm -3 The following applies:

[0025] The p-type layer 30 is a layer that forms a pn junction at the interface with the n-type layer 20, and is composed of a GaN single crystal doped with Mg as a p-type impurity, which is epitaxially grown on the n-type layer 20. The thickness of the p-type layer 30 is, for example, 0.2 μm to 1.5 μm. The concentration of p-type impurities (concentration of Mg) in the p-type layer 30 is, for example, 1 × 10⁻⁶ 17 cm -3 The above 1 x 10 20 cm -3 It is less than 1 × 10⁻¹⁰. From the viewpoint of improving the crystal quality of the p-type layer 30 and forming a good pn junction, the p-type impurity concentration (Mg concentration) in the p-type layer 30 is 1 × 10⁻¹⁰. 20 cm -3 It is preferable that it be less than [a certain value].

[0026] Furthermore, on the p-type layer 30 (for forming a pn junction with the n-type layer 20), a contact layer of Mg is provided between the p-type layer 30 and the p-side electrode, with a density of 1 × 10⁻¹⁴. 20 cm -3 Layers doped at the above high concentrations (p + A mold layer may be formed.

[0027] The substrate 10 is grown, for example, by the HVPE method. The n-type layer 20 and the p-type layer 30 are grown, for example, by the MOCVD method. As mentioned above, ammonia is used as the nitrogen raw material in these growth methods, so in conventional technology, 5 × 10 hydrogen atoms derived from ammonia are added to the substrate 10 and the n-type layer 20. 16 cm -3The above is included. Furthermore, the p-type layer 30 is more likely to incorporate hydrogen due to the Mg doping, so (even after dehydrogenation) 1 × 10 17 cm -3 It has a hydrogen concentration above a certain level.

[0028] In contrast, in the laminated substrate 100 according to this embodiment, the hydrogen concentration of the n-type layer 20 is 5 × 10 16 cm -3 It is reduced to less than 5 × 10. Furthermore, preferably, the hydrogen concentration in (at least) the surface layer 12 of the substrate 10 (in a region with a thickness of 50 μm or less from the main surface 11) is 5 × 10 16 cm -3 It has been reduced to less than 1 × 10⁻¹⁰. The hydrogen concentration in the n-type layer 20 and the hydrogen concentration in the surface layer 12 of the substrate 10 are, respectively, 1 × 10⁻¹⁰. 16 cm -3 The following is preferable: 7 × 10 15 cm -3 The following is even more preferable. A method for reducing the hydrogen concentration in the n-type layer 20 and the substrate 10 will be described later.

[0029] Since the self-supporting substrate 10 is thick, the hydrogen concentration is 5 × 10⁻¹⁰ 16 cm -3 It does not need to be reduced to less than 5 × 10. In other words, the hydrogen concentration in the lower layer 13 below the surface layer 12 (opposite to the n-type layer 20) is 5 × 10 16 cm -3 The above configuration is also acceptable. In this configuration, the hydrogen concentration in the GaN single crystal constituting the substrate 10 has a gradient distribution that gradually increases from the main surface 11 toward the thickness direction of the substrate 10.

[0030] The hydrogen concentration is measured by secondary ion mass spectrometry (SIMS). The hydrogen concentration in n-type layer 20 is 5 × 10⁻⁶. 16 cm -3 "Reduced to less than" means that the average hydrogen concentration in the thickness direction across the entire thickness of the n-type layer 20 is 5 × 10⁻⁶. 16 cm -3This means that it is less than 5 × 10. Also, the hydrogen concentration in the surface layer 12 of the substrate 10 (within a thickness of 50 μm from the main surface 11) is 5 × 10 16 cm -3 "Reduced to less than" means that the average hydrogen concentration in the thickness direction of the surface layer 12 of the substrate 10 (within a thickness of 50 μm from the main surface 11) is 5 × 10⁻¹⁰. 16 cm -3 This means less than 1. 16 cm -3 Below, 7 x 10 15 cm -3 The same regulations apply to the following hydrogen concentrations. Note that the approximate detection limit for hydrogen using SIMS (when using the raster change method) is 7 × 10⁻⁶. 15 cm -3 That is the case.

[0031] In the laminated substrate 100 according to this embodiment, the hydrogen concentration of the n-type layer 20 located directly beneath the p-type layer 30 is 5 × 10 16 cm -3 Less than (preferably 1 × 10) 16 cm -3 More preferably 7 × 10 15 cm -3 By reducing the hydrogen concentration to the following levels, hydrogen diffusion into the p-type layer 30 is suppressed. This makes it possible to suppress degradation of GaN devices having pn junctions, fabricated using the laminated substrate 100, due to current flow, etc. Furthermore, preferably, the hydrogen concentration in the surface layer 12 of the substrate 10 placed below the n-type layer 20 is also reduced to 5 × 10⁻⁶. 16 cm -3 Less than (preferably 1 × 10) 16 cm -3 More preferably 7 × 10 15 cm -3 By reducing the levels as described below, hydrogen diffusion into the p-type layer 30 is further suppressed, and degradation of the GaN device can be further suppressed.

[0032] Thus, according to this embodiment, a laminated substrate 100 composed of a substrate 10, an n-type layer 20, and a p-type layer 30, a laminated substrate 50 composed of a substrate 10 and an n-type layer 20, or a substrate 10, is provided, which is suitable for suppressing hydrogen diffusion into the p-type layer 30.

[0033] Next, a method for manufacturing a laminated substrate 100 according to an embodiment of the present invention (a method for reducing the hydrogen concentration of the n-type layer 20 and the substrate 10) will be described. The laminated substrate 100 is formed by growing an n-type layer 20 and a p-type layer 30 on the substrate 10. For example, MOCVD is used as the growth method for the n-type layer 20 and the p-type layer 30.

[0034] For example, trimethylgallium (TMG) is used as the Ga raw material. For example, a nitrogen hydrogen compound, such as ammonia (NH3), is used as the N raw material. For example, silane (SiH4) or germane (GeH4) is used as the n-type impurity raw material. For example, biscyclopentadienylmagnesium (Cp2Mg) is used as the p-type impurity raw material. For example, nitrogen (N2) gas is used as the carrier gas. The GaN growth temperature can be selected, for example, in the range of 900°C to 1400°C, and the V / III ratio, which is the flow rate ratio of N raw material gas to Ga raw material gas, can be selected, for example, in the range of 10 to 5000.

[0035] In the manufacturing method of the laminated substrate 100 of this embodiment, in addition to the growth treatment of the n-type layer 20 and the p-type layer 30, a hydrogen removal treatment is performed on the n-type layer 20 and the like, as described below. Figures 2, 3, and 4 are timing charts showing the first example, the second example, and the third example of the manufacturing method of the laminated substrate 100 according to the embodiment, respectively.

[0036] Referring to Figure 2, the manufacturing method of the first example will be described. A substrate 10 is prepared, and Ga raw material and N raw material are supplied on the substrate 10, along with n-type impurity raw material, to grow an n-type layer 20 (forming a laminated substrate 50). The growth temperature is, for example, 1100°C. The growth time is set appropriately according to the desired thickness of the n-type layer 20. Hydrogen contained in ammonia, which is the N raw material, is mixed into the grown n-type layer 20. If the n-type layer 20 is composed of multiple layers with different n-type impurity concentrations, the amount of n-type impurity raw material supplied may be adjusted according to the n-type impurity concentration of each layer.

[0037] Next, a hydrogen removal treatment is performed on the n-type layer 20 (on the laminated substrate 50). The hydrogen removal treatment for the n-type layer 20 is performed by heating the laminated substrate 50 to 500°C or higher (900°C or lower) in an atmosphere containing no hydrogen and holding the temperature for 30 minutes or longer. In this example, after the growth treatment of the n-type layer 20, the supply of ammonia, which serves as a hydrogen source (and an N source), is stopped (while the supply of the Ga raw material and the n-type impurity raw material is stopped), and the heat treatment is performed in an atmosphere of nitrogen that serves as a carrier gas, thereby performing the hydrogen removal treatment.

[0038] The temperature of the hydrogen removal treatment for the n-type layer 20 is, for example, 600°C. Since the temperature of the hydrogen removal treatment is lower than the temperature of the growth treatment for the n-type layer 20, the heat treatment is performed by lowering the treatment temperature from the temperature of the growth treatment to the temperature of the hydrogen removal treatment. The specific temperature and time of the hydrogen removal treatment for the n-type layer 20 are such that the hydrogen concentration of the n-type layer 20 becomes 5×10 16 cm -3 or less (preferably 1×10 16 cm -3 or less, more preferably 7×10 15 cm -3 or less), and may be appropriately set experimentally.

[0039] Next, a p-type layer 30 is grown (to form a laminated substrate 100) by supplying a Ga raw material and an N raw material, and also supplying a p-type impurity raw material onto the laminated substrate 50 that has been subjected to the hydrogen removal treatment for the n-type layer 20. The growth temperature is, for example, 1100°C. The growth time is appropriately set according to the thickness of the p-type layer 30 to be formed. Hydrogen contained in ammonia, which is the N raw material, is mixed into the grown p-type layer 30. Note that when forming a p + -type layer on the p-type layer 30, after growing the p-type layer 30, according to the p-type impurity concentration of the p + -type layer, the supply amount of the Ga raw material is decreased, or the supply amount of the p-type impurity raw material is increased, and the p + -type layer may be grown subsequently.

[0040] Next, the p-type layer 30 (the laminated substrate 100) is subjected to a hydrogen dehydrogenation treatment (activation treatment). The hydrogen dehydrogenation treatment of the p-type layer 30 is performed by heating the laminated substrate 100 to 500°C or higher (900°C or lower) in a hydrogen-free atmosphere and holding it for 30 minutes or more. In this example, after the growth treatment of the p-type layer 30, the supply of ammonia (N raw material), which serves as a hydrogen source, is stopped (along with the supply of Ga raw material and p-type impurity raw material), and the heat treatment is performed in an atmosphere of nitrogen, which is the carrier gas, to perform the hydrogen dehydrogenation treatment.

[0041] The temperature for the dehydrogenation treatment of the p-type layer 30 is, for example, 850°C. Since the dehydrogenation treatment temperature is lower than the growth treatment temperature of the p-type layer 30, the heat treatment is performed by lowering the treatment temperature from the growth treatment temperature to the dehydrogenation treatment temperature. The specific temperature and time for the dehydrogenation treatment of the p-type layer 30 may be experimentally set as appropriate to activate the p-type layer 30.

[0042] In Figure 2, an example is shown in which the p-type layer 30 is dehydrogenated in a nitrogen atmosphere (in the processing chamber of the crystal growth apparatus) after the growth of the p-type layer 30. However, the laminated substrate 100 may be removed from the crystal growth apparatus after the growth of the p-type layer 30 and dehydrogenated using another apparatus.

[0043] In this example, it is preferable that the growth treatment of the n-type layer 20 and the growth treatment of the p-type layer 30 be carried out continuously in the same processing chamber (without exposure to the atmosphere in between). This is to prevent contamination of the pn junction interface. On the other hand, this example is characterized in that after growing the n-type layer 20, the crystal growth treatment is temporarily interrupted, the n-type layer 20 is subjected to a hydrogen dehydrogenation treatment, and then the growth treatment of the p-type layer 30 is carried out again. Therefore, from the viewpoint of preventing contamination of the surface of the n-type layer 20, it is preferable that the growth treatment of the n-type layer 20, the hydrogen dehydrogenation treatment of the n-type layer 20, and the growth treatment of the p-type layer 30 be carried out continuously in the same processing chamber as the growth of the n-type layer 20.

[0044] That is, after growing the n-type layer 20, it is preferable to adjust the temperature in the processing chamber to the temperature for hydrogen removal treatment, replace the atmospheric gas with a hydrogen-free gas such as nitrogen, perform heat treatment for hydrogen removal, then return the atmosphere and temperature to the crystal growth conditions again to grow the p-type layer 30. If necessary, the laminated substrate 50 after the growth of the n-type layer 20 may be once taken out of the processing chamber of the crystal growth apparatus, subjected to hydrogen removal treatment using a dedicated heat treatment apparatus or the like, and then the laminated substrate 50 may be returned into the processing chamber of the crystal growth apparatus again to grow the p-type layer 30.

[0045] The temperature of the hydrogen removal treatment for the n-type layer 20 may be the same as the temperature of the hydrogen removal treatment for the p-type layer 30, but from the viewpoint of suppressing roughness caused by thermal etching on the surface of the n-type layer 20 (the base for growth of the p-type layer 30), it is preferably lower than the temperature of the hydrogen removal treatment for the p-type layer 30. In addition, since the time of the hydrogen removal treatment for the n-type layer 20 is determined depending on the thickness of the n-type layer 20, it is preferable to obtain the conditions necessary for the hydrogen removal treatment experimentally in advance.

[0046] The hydrogen concentration in the n-type layer 20 after the hydrogen removal treatment is preferably sufficiently lower than the hydrogen concentration in the p-type layer 30 after the activation treatment. Although the specific value of the hydrogen concentration in the p-type layer 30 after the activation treatment also depends on the Mg concentration, the hydrogen concentration in the n-type layer 20 is reduced compared to at least 5×10 16 cm -3 or higher in the conventional technology, that is, reduced to less than 5×10 16 cm -3 (from the viewpoint of further clarifying the reduction compared to 5×10 16 cm -3 or higher, the hydrogen concentration may be reduced to 3×10 16 cm -3 or lower). In addition, in order to further ensure the above effect, the hydrogen concentration in the n-type layer 20 is preferably reduced to 1×10 16 cm -3 or lower, and more preferably reduced to 7×10 15 cm -3 or lower. Such conditions also apply to the surface layer portion 12 of the substrate 10.

[0047] Although nitrogen gas was used as an example of a carrier gas, hydrogen (H2) gas may be used as a carrier gas along with nitrogen gas if necessary. However, if hydrogen gas is used as a carrier gas, the supply of hydrogen gas, which serves as the hydrogen source, must be stopped during the hydrogen removal process.

[0048] Referring to Figure 3, the manufacturing method of the second example will be described. The second example is a configuration in which a hydrogen desorption treatment of the substrate 10 is added before the growth treatment of the n-type layer 20 in the first example. The process from the growth treatment of the n-type layer 20 onward is the same as in the first example.

[0049] The dehydrogenation treatment of substrate 10 is performed by heating substrate 10 to 500°C or higher (900°C or lower) in a hydrogen-free atmosphere and holding it for 30 minutes or more. The temperature for the dehydrogenation treatment of substrate 10 is, for example, 600°C. The specific temperature and time for the dehydrogenation treatment of substrate 10 are determined when the hydrogen concentration of the surface layer 12 of substrate 10 is 5 × 10⁻¹⁶. 16 cm -3 Less than (preferably 1 × 10) 16 cm -3 More preferably 7 × 10 15 cm -3 The settings may be experimentally adjusted as appropriate to reduce the following:

[0050] In Figure 3, an example is shown in which the substrate 10 is dehydrogenated in a nitrogen atmosphere (in the processing chamber of the crystal growth apparatus) before the growth of the n-type layer 20. However, the substrate 10 may also be dehydrogenated by another apparatus (or in the atmosphere) before being brought into the crystal growth apparatus, and the dehydrogenated substrate 10 may be brought into the crystal growth apparatus to start the growth of the n-type layer 20.

[0051] Referring to Figure 4, the manufacturing method of the third example will be described. The third example is a configuration in which the hydrogen dehydrogenation treatment of the n-type layer 20 of the second example is (formally) omitted. First, as in the second example, the substrate 10 is subjected to hydrogen dehydrogenation treatment and the n-type layer 20 is grown, and then the p-type layer 30 is grown.

[0052] After the growth of the p-type layer 30, a dehydrogenation treatment is performed. In the third example, the dehydrogenation treatment after the growth of the p-type layer 30 is performed in a manner that combines the dehydrogenation treatment of the n-type layer 20 and the dehydrogenation treatment (activation treatment) of the p-type layer 30. Specifically, compared to the dehydrogenation treatment of only the p-type layer 30 as in the first and second examples, the treatment is performed for a longer time to ensure that the dehydrogenation of the n-type layer 20 is also sufficiently carried out. The specific temperature and time for the dehydrogenation treatment of the n-type layer 20 and the p-type layer 30 are determined when the hydrogen concentration of the n-type layer 20 is 5 × 10⁻⁶. 16 cm -3 Less than (preferably 1 × 10) 16 cm -3 More preferably 7 × 10 15 cm -3 The following values ​​may be experimentally set to reduce the p-type layer 30 and activate it.

[0053] As in the second example, it is preferable to perform separate dehydrogenation treatments on each of the substrate 10, the n-type layer 20, and the p-type layer 30. However, as in the third example, after the dehydrogenation treatment of the substrate 10, the dehydrogenation treatment may be performed in a manner that also treats both the n-type layer 20 and the p-type layer 30.

[0054] <Preferred Embodiments of the Invention> Preferred embodiments of the present invention are described below.

[0055] (Note 1) A step to prepare an n-type gallium nitride single crystal substrate with a diameter of 50 mm or more, in which the lowest index crystal plane closest to the main plane is the (0001) plane, The process involves growing an n-type gallium nitride single crystal layer on the aforementioned substrate, The process involves subjecting the laminated substrate, on which the n-type gallium nitride single crystal layer has been grown, to a hydrogen dehydrogenation treatment. The process involves growing a p-type gallium nitride single crystal layer on a laminated substrate that has undergone the hydrogen removal treatment, The process involves further subjecting the laminated substrate, on which the p-type gallium nitride single crystal layer has been grown, to a hydrogen removal treatment. A method for manufacturing a gallium nitride laminated substrate for fabricating a device having a pn junction.

[0056] (Note 2) Before growing the n-type gallium nitride single crystal layer, the n-type gallium nitride single crystal substrate is subjected to a hydrogen dehydrogenation treatment. The method for manufacturing a gallium nitride multilayer substrate as described in Appendix 1.

[0057] (Note 3) The process involves growing an n-type gallium nitride single crystal layer on the aforementioned substrate, The process involves subjecting the laminated substrate, on which the n-type gallium nitride single crystal layer has been grown, to a hydrogen dehydrogenation treatment. The process involves growing a p-type gallium nitride single crystal layer on a laminated substrate that has undergone the hydrogen removal treatment, This is done continuously within the same processing room. The method for manufacturing a gallium nitride multilayer substrate as described in Appendix 1.

[0058] (Note 4) The treatment temperature in the hydrogen removal treatment applied to the laminated substrate on which the n-type gallium nitride single crystal layer has been grown is A lower temperature than the treatment temperature in the hydrogen removal treatment applied to the laminated substrate on which the p-type gallium nitride single crystal layer is grown. The method for manufacturing a gallium nitride multilayer substrate as described in Appendix 1.

[0059] (Note 5) After the laminated substrate on which the p-type gallium nitride single crystal layer has been grown has been subjected to a hydrogen desorption treatment, the hydrogen concentration in the n-type gallium nitride single crystal layer is 5 × 10 16 cm -3 Less than (preferably 1 × 10) 16 cm -3 More preferably 7 × 10 15 cm -3 The following is: The method for manufacturing a gallium nitride multilayer substrate as described in Appendix 1.

[0060] (Note 6) After the laminated substrate on which the p-type gallium nitride single crystal layer has been grown has been subjected to a hydrogen desorption treatment, the hydrogen concentration in a region within a thickness of 50 μm from the main surface of the n-type gallium nitride single crystal substrate is 5 × 1016 cm -3 Less than (preferably 1 × 10) 16 cm -3 More preferably 7 × 10 15 cm -3 The following is: The method for manufacturing a gallium nitride multilayer substrate as described in Appendix 2.

[0061] (Note 7) A step to prepare an n-type gallium nitride single crystal substrate with a diameter of 50 mm or more, in which the lowest index crystal plane closest to the main plane is the (0001) plane, The process involves subjecting the aforementioned n-type gallium nitride single crystal substrate to a hydrogen removal treatment, The process involves growing an n-type gallium nitride single crystal layer on a substrate that has undergone the hydrogen removal treatment, The process involves growing a p-type gallium nitride single crystal layer on a laminated substrate on which the n-type gallium nitride single crystal layer has been grown, The process involves further subjecting the laminated substrate, on which the p-type gallium nitride single crystal layer has been grown, to a hydrogen removal treatment. A method for manufacturing a gallium nitride laminated substrate for fabricating a device having a pn junction.

[0062] (Note 8) After the laminated substrate on which the p-type gallium nitride single crystal layer has been grown has been subjected to a hydrogen desorption treatment, the hydrogen concentration in the n-type gallium nitride single crystal layer is 5 × 10 16 cm -3 Less than (preferably 1 × 10) 16 cm -3 More preferably 7 × 10 15 cm -3 The following is: The method for manufacturing a gallium nitride multilayer substrate as described in Appendix 7.

[0063] (Note 9) After the laminated substrate on which the p-type gallium nitride single crystal layer has been grown has been subjected to a hydrogen desorption treatment, the hydrogen concentration in a region within a thickness of 50 μm from the main surface of the n-type gallium nitride single crystal substrate is 5 × 10 16 cm -3 Less than (preferably 1 × 10) 16cm -3 More preferably 7 × 10 15 cm -3 The following is: The method for manufacturing a gallium nitride multilayer substrate as described in Appendix 7.

[0064] (Note 10) The hydrogen removal process is carried out by heating the laminated substrate to 500°C or higher in a hydrogen-free atmosphere and holding it there for 30 minutes or more. A method for manufacturing a gallium nitride multilayer substrate as described in any one of the appendices 1 to 9.

[0065] (Note 11) The structure has an n-type gallium nitride single crystal substrate with a diameter of 50 mm or more, where the lowest index crystal plane closest to the main plane is the (0001) plane, and at least an n-type gallium nitride single crystal layer and a p-type gallium nitride single crystal layer are stacked in this order. At a minimum, the hydrogen concentration in the region within a thickness of 50 μm from the main surface of the n-type gallium nitride single crystal substrate and in the n-type gallium nitride single crystal layer is 5 × 10 16 cm -3 Less than (preferably 1 × 10) 16 cm -3 More preferably 7 × 10 15 cm -3 The following is: A gallium nitride multilayer substrate for fabricating devices having a pn junction.

[0066] (Note 12) The n-type impurities contained in the n-type gallium nitride single crystal substrate and the n-type impurities contained in the n-type gallium nitride single crystal layer are silicon or germanium, and the p-type impurities contained in the p-type gallium nitride single crystal layer are magnesium. Gallium nitride multilayer substrate as described in Appendix 11.

[0067] (Note 13) The structure has at least 50 mm in diameter and the low-index crystal plane closest to the main plane is the (0001) plane, and at least n-type gallium nitride single crystal layers are stacked on this substrate. The hydrogen concentration in the region within a thickness of 50 μm from the main surface of the n-type gallium nitride single crystal substrate and the hydrogen concentration in the crystal of the n-type gallium nitride single crystal layer are both 5 × 10 16 cm -3 Less than (preferably 1 × 10) 16 cm -3 More preferably 7 × 10 15 cm -3 The following is: Gallium nitride multilayer substrate.

[0068] (Note 14) An n-type gallium nitride single crystal substrate having a diameter of 50 mm or more, a thickness of 300 μm or more, and in which the lowest index crystal plane closest to the main plane is the (0001) plane, The hydrogen concentration in the gallium nitride single crystal has a gradient distribution that gradually increases from the main surface toward the thickness direction of the substrate. The hydrogen concentration in the region with a thickness of 50 μm or less from the main surface is 5 × 10 16 cm -3 Less than (preferably 1 × 10) 16 cm -3 More preferably 7 × 10 15 cm -3 The following is: Gallium nitride single crystal substrate. [Explanation of symbols]

[0069] 10…n-type gallium nitride single crystal substrate, 11…main surface (of substrate 10), 12…surface layer 12 (of substrate 10), 13…lower layer (of substrate 10), 20…n-type gallium nitride single crystal layer, 30…p-type gallium nitride single crystal layer, 50…laminated substrate (composed of substrate 10 and n-type layer 20), 100…laminated substrate (composed of substrate 10, n-type layer 20 and p-type layer 30)

Claims

1. A step of preparing an n-type gallium nitride single crystal substrate with a diameter of 50 mm or more, wherein the lowest index crystal plane closest to the main plane is the (0001) plane, The process involves growing an n-type gallium nitride single crystal layer on the aforementioned substrate, The process involves subjecting the laminated substrate, on which the n-type gallium nitride single crystal layer has been grown, to a hydrogen dehydrogenation treatment. The process involves growing a p-type gallium nitride single crystal layer on a laminated substrate that has undergone the hydrogen removal treatment, The process involves further subjecting the laminated substrate, on which the p-type gallium nitride single crystal layer has been grown, to a hydrogen removal treatment. A method for manufacturing a gallium nitride laminated substrate for fabricating a device having a pn junction.

2. Before growing the n-type gallium nitride single crystal layer, the n-type gallium nitride single crystal substrate is subjected to a hydrogen dehydrogenation treatment. A method for manufacturing a gallium nitride multilayer substrate according to claim 1.

3. A step of preparing an n-type gallium nitride single crystal substrate with a diameter of 50 mm or more, wherein the lowest index crystal plane closest to the main plane is the (0001) plane, The process involves subjecting the aforementioned n-type gallium nitride single crystal substrate to a hydrogen removal treatment, The process involves growing an n-type gallium nitride single crystal layer on a substrate that has undergone the hydrogen removal treatment, The process involves growing a p-type gallium nitride single crystal layer on a laminated substrate on which the n-type gallium nitride single crystal layer has been grown, The process involves further subjecting the laminated substrate, on which the p-type gallium nitride single crystal layer has been grown, to a hydrogen removal treatment. A method for manufacturing a gallium nitride laminated substrate for fabricating a device having a pn junction.

4. The hydrogen removal process is carried out by heating the laminated substrate to 500°C or higher in a hydrogen-free atmosphere and holding it there for 30 minutes or more. A method for manufacturing a gallium nitride laminated substrate according to any one of claims 1 to 3.

5. The structure is formed by stacking at least an n-type gallium nitride single crystal layer and a p-type gallium nitride single crystal layer in this order on an n-type gallium nitride single crystal substrate with a diameter of 50 mm or more, where the lowest index crystal plane closest to the main plane is the (0001) plane. At a minimum, the hydrogen concentration in the region within 50 μm thickness from the main surface of the n-type gallium nitride single crystal substrate and in the n-type gallium nitride single crystal layer is 5 × 10 １６ cm －３ Less than, Gallium nitride multilayer substrate for fabricating devices having a pn junction.

6. The structure comprises at least one n-type gallium nitride single crystal layer stacked on an n-type gallium nitride single crystal substrate with a diameter of 50 mm or more, where the lowest index crystal plane closest to the main plane is the (0001) plane. The hydrogen concentration in the region within a thickness of 50 μm from the main surface of the n-type gallium nitride single crystal substrate and the hydrogen concentration in the crystal of the n-type gallium nitride single crystal layer are both 5 × 10 １６ cm －３ Less than, Gallium nitride multilayer substrate.

7. An n-type gallium nitride single crystal substrate having a diameter of 50 mm or more, a thickness of 300 μm or more, and the lowest index crystal plane closest to the main plane being the (0001) plane, The hydrogen concentration in the gallium nitride single crystal has a gradient distribution that gradually increases from the main surface toward the thickness direction of the substrate. The hydrogen concentration in the region with a thickness of 50 μm or less from the main surface is 5 × 10 １６ cm －３ Less than, Gallium nitride single crystal substrate.

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