Method for manufacturing nitride semiconductor device and nitride semiconductor substrate

Abstract

To provide a technology for forming a p-type region in a nitride semiconductor.SOLUTION: A manufacturing method of a nitride semiconductor substrate includes a defect formation step for forming a crystal defect from a surface of the substrate toward an inner side. The manufacturing method includes a Mg solid layer formation process for forming a Mg solid layer being a solid layer containing Mg on the surface of the substrate. The manufacturing method includes a first heat process step for heating the substrate in which the Mg solid layer is formed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a method for manufacturing a nitride semiconductor device and a nitride semiconductor substrate. [Background technology]

[0002] A known technique is to form a p-type region by ion-implanting magnesium (Mg) as an acceptor impurity into a desired position of a nitride semiconductor substrate. Note that Patent Document 1 discloses a related technique. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-28932 Summary of the Invention [Problem to be solved by the invention]

[0004] During Mg ion implantation, nitrogen vacancies are formed, which compensate for the acceptors, making it difficult to form p-type regions. [Means for solving the problem]

[0005] One embodiment of a method for manufacturing a nitride semiconductor substrate disclosed in this specification includes a defect formation step of forming crystal defects from the surface of the substrate toward the interior. The manufacturing method also includes an Mg solid layer formation step of forming an Mg solid layer, which is a solid layer containing Mg, on the surface of the substrate. The manufacturing method also includes a first heat treatment step of heating the substrate on which the Mg solid layer has been formed.

[0006] The diffusion rate can be increased by thermally diffusing Mg into regions where crystal defects are formed. Solid-phase diffusion also allows Mg to be diffused to a sufficient depth. Because Mg ion implantation is not required, the generation of nitrogen vacancies can be suppressed. As a result, it is possible to form p-type regions.

[0007] The method may further include a protective layer forming step of forming a protective layer on the surface of the Mg solid layer. The first heat treatment step may heat the substrate on which the protective layer is formed. Details of the effects will be described in the examples.

[0008] The method may further include a second heat treatment step in which the substrate is heated at a temperature lower than that of the first heat treatment step. The second heat treatment step may be performed after the Mg solid layer formation step and before the protective layer formation step. Details of the effects will be described in the examples.

[0009] The method may further include a step of removing an altered layer formed on the surface of the Mg solid layer by the second heat treatment step. A protective layer may be formed on the surface of the Mg solid layer from which the altered layer has been removed. Details of the effects will be described in the examples.

[0010] One embodiment of a method for manufacturing a nitride semiconductor substrate disclosed in this specification includes a defect forming step of forming crystal defects from the surface of the substrate to the interior thereof, and a step of bringing a melt containing Mg into contact with the surface of the substrate.

[0011] The melt may contain Zn and may have a temperature of 450°C or higher.

[0012] One embodiment of a method for manufacturing a nitride semiconductor substrate disclosed in this specification includes a defect formation step of forming crystal defects from the surface of the substrate to the interior thereof, a step of placing the substrate in a specific atmosphere containing Mg, and a heat treatment step of heating the substrate in the specific atmosphere.

[0013] The defect forming step may include a step of implanting nitrogen ions from the surface of the substrate. Details of the effects will be described in the examples.

[0014] In one embodiment of the nitride semiconductor substrate disclosed in this specification, the Mg concentration distribution in the direction perpendicular to the surface of the nitride semiconductor substrate has a maximum value in a first region extending from the surface to a depth of 100 nanometers.20 cm -3 That's all.

[0015] The Mg concentration distribution may vary by one order of magnitude or more within a second region having a width of 100 nanometers or less and extending in the depth direction from the maximum value.

[0016] The Mg concentration distribution may have a singular point in the second region where the concentration gradient suddenly decreases. A constant concentration region where the Mg concentration is approximately constant from the singular point in the depth direction may exist. The width of the constant concentration region in the depth direction may be 50 nanometers or more.

[0017] The planar density of loop defects in the cross section of the Mg-doped region is 1×10 5 [pcs / cm 2 ] or less. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a flowchart of a method for manufacturing a nitride semiconductor substrate. [Figure 2] 1A to 1C are cross-sectional views showing manufacturing steps of a nitride semiconductor substrate. [Figure 3] 1A to 1C are cross-sectional views showing manufacturing steps of a nitride semiconductor substrate. [Figure 4] 1A to 1C are cross-sectional views showing manufacturing steps of a nitride semiconductor substrate. [Figure 5] 1A to 1C are cross-sectional views showing manufacturing steps of a nitride semiconductor substrate. [Figure 6] 1 is a graph showing a Mg concentration distribution profile. [Figure 7] 1 is an SNDM cross-sectional observation image of a p-type GaN region in this example. [Figure 8] 1 is an SNDM cross-sectional observation image of a p-type GaN region of a comparative example. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0019] <Method for forming p-type GaN region> In this embodiment, a case where gallium nitride (GaN) is used as the nitride semiconductor, magnesium (Mg) is used as the acceptor impurity of group II elements, and silicon (Si) is used as the donor impurity will be described. The process of forming a p-type region on the substrate 1 will be described using the flowchart of FIG. 1 and the cross-sectional views of FIGS. 2 to 5. FIGS. 2 to 5 are partial enlarged views near the surface of the substrate 1. The substrate 1 has a structure in which a GaN layer 12 that is not doped with impurities is laminated on a GaN base substrate 11. The GaN layer 12 may be formed by epitaxial growth. In this embodiment, the thickness of the GaN layer 12 is set to 3 μm.

[0020] In step S1, a mask 30 is formed on the surface 12s of the GaN layer 12. The mask 30 has an opening OP corresponding to the location where the p-type region is to be formed. The mask 30 can be formed by known photolithography technology.

[0021] In step S2, nitrogen is ion-implanted through the mask 30 from the surface 12s (see FIG. 2). The nitrogen ion implantation is performed so as to have a so-called box profile in which the nitrogen concentration from the surface 12s to a predetermined depth is substantially constant. The box profile can be realized by performing ion implantation a plurality of times by changing the implantation energy and the implantation amount. As a result, an implanted region IA implanted with nitrogen ions is formed. In FIG. 2, the implanted region IA is indicated by a dotted line. In this embodiment, the depth D1 of the implanted region IA is set to 250 nm. The acceleration voltage of the nitrogen ions is within the range of 10 KV to 10 MV. The nitrogen concentrations are three types of 5×10 19 cm -3 、5×10 18 cm -3 、5×10 16 cm -3 、respectively.

[0022] The reason for nitrogen ion implantation will be explained. Ion implantation creates crystal defects such as Ga vacancies and nitrogen vacancies. Ga vacancies are necessary because Mg is substituted into the Ga vacancies to activate the Mg and convert them to p-type. On the other hand, nitrogen vacancies are donor defects, and they compensate for acceptors, preventing p-type conversion. Therefore, it is preferable to have few nitrogen vacancies. Therefore, in the technology of this example, nitrogen, which constitutes the nitride semiconductor, is ion implanted. Since the nitrogen vacancies formed by ion implantation are replaced by the implanted nitrogen, the generation of nitrogen vacancies can be suppressed. Therefore, Ga vacancies can be selectively formed by nitrogen ion implantation.

[0023] In step S3, an Mg-containing layer 13 is formed on the surface 12s (see FIG. 3). The Mg-containing layer 13 is a layer containing Mg. In this example, the Mg-containing layer 13 was formed by evaporating Mg using an electron beam (EB) evaporation method. The thickness T0 of the Mg-containing layer 13 was set to 50 nm.

[0024] In step S4, a pre-annealing step is performed. In this example, a RTA (Rapid Thermal Anneal) device is used to perform the pre-annealing at 800°C for 1 hour. The pressure and atmosphere during the pre-annealing are not particularly limited. In this example, the pre-annealing was performed in an air atmosphere at normal pressure.

[0025] The pre-annealing step can change the Mg-containing layer 13 (FIG. 3) into a layered structure (FIG. 4) of an Mg solid layer 13a and an MgO layer 13b. The Mg solid layer 13a is a layer containing Mg, Ga, and N. The chemical composition of the Mg solid layer 13a is not particularly limited. For example, it may be a mixture of magnesium nitride (MgN) and GaN. The MgO layer 13b is a layer containing magnesium oxide. The MgO layer 13b is an altered layer formed when the surface of the Mg-containing layer 13 reacts with oxygen in the annealing atmosphere. In this example, the thickness T1 of the Mg solid layer 13a and the thickness T2 of the MgO layer 13b were in the range of 20 to 50 nm.

[0026] The thickness T1 of the Mg solid layer 13a can be controlled by the thickness T0 of the Mg-containing layer 13 and the temperature of the pre-annealing step. For example, the thickness T1 of the Mg solid layer 13a can be reduced by reducing the thickness T0 of the Mg-containing layer 13. The Mg doping concentration, which will be described later, can be controlled by the thickness T1 of the Mg solid layer 13a. For example, reducing the thickness T1 of the Mg solid layer 13a can reduce the Mg supply source, thereby reducing the Mg doping concentration.

[0027] In step S5, the MgO layer 13b formed on the surface of the Mg solid layer 13a is removed. The oxygen contained in the MgO layer 13b functions as a donor impurity for GaN. Therefore, removing the MgO layer 13b prevents oxygen from inhibiting the development of p-type characteristics. Various removal methods may be used, such as wet etching, dry etching, or polishing. In this specification, the MgO layer 13b was removed by wet etching using aqua regia.

[0028] In step S6, a protective layer 14 is formed on the surface 13as of the Mg solid layer 13a from which the MgO layer 13b has been removed (see FIG. 5). The protective layer 14 preferably has high heat resistance and adhesiveness. The protective layer 14 can suppress nitrogen desorption from GaN in the diffusion annealing step described below. In this embodiment, the protective layer 14 is made of aluminum nitride (AlN) deposited by MOVPE. The thickness of the protective layer 14 is 300 nm.

[0029] In step S7, a diffusion annealing process is performed. The temperature of the diffusion annealing process is higher than the temperature of the pre-annealing process in step S4. For example, it may be within the range of 700°C to 1400°C. The annealing atmosphere is not particularly limited. The annealing atmosphere may contain nitrogen. Thereby, the effect of suppressing the thermal decomposition of the protective layer 14 and GaN can be obtained. The pressure may be 1000 atm or less. The annealing time may be determined according to the Mg concentration distribution profile described later, and for example, may be within the range of 30 seconds to 1 hour. From the perspective of the thermal budget, a correlation may be established such that the higher the temperature, the shorter the annealing time. For example, when the temperature is 1400°C, the annealing time may be 30 seconds, and when the temperature is 700°C, the annealing time may be 1 hour. In this embodiment, annealing was performed in an atmospheric atmosphere at 1300°C and normal pressure. The annealing time was 5 minutes.

[0030] In the implantation region IA, crystal defects are formed in a box profile. Also, the region where crystal defects are formed can enhance the diffusion rate of Mg compared to the region where no crystal defects are formed. Therefore, by the diffusion annealing process, Mg can be solid-phase diffused from the Mg solid layer 13a to the entire implantation region IA. Also, as described above, in the implantation region IA, Ga vacancies are selectively formed by ion implantation of nitrogen, so it can be activated by replacing Mg with Ga vacancies. Thereby, a p-type GaN region PR can be formed in the region where the implantation region IA was formed (see Fig. 5).

[0031] In step S8, the protective layer 14 is removed. The removal method can be various, such as wet etching or dry etching. In this specification, it was removed by wet etching using TMAH (Tetramethyl ammonium hydroxide). Thus, the formation flow of the p-type GaN region is completed.

[0032] <Mg concentration distribution profile> The Mg concentration distribution profile in the depth direction in the substrate 1 produced by the above-mentioned process will be described. Fig. 6 shows the Mg concentration distribution profile obtained using secondary ion mass spectrometry (SIMS). The vertical axis represents the Mg concentration, and the horizontal axis represents the depth from the surface 12s of the GaN layer 12.

[0033] The implantation region IA is a region into which nitrogen ions are implanted with a box profile. In this example, the depth D1 of the implantation region IA is about 250 nm. The Mg concentration distribution profiles MP1 to MP3 show the concentration distribution of Mg in the direction perpendicular to the surface 12s. The Mg concentration distribution profiles MP1 to MP3 show that the nitrogen concentration in the implantation region IA is 5×10 19 cm -3 , 5×10 18 cm -3 , 5×10 16 cm -3 , the profile formed in the case of

[0034] The Mg concentration distribution profiles MP1 to MP3 have a maximum value MV of the Mg concentration in the first region R1, which is located from the surface to a depth of 100 nm. The maximum value MV is 1×10 20 cm -3 The depth from the surface 12s of the region where the maximum value MV is reached is approximately 15 nm. The effect will be explained. Conventionally, when using ion implantation, the Mg concentration at the extreme surface, approximately 15 nm from the surface 12s, is set to 1×10 20 cm -3 In the technology of this specification, Mg is diffused from the surface 12s in a solid phase, so the Mg concentration at the extreme surface is 1×10 20 cm -3 This makes it possible to form an ohmic contact with an electrode formed on the surface 12s.

[0035] In the Mg concentration distribution profiles MP1 to MP3, the Mg concentration changes by more than one order of magnitude within the second region R2, which extends from the maximum value MV in the depth direction and has a width of 100 nm or less. In other words, as the depth increases from the maximum value MV (a depth of approximately 15 nm), the Mg concentration decreases to less than one-tenth of the maximum value MV. Furthermore, the Mg concentration distribution profiles MP1 to MP3 include singular points SP1 to SP3 within the second region R2, where the concentration gradient suddenly decreases. Furthermore, in the direction increasing from the singular points SP1 to SP3, there exists a constant concentration region CR, where the Mg concentration is almost constant. The width of the constant concentration region CR in the depth direction is 50 nm or more. From the above, it can be seen that the Mg concentration can be rapidly reduced in the depth direction. The effect will be explained. If the Mg concentration distribution profile changes gradually in the depth direction, a low-concentration p-type region exists at the bottom of the p-type region. This low-concentration p-type region will become a high-resistance region when forming a pn junction interface. On the other hand, the technology of this specification can make the Mg concentration distribution profile steep, so that there is no low-concentration p-type region at the bottom of the p-type region. Therefore, it is possible to fabricate a p-n junction interface where a high-concentration p-type region and a high-concentration n-type region are joined. This can prevent the formation of a high-resistance region at the p-n junction interface.

[0036] As can be seen from the Mg concentration distribution profile MP1, the Mg concentration is higher in the implantation region IA (region shallower than 0.25 μm) than in the region deeper than the implantation region IA (region deeper than 0.25 μm). This is because Mg can be captured by crystal defects formed by nitrogen ion implantation. Therefore, by forming the implantation region IA in the region where the Mg concentration is desired to be high, it is possible to form a desired Mg concentration distribution profile. In addition, the Mg concentration distribution profile MP1 (nitrogen concentration 5×10 19 cm -3 ), MP2 (nitrogen concentration 5 × 10 18 cm -3 ), MP3 (nitrogen concentration 5 × 10 16 cm -3), it can be seen that the higher the nitrogen concentration in the implantation region IA, the higher the Mg concentration can be. This is because the higher the nitrogen concentration, the higher the crystal defect density. Therefore, by controlling the nitrogen concentration, it is possible to indirectly control the Mg concentration.

[0037] <Effects> When Mg is diffused by solid-phase diffusion, the depth-wise Mg concentration distribution profile and Mg doping concentration are so-called error function profiles. Because they are uniquely determined by the heat treatment temperature and time, it is difficult to control the Mg concentration distribution profile and doping concentration. Therefore, it is difficult to form the box profile required for various devices or adjust the Mg concentration to the desired value. Furthermore, diffusing Mg deeper than 100 nm requires a long heat treatment time of several hours or more. Therefore, the technology of this embodiment is configured to solid-phase diffuse Mg into the implantation region IA where crystal defects are formed. Because Mg can be captured and activated by Ga vacancies, the Mg concentration distribution profile can be formed to follow the nitrogen profile in the implantation region IA. Furthermore, the higher the concentration of implanted nitrogen, the higher the Mg doping concentration. In other words, the Mg concentration distribution profile can be controlled by controlling the nitrogen profile in the implantation region IA, and the Mg doping concentration can be controlled by controlling the nitrogen concentration. Furthermore, since Mg is more easily diffused in regions where defects are formed than in regions where defects are not formed, the heat treatment time required to diffuse Mg into regions deeper than 100 nm can be significantly reduced (e.g., to 5 minutes).

[0038] Conventionally, in order to form a p-type GaN region by ion implantation of Mg, a heat treatment under ultra-high pressure was required to recover damages such as nitrogen vacancies generated inside the crystal. However, since it required a heat treatment under an extremely special environment of a pressure of 1 GPa (about 10,000 atmospheres), it was difficult to implement. In the technology of this specification, in order to form an implantation region IA by nitrogen ion implantation, it becomes possible to actively form Ga vacancies while suppressing the generation of nitrogen vacancies. Since damages such as nitrogen vacancies can be suppressed, a heat treatment under ultra-high pressure can be made unnecessary. It becomes possible to easily perform the heat treatment.

[0039] <Evaluation Results of p-Type GaN Region> Using a scanning non-linear dielectric microscope (SNDM), the formation state of the p-type GaN region was evaluated. SNDM is a microscope that two-dimensionally visualizes the carrier distribution. Figures 7 and 8 show an example of the cross-sectional observation results. The vertical axis is the depth from the substrate surface. The horizontal axis is the position in the direction horizontal to the surface. In Figures 7 and 8, the p-type GaN region PR is shown as a thin shading, the n-type GaN region NR is shown as a thick shading, and the high-resistance intrinsic GaN region IR is shown in white.

[0040] Figure 7 is a cross-sectional view of the p-type GaN region formed by the technology of this embodiment. n + - An undoped GaN layer 12 of about 3 μm is formed on the (0001) surface of the n-GaN base substrate 11. An implantation region IA is formed on the upper part of the GaN layer 12. The horizontal width of the implantation region IA is about 10.5 μm, and the depth D1 is about 200 nm. Nitrogen is implanted in the implantation region IA in a box profile, and the nitrogen concentration is 5×10 18 cm -3 -3.

[0041] In this embodiment shown in Figure 7, a p-type GaN region PR is formed within implantation region IA in a region extending from surface 12s to a depth of approximately 0.7 µm. Because surface 12s is p-type, an ohmic contact can be formed when an electrode is formed on implantation region IA. Outside implantation region IA, an n-type GaN region NR is formed in a region extending from surface 12s to a depth of approximately 1.0 µm. An intrinsic GaN region IR is formed in a region extending from a depth of approximately 0.5 µm to 3.0 µm.

[0042] On the other hand, Figure 8 shows a comparative example. The comparative example is a cross-sectional view of a p-type GaN region formed by ultra-high pressure annealing (UHPA) after Mg ion implantation. In the comparative example of Figure 8, + An Mg-implanted region MA is formed on top of the GaN substrate by implanting Mg ions. Within the Mg-implanted region MA, a p-type GaN region PR is formed in a region from approximately 0.5 μm to 2.0 μm deep. However, the region from the surface 112s to approximately 0.5 μm is an intrinsic GaN region IR. This means that it is difficult to convert the surface 112s to p-type GaN using ion implantation. Therefore, even if an electrode is formed on the Mg-implanted region MA, it is difficult to form an ohmic contact.

[0043] <Evaluation results of crystal defects> The formation state of crystal defects was evaluated using an annular dark-field scanning transmission electron microscope (ADF-STEM). As a comparative example, a p-type GaN region was created by Mg ion implantation followed by ultra-high pressure annealing (1 GPa, 1480°C, 5 minutes). The cross section of the (11-20) plane was then observed. In the comparative example, numerous vacancy-type dislocation loop defects were observed, with a planar density of approximately 3 × 10 10 [pcs / cm 2 ] was.

[0044] On the other hand, when a similar cross section was observed in the p-type GaN region created by the technology of this example, no oval dislocation loop defects or coffee bean defects due to vacancy defects were observed. In other words, the loop defect density in the Mg-doped region was 1×10 5[pcs / cm 2 The reason for this is explained below. Dislocation loop defects are formed when supersaturated point defects (vacancies, interstitial atoms) gather in a flat shape and closed dislocations form at their edges. In the comparative example, many nitrogen vacancies are formed by Mg ion implantation, which results in the formation of many dislocation loop defects. On the other hand, in the technology of this example, nitrogen ion implantation is performed without Mg ion implantation. As described above, nitrogen ion implantation can suppress the generation of nitrogen vacancies, making it possible to suppress the formation of dislocation loop defects. [Example]

[0045] In Example 1, a form in which Mg is diffused in the implantation region IA by solid phase diffusion is described. In Example 2, a form in which Mg is diffused in the implantation region IA by vapor phase diffusion is described. The steps (steps S1 to S2) up to the formation of the implantation region IA are similar, and therefore the description will be omitted.

[0046] In the vapor-phase diffusion process, the substrate 1 with the implanted region IA formed therein is annealed in an atmosphere containing Mg. Various types of vapor-phase Mg source materials are available. These include Mg vapor and magnesium chloride (MgCl2). They may also be various organometallic compounds (MOs) such as Cp2Mg and EtCp2Mg. Nitrogen may also be included in the annealing atmosphere. For example, ammonia or nitrogen gas may be supplied into the chamber. Supplying nitrogen from the atmosphere to the GaN substrate can suppress nitrogen loss from the GaN during annealing. In this example, annealing was performed at 830°C in an atmosphere containing Cp2Mg and ammonia.

[0047] After the vapor phase diffusion step, the formation of the protective layer 14 (step S6), the diffusion annealing step (step S7), and the removal of the protective layer 14 (step S8) may be performed. This completes the flow for forming a p-type GaN region by vapor phase diffusion.

[0048] <Effects> In the solid-phase diffusion of Example 1, the surface morphology of surface 12s after the formation of the p-type GaN region was deteriorated. For example, when the root-mean-square roughness (RMS) of surface 12s was measured using an AFM or the like, the RMS after nitrogen ion implantation (step S2) was 0.2 to 0.5 nm. On the other hand, the RMS after the completion of the p-type GaN region (step S8) was 7.0 nm. This is thought to be because the surface morphology was deteriorated when the Mg solid layer 13a was formed in the pre-annealing step (step S4).

[0049] On the other hand, the vapor phase diffusion method of Example 2 eliminates the need to form the Mg solid layer 13a, thereby improving the surface morphology of the surface 12s. For example, the RMS measured after the completion of the p-type GaN region was 0.3 nm. Furthermore, steps were observed in the AFM image of the surface 12s, indicating that a flat surface was maintained at the atomic level. This allows for improved characteristics when the substrate 1 is applied to a device. [Example]

[0050] A mode of liquid-phase diffusion of Mg into the implantation region IA will be described in Example 3. The steps (steps S1 to S2) up to the formation of the implantation region IA are similar, and therefore a description thereof will be omitted.

[0051] In the liquid phase diffusion process, the substrate 1 with the implanted region IA formed therein is brought into contact with a melt containing Mg. Various types of melt may be used. For example, melts of Zn-Mg binary metals, Al-Zn-Mg ternary metals, Cu-Mg-Zn ternary metals, etc. may be used. Alternatively, melts of metals with high nitrogen solubility may be used, such as a melt of an alkali metal such as Na. In this example, an MgZn melt with an Mg:Zn ratio of 51:20 was used. The temperature was 450°C.

[0052] The liquid phase diffusion process may be performed using a variety of apparatus configurations. A melt may be generated in a crucible under high temperature (e.g., 400 to 1000°C) and high pressure (e.g., several tens of atmospheres) conditions, and the substrate 1 may be brought into contact with the melt. Nitrogen loss from GaN may be suppressed by dissolving nitrogen gas (N2) in the melt.

[0053] After the liquid phase diffusion step, the formation of the protective layer 14 (step S6), the diffusion annealing step (step S7), and the removal of the protective layer 14 (step S8) may be performed. This completes the flow for forming a p-type GaN region by liquid phase diffusion. [Example]

[0054] In Example 4, a form in which Mg is plasma doped into the implantation region IA will be described. The steps (steps S1 to S2) up to the formation of the implantation region IA are similar, and therefore a description thereof will be omitted.

[0055] In the plasma doping process, the substrate 1 with the implantation region IA formed thereon is set on a bias electrode in a vacuum chamber, and a plasma consisting of a gas containing Mg is generated. Mg ions in the plasma are accelerated toward the surface 12s, thereby introducing Mg into the implantation region IA.

[0056] After the plasma doping step, the formation of the protective layer 14 (step S6), the diffusion annealing step (step S7), and the removal of the protective layer 14 (step S8) may be performed. This completes the flow for forming a p-type GaN region by plasma doping.

[0057] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives alone is technically useful.

[0058] (Variation) The nitride semiconductors to which the technology of this specification can be applied are not limited to GaN. For example, the technology can be applied to binary nitride semiconductors such as InN and AlN, ternary nitride semiconductors such as AlGaN, GaInN and AlInN, and quaternary nitride semiconductors such as AlGaInN. The technology can also be applied to sapphire, Si, SiC, SiO2, MgO, Ga2O3, ZrB2, spinel, diamond, PET, and other materials on which at least one AlGaInN-based nitride semiconductor layer is formed.

[0059] The Mg diffusion technique of this specification is not limited to the upper surface of the substrate 1, but can also be applied to surfaces of various structures, such as the surface of the inner wall of a trench.

[0060] The ions implanted in step S2 are not limited to simple nitrogen ions, but may include various other ions, such as hydrogen ions and fluorine ions.

[0061] Since step S2 is a process for introducing crystal defects, it is not limited to ion implantation, and crystal defects may be introduced by, for example, electron beam irradiation.

[0062] The Mg-containing layer 13 formed in step S3 may be a compound containing Mg, such as MgO or MgZnO.

[0063] The diffusion annealing step may be performed without forming the protective layer 14. In this case, step S6 may be skipped. The MgO layer 13b may not be removed. In this case, step S5 may be skipped.

[0064] In the above embodiment, magnesium (Mg) is used as an example of a Group II element for forming a p-type region, but this is not limited to this configuration. The Group II element may be, for example, beryllium (Be), calcium (Ca), etc. Also, silicon (Si) is used as an example of an element for forming an n-type region, but this is not limited to this configuration, and germanium (Ge), etc. may be used.

[0065] The process of step S2 is an example of a defect forming process. The diffusion annealing process of step S7 is an example of a first heat treatment process. The pre-annealing process of step S4 is an example of a second heat treatment process. The MgO layer 13b is an example of an altered layer. [Explanation of symbols]

[0066] 1: Substrate 11: Base substrate 12: GaN layer 12s: Surface 13: Mg-containing layer 13a: Mg solid layer 13b: MgO layer 14: Protective layer

Claims

1. A defect forming step of forming crystal defects from the surface of a substrate to the interior thereof; an Mg solid layer forming step of forming an Mg solid layer, which is a solid layer containing Mg, on the surface of the substrate; a protective layer forming step of forming a protective layer on the surface of the Mg solid layer; a first heat treatment step of heating the substrate on which the Mg solid layer and the protective layer are formed; A method for manufacturing a nitride semiconductor substrate, comprising: a second heat treatment step of heating the substrate at a temperature lower than that of the first heat treatment step; The method for manufacturing a nitride semiconductor substrate, wherein the second heat treatment step is performed after the Mg solid layer forming step and before the protective layer forming step.

2. a step of removing an altered layer formed on the surface of the Mg solid layer by the second heat treatment step, The method for manufacturing a nitride semiconductor substrate according to claim 1 , wherein the protective layer is formed on the surface of the Mg solid layer from which the altered layer has been removed.

3. 3. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein said defect forming step comprises a step of implanting nitrogen ions into the surface of said substrate.

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