Method for producing nitride laminate, and nitride laminate

Abstract

The present invention relates to a method for manufacturing a nitride laminate and a nitride laminate, which can reduce adverse effects of impurities adhering to the surface of a first group III nitride when re-growing a second group III nitride on the first group III nitride in a non-continuous growth manner. The method comprises: (a) a step for preparing a substrate, at least a surface layer portion of which is composed of a first group III nitride, in a state in which the substrate is taken out to the outside of a film-forming device for growing the first group III nitride; (b) a step in which the substrate is subjected to a predetermined oxidation treatment using an oxidation treatment device, and the outermost layer of the first group III nitride is changed into a protective layer containing a group III oxide; (c) a step of transferring the substrate into a predetermined processing chamber, heating the substrate in a reducing atmosphere, and removing the protective layer from the surface of the substrate; and (d) a step for growing a second group III nitride on the surface of the first group III nitride exposed by removing the protective layer without moving the substrate out of the processing chamber.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a nitride laminate and a nitride laminate. Background Art

[0002] Group III nitrides such as gallium nitride (GaN) are used as materials for semiconductor devices such as light-emitting elements and transistors. A nitride laminate obtained by epitaxially growing a GaN layer on a GaN substrate has attracted attention because the GaN layer has high quality (for the use of a GaN substrate for growing a high-quality GaN layer, see, for example, Non-Patent Document 1).

[0003] When growing a GaN layer on a GaN substrate, the GaN substrate is carried into a processing chamber of a film-forming apparatus for growing the GaN layer from the outside, and the GaN layer is grown on the GaN substrate. In other words, the GaN layer is regrown on the GaN substrate in a discontinuous growth manner.

[0004] Generally, as in the case of growing a GaN layer on a GaN substrate, a second Group III nitride is regrown on a first Group III nitride as a growth base in a discontinuous growth manner. In this case, since the first Group III nitride is taken out of the film-forming apparatus after the growth of the first Group III nitride, impurities adhere to the surface of the first Group III nitride. The attached impurities have an adverse effect on the growth of the second Group III nitride and the like.

[0005] Prior Art Documents

[0006] Non-Patent Documents

[0007] Non-Patent Document 1: Fujikura Foreword, et al. 8 persons, "Development of GaN single crystal substrate", Sumitomo Chemical, 2018, p. 38-47 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] An object of the present invention is to provide a technique capable of reducing the adverse effect of impurities attached to the surface of a first Group III nitride when a second Group III nitride is regrown on the first Group III nitride in a discontinuous growth manner.

[0010] Means for Solving the Problems

[0011] According to one aspect of the present invention, there is provided a method for manufacturing a nitride laminate, comprising the following steps:

[0012] (a) A step of preparing a substrate having at least a surface layer portion made of a first Group III nitride in a state of being taken out of a film-forming apparatus for growing the first Group III nitride;

[0013] (b) A step of performing a prescribed oxidation treatment on the substrate using an oxidation treatment apparatus to change the outermost layer of the first group-III nitride into a protective layer containing a group-III oxide;

[0014] (c) A step of loading the substrate into a prescribed processing chamber, heating it in a reducing atmosphere, and removing the protective layer from the surface of the substrate;

[0015] (d) A step of growing a second group-III nitride on the surface of the first group-III nitride exposed by removing the protective layer without unloading the substrate from the processing chamber.

[0016] According to another aspect of the present invention, there is provided a nitride laminate having:

[0017] A substrate at least the surface layer portion of which is composed of a first group-III nitride;

[0018] A protective layer containing a group-III oxide formed on the surface of the first group-III nitride.

[0019] According to another aspect of the present invention, there is provided a nitride laminate including:

[0020] A substrate at least the surface layer portion of which is composed of a first group-III nitride;

[0021] A film containing a second group-III nitride formed on the surface of the first group-III nitride,

[0022] The concentration distribution of iron (Fe) in the interface between the first group-III nitride and the second group-III nitride has a peak at the interface, and the peak concentration is 2×10 16 / cm 3 or less.

[0023] Effects of the Invention

[0024] There is provided a technique capable of reducing the adverse effects of impurities adhering to the surface of the first group-III nitride when the second group-III nitride is regrown on the first group-III nitride in a non-continuous growth manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 (a) is a schematic diagram showing a step of preparing a substrate 11 in a state of being taken out of the film forming apparatus in an embodiment of the present invention, Figure 1 (b) is a schematic diagram showing a step of forming a protective layer 15 on the substrate 11 in the embodiment.

[0026] Figure 2 (a) is a schematic diagram showing a step of removing the protective layer 15 from the substrate 11 in the embodiment,Figure 2 (b) is a schematic diagram showing the process of growing the film 21 on the substrate 11 in the embodiment.

[0027] Figure 3 This is an example of the SIMS cross-section of the sample of the embodiment, showing the concentration distributions of Fe, Mg, and Cr.

[0028] Figure 4 This is an example of the SIMS cross-section of the sample of the first comparative method, showing the concentration distributions of Fe, Mg, and Cr.

[0029] Figure 5 This is an example of the SIMS cross-section of the sample of the second comparative method, showing the concentration distributions of Fe, Mg, and Cr.

[0030] Figure 6 (a) and Figure 6 (b) are respectively the first example and the second example of the form in which the surface 13a of the first group-III nitride has an uneven structure.

[0031] Figure 7 This is an example of the SIMS cross-section of the existing nitride laminate, showing the concentration distributions of Fe, Mg, and Si.

[0032] Description of reference numerals

[0033] 11... Substrate, 12... Surface layer portion, 13... Surface, 13a... Surface, 14... Impurity, 15... Protective layer, 16... Intermediate, 21... Film, 31... Protrusion of Fe, 32... Protrusion of Mg, 41... Interface, 42... Interface region, 43... Laminated region, 51... Main surface, 52... Groove, 53... Mesa structure, 100... Nitride laminate, 200... Film-forming apparatus, 210... Processing chamber, 220... Base, 230... Heater, 240... Gas supply mechanism, 250... Processing gas Detailed description of the embodiment

[0034] Hereinafter, the nitride laminate and its manufacturing method according to the embodiment of the present invention will be described. First, as preliminary knowledge, the existing nitride laminate will be described. Figure 7 This is an example of the secondary ion mass spectrometry (SIMS) cross-section showing the thickness direction distribution of the impurity concentration such as iron (Fe) of the existing nitride laminate, showing the concentration distributions of Fe, magnesium (Mg), and silicon (Si).

[0035] Figure 7The exemplary sample is a nitride laminate obtained by epitaxially growing a GaN layer on a gallium nitride (GaN) substrate. In other words, it is a nitride laminate obtained by regrowing GaN that constitutes the GaN layer on GaN that constitutes the GaN substrate. The GaN substrate and the GaN layer in this example each contain Si intentionally added as an n-type impurity.

[0036] The GaN substrate is carried into the processing chamber of a film-forming apparatus for growing the GaN layer from the outside of the processing chamber. In other words, before being carried into this processing chamber, the GaN substrate is prepared in a state where it is taken out to the outside of the film-forming apparatus for growing the GaN that constitutes the GaN substrate. Subsequently, the surface of the GaN substrate is contaminated, and various impurities such as Fe adhere to the surface of the GaN substrate. In the conventional manufacturing technology of nitride laminates, the GaN layer is grown in a state where the impurities attached to the surface of the GaN substrate are not sufficiently removed.

[0037] In Figure 7 , the portion surrounded by the dashed ellipse indicates the vicinity of the stacking interface between the GaN substrate and the GaN layer. In the vicinity of the stacking interface, a raised portion indicating the impurity concentration distribution of Fe and Mg attached to the GaN substrate is observable. In addition, regarding the concentration distribution of Si, in the vicinity of the stacking interface, a raised portion indicating uneven distribution is also observable. Also, Si exists not only as an added impurity but also as an impurity attached due to contamination.

[0038] The impurities attached to the surface of the GaN substrate have an adverse effect on the quality of the crystal regrown thereon. When epitaxial growth is restarted on a contaminated surface, the crystallinity cannot be restored unless a growth of a certain thickness (for example, 4 μm or more) is performed.

[0039] In addition, the raised portion of the impurity concentration distribution in the vicinity of the stacking interface may deteriorate the device characteristics. For example, due to the inclusion of Fe or the inclusion of Mg, the group-III nitride becomes highly resistive. Therefore, the raised portion of the Fe concentration distribution or the raised portion of the Mg concentration distribution becomes an unintentionally formed high-resistance layer, for example, a factor that impedes the current flowing in the thickness direction in a vertical device. In addition, for example, the inclusion of Si causes the group-III nitride to become low resistive. Therefore, the raised portion of the Si concentration distribution becomes an unintentionally formed low-resistance layer, for example, a factor that increases the leakage current in a lateral device.

[0040] Also, in Figure 7 In the example shown, in order to compensate for the high resistance caused by Fe, etc., a GaN layer with a high Si concentration (Si highly doped layer) is formed on the GaN substrate, and then a GaN layer with a low Si concentration for device operation is formed. Due to impurity contamination, time and effort are also spent on forming the Si highly doped layer.

[0041] As described above, it is preferable to suppress the raised portion of the impurity concentration distribution formed near the stacking interface of the nitride stack. In the present embodiment, a manufacturing technique for a nitride stack is proposed that can suppress such a raised portion of the impurity concentration distribution.

[0042] Refer to Figure 1 Figs. (a) to Figure 2 Figs. (b), the manufacturing method of the nitride stack 100 of the embodiment will be described. As Figure 2 As shown in Figs. (b), the nitride stack 100 includes a substrate 11 and a film 21. The substrate 11 has at least a surface layer portion (a portion serving as a growth base for the film 21) 12 made of a group III nitride. The group III nitride constituting at least the surface layer portion 12 of the substrate 11 is referred to as a first group III nitride. The film 21 is made of a group III nitride. The group III nitride constituting the film 21 is referred to as a second group III nitride.

[0043] Figure 1 Fig. (a) is a schematic diagram showing a step of preparing the substrate 11 in a state where it is taken out of the film formation apparatus for growing the group III nitride (first group III nitride) constituting the surface layer portion 12. As described above, the substrate 11 is a substrate having at least a surface layer portion 12 made of a first group III nitride. The substrate 11 can be, for example, a self-supporting substrate having a total thickness made of a first group III nitride, or, for example, a stacked substrate having a film made of a first group III nitride formed on a base substrate.

[0044] Preparing the substrate 11 in a state where it is taken out of the film formation apparatus for growing the first group III nitride means a mode of discontinuous growth of the first group III nitride and the second group III nitride. In other words, it is a mode in which the first group III nitride is grown in the processing chamber of the film formation apparatus, and after being taken out of the processing chamber, it is transferred into the processing chamber of the same or another film formation apparatus, and the second group III nitride is regrown on the first group III nitride. After the first group III nitride is grown in the film formation apparatus, it is, for example, taken out into the atmosphere, or, for example, taken out into the atmosphere inside a glove box. Before regrowing the second group III nitride, for example, various processes can be performed on the first group III nitride using various apparatuses.

[0045] Since the first group III nitride, that is, the substrate 11 is taken out of the film formation apparatus to the outside, the first group III nitride is contaminated. As a result, impurities 14 such as Fe adhere to the surface 13 of the first group III nitride (the surface 13 of the surface layer portion 12 of the substrate 11). Here, in the present embodiment, the impurity 14 means at least any one impurity selected from the group consisting of Fe, Mg, chromium (Cr), and Si.

[0046] Figure 1(b) is a schematic diagram showing the process of forming the protective layer 15 on the substrate 11. In the process of forming the protective layer 15, a prescribed oxidation treatment is performed on the substrate 11 using the oxidation treatment apparatus 150, causing the outermost layer of the first group-III nitride to change into the protective layer 15 containing a group-III oxide. The oxidation treatment performed using the oxidation treatment apparatus 150 to form the protective layer 15 is hereinafter simply referred to as the oxidation treatment. As the oxidation treatment apparatus 150, a suitable one can be used according to the specific content of the oxidation treatment. As described below, for example, when performing steam oxidation treatment as the oxidation treatment, a steam oxidation treatment apparatus is used, and when performing anodic oxidation treatment, an anodic oxidation treatment apparatus is used.

[0047] The oxidation treatment is a treatment that changes the thickness of a part on the surface side (shallow side) of the outermost layer of the first group-III nitride, that is, the surface layer portion 12 of the substrate 11, into a group-III oxide. After the oxidation treatment, the first group-III nitride remains on the deeper side of the protective layer 15 with respect to the portion of the surface layer portion 12 that is oxidized. Thus, a surface 13a composed of the first group-III nitride is formed as the interface that contacts the protective layer 15 of the substrate 11. In other words, the protective layer 15 is formed on the surface 13a. Through the oxidation treatment, a nitride laminate 16, which is an intermediate of the nitride laminate 100 having the substrate 11 and the protective layer 15, is formed.

[0048] In the oxidation treatment, the protective layer 15 is formed by oxidizing the surface layer portion 12 while the impurity 14 is attached to the surface 13. Thus, the impurity 14 is disposed on the protective layer 15 side with respect to the surface 13a and exists in a state integrated with the protective layer 15. In other words, it is included in the protective layer 15. In the state where the impurity 14 exists integrally with the protective layer 15, the impurity 14 can exist in any form on the surface of the protective layer 15 or inside thereof.

[0049] Preferably, the protective layer 15 is formed so as to continuously cover the surface 13a of the first group-III nitride. In other words, it is preferable that the oxidation treatment continues until the surface 13a of the first group-III nitride is continuously covered by the protective layer 15.

[0050] In addition, it is preferable that the protective layer 15 has a thickness of 2 nm or more, preferably 5 nm or more, and more preferably 40 nm or more. In other words, it is preferable that the oxidation treatment continues until the thickness of the protective layer 15 reaches 2 nm or more, preferably 5 nm or more, and more preferably 40 nm or more.

[0051] Further, since the substrate 11 is taken out to the outside of the film-forming apparatus for growing the first group-III nitride, it is considered that an extremely thin natural oxide film is formed on the surface of the surface layer portion 12. However, in the present embodiment, the formation of the natural oxide film is not regarded as an oxidation treatment, and the natural oxide film is not regarded as the protective layer 15. This is because, as will be described in the comparison method described later, impurities 14 cannot be sufficiently removed during the formation and removal of the natural oxide film. In the present embodiment, the oxidation treatment means (non-natural oxidation,) a treatment for actively oxidizing the surface of the surface layer portion 12 using an oxidation treatment apparatus (an instrument for oxidation treatment) 150 to form the protective layer 15.

[0052] As the oxidation treatment for forming the protective layer 15, for example, a steam oxidation treatment is performed. In the steam oxidation treatment, steam is supplied to the substrate 11 as an oxidizing agent to oxidize the surface layer portion 12 of the first group-III nitride. Conditions for the steam oxidation treatment are as follows. N2 gas is bubbled in H2O heated to 96°C, and the N2 gas containing steam is supplied into the annealing chamber. Then, in the above atmosphere, heat treatment is performed at 950°C to oxidize the surface of the first group-III nitride (e.g., GaN). The thickness of the obtained oxide film is, for example, about 3.2 nm under a treatment time of 20 minutes.

[0053] As the oxidation treatment for forming the protective layer 15, additionally, for example, an anodic oxidation treatment is performed. Conditions for the anodic oxidation treatment are as follows. A solution in which propylene glycol and 3% tartaric acid are mixed at a ratio of 2:1 is used, and the pH is adjusted to 7.0 with sodium hydroxide. A potentiostat is used in the anodic oxidation, the electrode is Pt, and the reference electrode is Ag / AgCl. At room temperature, while irradiating the surface of the first group-III nitride (e.g., GaN) with UV light having a wavelength of 300 - 400 nm at an irradiation intensity of 4 mW / cm 2 a positive voltage is applied. The thickness of the obtained oxide film is, for example, about 100 nm under a treatment time of 20 minutes.

[0054] Further, the protective layer 15 can also be formed by other oxidation treatments. For example, the protective layer 15 can be formed by immersing the substrate 11 in high-concentration ozone water of 200 ppm or more for 10 minutes or more. Additionally, for example, the protective layer 15 can be formed by treating the substrate 11 with supercritical water at 30 MPa and 400°C for 10 minutes or more.

[0055] Figure 2 (a) is a schematic diagram showing the process of removing the protective layer 15 from the substrate 11, Figure 2(b) is a schematic diagram showing the process of growing the film 21 on the substrate 11. The manufacturing method of the nitride laminate 100 of the present embodiment is characterized in that, in the processing chamber 210 of the film forming apparatus 200 for growing the film 21, the process of removing the protective layer 15 and the process of growing the film 21 are continuously performed. In other words, between the process of removing the protective layer 15 and the process of growing the film 21, the substrate 11 is not taken out of the processing chamber 210 but remains inside the processing chamber 210.

[0056] The type of the film forming apparatus 200 is not particularly limited as long as it can perform the following processes. As the film forming apparatus 200, for example, a metalorganic vapor phase epitaxy (MOVPE) apparatus can be used. In Figure 2 (a) and Figure 2 (b), schematic diagrams of the film forming apparatus 200 are illustrated.

[0057] A susceptor 220 is provided in the processing chamber 210 of the film forming apparatus 200. The substrate 11 is placed on the susceptor 220. The susceptor 220 has a heater 230, and the heater 230 heats the substrate 11 to a predetermined processing temperature. A gas supply mechanism 240 supplies a processing gas 250 for each process into the processing chamber 210.

[0058] Referring to Figure 2 (a), the process of removing the protective layer 15 from the substrate 11 will be described. The process of removing the protective layer 15 from the substrate 11 is performed by heating the substrate 11 (nitride laminate 16) having the protective layer 15 formed thereon in a reducing atmosphere after being carried into the processing chamber 210 of the film forming apparatus 200. This process is preferably performed, for example, in an atmosphere containing hydrogen (more specifically, for example, an atmosphere containing H2 gas), and also, for example, in an atmosphere containing ammonia in addition to hydrogen. The heating temperature is, for example, preferably 900 °C or higher and 1300 °C or lower. The heating time is, for example, preferably 30 seconds or longer and 30 minutes or shorter. The H2 gas may also be supplied in a mixture with an inert gas such as N2 gas or Ar gas. By performing this process in an atmosphere added with ammonia, surface damage caused by thermal etching can be suppressed.

[0059] In this process, the removal of the protective layer 15 is continued until the entire surface 13a of the substrate 11 is exposed, in other words, until the group III nitride existing on the lower layer side of the protective layer 15 among the first group III nitrides is exposed. In this way, the protective layer 15 is removed, and then the impurity 14 is removed together with the protective layer 15.

[0060] Referring to Figure 2(b) A process of growing the film 21 on the substrate 11 will be described. The process of growing the film 21 on the substrate 11 is carried out as follows. After the process of removing the protective layer 15 from the substrate 11, without taking out the substrate 11 from the processing chamber 210, a second group-III nitride is grown on the surface 13a of the first group-III nitride exposed by removing the protective layer 15. Thus, the nitride laminate 100 having the substrate 11 and the film 21 is manufactured.

[0061] The second group-III nitride constituting the film 21 is grown, for example, by MOVPE. Among the group-III source gases, as the aluminum (Al) source gas, for example, trimethylaluminum (Al(CH3)3, TMA) gas is used. Among the group-III source gases, as the gallium (Ga) source gas, for example, trimethylgallium (Ga(CH3)3, TMG) gas is used. Among the group-III source gases, as the indium (In) source gas, for example, trimethylindium (In(CH3)3, TMI) gas is used. As the nitrogen (N) source gas as the group-V source gas, for example, ammonia (NH3) is used. As the carrier gas, for example, at least one of nitrogen gas (N2 gas) and hydrogen gas (H2 gas) can be used.

[0062] The growth temperature can be selected, for example, in the range of 700°C to 1400°C. The flow rate ratio of the group-V source gas to the group-III source gas, that is, the V / III ratio, can be selected, for example, in the range of 10 to 5000. The supply ratio of each source gas is adjusted according to the composition of the formed film 21.

[0063] Since the surface 13a of the first group-III nitride is a surface from which the impurity 14 has been removed, in the second group-III nitride grown thereon, the influence of the reduction in crystallinity caused by the impurity 14 is suppressed. Therefore, the second group-III nitride, that is, the film 21, does not necessarily need to be grown thick (for example, a thickness of 4 μm or more). Also, the film 21 can be grown thick (for example, a thickness of 4 μm or more) as needed.

[0064] As a target for suppressing the influence of the reduction in crystallinity caused by the impurity 14, for example, it can be cited that in a portion of the second group-III nitride (that is, the film 21) within a thickness of 4 μm from the interface with the first group-III nitride film (that is, from the surface 13a of the substrate 11), the full width at half maximum of the (0002) diffraction of the X-ray rocking curve is 300 seconds or less, and the full width at half maximum of the (10-12) diffraction is 400 seconds or less.

[0065] Refer to Figures 3 - 5 While comparing the characteristics of the impurity concentration distribution of the nitride laminate 100 of the embodiment with the characteristics of the impurity concentration distribution of the nitride laminates of the first and second comparative modes, it will be described. Figure 3 、 Figure 4 AndFigure 5 An example of the SIMS profiles of the samples of the embodiment, the first comparison method, and the second comparison method, showing the concentration distributions of Fe, Mg, and Cr.

[0066] The samples exemplified by the embodiment, the first comparison method, and the second comparison method are nitride laminates obtained by epitaxially growing a GaN layer on a GaN substrate. In this example, the GaN constituting the GaN substrate is the first group-III nitride, and the GaN constituting the GaN layer is the second group-III nitride. Hereinafter, the interface between the GaN substrate and the GaN layer, that is, the interface between the first group-III nitride and the second group-III nitride, will be simply referred to as the interface. The interface in the embodiment can usually be easily discriminated based on differences in crystal composition or doped impurities between the first group-III nitride and the second group-III nitride. However, even in the case where both the first group-III nitride and the second group-III nitride are undoped GaN crystals or low-Si doped crystals, the interface can still be discriminated. The details of the interface determination method in such an embodiment will be described later.

[0067] The sample of the embodiment is prepared by the following method: an oxidation treatment is performed on the GaN substrate exposed to the atmosphere to form a gallium oxide layer as a protective layer on the GaN substrate, and the GaN substrate with the protective layer formed thereon is transferred into a film-forming apparatus, and after removing the protective layer, the GaN layer is continuously grown.

[0068] The sample of the first comparison method is prepared by the following method: the GaN substrate exposed to the atmosphere is transferred into a film-forming apparatus to grow the GaN layer without performing the oxidation treatment as in the embodiment. The sample of the second comparison method is prepared by the following method: for the GaN substrate exposed to the atmosphere, an oxidation treatment is not performed, but after pickling treatment with a hydrofluoric acid solution, it is transferred into a film-forming apparatus to grow the GaN layer (that is, a method in which pickling treatment is added to the first comparison method). As the pickling treatment of the second comparison method, in addition to the above-mentioned hydrofluoric acid solution, a hydrochloric acid solution or the like can also be used. Generally, after pickling for 5 to 10 minutes, running water treatment with pure water is performed for 5 to 10 minutes.

[0069] Further, in the first and second comparison methods, before growing the GaN layer, in the film-forming apparatus, the native oxide film on the GaN substrate is removed by performing a heat treatment in a reducing atmosphere. This is the same as the heat treatment performed in the embodiment to remove the protective layer in a reducing atmosphere. However, the native oxide film is extremely thin compared to the protective layer. Therefore, the heat treatment time in the first and second comparison methods can be shorter than the heat treatment time in the embodiment. Specifically, compared to the heating time of 30 seconds or more (for removing the protective layer formed by the oxidation treatment) in the embodiment, the heating time (for removing the native oxide film) in the first and second comparison methods, for example, 10 seconds or less is sufficient. Further, in practice, even without performing an active heat treatment for removing the native oxide film, the native oxide film is sufficiently removed during the standby before growth.

[0070] In the first comparison method ( Figure 4 ), near the stacked interface between the GaN substrate and the GaN layer, a raised portion 31 of the Fe concentration distribution and a raised portion 32 of the Mg concentration distribution are clearly observed. In addition, near the stacked interface, a peak indicating the presence of trace amounts of Cr is also observed.

[0071] Further, in the first comparison method ( Figure 4 ), the formation of the native oxide film due to the atmospheric exposure of the GaN substrate and the removal of the native oxide film before growing the GaN layer are performed. However, in the formation and removal of the native oxide film, impurities such as Fe cannot be sufficiently removed.

[0072] In the second comparison method ( Figure 5 ), after the pickling treatment, compared to the first comparison method, Fe and Mg are in lower concentrations. The Cr concentration becomes below the detection limit of SIMS measurement (1×10 14 / cm 3 or less). The Fe concentration in the second comparison method is suppressed compared to the first comparison method, but the shape of the raised portion 31 is still at a significantly high level. The Mg concentration in the second comparison method is suppressed compared to the first comparison method, and the shape of the raised portion 32 is at a low level of trace degree.

[0073] In the embodiment ( Figure 3 ), through the process of forming and removing the protective layer, compared to the second comparison method of pickling treatment, Fe and Mg are in even lower concentrations. The Cr concentration becomes below the detection limit of SIMS measurement (1×10 14 / cm 3 or less). The Fe concentration in the embodiment is further suppressed compared to the second comparison method, and the shape of the raised portion 31 becomes as low as the trace degree level. The Mg concentration in the embodiment is further suppressed compared to the second comparison method, reaching a low level where the raised portion 32 is not observed.

[0074] Here, the so-called prominent bulge shape means that the concentration distribution shape of the bulge part showing a part with a prominently high impurity concentration is a curved shape. In a manner where the impurity concentration level is high, it can be said that the concentration distribution shape of the bulge part shows a curved shape. In contrast, the so-called trace-like bulge shape means that the contour shape of the bulge part is a discrete columnar shape where the measured value exceeds the detection lower limit. In a manner where the impurity concentration level is as low as approaching the detection lower limit, it can be said that the concentration distribution shape of the bulge part shows a trace shape.

[0075] In the first comparison method, a feature that the concentration level of Fe is higher than that of Mg can be seen. In the second comparison method and the embodiment, the same tendency can also be observed. Regarding Fe, it is considered that the concentration level is relatively high and it is difficult to remove, so the feature that there is a peak in the Fe concentration distribution near the stacking interface remains in the second comparison method and the embodiment. Also, by applying the method of the embodiment, Fe can be removed to the extent that there is no peak in the Fe concentration distribution near the stacking interface. Regarding Mg, it is considered that the concentration level is relatively low and it is easier to remove compared to Fe. The feature that there is a peak in the Mg concentration distribution near the stacking interface remains in the second comparison method, but does not remain in the embodiment.

[0076] Hereinafter, more detailed features of the impurity concentration distribution of the embodiment near the stacking interface will be described. In the first comparison method ( Figure 4 ), with respect to the bulge part 32, the level of the Mg concentration on the GaN substrate side is on the order of 1×10 14 / cm 3 , in other words, as low as approaching the detection lower limit. In addition, in the first comparison method, with respect to the bulge part 32, the level of the Mg concentration on the GaN layer side is as high as 1×10 15 / cm 3 . Thus, the concentration distribution shape of Mg shows such a stepped shape that it is relatively low in concentration on the GaN substrate side and relatively high in concentration on the GaN layer side with respect to the bulge part 32.

[0077] In the second comparison method ( Figure 5 ) where pickling treatment has been performed, as the concentration distribution shape of Mg, a stepped shape where it is relatively low in concentration on the GaN substrate side and relatively high in concentration on the GaN layer side with respect to the bulge part 32 is also observed. However, in the second comparison method, after pickling treatment, on the GaN substrate side, the level of the Mg concentration is further reduced, and almost no measured value higher than 1×10 14 / cm 3 is observed. In addition, on the GaN layer side, the Mg concentration is as low as 1×10 14 / cm 3 Level degree.

[0078] In the embodiment in which the formation and removal processes of the protective layer are performed ( Figure 3 ), as the concentration distribution shape of Mg, although the raised portion 32 was not observed, a stepped shape in which the concentration is relatively low on the GaN substrate side and relatively high on the GaN layer side was also observed. Almost no measurement value higher than 1×10 14 / cm 3 was observed on the GaN substrate side, and the Mg concentration on the GaN layer side was as low as 1×10 14 / cm 3 level degree, and this feature is the same as that of the second comparison method.

[0079] Based on the characteristic of such a stepped shape near the stacked interface according to the concentration distribution shape of Mg, for the concentration distribution evaluation of the second comparison method and the embodiment, the interface between the GaN substrate and the GaN layer, that is, the interface between the first group III nitride and the second group III nitride, is defined in the following manner.

[0080] Regarding the Mg concentration, in the region where the concentration is relatively low on the GaN substrate side, it can be called a region where the measurement values higher than 1×10 14 / cm 3 are sparse. Here, the so-called region where the measurement values higher than 1×10 14 / cm 3 are sparse means that starting from the first measurement value higher than 1×10 14 / cm 3 , within a depth of 0.5 μm on the GaN substrate side, there is no second measurement value higher than 1×10 14 / cm 3 such a region.

[0081] In contrast, regarding the Mg concentration, in the region where the concentration is relatively high on the GaN layer side, it can be called a region where the measurement values higher than 1×10 14 / cm 3 are dense. Here, the so-called region where the measurement values higher than 1×10 14 / cm 3 are dense means that starting from the first measurement value higher than 1×10 14 / cm 3 , within a depth of 0.5 μm on the GaN layer side, there is a second measurement value higher than 1×10 14 / cm 3 such a region.

[0082] This higher than 1×10 14 / cm 3The boundary between the sparse region and the dense region of the measurement values, that is, the depth position corresponding to the measurement value of the Mg concentration, is defined as the interface 41. In addition, a range with a thickness of 1 μm centered on the interface 41 is defined as the interface region 42, and a range with a thickness of 2 μm centered on the interface 41 is defined as the stacking region 43. The stacking region 43 represents the stack of the GaN substrate and the GaN layer. The interface region 42 represents the vicinity of the interface in the stack of the GaN substrate and the GaN layer.

[0083] In the so-called interface, it means the vicinity of the interface, that is, within the interface region 42. It is stipulated that the Fe concentration distribution has a peak in the interface, and the maximum value (peak concentration) CFe of the Fe concentration in the stacking region 43 exists within the interface region 42. Similarly, it is stipulated that the Mg concentration distribution has a peak in the interface, and the maximum value (peak concentration) CMg of the Mg concentration in the stacking region 43 exists within the interface region 42.

[0084] According to such a regulation, as the second comparison method Figure 5 The characteristics of the impurity concentration distribution in the exemplified sample, and those in the exemplified sample as an embodiment Figure 3 The characteristics of the impurity concentration distribution in the exemplified sample are compared in the following manner. The Fe concentration distribution of the second comparison method has a peak in the interface, and its peak concentration CFe is 4×10 16 / cm 3 or so. The Fe concentration distribution of the embodiment has a peak in the interface, and its peak concentration CFe is 3×10 15 / cm 3 or so. The peak concentration CFe of Fe in the embodiment is lower than the peak concentration CFe of Fe in the second comparison method, and can reach 2×10 16 / cm 3 or less, preferably 1×10 16 / cm 3 or less, and more preferably 5×10 15 / cm 3 or less.

[0085] The Mg concentration distribution of the second comparison method has a peak in the interface, and its peak concentration CMg is 3×10 15 / cm 3 or so. The Mg concentration distribution of the embodiment has the maximum value CMg (1×10 15 / cm 3 or so) of the Mg concentration in the stacking region 43 outside the interface region 42, that is, there is no peak in the interface, and the maximum value CMg2 of the Mg concentration within the interface region 42 is 7×10 14 / cm 3or less. The maximum value CMg2 of the Mg concentration in the interface region 42 in the embodiment is lower than the maximum value CMg of the Mg concentration in the interface region 42 in the second comparison method, and can reach 2×10 15 / cm 3 or less, preferably 1×10 15 / cm 3 or less. Also, in the embodiment, it can be said that Mg is removed to such an extent that the Mg concentration in the stacked region 43 has no significant difference between inside and outside the interface region 42. Therefore, by applying the method of the embodiment, the maximum value CMg of the Mg concentration in the stacked region 43 can (as in the example shown) exist outside the interface region 42 or inside the interface region 42. Figure 3 shown) can exist outside the interface region 42 or inside the interface region 42.

[0086] Also, as described above, by applying the method of the embodiment, the (maximum value of the) Cr concentration in the interface (inside the interface region 42) can be reduced to below the detection limit (1×10 14 / cm 3 or less).

[0087] In addition, it has also been confirmed that by applying the method of the embodiment, the Si concentration in the interface (inside the interface region 42) can be controlled as follows. When Si is not intentionally added to the first group-III nitride and the second group-III nitride, in other words, when Si is an impurity attached due to contamination, the (maximum value of the) Si concentration in the interface (inside the interface region 42) can be reduced to 1×10 16 / cm 3 or less, preferably 1×10 15 / cm 3 or less.

[0088] When Si is intentionally added to the first group-III nitride and the second group-III nitride (usually in the case where Si is added at a concentration level of about 1×10 16 / cm 3 in the first group-III nitride and the second group-III nitride respectively), the method of the embodiment is useful. For example, referring to Figure 7 , as described above, in the prior art, a raised portion showing uneven Si concentration distribution was observed at the stacked interface, and the maximum value of the Si concentration in the raised portion was a value as high as more than 10 times the added Si concentration, being 1×10 17 / cm 3 or more.

[0089] When Si is intentionally added to the first group-III nitride and the second group-III nitride, by applying the method of the embodiment, the height of such a protrusion can be made lower than before. As a specific target, it is possible to make the Si concentration at the interface (the maximum value of the Si concentration in the interface region 42) 5 times or less, preferably 2 times or less, with respect to the higher Si concentration at a position 1 μm above and below the interface (interface 41) between the first group-III nitride and the second group-III nitride (the upper and lower ends of the stacking region 43). In addition, the Si concentration (the maximum value) in the interface (in the interface region 42) can be made lower than 1×10 17 / cm 3 .

[0090] As described above, according to the present embodiment, impurities (such as Fe, Mg, Cr, etc.) attached to the surface of the first group-III nitride (due to contamination) can be removed. In addition, the growth of the second group-III nitride on the first group-III nitride can be achieved in a state where the non-uniform concentration distribution of impurities (such as Si) added to the first group-III nitride near the stacking interface is suppressed.

[0091] The stacking structure of the first group-III nitride and the second group-III nitride to which the method of the present embodiment is applied can be in various forms. The first and second group-III nitrides can both be n-type (for example, in the form of a vertical power device). The first and second group-III nitrides can also be p-type and n-type, or n-type and p-type, respectively (in the form of a pn diode). Also, the first and second group-III nitrides can both be p-type.

[0092] The first and second group-III nitrides can both be semi-insulating (for example, in the stacking form of the GaN channel termination in a GaN on GaN structure HEMT). The composition of the first group-III nitride and the composition of the second group-III nitride can also be different. For example, the first group-III nitride is GaN and the second group-III nitride is AlGaN (for example, in the form of a HEMT in which an AlGaN layer is regrown).

[0093] The surface (the interface with the second group-III nitride) 13a of the first group-III nitride does not have to be flat over the entire surface range and can have an uneven structure. Figure 6(a) is the first example of the manner in which the surface 13a of the first group-III nitride has a concavo-convex structure. In the first example, the surface 13a has a main surface 51 and a groove 52. The main surface 51 in the first example is a surface that is inclined within 3 degrees from the C-plane of the first group-III nitride crystal. The groove 52 in the first example has a side surface that is inclined, for example, by 30° or more and 90° or less from the main surface 51. In this example, it is, for example, conceived in the manner of a trench MOS. The first group-III nitride is, for example, GaN, and the second group-III nitride is, for example, AlGaN. In this example, after processing for forming the groove 52 is performed on the first group-III nitride (in other words, after the first group-III nitride is taken out of the film-forming apparatus), the second group-III nitride is regrown. In response to such regrowth, the second group-III nitride is formed at least on the side surface of the groove 52.

[0094] Figure 6 (b) is the second example of the manner in which the surface 13a of the first group-III nitride has a concavo-convex structure. In the second example, the surface 13a has a main surface 51 and a mesa structure 53. The main surface 51 in the second example is a surface that is inclined within 3 degrees from the C-plane of the first group-III nitride crystal. The mesa structure 53 in the second example has a side surface that is inclined, for example, by 30° or more and 90° or less from the main surface 51. In this example, it is, for example, conceived in the manner of a FINFET. The first group-III nitride is, for example, n-type GaN, and the second group-III nitride is, for example, p-type GaN. In this example, after processing for forming the mesa structure 53 is performed on the first group-III nitride (in other words, after the first group-III nitride is taken out of the film-forming apparatus), the second group-III nitride is regrown. In response to such regrowth, the second group-III nitride is formed at least on the side surface of the mesa structure 53.

[0095] In Figure 6 (a) and Figure 6 (b) In such a structure as shown, at the stacked interface between the first group-III nitride and the second group-III nitride, as described above, by the method of the present embodiment, the concentration of various impurities can be appropriately controlled. For example, the concentration of Fe at the interface can be suppressed to 2×10 16 / cm 3 or less.

[0096] As described above, in the method for manufacturing the nitride laminate 100 of the embodiment, for the substrate 11 (first group-III nitride) prepared in a state of being taken out of the film-forming apparatus, a prescribed oxidation treatment is performed using an oxidation treatment apparatus to form the protective layer 15, and the removal of the protective layer 15 and the growth of the film 21 (second group-III nitride) are continuously performed in the processing chamber 210 where the film 21 is grown.

[0097] Accordingly, it is possible to reduce the concentration of impurities (such as Fe, Mg, Cr, Si, etc.) on the surface 13a of the interface (regrowth interface) between the first group-III nitride and the second group-III nitride. In addition, accordingly, even if the second group-III nitride is not thickly stacked (even with a thickness of about 4 μm), it is possible to make the crystallinity of the second group-III nitride good. Further, by reducing the concentrations of Fe and Mg at the regrowth interface, it is possible to avoid a decrease in conductivity in this part, and there is no need to form a Si highly doped layer on the regrowth interface.

[0098] The oxidation treatment is performed in a state where impurities 14 are attached to the surface 13 of the substrate 11. Accordingly, instead of forming the protective layer 15 in situ after the formation of the first group-III nitride, it is possible to take out the substrate 11 to the outside of the film-forming apparatus and then perform it. In addition, there is no need to perform pickling or the like on the substrate 11 taken out to the outside of the film-forming apparatus in order to remove the impurities 14.

[0099] The oxidation treatment is preferably continued until the surface 13a of the first group-III nitride reaches a state where it is continuously covered by the protective layer 15 (the entire surface of the surface 13a is covered by the protective layer 15). By forming the protective layer 15 into a continuous layer (a dense layer without pinholes), there are no gaps on the surface 13a of the first group-III nitride, and it is possible to remove the impurities 14 along with the removal of the protective layer 15.

[0100] The oxidation treatment is preferably continued until the thickness of the protective layer 15 reaches 2 nm or more, preferably 5 nm or more, and more preferably 40 nm or more. By making the thickness of the protective layer 15 2 nm or more, it is possible to realize a protective layer 15 with few pinholes, and it is possible to effectively remove the impurities 14 when the protective layer 15 is removed. In addition, if the thickness of the protective layer 15 is 40 nm or more, it is possible to completely eliminate the pinholes, and it is possible to more reliably reduce the residual impurity concentration at the interface to about the background level of SIMS. Further, the thickness of the protective layer 15 has no upper limit in particular, but if it is too thick, its formation and removal require a long time, which may lead to a decrease in the productivity of the nitride laminate 100 and an increase in the manufacturing cost. Therefore, it is desirable that the thickness of the protective layer 15 is, for example, 300 nm or less, preferably 150 nm or less.

[0101] Further, in the present embodiment, as the substrate 11, an epitaxial substrate in which a first group-III nitride is epitaxially grown on a different substrate (not composed of a group-III nitride) (hereinafter referred to as the former method) can be used. However, as the substrate 11, it is preferable to use an epitaxial substrate in which a first group-III nitride is grown on a self-supporting substrate whose total thickness is composed of a first group-III nitride or a self-supporting substrate composed of a group-III nitride (the same substrate) (in other words, the substrate 11 includes a self-supporting substrate composed of a group-III nitride / hereinafter referred to as the latter method). This is based on the following insight: in the latter method, compared with the former method, the oxide film (protective layer 15) formed by the oxidation treatment is denser and has a flatter surface.

[0102] The oxidation treatment is performed, for example, by a steam oxidation method or, for example, by an anodic oxidation method. By performing the oxidation treatment using these methods, the protective layer 15 can be made into a continuous layer having the above thickness. As a result, the above-described effects can be obtained more reliably.

[0103] Through the oxidation treatment, a nitride laminate 16, which is an intermediate of the nitride laminate 100 having the substrate 11 and the protective layer 15, is formed. Since the protective layer 15 is formed on the surface 13a of the first group-III nitride, even when the nitride laminate (intermediate) 16 is exposed to the atmosphere, and also when it is housed in a resin container and stored and circulated in this state for a long time, further attachment of impurities to the surface 13a of the first group-III nitride can be avoided.

[0104] In addition, the protective layer 15 is composed of a group-III oxide having lower etching resistance than the group-III nitride, and thus can be more easily removed in the gas phase. Therefore, by removing the protective layer 15 in the processing chamber 210 in which the film 21 containing the second group-III nitride is grown, and then continuously forming the film 21 containing the second group-III nitride, contamination of the surface 13a, which is the interface (regrowth interface) between the first group-III nitride and the second group-III nitride, can be prevented, and the impurity concentration can be reduced.

[0105] In the process of removing the protective layer 15, the removal of the protective layer 15 is continued until the surface 13a of the substrate 11 is exposed, in other words, until the group-III nitride existing on the lower layer side of the protective layer 15 among the first group-III nitrides is exposed. The protective layer 15 contains impurities 14. By continuously removing (thermal etching) the protective layer 15 until the surface 13a is exposed, the impurities 14 can be removed from the surface 13a of the first group-III nitride together with the protective layer 15. As a result, the above-described effects can be obtained more reliably.

[0106] After the removal of the protective layer 15, a nitride laminate 100 having a substrate 11 and a film 21 is fabricated by growing the film 21 on the substrate 11. The concentration distribution of Fe in the interface between the substrate 11 and the film 21, that is, the interface between the first group-III nitride and the second group-III nitride, generally has a peak in this interface, and the peak concentration is 2×10 16 / cm 3 or less, preferably 1×10 16 / cm 3 or less, and more preferably 5×10 15 / cm 3 or less. In addition, the maximum value of the Mg concentration in this interface is 2×10 15 / cm 3 or less, preferably 1×10 15 / cm 3 or less.

[0107] In the nitride laminate 100, since the surface 13a of the substrate 11 that is the basis of the film 21, that is, the impurity concentration in the regrowth interface is low (contamination is suppressed), even if the second group-III nitride constituting the film 21 does not grow thickly (for example, even if the thickness is about 4 μm or less), its crystallinity can be made good. In addition, by reducing the concentrations of Fe and Mg in the regrowth interface, a decrease in the conductivity of this part can be avoided, and it is not necessary to form a Si highly doped layer on the regrowth interface.

[0108] <Preferred embodiments of the present invention>

[0109] Hereinafter, preferred embodiments of the present invention will be noted.

[0110] (Note 1)

[0111] A method for manufacturing a nitride laminate, comprising the following steps:

[0112] (a) A step of preparing a substrate having at least a surface layer portion made of a first group-III nitride in a state where it is taken out to the outside of a film-forming apparatus for growing the first group-III nitride;

[0113] (b) A step of subjecting the substrate to a prescribed oxidation treatment using an oxidation treatment apparatus to change the outermost layer of the first group-III nitride into a protective layer containing a group-III oxide;

[0114] (c) A step of loading the substrate into a prescribed processing chamber, heating it in a reducing atmosphere, and removing the protective layer from the surface of the substrate;

[0115] (d) A step of growing a second group-III nitride on the surface of the first group-III nitride exposed by removing the protective layer without taking out the substrate from the processing chamber.

[0116] (Note 2)

[0117] The method for manufacturing a nitride laminate according to Note 1, wherein in the step (b), the surface layer portion of the first group-III nitride is oxidized in a state where at least any one impurity selected from the group consisting of Fe, Mg, Cr, and Si adheres to the surface of the first group-III nitride.

[0118] (Note 3)

[0119] The method for manufacturing a nitride laminate according to Note 1, wherein in the step (b), the oxidation treatment is continued until the surface of the first group-III nitride reaches a state where it is continuously covered by the protective layer.

[0120] (Note 4)

[0121] The method for manufacturing a nitride laminate according to Note 1, wherein in the step (b), the oxidation treatment is continued until the thickness of the protective layer reaches 2 nm or more (preferably 5 nm, more preferably 40 nm or more).

[0122] (Note 5)

[0123] The method for manufacturing a nitride laminate according to Note 1, wherein in the step (b), water vapor is supplied to the substrate as an oxidant to oxidize the surface layer portion of the first group-III nitride.

[0124] (Note 6)

[0125] The method for manufacturing a nitride laminate according to Note 1, wherein in the step (b), an anodic oxidation method is used to oxidize the surface layer portion of the first group-III nitride.

[0126] (Note 7)

[0127] The method for manufacturing a nitride laminate according to Note 1, wherein in the step (c), the removal of the protective layer is continued until the group-III nitride existing on the lower layer side of the protective layer among the first group-III nitrides is exposed.

[0128] (Note 8)

[0129] The method for manufacturing a nitride laminate according to Note 2, wherein in the step (c), the impurity adhering to the surface of the first group-III nitride is removed together with the protective layer.

[0130] (Note 9)

[0131] According to the method for manufacturing a nitride laminate described in Note 1, in the step (c), the protective layer is removed from the surface of the substrate by heating the substrate to a temperature of 900 °C or higher in a processing chamber of a film-forming apparatus for growing the second group-III nitride in an atmosphere containing hydrogen.

[0132] (Note 10)

[0133] According to the method for manufacturing a nitride laminate described in Note 1, in the step (c), the protective layer is removed from the surface of the substrate by heating the substrate to a temperature of 900 °C or higher in a processing chamber of a film-forming apparatus for growing the second group-III nitride in an atmosphere containing hydrogen and ammonia.

[0134] (Note 11)

[0135] According to the method for manufacturing a nitride laminate according to any one of Notes 1 to 10, characterized in that both the first and second group-III nitrides are n-type.

[0136] (Note 12)

[0137] According to the method for manufacturing a nitride laminate according to any one of Notes 1 to 10, characterized in that both the first and second group-III nitrides are semi-insulating.

[0138] (Note 13)

[0139] According to the method for manufacturing a nitride laminate according to any one of Notes 1 to 10, characterized in that the first group-III nitride is GaN and the second group-III nitride is AlGaN.

[0140] (Note 14)

[0141] According to the method for manufacturing a nitride laminate according to any one of Notes 1 to 10, characterized in that the first and second group-III nitrides are p-type and n-type, respectively, or n-type and p-type, respectively.

[0142] (Note 15)

[0143] According to the method for manufacturing a nitride laminate according to any one of Notes 1 to 10, characterized in that the first group-III nitride is GaN, and the surface of the first group-III nitride has: a main plane inclined within 3° from the C plane; and a groove having a side surface inclined by 30° or more and 90° or less from the main plane, and the second group-III nitride is AlGaN.

[0144] (Note 16)

[0145] The method for manufacturing a nitride laminate according to any one of Notes 1-10, wherein the first group-III nitride is n-type GaN, and the surface of the first group-III nitride has: a main surface inclined within 3° from the C plane; a mesa structure having side surfaces inclined by 30° or more and 90° or less from the main surface, and the second group-III nitride is p-type GaN.

[0146] (Note 17)

[0147] A nitride laminate having:

[0148] a substrate at least in the surface layer portion thereof being composed of a first group-III nitride;

[0149] a protective layer containing a group-III oxide formed on the surface of the first group-III nitride.

[0150] (Note 18)

[0151] The nitride laminate according to Note 17, wherein the protective layer is formed so as to continuously cover the surface of the first group-III nitride.

[0152] (Note 19)

[0153] The nitride laminate according to Note 17, wherein the protective layer has a thickness of 2 nm or more (preferably 5 nm or more, more preferably 40 nm or more).

[0154] (Note 20)

[0155] The nitride laminate according to any one of Notes 17 to 20, wherein the protective layer contains at least any one impurity selected from the group consisting of Fe, Mg, Cr, and Si.

[0156] (Note 21)

[0157] A nitride laminate comprising:

[0158] a substrate at least in the surface layer portion thereof being composed of a first group-III nitride;

[0159] a film containing a second group-III nitride formed on the surface of the first group-III nitride,

[0160] the concentration distribution of Fe in the interface between the first group-III nitride and the second group-III nitride has a peak in the interface, and the peak concentration is 2×10 16 / cm 3 or less (preferably 1×10 16 / cm 3 or less, more preferably 5×10 15 / cm 3 or less).

[0161] (Note 22)

[0162] The nitride laminate according to Note 21, wherein the concentration of Mg in the interface between the first group-III nitride and the second group-III nitride is 2×10 16 / cm 3 or less (preferably 1×10 16 / cm 3 or less).

[0163] (Note 23)

[0164] The nitride laminate according to Note 21, wherein the concentration of Cr in the interface between the first group-III nitride and the second group-III nitride is 1×10 14 / cm 3 or less.

[0165] (Note 24)

[0166] The nitride laminate according to Note 21, wherein the concentration of Si in the interface between the first group-III nitride and the second group-III nitride is 1×10 16 / cm 3 or less (preferably 1×10 15 / cm 3 or less).

[0167] (Note 25)

[0168] The nitride laminate according to Note 21, wherein the concentration of Si in the interface between the first group-III nitride and the second group-III nitride is 5 times or less (preferably 2 times or less) relative to the higher Si concentration at a position 1 μm above or below the interface between the first group-III nitride and the second group-III nitride.

[0169] (Note 26)

[0170] The nitride laminate according to any one of Notes 21 to 25, wherein, among the second group-III nitrides, in a portion within a range of 4 μm in thickness from the interface with the first group-III nitride, the full width at half maximum of the (0002) diffraction of the X-ray rocking curve is 300 seconds or less, and the full width at half maximum of the (10-12) diffraction is 400 seconds or less.

[0171] (Note 27)

[0172] A nitride laminate comprising:

[0173] A substrate having at least a surface layer portion made of a first group-III nitride;

[0174] A film containing a second group-III nitride formed on the surface of the first group-III nitride,

[0175] The first group-III nitride is GaN, and the surface of the first group-III nitride has a main plane inclined within 3° from the C plane; a groove having a side surface inclined by 30° or more and 90° or less from the main plane,

[0176] The second group-III nitride is AlGaN, and the second group-III nitride is formed at least on the side surface of the groove of the first group-III nitride,

[0177] The concentration of Fe in the interface between the first group-III nitride and the second group-III nitride is 2×10 16 / cm 3 or less.

[0178] (Note 28)

[0179] A nitride laminate, comprising:

[0180] A substrate at least the surface layer portion of which is composed of a first group-III nitride;

[0181] A film containing a second group-III nitride formed on the surface of the first group-III nitride,

[0182] The first group-III nitride is n-type GaN, and the surface of the first group-III nitride has a main plane inclined within 3° from the C plane; a mesa structure having a side surface inclined by 30° or more and 90° or less from the main plane,

[0183] The second group-III nitride is p-type GaN, and the second group-III nitride is formed at least on the side surface of the mesa structure of the first group-III nitride,

[0184] The concentration of Fe in the interface between the first group-III nitride and the second group-III nitride is 2×10 16 / cm 3 or less.

Claims

1. A method for manufacturing a nitride laminate, wherein, It has the following processes: (a) A process of preparing a substrate having at least a surface layer portion composed of a first group-III nitride in a state of being taken out to the outside of a film forming apparatus for growing the first group-III nitride; (b) A process of subjecting the substrate to a prescribed oxidation treatment using an oxidation treatment apparatus to change the outermost surface layer of the first group-III nitride into a protective layer containing a group-III oxide; (c) A process of loading the substrate into a prescribed processing chamber, heating it in a reducing atmosphere, and removing the protective layer from the surface of the substrate; and (d) A process of growing a second group-III nitride on the surface of the first group-III nitride exposed by removing the protective layer without taking out the substrate from the processing chamber.

2. The manufacturing method of the nitride laminate according to claim 1, wherein, In the above (b), the surface layer portion of the first group-III nitride is oxidized in a state where at least any one kind of impurity selected from the group consisting of Fe, Mg, Cr, and Si adheres to the surface of the first group-III nitride.

3. The manufacturing method of the nitride laminate according to claim 1, wherein, In the above (b), the oxidation treatment is continued until the surface of the first group-III nitride reaches a state of being continuously covered by the protective layer.

4. The method for manufacturing a nitride laminate according to claim 1, wherein, In the above (b), the oxidation treatment is continued until the thickness of the protective layer reaches 2 nm or more.

5. The manufacturing method of the nitride laminate according to claim 1, wherein, In the above (b), water vapor is supplied to the substrate as an oxidizing agent to oxidize the surface layer portion of the first group-III nitride.

6. The manufacturing method of the nitride laminate according to claim 1, wherein, In the above (b), an anodic oxidation method is used to oxidize the surface layer portion of the first group-III nitride.

7. The manufacturing method of the nitride laminate according to claim 1, wherein, In the above (c), the removal of the protective layer is continued until the group-III nitride existing on the lower layer side of the protective layer among the first group-III nitrides is exposed.

8. The manufacturing method of the nitride laminate according to claim 2, wherein, In the above (c), the impurity adhering to the surface of the first group-III nitride is removed together with the protective layer.

9. The manufacturing method of the nitride laminate according to claim 1, wherein, In the above (c), the protective layer is removed from the surface of the substrate by heating the substrate to a temperature of 900 °C or higher in a hydrogen-containing atmosphere in the processing chamber of the film forming apparatus for growing the second group-III nitride.

10. The manufacturing method of the nitride laminate according to claim 1, wherein, In the above (c), the protective layer is removed from the surface of the substrate by heating the substrate to a temperature of 900 °C or higher in an atmosphere containing hydrogen and ammonia in the processing chamber of the film forming apparatus for growing the second group-III nitride.

11. The manufacturing method of the nitride laminate according to any one of claims 1 to 10, characterized in that, Both the first group-III nitride and the second group-III nitride are n-type.

12. The method for manufacturing a nitride laminate according to any one of claims 1 to 10, characterized in that, Both the first group-III nitride and the second group-III nitride are semi-insulating.

13. The manufacturing method of the nitride laminate according to any one of claims 1 to 10, characterized in that, The first group-III nitride is GaN, and the second group-III nitride is AlGaN.

14. The method for manufacturing a nitride laminate according to any one of claims 1 to 10, characterized in that, The first group-III nitride and the second group-III nitride are respectively p-type and n-type, or respectively n-type and p-type.

15. The method for manufacturing a nitride laminate according to any one of claims 1 to 10, characterized in that, The first group-III nitride is GaN, and the surface of the first group-III nitride has a main plane inclined within 3° with respect to the C plane; and a groove having a side surface inclined by 30° or more and 90° or less with respect to the main plane, and the second group-III nitride is AlGaN.

16. The manufacturing method of the nitride laminate according to any one of claims 1 to 10, characterized in that, The first group-III nitride is n-type GaN, and the surface of the first group-III nitride has a main plane inclined within 3° with respect to the C plane; a mesa structure having side planes inclined more than 30° and less than 90° with respect to the main plane. The second group-III nitride is p-type GaN.

17. A nitride laminate, comprising: a substrate having at least a surface layer portion composed of a first group-III nitride; a protective layer containing a group-III oxide formed on the surface of the first group-III nitride.

18. The nitride laminate according to claim 17, wherein, The protective layer is formed so as to continuously cover the surface of the first group-III nitride.

19. The nitride laminate according to claim 17, wherein, The protective layer has a thickness of 2 nm or more.

20. The nitride laminate according to any one of claims 17 to 19, wherein, The protective layer contains at least any one impurity selected from the group consisting of Fe, Mg, Cr, and Si.

21. A nitride laminate, comprising: a substrate having at least a surface layer portion composed of a first group-III nitride; a film containing a second group-III nitride formed on the surface of the first group-III nitride, The concentration distribution of Fe in the interface between the first group-III nitride and the second group-III nitride has a peak in the interface, and the peak concentration is 2×10 16 / cm 3 or less.

22. The nitride laminate according to claim 21, wherein, The concentration of Mg in the interface between the first group-III nitride and the second group-III nitride is 2×10 15 / cm 3 or less.

23. The nitride laminate according to claim 21, wherein, The concentration of Cr in the interface between the first group-III nitride and the second group-III nitride is 1×10 14 / cm 3 or less.

24. The nitride laminate according to claim 21, wherein, The concentration of Si in the interface between the first group-III nitride and the second group-III nitride is 1×10 16 / cm 3 or less.

25. The nitride laminate according to claim 21, wherein, The concentration of Si in the interface between the first group-III nitride and the second group-III nitride is 5 times or less with respect to the higher Si concentration at a position 1 μm above and below the interface between the first group-III nitride and the second group-III nitride.

26. The nitride laminate according to any one of claims 21 to 25, wherein, Among the second group-III nitrides, in the portion within a thickness of 4 μm from the interface with the first group-III nitride, the full width at half maximum of the (0002) diffraction of the X-ray rocking curve is 300 seconds or less, and the full width at half maximum of the (10-12) diffraction is 400 seconds or less.

27. A nitride laminate, comprising: a substrate having at least a surface layer portion composed of a first group-III nitride; a film containing a second group-III nitride formed on the surface of the first group-III nitride, The first group-III nitride is GaN, and the surface of the first group-III nitride has a main plane inclined within 3° with respect to the C plane; a groove having side planes inclined more than 30° and less than 90° with respect to the main plane, The second group-III nitride is AlGaN, and the second group-III nitride is formed at least on the side planes of the groove of the first group-III nitride. The concentration of Fe in the interface between the first group-III nitride and the second group-III nitride is 2×10 16 / cm 3 or less.

28. A nitride laminate, comprising: a substrate having at least a surface layer portion composed of a first group-III nitride; a film containing a second group-III nitride formed on the surface of the first group-III nitride, The first group-III nitride is n-type GaN, and the surface of the first group-III nitride has a main plane inclined within 3° with respect to the C plane; a mesa structure having side planes inclined more than 30° and less than 90° with respect to the main plane, The second group-III nitride is p-type GaN, and the second group-III nitride is formed at least on the side planes of the mesa structure of the first group-III nitride. The concentration of Fe in the interface between the first group-III nitride and the second group-III nitride is 2×10 16 / cm 3 or less.

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