Nitride laminate manufacturing method, and nitride laminate

Abstract

To provide a technique capable of reducing bad influences of impurities adhered to a surface of a first III-group nitride, when a second III-group nitride is regrown on the first III-group nitride in a non-continuous growth manner.SOLUTION: A nitride laminate manufacturing method has: a step (a) of preparing a substrate constituted of a first III-group nitride at least on a surface layer portion under a condition that it is picked up outside a film deposition device for growing the first III-group nitride; a step (b) of changing an outermost layer of the first III-group nitride to a protection layer made of a III-group oxide by applying predetermined oxidation treatment to the substrate using an oxidation treatment device; a step (c) of removing the protection layer from a surface of the substrate by delivering the substrate into a predetermined treatment chamber and heating it under a reduction atmosphere; and a step (d) of growing a second III-group nitride on the surface of the first III-group nitride exposed by removing the protection layer without delivering the substrate from the treatment chamber.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Group III nitrides such as gallium nitride (GaN) are used as materials for manufacturing semiconductor devices such as light-emitting elements, transistors, etc. Nitride stacks in which a GaN layer is epitaxially grown on a GaN substrate have attracted attention because of the high quality of the GaN layer (see, for example, Non-Patent Document 1, for the use of GaN substrates for growing high-quality GaN layers).

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

[0004] Typically, as in the case of growing a GaN layer on a GaN substrate, a second Group III nitride may be regrown on a first Group III nitride serving as a growth base in a non-continuous manner. In such cases, impurities may adhere to the surface of the first Group III nitride due to the first Group III nitride being removed from the deposition apparatus after growth of the first Group III nitride. The adhered impurities adversely affect the growth of the second Group III nitride. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Fujikura, Isamu, and 8 others, "Development of GaN Single Crystal Substrates," Sumitomo Chemical, 2018, pp. 38-47 Summary of the Invention [Problem to be solved by the invention]

[0006] One object of the present invention is to provide a technique capable of reducing the adverse effects of impurities adhering to the surface of a first group-III nitride when regrowing a second group-III nitride in a manner that is not continuous growth on the first group-III nitride.

Means for Solving the Problems

[0007] According to one aspect of the present invention, (a) preparing a substrate at least a surface layer portion of which is composed of a first group-III nitride, in a state where it is taken out of a film forming apparatus in which the first group-III nitride has been grown; (b) performing a predetermined 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 made of a group-III oxide; (c) introducing the substrate into a predetermined processing chamber and heating it in a reducing atmosphere to remove the protective layer from the surface of the substrate; (d) growing a second group-III nitride on the surface of the first group-III nitride exposed by the removal of the protective layer without taking the substrate out of the processing chamber; A method for manufacturing a nitride laminate having the above steps is provided. is provided.

[0008] According to another aspect of the present invention, a substrate at least a surface layer portion of which is composed of a first group-III nitride, and a protective layer made of a group-III oxide formed on the surface of the first group-III nitride, A nitride laminate having the above components is provided.

[0009] According to still another aspect of the present invention, a substrate at least a surface layer portion of which is composed of a first group-III nitride, and a film made of a second group-III nitride formed on the surface of the first group-III nitride. The concentration distribution of iron (Fe) at 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, in a nitride laminate is provided.

Advantages of the Invention

[0010] There is provided a technique capable of reducing the adverse effects of impurities adhering to the surface of a first group-III nitride when regrowing a second group-III nitride in a non-consecutive growth manner on the first group-III nitride.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0012] Hereinafter, a nitride laminate and a method for manufacturing the same according to embodiments of the present invention will be described. First, as preliminary knowledge, a conventional nitride laminate will be described. FIG. 7 is an example of a secondary ion mass spectrometry (SIMS) profile showing the thickness-direction distribution of impurity concentrations such as iron (Fe) in a conventional nitride laminate, and shows the concentration distributions of Fe, magnesium (Mg), and silicon (Si).

[0013] The sample illustrated in FIG. 7 is a nitride laminate in which a GaN layer is epitaxially grown on a gallium nitride (GaN) substrate, that is, a nitride laminate in which GaN constituting the GaN layer is regrown on GaN constituting the GaN substrate. Each of the GaN substrate and the GaN layer in this example contains Si intentionally added as an n-type impurity.

[0014] 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. That is, the GaN substrate is prepared in a state of being taken out of the film-forming apparatus that grew the GaN constituting the GaN substrate before being carried into the processing chamber. Along with this, the surface of the GaN substrate is contaminated, and various impurities such as Fe are attached to the surface of the GaN substrate. In the conventional manufacturing technology of nitride laminates, the growth of the GaN layer has been performed while the impurities attached to the surface of the GaN substrate are not sufficiently removed.

[0015] In FIG. 7, the portion surrounded by the dashed ellipse indicates the vicinity of the lamination interface between the GaN substrate and the GaN layer. In the vicinity of the lamination interface, a raised portion of the impurity concentration distribution indicating the presence of Fe and Mg attached to the GaN substrate is observed. Further, also with respect to the concentration distribution of Si, a raised portion indicating a bias in the distribution is observed in the vicinity of the lamination interface. Note that Si may exist not only as an added impurity but also as an impurity attached by contamination.

[0016] Impurities adhering 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 surface contaminated with impurities, the crystallinity does not recover unless growth to a certain thickness (for example, 4 μm or more) is performed.

[0017] In addition, the raised portion of the impurity concentration distribution near the stacking interface can deteriorate the device characteristics. For example, due to the inclusion of Fe or 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, which is a factor inhibiting the current flowing in the thickness direction in a vertical device, for example. Also, for example, due to the inclusion of Si, the group III nitride becomes low-resistive. Therefore, the raised portion of the Si concentration distribution becomes an unintentionally formed low-resistance layer, which is a factor increasing the leakage current in a lateral device, for example.

[0018] In the example shown in FIG. 7, a GaN layer with a high Si concentration (Si highly doped layer) for compensating for the high resistance caused by Fe or the like is formed on the GaN substrate, and then a GaN layer with a low Si concentration used for device operation is formed. Due to impurity contamination, the labor of forming the Si highly doped layer is also incurred.

[0019] As described above, it is preferable to suppress the raised portion of the impurity concentration distribution formed near the stacking interface of the nitride laminate. In the present embodiment, a manufacturing technique for a nitride laminate capable of suppressing such a raised portion of the impurity concentration distribution is proposed.

[0020] With reference to FIGS. 1(a) to 2(b), a method for manufacturing a nitride laminate 100 according to an embodiment will be described. As shown in FIG. 2(b), the nitride laminate 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.

[0021] FIG. 1(a) is a schematic diagram showing a step of preparing the substrate 11 in a state where it is taken out of a film formation apparatus in which a group III nitride (first group III nitride) constituting the surface layer portion 12 is grown. As described above, the substrate 11 is a substrate in which at least the surface layer portion 12 is made of the first group III nitride. The substrate 11 may be, for example, a self-supporting substrate entirely made of the first group III nitride, or may be, for example, a laminated substrate having a film made of the first group III nitride formed on a base substrate.

[0022] Preparing the substrate 11 in a state where it is taken out of the film formation apparatus in which the first group III nitride is grown means that the first group III nitride and the second group III are not continuously grown, that is, after growing the first group III nitride in the processing chamber of the film formation apparatus and carrying it out of the processing chamber, it is carried 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. The first group III nitride is carried out, for example, into the atmosphere after being grown in the film formation apparatus, or into the atmosphere in a glove box, for example. Before regrowing the second group III nitride, for example, a process of processing the first group III nitride using various apparatuses may be performed.

[0023] Due to the transfer of the first group-III nitride, i.e., the substrate 11, from the film-forming 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 of the impurities selected from the group consisting of Fe, Mg, chromium (Cr), and Si.

[0024] FIG. 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 predetermined oxidation treatment is performed on the substrate 11 using the oxidation treatment apparatus 150, and the outermost layer of the first group-III nitride is changed into the protective layer 15 made of group-III oxide. The oxidation treatment performed to form the protective layer 15 using the oxidation treatment apparatus 150 is hereinafter simply referred to as the oxidation treatment. As the oxidation treatment apparatus 150, an appropriate one may be used according to the specific content of the oxidation treatment. As described below, when, for example, steam oxidation treatment is performed as the oxidation treatment, a steam oxidation treatment apparatus is used, and when, for example, anodic oxidation treatment is performed, an anodic oxidation treatment apparatus is used.

[0025] The oxidation treatment is a treatment for changing a part of the thickness 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 group-III oxide. After the oxidation treatment, the first group-III nitride remains on the deeper side than the protective layer 15 which is the oxidized portion of the surface layer portion 12. As a result, a surface 13a composed of the first group-III nitride is formed as an interface in contact with the protective layer 15 of the substrate 11. In other words, the protective layer 15 is formed on the surface 13a. By 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.

[0026] In the oxidation treatment, the surface layer portion 12 is oxidized while the impurity 14 remains attached to the surface 13, thereby forming the protective layer 15. As a result, the impurity 14 is disposed on the protective layer 15 side rather than the surface 13a and exists integrally with the protective layer 15, that is, it is included in the protective layer 15. The state in which the impurity 14 exists integrally with the protective layer 15 can be either a form in which the impurity 14 exists on the surface of the protective layer 15 or a form in which it exists inside thereof.

[0027] The protective layer 15 is preferably formed so as to continuously cover the surface 13a of the first group III nitride. That is, 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.

[0028] Also, the protective layer 15 preferably has a thickness of 2 nm or more, preferably 5 nm or more, more preferably 40 nm or more. That is, it is preferable that the oxidation treatment continues until the thickness of the protective layer 15 reaches a thickness of 2 nm or more, preferably 5 nm or more, more preferably 40 nm or more.

[0029] Note that it is considered that a very thin natural oxide film is formed on the surface of the surface layer portion 12 by taking out the substrate 11 to the outside of the film forming apparatus in which the first group III nitride is grown. However, in the present embodiment, the formation of the natural oxide film is not treated as an oxidation treatment, and the natural oxide film is not treated as the protective layer 15. This is because sufficient removal of the impurity 14 cannot be achieved by the formation and removal of the natural oxide film, as will be described in the comparative form described later. In the present embodiment, the oxidation treatment means a treatment for forming the protective layer 15 by positively oxidizing the surface of the surface layer portion 12 using an oxidation treatment apparatus (a tool for oxidation treatment) 150 (not natural oxidation).

[0030] As the oxidation treatment for forming the protective layer 15, for example, 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. Examples of the conditions for the steam oxidation treatment are as follows. N2 gas is bubbled into H2O heated to 96°C, and the N2 gas containing steam is supplied into the annealing chamber. Then, heat treatment is performed at 950°C in the above atmosphere to oxidize the surface of the first group III nitride (for example, GaN). The obtained oxide film thickness is, for example, about 3.2 nm for a treatment time of 20 minutes.

[0031] As the oxidation treatment for forming the protective layer 15, for example, anodic oxidation treatment is also performed. Examples of the 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 for anodic oxidation, and the counter electrode is Pt and the reference electrode is Ag / AgCl. At room temperature, while irradiating the surface of the first group III nitride (for example, 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 obtained oxide film thickness is, for example, about 100 nm for a treatment time of 20 minutes.

[0032] Note that the protective layer 15 may also be formed by other oxidation treatments. For example, the protective layer 15 may be formed by immersing the substrate 11 in high-concentration ozone water of 200 ppm or more for 10 minutes or more. Also, for example, the protective layer 15 may be formed by treating the substrate 11 with supercritical water at 30 MPa and 400°C for 10 minutes or more.

[0033] FIG. 2(a) is a schematic view showing the step of removing the protective layer 15 from the substrate 11, and FIG. 2(b) is a schematic view showing the step of growing the film 21 on the substrate 11. The method for manufacturing the nitride laminate 100 according to 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. That is, between the process of removing the protective layer 15 and the process of growing the film 21, the substrate 11 is not carried out of the processing chamber 210 and remains inside the processing chamber 210.

[0034] 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 is used. FIGS. 2(a) and 2(b) illustrate a schematic view of the film forming apparatus 200.

[0035] 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 the processing gas 250 used for each process into the processing chamber 210.

[0036] Referring to FIG. 2(a), the step 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 loading the substrate 11 (nitride laminate 16) on which the protective layer 15 is formed into the processing chamber 210 of the film forming apparatus 200 and heating it in a reducing atmosphere. The process is preferably performed, for example, in an atmosphere containing hydrogen (more specifically, for example, containing H2 gas), or for example, in an atmosphere containing ammonia in addition to hydrogen. The heating temperature is preferably, for example, 900°C or higher and 1300°C or lower. The heating time is preferably, for example, 30 seconds or longer and 30 minutes or shorter. The H2 gas may be supplied in a mixture with an inert gas such as N2 gas or Ar gas. By performing the process in an atmosphere to which ammonia is added, surface damage due to thermal etching can be suppressed.

[0037] In this process, the removal of the protective layer 15 is continued until the entire surface 13a of the substrate 11 is exposed, that is, 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 the impurity 14 is removed together with the protective layer 15.

[0038] Referring to FIG. 2(b), the 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 performed by growing the second group-III nitride on the surface 13a of the first group-III nitride exposed by the removal of the protective layer 15 without carrying the substrate 11 out of the processing chamber 210 after the process of removing the protective layer 15 from the substrate 11. In this way, the nitride laminate 100 having the substrate 11 and the film 21 is manufactured.

[0039] The second group-III nitride constituting the film 21 is grown by, for example, MOVPE. As the aluminum (Al) source gas among the group-III source gases, for example, trimethylaluminum (Al(CH3)3, TMA) gas is used. As the gallium (Ga) source gas among the group-III source gases, for example, trimethylgallium (Ga(CH3)3, TMG) gas is used. As the indium (In) source gas among the group-III source gases, for example, trimethylindium (In(CH3)3, TMI) gas is used. As the nitrogen (N) source gas, which is a 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) is used.

[0040] The growth temperature can be selected, for example, in the range of 700°C to 1400°C, and the V / III ratio, which is the flow rate ratio of the group-V source gas to the group-III source gas, can be selected, for example, in the range of 10 to 5000. The ratio of the supply amounts of the respective source gases is adjusted according to the composition of the film 21 to be formed.

[0041] 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 due to the impurity 14 is suppressed. For this reason, the second group-III nitride, that is, the film 21, does not have to be grown thick (for example, to a thickness of 4 μm or more). Incidentally, the film 21 may be grown thick (for example, to a thickness of 4 μm or more) as necessary.

[0042] As a criterion for determining that the influence of the reduction in crystallinity due to the impurity 14 is suppressed, for example, in a portion within a thickness range of 4 μm from the interface of the second group-III nitride (that is, the film 21) 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.

[0043] With reference to FIGS. 3 to 5, the characteristics of the impurity concentration distribution of the nitride laminate 100 according to the embodiment will be described while comparing them with the characteristics of the impurity concentration distribution of the nitride laminates according to the first and second comparative forms. FIGS. 3, 4, and 5 are examples of SIMS profiles in the samples of the embodiment, the first comparative form, and the second comparative form, respectively, and show the concentration distributions of Fe, Mg, and Cr.

[0044] The samples exemplified as the embodiment, the first comparative form, and the second comparative form are nitride laminates in which a GaN layer is epitaxially grown 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 may be simply referred to as the interface. The interface in the embodiment can usually be easily discriminated by the difference in crystal composition or the difference in doped impurities between the first group-III nitride and the second group-III nitride. However, even when both the first group-III nitride and the second group-III nitride are undoped GaN crystals or low-Si doped crystals, the discrimination is possible. Details of how to define the interface in such an embodiment will be described later.

[0045] The sample of the embodiment is produced by a method in which an air-exposed GaN substrate is subjected to an oxidation treatment to form a gallium oxide layer as a protective layer on the GaN substrate, the GaN substrate with the protective layer formed is carried into a film forming apparatus, and after removing the protective layer, a GaN layer is continuously grown.

[0046] The sample of the first comparative form is produced by a method in which an air-exposed GaN substrate is carried into a film forming apparatus without performing an oxidation treatment as in the embodiment, and a GaN layer is grown. The sample of the second comparative form is produced by a method in which an air-exposed GaN substrate is not subjected to an oxidation treatment but is subjected to an acid washing treatment with a hydrofluoric acid solution and then carried into a film forming apparatus to grow a GaN layer (that is, a method in which an acid washing treatment is added to the first comparative form). As the acid washing treatment in the second comparative form, in addition to the above hydrofluoric acid solution, it may also be performed with a hydrochloric acid solution or the like. After performing acid washing for 5 to 10 minutes, it is common to perform running water treatment with pure water for 5 to 10 minutes.

[0047] In the first and second comparative embodiments, before growing the GaN layer, heat treatment is performed in a reducing atmosphere using a film forming apparatus, thereby removing the native oxide film on the GaN substrate. This is similar to the heat treatment in the reducing atmosphere for removing the protective layer in the embodiment. However, since the native oxide film is extremely thin compared to the protective layer, the heat treatment time in the first and second comparative embodiments may be shorter than the heat treatment time in the embodiment. Specifically, for 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 comparative embodiments may be, for example, 10 seconds or less. In fact, even without actively performing heat treatment for removing the native oxide film, the native oxide film is sufficiently removed during the standby before growth.

[0048] In the first comparative embodiment (FIG. 4), near the stacking 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. Also, near the stacking interface, a peak indicating the presence of Cr, although in trace amounts, is observed.

[0049] In the first comparative embodiment (FIG. 4), formation of the native oxide film due to exposure of the GaN substrate to the atmosphere and removal of the native oxide film before GaN layer growth are performed. However, in the formation and removal of the native oxide film, impurities such as Fe cannot be sufficiently removed.

[0050] In the second comparative embodiment (FIG. 5), by the pickling treatment, Fe and Mg are at lower concentrations compared to the first comparative embodiment. The Cr concentration is below the detection limit of SIMS measurement (1×10 14 / cm 3 or less). The Fe concentration in the second comparative embodiment is suppressed compared to the first comparative embodiment, but the shape of the raised portion 31 is still at a level that is clearly high. The Mg concentration in the second comparative embodiment is suppressed compared to the first comparative embodiment, and the shape of the raised portion 32 is at a level that is trace-like and low.

[0051] In the embodiment (FIG. 3), by the process of forming and removing the protective layer, Fe and Mg are at even lower concentrations compared to the second comparative form of the pickling treatment. The Cr concentration is 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 comparative form and is at a low level such that the shape of the raised portion 31 becomes trace-like. The Mg concentration in the embodiment is further suppressed compared to the second comparative form and is at a low level such that the raised portion 32 is not observed.

[0052] Here, a distinct raised shape means that the concentration distribution shape indicating the raised portion, which is a portion where the impurity concentration is prominently high, is a curved shape. In an aspect where the level of the impurity concentration is high, it can be said that the concentration distribution shape indicating the raised portion shows a curved shape. On the other hand, a trace-like raised shape means that the profile shape indicating the raised portion is a discrete columnar shape of measured values exceeding the detection limit. In an aspect where the level of the impurity concentration is low to the extent close to the detection limit, it can be said that the concentration distribution shape indicating the raised portion shows a trace-like shape.

[0053] In the first comparative form, a characteristic is seen that the concentration level of Fe is higher than that of Mg. The same tendency is also seen in the second comparative form and the embodiment. Regarding Fe, it is considered that in the second comparative form and the embodiment, a peak in the Fe concentration distribution remains near the lamination interface due to the relatively high concentration level and the difficulty of removal. Note that by applying the method of the embodiment, Fe may be removed to the extent that there is no peak in the Fe concentration distribution near the lamination interface. Regarding Mg, it is considered that in the second comparative form, a peak in the Mg concentration distribution remains near the lamination interface because the concentration level is relatively low and it is easier to remove compared to Fe, but in the embodiment, it does not remain.

[0054] Hereinafter, more detailed features of the impurity concentration distribution according to the embodiment in the vicinity of the stacking interface will be described. Also in the first comparative form (FIG. 4), the level of the Mg concentration on the GaN substrate side with respect to the raised portion 32 is on the order of 1×10 14 / cm 3 , that is, relatively low, close to the detection limit. Also in the first comparative form, the level of the Mg concentration on the GaN layer side with respect to the raised portion 32 is relatively high, on the order of 1×10 15 / cm 3 . Thus, the concentration distribution shape of Mg shows a step shape where it is relatively low on the GaN substrate side and relatively high on the GaN layer side with respect to the raised portion 32.

[0055] Also in the second comparative form (FIG. 5) that has been subjected to the pickling treatment, as the Mg concentration distribution shape, similarly, a step shape where it is relatively low on the GaN substrate side and relatively high on the GaN layer side with respect to the raised portion 32 is observed. However, in the second comparative form, due to the pickling treatment, on the GaN substrate side, the level of the Mg concentration further decreases, and almost no measured value exceeding 1×10 14 / cm 3 is observed. Also on the GaN layer side, the Mg concentration is relatively low, on the order of 1×10 14 / cm 3 .

[0056] Also in the embodiment (FIG. 3) in which the protective layer is formed and removed, although the raised portion 32 is not observed as the Mg concentration distribution shape, similarly, a step shape where it is relatively low on the GaN substrate side and relatively high on the GaN layer side is observed. On the GaN substrate side, almost no measured value exceeding 1×10 14 / cm 3 is observed, and the feature that the Mg concentration on the GaN layer side is relatively low, on the order of 1×10 14 / cm 3 , is the same as that of the second comparative form.

[0057] Based on such step-shaped characteristics near the lamination interface of the Mg concentration distribution shape, regarding the concentration distribution evaluation of the second comparative form 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 as follows.

[0058] Regarding the Mg concentration, the region with a relatively low concentration on the GaN substrate side can be said to be a region where the measured values exceeding 1×10 14 / cm 3 are sparse. Here, the region where the measured values exceeding 1×10 14 / cm 3 are sparse means a region where there is no second measured value exceeding 1×10 14 / cm 3 within a depth of 0.5 μm from the first measured value exceeding 1×10 14 / cm 3 on the GaN substrate side.

[0059] On the other hand, regarding the Mg concentration, the region with a relatively high concentration on the GaN layer side can be said to be a region where the measured values exceeding 1×10 14 / cm 3 are dense. Here, the region where the measured values exceeding 1×10 14 / cm 3 are dense means a region where there is a second measured value exceeding 1×10 14 / cm 3 within a depth of 0.5 μm from the first measured value exceeding 1×10 14 / cm 3 on the GaN layer side.

[0060] The depth position corresponding to the measured value of the Mg concentration, which is the boundary between the region where the measured values exceeding 1×10 14 / cm 3 are sparse and the dense region, is defined as interface 41. Also, the range with a thickness of 1 μm centered on interface 41 is defined as interface region 42, and the range with a thickness of 2 μm centered on interface 41 is defined as lamination region 43. Lamination region 43 indicates the lamination of the GaN substrate and the GaN layer. Interface region 42 indicates the vicinity of the interface in the lamination of the GaN substrate and the GaN layer.

[0061] In the interface means in the vicinity of the interface, that is, within the interface region 42. It is defined that the Fe concentration distribution has a peak at the interface when the maximum value (peak concentration) CFe of the Fe concentration in the stacking region 43 exists within the interface region 42. Similarly, it is defined that the Mg concentration distribution has a peak at the interface when the maximum value (peak concentration) CMg of the Mg concentration in the stacking region 43 exists within the interface region 42.

[0062] Based on such a definition, the characteristics of the impurity concentration distribution in the sample illustrated in FIG. 5 as the second comparative form and the characteristics of the impurity concentration distribution in the sample illustrated in FIG. 3 as the embodiment are compared as follows. The Fe concentration distribution of the second comparative form has a peak at the interface, and the peak concentration CFe is about 4×10 16 / cm 3 The Fe concentration distribution of the embodiment has a peak at the interface, and the peak concentration CFe is about 3×10 15 / cm 3 The peak concentration CFe of Fe in the embodiment is lower than the peak concentration CFe of Fe in the second comparative form, 2×10 16 / cm 3 or less, preferably 1×10 16 / cm 3 or less, more preferably 5×10 15 / cm 3 or less.

[0063] The Mg concentration distribution of the second comparative form has a peak at the interface, and the peak concentration CMg is about 3×10 15 / cm 3 The Mg concentration distribution of the embodiment has the maximum value CMg (about 1×10 15 / cm 3 or so) of the Mg concentration in the stacking region 43 outside the interface region 42, that is, it does not have a peak at the interface, and the maximum value CMg2 of the Mg concentration within the interface region 42 is 7×10 14 / cm 3is the level. 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 comparative form, 2×10 15 / cm 3 or less, preferably 1×10 15 / cm 3 or less, and can be set as such. In the embodiment, it can be said that Mg has been removed to such an extent that the Mg concentration in the stacking region 43 has little difference between inside and outside the interface region 42. For this reason, by applying the method of the embodiment, the maximum value CMg of the Mg concentration in the stacking region 43 may exist outside the interface region 42 (as in the example shown in FIG. 3), or may exist inside the interface region 42.

[0064] Note that, as described above, by applying the method of the embodiment, the Cr concentration (the maximum value) in the interface (inside the interface region 42) can be reduced to be below the detection lower limit (1×10 14 / cm 3 or less).

[0065] Also, it has 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, that is, when Si is an impurity attached due to contamination, the maximum value of the Si concentration (in the interface region 42) in the interface can be reduced to 1×10 16 / cm 3 or less, preferably 1×10 15 / cm 3 or less.

[0066] When Si is intentionally added to the first group-III nitride and the second group-III nitride (typically, 1×10 16 / cm 3Even when Si is added at a concentration of about the order of , the method of the embodiment is useful. For example, as described above with reference to FIG. 7, in the prior art, a raised portion showing a bias in the Si concentration distribution is observed at the stacked interface, and the maximum value of the Si concentration at the raised portion is a high value exceeding 10 times the added Si concentration, which is 1×10 17 / cm 3 or higher.

[0067] 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 raised portion can be made lower than before. As a specific guideline, the Si concentration at the interface (the maximum value of the Si concentration within the interface region 42) is set to 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 stacked region 43). Also, the Si concentration (the maximum value) at the interface (within the interface region 42) can be made less than 1×10 17 / cm 3 or less.

[0068] As described above, according to the present embodiment, impurities (such as Fe, Mg, Cr, etc.) attached (due to contamination) on the surface of the first group-III nitride are removed, and further, the second group-III nitride can be grown on the first group-III nitride while suppressing the bias in the concentration distribution near the stacked interface of the impurities (such as Si, etc.) added to the first group-III nitride.

[0069] The stacked structure of the first group-III nitride and the second group-III nitride to which the method of the present embodiment is applied may be in various forms. Both the first and second group-III nitrides may be n-type (for example, in the form of a vertical power device). The first and second group-III nitrides may be p-type and n-type, respectively, or n-type and p-type (in the form of a pn diode). Note that both the first and second group-III nitrides may be p-type.

[0070] The first and second group-III nitrides may both be semi-insulating (e.g., the stacking mode up to the GaN channel in a HEMT with a GaN-on-GaN structure). The composition of the first group-III nitride and the composition of the second group-III nitride may be different. For example, the first group-III nitride may be GaN, and the second group-III nitride may be AlGaN (e.g., the mode of a HEMT in which an AlGaN layer is regrown).

[0071] The surface (interface with the second group-III nitride) 13a of the first group-III nitride does not have to be flat over the entire surface and may have an uneven structure. FIG. 6(a) is a first example of a mode in which the surface 13a of the first group-III nitride has an uneven structure. The surface 13a in the first example has a main surface 51 and grooves 52. The main surface 51 in the first example is a surface with an inclination of within 3 degrees from the C-plane of the first group-III nitride crystal. The grooves 52 in the first example have side surfaces inclined, for example, by 30° or more and 90° or less from the main surface 51. This example is a mode assuming, for example, 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 the process of forming the grooves 52 in the first group-III nitride (that is, 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 surfaces of the grooves 52.

[0072] FIG. 6(b) is a second example of an embodiment in which the surface 13a of the first group-III nitride has an uneven structure. The surface 13a in the second example has a main surface 51 and a mesa structure 53. The main surface 51 in the second example is a surface with an inclination of 3 degrees or less from the C plane of the first group-III nitride crystal. The mesa structure 53 in the second example has a side surface inclined, for example, 30° or more and 90° or less from the main surface 51. This example is an embodiment assuming, for example, 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 the process of forming the mesa structure 53 on the first group-III nitride (that is, after the first group-III nitride is taken out of the film-forming apparatus), the second group-III nitride is regrown. Corresponding to such regrowth, the second group-III nitride is formed at least on the side surface of the mesa structure 53.

[0073] Also in the structure as shown in FIGS. 6(a) and 6(b), at the laminated interface between the first group-III nitride and the second group-III nitride, the concentrations of various impurities can be suitably controlled by the method of this embodiment as described above. For example, the concentration of Fe at the interface can be suppressed to 2×10 16 / cm 3 or less.

[0074] As described above, in the method for manufacturing the nitride laminate 100 according to the embodiment, the protective layer 15 is formed by subjecting the substrate 11 (the first group-III nitride) prepared in a state taken out of the film-forming apparatus to a predetermined oxidation treatment using an oxidation treatment apparatus, and the removal of the protective layer 15 and the growth of the film 21 (the second group-III nitride) are continuously performed in the processing chamber 210 where the film 21 is grown.

[0075] As a result, the concentration of impurities (such as Fe, Mg, Cr, Si, etc.) on the surface 13a, which becomes the interface (regrowth interface) between the first group-III nitride and the second group-III nitride, can be reduced. Also, as a result, even if the second group-III nitride is not deposited thickly (even with a thickness of about 4 μm), the crystallinity of the second group-III nitride can be made good. Further, by reducing the concentrations of Fe and Mg at the regrowth interface, a decrease in the conductivity of this portion can be avoided, and the formation of an Si high-doped layer on the regrowth interface becomes unnecessary.

[0076] The oxidation treatment is performed while the impurities 14 remain attached to the surface 13 of the substrate 11. As a result, it is not necessary to perform the formation of the protective layer 15 in situ after the formation of the first group-III nitride, and it can be performed after taking out the substrate 11 from the film-forming apparatus to the outside. Also, in order to remove the impurities 14, it is not necessary to perform pickling or the like on the substrate 11 after taking it out to the outside of the film-forming apparatus.

[0077] The oxidation treatment preferably continues until the surface 13a of the first group-III nitride is continuously covered by the protective layer 15 (the entire surface 13a is covered by the protective layer 15). By forming the protective layer 15 as a continuous layer (a dense layer without pinholes), the removal of the impurities 14 accompanying the removal of the protective layer 15 can be performed without gaps on the surface 13a of the first group-III nitride.

[0078] 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 setting the thickness of the protective layer 15 to 2 nm or more, a protective layer 15 with few pinholes can be realized, and impurities 14 can be effectively removed when the protective layer 15 is removed. Furthermore, when the thickness of the protective layer 15 is 40 nm or more, pinholes can be completely eliminated, and the residual impurity concentration at the interface can be more reliably reduced to about the SIMS background level. Although there is no particular upper limit to the thickness of the protective layer 15, if it is made too thick, it will take a long time for its formation and removal, 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 be, for example, 300 nm or less, preferably 150 nm or less.

[0079] In this 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) (this is referred to as the former aspect) may be used. However, as the substrate 11, a self-supporting substrate entirely composed of the first group III nitride, or an epitaxial substrate in which the first group III nitride is grown on a self-supporting substrate composed of a group III nitride (the same type of substrate) (that is, the substrate 11 includes a self-supporting substrate composed of a group III nitride / this is referred to as the latter aspect) is preferably used. This is because in the latter aspect, it has been found that the oxide film (protective layer 15) formed by the oxidation treatment is denser and has a flatter surface than in the former aspect.

[0080] The oxidation treatment is performed, for example, using a steam oxidation method or, for example, 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-described thickness. As a result, the above-described effects can be obtained more reliably.

[0081] By means of an acid treatment, a nitride laminate 16, which is an intermediate of the nitride laminate 100 having a substrate 11 and a 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, or when it is stored and distributed for a long time in a resin container, it is possible to avoid further adhesion of impurities to the surface 13a of the first group-III nitride.

[0082] Further, since the protective layer 15 is composed of a group-III oxide having lower etching resistance than the group-III nitride, it can be easily removed in the gas phase. Therefore, in the processing chamber 210 for growing the film 21 made of the second group-III nitride, the protective layer 15 is removed, and then the film 21 made of the second group-III nitride is continuously formed, thereby preventing contamination of the surface 13a, which is the interface (regrowth interface) between the first group-III nitride and the second group-III nitride, and reducing the impurity concentration.

[0083] 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, that is, until the group-III nitride existing on the lower layer side of the protective layer 15 in the first group-III nitride is exposed. The protective layer 15 contains impurities 14. By continuing the removal (thermal etching) of the protective layer 15 until the surface 13a is exposed, it is possible to remove the impurities 14 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.

[0084] After removing the protective layer 15, a nitride laminate 100 having a substrate 11 and a film 21 is manufactured by growing the film 21 on the substrate 11. The concentration distribution of Fe at the interface between the substrate 11 and the film 21, that is, at the interface between the first group-III nitride and the second group-III nitride, typically has a peak at the interface, and the peak concentration is 2×10 16 / cm 3 or less, preferably 1×10 16 / cm 3 or less, more preferably 5×1015 / cm 3 is as follows. Further, the maximum value of the Mg concentration at the interface is 2×10 15 / cm 3 or less, preferably 1×10 15 / cm 3 or less.

[0085] In the nitride laminate 100, since the surface 13a of the substrate 11 that serves as the base of the film 21, that is, the impurity concentration at the regrowth interface is low (contamination is suppressed), even if the second group III nitride constituting the film 21 is not grown thickly (for example, even if the thickness is about 4 μm or less), its crystallinity can be made good. Further, by reducing the concentrations of Fe and Mg at the regrowth interface, a decrease in the conductivity of this portion can be avoided, and the formation of an Si high-doped layer on the regrowth interface becomes unnecessary.

[0086] <Preferred Embodiment of the Present Invention> Hereinafter, preferred embodiments of the present invention will be appended.

[0087] (Appendix 1) (a) A step of preparing a substrate at least the surface layer portion of which is composed of a first group III nitride in a state taken out of a film forming apparatus in which the first group III nitride is grown; (b) A step of subjecting the substrate to a predetermined oxidation treatment using an oxidation treatment apparatus to change the outermost layer of the first group III nitride into a protective layer made of a group III oxide; (c) A step of loading the substrate into a predetermined processing chamber and heating it in a reducing atmosphere to remove the protective layer from the surface of the substrate; (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 the substrate out of the processing chamber; A method for manufacturing a nitride laminate having the above steps.

[0088] (Appendix 2) In the step (b), the surface layer portion of the first group-III nitride is oxidized while at least any one of the impurities selected from the group consisting of Fe, Mg, Cr, and Si remains attached to the surface of the first group-III nitride. The method for manufacturing a nitride laminate according to Addendum 1.

[0089] (Addendum 3) In the step (b), the oxidation treatment is continued until the surface of the first group-III nitride is continuously covered with the protective layer. The method for manufacturing a nitride laminate according to Addendum 1.

[0090] (Addendum 4) 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). The method for manufacturing a nitride laminate according to Addendum 1.

[0091] (Addendum 5) In the step (b), water vapor is supplied to the substrate as an oxidizing agent to oxidize the surface layer portion of the first group-III nitride. The method for manufacturing a nitride laminate according to Addendum 1.

[0092] (Addendum 6) In the step (b), an anodic oxidation technique is used to oxidize the surface layer portion of the first group-III nitride. The method for manufacturing a nitride laminate according to Addendum 1.

[0093] (Addendum 7) 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 in the first group-III nitride is exposed. The method for manufacturing a nitride laminate according to Addendum 1.

[0094] (Addendum 8) In the step (c), the impurities attached to the surface of the first group-III nitride are removed together with the protective layer. The method for manufacturing a nitride laminate according to Addendum 2.

[0095] (Appendix 9) In (c), in the processing chamber of the film forming apparatus for growing the second group III nitride, 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. The method for manufacturing a nitride laminate according to Appendix 1.

[0096] (Appendix 10) In (c), in the processing chamber of the film forming apparatus for growing the second group III nitride, 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. The method for manufacturing a nitride laminate according to Appendix 1.

[0097] (Appendix 11) The method for manufacturing a nitride laminate according to any one of Appendices 1-10, characterized in that both the first and second group III nitrides are n-type.

[0098] (Appendix 12) The method for manufacturing a nitride laminate according to any one of Appendices 1-10, characterized in that both the first and second group III nitrides are semi-insulating.

[0099] (Appendix 13) The method for manufacturing a nitride laminate according to any one of Appendices 1-10, characterized in that the first group III nitride is GaN and the second group III nitride is AlGaN.

[0100] (Appendix 14) The method for manufacturing a nitride laminate according to any one of Appendices 1-10, characterized in that the first and second group III nitrides are p-type and n-type, or n-type and p-type, respectively.

[0101] (Appendix 15) The first group-III nitride is GaN, and the surface of the first group-III nitride has a main surface inclined within 3° from the C-plane and a groove having a side surface inclined 30° or more and 90° or less from the main surface, and the second group-III nitride is AlGaN. A method for manufacturing a nitride laminate according to any one of Appendices 1-10, characterized in that.

[0102] (Appendix 16) 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 and a mesa structure having a side surface inclined 30° or more and 90° or less from the main surface, and the second group-III nitride is p-type GaN. A method for manufacturing a nitride laminate according to any one of Appendices 1-10, characterized in that.

[0103] (Appendix 17) A substrate at least the surface layer portion of which is composed of a first group-III nitride, A protective layer made of a group-III oxide formed on the surface of the first group-III nitride, A nitride laminate having the same.

[0104] (Appendix 18) The protective layer is formed so as to continuously cover the surface of the first group-III nitride The nitride laminate according to Appendix 17.

[0105] (Appendix 19) The protective layer has a thickness of 2 nm or more (preferably 5 nm or more, more preferably 40 nm or more) The nitride laminate according to Appendix 17.

[0106] (Appendix 20) The protective layer contains at least any impurity selected from the group consisting of Fe, Mg, Cr, and Si The nitride laminate according to any one of Appendices 17-20.

[0107] (Appendix 21) A substrate at least a surface portion of which is composed of a first group-III nitride, and a film made of a second group-III nitride formed on the surface of the first group-III nitride, wherein a concentration distribution of Fe at an interface between the first group-III nitride and the second group-III nitride has a peak at the interface, and a 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), a nitride laminate.

[0108] (Appendix 22) wherein a concentration of Mg at an 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) the nitride laminate according to Appendix 21.

[0109] (Appendix 23) wherein a concentration of Cr at an interface between the first group-III nitride and the second group-III nitride is 1×10 14 / cm 3 or less the nitride laminate according to Appendix 21.

[0110] (Appendix 24) wherein a concentration of Si at an 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) the nitride laminate according to Appendix 21.

[0111] (Appendix 25) The concentration of Si at the interface between the first group-III nitride and the second group-III nitride is 5 times or less (preferably 2 times or less) 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. The nitride laminate according to Supplementary Note 21.

[0112] (Supplementary Note 26) In the portion within a thickness of 4 μm from the interface with the first group-III nitride in the second 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. The nitride laminate according to any one of Supplementary Notes 21 to 25.

[0113] (Supplementary Note 27) A substrate at least having a surface layer portion composed of a first group-III nitride, A film made of 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 surface inclined within 3° from the C plane and a groove having a side surface inclined 30° or more and 90° or less from the main surface. 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. The concentration of Fe at the interface between the first group-III nitride and the second group-III nitride is 2×10 16 / cm 3 or less. The nitride laminate.

[0114] (Supplementary Note 28) A substrate at least having a surface layer portion composed of a first group-III nitride, A film made of 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 mesa structure having a main surface inclined within 3° from the C-plane and a side surface inclined 30° or more and 90° or less from the main surface. 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. The concentration of Fe at the interface between the first group-III nitride and the second group-III nitride is 2×10 16 / cm 3 or less, which is a nitride laminate.

Explanation of symbols

[0115] 11... substrate, 12... surface layer portion, 13... surface, 13a... surface, 14... impurity, 15... protective layer, 16... intermediate body, 21... film, 31... Fe protrusion, 32... Mg protrusion, 41... interface, 42... interface region, 43... stacking region, 51... main surface, 52... groove, 53... mesa structure, 100... nitride laminate, 200... film forming apparatus, 210... processing chamber, 220... susceptor, 230... heater, 240... gas supply mechanism, 250... processing gas

Claims

1. (a) A step of preparing a substrate at least the surface layer portion of which is composed of a first group-III nitride in a state where it is taken out of a film forming apparatus on which the first group-III nitride has been grown; (b) A step of subjecting the substrate to a predetermined oxidation treatment using an oxidation treatment apparatus, and changing the outermost layer of the first group-III nitride into a protective layer composed of a group-III oxide; (c) A step of loading the substrate into a predetermined processing chamber and heating it in a reducing atmosphere to remove the protective layer from the surface of the substrate; (d) A step of growing a second group-III nitride on the surface of the first group-III nitride exposed by the removal of the protective layer without taking the substrate out of the processing chamber; A method for manufacturing a nitride laminate having the above.

2. In the above (b), while at least any one impurity selected from the group consisting of Fe, Mg, Cr, and Si remains attached to the surface of the first group-III nitride, the surface layer portion of the first group-III nitride is oxidized The method for manufacturing a nitride laminate according to Claim 1.

3. In the above (b), the oxidation treatment is continued until the surface of the first group-III nitride is continuously covered with the protective layer. The method for manufacturing a nitride laminate according to Claim 1.

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

5. 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. The method for manufacturing a nitride laminate according to Claim 1.

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

7. 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 in the first group-III nitride is exposed. The method for manufacturing a nitride laminate according to Claim 1.

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

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

10. In (c), in the processing chamber of the film forming apparatus for growing the second group III nitride, 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. Method for manufacturing a nitride laminate according to claim 1.

11. The method for manufacturing a nitride laminate according to any one of claims 1 to 10, wherein both the first and second group III nitrides are n-type.

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

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

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

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

17. A substrate at least a surface layer portion of which is composed of a first group III nitride, A protective layer made of a group III oxide formed on the surface of the first group III nitride, A nitride laminate having the above.

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

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

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

21. A substrate in which at least a surface layer portion is composed of a first group-III nitride, and a film composed of a second group-III nitride formed on the surface of the first group-III nitride. A nitride laminate in which the concentration distribution of Fe at 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.

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

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

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

25. The concentration of Si at 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. The nitride laminate according to claim 21.

26. In the portion within a thickness of 4 μm from the interface with the first group-III nitride in the second 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. The nitride laminate according to any one of claims 21 to 25.

27. A substrate in which at least a surface layer portion is composed of a first group-III nitride, and a film composed of 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 surface inclined within 3° from the C plane and a groove having a side surface inclined 30° or more and 90° or less from the main surface. 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. A nitride laminate in which the concentration of Fe at the interface between the first group-III nitride and the second group-III nitride is 2×10 １６ / cm ３ or less.

28. A substrate in which at least a surface layer portion is composed of a first group-III nitride, and a film composed of 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 surface inclined within 3° from the C plane and a mesa structure having a side surface inclined 30° or more and 90° or less from the main surface. 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. A nitride laminate in which the concentration of Fe at 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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