JP3698061B2 - Nitride semiconductor substrate and growth method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for growing a nitride semiconductor (In _x Al _y Ga _1-xy N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and is particularly applicable to a light emitting element, a light receiving element, an electronic device, and the like. The present invention relates to a method for growing a nitride semiconductor substrate.
[0002]
[Prior art]
In recent years, various studies on growing a nitride semiconductor on a different substrate from a nitride semiconductor such as sapphire, spinel, and silicon carbide have been studied. This is because it is difficult to form a bulk single crystal of nitride semiconductor with good crystallinity that can be used for light-emitting devices, etc., using the current technology, and nitride semiconductor is grown on a different substrate from nitride semiconductor. The method of making it be studied. However, since there is no heterogeneous substrate having a lattice constant or thermal expansion coefficient that matches that of gallium nitride or the like, there is a situation in which when a nitride semiconductor is grown directly on the heterogeneous substrate, many crystal defects are generated in the nitride semiconductor. . In order to solve this problem, the following method has been reported .
[0003]
For example, as a method for forming a gallium nitride substrate, in JP-A-7-202265 and JP-A-7-165498, a buffer layer made of ZnO is formed on a sapphire substrate, and a nitride is formed on the buffer layer. A technique for dissolving and removing a buffer layer after growing a semiconductor is described. However, the crystallinity of the ZnO buffer layer grown on the sapphire substrate is poor, and it is difficult to obtain a high-quality nitride semiconductor substrate even if a nitride semiconductor is grown on the buffer layer. JPN. J. et al. Appl. Phys. Vol. 37 (1998) p. In L309-L312, as a growth method of ELOG (Epitaxial lateral overgrowth GaN), a protective film such as SiO ₂ is partially formed on a nitride semiconductor grown on the C-plane of sapphire, and on this, 100 Torr is formed. It discloses that a nitride semiconductor with few dislocations can be obtained by growing a nitride semiconductor under reduced pressure. In such ELOG growth, a protective film is formed and a nitride semiconductor is intentionally grown in the lateral direction, and when dislocations proceed with the growth of the nitride semiconductor, the dislocations occur only on the portion having no protective film. Therefore, a nitride semiconductor with few dislocation defects can be formed on the protective film. However, in the growth method described above, although a low defect region can be formed on the protective film, contamination due to decomposition of the protective film occurs during the lateral growth of the nitride semiconductor on the protective film and the growth of the nitride semiconductor element. Was. Therefore, the characteristic deterioration of the semiconductor element has been a problem.
[0004]
[Problems to be solved by the invention]
When forming a nitride semiconductor element used in an electronic device such as an LED element, an LD element, or a light receiving element, a substrate made of a nitride semiconductor with few crystal defects and high crystal purity can be formed on the substrate. The crystallinity of the grown nitride semiconductor device is dramatically improved. Accordingly, an object of the present invention is to provide a method for growing a nitride semiconductor substrate with good crystallinity that solves the above problems.
[0005]
[Means for Solving the Problems]
That is, the object of the present invention can be achieved by the configurations of the present invention shown in the following (1) to ( 6 ).
(1) a first nitride semiconductor on a substrate, has a step, a concave portion side surface and the bottom surface of the stepped and has a decomposition surface of the nitride semiconductor, the convex upper surface of the first nitride semiconductor the second has a layer of a nitride semiconductor, a nitride semiconductor substrate having a space recessed portion of said first nitride semiconductor provided.
(2) The first nitride semiconductor on the substrate has a step, and has a decomposition surface of the nitride semiconductor on a side surface of the concave portion of the step, the bottom surface of the concave portion is an exposed surface of the substrate, and the first A nitride semiconductor substrate having a second nitride semiconductor layer provided on an upper surface of a convex portion of one nitride semiconductor and having a space in a concave portion of the first nitride semiconductor.
(3) the first decomposition surface of the recess provided in the nitride semiconductor is more formed Netsusho sense (1) or a nitride semiconductor substrate according to (2).
(4) The nitride semiconductor substrate according to (3), wherein the heat treatment is annealing.
(5) A method for growing a nitride semiconductor substrate having a nitride semiconductor on the substrate,
A first step of growing a first nitride semiconductor on a substrate and forming a protective film having an opening in the first nitride semiconductor ;
A second step of forming a recess in the opening of the protective film and forming a stepped shape in the first nitride semiconductor;
A third step in which the exposed portion of the nitride semiconductor is decomposed by heat treatment to form a decomposition surface in the recess provided in the first nitride semiconductor;
The protective film on the first nitride semiconductor is removed, a second nitride semiconductor is selectively grown from the upper surface of the convex portion of the first nitride semiconductor , and the first nitride provided with the decomposition surface the fourth step and the nitride semiconductor substrate growth method having a forming the second layer of nitride semiconductor having between empty recess sEMICONDUCTOR.
(6) The method for growing a nitride semiconductor substrate according to (5), wherein heat treatment is performed at a temperature of 400 ° C. or higher in the second step.
[0006]
That is, in the nitride semiconductor substrate formed by the growth method of the present invention, the second nitride semiconductor is selectively grown from the upper surface of the convex portion of the first nitride semiconductor having a step grown on the substrate. This method uses the vertical and lateral growth of the nitride semiconductor, but does not have a protective film during the growth of the second nitride semiconductor, so the protective film decomposes unlike the lateral growth on the protective film. By doing so, there is no concern that the crystal characteristics will deteriorate.
Furthermore, in the ELOG growth, stress is generated when the nitride semiconductor is grown in the lateral direction on the protective film, and further, crystal defects converge at the junction formed by joining the nitride semiconductors, A step was formed. However, in the growth method of the present invention, the growth of the nitride semiconductor is not forcibly laterally grown, but is laterally grown without stress from the upper surface of the first nitride semiconductor, thereby causing the longitudinal and lateral directions to grow. Since the second nitride semiconductor grows and further grows, the second nitride semiconductors having no stress are joined together to form a joint, so that the above problem does not occur, and the flat and mirror shape Thus, a nitride semiconductor substrate with few crystal defects can be provided.
[0007]
Further, after forming irregularities on the first nitride semiconductor, the side and bottom surfaces of the recesses by a heat treatment while leaving a protective film on the upper surface of the protrusion roughness is formed. Accordingly, since the nitride semiconductor does not grow from the side surface and the bottom surface of the recess formed in the first nitride semiconductor, the first nitride film is selectively removed after removing the protective film when growing the second nitride semiconductor. The second nitride semiconductor can be grown from the upper surface of the convex portion of the nitride semiconductor.
[0008]
In the present invention, the temperature of the heat treatment is not particularly limited, but the upper limit is not higher than the growth temperature of the nitride semiconductor, and the temperature of the first nitride semiconductor under the protective film is 400 ° C. or higher and 1050 ° C. or lower. The nitride semiconductor in the surface partial region is preferable because it is not affected by the heat treatment and does not generate roughness.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 to FIG. 5 are schematic views showing an embodiment of the nitride semiconductor substrate and growth method of the present invention step by step.
[0010]
As an embodiment of the method for growing a nitride semiconductor substrate according to the present invention, first, in the first step shown in FIG. 1, a first nitride semiconductor 2 is grown on the substrate 1 and an opening is provided thereon. The protective film 3 is formed, and in the second step shown in FIG. 2, a recess is formed in the opening of the protective film 3, a step shape is formed in the first nitride semiconductor 2, and the third step shown in FIG. in step, a decomposition surface to produce an exposed portion of the substrate by Netsusho sense to Rukoto, then, in the fourth step shown in FIGS. 4 and 5, a protective film on the first nitride semiconductor raised portion on Subsequently, as shown in FIG. 5, a second nitride semiconductor 4 is grown on the first nitride semiconductor.
[0011]
Hereinafter, each step will be described in more detail with reference to the drawings.
FIG. 1 is a schematic cross-sectional view in which a step of growing a first nitride semiconductor 2 on a substrate 1 and further forming a protective film 3 having an opening is performed.
As this substrate 1, an insulating substrate such as sapphire or spinel (MgAl ₂ O ₄ ) having any one of the C-plane, R-plane, and A-plane as its main surface, SiC (6H, 4H, 3C), ZnS, An oxide substrate or the like that lattice-joins with ZnO, GaAs, Si, and a nitride semiconductor can be used. A nitride semiconductor that is the same type of substrate can also be used.
[0012]
Further, the first nitride semiconductor 2 may be grown on the substrate 1 via a buffer layer (not shown). As the buffer layer, AlN, GaN, AlGaN, InGaN or the like is used. The buffer layer is grown at a temperature of 300 ° C. or more and 900 ° C. or less and with a film thickness of 10 Å or more and 0.5 μm or less. This is to alleviate the lattice constant irregularity between the substrate 1 and the first nitride semiconductor 2 and is preferable in terms of reducing crystal defects.
[0013]
Furthermore, as the first nitride semiconductor 2 formed on the substrate 1, undoped GaN and GaN doped with n-type impurities such as Si, Ge, Sn, and S can be used. The physical semiconductor 2 is grown on a heterogeneous substrate at 900 ° C. to 1100 ° C., and if the thickness of the first nitride semiconductor 2 is 1.5 μm or more, a mirror surface with few pits may be formed on the crystal surface. it can.
[0014]
Then, as the protective film 3 is partially formed on the first nitride semiconductor 2 on the surface, after the step by Annie Le, the nitride semiconductor is generated decomposition surface nature difficult under the protective film Select the material you have. In the heat treatment step, preferably, oxidation of silicon oxide (SiO _x ), silicon nitride (Si _x N _y ), silicon nitride oxide (SiO _x N _y ), titanium oxide (TiO _x ), zirconium oxide (ZrO _x ), or the like. Further, materials such as oxides, nitrides, multilayer films thereof, and metals having a melting point of 1200 ° C. or higher can also be used.
[0015]
The shape of the protective film 3 is such that the nitride semiconductor can be removed from the opening of the protective film, and has a stripe shape, a lattice shape, an island shape, a circular shape, or a polygonal shape. Specific examples of the pattern shape having a polygonal opening include a hexagon punch type and a reverse pattern hexagonal column type.
[0016]
The width and planar shape of the opening of the protective film 3 are equal to the recess extraction width and the planar shape of the recessed portion of the first nitride semiconductor layer 2, and the size of the opening of the protective film 3 is, for example, a stripe shape. In this case, when the shape is a circle, the diameter width of the protective film extraction mold is 2 to 100 μm, preferably 10 to 50 μm.
[0017]
In addition, when the protective film 3 is formed in a stripe shape, the orientation flat surface may be formed as a sapphire A surface and shifted to the left or right with respect to the vertical axis of the orientation flat surface, and the growth surface is flat and good. Crystal is obtained. Specifically, it may be in the range of θ = 0 ° to 5 ° with respect to this vertical axis.
[0018]
As a method of forming the protective film 3, for example, the protective film 3 is formed by film formation using CVD, sputtering, vapor deposition, or the like, and further, a resist is applied, and the protective film is formed by photolithography. Etching is performed in a predetermined shape such as a stripe shape or a lattice shape.
Further, the stripe width and the lattice width of the protective film having a predetermined shape are not particularly limited. However, when the protective film is formed in stripes, the stripe width of the protective film is 5 to 50 μm, preferably 5 to 20 μm. Further, it is desirable that the window portion where the protective film 3 is not formed be narrower than the stripe width. When the protective film is formed in a lattice shape, the lattice width is 5 to 50 μm, preferably 10 to 20 μm.
Next, the thickness of the protective film is not particularly limited as long as the first nitride semiconductor portion under the protective film is not roughened in the heat treatment step, and is not particularly limited, but is in the range of 0.2 to 5 μm. Can be formed.
[0019]
Next, as shown in FIG. 2, after forming a protective film 3 having an opening on the first nitride semiconductor 2 in the first step, a step is formed in the first nitride semiconductor in the second step. Therefore, the recess is formed by etching from the opening of the protective film.
[0020]
Here, the depth of the recess is not particularly limited, and is 0.1 to 20 μm. The bottom surface of the recess is the first nitride semiconductor, but the substrate may be exposed.
In the first step, the shape of the protective film 3 includes a stripe shape, a lattice shape, an island shape, a circular shape, or a polygonal opening. Specific examples of the pattern shape having a polygonal opening include hexagonal punching and a hexagonal column having a reverse pattern.
When the concave portion is formed in such a planar shape such as a polygon, the stress strain generated in the joint formed by growing in the horizontal direction simultaneously with the vertical direction is concentrated at one point, and the joint point is dispersed over the entire substrate. Accordingly, it is possible to provide a nitride semiconductor substrate with good crystallinity in which the warpage is relaxed.
[0021]
The planar shape of the recess is circular or polygonal, and is preferably a regular circle or a regular polygon. The growth from the top surface of the first nitride semiconductor is substantially uniform, and the junction is a single point in the center of the recess. This is preferable because threading dislocations can be focused and reduced. Further, if the planar shape of the extraction mold is a hexagon, more preferably a regular hexagon, the distance from the side surface to the center of the recess is uniform, so that the defects to be focused are easily made into one point.
[0022]
The bottom surface after forming the recess may be the first nitride semiconductor surface or the substrate surface, and is circular or polygonal, preferably a regular triangle shape, a regular hexagon shape, or a perfect circle shape. . As a result, the nitride semiconductor substrate is suppressed in warpage, and a low defect and flat surface morphology can be easily formed.
[0023]
Here, the recess preferably has a cavity in the recess after the second nitride semiconductor layer is grown in a later step, and the etching depth of the first nitride semiconductor layer is 1 μm or more. May be exposed.
[0024]
When the extraction mold is circular, the diameter a can be 2 to 100 μm, more preferably 10 to 50 μm, and the distance b between the extraction molds can be 1 to 20 μm, more preferably 2 to 5 μm. it can.
In this case, the ratio (a / b) between a and b can be 2 ≦ a / b ≦ 25.
[0025]
In the case where the extraction mold is a polygon, the diagonal line a and the distance b between the extraction molds are 2 to 100 μm , more preferably 10 to 50 μm, and the distance b of the extraction mold is 1 to 20 μm. More preferably, it can be set to 2 to 5 μm. At this time, the ratio (a / b) between a and b can be 2 ≦ a / b ≦ 25.
[0026]
By selectively growing the second nitride semiconductor from the top surface of the first nitride semiconductor, the defects can be concentrated at one point by joining at the center of the recess and concentrating the joint at one point.
As for the second nitride semiconductor 4 obtained by the above process, a nitride semiconductor substrate having an uppermost mirror surface and a low defect in which the substrate stress is suppressed can be obtained. In addition, although the top surface remains as a crystal defect only in the center of the recess, which is a joint between the second nitride semiconductor layers, stress can be spread over the entire wafer, so that a flat surface morphology can be easily formed. Since a recess is formed in the recess obtained by etching, propagation of crystal defects from the bottom surface of the recess can be prevented, and an effect of reducing the warpage of the substrate can be obtained.
In the method for growing a nitride semiconductor substrate in the present invention, crystal defects can be further reduced by repeating the growth step.
Furthermore, it is possible to grow a substrate in combination with a nitride semiconductor layer in which a nitride semiconductor layer is formed by using a nitride semiconductor layer as a cylinder and a polygonal column, and a lateral growth layer obtained by repeating the above steps several times.
[0027]
With the polygonal or circular recess extraction shape as described above, the second nitride semiconductor can grow using the first nitride semiconductor as a nucleus and can be joined at one point in the center of the recess.
Further, as a method for forming a recess in the first nitride semiconductor layer, a blasting method can be used in addition to the etching method.
[0028]
Then after the second step, as shown in FIG. 3, the recess side by a heat treatment in a state having a protective film on the third convex portion of the patterned substrate to the step shape by etching on a step And the shape of the bottom surface is the decomposition surface.
[0029]
Here, the heat treatment is to raise the temperature in a state where a protective film is provided on a substrate on which irregularities are formed, and to form a decomposition surface on the surface of the first nitride semiconductor.
This decomposition surface is a layer in which the growth rate of the second nitride semiconductor has a growth rate difference between the region under the protective film and the decomposition surface in a later step. It is assumed that the semiconductor layer grows from the upper surface of the convex portion.
An example of the heat treatment is annealing, and the annealing temperature is 400 ° C. or higher , preferably 600 ° C. or higher. The annealing time is 1 to 60 minutes.
[0030]
Next, as shown in FIG. 4, as a fourth step, the protective film is removed after the third step, and a second nitride semiconductor is grown as shown in FIG.
As a method for removing the protective film, dry etching or wet etching can be used, and both methods can remove the protective film without reducing the crystallinity of the nitride semiconductor. Furthermore, since the depth at which the protective film is removed can be easily controlled by dry etching, it can be used for thin film formation and nitride semiconductor surface processing.
[0031]
By removing the protective film, problems such as abnormal growth of the nitride semiconductor and deterioration of crystallinity due to decomposition and diffusion of the protective film such as SiO ₂ during the growth of the nitride semiconductor grown on the protective film are suppressed. be able to.
[0032]
Thereafter, by removing the protective film and growing the second nitride semiconductor 4 from the first nitride semiconductor convex portion, the second nitride semiconductor is bonded to each other, and a nitride semiconductor substrate having a flat mirror surface is obtained. Can be formed.
In addition, since the nitride semiconductor does not grow or is difficult to grow from the end face and the bottom face of the recess, a space can be formed in the recess that is the lower portion of the portion having few crystal defects grown in the lateral direction. With this space, it is possible to suppress stress generated during the growth in which the second nitride semiconductor 4 grown on the first nitride semiconductor 2 is grown in the lateral direction.
[0033]
As the second nitride semiconductor 4, undoped GaN and GaN doped with n-type impurities such as Si, Ge, Sn, and S, or GaN doped with p-type impurities such as Mg and Zn can be used. The second nitride semiconductor 4 is grown at 900 to 1100 ° C.
The film thickness of the second nitride semiconductor 4 is 5 to 30 μm.
[0034]
In the present invention, each of the first nitride semiconductor 2 and the second nitride semiconductor 4 is expressed by the general formula In _x Al _y Ga _1-xy N (0 ≦ x, 0 ≦ y, x + y ≦ 1). Having the composition represented. However, these may have different compositions.
In the method for growing a nitride semiconductor according to the present invention, a method for growing a nitride semiconductor such as the first nitride semiconductor 2 and the second nitride semiconductor 4 is not particularly limited. Methods such as phase growth method), HVPE (halide vapor phase epitaxy), MBE (molecular beam epitaxy method), MOCVD (metal organic chemical vapor deposition) can be applied.
[0035]
In addition, as an etching method for forming irregularities in the nitride semiconductor, there are methods such as wet etching and dry etching, and dry etching is preferably used to form a smooth surface. Dry etching includes, for example, reactive ion etching (RIE), reactive ion beam etching (RIBE), electron cyclotron etching (ECR), and the like. It can be etched.
[0036]
【Example】
Although the Example of this invention is shown below, this invention is not limited to this.
[Example 1]
Using a sapphire substrate 1 with the C-plane as the principal plane and the orientation flat plane as the A-plane, using a MOCVD apparatus, using a temperature of 500 ° C., hydrogen as the carrier gas, ammonia and TMG (trimethylgallium) as the source gas, and sapphire A buffer layer made of GaN is grown on the substrate 1 to a thickness of 200 angstroms.
[0037]
Next, in a MOCVD apparatus, the temperature is set to 1050 ° C. under normal pressure conditions, TMG (trimethylgallium) is 230 μmol / min (V / III ratio = 900), and ammonia is 0.2 mol / min. The first nitride semiconductor 2 made of undoped GaN is grown to a thickness of 2.5 μm.
[0038]
A protective film made of SiO ₂ is formed with a film thickness of 0.5 μm on the first nitride semiconductor 2 by CVD, a striped photomask is formed, and a stripe width of 6 μm and a window of 14 μm are formed by etching. A protective film 3 made of SiO ₂ is formed. Note that the stripe direction of the protective film 3 is a direction perpendicular to the sapphire A surface, and then the first nitride semiconductor 2 that is the exposed portion is ground by 1 μm to form irregularities.
[0039]
Next, annealing is performed at 900 ° C. for 20 minutes, and then the SiO ₂ protective film remaining on the top surface of the first nitride semiconductor protrusion is completely removed with buffered hydrofluoric acid.
[0040]
Thereafter, in the MOCVD apparatus, the second nitride semiconductor 4 is selectively grown in the vertical direction and the horizontal direction from the upper surface of the convex portion of the first nitride semiconductor 2. As growth conditions, TMG 230 μmol / min (V / III ratio = 900) is used as the source gas, ammonia 0.2 mol / min, undoped GaN is used at normal pressure, the temperature is 1050 ° C., and the film thickness is 15 μm. Grow in.
[0041]
The surface of the second nitride semiconductor 4 obtained as described above is a nitride semiconductor substrate having a low defect and a flat surface, and is a substrate with less warpage in which stress applied to the substrate, which is the object of the present invention, is scattered throughout the substrate. be able to.
[0042]
[Example 2]
In the first embodiment, the second nitride semiconductor 4 is grown in the same manner except that the first nitride semiconductor 2 which is the opening of the protective film is etched until the sapphire substrate is exposed.
As a result, good results can be obtained as in the first embodiment.
[0043]
[Example 3]
In Example 1, the second nitride semiconductor 4 is grown in the same manner except that the width of the protective film is 10 μm and the width of the opening is 10 μm. As a result, good results can be obtained as in the first embodiment.
[0044]
[Example 4]
In Example 1, the nitride semiconductor is grown in the same manner except that the thickness of the first nitride semiconductor is 5 μm, the pattern formation of the protective film has a circular opening, and the circular extraction type recess is formed. . This circular mold has a diameter of 20 μm, and the distance between the windows is 5 μm.
The obtained second nitride semiconductor 4 can be a nitride semiconductor having low defects and uniform defects with the substrate warpage suppressed.
[0045]
[Example 5]
In Example 1, the film thickness of the first nitride semiconductor is 5 μm, the pattern formation of the protective film is a regular hexagonal opening, the regular hexagonal diagonal is 20 μm, and the distance between the openings is 5 μm. After forming the pattern of the protective film 3 having a regular hexagonal opening, a nitride semiconductor is grown in the same manner except that a recess by etching is formed to a depth of 3 μm.
The second nitride semiconductor 4 can be a nitride semiconductor that has low defects and uniform defects while suppressing warping of the substrate.
[0046]
[Example 6]
In Example 1, after removing the protective film, a second nitride semiconductor is grown at a temperature of 1050 ° C. using TMG, ammonia, and silane gas as source gases. The obtained nitride semiconductor substrate can obtain a Si-doped n-type nitride semiconductor.
[0047]
【The invention's effect】
According to the nitride semiconductor growth method of the present invention, the second nitridation is performed in the vertical direction and the horizontal direction by growing from the upper surface of the first nitride semiconductor, instead of growing the nitride semiconductor in a stressed state. Since the second nitride semiconductor is bonded to each other to form a bonded portion by growing the semiconductor and further growing, it is possible to provide a nitride semiconductor substrate that is flat and mirror-shaped and has few crystal defects.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate obtained in each step of the present invention.
FIG. 2 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate obtained in each step in the present invention.
FIG. 3 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate obtained in each step in the present invention.
FIG. 4 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate obtained in each step in the present invention.
FIG. 5 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate obtained in each step in the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... 1st nitride semiconductor 3 ... Protective film 4 ... 2nd nitride semiconductor

Claims (6)

The first nitride semiconductor on a substrate, has a step, a concave portion side surface and the bottom surface of the stepped and has a decomposition surface of the nitride semiconductor, provided on the protrusion upper surface of the first nitride semiconductor a layer of the second nitride semiconductor, a nitride semiconductor substrate having a space recessed portion of the first nitride semiconductor. The first nitride semiconductor on the substrate has a step, the side surface of the concave portion of the step has a decomposition surface of the nitride semiconductor, the bottom surface of the concave portion is an exposed surface of the substrate, and the first nitride A nitride semiconductor substrate having a second nitride semiconductor layer provided on the top surface of the convex portion of the semiconductor semiconductor, and having a space in the concave portion of the first nitride semiconductor. The first nitride semiconductor substrate according to claim 1 or 2 decomposition surface of the recess provided in the nitride semiconductor is more formed Netsusho sense.   The nitride semiconductor substrate according to claim 3, wherein the heat treatment is annealing. A method for growing a nitride semiconductor substrate having a nitride semiconductor on a substrate, comprising:
A first step of growing a first nitride semiconductor on a substrate and forming a protective film having an opening in the first nitride semiconductor ;
A second step of forming a recess in the opening of the protective film and forming a stepped shape in the first nitride semiconductor;
A third step of forming a decomposed surface by decomposing the exposed portion of the nitride semiconductor by heat treatment in the recess provided in the first nitride semiconductor;
The protective film on the first nitride semiconductor is removed, a second nitride semiconductor is selectively grown from the upper surface of the convex portion of the first nitride semiconductor , and the first nitride provided with the decomposition surface the fourth step and the nitride semiconductor substrate growth method having a forming the second layer of nitride semiconductor having between empty recess sEMICONDUCTOR.   The method for growing a nitride semiconductor substrate according to claim 5, wherein in the second step, heat treatment is performed at a temperature of 400 ° C. or higher.

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