JP2010042958A - Method for producing group iii-v nitride semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a group III-V nitride semiconductor substrate reducing the distribution of inclination of crystal axes within the face of the group III-V nitride semiconductor substrate. <P>SOLUTION: The method for producing a group III-V nitride semiconductor substrate includes heteroepitaxially growing a group III-V nitride semiconductor crystal on the following heterogeneous substrate 1. In the heterogeneous substrate 1, an inclination angle α of a crystal axis (a) of a crystal face as a reference of the heterogeneous substrate 1 with respect to the normal line (n) of the heterogeneous substrate surface 1a, and an inclination angle η of the crystal axis (a) at a position P of 20 mm distant in the radial direction from the center O of the heterogeneous substrate 1 with respect to the normal line (n) of the heterogeneous substrate surface 1a satisfy a relationship of 0.02°<¾η-α¾, as well as a crystal axis (a) at each point within the substrate surface 1a inclines outward in the radial direction of the heterogeneous substrate 1 with respect to the normal line (n) of the substrate surface 1a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a method for manufacturing a group III-V nitride semiconductor substrate in which a group III-V nitride semiconductor substrate is obtained by heteroepitaxial growth of a group III-V nitride semiconductor crystal on a different substrate.

  Nitride-based semiconductor materials such as gallium nitride (GaN), indium gallium nitride (InGaN), and gallium aluminum nitride (GaAlN) have a sufficiently large forbidden band and a direct transition type between bands. Application to is actively studied. In addition, application to electronic devices is also expected due to the high saturation drift velocity of electrons and the use of a two-dimensional carrier gas by heterojunction.

  Silicon (Si) and gallium arsenide (GaAs), which are already widely used in the world, are homoepitaxially grown on a substrate made of the same kind of material such as a Si substrate and a GaAs substrate, respectively. Have been used. In homoepitaxial growth on the same kind of substrate, crystal growth proceeds in the step flow mode from the initial stage of growth, so that there are few crystal defects and a flat epitaxial growth surface is easily obtained.

  Nitride-based semiconductors, on the other hand, are difficult to grow bulk crystals. Recently, GaN free-standing substrates of a level that can withstand practical use have recently been developed and are in use. It is a sapphire substrate. On this sapphire substrate, GaN is once heterogeneous by vapor phase growth methods such as metalorganic vapor phase epitaxy (MOVPE), molecular beam vapor phase epitaxy (MBE), and hydride vapor phase epitaxy (HVPE). A method is generally used in which an epitaxial layer of a nitride-based semiconductor is grown for epitaxial growth and a device is formed continuously or in another growth furnace.

Since the lattice constant of sapphire substrate is significantly different from that of GaN, a single crystal film cannot be grown by directly growing GaN on the sapphire substrate. For this reason, a method has been devised in which a buffer layer of AlN or GaN is once grown on a sapphire substrate at a low temperature of about 500 ° C., and lattice distortion is relaxed by this low temperature growth buffer layer, and then GaN is grown thereon. It was. Using this low-temperature grown nitride layer as a buffer layer, GaN single crystal epitaxial growth has become possible.
However, even with this method, it is difficult to shift the crystal lattice between the sapphire substrate and the low-temperature growth buffer layer. At the beginning of the growth, the crystal growth proceeds in the three-dimensional island growth mode instead of the above-described step flow mode. To do. For this reason, the GaN thus obtained has a dislocation density of 10 ⁹ to 10 ¹⁰ cm ⁻² . This defect becomes an obstacle in manufacturing GaN-based devices, particularly LD (laser diode) and ultraviolet LED (light emitting diode).

In recent years, growth techniques such as ELO (Epitaxially Lateral Overgrowth), FIELO, and pendeo epitaxy have been reported as methods for reducing the density of defects generated due to the difference in lattice constant between sapphire and GaN. In these growth techniques, a mask patterned with SiO ₂ or the like is formed on GaN grown on a substrate such as sapphire, and further a GaN crystal is selectively grown from the window portion of the mask. By covering GaN with lateral growth, the propagation of dislocations from the underlying crystal is prevented. With the development of these growth techniques, the dislocation density in GaN can be drastically reduced to about 10 ⁷ cm ⁻² .

Further, Patent Document 1 discloses a method in which a GaN layer having a reduced dislocation density is epitaxially grown thickly on a dissimilar substrate such as a sapphire substrate, and the GaN layer is peeled off from the base substrate after growth and used as a self-supporting GaN substrate. Various proposals have been made.
JP 2000-22212 A

  However, the following problems to be solved remain in the GaN substrate manufactured by the conventional method described above.

As described above, a GaN crystal for producing a GaN free-standing substrate is once heteroepitaxially grown on a heterogeneous substrate such as a sapphire substrate or a GaAs substrate having greatly different lattice constants. A GaN crystal grown on a heterogeneous substrate is warped due to a lattice constant difference or a linear expansion coefficient difference from the heterogeneous substrate serving as a base substrate. It is known that this warp is observed remarkably even in a GaN free-standing substrate from which the base substrate is removed. Warping has already begun to occur during crystal growth, and it may grow in a warped shape, or it may be warped by growing under the presence of strain and removing the underlying substrate.
For example, Patent Document 1 illustrates an example in which a convex warpage occurs in a GaN free-standing substrate manufactured using a GaAs substrate as a base substrate (FIGS. 11 and 15 of Patent Document 1). When the GaN substrate is warped, the crystal axis of the GaN substrate has a distribution in the plane so as to correspond to the warp. This is pointed out in the description using FIG.

  A GaN free-standing substrate is often marketed in the form of mirror polishing on the surface, like other semiconductor material substrates, and is a flat GaN substrate in appearance. Even if it is a flat GaN substrate, if the original GaN substrate before polishing is warped, it causes a distribution in the inclination of the crystal axis of the GaN substrate.

Next, the inclination distribution of the crystal axis due to the warp of the substrate W will be described.
FIG. 8 is an explanatory diagram for defining parameters representing the direction of the inclination of the crystal axis of the substrate W. In FIG. It is assumed that at a certain point A on the surface (front surface) S of the substrate W, the surface S has a certain slope with a low index surface (reference crystal plane) f closest to the surface S. At this time, the inclination of the crystal axis (direction of the crystal axis) a of the low index plane f indicates how much the normal vector V of the low index plane f closest to the surface S is relative to the normal line n of the surface S. Find out if it is tilted. This can be easily known by X-ray diffraction measurement. In order to know which side the original substrate before polishing is warped, the vector V _S generated when the normal vector V of the low index plane f closest to the surface S of this substrate is projected onto the surface S You can see if you are facing in the plane.

Figure 9 shows a freestanding GaN substrate W ₁ after the surface S ₀ is flat polished front and back surfaces of the GaN free-standing substrate W ₀ had a concave warp _(shown by a chain line). FIG. 9A is a cross-sectional view, and FIG. 9B is a plan view seen from the substrate surface side.
In the surface S ₀ is the original GaN free-standing substrate W before polishing with a concave warpage ₀ convergence, rather than the normal of the position of the surface S ₀ parallel to one another, the surface S ₀ above the one point (or a predetermined area) The crystal axis a has a similar distribution. Accordingly, the crystal axis a of the GaN free-standing substrate W ₁ after polishing, as shown in FIG. 9 (1), having a distribution as to converge to the GaN free-standing substrate W ₁ above the one point (or a predetermined region). This was displayed by using the vector V _S is 9 (2), the vector V _S in the substrate W ₁ side are both converge toward to a specific site near the center of the substrate W ₁ It becomes such a distribution, and the magnitude of the vector V _S is smaller at the center of the substrate W _1, the larger becomes the outer periphery of the substrate W _1.

  When an AlGaN mixed crystal epitaxial layer is grown on a GaN substrate having a crystal axis tilt distribution as shown in FIG. 9, in-plane emission wavelength variation caused by the crystal axis tilt distribution occurs, resulting in a decrease in yield. It was the cause. This is a problem that has not been seen in conventional semiconductor materials such as Si and GaAs, and is unique to III-V nitride semiconductor materials that use a thick film layer heteroepitaxially grown on a heterogeneous substrate as a substrate. It can be said that it is a problem.

The object of the present invention is to solve the above-mentioned problems and to achieve in-plane crystals of a group III-V nitride semiconductor substrate even if the group III-V nitride semiconductor substrate obtained by growing on a different substrate is warped. An object of the present invention is to provide a method for manufacturing a group III-V nitride semiconductor substrate capable of reducing the distribution of the inclination of the axis.

In the first aspect of the present invention, an angle α at which a crystal axis of a crystal plane serving as a reference of the heterogeneous substrate is inclined with respect to a normal line of the surface of the heterogeneous substrate at the center of the heterogeneous substrate, and an inclination direction thereof The relationship with the angle η at which the crystal axis is inclined with respect to the normal of the surface of the different substrate at a position 20 mm in the radial direction from the center of the different substrate is 0.02 ° <| η−α |. And using a heterogeneous substrate in which the crystal axis is inclined outward in the radial direction of the heterogeneous substrate with respect to the normal of the heterogeneous substrate surface at each point in the heterogeneous substrate surface, and III on the heterogeneous substrate A method for producing a group III-V nitride semiconductor substrate comprising heteroepitaxially growing a group V nitride semiconductor crystal.

The group III-V nitride semiconductor substrate is preferably hexagonal, and more preferably the C-plane is a low index plane that is hexagonal and closest to the substrate surface. Further, the C plane is preferably a group III plane. Alternatively, the group III-V nitride semiconductor substrate may be hexagonal and the low index plane closest to the substrate surface may be any one of the A plane, M plane, and R plane.
The surface of the group III-V nitride semiconductor substrate is preferably mirror-polished.

In a second aspect of the present invention, the group III-V nitride semiconductor crystal is heteroepitaxially grown on the heterogeneous substrate using the method for manufacturing a group III-V nitride semiconductor substrate according to the first aspect. Then, the heterogeneous substrate is removed to obtain the III-V group nitride semiconductor substrate, thereby producing a group III-V nitride semiconductor substrate.

According to the present invention, even if a group III-V nitride semiconductor substrate obtained by growing on a heterogeneous substrate is warped by giving a distribution of a predetermined crystal axis to the heterogeneous substrate, the III-V group caused by this warp. The distribution of the inclination of the crystal axis in the plane of the nitride semiconductor substrate can be reduced. Therefore, variations in in-plane characteristics of devices manufactured using the obtained group III-V nitride semiconductor substrate can be reduced, and the yield can be greatly improved.

Embodiments of a method for producing a group III-V nitride semiconductor substrate according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a heterogeneous substrate used in the present embodiment. 1A is an explanatory diagram for explaining the crystal axis distribution of a heterogeneous substrate, FIG. 1B is a cross-sectional view showing the crystal axis distribution of the heterogeneous substrate, and FIG. 1C is a heterogeneity of FIG. It is a top view which shows the crystal axis distribution which looked at the board | substrate from the surface side.

As shown in FIG. 1, the heterogeneous substrate 1 is a flat circular substrate (wafer) whose front surface (front surface) 1a and rear surface 1b are flat and parallel to each other.
The crystal axis a of the crystal plane serving as the reference of the heterogeneous substrate 1 is tilted by the angle α at the center O of the heterogeneous substrate 1 with respect to the normal n of the surface 1a. is doing. Further, the crystal axis a is inclined at an angle α at the substrate center O in the inclined direction, and at a position 20 mm in the radial direction from the center O of the heterogeneous substrate 1, the crystal axis a is at an angle η with respect to the normal n of the surface 1 a. Just tilted. The relationship between the angle α and the angle η is such that | η−α |, which is the absolute value of η−α, is 0.02 °.
It is larger, and | η−α |> 0.02 °.
For example, in the case of a hexagonal crystal system such as a sapphire substrate, the crystal plane serving as a reference for the heterogeneous substrate 1 is a C plane ((0001) plane), A plane ((11-20) plane), M plane ((( 10-10) plane), R plane ((-1012) plane), and the like.

Furthermore, at each point in the surface of the heterogeneous substrate 1, the crystal axis a is inclined outward in the radial direction of the heterogeneous substrate 1 with respect to the normal line n of the surface 1 a. That is, as shown in FIG. 1 (2), the crystal axis a at each point in the plane of the heterogeneous substrate 1 has a distribution that converges to one point (or a predetermined region) below the heterogeneous substrate 1. FIG. 1 (3) shows the in-plane distribution of the inclination of the crystal axis a of the heterogeneous substrate 1, and the normal vector V of the crystal plane as a reference defined in FIG. 8 is projected onto the surface 1a. The vector V _S is used for display. As shown in FIG. 1 (3), the vectors V _S in the surface of the heterogeneous substrate 1 are all distributed so as to diverge from a specific portion near the center of the substrate 1 to the outer peripheral side of the substrate 1, and the vector V _S. Is smaller at the center of the substrate 1 and is larger toward the outer peripheral side of the substrate 1.

  The direction of the inclination of the crystal axis a in the surface of the heterogeneous substrate 1 can be obtained by X-ray diffraction measurement. Specifically, an X-ray diffraction peak is measured while rotating the crystal around an axis perpendicular to the diffraction plane. Then, when the crystal axis a is inclined, the peak position is shifted and observed. The inclination direction of the crystal axis a can be determined by looking at which direction of the crystal the diffraction peak is shifted most greatly. If the inclination of the crystal axis a is measured at a plurality of points in the plane of the heterogeneous substrate 1, the distribution of the inclination can be easily discriminated.

Generally, when a group III-V nitride semiconductor layer such as GaN is grown on a heterogeneous substrate such as a sapphire substrate, internal stress caused by a difference in defect density between the front and back surfaces of the group III-V nitride semiconductor layer As a result, the surface of the separated group III-V nitride semiconductor layer is warped in a concave shape. For this reason, when the front and back surfaces of the group III-V nitride semiconductor layer are polished to produce a flat group III-V nitride semiconductor substrate, the crystal axis of the polished substrate is shown in FIG. When expressed using a distribution inclined to a specific portion near the center of the substrate as shown in FIG. 9B or a vector V _S on the substrate surface as shown in FIG. The distribution converges toward the target.

Since the nitride semiconductor layer epitaxially grown on the heterogeneous substrate inherits the distribution of crystal axes of the heterogeneous substrate, the heterogeneous substrate 1 of the present embodiment satisfies the relationship of 0.02 << η-α | A heterogeneous substrate 1 in which the crystal axis a is inclined outward in the radial direction of the heterogeneous substrate 1 with respect to the normal line n of the surface 1a of the heterogeneous substrate 1 at each point in the plane of the substrate 1 is used. A group III-V nitride semiconductor substrate generated by warping using a heterogeneous substrate 1 having a tilt angle distribution in a direction opposite to the tilt angle distribution inward in the radial direction of the crystal axis of the group V nitride semiconductor substrate The distribution of the tilt of the crystal axis is offset and reduced.
For this reason, the distribution and variation of the in-plane crystal axis inclination of the group III-V nitride semiconductor substrate obtained by the manufacturing method of the present embodiment is small, and this group III-V nitride semiconductor substrate is used for the production. In a device to be used, for example, a light emitting element, variation in the in-plane emission wavelength due to the tilt distribution of the crystal axis of the epitaxial layer can be reduced, and the yield of the light emitting element can be greatly improved.

The inclination angle α of the crystal axis a at the center O of the heterogeneous substrate 1 and 20 mm in the radial direction from the center O
The relationship between the inclination angle η of the crystal axis a at the position of η is set to | η−α |> 0.02 °.
This is because if | η−α | is 0.02 ° or less, the canceling effect by the inclination angle distribution cannot be sufficiently obtained.

FIG. 2 shows another embodiment of the heterogeneous substrate used in the present invention.
As shown in FIG. 2, the heterogeneous substrate 1 of this embodiment has a flat back surface 1b, a front surface 1a formed on the concave surface of the flat back surface 1b, a thin central portion of the heterogeneous substrate 1, The thickness increases toward the outer peripheral side of the substrate 1. The crystal axes a of the crystal plane serving as a reference in the heterogeneous substrate 1 are almost uniformly aligned in a direction perpendicular to the flat back surface 1b. For this reason, the normal line n of the surface 1a and the crystal axis a substantially coincide with each other at the center of the heterogeneous substrate 1, and the crystal axis a tilts outward in the radial direction with respect to the normal n of the surface 1a as the distance from the center of the substrate increases. The corner is large. When the heterogeneous substrate 1 having the concave surface 1a in FIG. 2 is bent to flatten the surface 1a, the inclination distribution of the crystal axis a of the surface 1a is the same as that of the heterogeneous substrate 1 in FIG. An offset effect equivalent to that of the different substrate 1 of FIG. 1 is obtained. Note that the back surface 1b of the heterogeneous substrate 1 is not necessarily flat.

  2 is produced, for example, by applying an external force to the heterogeneous substrate having a flat surface and curving the heterogeneous substrate so that the surface has a convex shape with a predetermined curvature. Later, it is obtained by releasing the external force.

The heterogeneous substrate is not limited to the sapphire substrate, and GaAs, SiC, ZnC, AlN, GaN, or the like can be used. In addition, the III-V group nitride semiconductor substrate includes a GaN substrate,
An AlN substrate etc. are mentioned.
In the above embodiment, the case where the surface of the separated group III-V nitride semiconductor layer is warped in a concave shape when the group III-V nitride semiconductor layer is grown on a different substrate is described. However, the present invention can also be applied to the case where the surface of the separated group III-V nitride-based semiconductor layer is warped convexly. Specifically, the relation of 0.02 << η−α | is satisfied, and the crystal axis a is different from the normal line n of the surface 1a of the heterogeneous substrate 1 at each point in the plane of the heterogeneous substrate 1. By using the dissimilar substrate 1 inclined inward in the radial direction, it is possible to offset and reduce the distribution of the inclination of the crystal axis of the group III-V nitride semiconductor substrate caused by warping.

Next, examples of the present invention will be described.
A self-supporting GaN substrate was produced using a void-assisted separation method (VAS method). The substrate manufacturing procedure and conditions are as follows.

First, ten commercially available single-crystal sapphire C-plane substrates having a diameter of 2 inches were prepared as different substrates, which are base substrates for GaN growth. The inclination distribution of the crystal axis (C axis) of these sapphire C-plane substrates was almost uniform in the plane as shown in FIG. With respect to these ten single crystal sapphire C-plane substrates, as shown in FIG. 1, the crystal axis (C axis) with respect to the normal of the substrate surface is located at the center of the substrate and in the off-direction position 20 mm away from the center. The tilt angle was measured. The measurement results are shown in Table 1. | Η−α | is 0.02 ° or less, and no distribution of specific inclination was found in the inclination distribution of crystal axes in the plane of the substrate surface. Table 1 shows the difference in surface height between the center position of the surface of the sapphire substrate and the position of radius r = 20 mm from the center as the amount of warp (μm). In Table 1 (the same applies to Tables 2 and 3), if a convex warp is generated upward when the substrate surface is turned up, it is convex, and if a concave warp occurs, it is concave. The next numerical values of convex and concave represent the amount of warpage. For example, in sample number No. 1, “convex 4” has a convex warp upward when the substrate surface is up, and the warpage amount is 4 μm at a position in the off direction 20 mm away from the substrate center. Represents.

  Five sapphire substrates of sample numbers No. 1 to No. 5 were used as sapphire substrates (different types of substrates) of a comparative example (conventional example). Further, the following processing was performed on the five sapphire substrates of sample numbers No. 6 to No. 10 to obtain sapphire substrates (heterogeneous substrates) of the examples. The sample numbers of the sapphire substrates of the examples after being processed into the sapphire substrates of sample numbers No. 6 to No. 10 are No. 11 to No. 15, respectively.

Processing applied to the five sapphire substrates 10 of sample numbers No. 6 to No. 10 will be described with reference to FIG.
For processing, a ceramic plate 2 having a spherical convex surface portion 3 as shown in FIG. Five types of ceramic plates 2 having a constant curvature in which the convex surface portion 3 of the ceramic plate 2 was bent by d = 10, 20, 30, 40, 50 μm at a distance P of radius r = 20 mm from the center O were prepared. .
Using the wax on the convex surface portion 3 of these five types of ceramic plates 2, the sample number No.
The back surfaces 10b of the sapphire substrates 10 of No. 6 to No. 10 were pasted (FIG. 3B).
Next, the surface 10a of the sapphire substrate 10 where the warp occurred was flattened corresponding to the convex surface portion 3 of the ceramic plate 2. First, grinding was performed using a grindstone having a diamond abrasive grain size of about 15 μm. Next, the platen was polished by rotating the platen while supplying a diamond abrasive slurry having an abrasive particle size of 3 μm to a tin platen whose surface was processed into a spiral groove. Finally, polishing was performed by rotating the surface plate while supplying the colloidal silica slurry to the surface plate to which the polishing cloth was pasted, and processed into a flat surface 10a having no processing distortion (FIG. 3C).
Next, the wax was heated and the sapphire substrate 10 was removed from the ceramic plate 2 and then washed (FIG. 3D). When the sapphire substrate 10 is removed from the ceramic plate 2, the sapphire substrate 10 that has been affixed to the convex surface portion 3 of the ceramic plate 2 and has been elastically deformed returns to its original state, the back surface 10 b becomes flat, and grinding processing, etc. The finished surface 10a became concave. The inclination distribution of the crystal axis a of these sapphire substrates 10 was almost uniform in the plane perpendicular to the back surface 10b as before the processing. In this way, the sapphire substrate 10 of the sample numbers No. 11 to No. 15 was produced. The sapphire substrate 10 of these examples has the same crystal axis distribution as the substrate 1 of the above embodiment shown in FIG.

For the sapphire substrate 10 of the embodiment subjected to the above processing, similarly to the sapphire substrate 10 of the sample numbers No. 1 to No. 10 described above, at the position in the off direction that is 20 mm away from the center and the center of the substrate, The tilt angle of the crystal axis with respect to the normal line of the substrate surface 10a was measured. The measurement results are shown in Table 2. As shown in FIG. 1C, the inclination distribution of the C-plane crystal axis with respect to the normal of the surface 10a has a distribution that increases toward the outer periphery of the substrate as the distance r from the substrate center increases. Table 2 also shows the amount of warpage of the sapphire substrate 10 at the position of r = 20 mm.

Next, single-crystal sapphire substrates of comparative examples of sample numbers No. 1 to No. 5, and sample number No. 1
A total of 10 single crystal sapphire substrates of Examples 1 to No. 15 were manufactured by a VAS method as shown in FIG.

The sapphire substrate 10 is prepared as described above (step (a)), and the undoped GaN layer 11 is formed on the prepared sapphire substrate 10 using TMG (trimethylgallium) and NH ₃ (ammonia) as raw materials by the MOVPE method. Was grown by 300 nm (step (b)). On this GaN epitaxial substrate, a Ti thin film 12 is deposited to a thickness of 20 nm (step (c)), and this is placed in an electric furnace, and in an air stream of H ₂ (hydrogen) mixed with 20% NH ₃ at 1050 ° C. A heat treatment for 5 minutes was performed to change the Ti thin film 12 into a mesh-like TiN film 14, and at the same time, voids (voids) were formed in the GaN layer 11 to form a void-formed GaN layer 13 (step (d)).

This was put in an HVPE furnace, and a GaN layer 15 was deposited thereon at 850 μm (step (e)). The raw materials used for the HVPE growth were NH ₃ and GaCl (gallium chloride), and a mixed gas of N ₂ and H ₂ was used as a carrier gas. The growth conditions are normal pressure and a substrate temperature of 1040 ° C. The GaN layer 15 was peeled from the sapphire substrate 10 with the void-formed GaN layer 13 as a boundary in the temperature lowering process after the growth was completed (step (f)). The peeled GaN layer 15 has a (0001) Ga surface on the surface (front surface).

  The peeled GaN layer 15 was used as a GaN free-standing substrate 16 (step (g)). The Ga surface which is the front surface (front surface) of the obtained GaN free-standing substrate 16 was all concave (the back surface was all convex). Further, when the amount of warpage at the position of radius r = 20 mm was measured, the results shown in Table 3 were obtained.

  The obtained GaN free-standing substrate 16 was mirror-polished on the front surface and the back surface to finish a GaN substrate 17 having a thickness of 400 μm. The 10 GaN substrates 17 are all transparent and have a flat mirror surface, and the surface roughness is all Ra (arithmetic mean roughness) values when scanning the 500 μm range using a surface step meter. It was 10 nm or less.

In order to examine the inclination direction of the C axis with respect to the surface of the GaN free-standing substrate 17 thus manufactured, X-ray diffraction measurement was performed on all GaN substrates. The measurement is 5 points indicated by black circles in FIG. The measurement points are the center position (1 point) of the substrate, the position 20 points away from the center position of the substrate in the direction parallel to the <1-100> direction of the substrate (2 points), and the center position of the substrate. A total of 5 points were measured, including a position (2 points) 20 mm away in the direction perpendicular to the <1-100> direction of the substrate. The distribution of the direction of the vector (V _S ) when the vector of the C-axis inclination measured at each point is projected onto the substrate surface, that is, the direction of the C-axis inclination is distributed in the substrate plane. Examined. As a result, a distribution in which the direction of the C-axis inclination converges toward a specific region inside the GaN substrate as shown in FIG. There was a difference in the variation in the inclination of the C axis (indicated by the difference between the maximum inclination value and the minimum inclination value of the C axis in the five-point measurement results). The results are shown in Table 3 above.

  From the above results, in the GaN substrate manufactured using the sapphire substrate of the example, the inclination of the crystal axis due to the warp caused by the growth of the GaN substrate is different from the inclination distribution of the crystal axis in the direction opposite to the sapphire substrate as the base substrate. It was confirmed that the variation in the tilt of the crystal axis in the GaN substrate surface after flattening was reduced.

Incidentally, when the dislocation density of the self-supporting GaN substrate 17 of the example manufactured under the above conditions was measured, the distribution of 5 points in the plane in the vertical and horizontal directions r = 20 mm from the center (the same as FIG. 5) is ( 3 ± 0.9) × 10 ⁶ cm ^−2, and it was confirmed that low dislocations were uniformly reduced over the entire surface of the substrate. That is, it was confirmed that the distribution regulation of the crystal axis inclination according to the present invention is not a factor that deteriorates the defect density of the GaN substrate.

An epitaxial layer for LED having a structure shown in FIG. 6 was grown on the GaN substrate 17 by using a reduced pressure MOVPE method. The grown layers are, in order from the GaN substrate 12 side, a Si-doped n-type GaN buffer layer 18, a Si-doped n-type Al _0.15 GaN cladding layer 19, and three periods of In
A GaN-MQW (multiple quantum well) layer 20 and an Mg-doped p-type Al _0.15 GaN cladding layer 21. The total thickness of the epitaxial layers 18 to 21 is 100 μm or less.

Epitaxial layers having the same LED structure were grown on all ten GaN substrates 17 to produce LED epitaxial wafers, and in-plane emission wavelength variations were examined by photoluminescence measurement. The result is shown in FIG.
In the LED epitaxial layer formed on the GaN substrate 17 produced using the sapphire substrate of the example (sample numbers No. 11 to No. 15), a commercially available sapphire substrate of the comparative example (sample numbers No. 1 to No. 1). Compared with the LED epitaxial layer formed on the GaN substrate 17 produced using 5), the in-plane emission wavelength variation could be greatly reduced.

FIG. 1 shows a heterogeneous substrate used in one embodiment of the present invention. FIG. 1 (1) is an explanatory diagram for explaining the crystal axis distribution of the heterogeneous substrate, and FIG. 1 (2) is a crystal of the heterogeneous substrate. FIG. 1C is a cross-sectional view showing the axis distribution, and FIG. 1C is a plan view showing the crystal axis distribution when the heterogeneous substrate of FIG. It is sectional drawing which shows the dissimilar board | substrate used in other embodiment of this invention. It is process drawing which shows the preparation methods of the sapphire substrate (heterogeneous substrate) of the Example of this invention. It is process drawing which shows the process of manufacturing a GaN self-supporting board | substrate by the VAS method on the sapphire board | substrate of an Example and a comparative example. FIG. 4 is a plan view of a GaN free-standing substrate showing measurement points measured by X-ray diffraction measurement in order to examine the inclination direction of the C axis with respect to the surface of the GaN free-standing substrate. It is sectional drawing which shows the structure of the epitaxial wafer for LED which laminated | stacked the epitaxial growth layer of LED structure on the GaN substrate. It is a graph which shows the result of having measured the variation in the light emission wavelength in a substrate surface by the photoluminescence measurement with respect to the epitaxial wafer for LED of FIG. FIG. 5 is an explanatory diagram for defining a parameter representing a tilt distribution of crystal axes due to warpage of a substrate W. FIG. 9 (1) is a cross-sectional view showing the crystal axis distribution of the GaN free-standing substrate after the front and back surfaces of the GaN free-standing substrate having a concave warpage are polished flatly. FIG. 9B is a plan view showing the crystal axis distribution as viewed from the surface side of the GaN free-standing substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Different board | substrate 1a Front surface 1b Back surface 2 Ceramic plate 3 Convex part 10 Sapphire C surface board (sapphire substrate)
10a Front surface 10b Back surface 16 GaN free-standing substrate (GaN substrate)
17 GaN free-standing substrate (GaN substrate)
a crystal axis n surface normal O center of substrate surface α tilted angle η tilted angle V normal vector V _S normal vector projected onto the surface W substrate W ₀ GaN with concave warpage Free-standing substrate GaN free-standing substrate after polishing the front and back surfaces of W ₁ W ₀ flatly

Claims (7)

The angle α at which the crystal axis of the crystal plane serving as the reference of the heterogeneous substrate is inclined with respect to the normal line of the surface of the heterogeneous substrate at the center of the heterogeneous substrate, and the tilt direction in the radial direction The relationship with the angle η at which the crystal axis is inclined with respect to the normal of the surface of the different substrate at a position of 20 mm is 0.02 ° <| η−α | Using a heterogeneous substrate in which the crystal axis is inclined outward in the radial direction of the heterogeneous substrate with respect to the normal of the surface of the heterogeneous substrate at each point of
A method for producing a group III-V nitride semiconductor substrate comprising heteroepitaxially growing a group III-V nitride semiconductor crystal on the heterogeneous substrate. The method for producing a group III-V nitride semiconductor substrate according to claim 1, wherein the group III-V nitride semiconductor crystal is a hexagonal crystal. 2. The III-V nitride semiconductor crystal is hexagonal and the low index plane closest to the surface of the III-V nitride semiconductor substrate is a C-plane. Described in III
A method for manufacturing a group V nitride semiconductor substrate. The group III-V nitride semiconductor crystal is hexagonal, and the low index plane closest to the surface of the group III-V nitride semiconductor substrate is a C-plane group III surface. A method for producing a group III-V nitride semiconductor substrate according to claim 1.   The group III-V nitride semiconductor crystal is hexagonal and the low index plane closest to the surface of the group III-V nitride semiconductor substrate is any one of the A plane, M plane, and R plane. The method for producing a group III-V nitride semiconductor substrate according to claim 1. 6. The method for producing a group III-V nitride semiconductor substrate according to claim 1, wherein the surface of the group III-V nitride semiconductor substrate is mirror-polished. . Using the method for producing a group III-V nitride semiconductor substrate according to any one of claims 1 to 6,
The group III-V nitride semiconductor substrate is obtained by heteroepitaxially growing the group III-V nitride semiconductor crystal on the heterogeneous substrate and then removing the heterogeneous substrate. A method for manufacturing a group nitride semiconductor substrate.

Images