JP2009167057A - Method for manufacturing nitride semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a nitride semiconductor substrate which enables manufacturing of a nitride semiconductor substrate having little dispersion in the off-angle. <P>SOLUTION: In the method for manufacturing the nitride semiconductor substrate, comprising forming a nitride semiconductor layer (2) on a ground substrate (1) and preparing a self-supporting nitride semiconductor substrate (3) by using the nitride semiconductor layer (2) separated from the ground substrate (1), when the warp amount of the ground substrate (1) is defined as the difference between the height of the surface being a crystal growth surface at the central position of the ground substrate (1) and the height of the surface being a crystal growth surface at a position separated from the center of the ground substrate (1) by a distance R (provided that the difference between the heights of the surfaces is set to be negative when the surface of the ground substrate (1) has a convex shape and set to be positive when the surface of the ground substrate (1) has a concave shape), the warp amount of the ground substrate (1) is in a range of -100 to -20 μm when R is 25 mm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a method of manufacturing a nitride semiconductor substrate, and more particularly, from a nitride semiconductor such as In _X Al _Y Ga _1-XY N (0 ≦ X, 0 ≦ Y, 0 ≦ X + Y ≦ 1). The present invention relates to a method for manufacturing a nitride semiconductor substrate capable of manufacturing a self-standing substrate having a small off-angle variation.

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

Nitride semiconductor substrates have extremely high vapor pressures of nitrogen, making it difficult to grow bulk crystals from melts found in boating and pulling methods. Only a very small substrate can be obtained from these methods using the principle of depressing.
For this reason, as a method for manufacturing a nitride semiconductor substrate, as shown in FIG. 8, generally, vapor phase growth is mainly performed on a heterogeneous substrate 21 different from a nitride semiconductor such as a sapphire substrate, a silicon substrate, or a gallium arsenide substrate. After heteroepitaxial growth of the nitride semiconductor layer 22 using the method (FIG. 8A), the heterogeneous substrate 21 is removed using a technique such as peeling, polishing or etching (FIG. 8B), and the heterogeneous substrate is removed. The so-called “self-supporting substrate” is obtained by leaving only the nitride semiconductor layer 22 formed on the surface 21 and polishing the front and back surfaces of the nitride semiconductor layer 22 (FIG. 8C). In addition, the arrow in FIG. 8 has shown the main surface orientation of the crystal | crystallization. The main plane orientation of the crystal is the orientation of the low index plane closest to the surface. For example, in the hexagonal system such as sapphire or GaN, the orientation is the C plane, A plane, or M plane. .

As a specific method for producing a self-standing substrate in this manner, a method as described in Patent Document 1, for example, is known.
In some cases, after removing the dissimilar substrate, only one free-standing substrate may be obtained from the remaining nitride semiconductor layer, but a plurality of free-standing substrates are obtained by epitaxially growing the nitride semiconductor layer thickly and slicing. There is also a case. Further, there are cases where a plurality of free-standing substrates are obtained by using the obtained nitride semiconductor free-standing substrate as a seed crystal and epitaxially growing it thickly and slicing it.
The self-standing substrate as used in this specification includes any of these cases.

Regarding the growth method of the nitride semiconductor layer, since the nitride semiconductor layer is heteroepitaxially grown on a heterogeneous substrate different from the nitride semiconductor, such as a sapphire substrate, a silicon substrate, or a gallium arsenide substrate, a so-called step is started at the beginning of the growth. Crystal growth proceeds not in the flow mode but in the three-dimensional island growth mode. For this reason, the nitride semiconductor layer obtained in this way has a dislocation density of 10 ⁹ to 10 ¹⁰ cm ⁻² . This defect becomes an obstacle in manufacturing an AlGaN-based device, particularly an LD or an ultraviolet light emitting LED.

In recent years, growth techniques such as ELO, FIELO, and pendeo epitaxy have been reported as methods for reducing the density of such defects. 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, various methods have been proposed in which a GaN layer with a reduced dislocation density is epitaxially grown on a dissimilar substrate such as a sapphire substrate, and the GaN layer is peeled off from the substrate after growth and used as a self-supporting GaN substrate. For example, it has been proposed to form a GaN layer on a sapphire substrate using the above-described ELO technique, and then remove the sapphire substrate by etching or the like to obtain a GaN free-standing substrate.
In addition, VAS (Void-assisted Separation: for example, Non-Patent Document 1) method, DEEP (Dislocation Elimi nation by the Epi-growth with inverted-Pyramidal pits: For example, Non-Patent Document 2) method and the like are disclosed. VAS grows GaN on a substrate such as sapphire via a TiN thin film with a network structure, thereby forming a void at the interface between the base substrate and the GaN layer, and simultaneously enabling peeling and low dislocation of the GaN substrate. It is a thing. Further, DEEP grows GaN using a mask such as SiN patterned on a GaAs substrate that can be removed by etching or the like to form a plurality of pits deliberately surrounded by facet surfaces on the crystal surface. By accumulating dislocations at the bottom, other regions are reduced in dislocation.

JP 2002-57119 A Y. Oshima et.al., Jpn.J.Appl.Phys., Vol.42 (2003), pp.L1-L3 K. Motoki et.al., Jpn.J.Appl.Phys., Vol.40 (2001), pp.L140-L143

However, since the nitride semiconductor layer 22 manufactured by the above-described conventional method has a defect density difference between the front and back surfaces, the nitride semiconductor after the crystal lattice is distorted and the internal stress is generated and peels from the base substrate 21. The layer 22 is warped so that the back surface 22b has a convex shape in any way (FIG. 8B). Even if the nitride semiconductor layer 22 warped as described above is flattened by polishing or the like, the off-angle is a surface because the plane orientation is not oriented in a uniform direction at each position in the surface 22a. There arises a problem that it varies within the range (FIG. 8C). The “off angle” here means “the angle of deviation of the normal of each position on the surface from the main plane orientation” (or “the angle between the surface and the main crystal plane”), “The off-angle varies” means that the angle of deviation of the normal of each position on the surface from the main surface orientation is not uniform, and the angle of deviation varies depending on the position in the surface. .
If the in-plane off-angle varies, it greatly affects the variation in the emission wavelength of the light-emitting element device formed thereon, and the yield is significantly reduced.
Further, even when epitaxial growth is performed on a nitride semiconductor free-standing substrate 23 (FIG. 8C) having an off-angle variation in the plane as a seed crystal, the orientation is inherited, so that the epitaxial layer is grown thickly. The free-standing substrate obtained by slicing will also vary in off-angle. Further, even when grown on a nitride semiconductor substrate having a uniform plane orientation, it is warped again due to a defect density difference between the front and back surfaces due to a decrease in threading dislocations, etc., which causes off-angle variation.

  An object of the present invention is to solve the above-described problems and to provide a method for manufacturing a nitride semiconductor substrate capable of manufacturing a nitride semiconductor substrate with small off-angle variation.

In order to solve the above problems, the present invention is configured as follows.
According to a first aspect of the present invention, a nitride semiconductor substrate is formed by forming a nitride semiconductor layer on a base substrate and using the nitride semiconductor layer separated from the base substrate to produce a self-supporting nitride semiconductor substrate. In the method, the amount of warpage of the base substrate is determined by a difference in height of a surface that is a crystal growth surface between a center position of the base substrate and a position of a distance R from the center of the base substrate (however, When the difference is defined as negative if the surface of the base substrate has a convex shape and positive if the surface of the base substrate is concave, the base substrate has a warpage amount of −25 mm when converted to R = 25 mm. A method for manufacturing a nitride semiconductor substrate, which is in a range of 100 μm or more and −20 μm or less.

  According to a second aspect of the present invention, in the method for manufacturing a nitride semiconductor substrate according to the first aspect, the surface of the base substrate having the warp has a uniform off-angle in a plane. To do.

  According to a third aspect of the present invention, in the method for manufacturing a nitride semiconductor substrate according to the first aspect or the second aspect, the base substrate is a sapphire substrate, a nitride semiconductor substrate, a silicon substrate, or a gallium arsenide substrate. It is characterized by.

  According to the present invention, it is possible to obtain a nitride semiconductor free-standing substrate in which cracks do not occur and off-angle variation is small. Moreover, the yield in the case where semiconductor light emitting devices such as LEDs and LDs are fabricated on the obtained nitride semiconductor free-standing substrate can be significantly improved.

  Hereinafter, embodiments of a method for manufacturing a nitride semiconductor substrate according to the present invention will be described with reference to the drawings.

FIG. 1 is a process diagram schematically showing the steps of the method for manufacturing a nitride semiconductor substrate according to the present embodiment.
In the method for manufacturing a nitride semiconductor substrate according to the present embodiment, first, a base substrate 1 is prepared, and a nitride semiconductor layer 2 is formed on the base substrate 1 (FIG. 1A).
As the base substrate 1, a heterogeneous substrate different from a nitride semiconductor, such as a sapphire substrate, a silicon substrate, or a gallium arsenide substrate, or a nitride semiconductor substrate is used. Nitride semiconductor layer 2 is, for _{example, In X Al Y Ga 1-} X-Y N (0 ≦ X, 0 ≦ Y, 0 ≦ X + Y ≦ 1) layer, and the like. As a method for forming the nitride semiconductor layer 2, a metal organic vapor phase epitaxy method (MOVPE method), a hydride vapor phase epitaxy method (HVPE method), or a vapor phase epitaxy method combining these is used.

  Next, the nitride semiconductor layer 2 formed on the base substrate 1 is separated from the base substrate 1 (FIG. 1B). As a separation method (removal method), in addition to peeling (illustrated example), methods such as polishing, etching, and laser irradiation may be used.

Finally, the front surface 2a and the back surface 2b of the separated nitride semiconductor layer 2 are polished (leaving the broken line portion in FIG. 1B), washed, etc., thereby producing a self-supporting nitride semiconductor substrate 3 ( FIG. 1 (c)). In addition, the arrow in FIG. 1 has shown the main surface orientation of the crystal | crystallization.
Even if only a single nitride semiconductor substrate 3 is obtained from the separated nitride semiconductor layer 2, a plurality of nitride semiconductor free-standing substrates can be obtained by epitaxially growing the nitride semiconductor layer 3 thickly and slicing. May be. Note that the “self-standing substrate” of nitride semiconductor is a substrate having a strength that allows substrate processing such as transportation, and the thickness of the substrate is preferably 200 μm or more, for example.

The manufacturing method of the above embodiment is characterized in that the warpage amount of the base substrate 1, which is the base for forming the nitride semiconductor layer 2, in particular, the base substrate 1 is defined within a predetermined range.
As shown in FIG. 2, the amount of warpage of the base substrate 1 was defined by the difference in height between the surface 1a, which is the crystal growth surface, at the center position of the base substrate 1 and the distance R from the center of the base substrate 1. However, the amount of warpage, which is the difference in height of the surface 1a of the base substrate 1, is negative when the surface 1a of the base substrate 1 is convex (FIG. 2 (a)), and when it is concave (FIG. 2 ( b)) shall be positive.
At this time, a substrate having a convex surface is used as the base substrate 1 when the amount of warpage when converted to R = 25 mm is in the range of −100 μm to −20 μm.
Here, “the range in which the amount of warpage when converted to R = 25 mm is −100 μm to −20 μm” is, in other words, “when the base substrate 1 is standardized to a diameter of 2 inches (= 50.8 mm)”. The amount of warpage is in the range of −100 μm or more and −20 μm or less ”, and the numerical value (absolute value) of the amount of warpage will be described later when the warpage amount is larger, for example, corresponding to the diameter of the base substrate. It becomes larger so that the warp canceling effect can be exhibited.

Since the nitride semiconductor layer 2 formed on the base substrate 1 has a low defect density on the front surface 2a and a high defect density on the back surface 2b, internal stress always acts so that the front surface 2a warps in a concave shape.
Therefore, as in the conventional base substrate 21 shown in FIG. 8A, when the surface of the base substrate is flat and has no warp, the nitride semiconductor layer 22 separated from the base substrate 21 is shown in FIG. As shown, the surface 22a warps in a concave shape. For this reason, even if the main plane orientation of the nitride semiconductor layer 22 on the base substrate 21 is formed in a uniform direction, the separated nitride semiconductor layer 22 is caused by internal stress due to the difference in defect density. The surface 22a is warped in a concave shape due to distortion, and the plane orientation is not directed to a uniform direction at each position within the surface of the nitride semiconductor free-standing substrate 23 that has been flattened by polishing or the like, and the off angle is in-plane It will vary.

  Therefore, in the present embodiment, by using the base substrate 1 having the convex warpage in the opposite direction to the concave warpage generated in the nitride semiconductor layer 2 after the separation, The concave warpage caused by the defect density difference in the nitride semiconductor layer 2 can be canceled (cancelled), and the main plane orientations are almost uniform as shown in FIG. The self-standing nitride semiconductor substrate 3 produced by polishing the front and back surfaces of the nitride semiconductor layer 2 also has less in-plane off-angle variation. That is, by defining the warpage amount of the base substrate 1, the warpage amount of the nitride semiconductor layer 2 after the epitaxial growth and separation can be adjusted and controlled. As a result, the surface orientation is uniform with small off-angle variation. The nitride semiconductor substrate 3 can be produced. Further, since the warpage is adjusted so as to cancel, the warpage of the nitride semiconductor layer 2 after separation is small, the amount of polishing for polishing the front and back surfaces is small, and the nitride semiconductor layer 2 after separation is not wasted. It can be used effectively and the polishing time can be reduced.

  However, even if the surface of the base substrate 1 is preferably warped in a convex shape, if the base substrate 1 is warped too much, the temperature of the nitride semiconductor layer 2 is epitaxially grown on the base substrate 1 in the plane. Non-uniformity occurs, resulting in defects such as formation of pits on the surface. In order to prevent this, it is preferable that the amount of warpage of the base substrate 1 when converted to R = 25 mm is −100 μm or more. As will be described later, in consideration of the yield when a semiconductor light emitting device such as an LED or LD is fabricated on the obtained nitride semiconductor free-standing substrate 3, the amount of warpage of the base substrate 1 when R = 25 mm is set. It is preferable to be −20 μm or less.

The nitride semiconductor layer 2 epitaxially grown on the base substrate 1 inherits the orientation of the base substrate 1 as shown in FIG. For this reason, the warp due to the defect density difference of the nitride semiconductor layer 2 after the separation is canceled by the warp of the base substrate 1, and the main plane orientations in the layer are almost parallel as shown in FIG. In order to separate the uniform nitride semiconductor layers 2, it is preferable that the surface of the base substrate 1 having the warp has a uniform off angle in the plane. Here, that the off-angles are uniformly aligned within the surface of the base substrate 1 means that the deviation between the surface normal and the main plane orientation substantially coincides at each position on the surface of the base substrate 1. That is, it means that the main plane orientation is within a range of variation of about ± 0.3 ° from the direction perpendicular to the surface of the base substrate 1 at each position in the surface of the base substrate 1.
In addition, when the base substrate is flat and has no warpage, and the off angles are substantially uniform in the plane (such as the base substrate 21 in FIG. 8A), the base substrate is bent slightly. If it is possible, a substrate having a convex spherical surface within the range of the above-described warpage amount and fixed by an adhesive or the like in a state where the substrate is bent and adhered may be used as the substrate. .

  Next, examples of the present invention will be described.

[Example 1]
In Example 1, a GaN layer is formed by a MOVPE method on a sapphire single crystal substrate (underlying substrate) having a diameter of 2 inches and having various warpage amounts. I investigated the relationship with the pit.

First, the sapphire substrate was set on a susceptor in the MOVPE growth furnace, heated to 1200 ° C., and subjected to thermal cleaning in a hydrogen atmosphere for 10 minutes. Thereafter, the temperature is lowered to 500 ° C., trimethyl gallium (TMG), trimethyl indium (TMI) and ammonia (NH ₃ ) are used as raw materials, and a mixed gas containing H ₂ and N ₂ is supplied as a carrier gas. Formed. Thereafter, the temperature was raised to 1100 ° C. in an atmosphere of NH _3, H ₂ , and N ₂ , TMG was flowed again, and a GaN layer was grown to 300 nm. After the growth, the temperature was lowered to 500 ° C. in an NH ₃ and N ₂ atmosphere. When the temperature dropped to 500 ° C. or lower, the temperature was lowered only with N ₂ and when the temperature dropped to 100 ° C. or lower, the sapphire substrate was taken out.

In Example 1, a sapphire substrate having a warp amount of 150 μm (warp amount−150 μm) to 20 μm concave (warp amount + 20 μm) shown in Table 1 below was used. Then, the surface of the GaN layer formed on the sapphire substrate was observed with a Nomarski optical microscope. As a result, pits (black dots) as seen in FIG. 3 are densely packed over the entire circumference of the range of about 10 mm from the end of the sapphire substrate, with the convex warpage of 150 μm and the convex warpage of 120 μm. It was seen. In other sapphire substrates with warpage, no pit was generated, and a flat GaN film was obtained.
From the above results, it has been found that the warpage of the base substrate needs to be 100 μm or less with respect to the convex warpage (the amount of warpage is negative).

[Example 2]
A GaN epitaxial layer is grown on the sapphire substrate using the Void-Assisted Separation Method (VAS method), and then the sapphire substrate is removed to obtain a self-supporting GaN substrate for evaluation. It was.
The VAS method is a method of performing crystal growth by sandwiching a titanium nitride thin film having a network structure between a sapphire substrate and a GaN growth layer, and details thereof are described in Non-Patent Document 1, for example.

Hereinafter, a method for manufacturing the GaN free-standing substrate of Example 2 will be described.
First, an undoped GaN layer was grown to a thickness of 300 nm on a sapphire C-plane substrate having a diameter of 2 inches by MOVPE using trimethyl gallium (TMG) and NH ₃ as raw materials. Next, a Ti thin film is deposited on the GaN epitaxial substrate to a thickness of 20 nm, and this is put in an electric furnace, and at 1050 ° C. in an atmosphere of a mixed gas of 20% NH ₃ and 80% H _2. Heat treatment was applied for 20 minutes. As a result, a part of the undoped GaN layer is etched to generate high-density voids and change into a void-formed GaN layer, and the Ti thin film is nitrided to form submicron fine holes at high density on the surface. It changed into the hole formation TiN layer.
This substrate was placed in an HVPE furnace, and GaN was deposited to a total thickness of 800 μm. The Ga metal boat was heated to 900 ° C., the substrate side was set to 1100 ° C., and a mixed gas of 5% hydrogen and 95% nitrogen was used as a carrier gas. HCl gas and Ga were reacted as source gases to generate GaCl, and ammonia gas was supplied at the same time, and the flow rate was adjusted so that the V / III ratio was 10 at the start of growth.
Under these conditions, the GaN nuclei grew in a three-dimensional island shape on the TiN layer, and then the crystals grew laterally and joined to each other, and the surface was flattened. This state was confirmed by observing the substrate surface and cross-section taken out of the furnace with different growth times under a microscope. We continued to grow by extending the growth time. In the process of cooling the HVPE apparatus after completion of the GaN crystal growth, the GaN layer naturally separated from the sapphire base substrate with the void layer as a boundary, and a GaN free-standing substrate having a thickness of 800 μm was obtained.

In this example, the above growth was performed using a sapphire substrate having a warpage amount of 150 μm to 20 μm in Table 1.
As shown in Table 1, GaN free-standing substrates obtained from sapphire substrates having different warpage amounts grew on a sapphire substrate (warp amount−100 μm) warped to a convex shape, and the warpage amount is the smallest. On the contrary, those grown on a sapphire substrate (warp amount + 20 μm) warped in a concave shape by 20 μm resulted in the largest warp amount. In addition, those grown on a sapphire substrate warped in a convex shape of 150 μm and 120 μm both cracked during HVPE growth.

Next, the front and back surfaces were further polished so that the GaN free-standing substrate was flat, and a flat GaN free-standing substrate having a thickness of 400 μm was obtained.
As shown in FIG. 4, the off-angles of these GaN free-standing substrates were measured with an X-ray diffractometer (manufactured by Panalical) at five points in the plane, that is, at the four corners of the square and 20 mm away from the center. . As a result, the variation in off angle was as shown in Table 1. The variation (± degree) is obtained by calculating (| maximum off angle | − | minimum off angle |) / 2 from the measurement results at five points in the plane as described below.

As described above, the “off angle” means “an angle formed between the surface and the crystal plane” and can be measured using an X-ray diffractometer. The diffraction angle of the crystal plane is, for example, the diffraction angle of the C plane and can be obtained from the diffraction peak angle such as the {0002} plane. The surface angle can be obtained from the diffraction peak angle obtained by utilizing the total reflection phenomenon on the surface of the X-ray generated at the position where the incident angle = the reflection angle.
By measuring the difference between the diffraction peak angle on the crystal plane and the diffraction peak angle on the surface from all directions (4 directions at least every 90 °), the “angle between the surface and the crystal plane”, that is, the off-angle Can be determined. When the off angle is measured at each point in the plane, the off angle may vary in size and direction depending on the position. Among the above five measurement results, when the maximum off-angle value (absolute value) is | maximum off-angle |, and the smallest value (absolute value) is | minimum off-angle | The maximum off angle | − | minimum off angle | (degrees) represents the size of the range of variation, which is divided by 2 to express “variation” in units of “± degrees”. Also, (| maximum off angle | + | minimum off angle |) / 2 is the center value of the off angle.

  As shown in Table 1, those grown on a sapphire substrate warped to a convex shape by 100 μm resulted in the smallest variation in off-angle. Further, referring to FIG. 5 which is a graph showing the relationship between the amount of warpage of the sapphire substrate (underlying substrate) and the variation in off-angle in Table 1, the amount of warpage of the convex shape of the underlying substrate in the range of the amount of warping −100 μm to +20 μm. As the angle decreases, the off-angle variation increases, and in the case of the concave shape, the off-angle variation is reversed. As the amount of warpage increases, the off-angle variation increases.

[Example 3]
A growth layer having the following light-emitting element structure was formed on the GaN free-standing substrate produced in Example 2. FIG. 7 is a structural sectional view showing the nitride semiconductor light emitting device according to the third embodiment.
The semiconductor active layer of Example 3 has a quantum well structure. A multilayer film for a light emitting diode was produced by metal organic chemical vapor deposition (MOCVD). Trimethylgallium (TMG), trimethylaluminum (TMA), trimethylindium (TMI), and biscyclopentadienylmagnesium (Cp ₂ Mg) were used as organometallic raw materials. Ammonia (NH ₃ ) and silane (SiH ₄ ) were used as gas raw materials. Moreover, hydrogen and nitrogen were used as carrier gas.

The semiconductor light emitting device of this example was manufactured as follows.
First, using the GaN free-standing substrate 11 obtained by the above-described Example 2 (with different variations in off-angle), Si is deposited on the GaN free-standing substrate 11 at 1050 ° C. with a carrier concentration of 1 × 10 ¹⁹ cm. ^-3 doped n-type GaN layer 12 was grown to a thickness of 4 μm. Next, at 800 ° C., as an active layer, a GaN barrier layer 13 (four layers) having a thickness of 10 nm, and In _0.1 having a thickness of 3 nm.
An InGaN-based active layer 15 having a multiple quantum well structure (MQW) in which Ga _0.9 N well layers 14 (three layers) were alternately stacked was grown. A p-type Al _0.1 Ga _0.9 N clad layer 16 and a p-type GaN contact layer 17 were formed in this order on the top. Further, a positive electrode 19 was formed on the p-type GaN contact layer 17 and a negative electrode 18 was formed on the back surface of the GaN free-standing substrate 11, and then fabricated as a chip.

For all the samples produced in this example, five chips (light-emitting elements) located at the same location as the off-angle measurement location were selected, and the emission wavelength of each chip was determined by EL (Electro Luminescence) measurement. Measurements were made to determine the variation in emission wavelength within the substrate surface. Of the measured values of the five emission wavelengths, “the maximum value of the emission wavelength−the minimum value of the emission wavelength” was defined as the variation in the emission wavelength.
The results of measuring the emission wavelength variation are shown in Table 1. A sample with a small variation in off-angle gave a result that the variation in emission wavelength was small.
Of course, the variation in the emission wavelength is preferably small, but in practice, it should be within 20 nm or less. For this purpose, from the graph (FIG. 6) showing the relationship between the variation in the off-angle of the GaN free-standing substrate and the variation in the emission wavelength, the variation in the off-angle of the nitride semiconductor free-standing substrate is ± 0.25.
It is preferable to make it below the degree. Furthermore, it was found from FIG. 5 that the warpage amount of the base substrate should be −20 μm or less in order to make the variation in the off angle ±± 0.25 degrees or less.

It is process drawing which shows schematically the manufacturing method of the nitride semiconductor substrate which concerns on one Embodiment of this invention. It is explanatory drawing for demonstrating the curvature amount of the base substrate used with the manufacturing method of the nitride semiconductor substrate which concerns on this invention. It is a microscope picture which shows the mode of the pit (black dot shape) which generate | occur | produced on the surface of the GaN layer grown on the sapphire substrate. It is a figure which shows the measurement point of the off angle of a GaN self-supporting substrate. It is the graph which showed the relationship between the curvature amount of a sapphire substrate (underlying substrate), and the dispersion | variation in the off angle in the GaN self-supporting substrate after growing on it, peeling and processing. 4 is a graph showing a relationship between variation in off-angle of a GaN free-standing substrate and variation in emission wavelength when a light-emitting element structure is further formed on the GaN free-standing substrate. It is a schematic sectional drawing which shows the cross-section of the nitride semiconductor light-emitting device produced in the Example. It is process drawing which shows the manufacturing method of the conventional nitride semiconductor substrate roughly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ground substrate 1a Surface 1b of ground substrate 2 Back surface of ground substrate 2 Nitride semiconductor layer 2a Surface 2b of separated nitride semiconductor layer 3 Back surface of separated nitride semiconductor layer 3 Free standing nitride semiconductor substrate 11 GaN free standing substrate 15 InGaN-based active layer

Claims (3)

In a method for manufacturing a nitride semiconductor substrate, a nitride semiconductor layer is formed on a base substrate, and a self-standing nitride semiconductor substrate is manufactured using the nitride semiconductor layer separated from the base substrate.
The amount of warpage of the base substrate is defined as the difference in the height of the surface that is the crystal growth surface between the center position of the base substrate and the position of the distance R from the center of the base substrate (however, the sign of the difference in the height of the surface is positive or negative) Is defined as negative when the surface of the base substrate is convex, and positive when the surface of the base substrate is concave), the warpage amount of the base substrate when converted to R = 25 mm is −100 μm or more− A method for manufacturing a nitride semiconductor substrate, which is in a range of 20 μm or less.   2. The method of manufacturing a nitride semiconductor substrate according to claim 1, wherein a surface of the base substrate having the warp has a uniform off angle in a plane.   3. The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein the base substrate is a sapphire substrate, a nitride semiconductor substrate, a silicon substrate, or a gallium arsenide substrate.