JP5271489B2 - Group III nitride semiconductor substrate and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a group-III nitride semiconductor substrate which is formed by forming a surface consisting of a nonpolar or semipolar face by slicing or polishing a bulk crystal of group-III nitride semiconductor having a thickness of 1 mm or more in the c axis direction and processing the face into a flat surface. <P>SOLUTION: A substrate which is necessary for obtaining a thin film having a flat nonpolar face or semipolar face is provided. In this way, generation of a piezo electric field is prevented. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

    The present invention relates to a group III nitride semiconductor substrate that can be used as a substrate for light emitting and electronic devices, and a method for manufacturing the same.

  Group III nitride semiconductor materials such as gallium nitride (GaN), indium nitride (InN), aluminum nitride (AlN), and mixed crystals thereof such as indium gallium nitride (InGaN) and aluminum gallium nitride (AlGaN) are forbidden bands. Since the width is large and the transition between bands is a direct transition type, application to a short wavelength light emitting element is actively studied. Among them, InGaN can change the band gap from near ultraviolet (GaN: 3.4 eV) to infrared (InN: 0.7 eV) depending on the group III mixed crystal composition ratio, and can cover the entire visible region. LEDs and LDs used for the light emitting layer have been put into practical use.

  The current mainstream white LED has a structure in which a yellow LED YAG phosphor is combined with a blue LED chip using InGaN as a light emitting layer. It has features such as easy drive, and is now spreading rapidly, as it is used as a backlight in the small color liquid crystal displays of most mobile phones.

  InGaN-based LEDs have been manufactured on the (0001) polar face of sapphire substrates and SiC substrates, and the efficiency is improving year by year. For example, the external quantum efficiency of a blue LED reaches about 50%, and the luminous efficiency of a white LED using it reaches a level exceeding 100 lm / W.

  However, such high luminous efficiency can be obtained from the ultraviolet of 360 nm to the purple of 400 nm and the blue of 460 nm, and the reduction in efficiency becomes remarkable in the wavelength longer than 500 nm.

  Particularly serious is green (530 nm region), which is about half the efficiency of blue, and is currently attracting attention as a promising application for LEDs, blue (InGaN-based), green (InGaN-based), red (AlGaInP) The improvement of the efficiency of the green LED is an important issue in the practical application of the liquid crystal display using the three primary color LEDs as the backlight (Non-patent Documents 2 and 3).

The above problem is a phenomenon caused by increasing the In mixed crystal composition of InGaN used as the active layer. This is due to the fact that a large piezo electric field is generated in InGaN produced on the (0001) polar plane, and the emission transition probability is lowered because electrons and holes injected into the active layer are separated. It has become clear. In order to solve this problem, it has been proposed to fabricate an element structure on a nonpolar plane or a semipolar plane where no piezoelectric field is generated, and active research has been conducted as shown in Patent Documents 1 and 2 and Non-Patent Document 1. It was.
Special table 2006-510227 Special table 2006-514780 Mitsuru Funato, Masaya Ueda, Yoichi Kawakami, Yukio Narukawa, Takao Kosugi, Masayoshi Takahashi and Takashi Mukai "Blue, Green, andAmber InGaN / GaN Light-Emitting Diodes on Semipolar {11-22} GaN Bulk Substrates.", Jpn. J. et al. Appl. Phys. vol. 45, no. 26, 2006, pp. L659-L662. Yukio Narukawa, Shinichi Nagahama, Hiroto Tamaki, Takashi Mukai, "Development of a high-intensity white light source using GaN-based light-emitting elements", Journal of Applied Physics Society, Vol. 74, no. 11, pp1423-1432, (2005) Satoshi Watanabe, “Current Status and Applications of InGaN High Power LEDs”, Journal of Applied Physics Society, Vol. 74, no. 11, pp. 1437-1442, (2005) Troy J.H. BAKER, Benjamin A. HASKELL, Feng Wu, Paul T .; FINI, James S .; SPECK and Shuji NAKAMUURA "Characterization of Planar Semipolar Gallium Nitride Films on Spinel Substrate.", Jpn. J. et al. Appl. Phys. vol. 44, no. 29, 2005, pp. L920-L922

    Conventionally, when a group III nitride semiconductor such as InGaN is grown on a nonpolar surface or a semipolar surface, a substrate of a different material is used as a base substrate, and a group III nitride semiconductor having a desired plane orientation is formed thereon. Grow.

For example, as described in Patent Documents 1 and 2, (11-20) GaN is grown on r-plane (1-102) sapphire, or as shown in Non-Patent Document 4, spinel (MgAl ₂ O ₄ ), (10-1-1) GaN is grown on (100) MgAl ₂ O ₄ and (10-1-3) GaN is grown on (110) MgAl ₂ O ₄ . As described in Non-Patent Document 1, since the film has a high dislocation density and is difficult to grow on the heterogeneous substrate, it is difficult to optimize the growth conditions. The problem remains that a flat film cannot be obtained.

  According to the present invention, a bulk crystal of a group III nitride semiconductor having a thickness of 1 mm or more in the c-axis direction is sliced or polished to form a surface composed of a nonpolar surface or a semipolar surface, There is provided a group III nitride semiconductor substrate processed to have a flat surface.

The nonpolar plane is the ( 11-20) plane or (10-10) plane, and the semipolar plane is the (10-1-1) plane, (10-1-3) plane, (10-11) plane, The (10-13) plane or the (11-22) plane is used . Furthermore, in the production of a nonpolar plane or a semipolar plane, the inclination of the crystal orientation perpendicular to the surface can be within ± 1 °. As a result, a device having nonpolar or semipolar characteristics expected in the production of an LED system after epitaxial growth can be obtained.

  In the above-described substrate, the c-axis growth surface of the group III nitride semiconductor bulk crystal may be formed as the as-grown surface. In addition, the substrate may be nonpolar after processing a flat surface on a (0001) plane, a (000-1) plane, a (11-20) plane, or a (10-10) plane of a group III nitride semiconductor bulk crystal. A semipolar substrate can be manufactured. Further, the substrate may be surface-treated so as to exhibit different appearances on the growth surface and the back surface of the group III nitride semiconductor bulk crystal.

  What has a different appearance may be anything as long as it can be identified visually or by some means. For example, it can be said that a surface treated so that one surface is a smooth surface and the other surface is a rough surface exhibits a different appearance. For example, it may be processed so that one surface is a mirror surface and the other surface is a satin surface. Thereby, it can utilize as an orientation flat for discriminating the front and back of a substrate.

As a specific example of the surface treatment, there is a method of lapping so that the Ga surface side of the bulk substrate becomes a mirror surface and the N surface side becomes a satin surface. By doing so, it becomes possible to distinguish the upper and lower directions. At this time, the front and back rear surface is an acute angle of the surface with respect to the Ga face of the (11-22), an obtuse angle of face surface ((11 22) plane).

  In the substrate, the surface roughness of a nonpolar surface or a semipolar surface can be RMS ≦ 1 nm in the range of 1 μm × 1 μm. Thereby, the flatness after epitaxial growth can be made favorable.

  The substrate may be a free-standing substrate obtained by growing a group III nitride semiconductor on a base substrate made of sapphire or SiC and then removing the base substrate.

  The group III nitride semiconductor bulk crystal may be a group III nitride semiconductor substrate that is a wurtzite crystal. An example of the wurtzite crystal is GaN.

  According to the present invention, it is possible to grow an epitaxial thin film on a group III nitride semiconductor substrate having a desired plane orientation without using a different substrate as a base, and the film quality is improved.

  In addition, according to the present invention, a step of slicing or polishing a bulk crystal of a group III nitride semiconductor grown to a thickness of 1 mm or more in the c-axis direction to form a surface composed of a nonpolar surface or a semipolar surface; And a step of processing the surface to be a flat surface. A method of manufacturing a group III nitride semiconductor substrate is provided.

  According to the present invention, a substrate necessary for obtaining a flat nonpolar plane or semipolar plane thin film is provided. Further, according to the present invention, there is provided a method for manufacturing a substrate necessary for obtaining a flat nonpolar surface or semipolar surface thin film. By using this substrate, a group III nitride light-emitting device in which generation of a piezoelectric field is suppressed is realized.

  Embodiments of the present invention will be described below with reference to the drawings.

<Example 1>
FIG. 1 shows a photograph of a bulk GaN crystal obtained by growing GaN on a sapphire substrate by the HVPE method and growing about 3 mm in the c-axis direction. A photograph of the substrate sliced by tilting 58.4 ° from the c-plane toward the a-plane (11-20) direction so that the (11-22) -plane substrate shown in FIGS. 2 and 3 can be obtained. Shown in Here, FIG. 4 shows a table showing diffraction angles (2θ) with respect to Miller indices (hkil) of various surfaces of GaN. From this table, 2θ of the (11-22) plane is about 69.1 °. When XRD measurement was performed in order to confirm the surface index of this surface, a peak appeared at about 69.1 ° as shown in FIG. 5, and it was confirmed that this surface was the (11-22) surface.

<Example 2>
Next, this (11-22) plane substrate was lapped using diamond coating grains, and CMP was performed using colloidal silica. As shown in FIG. 7, the surface roughness was RMS = 0.19 nm in the range of 1 μm × 1 μm.

<Example 3>
FIG. 8 shows the result of polishing the back surface (−1-12-1) of the (11-22) surface obtained in Example 1 in the same manner as in Example 1. RMS = 0.19 nm was obtained in the range of 1 μm × 1 μm.

<Example 4>
When a bulk GaN free-standing substrate grown 6 to 8 mm in the c-axis direction is cut out as a (11-22) substrate as shown in FIG. 9, the (0002) Ga face is the as grown face and the (0002) N face is peeled off. If it is a plane, when it is processed as a (11-22) substrate as shown in FIG. 10, it is difficult to judge the Ga plane side and the N plane side. Therefore, when lapping is performed so that the Ga surface side of the bulk substrate is a mirror surface and the N surface side is a satin surface, it is possible to distinguish the upper and lower orientations (the −X direction is the Ga surface side and the + X direction is the N surface side). In the front and back of (11-22), an acute angle surface with respect to the Ga surface is the back surface, and an obtuse angle surface is the surface ((11-22)) surface. When the ± X direction of the (11-22) plane is determined in the bulk crystal, the direction (± Y direction) perpendicular thereto is determined as <10-10>. FIG. 11 shows the result of measuring the tilt of the crystal orientation perpendicular to the surface of the (11-22) plane in the ± X and Y directions. FIG. 11A is a photograph showing the size of the substrate, and FIG. 11B is a sketch showing ± X and Y directions with respect to the (11-22) plane. Here, the absolute value of the inclination of the crystal orientation with respect to the surface is the sum of the vectors in the X and Y directions as shown in FIG. 11 (d). Therefore, the calculation formula is √ ((± X direction inclination) ² + (± Y direction inclination) ² ). The measurement results are shown in FIG. 11 (c), but all were within ± 1 °.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

2 is a photograph of a bulk GaN crystal according to Example 1. It is the figure which showed typically the board | substrate of the (11-22) plane which concerns on Example 1. FIG. It is the figure which showed typically the board | substrate of the (11-22) plane which concerns on Example 1. FIG. 4 is a table showing diffraction angles (2θ) with respect to Miller index (hki) of various surfaces of GaN according to Example 1. FIG. 6 is a diagram showing an XRD measurement result according to Example 1. 2 is a photograph showing a sliced substrate according to Example 1; FIG. 6 is a diagram illustrating the roughness of the surface of a substrate according to Example 2. FIG. 6 is a view showing the roughness of the surface of a substrate according to Example 3. It is the figure which showed cutting out of the board | substrate which concerns on Example 4. FIG. FIG. 6 is a view showing a substrate according to Example 4; (A) is a photograph showing the size of the substrate according to Example 4. FIG. (B) is a diagram showing ± X and Y directions with respect to the (11-22) plane according to Example 4. FIG. (C) is a table showing measurement results according to Example 4. (D) It is the figure which showed the absolute value of the inclination of the crystal orientation based on Example 4. FIG.

Claims (11)

By slicing or polishing the bulk crystal while leaving the c-axis growth surface of the bulk crystal of the group III nitride semiconductor having a thickness of 1 mm or more in the c-axis direction as the grown surface, the (11-20) plane is obtained. Alternatively, a nonpolar plane consisting of (10-10) plane, or (10-1-1) plane, (10-1-3) plane, (10-11) plane, (10-13) plane or (11- 22) A group III nitride semiconductor substrate in which a semipolar plane composed of a plane is formed and the plane is processed to be a flat surface. Processing a flat surface on the (0001), (000-1), (11-20) or (10-10) plane of a bulk crystal of a group III nitride semiconductor having a thickness of 1 mm or more in the c-axis direction Then, by slicing or polishing the bulk crystal, a nonpolar plane consisting of (11-20) plane or (10-10) plane, or (10-1-1) plane, (10-1- 3) Group III nitride semiconductor formed by forming a semipolar plane consisting of a plane, a (10-11) plane, a (10-13) plane, or a (11-22) plane, and processing the plane to be a flat surface substrate. After the surface treatment is performed so that the growth surface and the back surface of the bulk crystal of the group III nitride semiconductor having a thickness of 1 mm or more in the c-axis direction have different appearances, the bulk crystal is sliced or polished. By doing so, a nonpolar surface consisting of (11-20) plane or (10-10) plane, or (10-1-1) plane, (10-1-3) plane, (10-11) plane, A group III nitride semiconductor substrate in which a semipolar plane consisting of a (10-13) plane or a (11-22) plane is formed, and the plane is processed to be a flat surface.   The group III nitride semiconductor substrate according to any one of claims 1 to 3, wherein the surface formed of a nonpolar surface or a semipolar surface is a (11-22) surface.   The group III nitride semiconductor substrate according to any one of claims 1 to 4, wherein a surface roughness of the nonpolar or semipolar surface is RMS ≦ 1 nm in a range of 1 μm × 1 μm.   The bulk crystal of the group III nitride semiconductor is a self-supporting substrate obtained by growing a group III nitride semiconductor on a base substrate made of sapphire or SiC and then removing the base substrate. The group III nitride semiconductor substrate as described in any one of Claims.   The group III nitride semiconductor substrate according to claim 1, wherein the group III nitride semiconductor bulk crystal is a wurtzite crystal. By slicing or polishing the bulk crystal while leaving the c-axis growth surface of the bulk crystal of the group III nitride semiconductor grown to a thickness of 1 mm or more in the c-axis direction as the grown plane, (11-20 ) plane or (10-10) plane nonpolar plane consisting of, or, (10-1-1) plane, (10-1-3) plane, (10-11) plane, (10-13) plane or ( 11-22) forming a semipolar plane comprising a plane ;
Processing the surface to be a flat surface;
A method for producing a group III nitride semiconductor substrate, comprising: A flat surface on a (0001) plane, a (000-1) plane, a (11-20) plane, or a (10-10) plane of a bulk crystal of a group III nitride semiconductor grown to a thickness of 1 mm or more in the c-axis direction After processing the bulk crystal, the bulk crystal is sliced or polished to obtain a nonpolar plane consisting of (11-20) plane or (10-10) plane, or (10-1-1) plane, (10- 1-3) forming a semipolar plane composed of a plane, a (10-11) plane, a (10-13) plane, or a (11-22) plane;
Processing the surface to be a flat surface;
A method for producing a group III nitride semiconductor substrate, comprising: After the surface treatment is performed on the growth surface and the back surface of the bulk crystal of the group III nitride semiconductor grown to a thickness of 1 mm or more in the c-axis direction so as to exhibit different appearances, the bulk crystal is sliced. Or, by polishing, a nonpolar surface consisting of (11-20) plane or (10-10) plane, or (10-1-1) plane, (10-1-3) plane, (10-11) Forming a semipolar plane consisting of a plane, (10-13) plane or (11-22) plane;
Processing the surface to be a flat surface;
A method for producing a group III nitride semiconductor substrate, comprising: Growing the group III nitride semiconductor on a base substrate made of sapphire or SiC;
Removing the base substrate;
The manufacturing method of the group III nitride semiconductor substrate as described in any one of Claims 8 thru | or 10 further including these.