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Patent Issued for Group III Nitride Crystal Substrate, Epilayer-Containing Group III Nitride Crystal Substrate, Semiconductor Device and Method of...

July 23, 2014



Patent Issued for Group III Nitride Crystal Substrate, Epilayer-Containing Group III Nitride Crystal Substrate, Semiconductor Device and Method of Manufacturing the Same

By a News Reporter-Staff News Editor at Electronics Newsweekly -- Sumitomo Electric Industries, Ltd. (Osaka, JP) has been issued patent number 8771552, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Ishibashi, Keiji (Itami, JP); Yoshizumi, Yusuke (Itami, JP).

This patent was filed on July 16, 2010 and was published online on July 8, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "The present invention relates to a group III nitride crystal substrate, an epilayer-containing group III nitride crystal substrate, a semiconductor device and a method of manufacturing the same, and particularly to a group III nitride crystal substrate that can be preferably used as a substrate for growing an epitaxial crystal semiconductor layer when producing a semiconductor device.

"As is well known, various devices using nitride semiconductor crystals (e.g., group III nitride crystals) have been produced in recent years, and nitride semiconductor light emitting devices (e.g., group III nitride semiconductor light emitting devices) have been produced as a typical example of such semiconductor devices.

"Generally, in a process of manufacturing a nitride semiconductor device, a plurality of nitride semiconductor layers (e.g., group III nitride semiconductor layers) are epitaxially grown on a substrate. Crystal quality of the epitaxially grown nitride semiconductor layer is affected by a state of a surface layer of the substrate used for the epitaxial growth, and this quality affects performance of the semiconductor device including the nitride semiconductor layer. Therefore, in the case where the nitride semiconductor crystal is used as the above kind of substrate, it is desired that at least a main surface of the substrate providing a base of epitaxial growth has a smooth form without a distortion.

"More specifically, the main surface of the nitride semiconductor substrate used for the epitaxial growth is generally subjected to smoothing processing and distortion removal processing. Among various compound semiconductors, gallium-nitride-based semiconductors are relatively hard so that the surface smoothing processing thereof is not easy, and the distortion removal processing after the smoothing processing is not easy.

"U.S. Pat. No. 6,596,079 (Patent Document 1) has disclosed a method of forming a substrate surface in the case where the substrate is produced from an (AlGaIn)N bulk crystal grown by vapor phase epitaxy on an (AlGaIn)N seed crystal, and more specifically a method of forming a substrate surface that has an RMS (Root Mean Square) surface roughness of 1 nm or lower, and does not have a surface damage owing to effecting CMP (Chemical-Mechanical Polishing) or etching on the substrate surface subjected to mechanical polishing. U.S. Pat. No. 6,488,767 (Patent Document 2) has disclosed an Al.sub.xGa.sub.yIn.sub.zN (0

"In the prior art, as described above, the CMP processing or dry etching is effected after mechanically polishing the GaN crystal so that the process-induced degradation layer formed by the mechanical polishing is removed, and the GaN substrate having the finished substrate surface is formed. However, the processing rate of the CMP processing is low, and causes problems in cost and productivity. Further, the dry etching causes a problem in surface roughness.

"The finishing method of the Si substrate using the CMP as well as the polishing agent for the method are not suitable for the hard nitride semiconductor substrate, and lower the removal speed of the surface layer. In particular, GaN is chemically stable, and is relatively resistant to the wet etching so that the CMP processing is not easy. Although the dry etching can remove the nitride semiconductor surface, it does not have an effect of flattening the surface in a horizontal direction so that the surface smoothing effect cannot be achieved.

"For epitaxially growing the compound semiconductor layer of good crystal quality on the main surface of the substrate, it is necessary to use the substrate surface having a surface layer of good crystal quality as well as less process damage and less distortion as described above. However, the crystal quality of the surface layer that is required at the main surface of the substrate is not clear."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "Each of substrates illustrated in U.S. Pat. No. 6,596,079 (Patent Document 1) and U.S. Pat. No. 6,488,767 (Patent Document 2) is made of hexagonal wurtzite group III nitride crystals, with the main surface implemented by (0001) planes. In a light emitting device which is a semiconductor device including at least one semiconductor layer epitaxially grown on the main surface of such a crystal substrate, with the main surface of the semiconductor layer also implemented by the (0001) planes, the (0001) planes being polar planes that change polarity in the direction normal to the planes, the quantum-confined Stark effect resulting from piezoelectric polarization caused by such polarity leads to a large blue shift of an emission accompanied by an increased amount of current injection, and results in lower emission intensity.

"To manufacture a light emitting device with a blue shift of the emission suppressed, it is required to reduce the polarity at the main surface of a substrate used in manufacturing the light emitting device, in other words, to implement the main surface of the substrate by planes different from the (0001) planes.

"However, the substrate suitable for manufacturing the light emitting device with a blue shift of the emission suppressed has not been clarified concerning the plane orientation of its main surface, the surface roughness of its main surface, the crystallinity of its surface layer, and the like.

"It is therefore an object of the present invention to provide a group III nitride crystal substrate suitable for manufacturing a light emitting device with a blue shift of the emission suppressed, an epilayer-containing group III nitride crystal substrate, a semiconductor device and a method of manufacturing the same.

"According to an embodiment of the invention, in a group III nitride crystal substrate, wherein a plane spacing of arbitrary specific parallel crystal lattice planes of the crystal substrate being obtained from X-ray diffraction measurement performed with variation of X-ray penetration depth from a main surface of the crystal substrate while X-ray diffraction conditions of the specific parallel crystal lattice planes of the crystal substrate are satisfied, a uniform distortion at a surface layer of the crystal substrate represented by a value of |d.sub.1 -d.sub.2 |/d.sub.2 obtained from a plane spacing d.sub.1 at the X-ray penetration depth of 0.3 .mu.m and a plane spacing d.sub.2 at the X-ray penetration depth of 5 .mu.m is equal to or lower than 1.9 .times.10.sup.-3, and the main surface has a plane orientation inclined in a direction at an angle equal to or greater than 10.degree. and equal to or smaller than 80.degree. with respect to one of (0001) and (000-1) planes of the crystal substrate.

"According to another embodiment of the invention, in a group III nitride crystal substrate, wherein on a diffraction intensity profile of arbitrary specific parallel crystal lattice planes of the crystal substrate being obtained from X-ray diffraction measurement performed with variation of X-ray penetration depth from a main surface of the crystal substrate while X-ray diffraction conditions of the specific parallel crystal lattice planes are satisfied, an irregular distortion at a surface layer of the crystal substrate represented by a value of |v.sub.1 -v.sub.2|obtained from a half value width v.sub.1 of a diffraction intensity peak at the X-ray penetration depth of 0.3 .mu.m and a half value width v.sub.2 of the diffraction intensity peak at the X-ray penetration depth of 5 .mu.m is equal to or lower than 130 arcsec, and the main surface has a plane orientation inclined in a direction at an angle equal to or greater than 10.degree. and equal to or smaller than 80.degree. with respect to one of (0001) and (000-1) planes of the crystal substrate.

"According to a still another embodiment of the invention, in a group III nitride crystal substrate, wherein on a rocking curve being measured by varying an X-ray penetration depth from a main surface of the crystal substrate in connection with X-ray diffraction of arbitrary specific parallel crystal lattice planes of the crystal substrate, a plane orientation deviation of the specific parallel crystal lattice planes of the surface layer of the crystal substrate represented by a value of |w.sub.1 -w.sub.2|obtained from a half value width w.sub.1 of a diffraction intensity peak at the X-ray penetration depth of 0.3 .mu.m and a half value width w.sub.2 of the diffraction intensity peak at the X-ray penetration depth of 5 .mu.m is equal to or lower than 350 arcsec, and the main surface has a plane orientation inclined in a direction at an angle equal to or greater than 10.degree. and equal to or smaller than 80.degree. with respect to one of (0001) and (000-1) planes of the crystal substrate.

"In the above group III nitride crystal substrate, the main surface can have a surface roughness Ra of 3 nm or lower. The main surface of the group III nitride crystal substrate can have a plane orientation inclined at an angle falling within .+-.4.degree. with respect to any of {20-21}, {10-11}, {20-2-1}, and {10-1-1} planes of the crystal substrate. The main surface can have a plane orientation inclined at an inclination angle having an absolute value of less than 0.1.degree. with respect to any of the {20-21}, {10-11}, {20-2-1}, and {10-1-1} planes of the crystal substrate so as to be substantially parallel thereto. The main surface can have a plane orientation inclined at an inclination angle having an absolute value of equal to or more than 0.1.degree. and equal to or less than 4.degree. with respect to any of the {20-21}, {10-11}, {20-2-1}, and {10-1-1} planes of the crystal substrate. The oxygen present at the main surface of the group III nitride crystal substrate can have a concentration of equal to or more than 2 at. % and equal to or less than 16 at. %. The dislocation density at the main surface of the group III nitride crystal substrate can be equal to or less than 1.times.10.sup.7 cm.sup.-2. The group III nitride crystal substrate can have a diameter equal to or more than 40 mm and equal to or less than 150 mm. The specific parallel crystal lattice planes can be not parallel to the main surface, and can be parallel to any of (10-10), (10-11), (10-13), (11-20), (11-22), (11-24), (10-1-1), (10-1-3), (11-2-2), and (11-2-4) planes.

"According to a still another embodiment of the invention, an epilayer-containing group III nitride crystal substrate includes at least one semiconductor layer provided by epitaxial growth on the main surface of the group III nitride crystal substrate.

"According to a still another embodiment of the invention, a semiconductor device includes the epilayer-containing group III nitride crystal substrate. In the semiconductor device, the semiconductor layer contained in the epilayer-containing group III nitride crystal substrate can include a light emitting layer emitting light having a peak wavelength equal to or more than 430 nm and equal to or less than 550 nm.

"According to a still another embodiment of the invention, a method of manufacturing a semiconductor device includes the steps of: preparing a group III nitride crystal substrate, wherein, a plane spacing of arbitrary specific parallel crystal lattice planes of the crystal substrate being obtained from X-ray diffraction measurement performed with variation of X-ray penetration depth from a main surface of the crystal substrate while X-ray diffraction conditions of the specific parallel crystal lattice planes of the crystal substrate are satisfied, a uniform distortion at a surface layer of the crystal substrate represented by a value of |d.sub.1-d.sub.2|/d.sub.2 obtained from a plane spacing d.sub.1 at the X-ray penetration depth of 0.3 .mu.m and a plane spacing d.sub.2 at the X-ray penetration depth of 5 .mu.m is equal to or lower than 1.9 .times.10.sup.-3, and the main surface has a plane orientation inclined in a direction at an angle equal to or greater than 10.degree. and equal to or smaller than 80.degree. with respect to one of (0001) and (000-1) planes of the crystal substrate; and epitaxially growing at least one semiconductor layer on the main surface of the crystal substrate, thereby forming an epilayer-containing group III nitride crystal substrate.

"According to a still another embodiment of the invention, a method of manufacturing a semiconductor device includes the steps of: preparing a group III nitride crystal substrate, wherein, on a diffraction intensity profile of arbitrary specific parallel crystal lattice planes of the crystal substrate being obtained from X-ray diffraction measurement performed with variation of X-ray penetration depth from a main surface of the crystal substrate while X-ray diffraction conditions of the specific parallel crystal lattice planes are satisfied, an irregular distortion at a surface layer of the crystal substrate represented by a value of |v.sub.1 -v.sub.2|obtained from a half value width v.sub.1 of a diffraction intensity peak at the X-ray penetration depth of 0.3 .mu.m and a half value width v.sub.2 of the diffraction intensity peak at the X-ray penetration depth of 5 .mu.m is equal to or lower than 130 arcsec, and the main surface has a plane orientation inclined in a direction at an angle equal to or greater than 10.degree. and equal to or smaller than 80.degree. with respect to one of (0001) and (000-1) planes of the crystal substrate; and epitaxially growing at least one semiconductor layer on the main surface of the crystal substrate, thereby forming an epilayer-containing group III nitride crystal substrate.

"According to a still another embodiment of the invention, a method of manufacturing a semiconductor device includes the steps of: preparing a group III nitride crystal substrate, wherein, on a rocking curve being measured by varying an X-ray penetration depth from a main surface of the crystal substrate in connection with X-ray diffraction of arbitrary specific parallel crystal lattice planes of the crystal substrate, a plane orientation deviation of the specific parallel crystal lattice planes of the surface layer of the crystal substrate represented by a value of |w.sub.1-w.sub.2| obtained from a half value width w.sub.1 of a diffraction intensity peak at the X-ray penetration depth of 0.3 .mu.m and a half value width w.sub.2 of the diffraction intensity peak at the X-ray penetration depth of 5 .mu.m is equal to or lower than 350 arcsec, and the main surface has a plane orientation inclined in a direction at an angle equal to or greater than 10.degree. and equal to or smaller than 80.degree. with respect to one of (0001) and (000-1) planes of the crystal substrate; and forming an epilayer-containing group III nitride crystal substrate by epitaxially growing at least one semiconductor layer on the main surface of the crystal substrate.

"In the step of forming the epilayer-containing group III nitride crystal substrate in the method of manufacturing a semiconductor device, the semiconductor layer can be configured to include a light emitting layer emitting light having a peak wavelength equal to or more than 430 nm and equal to or less than 550 nm. In the method of manufacturing a semiconductor device, the specific parallel crystal lattice planes can be not parallel to the main surface, and can be parallel to any of (10-10), (10-11), (10-13), (11-20), (11-22), (11-24), (10-1-1), (10-1-3), (11-2-2), and (11-2-4) planes.

"The present invention can provide a group III nitride crystal substrate suitable for manufacturing a light emitting device with a blue shift of an emission suppressed and having an increased emission intensity, an epilayer-containing group III nitride crystal substrate, a semiconductor device and a method of manufacturing the same.

"The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings."

For the URL and additional information on this patent, see: Ishibashi, Keiji; Yoshizumi, Yusuke. Group III Nitride Crystal Substrate, Epilayer-Containing Group III Nitride Crystal Substrate, Semiconductor Device and Method of Manufacturing the Same. U.S. Patent Number 8771552, filed July 16, 2010, and published online on July 8, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8771552.PN.&OS=PN/8771552RS=PN/8771552

Keywords for this news article include: Electronics, Semiconductor, Sumitomo Electric Industries Ltd.

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Source: Electronics Newsweekly


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