JP2007149984A - Manufacture of nitride semiconductor light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a nitride semiconductor light-emitting element capable of preventing light absorption on an SiC substrate and easily performing the ohmic contact between the SiC substrate and a nitride semiconductor layer by a simple method. <P>SOLUTION: A metal film 2 is formed on the upper surface of the conductive SiC substrate 1 doped with impurities by vapor deposition or sputtering by selecting one metal from Ni, Ti, Pd, Fe, Ru, Os, Ge, Sn, V, Ta and Nb. The SiC substrate 1 where the metal film 2 is formed on the upper surface is annealed at a high temperature. An ohmic contact region 3 is formed on the interface between the SiC substrate 1 and the metal film 2 by high-temperature annealing. Then, the nitride semiconductor crystal is laminated on a surface where an ohmic contact region 3 is formed on the SiC substrate 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a nitride semiconductor light emitting device using a nitride semiconductor.

  Nitride semiconductors are used in blue LEDs used as light sources for lighting, backlights, etc., LEDs used in multicoloring, LDs, and the like. Light emitting diodes using nitride semiconductors have an emission wavelength from the green range to the ultraviolet range and are expected as light sources for displays, and lasers using nitride semiconductors have an emission wavelength from the green range to the ultraviolet range. In particular, a 405 nm band semiconductor laser or the like has been developed.

  Since it is difficult to manufacture a bulk single crystal in a nitride semiconductor, GaN is grown on a heterogeneous substrate such as sapphire or SiC by using MOCVD (metal organic chemical vapor deposition). A sapphire substrate is particularly used as a growth substrate because it is excellent in stability in a high-temperature ammonia atmosphere in an epitaxial growth process. However, the sapphire substrate is an insulating substrate, and cannot conduct, and electrodes cannot be provided with the sapphire substrate interposed therebetween.

  Therefore, the nitride semiconductor on the sapphire substrate is etched until the n-type gallium nitride layer is exposed after epitaxial growth, an n-type contact is formed on the etched surface, and two p-type and n-type are formed on the same surface side. A structure in which an electrode is provided is common.

  When two p-type and n-type electrodes are provided on the same surface as described above, an ESD (electrostatic breakdown) voltage can be increased because current tends to concentrate on a mesa portion close to the n-electrode. Can not. In addition, it is difficult to uniformly inject current into the active layer, and it becomes difficult to cause the active layer to emit light uniformly. In addition, since wire bonding electrodes are required for both the p-electrode and the n-electrode on the same surface side, light emission is more effective than a nitride semiconductor on a conductive substrate, which may be provided with either wire-bonding electrode. As the area is reduced, the chip (element) area is increased, and the number of chips that can be taken from the same wafer is reduced. In addition, since sapphire has a high hardness and a hexagonal crystal structure, when sapphire is used as a growth substrate, it is necessary to separate the sapphire substrate by scribing, and the manufacturing process becomes complicated and the yield is poor.

Therefore, a structure has been proposed in which a p-type electrode and an n-type electrode are provided so as to face each other with a nitride semiconductor layer interposed therebetween using a conductive substrate (see, for example, Patent Document 1). As this conductive substrate, a hexagonal SiC substrate that is lattice-matched with a nitride semiconductor is most often used. Compared with sapphire, the SiC substrate has a smaller lattice constant difference from GaN (about 3%) and good heat dissipation characteristics. In addition, since the substrate is conductive, a contact can be made directly, an element having a p-electrode and an n-electrode facing each other can be formed, and wire bonding can be performed on only one electrode side during assembly, and a chip that can be taken from the same wafer There are advantages such as an increase in number.
JP-A-6-326416

  However, when a nitride semiconductor light emitting element is formed using a conductive SiC substrate as in the above-described prior art, there are the following problems. Normally, SiC doped with n-type impurities is used for the conductive SiC substrate. There is a buffer layer or the like as the first nitride semiconductor layer to be stacked on the SiC substrate. This buffer layer is made of AlN, AlGaN, GaN, etc., and the band gap between these semiconductor layers and the SiC substrate is The difference is large and it is difficult to make contact with the SiC substrate.

  Therefore, if the doping amount of the n-type impurity is increased in order to facilitate the ohmic contact with the nitride semiconductor layer such as the buffer layer, the SiC substrate is colored and absorbs visible light. Since a part of the light emitted in all directions from the light emitting region of the nitride semiconductor light emitting device is absorbed by the SiC substrate, the light extraction efficiency is lowered, and a high luminance light emitting device cannot be obtained.

  On the other hand, when the doping amount of the n-type impurity is decreased in order to reduce the light absorption, the contact resistance with the n-electrode is increased and the specific resistance of the SiC substrate is increased, so that the driving voltage is increased. Further, since the carrier concentration of the SiC substrate is low, the efficiency of carrier injection into the light emitting region is reduced, the light emission amount is reduced, and the laser may not oscillate. In order to solve these problems, the contact resistance between the SiC substrate and the nitride semiconductor layer must be reduced. In order to reduce the contact resistance, it is necessary to reduce the difference in the band gap, and the semiconductor layer in which the band gap is between the SiC substrate and the nitride semiconductor layer between the SiC substrate and the nitride semiconductor layer. Is further provided to facilitate the flow of current.

  However, this method requires an increase in the number of intermediate semiconductor layers, which complicates the manufacturing process, increases the size of the device, and sometimes makes it difficult to find a material having an appropriate band gap. is there.

  The present invention was devised to solve the above-described problems, and prevents light absorption of the SiC substrate and facilitates ohmic contact between the SiC substrate and the nitride semiconductor layer by a simple method. It is an object of the present invention to provide a method for manufacturing a nitride semiconductor light emitting device that can be manufactured.

  In order to achieve the above object, the invention described in claim 1 is a method of manufacturing a nitride semiconductor light emitting device in which a nitride semiconductor crystal is stacked on a conductive SiC substrate, and the conductive on the side on which the nitride semiconductor crystal is stacked. A metal film using any one of Ni, Ti, Pd, Fe, Ru, Os, Ge, Sn, V, Ta, and Nb is formed on a conductive SiC substrate, and an ohmic contact is formed by annealing. Thereafter, the metal film is removed, and a nitride semiconductor crystal is laminated on the conductive SiC substrate.

  According to the present invention, any one of Ni, Ti, Pd, Fe, Ru, Os, Ge, Sn, V, Ta, and Nb is used on the conductive SiC substrate on the side where the nitride semiconductor crystal is laminated. After forming a metal film and forming an ohmic contact by annealing, the metal film is removed and a nitride semiconductor crystal is stacked, so that an ohmic contact between the SiC substrate and the nitride semiconductor crystal is easy. In addition, it is not necessary to increase the impurity concentration of the conductive SiC substrate to reduce the contact resistance, and visible light absorption can be prevented.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 to 4 show a method for manufacturing a nitride semiconductor light emitting device of the present invention.

First, as a conductive SiC substrate, for example, an n-type SiC substrate doped with nitrogen of an n-type impurity is prepared. The conductive SiC substrate 1 is doped with impurities at 10 ¹⁸ cm ⁻³ or less, for example, 10 ¹⁷ cm ⁻³ , so that the conductive SiC substrate 1 does not absorb visible light.

  As shown in FIG. 1, a metal film 2 is formed on the upper surface of the SiC substrate 1 by selecting one metal from Ni, Ti, Pd, Fe, Ru, Os, Ge, Sn, V, Ta, and Nb by vapor deposition or sputtering. Form. The thickness of the metal film 2 is 10 nm to 1 μm, preferably 10 nm to 100 nm.

  SiC substrate 1 on which metal film 2 is formed is heated at 1000 ° C. to 1400 ° C. in a nitrogen atmosphere. By doing so, the bond between Si and C in the SiC substrate 1 is broken, and a compound silicide of Si and the metal used in the metal film 2 is formed at the interface between the SiC substrate 1 and the metal film 2, An ohmic contact region 3 is formed. By the way, when the ohmic contact region 3 is formed, the metal film 2 uses one of the metals Ni, Ti, Pd, Fe, Ru, Os, Ge, Sn, V, Ta, and Nb. These metals have a small work function and are easy to form compounds. Of the above metals, Ni, Ti, and Pd are more desirable because they are easy to handle by vapor deposition.

  Next, as shown in FIG. 2, the metal film 2 is removed by etching. Thereafter, nitride semiconductor crystal 4 is formed by MOCVD as shown in FIG.

  After the nitride semiconductor crystal 4 is epitaxially grown and then the n-electrode 6 and the p-electrode 5 are formed by vapor deposition or sputtering, the nitride semiconductor light emitting device shown in FIG. 4 is completed.

  At the interface between the conductive SiC substrate doped with impurities at a low concentration so as not to absorb visible light and the AlGaN semiconductor layer, the AlN semiconductor layer, the GaN semiconductor layer, etc. constituting the nitride semiconductor crystal 4, a band gap is usually used. Since the difference is large and the potential barrier at the interface is large, it becomes difficult for current to flow, leading to an increase in driving voltage, etc. As described above, the ohmic contact region 3 is applied to the SiC substrate 1 by thermal alloying. Therefore, the potential barrier at the interface between the conductive SiC substrate and the AlGaN semiconductor layer, the AlN semiconductor layer, the GaN semiconductor layer, or the like can be reduced, and an increase in driving voltage can be prevented.

  FIG. 5 shows a structure of a semiconductor laser as an example of the nitride semiconductor light emitting device shown in FIG.

First, an ohmic contact region 3 is formed on a conductive n-type SiC substrate 1 by the method shown in FIG. 1, and then an n-type buffer layer 43 made of Si-doped AlGaN and Si-doped AlGaN are formed by MOCVD. n-type cladding layer 44, n-type light guide layer 45 made of Si-doped GaN, MQW active layer 46 having a multiple quantum well structure in which InGaN well layers and GaN or InGaN barrier layers are alternately stacked, Mg-doped A p-type light guide layer 47 made of GaN, a p-type cladding layer 48 made of Mg-doped AlGaN, and a p-type contact layer 49 made of Mg-doped GaN are sequentially formed. Finally, the p electrode 5 and the n electrode 6 are formed by vapor deposition or sputtering. Here, the n-type buffer layer 43 to the p-type contact layer 49 correspond to the nitride semiconductor crystal 4 shown in FIG.

  The n-type buffer layer 43 made of AlGaN, the cladding layers 44 and 48 made of AlGaN, the light guide layers 45 and 47 made of GaN, the contact layer 49, the barrier layer in the MQW active layer 46, etc. The temperature is increased to about 1100 ° C. to grow, but the InGaN well layer in the MQW active layer 46 is grown at a low temperature of 700 ° C. to 800 ° C.

  As described above, the ohmic contact region 3 is formed on the conductive n-type SiC substrate 1, and the n-type buffer layer 43 made of Si-doped AlGaN is formed thereon, so that the SiC substrate The potential barrier at the interface between 1 and the n-type buffer layer 43 can be reduced, and an increase in driving voltage can be prevented.

  FIG. 6 shows the structure of an LED as an example of the nitride semiconductor light emitting device shown in FIG. First, the ohmic contact region 3 is formed on the conductive n-type SiC substrate 1 by the method shown in FIG. 1, and then the n-type nitride semiconductor 22, the active layer 23, and the p-type nitride semiconductor 24 are formed by MOCVD. Form in order.

  The n-type nitride semiconductor layer 22 includes, for example, an n-type impurity Si-doped GaN contact layer or an n-type impurity Si-doped AlGaN contact layer and an n-type impurity Si-doped InGaN / GaN superlattice layer. As an example, the active layer 23 as the light emitting region has a multiple quantum well structure in which InGaN well layers and GaN or InGaN barrier layers are alternately stacked. The p-type nitride semiconductor layer 24 is configured by, for example, a stack of a p-type impurity Mg-doped AlGaN electron barrier layer and a p-type impurity Mg-doped GaN contact layer. Finally, the p electrode 25 and the n electrode 26 are formed by vapor deposition or sputtering.

  The GaN layer and the AlGaN layer in the n-type nitride semiconductor 22, the active layer 23, and the p-type nitride semiconductor 24 are grown to a temperature of about 1100 ° C., but the InGaN well layer or Si in the MQW active layer 46 is grown. The InGaN layer of the doped InGaN / GaN superlattice layer is grown at a low temperature of 700 ° C. to 800 ° C.

  As described above, the ohmic contact region 3 is formed on the conductive n-type SiC substrate 1, and the n-type GaN contact layer or the n-type AlGaN contact layer is formed thereon. The potential barrier at the interface with the n-type GaN contact layer or the n-type AlGaN contact layer can be reduced, and an increase in driving voltage can be prevented.

In addition, since the n-type impurity is doped in the conductive SiC substrate 1 at a concentration that does not absorb visible light, the light emitted from the active layer 23 is not absorbed by the SiC substrate 1 and is exposed to the outside. The formation of the ohmic contact region 3 can prevent the light extraction efficiency from being lowered.

It is a figure which shows the first manufacturing process of the manufacturing method of the nitride semiconductor light-emitting device in this invention. It is a figure which shows the manufacturing process of the manufacturing method of a nitride semiconductor light-emitting device. It is a figure which shows the manufacturing process of the manufacturing method of a nitride semiconductor light-emitting device. It is a figure which shows the manufacturing process of the manufacturing method of a nitride semiconductor light-emitting device. It is a figure which shows the structure of a semiconductor laser as an example of the nitride semiconductor light-emitting device. It is a figure which shows the structure of LED as an example of the nitride semiconductor light-emitting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 SiC substrate 2 Metal film 3 Ohmic contact area 4 Nitride semiconductor crystal 5 P electrode 6 N electrode

Claims (1)

In the method for manufacturing a nitride semiconductor light emitting device in which a nitride semiconductor crystal is stacked on a conductive SiC substrate, Ni, Ti, Pd, Fe, Ru, Os is formed on the conductive SiC substrate on the nitride semiconductor crystal stacking side. , Ge, Sn, V, Ta, and Nb, and after forming an ohmic contact by annealing, the metal film is removed and the conductive SiC substrate is formed on the conductive SiC substrate. A method of manufacturing a nitride semiconductor light emitting device, comprising: laminating a nitride semiconductor crystal.

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