Semiconductor apparatus, method for growing nitride semiconductor and method for producing semiconductor apparatus

Abstract

A semiconductor apparatus includes a substrate made of a diboride single crystal expressed by a chemical formula XB₂, in which X includes at least one of Tl, Zr, Nb and Hf, a semiconductor buffer layer formed on a principal surface of the substrate and made of Al_yGa_1-yN (0<y≦1), and a nitride semiconductor layer which is formed on the semiconductor buffer layer and which includes at least one kind or plural kinds selected from among 13 group elements and As.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The invention relates to a semiconductor apparatus and specifically relates to a semiconductor apparatus, a method for growing a nitride semiconductor and a method for producing a semiconductor apparatus which are suitable for a light emitting device and a light receiving device such as a light emitting diode (LED), a laser diode (LD), a solar cell and a photosensor, and an electronic device such as a transistor and a power device. [0003] 2. Description of the Related Art [0004] A nitride semiconductor containing Ga as a main constituent (a GaN semiconductor) is utilized as a material for an optical device such as a light emitting diode of blue light or violet light, a laser diode and a photodetector. Moreover, attention is given to the GaN semiconductor as a high-performance material for an electronic device as well, because the GaN semiconductor is capable of satisfying high frequency and high electric power, and ...

AI Technical Summary

Benefits of technology

[0104] As described above, according to a method for producing a semiconductor apparatus of the invention, by going through the step of carrying out crystal growth of a nitride semiconductor layer on one principal surface of a single crystal substrate of a hexagonal symmetry structure having electrical conductivity, and the step of eroding and removing the single crystal substrate by etching, it is possible to avoid a warp and cracks of the semiconductor apparatus, decrease dislocation density, curve dislocation, prevent inclination of crystal orientation in a horizontal direction of the semiconductor apparatus, and thereby provide a nitride semiconductor apparatus in which in-plane uniformity of dislocation density is good.

Problems solved by technology

Since production of a single crystal substrate of the GaN semiconductor is difficult, there is a need to form a semiconductor apparatus using the GaN semiconductor on a substrate made of a different material.

In the case of growing the GaN semiconductor layers on the sapphire substrate 20, a problem is a lattice mismatch between them.

Consequently, a good quality crystal cannot be obtained when GaN is directly grown on sapphire.

The dislocation density of the GaN growth layer significantly restricts performance of a semiconductor apparatus to be produced from this, and moreover, there is a need to increase the amount of additive elements in the semiconductor layer for generation of sufficient carrier.

This has a problem of deteriorating a characteristic of a semiconductor apparatus, such as a life, a withstand voltage, a driving voltage, consumed electric power (operation efficiency), an operation speed or a leak current.

Consequently, a lattice defect occurs on the interface even when GaN is grown on the diboride single crystal substrate as described above, and a good quality crystal cannot be obtained.

Moreover, differences in the coefficient of thermal expansion between the above single crystal substrates and the nitride semiconductor are large, and a difference in contraction amounts after crystal growth at a high temperature of approximately 1000° C. causes cracks.

However, this technique has a problem that it is inferior in mass production because it uses the MBE method.

Further, in the prior art, a GaN film grown on the (0001) plane of a ZrB2 single crystal substrate by an MOVPE method has a problem that a surface shape thereof tends to become uneven as shown in FIG. 13.

However, according to both the techniques, in the GaN film grown on the (0001) plane of the ZrB2 single crystal substrate, a rocking curve half value width of (0002) plane omega scan by an X-ray diffraction method, which becomes an indicator of evaluation of quality, is approximately 1000 seconds, which is not sufficiently good (refer to “Study on the crystal growth and properties of group-III nitride semiconductors on ZrB2 substrate by metalorganic vapor phase epitaxy” master's thesis written by Yohei Yukawa, graduate school of Meijo University, 2001).

Still further, a band gap of AlN is as large as 6.2 eV, and therefore, it is difficult to decrease resistance by doping.

Up to now, there is no substrate that achieves a lattice match with the nitride semiconductor.

However, for example, regarding the sapphire substrate and GaN, a ratio of lattice mismatch is 13.8% and a difference in the coefficient of thermal expansion is 3.2×10−6 / K, and there is a problem resulting from the mismatch such that dislocations of 108 to 1010 cm−2 arises in the GaN film because of a crystal defect caused on an interface between the sapphire substrate and the GaN film.

Further, because of the defect and thermal distortion, the GaN film is warped, and crystalline quality is significantly deteriorated.

Furthermore, considering production of a device such as a laser diode, the nitride semiconductor is formed on a substrate made of a material of different kind from the nitride semiconductor such as GaN and the like, and therefore, there arises such a problem that, in the case of forming a reflection surface of a laser resonator, cleaved planes of the substrate made of a material and the nitride semiconductor are different, and that formation by cleavage is difficult.

However, regarding the nitride semiconductor such as GaN, a melting point is high and a dissociation pressure of nitride is high at the melting point, and therefore, production of a bulk single crystal is difficult.

However, in the step of separating the substrate and the nitride semiconductor in the aforementioned production method, a method of abrading the substrate arises a problem that stress from the nitride semiconductor thick film becomes large as the substrate becomes thin, and that the stress acts on the substrate, thereby worsening a warp thereof and causing cracks.

However, according to this method, only a small part of the interface is separated because an area irradiated is small, and stress concentrates on a small attaching part, with the result that cracks are caused.

Moreover, since the area irradiated is small, a time period for treatment is long.

However, since SiO2 is filled in, it is difficult to carry out mask treatment on SiO2.

Moreover, since curved dislocations concentrate on a central portion on the SiO2 line, there arises a problem of inclination of crystal orientation in a horizontal direction of the substrate, for example.

In addition, the ELO growth method needs a complicated production process, and therefore, brings about cost increase.

As described above, according to the conventional production methods, when the substrate made of a material of different kind from nitride semiconductor and the nitride semiconductor thick film are separated, stress resulting from differences in lattice constants and the coefficient of thermal expansion causes a warp and cracks on the produced nitride semiconductor apparatus.

Moreover, the production process is complicated in the ELO growth that reduces dislocations, and it is difficult to keep away from a portion on the which penetration dislocation density concentrates, and to carry out the mask treatment on contained SiO2.

Furthermore, there arises a problem of inclination of crystal orientation in a horizontal direction of the substrate because of curved dislocation, for example.

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