Method of manufacturing a semiconductor and a semiconductor...

Details Method of manufacturing a semiconductor and a semiconductor... Method of manufacturing a semiconductor and a semiconductor...

1999-02-03

2001-08-28

Clark, Sheila V. (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

Specified wide band gap semiconductor material other than...

Diamond or silicon carbide

C257S098000, C257S079000, C257S086000, C257S080000

Reexamination Certificate

active

06281522

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a semiconductor used in light-emitting devices such as a light-emitting diode device or a semiconductor laser diode device having wavelengths in the region from blue to ultraviolet, and more specifically to a method of manufacturing a gallium nitride semiconductor which has excellent electric and optical properties by using a vapor-phase growth process.
Recently, short-wave light-emitting devices which have wavelengths shorter than blue light have been promising as a light source for full-color display or an optical disk capable of performing high-density recording. Such short-wave light-emitting devices have been vigorously studied by utilizing semiconductors which employ II-IV family compounds such as zinc selenide (ZnSe), IV family compounds such as silicon carbide (SiC), and III-V family compounds such as gallium nitride (GaN). Since blue light-emitting diodes which employ GaN, GaInN, or the like among the III-V family compounds have been realized, light-emitting devices which utilize these gallium nitride semiconductors have been drawing attention.
In order to grow crystals in gallium nitride semiconductors, a metalorganic vapor-phase epitaxy process (MOVPE) and a molecular beam epitaxy process (MBE) are generally used. When the single crystal of GaN is grown by a vapor-phase process, either SiC or sapphire (Al
2
O
3
) is used as the substrate.
In the case where SiC is used as the substrate, a SiC substrate consisting of 6H polycrystal-type and having a (0001) surface is used. As shown in
FIG. 10
, SiC has a lattice mismatching rate of as small as about 3% with GaN, and has a much smaller lattice mismatching rate of 1% with aluminum nitride (AlN). For this reason, SiC has become promising especially in these days as the substrate of a nitride compound semiconductor. Unlike sapphire, SiC has a conductivity, which enables a SiC substrate to have an electrode on the back side thereof. Consequently, a light-emitting device such as a laser device can be obtained by a simple process.
According to the above-mentioned MOVPE, trimethylaluminum (TMA), which is metalorganic, and ammonia (NH
3
) are supplied onto a SiC substrate by using hydrogen (H
2
) as a carrier gas, and as a result, a single crystal consisting of AlN is grown as a buffer layer on the substrate at a temperature of about 1000° C. Then, the supply of TMA is suspended and in turn trimethylgallium (TMG) is supplied onto the substrate with a temperature fixed at 1000° C., thereby a single crystal consisting of GaN being grown on the buffer layer. The buffer layer consisting of AlN most generally has a thickness of about 50 nm, and has not been doped, so that it has a high resistance and a low conductivity. It has been reported that the dislocation density of GaN on the buffer layer on the SiC substrate in this case is 10
9
cm
−2
.
However, the conventional method of manufacturing a gallium nitride semiconductor has the following problem. When a semiconductor crystal layer which composes a device such as a clad layer or an active layer grows on the buffer layer which has grown on the SiC substrate, the semiconductor crystal layer suffers cracks.
SUMMARY OF THE INVENTION
The present invention has an object of solving the above-mentioned conventional problem, thereby manufacturing a gallium nitride semiconductor which suffers no cracks, and has an even surface and excellent electric and optical properties.
The first method of manufacturing a semiconductor in accordance with the present invention comprises the steps of growing a buffer layer consisting of AlN on a semiconductor layer consisting of silicon carbide in such a manner that the buffer layer has a thickness of between 10 nm and 25 nm, inclusive; and growing on the buffer layer a single crystal layer consisting of Al
x
Ga
1-x-y
In
y
N (x and y are real numbers where 0≦x≦1, 0≦y≦1, and x+y≦1).
In the first method of manufacturing a semiconductor, because the buffer layer consisting of AlN is grown to have a thickness of between 10 nm and 25 nm, inclusive on the semiconductor layer consisting of silicon carbide, the crystallinity of the buffer layer is not sufficient. As a result, dislocation is caused on the interface between the SiC semiconductor layer and the buffer layer, and on the interface between the buffer layer and the single crystal layer consisting of Al
x
Ga
1-x-y
In
y
N. This dislocation reduces the lattice mismatching between the buffer layer and the single crystal layer, which prevents the single crystal layer which grows on the buffer layer from suffering cracks. Consequently, a satisfactory single crystal layer with excellent surface evenness can be obtained.
In the first method of manufacturing a semiconductor, it is preferable that the step of growing the buffer layer includes a step of growing the buffer layer at a temperature of 1000° C. Under this condition, unlike a polycrystalline buffer layer, the AlN buffer layer has a single crystal and has a conductivity, so that current can be injected from the opposite side of the main surface of the semiconductor substrate. Consequently, it becomes easier to construct a p-n junction with an n-type semiconductor substrate when a device is manufactured.
In the first method of manufacturing a semiconductor, it is preferable that the step of growing the buffer layer includes a step of growing the buffer layer without doping it with impurities. Under this condition, the single crystal which grows on the buffer layer hardly suffers cracks. Even if not being doped with impurities, the buffer layer, which has a thickness of between 10 nm and 25 nm, inclusive, can be supplied with tunnel current. As a result, the semiconductor can have a simple structure by forming an electrode on the side opposite to the main surface of the buffer layer on the semiconductor substrate.
The second method of manufacturing a semiconductor in accordance with the present invention comprises the steps of growing a buffer layer consisting of AlGaN on a semiconductor layer consisting of silicon carbide in such a manner that the buffer layer has a thickness of between 10 nm and 25 nm, inclusive; and growing on the buffer layer a single crystal layer consisting of Al
x
Ga
1-x-y
In
y
N (x and y are real numbers where 0≦x≦1, 0≦y≦1, and x+y≦1).
In the second method of manufacturing a semiconductor, because the buffer layer consisting of AlGaN is grown to have a thickness of between 10 nm and 25 nm, inclusive on the semiconductor layer consisting of silicon carbide, the crystallinity of the buffer layer is not sufficient. As a result, dislocation is caused on the interface between the SiC semiconductor layer and the buffer layer, and on the interface between the buffer layer and the single crystal layer consisting of Al
x
Ga
1-x-y
In
y
N. This dislocation reduces the lattice mismatching between the buffer layer and the single crystal layer. The lattice mismatching is further reduced by the lattice constant of AlGaN in the buffer layer having a value between that of SiC and that of GaN. Consequently, a gallium nitride single crystal layer with a higher quality can be obtained.
The third method of manufacturing a semiconductor in accordance with the present invention comprises the steps of growing a first buffer layer consisting of AlN on a semiconductor layer consisting of silicon carbide in such a manner that the first buffer layer has a thickness of between 10 nm and 25 nm, inclusive; growing a second buffer layer consisting of AlGaN on the first buffer layer; and growing on the second buffer layer a single crystal layer consisting of Al
x
Ga
1-x-y
In
y
N (x and y are real numbers where 0≦x<1, 0<y≦1, and x+y≦1).
In the third method of manufacturing a semiconductor, because the first buffer layer consisting of AlN and the second buffer layer consisting of AlGaN are grown to have a thickness of between 10 nm and 25 nm, inclusive on the semiconductor layer consisting of silicon carbide, th

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