Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
2000-05-09
2003-11-11
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C117S094000, C117S095000, C117S096000, C117S952000
Reexamination Certificate
active
06645295
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a group III nitride compound semiconductor. Especially, the present invention relates to a method for manufacturing a group III nitride compound semiconductor in which an epitaxial lateral overgrowth (ELO) method is used to form a layer on a substrate. The present invention also relates to a light-emitting device using a group III nitride compound semiconductor formed on a group III nitride compound semiconductor layer using the ELO method. A group III nitride compound semiconductor can be made of binary compounds such as AlN, GaN or InN, ternary compounds such as Al
x
Ga
1−x
N, Al
x
In
1−x
N or Ga
x
In
1−x−y
N (0<x<1), or quaternary compounds Al
x
Ga
y
In
1−x−y
N (0<x<1, 0<y<1, 0<x+y<1), that is, those are represented by a general formula Al
x
Ga
y
In
1−x−y
N (0≦x≦1, 0≦y≦1, 0≦x+y≦1).
2. Description of the Related Art
A group III nitride compound semiconductor is a direct-transition-type semiconductor having a wide emission spectrum range from ultraviolet to red, and is applied to light-emitting devices such as light-emitting diodes (LEDs) and laser diodes (LDs). The group III nitride compound semiconductor is, in general, formed on a sapphire substrate.
However, in the above-described conventional technique, when a layer of a group III nitride compound semiconductor is formed on a sapphire substrate, cracks and/or warpage are generated in the semiconductor layer due to a difference in thermal expansion coefficient between sapphire and the group III nitride compound semiconductor, and dislocations are generated in the semiconductor layer due to misfit, which result in degraded device characteristics. Especially, dislocations due to misfit are feedthrough dislocations which penetrate the semiconductor layer in longitudinal direction, resulting in propagation of about 10
9
cm
−2
of dislocation in the group III nitride compound semiconductor.
FIG. 6
illustrates a schematic view showing a structure of a conventional group III nitride compound semiconductor. In
FIG. 6
, a buffer layer
2
and a group III nitride compound semiconductor layer
3
are formed successively on a substrate
1
. In general, the substrate
1
and the buffer layer
2
are made of sapphire and aluminum nitride (AlN), respectively. Although the AlN buffer layer
2
is formed to relax misfit between the sapphire substrate
1
and the group III nitride compound semiconductor layer
3
, possibility of generating dislocations cannot be 0. Feedthrough dislocations
4
are propagated from dislocation generating points
40
in longitudinal direction (a direction vertical to a surface of the substrate), penetrating the buffer layer
2
and the group III nitride compound semiconductor layer
3
. Thus, manufacturing a semiconductor device by laminating various group III nitride compound semiconductor layers on the group III nitride compound semiconductor layer
3
results in propagating feedthrough dislocations
4
from dislocation generating points
41
which reach the surface of the group III nitride compound semiconductor layer
3
, further through the semiconductor device in longitudinal direction. Accordingly, it had been difficult to prevent dislocations from propagating in the semiconductor device at the time when a group III nitride compound semiconductor layer is formed.
SUMMARY OF THE INVENTION
Accordingly, in light of the above problems, an object of the present invention is to realize an efficient method capable of forming a layer of a group III nitride compound semiconductor without generation of cracks and dislocations to thereby improve device characteristics.
In order to solve the above problems, the present invention has a first feature that resides in a method for manufacturing a group III nitride compound semiconductor, which hardly grows epitaxially on a substrate, by crystal growth, comprising: forming a buffer layer on a substrate into an island pattern such as a dot pattern, a striped pattern, or a grid pattern such that substrate-exposed portions are formed in a scattered manner; and forming a group III nitride compound semiconductor layer on the buffer layer by growing a group III nitride compound epitaxially in longitudinal and lateral directions.
Here forming substrate-exposed portions in a scattered manner does not necessarily represent the condition that each substrate-exposed portions is completely separated, but represents the condition that the buffer layer exists around arbitrary substrate-exposed portions. In order to form the buffer layer into an island pattern such as a dot pattern, a striped pattern or a grid pattern, the following method can be applied: forming the buffer layer on the entire surface of the substrate and then removing the desired portions of the buffer layer by etching; or forming a selective mask such as an SiO
2
film on the substrate and partially forming the buffer layer.
The “lateral” direction as used in the specification refers to a direction parallel to a surface of the substrate. By using the above-described method, the group III nitride compound semiconductor grows on the buffer layer in a longitudinal direction. The group III nitride compound semiconductor which grows on the buffer layer in a longitudinal direction also grows in a lateral direction in order to cover the substrate-exposed portions. The growth velocity of the group III nitride compound semiconductor in the longitudinal and lateral directions can be controlled by conditions of, for example, temperature, pressure, or supplying conditions of source materials. Accordingly, a group III nitride compound semiconductor layer reunited into one layer can cover the substrate-exposed portions which are not covered by the buffer layer from a base of the buffer layer which is formed into an island pattern such as a dot pattern, a striped pattern or a grid pattern. As a result, feedthrough dislocations of the group III nitride compound semiconductor exists only in the regions of group III nitride compound semiconductor layer formed on the buffer layer, which is formed into an island pattern such as a dot pattern, a striped pattern or a grid pattern. This is because feedthrough dislocations are not generated when the group III nitride compound semiconductor grows in a lateral direction but are generated when it grows in a longitudinal direction. Accordingly, surface density of longitudinal feedthrough dislocations of the group III nitride compound semiconductor layer decreases, and crystallinity of the device is improved. When a group III nitride compound semiconductor device which is manufactured using only a group III nitride compound semiconductor layer which is formed on the substrate-exposed portions, or the regions which are not covered by a buffer layer, surface density of feedthrough dislocations of the device can become 0.
The second feature of the present invention is a method for manufacturing a group III nitride compound semiconductor, which hardly grows epitaxially on a substrate, by crystal growth, comprising: forming a buffer layer on a substrate into an island pattern such as a dot pattern, a striped pattern, or a grid pattern such that substrate-exposed portions are formed in a scattered manner; forming a group III nitride compound semiconductor layer on the buffer layer by growing a group III nitride compound epitaxially in longitudinal and lateral directions; etching at least one of the regions of the group III nitride compound semiconductor layer, growing in a longitudinal direction on the buffer layer which is formed into an island pattern; and growing the group III nitride compound semiconductor, which is left without being etched, in a lateral direction. Forming substrate-exposed portions in a scattered manner is explained in the first feature.
In the second feature of the present invention, the group III nitride compound semiconductor layer is etched after carryi
Koike Masayoshi
Nagai Seiji
Kunemund Robert
McGinn & Gibb PLLC
Toyoda Gosei Co,., Ltd.
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