Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
2000-04-10
2001-08-14
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S459000, C438S785000, C438S800000
Reexamination Certificate
active
06274518
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a group III nitride compound semiconductor substrate.
2. Description of the Prior Art
A group III nitride compound semiconductor expressed by the general formula Al
X
Ga
1−X−Y
In
Y
N (where 0≦X≦1, 0≦Y≦1, 0≦X+Y≦1) can have a band gap energy in a wide range from 1.9e V to 6.2e V. For this reason, the group III nitride compound semiconductor (hereinafter, also referred to as III-N semiconductor) is a promising semiconductor material for a light-emitting/receiving device that covers a wide range from visible light to UV rays.
A large-area III-N semiconductor substrate with good quality is in demand as a substrate for producing a III-N semiconductor device. As an attempt to meet this demand, there is a conventional method for producing a III-N semiconductor substrate (reported, for example in Japanese Journal of Applied Physics Vol. 37 (1998) pp. L309-L312). This conventional method will be described with reference to FIG.
8
.
In the conventional method, first, a sapphire substrate
1
with a diameter of 2 inches is placed in a metal organic vapor phase epitaxy apparatus (hereinafter, also referred to as MOVPE apparatus). Then, a GaN buffer layer
2
and GaN layer
3
are formed on the sapphire substrate
1
sequentially by a MOVPE technique (FIG.
8
A). Hereinafter, a sapphire substrate
1
provided with a layer or layers may be referred to as a wafer, regardless of the type of the layer.
Next, the wafer is removed from the MOVPE apparatus. Then, a SiO
2
film
4
is formed on a surface of the GaN layer
3
, and windows
4
a
are formed in a stripe geometry with a pitch of several &mgr;m in the SiO
2
film
4
(FIG.
8
B).
Thereafter, the wafer is placed in a hydride vapor phase epitaxy (hereinafter, also referred to as HVPE) apparatus, and a GaN thick film
5
a
(having a thickness of about 100 &mgr;m) is formed on the SiO
2
film
4
(FIG.
8
C).
Thereafter, the wafer is removed from the HVPE apparatus. Finally, the wafer is polished from the sapphire substrate
1
side until the GaN thick film
5
a
is exposed. Thus, a GaN substrate
5
having a thickness of about 80 &mgr;m can be obtained (FIG.
8
D).
However, the above-described conventional method has the following problems.
The sapphire substrate
1
and the GaN thick film
5
a
have different lattice constants and thermal expansion coefficients. Therefore, in the above-described method, a stress is applied between the sapphire substrate
1
and the GaN thick film
5
a
in the process of lowering the temperature of the wafer after the GaN thick film
5
a
is formed by causing crystal growth. Consequently, in this method, the wafer is curved so that cracks are generated in the direction perpendicular to the principle plane of the GaN thick film
5
a
, or the GaN thick film
5
a
is partially peeled. As a result, the size of the GaN substrate
5
obtained by this conventional method is at most about 1 cm×1 cm. Therefore, it has been difficult to obtain the GaN substrate
5
that is substantially as large as the sapphire substrate
1
in high yields and with high reproducibility. In particular, in the conventional method, stresses concentrate on the interfaces between the sapphire substrate
1
and the GaN buffer layer
2
and between the GaN buffer layer
2
and the GaN layer
3
, and they adhere to each other tightly across the entire principle planes. Therefore, cracks are generated at random.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a method for producing a group III nitride compound semiconductor substrate that can provide a large-area group III nitride compound semiconductor substrate in high yields and with high reproducibility.
A method for producing a group III nitride compound semiconductor substrate of the present invention includes (a) forming a first semiconductor film over a substrate, the first semiconductor film made of a first group III nitride compound semiconductor and provided with a step; (b) forming a second semiconductor film made of a second group III nitride compound semiconductor having a different thermal expansion coefficient from that of the first group III nitride compound semiconductor on the first semiconductor film; and (c) cooling the substrate and separating the second semiconductor film from the first semiconductor film. In the method of the present invention, when the substrate is cooled in the process (c), cracks are generated in the second semiconductor film in the direction in parallel to the principal plane of the second semiconductor film, starting from the step portion in the first semiconductor film. Therefore, the method of the present invention can provide a large-area group III nitride compound semiconductor substrate in high yields and with high reproducibility.
In the above-described method of the present invention, it is preferable that the process (a) includes (a-1) forming a film made of the first group III nitride compound semiconductor on the substrate; and (a-2) removing a part of the film, thereby forming a first semiconductor film provided with a plurality of grooves. In this case, it is preferable that in the process (a-2), the plurality of grooves are formed in a stripe geometry. This embodiment makes it possible to produce a particularly large-area group III nitride compound semiconductor substrate easily.
In the above-described method of the present invention, it is preferable that the substrate is a (0001) plane sapphire substrate, and the grooves are formed in the [11-20] direction. This embodiment makes it possible to form the second semiconductor film having good crystallinity easily.
In the above-described method of the present invention, it is preferable that the process (a) includes (a-1) forming a film made of the first group III nitride compound semiconductor and an insulating film in this order on the substrate; and (a-2) removing a part of the film, thereby forming a first semiconductor film provided with a plurality of grooves. This embodiment makes it possible to generate cracks between the film made of the first group III nitride compound semiconductor and the insulating film or between the insulating film and the second semiconductor film easily. Therefore, this embodiment makes it possible to produce a particularly large-area group III nitride compound semiconductor substrate easily. In this case, it is preferable that in the process (a-2), the plurality of grooves are formed in a stripe geometry. Furthermore, in this case, it is preferable that the substrate is a (0001) plane sapphire substrate, and the grooves are formed in the [11-20] direction.
In the above-described method of the present invention, it is preferable that the insulating film is made of at least one selected from the group consisting of SiO
2
and Si
3
N
4
. In this embodiment, since SiO
2
or SiN
X
and the group III nitride compound semiconductor deposited on the surface thereof are different materials and have different crystal structures, stable chemical bonds are not formed at the interface therebetween so that it becomes easy to peel the second semiconductor film.
It is preferable that the above-described method of the present invention further includes removing the insulating film selectively after the process (b) and before the process (c). In this embodiment, when the group III nitride compound semiconductor substrate is separated from the first semiconductor film, the insulating film does not remain on the group III nitride compound semiconductor substrate. Therefore, the group III nitride compound semiconductor substrate can be produced in high yields and with high reproducibility.
In the above-described method of the present invention, it is preferable that the lattice constant of the first group III nitride compound semiconductor is smaller than that of the second group III nitride compound semiconductor. This embodiment provi
Imafuji Osamu
Ishida Masahiro
Nakamura Shinji
Orita Kenji
Yuri Masaaki
Anya Igwe U.
Matsushita Electronics Corporation
Merchant & Gould P.C.
Smith Matthew
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