Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
2001-08-30
2004-11-23
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
C438S483000
Reexamination Certificate
active
06821807
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates a method of manufacturing a semiconductor device having a compound semiconductor layer made of a group III-V nitride-based semiconductor (hereinafter referred to as nitride-based semiconductor) such as GaN (gallium nitride), AlN (aluminum nitride), InN (indium nitride), or TlN (thallium nitride) or mixed crystal thereof, and a method of forming a nitride-based semiconductor layer.
2. Description of the Prior Art
In recent years, GaN-based semiconductor light emitting devices have been developed for commercial use as a light emitting diode emitting blue or violet light or a semiconductor light emitting device such as a semiconductor laser device.
In the manufacture of the GaN-based semiconductor light emitting device, a GaN-based semiconductor layer is formed by epitaxy growth on an insulator substrate such as a substrate of sapphire (Al
2
O
3
), since there is no substrate made of GaN.
In this case, GaN and sapphire have different lattice constants, and the GaN-based semiconductor layer cannot be grown at a high temperature directly on the sapphire substrate. Therefore, when a GaN-based semiconductor layer is to be grown on a sapphire substrate, a low temperature buffer layer made of GaN or AlN in an amorphous state is grown on the sapphire substrate at a substrate temperature near the range of 500° C. to 600° C., and then a GaN-based semiconductor layer is grown at a high temperature near 1000° C. on the low temperature buffer layer. Thus, the GaN-based semiconductor layer can be grown on the sapphire substrate.
In the disclosure of Japanese Patent Publication No. 8-8217, for example, GaN is grown for one minute on a sapphire substrate at a substrate temperature of 500° C., and a GaN low temperature buffer layer having a film thickness of 200 Å is formed. According to Japanese Patent No. 3026087, AlN is grown for two minutes on a sapphire substrate at a substrate temperature of 650° C., and an AlN low temperature buffer layer having a film thickness of 300 Å is formed.
Meanwhile, the low temperature buffer layer has a film thickness as small as in the range from 200 Å to 500 Å, the growth rate is lowered so that the film thickness can readily be controlled at the time of growing the low temperature buffer layer. In the above Japanese Patent Publication No. 8-8217, for example, a GaN low temperature buffer layer is grown at a growth rate of 3.33 Å/sec, while according to Japanese Patent No.3026087, the growth rate is 2.5 Å/sec. Note that the growth rate of the low temperature buffer layer is adjusted by the supply amount of a material gas such as gallium and aluminum.
In the growth of the low temperature buffer layer, the low temperature buffer layer is typically grown at such a low growth rate as the above. Note that the effect of the growth rate of the low temperature buffer layer upon the crystallinity of the GaN-based semiconductor layer has not been examined, and the low temperature buffer layer is typically grown at the low growth rate as the above.
When a GaN-based semiconductor layer is grown on a low temperature buffer layer which has been grown under the optimum growth conditions, more specifically at the optimum growth temperature and into the optimum film thickness, good crystallinity and good electrical characteristics are achieved in the GaN-based semiconductor layer. Meanwhile, a GaN-based semiconductor layer grown on a low temperature buffer layer which has been grown under conditions departed from the optimum conditions does not have good crystallinity and good electrical characteristics. As a result, in order to manufacture a semiconductor light emitting device having good device characteristics and high reliability, a low temperature buffer layer must be grown under the optimum growth conditions and then a GaN-based semiconductor layer must be grown on the buffer layer.
However, the range of the optimum growth conditions for such a low temperature buffer layer would tend to be very small. The range of the optimum growth conditions would be particularly narrow for the lower temperature buffer layer made of GaN.
Therefore, when a GaN-based semiconductor layer is grown on a sapphire substrate in a new crystal growth system, the optimum growth conditions for the low temperature buffer layer must be specified. Much labor and time should be necessary for specifying the optimum growth conditions for such a low temperature buffer layer.
If the optimum growth conditions are specified for the low temperature buffer layer and the crystal growth system is set so that the conditions are satisfied, the conditions under which the low temperature buffer layer grows sometimes depart from the range of the optimum growth conditions as the condition of the crystal growth system changes. As a result, a GaN-based semiconductor layer having good crystallinity and electrical characteristics can hardly be stably provided with high reproducibility.
For example, the repetition of a crystal growth process for a long period of time in a crystal growth system causes byproducts by crystal growth to be obtained, and the byproducts accumulated in the reaction tube of the crystal growth system change the condition of the reaction tube. The change in turn causes the conditions in the growth of the low temperature buffer layer to depart from the range of the optimum growth conditions during growth. Therefore, a high quality, GaN-based semiconductor layer cannot stably be produced with good reproducibility.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of forming a nitride-based semiconductor layer allowing a high quality, nitride-based semiconductor layer to be stably provided with good reproducibility.
Another object of the present invention is to provide a method of manufacturing a nitride-based semiconductor device allowing a nitride-based semiconductor device having a high quality, nitride-based semiconductor layer and good device characteristics and high reliability to be stably provided with good reproducibility.
A method of forming a nitride-based semiconductor layer according to one aspect of the present invention includes the steps of growing a buffer layer of Al
X
Ga
1−X
N (0≦X≦1) on a substrate at a growth rate of at least 7 Å/sec, and growing a nitride-based semiconductor layer of Al
a
B
b
In
c
Tl
d
Ga
1−a−b−c−d
N(0≦a<1, 0≦b<1, 0≦c<1, 0≦d<1, a+b+c+d<1) on the buffer layer.
According to the method of forming a nitride-based semiconductor layer, the buffer layer is grown at a high growth rate, and therefore a good buffer layer can stably be provided with good reproducibility regardless of changes in the condition of a crystal growth system. Therefore, a nitride-based semiconductor layer is grown on such a buffer layer, so that a nitride-based semiconductor layer having good crystallinity and good electrical characteristics can stably be provided with good reproducibility if there is a change in the condition of the crystal growth system.
The buffer layer is preferably grown at a growth rate of at most 51 Å/sec. Thus, a good buffer layer can stably be provided with good reproducibility regardless of changes in the condition of the crystal growth system, and the film thickness of the buffer layer can readily be controlled.
The buffer layer is more preferably grown at a growth rate in the range from 16 Å/sec to 42 Å/sec. The growth of the buffer layer at the growth rate allows a good buffer layer to be stably provided with good reproducibility. Thus, a nitride-based semiconductor layer having better cyrstallinity and electrical characteristics can stably be provided with good reproducibility.
The buffer layer is more preferably grown at a growth rate in the range from 25 Å/sec to 29 Å/sec. The growth of the buffer layer at the growth rate allows an even better buffer layer to be stably provided with good reproducibil
Hayashi Nobuhiko
Kano Takashi
Ohbo Hiroki
Mulpuri Savitri
Sanyo Electric Co,. Ltd.
Westerman Hattori Daniels & Adrian LLP
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