Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – On insulating substrate or layer
Reexamination Certificate
1999-11-24
2004-01-27
Fourson, George (Department: 2823)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
On insulating substrate or layer
C438S047000
Reexamination Certificate
active
06682991
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a growth method of a nitride III-V compound semiconductor, manufacturing method of a semiconductor device, and semiconductor device which are especially suitable for application to semiconductor lasers, light emitting diodes or electron transport devices using nitride III-V compound semiconductors.
2. Description of the Related Art
GaN compound semiconductors are direct transitional semiconductors having forbidden band widths ranging from 1.9 eV to 6.2 eV and enabling realization of light emitting devices capable of emitting light over a wide range from the visible spectrum to the ultraviolet. For these properties, they have lately become of major interest and placed under active developments. Additionally, GaN semiconductors have a large possibility as material of electron transport devices such as FET. Saturation electron velocity of GaN is approximately 2.5×10
7
cm/s, which is larger than those of Si, GaAs and SiC, and its breakdown electric field is as large as approximately 5×10
6
V/cm next to diamond. For these reasons, GaN semiconductors have been expected to be greatly hopeful as materials of high-frequency, high-temperature, high-power electron transport devices.
These semiconductor devices, in general, are made of GaN semiconductors grown on a substrate. Therefore, crystalline qualities of GaN semiconductors are of great importance for ensuring and improving performances of these semiconductor devices. However, since there is no appropriate substrate good in lattice matching with GaN, sapphire substrates are mainly being used for growing GaN semiconductors, their lattice mismatching with GaN is very large.
Failure in lattice matching with a substrate largely affects crystalline properties of GaN compound semiconductors grown thereon, and it can be a large factor of crystal defects produced in GaN semiconductor layers.
To minimize crystal defects, conventionally employed was a technique of growing a buffer layer of GaN or AlN on a sapphire substrate under a low temperature, then increasing the substrate temperature to about 1000° C. to re-crystallize it, and thereafter growing GaN semiconductors thereon, thereby to improve the quality of GaN semiconductors (for example, Appl. Phys. Lett. 48(1986)353, Jpn. J. Appl. Phys. 30(1991)L1705).
Even with this technique, however, reduction of crystal defects is limited, and the density of defects (especially, threaded dislocation) is still as high as 10
8
through 10
10
cm
−2
.
For the purpose of decreasing the density of such defects, it has been reported to grow a GaN layer on a substrate conventionally used to grow III-V compound semiconductor like GaAs conventionally, then provide a mask of an insulating film such as silicon oxide film in form of elongated belts extending in the <
11
-
20
> direction in predetermined intervals on the GaN layer, and thereafter selectively grow a GaN layer by hydride vapor phase epitaxy (HVPE) (for example, Jpn. J. Appl. Phys. 36(1997)L899). This technique can certainly decrease the density of threading dislocation to approximately 6×10
7
cm
−2
.
There are also other techniques of performing selective growth on a substrate via a mask made on the substrate to extend in a direction different by 90° from that of the above-introduced example, and making a semiconductor light emitting structure on the selectively grown film. This technique is configured to grow a GaN layer on a sapphire substrate, for example, by metal organic chemical vapor deposition (MOCVD), next make a mask of silicon oxide to extend in the <
1
-
100
> direction in form of elongated belts in predetermined intervals, thereafter grow a GaN layer thereon by MOCVD and further make a light emitting structure (Appl. Phys. Lett. 72(1998)211, Jpn. J. Appl. Phys. 36(1997)L899). According to these reports, the density of threading dislocation can be decreased to approximately 1×10
7
cm
−2
. In these examples, it has been confirmed that the lifetime of a semiconductor laser made above is elongated to 1000 hours or more.
However, according to the Inventor's own knowledge, the GaN semiconductor layer obtained by conventional growth methods introduced above still include a lot of crystal defects near the boundary with the substrate, and the density of defects has not been reduced sufficiently.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a growth method of a nitride III-V compound semiconductor capable of growing a single-crystal nitride III-V compound semiconductor of a high quality with a low density of crystal defects, and also relates to a semiconductor device manufactured by using this growth method and a manufacturing method of the semiconductor device.
The inventor conducted research to overcome the problems involved in the conventional techniques. The inventor's research is summarized below.
FIGS. 1 and 2
show results of measurement of X-ray diffraction spectrum, taking samples each prepared by growing a GaN layer by MOCVD on a c-plane sapphire substrate via a mask of SiO
2
made in form of elongated belts extending in the <
1
-
100
> direction in predetermined intervals on the c-plane sapphire substrate, and introducing X-rays into one of the samples from a direction horizontal to the mask (see
FIG. 3
) and into the other sample from a direction vertical to the mask (see FIG.
4
).
It is confirmed from
FIGS. 1 and 2
that, although the c-axis inclination exhibits a single-peak property in the samples in which the X-rays enter in parallel to the mask, it exhibits a multi-peak property in the samples in which X-rays enter vertically in the mask. It has been noted through Transmission Electron Microscopic (TEM) analysis that the longitudinal crystal axes deviate at three positions on areas of the mask for selective growth and areas without the mask as shown in FIG.
5
. In
FIG. 5
, inclination of the crystal axes on the mask is not limited to the illustrated example.
If a selectively grown film includes any inclination in crystal axis, especially if it includes discontinuous changes as indicated above, then it is presumed that lattice defects such as dislocation have been introduced along the boundary. Actually, dislocation was observed through TEM, and introduction of such defects may be a factor of deteriorating characteristics of a semiconductor laser made thereon.
The Inventor found, as a result of various researches, that the use of a nitride to form the outermost surface of the mask be effective to prevent inclination of crystal axes of a film grown on the mask for selective growth.
FIGS. 6 and 7
show results of measurement of X-ray diffraction spectrums, taking samples each prepared by growing a GaN layer by MOCVD on a c-plane sapphire substrate via a SiN/SiO
2
mask made by stacking a SiN film on a SiO
2
film in form of elongated belts extending in the <
1
-
100
> direction in predetermined intervals on the c-plane sapphire substrate, and introducing X-rays into one of the samples from a direction horizontal to the mask and into the other sample from a direction vertical of the mask.
It is confirmed from
FIGS. 6 and 7
that, by selective growth using the mask whose outermost surface is SiN, whichever of the parallel and vertical directions of the mask the X-rays are introduced in, each sample exhibits only one as the peak indicating inclination of crystal axes. Additionally, it is confirmed that the full width half maximum indicating variance in inclination of crystal axes within the measured range. This demonstrates a high crystalline quality of the selectively grown film.
This does not mean that crystal axes of the selectively grown film change in every region as shown in
FIG. 5
, but does demonstrate that longitudinal crystal axes are aligned over the entirety of the selectively grown film as shown in FIG.
8
and that the entirety of the film is uniform in quality.
Especially in a semiconductor light emitting dev
Asano Takeharu
Asatsuma Tsunenori
Funato Kenji
Hino Tomonori
Kijima Satoru
Fourson George
Garcia Joannie Adelle
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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