Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
2000-11-15
2003-04-29
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C117S084000, C117S952000, C438S692000
Reexamination Certificate
active
06554896
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an epitaxial growth substrate comprising a base material composed of a sapphire substrate, a SiC substrate, a GaN substrate or the like and an Al
x
Ga
y
In
z
N film (x+y+z=1,x>0,y,z≧0) on the base material, and a method for producing the same.
BACKGROUND OF THE INVENTION
An epitaxial growth substrate is employed for an electronic device such as a light emitting diode (LED), a laser diode (LD) or a field effect transistor (FET). In producing such an electronic device, semiconductor films such as Al
x
Ga
y
In
z
N film (x+y+z=1,x,y,z≧0) are formed on the epitaxial growth substrate by epitaxial growth. Attention is paid to an Al
x
Ga
y
In
z
N film (x+y+z=1,x,y,z≧0) because it has a large bandgap to generate and emit a short wavelength light in a light emitting element.
FIG. 1
is a cross sectional view showing a conventional light emitting diode to generate a blue light, which is composed of the above Al
x
Ga
y
In
z
N films.
For example, a GaN film
2
as a buffer layer is formed on a C-face sapphire (Al
2
O
3
) substrate
1
at a low temperature by CVD, and an n-type Al
x
Ga
y
In
z
N film
3
is formed on the GaN film
2
by epitaxial growth through CVD. Then, a p-type Al
x
Ga
y
In
z
N film
4
is epitaxially grown on the n-type Al
x
Ga
y
In
z
N film
3
by epitaxial growth through CVD, and a low resistive p-type Al
x
Ga
y
In
z
N film
5
is epitaxially grown on the p-type Al
x
Ga
y
In
z
N film
4
.
Electrodes
6
and
7
are formed on the n-type Al
x
Ga
y
In
z
N film
3
and the p-type Al
x
Ga
y
In
z
N film
5
, respectively.
If the n-type Al
x
Ga
y
In
z
N film
3
is directly formed on the sapphire substrate
1
by CVD, it has a large amount of defects, degraded crystallinity and a relatively rough surface. Therefore, in this case, the light emitting diode having the directly formed n-type Al
x
Ga
y
In
z
N film can have a relatively small light emission efficiency.
Therefore. as shown in
FIG. 1
, the GaN film
2
, which is formed at a low temperature by CVD, intervenes as th e buffer layer between the sapphire substrate
1
and the n-type Al
x
Ga
y
In
z
N film
3
. Since the GaN film
2
is grown at a low temperature by CVD, the lattice constant difference of approximately 10% between the sapphire substrate
1
and the n-type GaN film
3
is compensated. Moreover, it is proposed that an AlN film is employed as the buffer layer instead of the GaN film
2
.
Moreover, instead of forming the GaN film or the AlN film by epitaxial growth at a low temperature by CVD, the sapphire substrate
1
is exposed to an ammonia atmosphere under a high temperature of 1000° C. to nitride its surface and form an AlN film with a thickness of 100 Å or below thereon. The AlN film serves as the above buffer layer, so that the lattice constant difference between the sapphire substrate
1
and the GaN film
3
is compensated.
The present invention is directed at providing an epitaxial growth substrate comprising a base material composed of a sapphire substrate, a SiC substrate, a GaN substrate or the like and a Al
x
Ga
y
In
z
N film (x+y+z=1,x,y,z≧0) formed on one main surface of the base material. However, as mentioned above, if the Al
x
Ga
y
In
z
N film is directly formed on such a sapphire substrate by CVD, it can have only a degraded crystallinity and a relatively rough surface.
Then, using the above epitaxial growth technique for the above GaN film, a GaN film or an AlN film is formed, as a buffer layer, in a thickness of 1001-300 Å on the sapphire substrate by epitaxial growth at a low temperature by CVD. As a result, the Al
x
Ga
y
In
z
N film, formed on the buffer layer, can have a relatively good crystallinity and a flat surface. However, the crystallinity of the Al
x
Ga
y
In
z
N film is sensitive to the buffer layer configuration such as thickness and the buffer layer-forming conditions, and the buffer layer itself is formed at a low temperature, so that the crystallinity of the Al
x
Ga
y
In
z
N film can not be sufficiently improved because of its low crystallization.
Moreover, when an n-type Al
x
Ga
y
In
z
N (x+y+z=1,x,y,z≧0) film is formed, by epitaxial growth at a high temperature by CVD, on an AlN film having a thickness of 100 Å or below formed by the exposure of the sapphire substrate to a high temperature ammonia atmosphere, it can have excellent crystallinity, but usually does not have a flat surface. The rough surface flatness may result from the thermal treatment at a high temperature in forming the AlN film. On the other hand, the high crystallinity may result from the crystallinity of the sapphire substrate because the AlN film is obtained by improving the surface layer of the substrate.
The above rough surface flatness and high crystallinity is observed for an Al
x
Ga
y
In
z
N (x+y+z=1,x,y,z≧0) film formed on a SiC substrate and a GaN substrate instead of the sapphire substrate. In this way, the above-mentioned conventional technique can provide only the Al
x
Ga
y
In
z
N film having excellent surface flatness but degraded crystallinity, or the Al
x
Ga
y
In
z
N film having excellent crystallinity through a small amount of defects but degraded surface flatness. Up to now, the Al
x
Ga
y
In
z
N film having both excellent crystallinity and surface flatness could not be provided.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an epitaxial growth substrate on which the Al
x
Ga
y
In
z
N (x+y+z=1,x,y,z≧0) film having both excellent crystallinity through a small amount of defects and surface flatness formed by epitaxial growth.
It is another object of the present invention to provide a method for producing the above epitaxial growth substrate.
This invention relates to an epitaxial growth substrate comprising a base material and an Al
x
Ga
y
In
z
N (x+y+z=1,x,y,z≧0) film, on one surface of the base material, of which the opposite surface to the base material is polished and thus, flattened.
Since the Al
x
Ga
y
In
z
N film constituting the epitaxial growth substrate of the present invention is epitaxially grown and flattened by polishing, it can have its excellent crystallinity and surface flatness. Accordingly, when an additional Al
x
Ga
y
In
z
N (x+y+z=1,x,y,z≧0) film is formed on the epitaxial growth substrate by epitaxially growth, it can have excellent crystallinity and surface flatness.
For enhancing the crystallinity and surface flatness of the additional Al
x
Ga
y
In
z
N film, it is preferable that the epitaxial growth substrate has a high crystallinity nitride film between the base material and the Al
x
Ga
y
In
z
N film.
This invention also relates to a method for producing an epitaxial growth substrate comprising the steps of:
preparing a base material,
epitaxially growing an Al
x
Ga
y
In
z
N (x+y+z=1,x,y,z≧0) film on one surface of the base material, and
polishing and thus, flattening the opposite surface of the Al
x
Ga
y
In
z
N film on the base material.
According to the producing method of the present invention, the above epitaxial growth substrate can be easily and precisely formed. Therefore, in this case, it is preferable to form a high crystallinity nitride film between the base material and the Al
x
Ga
y
In
z
N film, in view of the above enhancement for the crystallinity and surface flatness of the additional Al
x
Ga
y
In
z
N film.
REFERENCES:
patent: 6020602 (2000-02-01), Sugawara et al.
patent: WO 98/45511 (1998-10-01), None
Weyher et al, Chemical Polishing of Bulk and Epitaxial GaN Journal of Crystal Growth, vol. 182 p. 17-22, 1997.
Asai Keiichiro
Nakamura Yukinori
Shibata Tomohiko
Burr & Brown
Kunemund Robert
NGK Insulators Ltd.
LandOfFree
Epitaxial growth substrate and a method for producing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Epitaxial growth substrate and a method for producing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Epitaxial growth substrate and a method for producing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3053605