Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
2002-03-06
2004-05-11
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C257S088000
Reexamination Certificate
active
06734030
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to semiconductor light emitting devices and processes for producing same. More particularly, the present invention relates to a semiconductor light emitting device fabricated by forming a growth layer having a stacked structure of a first conductive layer, a light emission layer, and a second conductive layer by selective growth on a growth substrate, and a method of fabricating the semiconductor light emitting device, the semiconductor light emitting device being fabricated by forming a wurtzite type compound semiconductor layer such as a gallium nitride based compound semiconductor layer by selective growth.
Conventionally, when manufacturing a semiconductor light emitting device of this type, a device is fabricated by forming a low temperature buffer layer overall on a sapphire substrate, forming an n-side contact layer made from Si-doped GaN thereon, and stacking, on the n-side contact layer, an n-side cladding layer made from Si-doped GaN, an active layer made from Si-doped InGaN, a p-side cladding layer made from Mg-doped AlGaN, and a p-side contact layer made from Mg-doped GaN. As commercial products of semiconductor light emitting devices having such a structure, light emitting diodes and semiconductor lasers allowing emission of light of blue and green in a wavelength ranging from 450 nm to 530 nm have been fabricated on a large scale.
A sapphire substrate has been often used for growing gallium nitride thereon. However, dislocations may occur in crystal, at a high density, due to mismatches between crystal lattices of the sapphire substrate and gallium nitride. A method of forming a low temperature buffer layer on a substrate is one way of suppressing such defects occurring in crystal during growth thereof. In a method disclosed in Japanese Patent Laid-open No. Hei 10-312971, usual crystal growth is combined with selective crystal growth in the lateral direction (ELO: Epitaxial Lateral Overgrowth) for reducing crystal defects. The method of fabricating a semiconductor light emitting device disclosed in Japanese Patent Laid-open No. Hei 10-312971 has also described that through-dislocations propagated in the direction perpendicular to a principal plane of a substrate are bent in the lateral direction by a facet structure formed in a growth region during fabrication and are thereby prevented from being further propagated, thereby reducing crystal defects.
On the other hand, there has been known a method of fabricating a semiconductor light emitting device in a fine region by forming a layer of a nitride based semiconductor such as GaN into a pyramid shape by selective growth. In particular, a method of fabricating a light emitting device by forming a hexagonal pyramid shaped nitride based semiconductor layer by selective growth has been disclosed, for example, in “Spatial Control of InGaN Luminescence by MOCVD Selective Epitaxy, D. Kapolnek et al., Journal of Crystal Growth, 189/190 (1998) 83-86”. According to the selective growth technique described in this document, a plurality of nitride based semiconductor light emitting devices, each of which is composed of a fine hexagonal pyramid shaped GaN/InGaN layer structure, can be formed. With respect to such a fine hexagonal pyramid shaped light emitting device, it has been known that an active layer is formed on an S-plane (i.e., a (1-101) plane) formed in self-alignment, thereby improving crystallinity and light emergence efficiency.
When forming a light emitting device composed of a hexagonal pyramid shaped nitride based semiconductor layer having a stacked structure by selective growth, a p-side electrode and an n-side electrode are required to be formed on a selectively grown stacked layer for supplying a current to a light emission layer. In general, at the time of selective growth, a p-side conductive layer is stacked on an inside conductive layer. Accordingly, to form both n-side and p-side electrodes, part of the p-side conductive layer must be removed by etching or the like. To be more specific, an n-side electrode is typically formed by forming an n-type first growth layer, forming a growth obstruction film for selective growth on the first growth layer, forming a second growth layer by selective growth, forming a window in the growth obstruction film at a position where the second growth layer is not formed, and forming the n-side electrode in the window.
FIGS. 4A and 4B
are views showing a hexagonal pyramid shaped semiconductor light emitting device formed by typical selective growth. As shown in
FIG. 4A
, a first growth layer
81
made from GaN or AlN is formed on a sapphire substrate
80
, and a growth obstruction film
82
made from silicon oxide or silicon nitride is formed on the first growth layer
81
. Subsequently, in each device region, an opening portion
83
is formed in the growth obstruction film
82
, and a second growth layer is formed by selective growth from the opening portion
83
. The second growth layer has a stacked structure of an n-type first conductive layer
84
, an active layer
85
, and a p-type second conductive layer
86
.
The second growth layer is a hexagonal pyramid shaped growth layer, and a p-side electrode
87
is formed on the second conductive layer
86
as the outermost portion of the second growth layer. On the other hand, in each device region, a window
89
is formed in the growth obstruction film
82
, and an n-side electrode
88
is formed in the window
89
. After formation of the n-side electrodes
88
and the p-side electrodes
87
, as shown in
FIG. 4B
, device isolation for isolating light emitting devices from each other is performed. To be electrically connected to the n-side electrodes
88
, the first growth layer
81
positioned under the growth obstruction film
82
is doped with an n-type impurity. Such a conductive first growth layer
81
is required to be divided into parts belonging to respective device regions. The device isolation is generally preformed by forming device isolation trenches
90
by etching. A principal plane of the sapphire substrate
80
is exposed at bottoms of the device isolation trenches
90
.
When fabricating light emitting devices by forming growth layer portions each having a hexagonal pyramid or a truncated shape thereof, or another pyramid shape or a truncated shape thereof by selective growth and independently driving respective devices or transferring or mounting respective devices on another substrate, the first growth layer
81
as an under growth layer must be isolated into parts belonging to respective device regions.
In this case, however, since the second growth layer is formed into a hexagonal pyramid shape or another pyramid shape by selective growth from the opening portion formed in the growth obstruction film at a position in each device region, there is a relatively large difference-in-height between a top portion of the pyramid shaped second growth layer and the surface of the growth obstruction layer. In particular, the surface portion of the growth obstruction film becomes the recessed side of the difference-in-height. As a result, the device isolation trenches
90
for isolating the devices from each other must be formed in the recessed regions by etching. Because of the difference-in-height between the top portion of the second growth layer and the surface of the growth obstruction film
82
, it is not easy to form the device isolation trenches
90
with desirable repeatability, and in the worst case, device isolation becomes impossible due to positional deviation of a mask for forming the device isolation trenches.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore, to provide a semiconductor light emitting device and a method of fabricating the semiconductor light emitting device, which are capable of isolating respective devices from each other with desirable repeatability.
According to an embodiment of the present invention, a semiconductor light emitting device is provided. The device includes a growth substrate, a fir
Biwa Goshi
Doi Masato
Okuyama Hiroyuki
Oohata Toyoharu
Bell Boyd & Lloyd LLC
Hoang Quoc
Sony Corporation
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