Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
1999-10-20
2003-01-07
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C438S046000, C438S718000
Reexamination Certificate
active
06503769
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device of a nitride-based compound semiconductor and a method for fabricating the semiconductor device. More particularly, the present invention relates to a semiconductor laser device emitting blue/violet light having a wavelength of around 400 nm.
2. Description of the Related Art
A nitride-based compound semiconductor made of gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), or a mixed crystal composed thereof has wide bandgap energy in a range of 1.9-6.2 eV, and is thus expected to be useful as a semiconductor material for a light-emitting or light-receiving device covering a range from visible light to ultraviolet light. In particular, a semiconductor laser device emitting a light having a wavelength of around 400 nm, such as that realized using this material, is expected to be a very feasible light source for a next-generation hyper-density optical disk, and the research and development thereof has been vigorously conducted throughout the world.
The practical use of such a semiconductor laser device as a light source for an optical disk critically requires the precision and uniformity of: thicknesses of a plurality of semiconductor layers included in the semiconductor laser device; and a structure of a waveguide, such as a buried structure, for achieving the single transverse mode oscillation. For a semiconductor laser device of a nitride-based compound semiconductor, in particular, it is important to use an etching technique which can control formation of the waveguide structure precisely and uniformly.
Some of conventional etching techniques for the nitride-based compound semiconductor will be described below.
One of the techniques is a dry etching technique using boron chloride (BCl
3
) and nitrogen (N
2
) as etching gases (F. Ren et al., Journal of Electronic Materials, Vol. 26, No. 11, 1997, pp. 1287-1291).
Another technique is an etching technique, so-called wet etching, in which a carrier-doped nitride-based compound semiconductor is etched by immersion in an aqueous solution of potassium hydroxide or phosphoric acid and illumination with light of larger energy than the bandgap energy of the nitride-based compound semiconductor (Japanese Laid-Open Publication No. 9-232681; C. Youtsey et al., Applied Physics Letters, Vol. 72, No. 5, 1998, pp. 560-562; and L.-H. Peng et al., Applied Physics Letters, Vol. 72, No. 8, 1998, pp. 939-941).
A nitride-based compound semiconductor laser device capable of obtaining the single transverse mode oscillation, which is fabricated using such techniques, is, for example, disclosed in Japanese Laid-Open Publication No. 6-19801. This semiconductor laser device will be described with reference to FIG.
5
.
Referring to
FIG. 5
, the nitride-based compound semiconductor laser device includes a substrate
1
, and further includes a buffer layer
2
of undoped GaN, an n-type contact layer
3
of n-type GaN, an n-type cladding layer
4
of n-type Al
0.1
Ga
0.9
N, an n-type light guiding layer
5
of n-type GaN, an active layer
6
being a multi-quantum-well layer produced by alternative formation of an In
0.15
Ga
0.85
N well layer and an In
0.02
Ga
0.98
N barrier layer, a p-type light guiding layer
7
of p-type GaN, and a first p-type cladding layer
8
of p-type Al
0.1
Ga
0.9
N, which are successively formed on the substrate
1
. The nitride-based compound semiconductor laser device still further includes a groove structure
9
formed on the cladding layer
8
, and a p-type contact layer
10
of p-type GaN formed on the groove structure
9
. The groove structure
9
serves as part of a waveguide.
The groove structure
9
includes an n-type current blocking layer
12
of n-type Al
0.1
Ga
0.9
N in which a groove stripe is formed, and a second p-type cladding layer
11
of p-type Al
0.5
Ga
0.95
N formed on the current blocking layer
12
.
A portion of a surface of the n-type contact layer
3
is exposed, and an n-type electrode
13
is formed on the exposed surface of the n-type contact layer
3
. Also, a p-type electrode
14
is formed on the p-type contact layer
10
.
A method of producing the groove structure
9
will now be described with reference to
FIGS. 6A through 6C
.
After the first p-type cladding layer
8
has been formed over the substrate
1
, the n-type current blocking layer
12
is formed on the first p-type cladding layer
8
. A mask
15
having an opening in the shape of a stripe with a predetermined width is attached on the n-type current blocking layer
12
(FIG.
6
A).
Then, a portion of the n-type current blocking layer
12
corresponding to the opening of the mask
15
is removed by etching to form a groove (FIG.
6
B). Subsequently, the mask
15
is removed. The second p-type cladding layer
11
is formed on the groove and the remaining n-type current blocking layer
12
(FIG.
6
C).
The above-described conventional techniques have the following problems.
To provide satisfactory manufacturing yields of the nitride-based compound semiconductor laser device capable of the single transverse mode oscillation, it is critically important to control the shape and thickness of the groove structure
9
. To achieve this end, it is necessary to precisely and uniformly control etching so as to obtain a precise and uniform depth of the groove resulting from the etching removal of the portion of the n-type current blocking layer
12
corresponding to the opening of the mask
15
.
For conventional wet etching techniques, the above-mentioned reference discloses a technique in which an etch stop layer is used to stop etching at the etch stop layer. In this case, however, a layer to be etched and the etch stop layer are produced by changing the carrier densities thereof, although it is difficult to precisely and uniformly control the carrier densities. Therefore, the etching selectivity of the layer to be etched and the etch stop layer varies, which causes roughness on the etched surfaces of the layer to be etched and the etch stop layer.
For conventional dry etching techniques, an etching selectivity has not ben known with respect to the nitride-based compound semiconductor, so that it is not believed that an etch stop layer may be provided. In general, as the n-type current blocking layer
12
and the first p-type cladding layer
8
have the same or similar composition, etching does not stop at the n-type current blocking layer
12
and proceeds in the first p-type cladding layer
8
. Accordingly, in the step of removing the n-type current blocking layer
12
, it is difficult to precisely and uniformly control the etching depth.
Thus, it is difficult to provide satisfactory manufacturing yields of the nitride-based compound semiconductor laser device capable of the single transverse mode oscillation.
SUMMARY OF THE INVENTION
A semiconductor device of the present invention includes: a substrate; a multi-layer structure provided on the substrate; a first-conductive-type etch stop layer of a III nitride provided on the multi-layer structure; and a second-conductive-type first semiconductor layer of a III nitride provided on the etch stop layer. A molar fraction of Al is lower in a composition of the III nitride included in the first semiconductor layer than in a composition of the III nitride included in the etch stop layer.
Accordingly, since the etch stop layer having a larger molar fraction of Al in the composition thereof than the first semiconductor layer is formed immediately under the first semiconductor layer, etching performed in the first semiconductor layer is substantially stopped at the etch stop layer.
In one embodiment of the present invention, the multi-layer structure includes a second semiconductor layer of a III nitride, a molar fraction of Al being lower in a composition of the III nitride included in the second semiconductor layer than in a composition of the III nitride included in the etch stop layer.
Accordingly, the second semiconductor layer has a higher refractive index than the etch st
Nakamura Shinji
Orita Kenji
Yuri Masaaki
Matsushita Electronics Corporation
Mulpuri Savitri
RatnerPrestia
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