Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
2003-03-07
2004-09-28
Pham, Long (Department: 2814)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
C438S031000, C438S047000, C438S439000, C438S795000, C438S796000
Reexamination Certificate
active
06797532
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device such as a short-wavelength light emitting diode device or a short-wavelength semiconductor laser device, and a method for manufacturing the same.
A semiconductor material made of a group III-V nitride semiconductor, having a wide forbidden band, can be used in light emitting devices, specifically, light emitting diode devices and short-wavelength semiconductor laser devices that are capable of emitting light of a color in a visible region such as blue, green or white. Among others, light emitting diode devices have already been in practical use in large-size display apparatuses, traffic signals, etc. Particularly, white light emitting diode devices, which give white light by exciting a fluorescent substance, are expected to replace conventional lighting fixtures such as electric bulbs and fluorescent lamps. Moreover, the development of semiconductor laser devices has reached a point where samples are being shipped and products are being manufactured although in small quantities, for use in high-density, large-capacity optical disk apparatuses using blue-violet laser light.
The crystal growth of a group III-V nitride semiconductor, or a so-called “gallium nitride (GaN) semiconductor”, has been difficult, as is also the case with other wide gap semiconductors. However, with the recent significant improvements in crystal growth techniques such as a metal organic chemical vapor deposition method, light emitting diode devices capable of emitting light of short wavelengths such as blue light have already been in practical use.
Moreover, since a substrate made of gallium nitride is difficult to produce, a gallium nitride semiconductor cannot be grown by a crystal growth technique that is used with silicon (Si) or gallium arsenide (GaAs), i.e., growing a semiconductor layer (epitaxial growth layer) on a substrate having the same composition as that of the semiconductor layer. Therefore, a so-called “heteroepitaxial growth process” is typically employed, in which the epitaxial growth layer is grown on a substrate having a different composition from that of the epitaxial growth layer, e.g., a sapphire substrate.
As a result, a gallium nitride semiconductor layer grown on a sapphire substrate is currently exhibiting the most desirable device characteristics, where the crystal defect density of the epitaxial growth layer is about 1×10
7
cm
−2
. However, since sapphire is insulative, in order to form a device including a p-n junction on a substrate made of sapphire, it is necessary to selectively remove the p-type semiconductor layer or the n-type semiconductor layer after the epitaxial growth and to form a p-type electrode and an n-type electrode on the principal surface of the substrate.
Moreover, since it is typically difficult to perform a wet etching process with an acidic solution, or the like, on a nitride semiconductor, a dry etching method such as reactive ion etching is normally used in such a selective removal step.
First Conventional Example
A method for manufacturing a semiconductor device according to a first conventional example will now be described with reference to the drawings.
FIG. 21
is a cross-sectional view illustrating a light emitting diode device, which is a semiconductor device of the first conventional example.
As illustrated in
FIG. 21
, first, a buffer layer (not shown) made of gallium nitride or aluminum nitride, an n-type cladding layer
102
made of n-type aluminum gallium nitride, an active layer
103
including a quantum well structure made of undoped indium gallium nitride, and a p-type cladding layer
104
made of p-type aluminum gallium nitride are grown in this order on a substrate
101
made of sapphire by a metal organic chemical vapor deposition method, or the like, to form an epitaxial layer. As a current is externally injected into the n-type cladding layer
102
and the p-type cladding layer
104
, electrons and holes are confined in the active layer
103
, and output light is produced through recombination of electrons and holes.
Then, the p-type cladding layer
104
, the active layer
103
and an upper portion of the n-type cladding layer
102
are selectively etched by a reactive ion etching method to form a current constriction section
200
in the epitaxial layer. Then, the p-side electrode
105
is formed on the p-type cladding layer
104
in the current constriction section
200
, and an n-side electrode
106
is formed on the exposed region of the n-type cladding layer
102
.
Second Conventional Example
FIG. 22
is a cross-sectional view illustrating a semiconductor laser device, which is a semiconductor device of the second conventional example.
As illustrated in
FIG. 22
, in order to produce a semiconductor laser device, an upper portion of the current constriction section
200
is again subjected to a reactive ion etching method to form a ridge portion
201
to be a waveguide, and then the p-side electrode
105
is formed in a stripe pattern. Furthermore, the structure is cleaved along a plane perpendicular to the direction in which the p-side electrode
105
having a stripe pattern extends, thereby forming a cavity with the two opposing cleaved surfaces being mirrors. Herein, the upper surface excluding the p-side electrode
105
and the n-side electrode
106
is covered by an insulating film
107
made of silicon oxide.
However, with the methods for manufacturing a semiconductor device of the first and second conventional examples, a nitride semiconductor layer for forming the current constriction section
200
needs to be subjected to a dry etching process. The dry etching process damages the side surfaces of the current constriction section
200
. With such a damage, when a current is supplied through the semiconductor device, a leakage current occurs through the damaged portions, thereby increasing the operating current of a light emitting diode device, or the threshold current value of a semiconductor laser device.
Moreover, as described above, sapphire, which is insulative, is used for the substrate
101
, whereby both of the p-side electrode
105
and the n-side electrode
106
need to be formed on the principal surface of the substrate
101
. This increases the series resistance value as a p-n junction, while increasing the device cost because of an increase in the chip area.
Moreover, sapphire has a relatively small thermal conductivity, and thus a poor heat radiating property. Therefore, when a semiconductor laser device, for example, is produced using sapphire, it is difficult to increase the operating lifetime of the semiconductor laser device.
SUMMARY OF THE INVENTION
In view of these problems in the prior art, a first object of the present invention is to provide a semiconductor device using a group III-V nitride semiconductor, in which a current constriction section can be formed without damaging an exposed surface (side surface) of an active region. Moreover, a second object of the present invention is to reduce the series resistance value and improve the heat radiating property.
In order to achieve the first object, the present invention employs a structure in which a semiconductor layer including an active region is oxidized at positions spaced apart from each other to form oxidized regions so that the oxidized regions form a current constriction section. Moreover, even when the semiconductor layer is dry-etched, the side surface of the current constriction section is oxidized.
Moreover, in order to achieve the second object in addition to the first object, a semiconductor layer is formed on a substrate so that an active region is included in the semiconductor layer, after which the substrate is removed from the semiconductor layer.
Specifically, a semiconductor device of the present invention, which achieves the first object, includes a first semiconductor layer of a first conductivity type and a second semiconductor layer of a second conductivity type, including an active region, wherein at least one of the first s
McDermott Will & Emery LLP
Pham Long
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