Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – On insulating substrate or layer
Reexamination Certificate
2002-02-05
2003-05-13
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
On insulating substrate or layer
C438S483000, C438S796000, C438S459000, C438S460000, C438S033000
Reexamination Certificate
active
06562701
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a nitride semiconductor substrate for use in a visible light emitting diode or a blue violet laser.
Group III-V nitride semiconductor such as gallium nitride (GaN), indium nitride (InN) and aluminum nitride (AlN) is preferably used as a compound semiconductor material for a blue or green light emitting diode (LED), a blue semiconductor laser or a high speed transistor device capable of operating at a high temperature. There is a well-known substrate to grow nitride semiconductor thereon such as an insulating substrate of sapphire (monocrystalline Al
2
O
3
), silicon carbide (SiC), silicon (Si) or gallium arsenic (GaAs).
However, it is known that if nitride semiconductor is grown on a substrate of a different material such as sapphire, the difference between the thermal expansion coefficients of the nitride semiconductor to grow and the substrate causes the substrate to bow or have cracks, which degrades the crystallinity of the nitride semiconductor.
In recent years, there have been attempts to solve the problem related to the difference between the materials of the substrate and the layer grown thereon by forming the substrate with nitride semiconductor and forming an element structure of the same kind of nitride semiconductor thereon.
According to one method of manufacturing a nitride semiconductor substrate, for example, a nitride semiconductor layer is grown to have a relatively large thickness on a substrate to be a base member (base member substrate), and a laser beam is irradiated on the interface between the grown nitride semiconductor layer and the base substrate. According to the proposed method, the nitride semiconductor layer irradiated with the laser beam is locally heated and sublimed, and separated from the base substrate, so that a nitride semiconductor substrate may be provided from the nitride semiconductor layer.
According to the conventional method of manufacturing the nitride semiconductor substrate, when the nitride semiconductor layer is separated from the base substrate, however, only the part of the interface being irradiated with the laser beam between the nitride semiconductor layer and the base substrate is separated, while the other part remains connected. In this case, stress concentrates on the connected part of the nitride semiconductor layer and the base substrate, and cracks are generated in the nitride semiconductor layer. This makes it difficult to manufacture the nitride semiconductor substrate with high yield by irradiation of a laser beam about at a room temperature.
At the time of growing nitride semiconductor on a base substrate, threading defects caused by lattice mismatch are introduced, so that a resulting nitride semiconductor substrate has a high defect density.
SUMMARY OF THE INVENTION
The present invention is directed to a solution to the above disadvantage associated with the conventional method and it is an object of the present invention to surely provide a highly productive nitride semiconductor substrate free from cracks and having a reduced defect density.
In order to achieve the above object, according to the present invention, a mask film is formed. The mask film is used to selectively grow a semiconductor layer of nitride on a main surface of a base substrate.
More specifically, a first method of manufacturing a nitride semiconductor substrate according to the present invention includes a first step of forming a mask film of a material on which substantially no nitride semiconductor grows and having a plurality of openings on a main surface of a base substrate, a second step of selectively growing a semiconductor layer of nitride on the base substrate through the mask film, and a third step of irradiating an interface between the semiconductor layer and the base substrate with a laser beam, thereby separating the semiconductor layer from the base substrate to form a semiconductor substrate from the semiconductor layer.
According to the first manufacturing method, the semiconductor layer is selectively grown on the base substrate through the mask film, and therefore stress can be concentrated on the mask film, so that the stress generated in the semiconductor layer can be reduced. As a result, breaks or cracks generated in the semiconductor layer can be reduced. In addition, since a material on which substantially no semiconductor layer grows is used for the mask film, the semiconductor layer grows over the mask film. Therefore, threading defects introduced into the semiconductor layer can be reduced. Thus, a nitride semiconductor substrate having high crystal quality and allowing high productivity can be provided.
Preferably in the first method, the base substrate is composed of sapphire whose main surface is in a {0001} plane orientation, and in the first step, each opening is formed in a stripe shape substantially in a direction of a zone axis, a <1-100> direction in the base substrate. In this manner, with respect to the sapphire whose main surface is the {0001} plane forming the base substrate, the zone axis direction of the semiconductor of the nitride grown thereon is shifted by 30°. Therefore, the stripe shaped opening in the mask film is formed to have its lengthwise direction arranged along the zone axis direction of the base substrate, the <1-100> direction, so that the surface of the semiconductor layer growing to extend over the mask film can be formed into a good {1-101} plane.
Preferably in the first method, the base substrate is composed of silicon carbide or aluminum nitride whose main surface is in a {0001} plane orientation, and in the first step, each opening is formed in a stripe shape in a direction of the zone axis, a <11-20> direction in the base substrate. Thus, the zone axis of the silicon carbide or aluminum nitride forming the base substrate whose main surface is the {0001} plane and the zone axis of the semiconductor layer of nitride grown thereon are in coincidence. As a result, when the stripe shaped opening in the mask film is formed to have its lengthwise direction arranged along the zone axis of the base substrate, the <11-20> direction, the growing surface of the semiconductor layer to extend over the mask film can be a good {1-101} plane.
Preferably, the first method further includes the step of forming an irregular region on the main surface of the base substrate before the first step, and the first step includes the step of forming the mask film so that a top surface of a raised portion in the irregular region is exposed through the opening.
Thus, when a semiconductor layer is formed on the base substrate through the mask film, stress is concentrated on a raised part in the irregular region formed on the main surface of the base substrate, and therefore the stress caused in the growing semiconductor layer is reduced. As a result, breaks or cracks in the semiconductor layer during the growth are more reduced.
Preferably in this case, the base substrate is composed of sapphire whose main surface is in a {0001} plane orientation, and the step of forming the irregular region includes the step of forming a plurality of grooves extending parallel to each other on the main surface of the base substrate so that the grooves are substantially in a direction of a zone axis, a <1-100> direction in the base substrate.
Also preferably in this case, the base substrate is composed of silicon carbide or aluminum nitride whose main surface is in a {0001} plane orientation, and the step of forming the irregular region includes the step of forming a plurality of grooves parallel to each other on the main surface of the base substrate so that the grooves are substantially in a direction of a zone axis, a <11-20> direction in the base substrate.
Also preferably in this case, the first step includes the steps of forming a mask forming film on the entire surface of the irregular region in the base substrate,
Ishida Masahiro
Ueda Daisuke
Yuri Masaaki
Matsushita Electric - Industrial Co., Ltd.
Mulpuri Savitri
Nixon & Peabody LLP
Studebaker Donald R.
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