Active solid-state devices (e.g. – transistors – solid-state diode – Specified wide band gap semiconductor material other than... – Diamond or silicon carbide
Reexamination Certificate
2002-02-19
2004-08-03
Eckert, George (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Specified wide band gap semiconductor material other than...
Diamond or silicon carbide
C257S019000, C257S063000, C257S065000, C257S054000, C257S055000
Reexamination Certificate
active
06770912
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device in which an ohmic electrode is formed on a substrate made of silicon carbide with a large bandgap, and a method for producing the same.
2. Description of the Related Art
In recent years, a semiconductor made of silicon carbide (SiC) is drawing attention as a next-generation semiconductor material due to its physical advantage of a wide bandgap and the substantially unlimited availability of its constituent elements. SiC has a crystal structure formed by a covalent bond, so that it is very stable physically and has a large bandgap. Therefore, a Schottky contact can be formed easily on a junction surface between metal and SiC, whereas it is difficult to form an ohmic contact thereon. In order to form an ohmic contact, it is required to select a material appropriately and conduct a heat treatment at a very high temperature.
Hereinafter, a method for forming an ohmic electrode using a conventional construction will be described with reference to the drawings.
FIG. 6
is a cross-sectional view showing a configuration of a field-effect transistor that is one of the conventional SiC semiconductor devices.
FIGS. 12A
to
12
D are cross-sectional views illustrating the processes of a method for producing the field-effect transistor. First, as shown in
FIG. 12A
, a SiC member
62
doped with an impurity in a low concentration, and a SiC member
63
doped with an impurity in a high concentration are formed on the upper surface of a SiC substrate
61
by crystal growth. Then, as shown in
FIG. 12B
, a part of the SiC member
63
that is the uppermost member is removed to expose the SiC member
62
. Thereafter, as shown in
FIG. 12C
, ohmic electrodes
68
are formed on the SiC member
63
, and a heat treatment is conducted at a high temperature, whereby an ohmic contact is obtained. The ohmic electrodes
68
will function as a drain electrode and a source electrode. Furthermore, as shown in
FIG. 12D
, a gate electrode
69
is formed on the SiC member
62
to obtain a Schottky contact.
As a result of the above-mentioned processes, a SiC field-effect transistor with a conventional construction as shown in
FIG. 6
is completed. A part of the SiC member
63
may be removed after the ohmic electrodes
68
are formed. An ohmic contact generally is obtained by inserting the SiC substrate
61
into a heating coil of a high-frequency heating furnace, and conducting a heat treatment at a high temperature of about 1000° C. to 1600° C. This method is disclosed by, for example, C. Arnodo et al., “Nickel and Molybdenum Ohmic Contacts on Silicon Carbide”, Institute of Physics Conference Series Number 142, pp. 577-580, 1996 and the like.
However, according to the above-mentioned method for forming an ohmic electrode with the conventional construction, a heat-treatment temperature is much higher than heat-resistant temperatures of conventional semiconductor materials such as Si and GaAs, and the resistance of an ohmic contact thus obtained also is high. In addition, a metal material for an ohmic electrode needs to have a melting point higher than the heat-treatment temperature, so that the selection is limited to refractory metals and the like. Furthermore, this heat-treatment temperature is close to a growth temperature of SiC crystal and an annealing temperature for activation conducted after ion implantation. This may degrade the crystal structure and cause an impurity to diffuse again. In terms of facility, the conventional method also has various problems. More specifically, the conventional method requires a special apparatus such as a high-frequency heating furnace for conducting a heat treatment at a high temperature, complicated management of a temperature and an atmospheric gas, safety management with respect to a high temperature, and the like. These problems hinder the practical use and mass-production of a SiC semiconductor device.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a construction in which an ohmic electrode with a low resistance is formed on a SiC substrate without conducting a heat treatment at a high temperature, and a method for producing the same.
In order to achieve the above-mentioned object, the semiconductor device of the present invention includes a SiC substrate and an ohmic electrode, wherein a semiconductor member including a SiC member and a SiGe member is formed between the SiC substrate and the ohmic electrode.
Furthermore, in the semiconductor device of the present invention, the semiconductor member may be composed of a SiGe member formed on a SiC member, and the ohmic electrode may be formed on the SiGe member.
Furthermore, in the semiconductor device of the present invention, the semiconductor member may be composed of a Si member formed on a SiC member and a SiGe member formed on the Si member, and the ohmic electrode may be formed on the SiGe member.
Furthermore, in the semiconductor device of the present invention, the semiconductor member may be composed of a semiconductor member in which a mole fraction is varied continuously from SiC to Si and from Si to SiGe, and the ohmic electrode may be formed on the semiconductor member.
Furthermore, in the semiconductor device of the present invention, the semiconductor member may be composed of a semiconductor member in which a C mole fraction is decreased while a Ge mole fraction is increased continuously from SiC to SiGe, and the ohmic electrode is formed on the semiconductor member.
Furthermore, in the semiconductor device of the present invention, the semiconductor member may be formed on both a p-type region and an n-type region.
Furthermore, in the semiconductor device of the present invention, a gate electrode may be formed on the SiC member.
Furthermore, in the semiconductor device of the present invention, the gate electrode may be formed on a Si oxide film.
Furthermore, the method for producing a semiconductor device of the present invention includes: forming a semiconductor member including a SiC member and a SiGe member on a SiC substrate by crystal growth; and forming an ohmic electrode on the semiconductor member.
Furthermore, in the method for producing a semiconductor device of the present invention, the process of forming the semiconductor member by crystal growth may include forming a SiGe member on a SiC member by crystal growth.
Furthermore, in the method for producing a semiconductor device of the present invention, the process of forming the semiconductor member by crystal growth may include forming a Si member on a SiC member by crystal growth; and forming a SiGe member on the Si member by crystal growth.
Furthermore, in the method for producing a semiconductor device of the present invention, the process of forming the semiconductor member by crystal growth may include forming a semiconductor member, in which a mole fraction is varied continuously from SiC to Si and from Si to SiGe, on a SiC member by crystal growth.
Furthermore, in the method for producing a semiconductor device of the present invention, the process of forming the semiconductor member by crystal growth may include forming a semiconductor member, in which a C mole fraction is decreased while a Ge mole fraction is increased continuously from SiC to SiGe, on a SiC member by crystal growth.
Furthermore, in the method for producing a semiconductor device of the present invention, the semiconductor member may be formed on both a p-type region and an n-type region by crystal growth.
Furthermore, the method for producing a semiconductor device of the present invention may include forming a gate electrode on the SiC member.
Furthermore, in the method for producing a semiconductor device of the present invention, the gate electrode may be formed on a Si oxide film.
According to the semiconductor device and method for producing the same of the present invention, an ohmic electrode is formed on SiGe with a small bandgap. Therefore, a heat treatment for o
Eckert George
Matsushita Electric - Industrial Co., Ltd.
Nguyen Joseph
LandOfFree
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