Semiconductor device with a silicon carbide substrate and ohmic metal layer
A semiconductor device provided with a silicon carbide semiconductor substrate, and an ohmic metal layer joined to one surface of the silicon carbide semiconductor substrate in an ohmic contact and composed of a metal material whose silicide formation free energy and carbide formation free energy respectively take negative values. The ohmic metal layer is composed of, for example, a metal material such as molybdenum, titanium, chromium, manganese, zirconium, tantalum, or tungsten.
1. A semiconductor device, comprising:
a silicon carbide semiconductor substrate;
an ohmic metal layer joined to one surface of the silicon carbide semiconductor substrate in an ohmic contact and composed of a metal material whose silicide formation free energy and carbide formation free energy respectively take negative values, said ohmic metal layer being composed of manganese, wherein the carrier concentration of a first semiconductor layer on the side of the one surface of the silicon carbide semiconductor substrate is higher than the carrier concentration of a second semiconductor layer on the side of the other surface of the silicon carbide semiconductor substrate; and
a Schottky metal layer joined to the other surface of the silicon carbide semiconductor substrate in a Schottky contact and composed of the same material as that composing the ohmic metal layer.
2. The semiconductor device according to claim 1 , wherein the ohmic metal layer is composed of a metal material whose silicide formation free energy and carbide formation free energy at a temperature at a time of a heat treatment for joining the ohmic metal layer to the surface of the silicon carbide semiconductor substrate in an ohmic contact respectively take negative values.
3. The semiconductor device according to claim 1 , wherein the carrier concentration of one of the first and second semiconductor layers is within a range of 10 17 to 10 21 /cm 3 .
4. The semiconductor device according to claim 1 , further comprising a multi-layer metal structure in which another metal layer composed of a metal material different from that composing the ohmic metal layer is formed on a surface of the ohmic metal layer.
5. The semiconductor device according to claim 1 , wherein
the carrier concentration of the first semiconductor layer is within a range of 10 17 to 10 16 /cm 3 , and
the carrier concentration of the second semiconductor layer is within a range of 10 14 to 10 16 /cm 3 .