Semiconductor device and method of manufacturing the same

Abstract

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; 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 silicate formation free energy and carbide formation free energy respectively take negative values.   
     
     
         2 . The semiconductor device according to  claim 1 , wherein
 the ohmic metal layer is composed of a metal material whose silicate 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 ohmic metal layer is composed of at least one metal material selected from a group consisting of molybdenum, titanium, chromium, manganese, zirconium, tantalum, and tungsten.   
     
     
         4 . The semiconductor device according to  claim 1 , wherein
 carrier concentration of a semiconductor layer on the side of the one surface of the silicon carbide semiconductor substrate is within a range of 10 17  to 10 21 /cm 3 .   
     
     
         5 . 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.   
     
     
         6 . The semiconductor device according to  claim 1 , 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, further comprising
 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.   
     
     
         7 . The semiconductor device according to  claim 6 , wherein
 the carrier concentration of the first semiconductor layer is within a range of 10 17  to 10 21 /cm 3 , and   the carrier concentration of the second semiconductor layer is within a range of 10 14  to 10 16 /cm 3 .   
     
     
         8 . A method of manufacturing a semiconductor device, comprising:
 a film forming step for forming a metal layer on one surface of a silicon carbide semiconductor substrate; and   a heat-treating step for subjecting the metal layer to a heat treatment in a temperature range of 300° C. to 500° C. after the film forming step, to form an ohmic junction between the metal layer and the one surface of the silicon carbide semiconductor substrate,   the film forming step including the step of forming the metal layer brought into contact with the silicon carbide semiconductor substrate using a metal material whose silicate formation free energy and carbide formation free energy at the temperature of the silicon carbide semiconductor substrate in the heat-treating step respectively take negative values.   
     
     
         9 . The method according to  claim 8 , wherein
 the film forming step includes the step of forming the metal layer brought into contact with the silicon carbide semiconductor substrate using at least one metal material selected from a group consisting of molybdenum, titanium, chromium, manganese, zirconium, tantalum, and tungsten.   
     
     
         10 . A method of manufacturing a semiconductor device using a silicon carbide semiconductor substrate in which carrier concentration of a first semiconductor layer on a side of its one surface is higher than carrier concentration of a second semiconductor layer on a side of the other surface, comprising:
 a first film forming step for forming a first metal layer brought into contact with the first semiconductor layer in the silicon carbide semiconductor substrate;   a second film forming step for forming a second metal layer brought into contact with the second semiconductor layer in the silicon carbide semiconductor substrate and composed of the same metal material as that composing the first metal layer; and   a heat-treating step for simultaneously heat-treating the first metal layer and the second metal layer at a predetermined temperature after the first film forming step and the second film forming step, to form an ohmic junction between the first metal layer and the first semiconductor layer as well as to form a Schottky junction between the second metal layer and the second semiconductor layer,   the first and second film forming steps including the steps of respectively forming the first and second metal layers brought into contact with the silicon carbide semiconductor substrate using a metal material whose silicate formation free energy and carbide formation free energy at the temperature of the silicon carbide semiconductor substrate in the heat-treating step respectively take negative values.   
     
     
         11 . The method according to  claim 10 , wherein
 the heat-treating step is the step of carrying out the heat treatment in a temperature range of 300° C. to 500° C.   
     
     
         12 . The method according to  claim 10 , wherein
 the first and second film forming steps include the steps of respectively forming the first and second metal layers brought into contact with the silicon carbide semiconductor substrate using at least one metal material selected from a group consisting of molybdenum, titanium, chromium, manganese, zirconium, tantalum, and tungsten.