Method of manufacturing silicon carbide semiconductor device
In a method of manufacturing a silicon carbide semiconductor device that is a silicon carbide diode having a JBS structure including a mixture of a Schottky junction and a pn junction and that maintains low forward voltage through a SBD structure and enhances surge current capability, nickel silicide films are formed in an oxide film by self-alignment by causing a semiconductor substrate and a metal material film to react with one another through two sessions of heat treatment including a low-temperature heat treatment and a high-temperature heat treatment, the metal material film including sequentially a first nickel film, an aluminum film, and a second nickel film, the first nickel film being in contact with an entire area of a connecting region of a FLR and p-type regions respectively exposed in openings of the oxide film.
1. A method of manufacturing a silicon carbide semiconductor device, the method comprising:
preparing a semiconductor substrate having a first main surface and a second main surface opposite to the first main surface, the semiconductor substrate containing silicon carbide, and including a first-conductivity-type region having a main surface that forms the first main surface of the semiconductor substrate, the first-conductivity-type region having surface regions at the main surface thereof;
selectively forming a plurality of first second-conductivity-type regions in the surface regions of the first-conductivity-type region;
forming an oxide film on the first main surface of the semiconductor substrate, the oxide film covering the first-conductivity-type region and the first second-conductivity-type regions;
forming a plurality of first openings in the oxide film by selectively removing the oxide film, the first openings exposing the first second-conductivity-type regions;
forming a metal material film in the first openings of the oxide film, the metal material film being in direct contact with the first main surface of the semiconductor substrate and including sequentially from the first main surface, a first nickel film, an aluminum film, and a metal film having a melting point higher than that of aluminum;
forming a compound layer on the first main surface of the semiconductor substrate in each of the first openings of the oxide film by self-alignment using the oxide film as a mask and causing the metal material film and the semiconductor substrate to react through a first heat treatment;
after forming the compound layer, removing an excess portion of the metal material film excluding the compound layer;
after removing the excess portion, forming a plurality of nickel silicide films in ohmic contact with the semiconductor substrate by generating a nickel silicide in the compound layer in each of the first openings through a second heat treatment at a temperature higher than a temperature of the first heat treatment;
after forming the nickel silicide films, forming a contact hole connecting all of the first openings by removing the oxide film remaining between the nickel silicide films;
forming a first electrode on the first main surface of the semiconductor substrate in the contact hole, the first electrode including sequentially from the first main surface, a titanium film in direct contact with the first-conductivity-type region and forming a Schottky junction therewith, and a metal electrode film containing aluminum; and
forming a second electrode on the second main surface of the semiconductor substrate.
2. The method according to claim 1 , wherein
the metal film having a melting point higher than that of aluminum is a second nickel film.
3. The method according to claim 2 , wherein
a rate of a film thickness of the aluminum film relative to a film thickness of the metal material film is in a range from 20% to 55%.
4. The method according to claim 3 , wherein
the first nickel film has a film thickness in a range from 50 nm to 120 nm,
the film thickness of the aluminum film is in a range from 25 nm to 250 nm, and
the second nickel film has a film thickness in a range from 50 nm to 120 nm.
5. The method according to claim 1 , wherein
the metal film having a melting point higher than that of aluminum is a titanium film, a molybdenum film, or a tungsten film.
6. The method according to claim 5 , wherein
a rate of a film thickness of the aluminum film relative to a film thickness of the metal material film is in a range from 33% to 63%.
7. The method according to claim 6 , wherein
the first nickel film has a film thickness in a range from 50 nm to 120 nm, and
the film thickness of the aluminum film is in a range from 25 nm to 210 nm.
8. The method according to claim 1 , wherein
the temperature of the first heat treatment is in a range from 500 degrees C. to 700 degrees C.
9. The method according to claim 1 , wherein
the temperature of the second heat treatment is in a range from 900 degrees C. to 1100 degrees C.