Method for manufacturing semiconductor device

1. A method for manufacturing a semiconductor device, the method comprising:

(a) preparing a silicon carbide substrate of a first conductivity;

(b) forming a well layer of a second conductivity in the silicon carbide substrate;

(c) forming a first diffusion layer of the first conductivity over the well layer in the silicon carbide substrate, the first diffusion layer including a source region and a drain region;

(d) forming a trench penetrating through the first diffusion layer and the well layer and reaching the silicon carbide substrate;

(e) forming a first insulating film over the trench and the top surface of the silicon carbide substrate;

(f) carrying out a first heat treatment accompanied by nitration on the first insulating film and the silicon carbide substrate in a first gas atmosphere;

(g) after the carrying out of the first heat treatment and after a temperature of the silicon carbide substrate has become 700° C. or less, removing the silicon carbide substrate from a processing apparatus and exposing the silicon carbide substrate to air in an atmosphere outside of the processing apparatus;

(h) after the exposing of the silicon carbide substrate to air in the atmosphere, carrying out a second heat treatment on the first insulating film and the silicon carbide substrate in a second gas atmosphere which is an inert gas; and

(i) after the carrying out of the second heat treatment, forming a gate electrode through the first insulating film over the silicon carbide substrate,

wherein the gate electrode, the first insulating film, the source region and the drain region include a field effect transistor.

2. The method for manufacturing a semiconductor device according to claim 1 , further comprising:

(j) forming a second diffusion layer of the second conductivity in the silicon carbide substrate after the step (c).

3. The method for manufacturing a semiconductor device according to claim 2 , wherein the second diffusion layer comprises a p-type semiconductor layer formed by introducing aluminum or boron.

4. The method for manufacturing a semiconductor device according to claim 3 , further comprising:

after the performing of the heat treatment and before the forming of the other insulating film, carrying out a heat treatment accompanied by nitration on the insulating film and the silicon carbide substrate in the first gas atmosphere.

5. The method for manufacturing a semiconductor device according to claim 2 , wherein the performing of the heat treatment is carried out in an atmosphere comprising at least one member selected from the group consisting of oxygen and vapor.

6. The method for manufacturing a semiconductor device according to claim 1 , wherein the silicon carbide substrate is formed a semiconductor substrate and an epitaxial layer over the semiconductor substrate, and

wherein the depth of the well layer is shallower than the interface between the epitaxial layer and the semiconductor substrate.

7. The method for manufacturing a semiconductor device according to claim 1 , wherein the first diffusion layer comprises an n-type semiconductor layer formed by introducing nitrogen, phosphorus or arsenic.

8. The method for manufacturing a semiconductor device according to claim 1 , wherein the forming of the first insulating film comprises performing a heat treatment on the silicon carbide substrate to form the first insulating film over the top surface of the silicon carbide substrate.

9. The method for manufacturing a semiconductor device according to claim 1 , wherein the first insulating film is formed by using an atomic layer deposition (ALD) or chemical vapor deposition (CVD) method in the forming of the first insulating film.

10. The method for manufacturing a semiconductor device according to claim 1 , wherein the forming of the first insulating film comprises:

performing a heat treatment on the silicon carbide substrate to form an insulating film over the top surface of the silicon carbide substrate, and

forming an other insulating film over the insulating film by using an atomic layer deposition (ALD) or chemical vapor deposition (CVD) method, to form the first insulating film including the insulating film and the other insulating film.

11. The method for manufacturing a semiconductor device according to claim 1 , wherein the first gas comprises at least one member selected from the group consisting of dinitrogen monoxide, nitrogen monoxide and ammonia gases.

12. The method for manufacturing a semiconductor device according to claim 1 , wherein the second gas comprises at least one member selected from the group consisting of nitrogen, argon and helium gases.

13. The method for manufacturing a semiconductor device according to claim 1 , wherein the second heat treatment is carried out at 850° C. or higher.