Method of manufacturing silicon carbide semiconductor device

1. A method of manufacturing a silicon carbide semiconductor device having a metal-oxide semiconductor structure, the method comprising:

preparing a substrate made of silicon carbide;

forming a channel region made of silicon carbide on the substrate, wherein the channel region provides an electric current passage;

forming a first impurity region on the substrate on an upstream side of the electric current passage;

forming a second impurity region on the substrate on a downstream side of the electric current passage;

forming a gate insulation layer on a surface of the channel region;

forming a gate electrode on the gate insulation layer to form a semiconductor element;

forming a film on the semiconductor element to provide a material of an interlayer insulation layer;

performing a reflow process at a temperature about 700° C. or over in an wet atmosphere so that the interlayer insulation layer is formed from the film;

decreasing the temperature at about 700° C. or lower after performing the reflow process;

changing the wet atmosphere to an inert gas atmosphere after the temperature is decreased at about 700° C. or lower; and

performing a dehydration process in the inert gas atmosphere so that the interlayer insulation layer is dehydrated, wherein:

the channel region provides a channel of the semiconductor element; and

the channel is controlled by controlling a voltage applied to the gate electrode so that an electric current flowing between the first impurity region and the second impurity region is controlled.

2. The method according to claim 1 , wherein:

the inert gas atmosphere includes nitrogen gas.

3. The method according to claim 1 , wherein:

the inert gas atmosphere includes argon gas.

4. The method according to claim 1 , wherein:

the decreasing the temperature at about 700° C. or lower is performed with a temperature decreasing rate about 10° C./min or less.

5. The method according to claim 1 , wherein:

the dehydration process is performed with decreasing the temperature at about 10° C./min or less.

6. The method according to claim 5 , wherein:

the dehydration process is performed with decreasing the temperature at a fixed rate about 10° C./min or less.

7. The method according to claim 5 , wherein:

the dehydration process includes a first step and a second step;

the temperature is decreased at a first rate at the first step;

the temperature is decreased at a second rate at the second step; and

the first rate is about 10° C./min or less and the second rate is less than the first rate.

8. The method according to claim 5 , wherein:

the dehydration process includes a first step and a second step;

the temperature is decreased to a first predetermined temperature with a temperature decreasing rate about 10° C./min or less at the first step; and

the temperature is increased from the first predetermined temperature to a second predetermined temperature with a temperature increasing rate 10° C./min or less at the second step.

9. The method according to claim 8 , wherein:

the second predetermined temperature is about 700° C. or lower.

10. The method according to claim 9 , wherein:

the dehydration process further includes a third step; and

the temperature is kept at the second predetermined temperature for a predetermined time at the third step.

11. The method according to claim 7 , wherein:

the dehydration process further includes a step of keeping the temperature at a predetermined temperature for a predetermined time.

12. The method according to claim 1 , wherein:

the semiconductor element is formed on a face A of the substrate.