A method of manufacturing a silicon carbide semiconductor device, the method comprising:
- preparing a silicon carbide semiconductor substrate of a first conductivity type, the silicon carbide semiconductor substrate having a first surface and a second surface that are opposite to each other;
- forming a first semiconductor layer of the first conductivity type on the first surface of the silicon carbide semiconductor substrate, the first semiconductor layer having an impurity concentration that is lower than an impurity concentration of the silicon carbide semiconductor substrate, the first semiconductor layer having a first surface and a second surface that are opposite to each other, the second surface of the first semiconductor layer facing the silicon carbide semiconductor substrate;
- forming a second semiconductor layer of a second conductivity type on the first surface of the first semiconductor layer, the second semiconductor layer having a first surface and a second surface that are opposite to each other, the second surface of the second semiconductor layer facing the silicon carbide semiconductor substrate;
- selectively forming a plurality of first semiconductor regions of the first conductivity type in the second semiconductor layer, at the first surface of the second semiconductor layer;
- forming a plurality of trenches that penetrate through the first semiconductor regions and the second semiconductor layer, and reach the first semiconductor layer;
- forming a gate insulating film in the trenches, along sidewalls and bottoms of the trenches;
- forming a plurality of gate electrodes on the gate insulating film in the trenches;
- forming a first electrode on surfaces of the first semiconductor regions and the first surface of the second semiconductor layer;
- and
- forming a second electrode on the second surface of the silicon carbide semiconductor substrate, wherein
- forming the gate insulating film includes forming the gate insulating film using a nitriding heat treatment that has a first stage and a second stage, by
- performing the first stage of the nitriding heat treatment by a first gas containing oxygen and nitrogen,
- depositing an oxide film after performing the first stage of the nitriding heat treatment, and
- performing the second stage of the nitriding heat treatment by a second gas containing nitric oxide and nitrogen, after depositing the oxide film;
- an amount of the nitrogen at a treatment starting point of the first stage of the nitriding heat treatment is greater than an amount of the nitrogen at a treatment starting point of the second stage of the nitriding heat treatment;
- and
- an amount of the nitrogen at a treatment ending point of the second stage of the nitriding heat treatment is greater than an amount of the nitrogen at a treatment ending point of the first stage of the nitriding heat treatment.