Silicon carbide semiconductor device and manufacturing method of the same

A silicon carbide semiconductor device comprising:

• a substrate made of silicon carbide and having a Si-face as a main surface, the substrate having a first conductive type or a second conductive type;
• a drift layer made of silicon carbide and formed on the substrate, the drift layer having the first conductive type and having an impurity concentration that is lower than an impurity concentration of the substrate;
• a base region made of silicon carbide and formed on the drift layer, the base region having the second conductive type;
• a source region made of silicon carbide and formed in a surface portion of the base region, the source region having the Si-face, the source region having the first conductive type and having an impurity concentration that is higher than the impurity concentration of the drift layer;
• a trench provided from a surface of the source region to a portion deeper than the base region, the trench extending longitudinally in one direction and having a Si-face bottom;
• a gate oxide film formed on an inner wall of the trench;
• a gate electrode formed on the gate oxide film in the trench;
• a source electrode electrically coupled to the source region and the base region;
• and
• a drain electrode formed on a rear surface of the substrate,
• wherein a channel region is formed in a surface portion of the base region, which is in contact with the trench, by controlling a voltage applied to the gate electrode, and current flows between the source electrode and the drain electrode through the source region and the drift layer, and
• wherein the trench has an inverse tapered shape, which has a smaller width at an entrance portion than at a bottom, at least at a portion that is in contact with the base region.