Silicon carbide semiconductor device and method for producing the same

A silicon carbide semiconductor device comprising:

• a first or second conductivity type substrate made of silicon carbide;
• a drift layer disposed on the substrate, the drift layer made of a first conductivity type silicon carbide having an impurity concentration lower than that of the substrate, the drift layer including a lower layer portion and an upper layer portion, the upper layer portion being disposed above the lower layer portion and having an impurity concentration lower than that of the lower layer portion;
• a base region disposed on the drift layer, the base region made of a second conductivity type silicon carbide;
• a source region disposed in an upper layer portion of the base region, the source region made of a first conductivity type silicon carbide having an impurity concentration higher than that of the drift layer;
• a trench gate structure disposed in a first trench that extends from a surface of the source region to a position deeper than the base region, the trench gate structure including a gate insulation film disposed on an inner wall surface of the first trench and a gate electrode disposed on the gate insulation film;
• a second conductivity type region disposed in a second trench that extends from the surface of the source region to the drift layer while passing through the base region and is deeper than the first trench, the second conductivity type region including a second conductivity type first low concentration region and a second conductivity type first high concentration region, the first high concentration region being disposed on a surface of the first low concentration region and having a second conductivity type impurity concentration being set higher than that of the first low concentration region, the first high concentration region being deeper than the first trench to provide a deep layer, the first high concentration region having a depth equal to or shallower than an interface of the lower layer portion and the upper layer portion of the drift layer;
• a source electrode electrically connected to the base region through the source region and the second conductivity type region;
• and
• a drain electrode disposed on a rear surface of the substrate,
• wherein the silicon carbide semiconductor device is provided with a semiconductor switching element with an inversion type trench gate structure in which an inversion type channel region is formed on a surface portion of the base region located on a side surface of the first trench by controlling an application voltage to the gate electrode to cause an electric current between the source electrode and the drain electrode through the source region and the drift layer, and a super junction structure is provided by alternately arranged P and N columns that are provided by the first low concentration region and the lower layer portion of the drift layer opposing to the first low concentration region, and
• wherein each of the upper layer portion, lower layer portion first high concentration region and first low concentration region has a uniform dopant concentration.