Silicon carbide semiconductor device and method for manufacturing same

A silicon carbide semiconductor device comprising:

• a substrate with a principal surface;
• a silicon carbide layer which is arranged on a side of the principal surface of the substrate and which includes a first impurity region of a first conductivity type;
• a trench which is arranged in the silicon carbide layer and which has a bottom located in the first impurity region;
• a trench bottom impurity layer which is arranged in the trench to contact with at least a portion of the bottom of the trench and which is a silicon carbide epitaxial layer of a second conductivity type;
• a gate insulating film which covers a side surface of the trench and the trench bottom impurity layer;
• and
• a gate electrode which is arranged over at least a portion of the gate insulating film, the portion of the gate insulating film being located in the trench,
• wherein the trench bottom impurity layer is arranged to cover the bottom of the trench entirely and is in contact with a portion of the side surface of the trench,
• wherein the trench bottom impurity layer has a concave upper surface, and
• wherein the density of dislocations which extend in the trench bottom impurity layer in its growing direction from the lower surface toward the upper surface of the trench bottom impurity layer is higher than the density of dislocations which extend in the first impurity region in a growing direction of the silicon carbide layer.

A method for fabricating a silicon carbide semiconductor device, the method comprising:

• (A) providing a substrate having a silicon carbide layer including a first impurity region of a first conductivity type, the silicon carbide layer being arranged on a side of a principal surface of the substrate;
• (B) forming a trench in the silicon carbide layer, a bottom of the trench being located in the first impurity region;
• (C) forming a stack including a silicon film and an aluminum film on at least a portion of the bottom of the trench;
• (D) conducting a heat treatment within a gas including carbon and allowing silicon and aluminum in the stack to react with the carbon, thereby forming a trench bottom impurity layer, which is a silicon carbide epitaxial layer of a second conductivity type, on at least the portion of the bottom of the trench;
• (E) forming a gate insulating film on a side surface of the trench and on the trench bottom impurity layer;
• and
• (F) forming a gate electrode on at least a portion of the gate insulating film, the portion of the gate insulating film being located in the trench,
• the method further comprising, between the steps (B) and (C), the step of forming a protective film which is arranged on the side surface of the trench and which exposes the bottom of the trench at least partially,
• wherein in the step (C), the stack is formed on a portion of the bottom of the trench which is exposed by the protective film and on the protective film,
• in the step (D), a portion of the stack which is located on the protective film remains unreacted with the carbon, and
• the method further includes, between the steps (D) and (E), the step of removing the portion of the stack that remains unreacted with the carbon and the protective film.

A method for fabricating a silicon carbide semiconductor device, the method comprising:

• (A) providing a substrate having a silicon carbide layer including a first impurity region of a first conductivity type, the silicon carbide layer being arranged on a side of a principal surface of the substrate;
• (B) forming a trench in the silicon carbide layer, a bottom of the trench being located in the first impurity region;
• (C) forming a stack including a silicon film and an aluminum film on at least a portion of the bottom of the trench;
• (D) conducting a heat treatment within a gas including carbon and allowing silicon and aluminum in the stack to react with the carbon, thereby forming a trench bottom impurity layer, which is a silicon carbide epitaxial layer of a second conductivity type, on at least the portion of the bottom of the trench;
• (E) forming a gate insulating film on a side surface of the trench and on the trench bottom impurity layer;
• and
• (F) forming a gate electrode on at least a portion of the gate insulating film, the portion of the gate insulating film being located in the trench,
• wherein the step (C) includes forming the stack on the bottom of the trench and side surface, and
• the method includes, between the steps (C) and (D), the steps of:
• forming a mask to cover a portion of the stack which is located on the bottom of the trench;
• and
• removing a portion of the aluminum film by etching using the mask.