Silicon carbide epitaxial substrate and method for manufacturing silicon carbide semiconductor device

A silicon carbide epitaxial substrate comprising:

• a silicon carbide single crystal substrate having a first main surface;
• and
• a silicon carbide layer on the first main surface,
• the silicon carbide layer including a second main surface opposite to a surface of the silicon carbide layer in contact with the silicon carbide single crystal substrate,
• the second main surface corresponding to a plane inclined by more than or equal to 0.5° and less than or equal to 8° relative to a (0001) plane,
• the second main surface having a maximum diameter of more than or equal to 100 mm,
• the silicon carbide layer having a polytype of 4H-SiC,
• the silicon carbide layer having n type conductivity,
• the second main surface having an outer circumferential region and a central region, the outer circumferential region being within 3 mm from an outer edge of the second main surface, the central region being surrounded by the outer circumferential region,
• in a direction parallel to the central region, a ratio of a standard deviation of a carrier concentration of the silicon carbide layer to an average value of the carrier concentration of the silicon carbide layer being less than 5%,
• the average value of the carrier concentration being more than or equal to 1×1014 cm−3 and less than or equal to 5×1016 cm−3,
• in the direction parallel to the central region, a ratio of a standard deviation of a thickness of the silicon carbide layer to an average value of the thickness of the silicon carbide layer being less than 5%,
• the central region having an arithmetic mean roughness (Sa) of less than or equal to 1 nm,
• pits originated from threading screw dislocations are in the central region,
• when viewed in a direction perpendicular to the central region, each of the pits has a planar shape including a first side and a second side, the first side extending in a first direction, the second side extending in a second direction perpendicular to the first direction, and
• a width of the first side is twice or more as large as a width of the second side.