Substrate with silicon carbide film, semiconductor device, and method for producing substrate with silicon carbide film

A substrate with a silicon carbide film includes a silicon substrate, a SiC film, and a mask 4. The SiC film has a film 31 including openings 35 on the silicon substrate and a film 32 provided on the upper side of the film 31. The mask 4 has a mask 41 provided on the upper side of the silicon substrate and including openings 45 and a mask 42 covering at least part of the mask 41 located in the openings 35 and the side surfaces of the openings 35 and including openings 46. The width W1 of the opening 45, the thickness T1 (μm) of the mask 41, and the thickness D (μm) of the film 31 at a position corresponding to the opening 45 satisfy the following relationships: T1