Silicon carbide substrate production method and silicon carbide substrate

A method for producing a silicon carbide substrate, comprising steps of:

• providing covering layers each containing silicon oxide, silicon nitride, silicon carbonitride or silicide on both surfaces of a base substrate made of carbon, silicon or silicon carbide to prepare a support substrate having the covering layers each with a smooth surface that has an arithmetic mean roughness Ra of 0.3 nm or less;
• forming polycrystalline silicon carbide films on both surfaces, each being the smooth surface of a corresponding one of the covering layers, of the support substrate by a vapor deposition method or a liquid phase growth method;
• and
• chemically removing at least the covering layers in the support substrate to separate the polycrystalline silicon carbide films from the support substrate such that a newly exposed, uncovered surface of each polycrystalline silicon carbide film, which has been in contact with the smooth surface of the corresponding one of the covering layers, has an arithmetic mean roughness Ra of 0.3 nm or less, and obtaining the polycrystalline silicon carbide films as silicon carbide substrates each having a crystal grain size of 10 nm or more and 10 μm or less, and an arithmetic mean roughness Ra of at least one of its main surfaces, being the newly exposed, uncovered surface, of 0.3 nm or less.