Atmosphere in processing apparatus is adjusted to, for example, oxygen atmosphere, by gas supply source and the like. Interior of thermal processing apparatus is set to oxygen atmosphere and raised to predetermined temperature. A wafer boat containing wafer W having dielectric precursor layer formed is loaded into thermal processing apparatus at speed at which no defects are produced in wafer W. Thereafter, reaction tube of thermal processing apparatus has its internal temperature raised to baking temperature, to perform baking for predetermined time. The wafer W is cooled to predetermined temperature in thermal processing apparatus and then to room temperature in processing apparatus, and carried out from processing apparatus. Before dielectric precursor layer is baked, it is maintained for predetermined time at temperature higher than temperature at which solvent in dielectric precursor layer is volatilized and lower than temperature at which dielectric precursor layer starts crystallization to vaporize residual solvent.