A method for manufacturing a semiconductor device includes the steps of: loading a substrate into a reaction chamber; supplying reactive gases into the reaction chamber and processing the substrate; and unloading the processed substrate from the reaction chamber, wherein the step of processing the substrate includes: a first film formation step of setting the substrate to a first temperature and forming a first silicon film including impurity atoms on the substrate and a second film formation step of setting the substrate to a second temperature, which is lower than the first temperature, and forming a second silicon film that includes no impurity atoms or has an impurity concentration lower than that of the first silicon film on at least the first silicon film.