A method for manufacturing a thin film includes: applying a liquid to a surface of a processing target member having at least one of a trench and a concave portion. The liquid includes a solvent and at least one of fine particles of a metal, fine particles of a semiconductor, fine particles containing a metal oxide, and fine particles containing a semiconductor oxide. A first heat treatment is included for volatilizing the solvent of the liquid applied to the surface of the processing target member. The fine particles are remained on the surface of the processing target member. A second heat treatment is also included for heating the fine particles by using microwave irradiation. At least one of the trench and the concave portion is filled with the thin film containing the fine particles or a component of the fine particles.