Abstract: A first reactive gas is introduced into a vacuum chamber and a plasma of the thus introduced reactive gas is produced. A second reactive gas is introduced into a radical generating chamber and is dissociated to generate radicals whose density and composition are well controlled. Then, the thus generated radicals are injected into the plasma generated within the vacuum chamber such that an amount of a desired kind of radicals within the plasma is selectively increased or decreased. In this manner, a thin film having an excellent property can be deposited on a substrate placed in the vacuum chamber. Alternatively, a surface of a substrate placed in the vacuum chamber can be processed precisely and selectively.