Abstract: A substrate processing method includes the steps of removing carbon from a surface of a silicon substrate by irradiating an ultraviolet light on the surface in an essentially ultraviolet nonreactive gas atmosphere and forming an oxide film or an oxynitride film on the surface of the silicon substrate by irradiating an ultraviolet light thereon in an essentially ultraviolet reactive gas atmosphere. Further, a computer readable storage medium stores therein a program for controlling the substrate processing method.