US Patent 7789965 Method of cleaning UV irradiation chamber

A method of cleaning a UV irradiation chamber includes steps of: (i) after completion of irradiating a substrate with UV light transmitted through an optical transmitted window provided in the UV irradiation chamber, generating radical species of a cleaning gas outside the UV irradiation chamber; and (ii) introducing the radical species from the outside of the UV irradiation chamber into the UV irradiation chamber, thereby cleaning the optical transmitted window.