A method of cleaning a collector of an extreme ultraviolet light source system includes introducing the collector separated from the extreme ultraviolet light source system into a chamber; capturing an optical image of a reflective surface of the collector; measuring a contamination level of the reflective surface by comparing the optical image with a prestored standard image; performing a first cleaning operation if the contamination level exceeds a preset first reference value, the first cleaning operation including cleaning the reflective surface by spraying dry ice particles onto the reflective surface; and performing a second cleaning operation if the contamination level is less than or equal to the preset first reference value. The second cleaning operation includes cleaning the reflective surface by radiating atmospheric plasma onto the reflective surface and measuring a microcontamination level and a damage level of the reflective surface.