An extreme ultraviolet radiation source is provided, including a vessel, an optical collector, and a gas scrubber. The vessel has a gas inlet and a gas outlet. The optical collector is disposed within the vessel and configured to collect and reflect extreme ultraviolet light produced in the vessel. A cleaning gas is introduced into the vessel through the gas inlet to clean the surface of the optical collector. The gas scrubber is disposed within the vessel, arranged such that the cleaning gas leaves the vessel through the gas outlet after flowing through the gas scrubber. The gas scrubber has a number of gas passages to allow the cleaning gas to flow through, and the size of the gas passage close to the gas outlet is smaller than the size of the gas passage away from the gas outlet.