The invention is concerned with a filter system for a light source in a lithography process for the production of semiconductor devices with a flowing absorber gas for at least one wavelength (λ) in the range between 20 to 250 nm, the flowing absorber gas intersecting the light path emitted by the light source. Furthermore, the invention is concerned with a lithography apparatus for processing semiconductor substrates, the use of a filter system, a method for filtering light and a semiconductor device manufactured by the method.