Lithographic apparatus, device manufacturing method, and device manufactured thereby

摘要

In a lithographic projection system using exposure radiation of 157 nm, compositions of gas, e.g. levels of oxygen and water vapor, are measured in regions traversed by the projection beam. The attenuation caused by said gases is predicted and the dose of radiation accumulated during an exposure, the uniformity and angular distribution of radiation energy delivered by said projection beam to a substrate during an exposure is controlled accordingly. The control may comprise a controlled supply of O2 to a volume traversed by the projection beam so as to effect a controlled attenuation of the projection beam. The O2 distribution may be non-uniform, e.g. to selectively filter spatially separated diffraction orders or to eliminate non-uniformity's in the projection beam.