Abstract: In a lithographic projection system, the radiation energy delivered to the substrate needs to be accurately controlled. Attenuation by injecting an absorbent gas into a volume through which the radiation passes is a convenient way to control the energy. Additionally, the interaction between gasses and the radiation may be used to measure the energy of the radiation with minimal disruption to the radiation.

Abstract: In-situ cleaning of optical components for use in a lithographic projection apparatus can be carried out by irradiating a space within the apparatus containing the optical component with UV or EUV radiation having a wavelength of less than 250 nm, in the presence of molecular oxygen. Generally, the space will be purged with an ozoneless purge gas which contains a small amount of molecular oxygen in addition to the usual purge gas composition. The technique can also be used in an evacuated space by introducing a low pressure of molecular oxygen into the space.

Abstract: In-situ cleaning of optical components for use in a lithographic projection apparatus can be carried out by irradiating a space within the apparatus containing the optical component with UV or EUV radiation having a wavelength of less than 250 nm, in the presence of molecular oxygen. Generally, the space will be purged with an ozoneless purge gas which contains a small amount of molecular oxygen in addition to the usual purge gas composition. The technique can also be used in an evacuated space by introducing a low pressure of molecular oxygen into the space.

Abstract: Cleaning of optical components for use in a lithographic projection apparatus can be carried out by irradiating a space within the apparatus containing the optical component with UV or EUV radiation having a wavelength of less than 250 nm, in the presence of an oxygen-containing species selected from water, nitrogen oxide and oxygen-containing hydrocarbons. Generally, the space will be purged with an ozone-less purge gas which contains a small amount of the oxygen-containing species in addition to the usual purge gas composition. The technique can also be used in an evacuated space by introducing a low pressure of the oxygen-containing species into the space.

Abstract: 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.

Abstract: In a system for flushing at least one internal space of an objective, in particular an exposure projection objective for semiconductor lithography, flushing is performed by mixing at least two inert gasses in such a way that the refractive index resulting therefrom corresponds at least approximately to the refractive index of air.

Abstract: Pre-cleaning or in situ cleaning of optical components for use in a lithographic projection apparatus can be carried out by irradiating the optical component with microwave and/or infra-red radiation, preferably infra-red radiation having a wavelength or a range of wavelengths in the range of from 1000 cm−1 to 4600 cm−1. This technique may be suitable for cleaning a mask. By monitoring the absorption of microwave and/or infra-red radiation directed at a contaminated optical component, the degree of contamination of said component can be qualified. This method may also be suitable for reducing the partial pressure of water in EUV apparatus.

Abstract: 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.