Importance

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Abstract

In a projection exposure method, primary radiation having a center wavelength λ is generated and guided through an illumination system along an illumination path and through a projection system along a projection path. The center wavelength is varied within a wavelength variation range Δλ having a lower limit λ_MIN≦λ and an upper limit λ_MAX≧λ. A specific absorption coefficient k(λ) of at least one gaseous absorbent species selected from the group consisting of oxygen (O₂), ozone (O₃) and water vapor (H₂O) present in at least one gas-filled space along at least one of the illumination path and the projection path varies between a minimum absorption coefficient k_MIN and a maximum absorption coefficient k_MAX within the wavelength variation range such that an absorption ratio (k_MAX/k_MIN) exceeds 10. A concentration of the absorbent species within the gas-filled space is controlled such that an overall absorption variation effected by the absorbent species for all rays running along differing ray paths towards the image field is maintained below a predetermined absorption variation threshold value.

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First Claim