Patent ID: 6992753

Claim:
A projection exposure apparatus comprising: an illumination optical system including a light source for illuminating a patterning structure; a projection optical system for projecting an image of the illuminated patterning structure onto a substrate; the illumination optical system and the projection optical system each comprising a plurality of lenses; wherein each of the lenses has a maximum design fluence value associated therewith, the maximum design fluence value representing a predetermined expected maximum fluence that the respective lens will be exposed to during a standard mode of operation of the projection exposure apparatus; at least one lens being made of a lens material selected from a first group of lens materials wherein, after exposure to a given number of pulses of radiation of a given pulse length, each lens material of the first group has a characteristic transition point representative of a fluence value, wherein each lens material of the first group will have rarefied after exposure to the given number of pulses of radiation of the given pulse length having any fluence value below its transition point, and wherein each lens material of the first group will have densified after exposure to the given number of pulses of radiation of the given pulse length having any fluence value above its transition point; and wherein the transition point of each lens material of the first group satisfies the following condition: T RC <0.8 ·H D wherein T RC represents the transition point of the respective lens material, H D represents the design fluence value of the respective lens, and wherein at least one lens is made of a first fused silica material comprised in the first group of lens materials, wherein a transmittance of the first fused silica material obeys the relationship T= 10 −(k o +k ind )·l with T denoting the transmittance, k 0 being an absorption coefficient of the first fused silica material before exposure to light of a wavelength of 193.4 nm, k 0 +k ind being a total absorption coefficient after the first fused silica material has been exposed to 160 million pulses of radiation having a fluence of 5 mJ/cm 2 and a wavelength of 193.4 nm, and l being a length of a path of light through the first fused silica material, and wherein the following condition is fulfilled: k ind <10 −3 cm −1 .