Microlithographic projection exposure apparatus with immersion projection lens
View Patent ↗A microlithographic projection exposure apparatus includes an illumination system and a projection lens which images a reticle onto a photosensitive layer. The projection exposure apparatus further includes an immersion arrangement for introducing an immersion liquid into an immersion interspace between a last optical element of the projection lens on the image side and the photosensitive layer. A transmission filter is designed and arranged in the projection lens in such a way that rays which enter the immersion interspace from the last optical element at an angle of incidence α are attenuated more strongly the smaller the angle of incidence α is. The transmission filter may be arranged e.g. in a pupil plane of the projection lens and may have a transmittance which increases with increasing distance from an optical axis of the projection lens. In this way compensation is provided for angle-dependent absorption in the immersion liquid.
1. A microlithographic projection exposure apparatus, comprising:
a) an illumination system for generating projection light;
b) a projection lens for imaging a reticle arranged in an object plane of the projection lens onto a photosensitive layer, which is arranged in an image plane of the projection lens and is applied to a carrier, said projection lens comprising a last optical element on the image side;
c) an immersion arrangement for introducing an immersion liquid into an immersion interspace formed between the last optical element and the photosensitive layer; and
d) a transmission filter which is designed and arranged in the projection lens in such a way that all rays, which leave the last optical element and enter the immersion interspace at an angle of incidence α, are attenuated more strongly the smaller the angle of incidence α is.
2. The apparatus of claim 1 , wherein the transmission filter is arranged at least approximately in a field plane of the projection lens and has an angle-dependent transmittance which increases with increasing ray angles with respect to an optical axis of the projection lens.
3. The apparatus of claim 1 , wherein the transmission filter is arranged at least approximately in a pupil plane of the projection lens, and wherein the transmission filter has a transmittance distribution which is rotationally symmetrical with respect to an optical axis of the projection lens.
4. The apparatus of claim 1 , wherein the transmission filter attenuates rays of projection light in such a way that for all occurring angles of incidence α the rays have substantially the same radiation intensity when impinging on the photosensitive layer.
5. The apparatus of claim 1 , wherein the dependence of attenuation on the angle of incidence α is given by a transmission function T(α) which depends on an absorption constant k of the immersion liquid and on a distance d between the last optical element of the projection lens on the image side and the photosensitive layer.
6. The apparatus of claim 5 , wherein the transmission function T(α) is at least approximately given by
T (α)= T 0 exp( −kd /cos(α)),
where T 0 is a constant.
7. The apparatus of claim 6 , wherein the constant T 0 is at least approximately given by
T 0 =exp(− kd /cos(α max )),
where α max is a maximum angle of incidence at which rays enter the immersion interspace.
8. A microlithographic projection exposure apparatus, comprising:
an illumination system for generating projection light;
a projection lens for imaging a reticle arranged in an object plane of the projection lens onto a photosensitive layer, which is arranged in an image plane of the projection lens and is applied to a carrier, said projection lens having an optical axis and comprising a last optical element on the image side;
an immersion arrangement for introducing an immersion liquid into an immersion interspace formed between the last optical element and the photosensitive layer; and
a transmission filter which is arranged at least approximately in a pupil plane of the projection lens and has a transmittance that increases with increasing distance from an optical axis of the projection lens, so that all rays, which leave the last optical element and enter the immersion interspace at an angle of incidence α, are attenuated more strongly the smaller the angle of incidence α is.
9. The apparatus of claim 8 , wherein the transmission filter has a transmittance distribution which is rotationally symmetrical with respect to the optical axis of the projection lens.
10. A microlithographic projection exposure apparatus, comprising:
a) an illumination system for generating projection light;
b) a projection lens for imaging a reticle arranged in an object plane of the projection lens onto a photosensitive layer, which is arranged in an image plane of the projection lens and is applied to a carrier, said projection lens comprising a last optical element on the image side;
c) an immersion arrangement for introducing an immersion liquid into an immersion interspace formed between the last optical element and the photosensitive layer; and
d) a transmission filter which is arranged at least approximately in a field plane of the projection lens and has an angle-dependent transmittance which increases with increasing ray angles with respect to an optical axis of the projection lens, so that all rays, which leave the last optical element and enter the immersion interspace at an angle of incidence α, are attenuated more strongly the smaller the angle of incidence α is.