Patent ID: 7557996
Filing Date: 2009-07-07
Classification: G02B,G03F

Abstract:
1. A projection objective for imaging a pattern arranged in an object surface of the projection objective onto an image surface of the projection objective using ultraviolet radiation, the projection objective comprising: a plurality of optical elements including transparent optical elements transparent for radiation at an operating wavelength λ, where 260 nm>λ>150 nm; an image-side pupil surface being the pupil surface closest to the image surface; and an aperture-defining lens group arranged between the image-side pupil surface and the image surface for converging radiation coming from the image-side pupil surface towards the image surface to define an image-side numerical aperture NA, where 0.7≦NA≦1.4; wherein: the aperture-defining lens group comprises a high-index lens made from a transparent high-index material having a refractive index n the high-index material is a solid material, and the solid material is magnesium aluminum oxide (MgAl