Lithographic methods of imaging in resist can be extended with the addition of immersion fluid. The higher index of refraction fluid can be used to print smaller features by increasing the numerical aperture beyond the limits of dry lithography. Alternately, an immersion optical system can achieve a larger depth of focus at the same numerical aperture as the equivalent dry lithography system. When numerical apertures are significantly greater than 1.0, polarization effects start to impact resolution seriously. Special illumination conditions will be used to extend resolution limits. Additional factors that affect imaging in resist need to be included if we are to achieve new resolution limits using high index of refraction materials to increase numerical apertures. In addition to material inhomogeneities, birefringence and optical surface effects, material absorption, coatings and index differences at boundaries will have a larger impact on image resolution as ray angles in the imaging system continue to increase with numerical aperture. Aerial and resist imaging effects that material characteristics have on polarization, uniformity and aberrations in the lens pupil will be studied.
展开▼
