| 摘要 |
A catadioptric projection optical system for use in photolithography used in manufacturing semiconductors having a quarter waveplate (12) following a reticle (10) and multiple aspheric surfaces and calcium fluoride lens elements. A quarter waveplate (12) following the reticle (10) eliminates asymmetry in reticle diffraction caused by polarized illumination. The use of additional aspheric surfaces reduces the number of lens elements and aids in reducing aberrations. Calcium fluoride elements are used in the lens group adjacent the wafer (50) to help minimize compaction. In one embodiment, only calcium fluoride material is used. The present invention provides a projection optics system having a numerical aperture of 0.75 for use with wavelengths in the 248, 193, and 157 nanometer range. The object and image locations are separated by a predetermined distance, making possible retrofitting of older optical systems. The present invention is particularly suited for use in semiconductor manufacturing and has improved imaging with less aberrations, particularly at shorter wavelengths. <IMAGE> |
