Laser Plasmas As X-Ray Sources For Lithographic Imaging Of Submicron Structures

Laser radiation can be used efficiently to generate X rays for lithographic imaging of submicron patterns, e.g. for VLSI device fabrication. Due to their short wavelength and high average power, excimer lasers show much potential for this application. Results are presented of scaling studies for high repetition rate excimer laser application, using the frequency doubled output of a low repetition rate Nd:YAG/Glass laser. Spectral and spatial characteristics of X-ray emission of the laser plasma are shown. The power density in the laser focus was 3x1012 W/cm2. With this source Si X-ray masks with submicron Au absorber profiles are imaged into high sensitivity X-ray photoresist. For the exposures 80 lasershots sufficed to yield high quality submicron structures. Extrapolation of the results to a high power excimer laser reduces the exposure time of the photoresists to several seconds, enabling a wafer throughput at an industrial level.