Abstract

An excimer laser-driven source of 13.9 nm radiation has been developed for use in an integrated soft x-ray projection lithography facility. The source consists of a 0.65J, 20 ns, 200 Hz KrF laser focussed down upon a high-Z target at intensities in the low 10¹¹ W/cm² range. The laser target consists of either a plating on a semi-infinite substrate or a metal film coated onto a thin plastic base. Extensive measurements have been made of x-ray yield by using absolutely calibrated x-ray diodes. These indicate a 1–1.5% conversion of incident laser light into a 4.5% band about 13.9 nm. Simulations of these experiments by using lasnex/xsn-u (a Lagrangian hydrodynamics code with average-atom radiation production and transport) accurately reproduce all measured parameters. We have been able to predict techniques for optimizing conversion efficiency based upon laser intensity, pulse width, and target design. Projection lithography mandates the minimization of debris to protect multilayer-coated collection optics. This concern has been addressed by the fabrication of a continuous-feed high-vacuum compatible, low-mass tape drive.

© 1992 Optical Society of America