Abstract

High resolution soft-x-ray projection images are recorded by using a laser plasma source (LPS) and multilayer coated optics. Soft x-rays are generated by focusing a KrF excimer laser beam on a moving gold target. The resulting 15-eV plasma emits an intense burst of soft x-rays from a spot 150 μm in diameter. The soft x-rays are collected by an off-axis ellipsoidal condenser to illuminate a transmission mask composed of a germanium absorber supported by a silicon membrane. A magnified image of the LPS is projected by the condenser into the entrance pupil of the imaging objective to provide Kohler illumination of the mask. The imaging objective is a 20× reduction Schwarzschild having a numerical aperture of 0.08 and operating at a wavelength of 14 nm. Features as small as 0.1 μm have been recorded in polymethylmethacrylate (PMMA). A second-generation system is being fabricated based on a 10× Schwarzschild objective and a near-on-axis ellipsoidal condenser. This system is designed to image a reflecting mask onto a resist-coated wafer.

© 1992 Optical Society of America