Abstract

Soft x-ray projection lithography is currently under development for future semiconductor circuits with features less than 0.2 µm. These projection systems are designed to operate with narrow bandwidths around 130 Å, where the highest reflectivity mirrors have been demonstrated.¹ Several possible sources are under consideration. The laser-produced plasma is an attractive choice provided sufficient light can be generated in the bandwidth of interest. However, only limited experiments have previously been done in the operating region for soft x-ray projection lithography.² In this work, a systematic study was undertaken to provide a comprehensive soft x-ray database for laser plasma lithographic sources. We determined the absolute conversion efficiency from laser light into x-rays for various target materials, laser wavelength, pulse length, incident intensity, and spot size. Measured conversion efficiencies for Sn targets of greater than 1% into a 3 Å bandwidth at 130 Å meet the necessary system requirements.

© 1993 Optical Society of America