Photolithography at 193 nm

Abstract

Photolithography at 193 nm is a natural continuation of the progression from 436 to 365 to 248 nm in lithography, dictated by the requirement for continually higher resolution. It is anticipated that 193-nm lithography will enable 0.25-μm patterning in volume production with conventional masks, and 0.18-μm resolution with phase-shifting masks. The main issues related to lithography at this new wavelength are being addressed. It has been shown that highly transparent optical materials are available at 193 nm. Also, they are damaged by the laser radiation at a slow enough rate that high-quality projection optics are expected to perform within specifications for ten years of full-time operation. Consequently, a 193-nm step-and-scan system is being constructed, and it has been designed to attain 0.25-μm resolution over a 22 by 35 mm field. A range of 193-nm photoresist schemes has been demonstrated. They include semitransparent single-layer resists, positive-tone surface imaging (silylation), and negative-tone bilayers using ultrathin silicon-based polymers. In most instances we have demonstrated sub-0.25-μm resolution, high photosensitivity, good exposure–defocus latitude, and very low levels of etch residue. In sum, the first successful steps towards a fully engineered 193-nm photolithography have been taken, and no major obstacles are anticipated.