0.5 μm Device Processing with Excimer Laser-Based Lithography

The potential of optical lithography for production of VLSI circuits with design rules below 0.5 μm has been demonstrated by the performance of a first generation laser-based deep ultraviolet wafer stepper. The system, which has been described previously, consists of a fused silica reduction lens and illumination optics and a KrF excimer laser retrofitted to a commercial production tool [1-3]. It operates at a wavelength of 248 nm with a numerical aperture which is variable from 0.20 to 0.38. Resolution of 0.5 μm lines and spaces and 0.5 μm windows is routinely obtained over a 14.5 mm field, while 0.35 μm lines and spaces are obtained under laboratory conditions. The system is currently in a pilot production line, where it is being used to develop submicron processing, as well as fabricate devices with 0.5 μm design rules. This paper will describe the system, present results of resolution studies and processing applications, discuss the problems associated with laser-based lithography, and discuss the application of optical lithography to production of submicron circuits.