Deep-UV wafer stepper with through-the-lens wafer to reticle alignment

Abstract

A new excimer laser stepper at 248 nm wavelength Is described wilti an all quartz 5x reduction lens with NA 0. 42 and 21 . 2 mm field size. Design aspects and experimental data are reported. A key feature of the system is a ilL alignment system with direct referencing of reticle to wafer operating at 633 nm The problem of the large focal plane difference beiween exposure and alignment wavelength is solved by special correcflon oplics in the lens. The introducflon of exclmer lasers as new light sources for produclion optical lithography has been facilitated by a flexible optical interface beiween laser and stepper and by an on line calibrafion system to control the laser wavelength. Experimental results for resolution and overlay performance are gtven. 1 .