Effects of Absorption on Resist Performance in Soft X-Ray Projection Lithography

Abstract

Projection x-ray lithography has been proposed as a possible candidate for the delineation of integrated circuit features below 0.25µm (1). Recently it was demonstrated that near diffraction limited imaging could be achieved at several soft x-ray wavelengths (2) (3). Using 0.06pm thick films of PMMA, features of 0.2µm nd 0.1µm were printed at 37.5 and 14nm respectively. Figure 1 shows a scanning electron micrograph of these features. Note that the resist sidewalls exposed at 14nm are significantly more vertical than those printed at 37.5nm. The purpose of this work is to investigate the reasons for this difference by developing a simulation tool that would accurately model resist profiles in the soft x-ray regime (5 to 40nm).