Printability of substrate and absorber defects on extreme ultraviolet lithographic masks

摘要

This paper reports results from a study of defect printability for extreme ultraviolet lithographic masks (EUVL). Imaging experiments were performed with an EUVL mask containing programmed defects. The mask contained defects of different sizes and locations with respect to the absorber patterns. Since an EUVL mask consists of absorber layer patterned above a multilayer-coated substrate, both substrate defects, located below the reflective coating, and absorber defects, located above the reflective coating, were included on the programmed defect mask. The absorber layer was patterned using a process previously described by Tennant et al. Imaging was performed using a 1OX Schwarzschild camera operating at 13.4 nm with a numerical aperture of 0.08, corresponding to a Rayleigh resolution of 0.1 gm. This system has an effective exposure field of 0.4 mm diameter. Both positive-tone and negative-tone resists were used. Measurements of the defect-induced linewidth variations on the printed resist lines were performed with scanning electron microscopy (SEM) and atomic force microscopy (AFM). Results show that substrate defects are more printable compared to defects of the same sizes located above the reflective coating. In addition, defects located in the center of a clear region in lines-and-space pattern are more printable compared to those located nearer to the absorber lines.