Line top loss and line top roughness characterizations of EUV resists

Abstract

EUV resist characterizations for line and space patterning as a function of dose and illumination conditions for varying pitches down to 28 nm are discussed. The unintentional resist line top loss (LTL) after development has been monitored and analyzed for all experimental conditions. Furthermore, line top roughness (LTR) is introduced, which is a 3-3 stochastic metric characterizing in-plane roughness related to the top of the resist lines. The main characterization technique employed for this study is atomic force microscopy (AFM) with novel probing algorithms as well as novel tips with diameters down to 5 nm and aspect ratios of 10:1. Additionally, results acquired by critical dimension scanning electron microscopy and optical critical dimension scatterometry are presented. It was found that the unintentional LTL is resist-and pitch-dependent and can be higher than 9 nm at 16 nm half-pitch but does not correlate with line break defect density results. However, LTR measurements of small area scans at dense line/space pitches may be used to draw conclusions about line break defect densities and hence yield. The resist specific metrics, LTR and LTL, allow for fast and early-on evaluation of new chemical formulations and help to forecast pitch-and dose-dependent performance. Furthermore, the results can be used to improve resist model accuracy for optical proximity correction calculations.