Exploring the limitations of x-ray reflectivity as a critical dimension pattern shape metrology

Abstract

Specular X-ray reflectivity (SXR) can be used, in the limit of the effective medium approximation (EMA), as a highresolution shape metrology for periodic and irregular patterns on a smooth substrate. The EMA defines as that the density of the solid pattern and the space separating the patterns are averaged together. In this limit the density profile as a function of pattern height obtained by SXR can be used to extract quantitative information on the cross-sectional pattern profile. Here we explore the limitations of SXR as a pattern shape metrology by studying diblock copolymer films with irregularly shaped bicontinuous terraces on quantized flat layers alternating with two polymer blocks. We conclude that SXR can be extended to irregular shaped patterns encountered in current electronic devices as long as average lateral length scale is smaller than coherence length of X-ray source. The detailed cross-sectional profiles of irregular patterns are discussed along with atomic force microscope results.