Optical CD metrology for directed self-assembly assisted contact hole shrink process

Abstract

Simulations of Mueller matrix spectroscopic ellipsometry (MMSE) based scatterometry are used to predict sensitivity to dimensional changes and defects in directed self-assembly (DSA) patterned contact hole structures fabricated with phase-separated polystyrene-b-polymethylmethacrylate (PS- b -PMMA) before and after etch. The optical signature of Mueller matrix (MM) elements has a complex dependence on the structure topography and orientation, depolarization, and optical properties of the materials associated with the surface and any underlying layers. Moreover, the symmetry properties associated with MM elements provide an excellent means of measuring and understanding the topography of periodic nanostructures. A forward problem approach to scatterometry or optical model based simulations is used to investigate MMSE sensitivity to various DSA based contact hole structures and its limits to characterize DSA induced defects such as hole placement inaccuracy, missing vias, profile inaccuracy of the PMMA cylinder, and process induced defects such as presence of residual PMMA after etching.