Acid diffusion length in contact hole imaging of chemically amplified extreme ultraviolet resists

Abstract

Contact holes and line-and-space patterns are the most basic elements in the fabrication of semiconductor devices. In this study, the chemical processes in contact hole imaging were investigated to clarify the optimum acid diffusion length in terms of the quality of latent images. The chemical processes were simulated using a Monte Carlo method based on the reaction mechanisms of chemically amplified extreme ultraviolet (EUV) resists. The theoretical dependence of the optimum acid diffusion length on the exposure dose and half-pitch (diameter) was clarified. At an exposure dose of 20 mJ cm−2, the optimum acid diffusion length (three-dimensional) was 10.7 nm for 28 nm contact holes (56 nm pitch). By decreasing the diameter to 16 nm (32 nm pitch), the optimum acid diffusion length (three-dimensional) was decreased to 8.9 nm, which was smaller than that of line-and-space patterns by 12%. The chemical reactions for the dissolution of resist polymers should be sufficiently induced within these acid diffusion lengths for contact hole imaging.