Acid diffusion length limitation for 45 nm node attenuated and chromeless phase shift mask

Abstract

Microlithography has shown an amazing development over the last decade and has continued to be one of the critical success factors for enabling ever smaller feature sizes. The fabrication of leading edge devices strongly relies on the use of chemically amplified resist, where the post exposure bake (PEB) is among the most important process steps for obtaining smaller feature size with better linewidth control. PEB sensitivity is defined as the dependency of pattern size (or critical dimension, CD) variation on the perturbation of the PEB temperature and time throughout this paper. From the beginning of ArF (193 nm) lithography, PEB sensitivity becomes serious problem because ArF photoresist shows very severe dependency on PEB temperature and time. PEB sensitivity relies largely on photo-generated acid diffusion. If acid diffusion can be effectively controlled, PEB sensitivity will be improved. As pattern size decreases for a higher density device, this variation can be more than 10 % of target CD. Therefore, PEB sensitivity and diffusion length becomes very important property for sub-90 nm pattern. This paper demonstrates the effect of acid diffusion length for each PEB temperature and time for the mask types of attenuated and chromeless phase shift mask. Differences can between the attenuated and chromeless phase shift masks as functions of PEB temperature and time and develop time. We compared the acid diffusion lengths as a function of PEB time. And we calculated acid distribution as functions of PEB time and diffusion length. CD uniformity, thickness loss and exposure latitude are also compared.