Line edge roughness of a latent image in post-optical lithography

The progress of electronic devices has been supported by advances in 'top-down' nanotechnology, namely lithography, which reached a scale of 90 nm on the mass production stage in 2005. The energy of the exposure source would exceed the ionization potential of the resist materials at the 32 nm scale with the deployment of extreme ultraviolet (EUV) light or an electron beam (EB). Among the issues of nanoscale fabrication with chemically amplified (CA) resists, line edge roughness (LER) is the most serious concern. Here, we report a Monte Carlo simulation of a latent image LER caused by ionization, in terms of proton dynamics, acid diffusion, and the effect of amine additives. The minimum LER (defined as three times the standard deviation) after post-exposure baking was ∼9.5 nm for a 5 µC cm(-2) exposure dose with 0.5 wt% amine. Although the deployment of a high-energy exposure source is the only method that allows further miniaturization after ArF immersion lithography, the acid generation mechanism, clarified for the first time in this paper, will emerge as a critical factor in limiting the availability of post-optical lithography.