In chemically amplified resists for extreme ultraviolet (EUV) and electron beam (EB) lithographies, the reaction
mechanism of acid generation is different from that for photolithography. However, details of acid generation are still
unclear. In particularly, details of the deprotonation dynamics of radical cations in solid resist films have not been
investigated. The dynamics of radical cations of resist polymer is important for understanding proton generation.
Poly(4-hydroxystyrene) (PHS) is a typical polymer for EUV and EB lithographies. We observed the dynamics of PHS radical cation in PHS film by using pulse radiolysis.
KEYWORDS: Line edge roughness, Monte Carlo methods, Diffusion, Lithography, Chemically amplified resists, Image processing, Electron beams, Extreme ultraviolet, Electron beam lithography, Extreme ultraviolet lithography
It is well-known that line edge roughness (LER) of patterned features in chemically amplified (CA) resists is formed in
the acid generation stage and expected to be moderated by the acid diffusion and development process. To provide an
insight into the limit of LER is essential for the realization of next-generation lithographies such as electron beam or
extreme ultraviolet. Based on the results of Monte Carlo simulation which reproduces dynamics of chemical
intermediates in positive-tone CA resist, we discuss the possibility of low LER (high frequency) after development. It is
found that low LER is achievable; however, the process condition is still strict.
KEYWORDS: Line edge roughness, Monte Carlo methods, Lithography, Molecules, Diffusion, Image enhancement, Electron beam lithography, Ionization, Electron beams, Polymers
Of great importance in post-optical lithographies, such as electron beam (EB) and extreme ultraviolet, is the improvement of line edge roughness or line width roughness of patterned resists. We provide an exposure dose dependence on LER of a latent image in chemically amplified EB resist from 1 to 50 µC/cm2. By using a Monte Carlo simulation and empirical equations, the effects of exposure dose and amine concentration on LER are investigated in terms of shot noise and image contrast. We make clear the correlation between LER and the fluctuation of the initial number of acid molecules generated in resists.
KEYWORDS: Line edge roughness, Diffusion, Polymers, Ionization, Chemically amplified resists, Line width roughness, Electron beams, Lithography, Optical lithography, Monte Carlo methods
Nanoscale resist topography such as line edge roughness (LER) or line width roughness (LWR) is the most serious concern in sub-100 nm fabrication. Although many factors have been reported to affect LER, the generation mechanism of LER is still unclear. It is well known that the slope of image contrast correlates to the degree of roughness. However, significant LER is sill observed in chemically amplified resists for electron beam (EB) lithography, which can produce a steeper slope of image contrast than photolithography. To make clear a cause of LER, the distribution of protons and counter anions generated in chemically amplified EB resists was investigated. It was found that counter anion distribution is significantly different from proton distribution. Counter anions are inhomogeneously distributed outside a relatively smooth edge of proton distribution. This is caused by the fact that acid generators can react with low energy (~ 0 eV) electrons. The inhomodeneous distribution of counter anions outside proton distribution is considered to contribute to LER formation in chemically amplified resists for EB lithography.
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