Dependency analysis of line edge roughness in electron-beam lithography

• Behaviors of LER caused by the stochastic exposure have been analyzed.
• LER decreases from the inside of a feature to the outside.
• LER is smaller for a higher beam energy, a higher dose, or a thinner resist.
• LER is smaller for a smaller exposing interval, or an upper layer of the resist.
• Shot noise has less effect on LER for a higher dose or an upper layer of resist.

The line edge roughness (LER) has become one of the critical issues which affect the minimum feature size and the maximum circuit density realizable in most lithographic processes. Since the LER does not scale with the feature size, it needs to be minimized as the feature size is reduced well below 100 nm. One of the main factors contributing to the LER is the stochastic fluctuation of exposure. In the past, most of the LER researches were based on a 2-D model without considering the resist depth dimension. In this study, the dependency of the LER, caused by the stochastic fluctuation of exposure due to electron scattering in the resist and the shot noise due to variation of electron influx, on lithographic parameters such as shot noise, beam energy, exposing interval, dose, etc., has been investigated with a 3-D model, as the first step toward developing an effective method for minimizing the LER. In the case of CAR, the effect of developing process on LER is also considered. In this paper, the results from an extensive simulation are reported with a detailed discussion.

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