3d modeling of LER transfer from the resist to the underlying substrate: the effect of the resist roughness

The line edge roughness transfer from the resist to the underlying substrate via plasma etching is studied with a 3d modeling framework. The framework includes the generation of 3d rough resist lines with predetermined roughness parameters [root mean square roughness (σ), correlation length (ξ), and roughness exponent]. The pattern transfer of the generated 3d lines to the substrate is captured by an abstractive geometric model: Plasma etching is considered anisotropic and the shadowing of the incident ions by the protrusions of the initial resist sidewall determines the roughness of the substrate sidewall. Shadowing is enough to induce the striations and the reduction of σ at the substrate sidewall. The effect of the sidewall roughness (σ and ξ) and shape (thickness and sidewall slope) of the initial resist line as well as the etching selectivity and etching depth on a) σ and b) the slope of the substrate sidewall is investigated. A linear relation between σ of the substrate and σ of the initial resist sidewalls is found, consistently with pertinent experimental studies. It is found that the reduction of σ is favored by a low correlation length of the initial resist sidewall and by thicker resist films. The decrease of σ of the initial resist sidewall, the increase of the etching selectivity, and the increase of the initial resist thickness favors a slope of the substrate sidewall closer to 90°. The slope of the initial resist sidewall affects the slope of the substrate sidewall only for low values of σ.

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