The tri-lateral challenge of resolution, photospeed, and LER: Scaling below 50nm? - art. no. 65190W

A simple analytical model for line-edge roughness in chemically amplified resists is derived from an accounting of stochastic fluctuations of photon ("shot noise") and acid number densities. Statistics from this counting exercise are applied to a region defined by the effective acid diffusion length; these statistics are then modulated by the slope of the image intensity to produce a value for LER. The model produces the familiar dependence of LER on aerial image (more specifically on latent image) and dose also seen in many other models and data. The model is then applied to the special case of interference imaging, for which the aerial image is a simple, known analytic function. The resulting expression is compared to experimental data at both relatively large half-pitches, shot with 257nm, and sub-50nm half-pitches shot with 13.5nm and hyper-NA 193nm. The model captures the primary scaling trends seen at the larger length scales, however at the sub-50nm problems arise. It appears that additional effects not covered by counting photons and acids are becoming increasingly important as length scales drop below about 50nm. These additional effects will require increased attention in order to improve LER in lockstep with diminishing CD and pitch.