Lithographic importance of base diffusion in chemically amplified photoresists

Mesoscopic (i.e., discrete and stochastic) models are applied to study the impact of photoresist processing and material conditions on process performance. The modeling approach includes all exposure, post-exposure bake, and development related parameters for chemically amplified resists. Resist process performance is evaluated in terms of required exposure dose (i.e., sensitivity), dose latitude (i.e., resolution), and line-edge roughness (LER). There exists a well-known trade-off between sensitivity, resolution, and LER. Theoretical models have concluded that optimization of any one or two of these properties go at the expense of the other properties. This paper shows that the effects of base diffusion, which have not been taken into account in previous studies, allow a simultaneous improvement of photoresist sensitivity, resolution, and LER. A putative explanation is given about the mechanism how the coupled diffusion of acid and base can allow a simultaneous improvement of all three process properties.