Understanding Acid Reaction and Diffusion in Chemically Amplified Photoresists: An Approach at the Molecular Level

Acid diffusion in chemically amplified resist might limit the ultimate minimum half-pitch that can be achieved with high sensitivity resists unless diffusion length is reduced until new methods of sensitizing resists are found. Precise knowledge of molecular dynamics of resist materials and advanced techniques need to be developed actively for this issue. In this sense, computer simulations have become a valuable tool in terms of reducing time and costs. However, simulations are generally based on continuum or mesoscale models, which are unable to accurately predict variations at the molecular level. Deeper understanding and investigation of the coupled reaction-diffusion kinetics at the molecular scale during the postexposure bake (PEB) become crucial to achieve nanoscale features with good critical dimension control and good line-edge roughness. In this work we have developed a molecular level approach for understanding of the coupled acid-catalyzed diffusion process in chemically amplified resist systems. Here, the molecules of photoacid generator are selected as the building blocks of a three-dimensional grid. Reaction and diffusion of the photoconverted acid molecules during the PEB step will produce resist volumes of cleaved polymers. After a certain PEB time τ, these created volumes produced by adjacent acids will almost contact each other, enabling the subsequent development of the polymer. We also determine this parameter τ by means of experiments with real resist systems and investigate the influence of the process conditions on it.