Analysis of molecular diffusion in resist polymer films simulated by molecular dynamics

The diffusion process of acids plays important roles in chemically amplified resists. Polymer matrices form the diffusion path, and the structure significantly influences the behavior of the acid diffusion. We have simulated the diffusions of molecules in polymer matrices by molecular dynamics in order to analyze the diffusion mechanism in chemically amplified resist systems. To represent bulk state conditions of the polymer film, we prepared the molecular structures under the three-dimensional periodic boundary conditions utilizing the molecular simulation. This amorphous cell contained three chains of methacrylate polymers such as poly(methylmethacrylate), poly(tert-butylmethacrylate), poly(isobornylmethacrylate) and one diffusion molecule such as oxygen and methanesulfonic acid. The structure was energy-minimized and equilibrated under stable conditions. The free volumes in the system were estimated as. the volumes enclosed by the iso-potential surfaces around the polymer using the Gusev-Suter method. The average size of the free volumes in the poly(methylmethacrylate) system was obtained as 3.7 Angstrom(3) with large standard deviation of 11.1 Angstrom(3), which indicates the large width of the size-distribution of free volumes scattered at random iii the system. Molecular diffusion in the energy-minimized cell was simulated for 50 picoseconds by the molecular dynamics. The time dependence of the mean-square displacements of diffusing molecules was obtained from the dynamics treatments and it determined the diffusion constant in the resist systems. It is shown that the molecules do not always rapidly diffuse with larger free volumes, but the diffusions also depend upon the interaction with the polymer, and that the computer simulation tools provide the potential for the molecular level, study of resist chemistry.