The diffusion of molecules in polymer matrices was simulated using molecular dynamics in order to analyze the diffusion mechanism in chemically amplified resist systems. To represent bulk state conditions of the polymer film, molecular structures under three-dimensional periodic boundary conditions were prepared. This amorphous cell contained three chains of methacrylate polymers and one diffusing 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 polymethylmethacrylate system was obtained as 3.7Å3 with large standard deviation of 11.1Å3, which indicated the large width of the size-distribution of free volumes scattered at random in the system. Molecular diffusion in the energy-minimized cell was simulated for 50ps 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 was shown that the molecules did not always rapidly diffuse with larger free volumes, but the diffusions also depended upon the interaction with the polymer, and that the computer simulation tools provided the potential for the molecular level study of resist chemistry.

Analysis of Molecular Diffusion in Resist Polymer Films Simulated by Molecular Dynamics. Toriumi, M., Ohfuji, T., Endo, M., Morimoto, H.: Proceedings of SPIE , 1999, 3678[I], 368-79