Recent studies have shown that the semiconductor industry is seeking the possibility of utilizing both positive tone
photoresist development (PTD) and negative tone photoresist development (NTD) to pursue ultimate pattern resolution.
In particular, a minimal line edge roughness (LER) is one of the key performance indicators. Our current work is aimed
at studying mechanisms of LER generation by simulating dynamics of polymer molecules in NTD using a meso-scale
simulation technique called Dissipative Particle Dynamics (DPD). In DPD method, several neighboring monomers in a
polymer chain are represented by one DPD particle with soft interaction potentials to accelerate calculation of polymer
dynamics. In our previous studies, we performed virtual lithography experiments to study the molecular level polymer
configuration, and investigated the polymer dissolution rate and the resulting LER generation. In the current work, in
order to make this simulation method more practical for resist polymer design, we develop a method to tune the model
parameters by calibrating to the experimental data obtained by development of actual resist polymers.
The diffusion process of acids plays important roles in chemically amplified resists. Polymer matrices form diffusion paths and the structure significantly influences the behavior of 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 the bulk-state conditions of the polymer film, the molecular structures were prepared under the three-dimensional periodic boundary conditions utilizing the molecular simulation software, Insight II and Discover from Molecular Simulations, Inc. This amorphous cell contained three chains of methacrylate polymers such as poly(methylmethacrylate), PMMA, poly(tert-butylmethacrylate), PtBuMA, poly(isobornylmethacrylate), PIBMA and poly(adamantylmethacrylate), PAdMA and one diffusion molecule, methanesulfonic acid, MSA. The free volumes in the system were also estimated as the volumes enclosed by the isopotential surfaces around the polymer. Molecular diffusion in the energy-minimized cell was simulated for 50 picoseconds by the molecular dynamics to determine the diffusion coefficient in the resist systems. The temperature dependence of the diffusion coefficient was studied. The flexible polymers such as PMMA and PtBuMA showed a lower activation-energy value than the rigid polymers such as PIBMA and PAdMA. It was also shown that the molecules did not always rapidly diffuse with larger free volumes, but the diffusions also depended upon the interaction with the polymer.
It is generally known that a highly transparent ArF resists is preferable for the bottom ARC process to maintain the vertical sidewall of resist patterns. Therefore we developed some transparent resists with a low concentration of photo acid generator. However, our careful analysis clarified that the completely transparent resist caused a serious deterioration of the exposure-defocus (E-D) process window. Therefore, there should be an optimum transparency in the ArF resists. Our experiment clarified that the medium transparency resists had the largest E-D process window. This resist produced 120 nm nested lines using an ArF stepper without any resolution enhancement technique.
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