Applications of molecular modeling in nanolithography

The design of resist materials capable of resolution below 100 nm requires a fundamental understanding of the chemical and physical processes that occ ur at length scales comparable to the dimensions of individual molecules. A t these length scales, the thermophysical properties of photoresist films a re different from those of the bulk; molecular simulations provide a useful tool to study the behavior of these materials at the molecular level, ther eby providing much needed insights into phenomena that are difficult to cha racterize experimentally. In our group we have developed and implemented mo lecular based simulations to study materials for nanolithography at various levels of detail. At the chemically detailed, atomistic level, molecular d ynamics techniques are used to determine specific effects arising from the molecular architecture of the resist components. In these systems, we explo re the intra- and intermolecular structure of the resist resin polymer. The chemical architecture of the resin influences the extent of hydrogen bondi ng throughout the resist, leading to differences between the diffusivity of water within each of the resins. At a more coarse-grained level, discontin uous molecular dynamics methods are employed to simulate entire resist film s modeled as collections of atoms lumped into single interaction sites. Whi le these models lose atomic resolution, the system sizes that can be invest igated are two orders of magnitude larger than those studied at the atomist ic level. This allows for the modeling of properties of entire photoresist films. We apply these calculations to investigate how the glass transition temperature changes at small film thickness (e.g., below 100 nm), and to in vestigate how the Young's modulus of a developed photoresist feature is inf luenced by its dimensions. Our findings have important implications for the problem of feature collapse. (C) 1999 American Vacuum Society. [S0734-211X (99)13306-7].