The challenges of 157 nm nanolithography: surface morphology of silicon-based copolymers

Lithography at 157 nm using F2 laser is the next step after 193 nm for ULSI fabrication with dimensions below 50 nm. However, there are problems related to the development of the 157 nm technology, the most important being the design of photoresists with suitable absorption at 157 nm and low outgassing. On the other hand, high-resolution capabilities of resist depend on the surface roughness and its modification following 157 nm illumination of the resist. In this communication, a copolymer of ethyl-polyhedral oligomeric silsesquioxane (ethyl-POSS) and tert-butyl methacrylate (TBMA) was evaluated for surface homogeneity, before and after exposure to 157 nm at different concentrations of the homopolymers. Surface roughness depends on the chemical composition of the resist, and atomic force microscope (AFM) images of exposed areas indicate accumulation of matter at the edge of the boundaries between exposed and non-exposed areas.