Resist Surface Roughness Calculated using Theoretical Percolation Model.

One of the most probable causes for the surface roughness on resist patterns is the locally ununiform distribution of photochemical events. This ununiformity arises because the photochemical events occur with a probability density as a function of illumination. This inevitable roughness is estimated by applying the percolation theory in the evaluation of the cross-linking reactions in negative resists. The calculation demonstrates that nanometer-scale roughness is formed at the surface of resist, and is larger in a chemically amplified resist than that in a conventional resist. The surface morphology of chemically amplified resists exposed to X-rays is also experimentally evaluated using atomic force microscopy.