Mechanism of radical control in capacitive RF plasma for ULSI processing

The radicals of capacitive plasmas actually used in mass production were analyzed using various measurement systems. The composition of radicals in bulk plasma depends on the gas chemistry, the dissociation process, and interaction with the wall. It is revealed that parent gas (C₄F₈) is dissociated by multiple collision with electrons according to τ · n_e〈συ〉, where τ is the residence time, n_e is the electron density, σ is the dissociation collision cross section and υ is the electron velocity. A high-performance etching process, which can realize 0.09 μmφ contact holes with aspect ratio of 11, was achieved using a short residence time to suppress the excess dissociation and the control of deposition species through the addition of O₂ to C₄F₈/Ar plasma as well as the reduction of the density of F radicals through the reaction with the Si wall.