Evaluation of Plasma Ashing Damages on Porous SiOCH Films by Measurement of H and N Radical Densities

The damage free plasma processes for Low dielectric constant (low-k) films are required for next generation ULSIs devices. Measurement of the radical densities which have a large impact on the damage generation in low-k film is important for clarification of plasma damage mechanism. We built up an \textit{in situ} measuring system to evaluate the properties of low-k films and behavior of radicals. H$_{2}$/N$_{2}$ ashing plasma damages on porous SiOCH films have been investigated. The surface reactions were measured by using \textit{in situ} Fourier transform infrared reflection absorption spectroscopy and spectroscopic ellipsometry. The H and N radical densities were measured by vacuum ultraviolet absorption spectroscopy. When the flow rate ratios of H$_{2}$/(H$_{2}$+N$_{2})$ for the plasma ashing were changed, the variation of damaged layer thickness agreed well with the H radical density in the plasma. From these result, damages on the porous SiOCH are probably determined by chemical reactions of H radicals which reduce the Si-CH$_{3}$ bonds and N radicals which have an effect of inhibition of the damages.