Deposited thin silicon-based films used for electronic devices as insulators in interconnections should have low and ultra low permittivity (ULK) to be acceptable to the future integration requirements, especially for the advanced technology (45 nm and below). Diffusion dielectric barrier should have also low permittivity to limit the increase of the effective global constant and should be also acceptable for etch selectivity. After an explanation of the different factors that can increase the dielectric permittivity as a function of the working frequency and the chemical bonds and atoms present in silicon-based materials, examples of plasma-polymerised materials a-SiOC:H obtained by plasma enhanced chemical vapour deposition are presented, starting with different single precursor vapours and mixed vapours.
A way to get a low dielectric constant is to decrease the weight density of the bulk material, keeping the same material family, by choosing complex precursors. Voids inside the bulk material could be obtained with macropores or larger (air gap), mesopores (xerogels, SOD) or micropores up to free volume. In that case, cyclic chain precursors and/or a porogen approach can be selected in agreement with plasma experimental conditions to synthesise low density plasma-polymers with intrinsic free volume or with microporosity revealed by a post treatment.