Water diffusion and fracture in organosilicate glass film stacks

Organosilicate glass (OSG) coatings with low dielectric permittivity are widely used as dielectrics in high-performance integrated circuits. OSG is very brittle and it is susceptible to stress-corrosion cracking in water-containing environments. We have investigated the adhesion degradation of silicon nitride/OSG and silicon carbonitride/OSG interfaces caused by water diffusion. Experimental results are in good quantitative agreement with an analytical model that combines water diffusion with subcritical crack growth. Fracture experiments show that water diffusion in OSG film stacks is remarkably fast and that it has an activation energy of 0.27 eV. The adhesion degradation is completely reversible under mild annealing conditions. Interfacial plasma treatments result in a significant enhancement of the adhesion in the absence of water, but this enhancement is lost almost completely upon exposure of the film stack to water. A diffusion study using deuterium as an isotopic tracer shows that the Si/OSG interface is the main diffusion path.