Study of Cu diffusion in porous dielectrics using secondary-ion-mass spectrometry

Abstract

Secondary-ion-mass spectrometry measurements were used to study Cu diffusion in porous silica. The total concentration of Cu+ decreases with increasing porosity of the dielectric. This behavior is the combined result of both the chemistry and the morphology of the dielectric. The injection of Cu is triggered by outgassing of hydroxyl and water-related species from the dielectric; furthermore, the reduced available cross-sectional area of solid for diffusion, due to porosity, leads to reduced diffusion through the porous film. This suggests that surface diffusion does not play an important role in this process. The Cu+ concentration at the Cu/dielectric interface is on the order of 1023at.∕m3, but decreases with time and exponentially with porosity, which suggests the occurrence of a chemical reaction at the interface. A model of molecular diffusion and ion drift that considers the porosity of the film is developed and the results are consistent with the experimental data.