Evaluation of the diffusion barrier continuity on porous low- k films using positronium time of flight spectroscopy

A depth-profiled positronium time of flight experiment was performed to investigate a diffusion barrier on a spin-on low dielectric constant (low-k) porous silica film. We studied a capping layer of 50 nm SiO₂, which was optimized for 3-keV positron (e⁺) penetration through the capping and stopping in the porous layer. Maximum positronium intensity was found with a positron implantation energy of 3 keV that reflects the sample structure and is consistent with an open pore fraction η<2×10^-4 of the capping layer.