Nanoporous structure of low-dielectric-constant films: A process compatibility study

Positron annihilation lifetime spectroscopy (PALS) was used to study the nanoporous structure of spin-on and chemical vapor deposited low dielectric constant (low-k) films. Orthopositronium (o-Ps) lifetimes provided information on pore size, open and closed porosities, and depth profile of pore sizes in low-k films. In combination with three-photon (3γ) yield obtained from positron annihilation spectroscopy, the formation, diffusion, and annihilation of o-Ps are correlated with the chemical composition of matrix. The weak interaction between o-Ps and matrix with the network structure composed of Si, C, O, and H atoms allows us to extract nanoporous information from o-Ps lifetime and 3γ yield. The effects of pore generator (porogen) chemistry, thin film capping, plasma treatment, and positron radiation on nanoporous structure in several low-k films were demonstrated, which provided the information on process compatibility of low-k films. Unsolved issues related with Ps probing nano-structure of porous low-k films are summarized.