Dependence of porosity in methyl-silsesquioxane thin films on molecular weight of sacrificial triblock copolymer

Positron annihilation spectroscopy is used to characterize pore sizes and their interconnectivity for porous low dielectric constant methyl-silsequioxane thin films, which are templated by triblock copolymers. More than 1 μm of ortho-positronium (o-Ps) diffusion length has been observed for certain films, indicating high interconnectivity of pores. S parameters from Doppler broadening of annihilation photons (DBAP) show homogeneous depth profiles of these films. o-Ps 3γ emission and lifetimes show that the pore interconnectivity depends on the characteristics of the triblock copolymers. Pores generated from polymers with higher molecular mass are smaller and more closed, while pores generated by polymers with lower molecular mass and smaller ethylene oxide fraction are more interconnected.