Porosity characterization by beam-based three-photon positron annihilationspectroscopy

We present a straightforward and fast positron annihilation spectroscopy (P AS) technique for measuring the 2 to 3 photon annihilation ratio of Ps (ele ctron-positron) atoms (3 gamma PAS), utilized here for the nondestructive c haracterization of mesoporous (pore size >1 nm) dielectric films. Examples are given for similar to1-mum-thick foamed methyl-silsesquioxane (MSSQ) fil ms, produced by mixing MSSQ (0-90 wt % fraction) with a sacrificial foaming agent (porogen). Probing these films as a function of depth allows one to monitor Ps escape from interconnected pores and to determine the threshold for pore interconnectivity to the film surface. A classical treatment of Ps diffusion is used to calculate the open and closed porosity fractions as a function of the initial porogen load. (C) 2001 American Institute of Physi cs.