Several issues regarding the nanopore structure in low-dielectric-constant films detected by positron annihilation lifetime spectroscopy

Positron beam based lifetime spectra were measured for mesoporous low-dielectric constant (low-k) methyl-silsesquioxane (MSSQ) as a function of porogen load. The ortho-positronium (o-Ps) lifetime distributions for MSSQ films were evaluated using the maximum entropy method (MELT). The influence of statistics on bimodal or unimodal o-Ps lifetime distributions corresponding to closed pores is discussed in detail. The average o-Ps lifetime correlated with the R parameter, which is a measure of the 3γ fraction. In porous SiLK® films, there is no o-Ps lifetime longer than 10ns. This work showed that the positron lifetime technique is promising for studying the nanoporous structure of low-k films, but caution is required when interpreting positron lifetime results. © 2003 Elsevier Science Ltd. All rights reserved.