Thermal and mechanical properties of hybrid methylsilsesquioxane/poly(styrene-b-4-vinylpyridine) low-k dielectrics using a late porogen removal scheme

Abstract

A late porogen removal scheme was used to make low-k materials (k = 2.72 to 2.02) using methyl silsesquioxane (MSQ) and a high-temperature porogen, poly(styrene-b-4-vinylpyridine) (PS-b-P4VP), to circumvent the reliability issues related to as-deposited porous dielectric. Based on the nanoindentation and Fourier transform infrared spectroscopy (FTIR) analysis, the moduli of the hybrid films were found to be higher than their porous forms, and even better than the dense MSQ film, for porogen loading below a critical level (similar to 69.5 vol%). This could be attributed to their enhanced degree of cross-linking in MSQ as evidenced by the network/cage structural ratios. Besides, high-temperature porogen plays different roles during the cross-linking of MSQ depending on its loadings. In this study, with immediate loading at 16.7 vol%, PS-b-P4VP can serve as plasticizer to enhance the degree of cross-linking, but at a large loading >16.7 vol%, it becomes a steric hindrance reducing the degree of cross-linking.