Strengthening mechanism of reactive porogens for ultra-low dielectrics

A significant challenge in developing low k materials is the maintenance of adequate mechanical properties as well as low dielectric constant in case of nanoporous low dielectrics. Therefore, improving reactivity between matrix and porogen is the most promising way for high mechanical strengths. Thus, we have synthesized reactive porogens, which had alkoxysilyl groups, based on ß-cyclodextrin (ß-CD) and glucose (GC) by allylation and hydrosilylation reactions. These improved reactivities of porogens are able to cause the condensation reaction with silanol groups of the organoslicate matrix and structural change of siloxane group in ultra-low dielectrics. According to decomposition process, the chemical structure of the silicate network has changed from T structure to Q structure to some significant extent, which is related with strengthening mechanism, resulting in the increase of cross-linking density of nanoporous films. In order to confirm the strengthening mechanism, we used the solid phase ²⁹Si-NMR on the reactive porogen. This was also confirmed by FT-IR spectroscopy. Finally, we have prepared the nanoporous ultra-low dielectrics (k∼2.3) with remarkably higher mechanical strength (E∼8.1 GPa, H∼1.2 GPa) using reactive porogens than using non-reactive porogen.