From single molecules to micelles – An in situ study of porogen aggregation and nanopore formation mechanisms in porous thin films

Abstract

The generation and formation mechanisms of nanopore structure using a degradable porogen, 5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41,42-hexa-acetoxyl calix[6] arene (CA[6]), in a silsesquioxane (SSQ) matrix have been studied by means of ellipsometric porosimetry (EP) and in situ positron annihilation lifetime spectroscopy (PALS). A clear transition of the final nanopore structure resulting from a transition from molecularly dispersed porogen to micelle-like assembled porogen domains was observed in the range of 13–16% CA[6] porogen loading. By utilizing PALS measurements during in situ heating of hybrid nanocomposite samples, the curing temperature for decomposition and removal of the porogen to produce nanopores is completely different for samples where the porogen is dispersed as single molecules as compared to those where assembled porogen domains are present. It is determined that this is largely due to inherently different paths for diffusion of the degraded porogen fragments. This methodology for investigating pore generation mechanisms in porous low-k films can be used as a characterization tool for a wide range of thermally degradable porogen systems.