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Observation of Intrusion Rates of Hexamethyldisilazane During Supercritical Carbon Dioxide Functionalization of Triethoxyfluorosilane Low-k Films

Water adsorption by porous low-k silica films results in increased dielectric constants and is often due to silanol groups on the pore surfaces. Reacting the silanols with silylating agents (e.g., hexamethyldisilazane (HMDS) and trimethylchlorosilane (TMCS)) in supercritical CO2 (SC-CO2) can increase film hydrophobicity and can remove adsorbed water. In porous methylsilsesquioxane (MSQ) films (average pore size ∼ 3-4nm), it has been determined that supercritical silylation reactions do not substantially penetrate beyond the film surface.1,2 In this work we have examined the supercritical penetration behavior of silylating agents in low-k films with larger pore sizes (5-10nm). The depth and extent of reactants was determined by in situ infrared spectroscopy (FTIR), and surface hydrophobicity was examined by contact angle experiments.