Surface modified silica xerogel films of high porosity (25-90 %) and uniform thickness (0.4-2 µm) were fabricated at ambient pressure on silicon and other substrates. Mechanical reliability of the films was determined by measuring fracture toughness (adhesive) as a function of aging time and temperature using the modified edge-lift-off technique. There is an optimum aging time at 60 °C aging to obtain maximum fracture toughness for the procedure used here.
Cu/xerogel/Si and Ta/xerogel/Si structures were annealed at different temperatures and in different ambient environments were analyzed using RBS and optical microscopy to assess the extent of interaction with the xerogel film. When annealed in N2 with trace amounts of O2 (equivalent to 10-7-10-6 Torr vacuum), RBS analysis does not show diffusion of Cu or Ta through the xerogel up to 450 °C. At higher temperatures, or in the presence of larger concentrations of O2, Cu and Ta oxidize. Cu oxidation leads to significant diffusion through the xerogel. Ta oxidation also results in diffusion-like RBS spectra. Using the micron-size ion beam to probe the Ta surface, this was found to be solely due to buckling of Ta films on xerogel. A thin SiNx layer on top of Cu and Ta prevents metal oxidation up to 640 °C, Cu diffusion, and Ta buckling.