Effect of moisture adsorption on the properties of porous-silica ultralow-k films

The effect of adsorbed moisture on the dielectric constant of porous silica was investigated for various TMCTS (tetramethyl-cyclo-tetrasiloxane) vapor-annealing treatment conditions, which change the hydrophobicity of the film. The treatment causes the TMCTS molecules to polymerize on the pore wall surfaces with the coverage controlled by the treatment time and temperature. The amount of adsorbed moisture was estimated from thermal desorption measurements. The results of infrared absorption spectra indicate that the pore wall surfaces without TMCTS coverage react with moisture to form Si–OH bonds. Thus, it is possible to reduce the concentration of Si–OH bond by increasing the TMCTS coverage, thereby preventing the dielectric constant increase.