Low dielectric constant nanoporous SiO_2 films formed by twice-modification processing

摘要

Silica sol synthesized by a two-step acid-base catalyst procedure was deposited on Si (100) substrate by spin coating. Then the wet gel film was modified twice with trimethylchlorosilane (TMCS). The proper annealing temperature of the film, determined by Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric and Differential thermal analysis (TG-DTA), is 300 deg C. The twice-modified film doesn't shrink and can keep continuous while diying. The differences brought by surface modification mainly depend on the compositional changes (hydrophobic -CH_3 groups substituted for hydrophilic -OH species) of the firm. The network structure of the twice-modified SiO_2 porous film was clearly observed by scanning electron microscopy (SEM). The pore size about 70-80 nm can be seen from SEM and transmission electron microscope (TEM). As for the films with no modification, only 23.6 percent porosity can be obtained and its corresponding dielectric constant (1) is 3.29. However, with twice modification, the porosity increases to 73.5 percent and k reaches 1.8.