Effect of UV Pretreatment on the Nanopore Formation within Organosilicate Thin Films

Abstract

We have investigated the low-temperature cure process to realize nanoporous organosilicate thin films at temperature below 150°C by adding a small amount of photoacid generator PAG followed by UV irradiation. The Gemini surfactant, which decomposes in the temperature range from 170 to 420°C, was used as a pore-generating material porogen for organosilicate matrix. The UV pretreatment in the presence of PAG lowers the condensation temperature of poly methyl silsesquioxane matrix and leads to the fast matrix vitrification enabling the addition of increased amount of porogens. Because the full vitrification of the matrix 150°C by UV pretreatment in the presence of PAG below the decomposition temperature of porogens 170°C prevents the pore collapse, the porosity up to 35.5% was achieved with an average pore size of 3.4 nm, as measured from X-ray reflectivity as well as ellipsometric porosimetry. It is shown that both dielectric constant and refractive index continue to decrease to 2.0 and 1.26, respectively. The present experimental system demonstrates that porogens with low degradation temperature can be successfully incorporated to realize nanoporous films without pore collapse. Consequently, this process can widen the choice of porogens to prepare nanoporous films.