Effects of processing history on the modulus of silica xerogel films

Abstract

Sintered xerogel films (porous SiO2) show a higher elastic modulus than other amorphous low dielectric constant (K) materials available for the same value of K. By comparing xerogels that were sintered, templated or made with ethylene glycol or ethanol as solvents, we show that process history is at least as important as the chemistry of the solid matrix or the porosity. The modulus extrapolated to zero porosity for the porous sintered and templated films is the same as those of the dense films made by chemical vapor deposition of SiO2. This suggests that the solid matrix for sintered xerogel films is close to ideal and their modulus is better because of the ordered arrangement of pores and fusion of particles making up the matrix. The modulus measured by nanoindentation on thick xerogel films (>0.8 μm) is well explained by the open cell foam model.