Porosity Effects on Properties of Mesoporous Silica Low-k Films Prepared Using Tetraethylorthosilicate with Different Templates

Abstract

A series of mesoporous silica films with different porosities and different pore sizes were prepared using different templates or different template concentrations in tetraethylorthosilicate colloid solutions. The amphiphilic templates such as cetyltrimethylammonium bromide (), Brij-56, Tween80, and Pluronic P123 were used. To investigate the effect of self-assembly surfactants on the film properties and to make a comparison, polyethylene glycol (molecular weight = 1450) which is not a surfactant was also used as a template in this research. Various film properties such as porosity, refractive index, dielectric constant, leakage current density, flatband voltage, hardness, and Young’s modulus were measured. For the film templated with , the high leakage current density and positive flatband voltage were attributed to the residual bromide in the framework, which was from bromine in after the calcination process. Moreover, its abnormally low dielectric constant was mainly due to the high leakage current density. For the films made with nonionic templates, the dielectric constant and the refractive index can be reduced linearly by increasing the film porosities; in other words, they are strongly related to the porosity rather than the pore size or the ordering of pore structure. However, the larger leakage current density and the weaker mechanical strength for more porous films are the drawbacks. According to higher values of flatband voltage, the elevation of leakage current densities are attributed to more silanol groups in the films. It was shown that the films with more ordered structures or thicker pore wall possessed better mechanical strength. Nevertheless, the porosity is the most influential factor upon mechanical strength of the films.