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 anddifferent pore sizes were prepared using different templates or differenttemplate concentrations in tetraethylorthosilicate colloid solutions.The amphiphilic templates such as cetyltrimethylammonium bromideC16TMABr, Brij-56, Tween80, and Pluronic P123 were used. To investigatethe effect of self-assembly surfactants on the film properties andto make a comparison, polyethylene glycol molecular weight 1450which is not a surfactant was also used as a template in this research.Various film properties such as porosity, refractive index, dielectricconstant, leakage current density, flatband voltage, hardness, andYoung�s modulus were measured. For the film templated with C16TMABr,the high leakage current density and positive flatband voltage wereattributed to the residual bromide in the framework, which was frombromine in C16TMABr after the calcination process. Moreover, itsabnormally low dielectric constant was mainly due to the high leakagecurrent density. For the films made with nonionic templates, thedielectric constant and the refractive index can be reduced linearlyby increasing the film porosities; in other words, they are stronglyrelated to the porosity rather than the pore size or the orderingof pore structure. However, the larger leakage current density andthe weaker mechanical strength for more porous films are the drawbacks.According to higher values of flatband voltage, the elevation ofleakage current densities are attributed to more silanol groups inthe films. It was shown that the films with more ordered structuresor thicker pore wall possessed better mechanical strength. Nevertheless,the porosity is the most influential factor upon mechanical strengthof the films.