Effect of water uptake on the fracture behavior of low-k organosilicate glass

Abstract

Water uptake in porous low-k dielectrics has become a significant challenge for both back-end-of-the-line integration and circuit reliability. This work examines the effects of water uptake on the fracture behavior of nanoporous low-k organosilicate glass. By using annealing dehydration and humidity conditioning, the roles of different water types and their concentrations are analyzed in detail. For as-deposited SiCOH films, annealing dehydration can enhance the resistance to crack occurrence, and these enhancements can be offset by higher humidity conditioning. It was found that the film-cracking threshold can be lowered by in-diffused water in the film as well as by water at the SiCOH/subtract interface. This occurs because the water decreases the film fracture energy and adhesion energy, respectively. By conditioning at high humidity, the variation of the film cracking threshold agrees well with the behavior of the film hardness and modulus of elasticity as a function of relative humidity. The crack morphologies of low-k porous films are also implicitly related to water uptake in the materials. Film cracking thresholds and crack morphologies of UV-cured low-k materials exhibit a weaker dependence on the water uptake, indicating a low degree of hydrophilicity of the SiCOH film after UV curing, which corroborates the previous results. Furthermore, by measuring the surface crack length, the material–fracture toughness can be found. The results demonstrate that neither annealing dehydration nor water uptake have significant effects on fracture toughness of as-deposited SiCOH, while for UV-cured SiCOH, annealing enhances the film-fracture toughness.