Moisture and oxygen uptake in Low K/ copper interconnect structures

Abstract

It is shown that capacitance measurements can be used to quantify the amount and rate at which moisture uptake occurs in low K dielectric films. A complete study of SiLK ™* dielectric is presented. Both the temperature and relative humidity dependence of the moisture uptake are measured. It is shown that the equilibrium moisture content of the film increases linearly with both relative humidity and temperature. Measurements of the kinetics of moisture uptake show ingress and egress is reversible with a diffusivity of 2.7 × 10 -2 exp (0.25eV/KT). A technique is also presented to quantify the permeability in low K dielectrics to oxygen. The diffusivity of oxygen in SiLK is found to be comparable to that of water with an activation energy of 0.26 eV. CVD dielectrics based on SiCOH are found to have a similar or lower permeability to oxygen depending on their dielectric constant. The results of our study indicate that, with Low K dielectrics, both oxygen and moisture can diffuse though out the BEOL structure of a chip at room temperature. Thus, there is the potential that oxidation and corrosion of metal structures my occur under use conditions unless the structures are protected by a defect free diffusion barrier. © 2004 Materials Research Society.