Cu diffusion into the glass under bias temperature stress condition for through glass vias (TGV) applications

For Through Glass Via (TGV) applications, significant copper migration in-between vias would result in failure of the device. The Cu migration occurs due to a combination of thermal and applied electrical field. Thus, it is critical to generate data of Cu diffusivity through glass as function of temperature and electrical field to determine whether a Cu diffusion barrier is required for this application. In this study, the Cu diffusion profiles in the Corning SG 3.4 glass, under varying electrical fields and temperature are evaluated. Using a planar capacitance test structure and a bias temperature stress test at elevated temperature, an Arrhenius plot of Cu diffusivity was obtained. Cu diffusion in the SG 3.4 glass has an activation energy of 1.1 eV which is in the range of thermal SiO2 and low-k of the references. Based on this Arrhenius plot, Cu diffusion depth at various combinations of operating temperatures and electrical fields can be determined. Based on the calculated diffusion lengths we infer that Cu diffusion barrier may not be required in most TGV applications.