Interdiffusion of Cu substrate/electrodeposits for Cu/Co, Cu/Co-W, Cu/Co/Ni and Cu/Co-W/Ni systems

Abstract

The interdiffusion of electrodeposited Ni, Co and Co-W with Cu substrate were studied, at temperature ranging from 400 to 800 °C, using energy dispersive X-ray spectroscopy (EDS). Chemical interdiffusion coefficients were calculated using the Boltzmann-Matano analysis. Intermetallic phase formation was studied by X-ray diffraction (XRD) and microstructures were observed with a scanning electron microscopy (SEM). No remarkable interdiffusion was observed in the Cu/Co and Cu/Co-W systems up to 800 °C. However, after annealing at 400–800 °C for the Cu/Co/Ni system, accumulation of Cu atoms was found at the /Ni interface in which Cu had further diffused into the Ni electrodeposit. It is suggested that Cu diffuses through the Co layer by the grain-boundary diffusion mechanism. Interdiffusion of Cu through electroplated Co coating to Ni was compared with electroplated alloy coating of 65 wt.% Co-35 wt.% W. The structure of the Co-W coating has changed from a mixture of Co-like hcp and fcc structures to a solely fcc structure upon annealing at 1100 °C for 90 min. The diffusion barrier properties of Co and Co-W were compared with those of Ni. The results show that Co is a more effective barrier than Ni for Cu diffusion up to 219 h at 400 °C. A Co-W alloy coating, of 36 wt.% W, is a more effective barrier for Cu diffusion than Ni heated up to 72 h at 500 °C. However, interpenetration of Cu through Co is more pronounced than diffusion of Cu through Ni for temperatures ranging from 500 to 800 °C. Interdiffusion of Cu through the Co-36 wt.% W coating is more pronounced than diffusion of Cu through Ni for temperatures ranging from 600 to 800 °C whereas Co-W is a more effective barrier than Co for Cu diffusion.