Barrier properties of Ni, Pd and Pd-Fe for Cu diffusion

Abstract

The interdiffusion properties of electrodeposited Ni, Pd, Pd-Fe with Cu substrate were studied at temperature ranging from 300 to 900 °C, using energy dispersive X-ray spectroscopy (EDS). Chemical interdiffusion coefficients were derived using the Boltzmann–Matano Analysis. Intermetallic phase formation was studied by X-ray diffraction (XRD). Grain sizes of electrodeposits were estimated by particle size boardening method. Microstructures were observed by optical microscopy and scanning electron microscope. The difference in interdiffusion coefficients observed for Cu–Ni couples plated from different nickel baths originates from different initial grain size and different microstructure. The grain growth rate of the Cu–Ni couple at 500 °C for the first 30 min of heat treatment was observed to be higher than the same couple after 48 h of heat treatment, resulting to higher diffusivities. A transition range at about 700–750 °C was observed from the Arrhenius plot of diffusivities for the Cu–Ni system indicating a transition between different diffusion mechanism. Interdiffusion coefficients of the Pd–Cu system determined in the temperature range 300–700 °C are higher than those of Cu–Ni systems for more than one order of magnitude. Interdiffusion of Cu–Pd was reduced when Fe was alloyed with Pd as 75 wt% Pd–25 wt% Fe alloy by electroplating. Apparent interdiffusion coefficients of the Cu–Pd–Fe system are higher than those of the Cu–Ni for heat treatment temperatures above 300 °C but are comparable to those of Cu–Ni at 300 °C. The as-deposited Pd–Fe coating consists of FePd 3 and FePd phases. PdCu 3 was observed after heat treatment. The rapid interdiffusion of the Cu–Pd–Fe system at 500 °C is suggested to originate from vacancies formation.