Surface diffusion of copper on tantalum substrates by Ostwald ripening

Abstract

In this work, we report on the determination of surface diffusion coefficient of copper on tantalum substrates by Ostwald ripening. It is shown that impurities, such as oxygen, strongly influence the kinetics of dewetting of copper films on tantalum substrates. Two technologically important interfaces with copper were investigated: Cu/β-Ta and Cu/α-Ta. For copper surface diffusion on β-Ta surface, a surface diffusion coefficient of D S betaTa = 2.6 1.0 3.7 · 10 - 11 ( cm 2 / s ) was measured at 550 °C. The temperature dependence of surface diffusion was investigated between 400 °C and 550 °C. Using an Arrhenius relationship, an activation energy of 0.83 ± 0.1 eV and a pre-exponential factor of D S 0 betaTa = 2.8 0.2 7.5 · 10 - 6 ( cm 2 / s ) were calculated. For copper surface diffusion on α-Ta surface, a diffusion coefficient of D S alphaTa = 2.0 1.5 3.1 · 10 - 12 ( cm 2 / s ) was measured at 550 °C. We discuss the diffusion mechanism involved during the cluster growth and the origin of the faster surface diffusion of copper on the β-Ta substrate as compared to the α-Ta phase.