Influence of Au alloying on solid state dewetting kinetics and texture evolution of Ag and Ni thin films

Abstract

In this contribution, the effect of Au alloying on the solid state dewetting (SSD) kinetics and texture evolution of AuNi and AuAg thin films is investigated. For that bilayers of a high (AuNi) and low (AuAg) atomic mismatch system are fabricated on different substrates and annealed utilizing a rapid thermal annealing furnace. Afterwards, the degree of SSD, as well as the texturing, are investigated by correlating X-ray diffraction and electron microscopy techniques. A quantitative texture analysis yields that pure metal films (Ni, Au, Ag) exhibit the same degree of 〈111〉 texturing after SSD. In contrast, a reduced degree of texturing is observed for alloys as well as for pure Ni films on amorphous substrates. The texture loss is less pronounced for AuNi on sapphire which is likely due to in-plane texturing along densely packed directions stabilizing the 〈111〉 out-of-plane texture. Further the effect of alloying on the SSD kinetics is investigated. We found that the SSD kinetics of the low-misfit AuAg system continuously changes with the Au concentration and can be perfectly described by composition dependent hole growth as reflected by the Mullins’ coefficient. In contrast, the high-misfit AuNi system resembles this behaviour only during early stages of SSD. For prolonged annealing times at 850 °C as well as 890 °C a strong deviation is observed, which in particular manifests in the concentration range from 50 at% to 70 at% Au, where a drastic increase in the dewetting rate is observed. The deviation from the Mullins coefficient indicates a shift in the prevailing mechanism, suggesting that this accelerated SSD occurs at compositions where the annealing temperature (T) approaches the melting temperature (Tm), i.e. liquidus line. Indeed, the reduced temperature (T/Tm) exhibits its maximum within the compositional range where accelerated SSD is prominent. Additionally, Au segregation at grain boundaries, an increase in surface anisotropy, and a decrease in surface energy are discussed as stabilizing factors for low and high Au concentrations, respectively.