The orientation relationships of Ag3Al/Ag interfaces and formation sequence of Ag2Al and Ag3Al at the Ag/Al interface

Abstract

The silver-aluminum interface reaction has continued to attract significant interest in recent years, particularly with the development of silver and silver alloy wires for advanced wire bonding techniques. The purpose of this study is to investigate the orientation relationships and interface between mu (μ)-Ag₃Al and Ag, as well as formation sequence of gamma (γ)-Ag₂Al and μ-Ag₃Al at the Ag/Al interface. The orientation relationships and interfaces between μ-Ag₃Al and Ag have been studied by transmission electron microscopy (TEM). Epitaxial (001)_Ag thin films was grown on the NaCl (001) surface and then Al was evaporated onto the Ag film form μ-Ag₃Al. Results showed that the γ-Ag₂Al first formed at Ag/Al interface and then the μ-Ag₃Al formed after annealing at 350 °C for 5 min. The orientation relationships were found: (1) [221]_μ//[001]_Ag (zone axis), $\left(\overline{1}10\right)$_μ//(110)_Ag, and $\left(11\overline{4}\right)$_μ//$\left(\overline{1}10\right)$_Ag at γ-Ag₂Al/Ag interface and (2) [0001]_γ//[221]_μ (zone axis), $\left(\overline{1}100\right)$_γ//$\left(1\overline{1}0\right)$_μ, and $\left(\overline{1}\overline{1}20\right)$_γ//$\left(11\overline{4}\right)$_μ at Ag/Al interface. The μ/Ag and γ/μ interfaces were further analyzed by the surface structures and the orientation relationships.

That γ-Ag₂Al forms before μ-Ag₃Al in the solid-state Ag/Al interfacial reactions was discussed by heterogeneous nucleation theory. Analysis of the interfaces showed that the γ-Ag₂Al/Ag interfacial energies with better interfacial coherency were lower than those that of the μ-Ag₃Al/Ag. In addition, the energy of formation of γ-Ag₂Al is slightly larger than that of μ-Ag₃Al. Therefore γ-Ag₂Al forms before μ-Ag₃Al.