Gold silicide formation and preferential grain boundary etching of gold by quartz deposition and removal

Gold–silicon interactions are vital for semiconducting industry, microelectromechanical systems and chemical reactions, where gold serves as a conductor, protective layers, coatings, and as a catalyst. However, gold and silicon exhibit complex behavior, even at low temperatures, including mutual inter-diffusion, alloy formation, and gold-induced silicon oxidation. Here we show that preferential grain-boundary etching occurs on highly (111)-textured polycrystalline gold films, when we sputter-deposit a thin quartz film that we remove afterwards via reactive ion etching. During the quartz deposition silicon atoms diffuse, enabled by the high dislocation and vacancy density, into the grain boundaries of gold forming there a gold-silicide. A gold-silicon reaction happens also on the flat (111) terraces, however, limited by outwards-diffusion of gold, its layer thickness is restricted to around 7 nm. Upon reactive ion etching the gold-silicide is removed leading to small, 6 nm-high gold islands on the flat terraces and grooves at the grain boundaries as deep as 15 nm. Although the maximum sample temperature was only 150 °C, we surprisingly have evidence that Au 4 Si is formed, which is the first stable low-temperature composition occurring at the eutectic temperature of 363 °C. The above procedure can be used for preferential grain boundary etching of gold, gold nanoparticle creation, and delivers further insight into the complex nature of gold-silicide formation.