Synthesis, Structure and Thermal Properties of Volatile Group 11 Triazenides as Potential Precursors for Vapor Deposition

Group 11 thin films are desirable as interconnects in microelectronics. Although many M–N bonded Cu precursors have been explored for vapor deposition, there is currently a lack of suitable Ag and Au derivatives. Herein, we present monovalent Cu, Ag and Au 1,3-di-tert-butyltriazenides that have potential for use in vapor deposition. These compounds possess thermal stability and volatility that rival that of current state-of-the-art group 11 precursors with bidentate M–N bonded ligands. All compound sublime quantitatively between 120 and 130 °C at 0.5 mbar. Thermogravimetric analysis showed the Cu and Ag compounds both volatilized at ~200 °C with 0 and 2% residual mass, respectively. The Au triazenide showed two separated mass loss events at ~175 and 240 °C, and 35% residual mass. The crystal structure of the Cu compound showed a dimer, whilst the Ag and Au derivatives were tetrameric. Nuclear magnetic resonance spectroscopy showed dimers for the Cu and Au compounds and a dimer/tetramer equilibrium for the Ag compound. Electronic energies from density functional theory calculations confirmed dimeric preference for the Cu triazenide while Ag and Au preferred the tetrameric. However, all three compounds showed dimeric preference when accounting for entropy. Dimers are, therefore, expected to dominate in the gas phase for all three compounds during sublimation. Natural bond orbital analysis was used to identify orbital interactions important for the dimer/tetramer preference. Three factors were identified, in conjunction with strong metal-metal interactions, to increase the preference for rhombic tetramers.