Abstract
Cu–Ag thin films with various atomic ratios were prepared using a co-sputtering technique, followed by rapid thermal annealing at various temperatures. The films’ structural, mechanical, and electrical properties were then characterized using X-ray diffractometry (XRD), atomic force microscopy (AFM), FESEM, nano-indentation, and TEM as functions of compositions and annealing conditions. In the as-deposited condition, the structure of these films transformed from a one-phase to a dual-phase state, and the resistivity shows a twin-peak pattern, which can be explained in part by Nordheim’s Rule and the miscibility gap of Cu–Ag alloy. After being annealed, the films’ resistivity followed the mixture rule in general, mainly due to the formation of a dual-phase structure containing Ag-rich and Cu-rich phases. The surface morphology and structure also varied as compositions and annealing conditions changed. The recrystallization of these films varied depending on Ag–Cu compositions. The annealed films composed of 40 at % to 60 at % Cu had higher hardness and lower roughness than those with other compositions. Particularly, the Cu50Ag50 film had the highest hardness after being annealed. From the dissolution testing, it was found that the Cu-ion concentration was about 40 times higher than that of Ag. The galvanic effect and over-saturated state could be the cause of the accelerated Cu dissolution and the reduced dissolution of the Ag.
Highlights
Cu–Ag alloys have recently been considered an alternative material for interconnections in microelectronic circuits and have been used in high-field magnets [1,2]
When the Cu90 Ag10 film was further examined with high resolution transmission electron microscopy (HRTEM), nano-crystalline
It is quite possible that all the as-deposited alloy films, except for the sample Cu10 Ag90, have a dual-phase structure, and each phase may be supersaturated with another alloy element
Summary
Cu–Ag alloys have recently been considered an alternative material for interconnections in microelectronic circuits and have been used in high-field magnets [1,2]. Their nanoparticles show excellent optical, electronic, and catalytic properties [3]. For modern ultra-large-scale-integration interconnect applications, Cu–Ag alloys can be used to increase reliability. This can be achieved by an improved interconnect architecture and by tailoring the copper microstructure in terms of low-grain boundary and interface diffusion, low electrical resistivity, and high mechanical strength [4]. If Cu–Ag alloys are to be used as satisfactory interconnections in modern microelectronic devices, one must prove that one of these alloys can provide an increased resistance against electromigration, improved mechanical properties, improved reliability, and decreased electrical resistivity
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