Abstract
With the rapid development of copper metallization technology, the line spacing of integrated circuits is drastically reduced. To prevent rapid Cu diffusion and silicide formation in interconnect structures, diffusion barriers are strongly demanded. In recent years, more stable and diffusion-resistant barriers have been intensively studied, including those of ternary components, of layered structures and of multi-principal components (high-entropy materials and their stacking structures). Due to the difficulty in uniform depositions of ultrathin barrier layers in nanoscale trenches, self-forming diffusion barriers (barrierless metallization) have further been developed in the past few years. The segregation of minor alloying elements in Cu films to Cu/dielectric interfaces under thermal annealing will self-form an ultrathin barrier layer. Thus in this study, Cu alloy films were deposited on Si substrates by magnetron sputtering, and alloyed solute elements would segregate during thermal annealing. Experimental results indicated that, in the six Cu alloy films, different solute segregation behaviors were observed under the competition of mixing enthalpy and mixing entropy. For the Cu(V) alloy film, the solute segregated to the Cu/Si interface, dominated by the large positive mixing enthalpy of V and Cu. For the Cu(V,Nb), the Cu(V,Nb,Mo) and the Cu(V,Nb,Mo,Ta) alloy films, the solutes formed intermetallic compounds due to the negative mixing enthalpies and the low-to-medium mixing entropies of the solute elements. For the Cu(V,Nb,Mo,Ta,Cr) alloy film, the solutes again segregated to the Cu/Si interface owing to the high mixing entropy of the solute elements.