Co-precipitation of MnO and Cu in an ionic liquid as a first step toward self-formed barrier layers

The deposition and sintering of nanoparticles (NPs) containing both Cu and Mn could be an economically and technically interesting alternative to current processes for the metallisation of through Si vias (TSVs). We propose to use ionic liquids (ILs) to (i) synthesise suspensions of suitable NPs and (ii) spread and anneal those suspensions directly on technological substrates. Indeed, ILs readily stabilise NPs and possess good thermal stability. Suspensions of metallic Cu and MnO are formed upon decomposition of solutions of selected Cu and Mn precursors in an IL, C1C4ImNTf2. Upon decomposition of mixed solutions of both precursors, single populations of NPs are obtained, a good indication that both elements are incorporated in these NPs. Finally, upon spreading and annealing these suspensions on samples coated with SiO2, typical of TSV technology, a partial reduction of SiO2 is observed, in agreement with the formation of a MnSiO3 phase typical of self-formed barriers.