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Structure Analyses of Ti-Based Self-Formed Barrier Layers

Self-formed Ti-based barrier layer using Cu(Ti) alloy seed applied to 45-nm-node dual-damascene interconnects was reported to have sufficient barrier strength to prevent Cu diffusion into dielectrics. The constituent Ti compounds in the self-formed Ti-based barrier layers and the barrier structures in Cu(Ti)/dielectric samples were identified by X-ray photoelectron spectroscopy (XPS) analyses. Two types of SiOC with low dielectric constants, SiO2, and SiCN were used as dielectrics. The Ti-based barrier layers consisted mainly of amorphous Ti oxides such as TiO2, Ti2O3, and TiO, regardless of the dielectric. In addition to Ti oxides, barrier layers containing TiC, TiSi, and TiN were observed, depending on the dielectric. TiC and TiSi were in crystalline state. They were formed beneath the Cu(Ti) alloy films, and had orientation relationship with the crystalline Cu(Ti) alloy films. The amorphous Ti oxides were formed above the amorphous dielectric layers. The amorphous Ti oxides are believed to be formed continuously above the dielectric layers and prevent Cu diffusion into the dielectric layers.