Structural and electrical characterization of CoNiO monolayer as copper diffusion barrier in integrated circuits

Abstract

Diffusion barrier properties of CoNiO monolayer, deposited by Langmuir Blodgett (LB) technique, were studied against the diffusion of copper through SiO2. Cu/CoNiO/SiO2/Si and Cu/SiO2/Si test structures were prepared and compared for this purpose. These test structures were annealed at temperatures starting from 100°C up to 650°C in vacuum. Samples were characterized using Energy Dispersive X-ray Spectroscopy (EDS), Atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscope (SEM), four probe resistivity measurement, Capacitance-Voltage (C‒V), Current-Voltage (I‒V) characterization techniques. EDS and AFM confirmed the composition and structure of the deposited monolayer. Thermal stability was studied using X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and four probe techniques. Results indicated that structure with barrier was stable up to 600°C whereas its counterpart could sustain only up to 300°C. Sheet resistance of Cu/SiO2/Si structure starts increasing at 300°C and that of Cu/CoNiO/SiO2/Si test structure was almost unchanged up to 600°C in. SEM analysis of samples annealed at different temperatures also confirmed the XRD and four probe results. Biased Thermal Stress (BTS) was applied to the samples and its effect was observed using C‒V analysis. C‒V curves showed that in the presence of CoNiO barrier layer there was no shift in the C‒V curve even after 120min of BTS while in the absence of barrier there was a significant shift in the C‒V curve even after 30min of BTS. Leakage current density (jL) was plotted against the BTS duration under same BTS conditions. It was found that the Cu/CoNiO/SiO2/Si stack could survive about two times more than the Cu/SiO2/Si stack.