Diffusion barrier characteristics of co monolayer prepared by Langmuir Blodgett technique

Abstract

Monolayers of Co over SiO2/Si substrate were deposited using Langmuir Blodgett (LB) technique. The diffusion barrier capability of Co layer was evaluated against copper diffusion. The structure of the deposited Co layer was analyzed using X-ray photoelectron spectroscopy (XPS), Energy Dispersive X-ray Spectroscopy (EDS) and Atomic force microscopy (AFM) techniques. Thermal stability of Cu/SiO2/Si and Cu/Co/SiO2/Si test structures was studied and compared using X-ray diffraction (XRD), scanning electron microscope (SEM) and four probe techniques. The samples were annealed at different temperatures starting from 200°C up to 700°C in vacuum for 30min. XRD results indicated that combination of Co/SiO2 worked as diffusion barrier up to 550°C whereas SiO2 alone could work as barrier only up to 300°C. Sheet resistance of these samples was measured as a function of annealing temperature which also supports XRD results. C–V curves of these structures under the influence of Biased Thermal Stress (BTS) were analyzed. BTS was applied at 2.5MVcm−1 at 150°C. Results showed that in the presence of Co barrier layer there was no shift in the C–V curve even after 90min of BTS while in the absence of barrier there was a significant shift in the C–V curve even after 30min of BTS. Further these test structures were examined for leakage current density (jL) at same BTS conditions and leakage current density (jL) was plotted against the BTS duration. It was found that the Cu/Co/SiO2/Si test structure could survive about one and half time more than the Cu/SiO2/Si test structure.