Effectiveness of reactive sputter-deposited Ta–N films as diffusion barriers for Ag metallization

Abstract

Tantalum nitride films on silicon were prepared by reactive sputtering of Ta under nitrogen partial flow rates varying from 15% to 40% N2. Rutherford backscattering spectroscopy (RBS) and x-ray diffraction (XRD) analysis revealed that the composition and phases of the Ta–N films were influenced by the N2 flow rate. Increasing the nitrogen partial flow rate from 25% to 40% N2, results in the films changing from metal-rich to stoichiometric Ta–nitride. High N2 flow rates (30%–40% N2) resulted in a disordered tantalum–nitride. The tantalum nitride films were evaluated as potential diffusion barriers for Ag metallization. Sheet resistance measurements, XRD and RBS analysis confirmed that Ta–N films, used as diffusion barriers in the Ag∕Ta–N∕Si system, were thermally stable up to 650°C when annealed for 30min in vacuum. The thermal stability was independent of N2 flow rate within this temperature range. However, at 700°C, the barrier failed as a result of Ta–silicide formation by reaction with the underlying Si substrate, and dewetting of Ag on Ta–N occurred.