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

摘要

Tantalum nitride films on silicon were prepared by reactive sputtering of Ta under nitrogen partial flow rates varying from 15% to 40% N_2. 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 N_2 flow rate. Increasing the nitrogen partial flow rate from 25% to 40% N_2, results in the films changing from metal-rich to stoichiometric Ta-nitride. High N_2 flow rates (30%-40% N_2) 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℃ when annealed for 30 min in vacuum. The thermal stability was independent of N_2 flow rate within this temperature range. However, at 700℃, 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.