Optimization of Ta-Si-N thin films for use as oxidation-resistant diffusion barriers

We have demonstrated that the optimum Ta-Si-N compositions for use as oxygen diffusion barriers in stacked-capacitor dynamic random-access memory structures with perovskite dielectrics are in the range Ta(20-25 at.%)-Si(20-45 at.%)-N(35-60 at.%). Twenty-two different Ta-Si-N compositions were evaluated, starting from six sputter-deposited Ta-Si alloys of which four were reactively deposited in 2-8% nitrogen in an argon plasma. The barriers were evaluated after an aggressive 650 degrees C/30 min oxygen anneal to determine if they remained electrically conductive, prevented oxygen diffusion and formation of low dielectric constant oxides, and had minimal interaction with the Pt electrode and underlying Si plug. Rutherford backscattering spectroscopy, four-point probe sheet resistance, through-film-resistance, and x-ray diffraction analysis techniques were used in the evaluation.