MOCVD of tantalum nitride thin films from TBTEMT single source precursor as metal electrodes in CMOS applications

Tantalum nitride films obtained by MOCVD using a tert-butylimido-tris-ethylmethylamido-tantalum (TBTEMT, Ta(NCMe3)(NEtMe)3) compound were physically and electrically investigated. Lowest resistivity of 2.5 mΩcm was obtained at 600 °C and 0.25 mbar total pressure. Deposition rate under these conditions was 4 nm/min, but step coverage was poor. Values of 50 to 75% are obtained at the side walls (10% of trench depth) and 25% at the bottom of a 5 μm deep trench with an aspect ratio of 2:1. Film analysis by XPS reveals Ta rich layers (e.g., Ta:N ratios of 1:0.85 for 400 °C and 1:0.6 for 650 °C deposition temperature, respectively) with a high oxygen contents of about 35 at.%. Oxygen contamination is due to both, continuous incorporation during film growth caused by leakage of the reactor and post-deposition oxidation. TaN electrodes deposited at 600 °C and 0.25 mbar reveal a metal work function of about 4.5 eV independent on thickness of TaN. However, thicker TaN layers show lower leakage current densities. Post-deposition annealing at 900 °C for 10 s does not cause changes in TaN layer thickness, resistivity, or oxide charge, though annealing in NH3 atmosphere reduces O contamination. Leakage current densities of annealed MOS capacitors (900 °C, 10 s, NH3) are reduced by nearly one order of magnitude, but leakage current characteristics are strongly degraded after post-deposition annealing. Metal work function is shifted towards mid gap and, in dependence on TaN layer thickness, values of 4.65 eV (90 nm TaN) to 4.79 eV (30 nm TaN) are obtained.