A surface nitridation technique using NH3 anneal has been investigated to reduce interface reaction and consequently the equivalent oxide thickness (EOT) of TaN/HfO2/Si metal-oxide-semiconductor capacitor. For the same EOT, the nitrided samples showed 1-2 order of magnitude lower leakage current density compared to the non-nitrided ones. Furthermore, the nitrided samples showed better thermal stability. However, nitridation induced higher interface state density and larger hysteresis. The degraded interface quality due to the nitridation was improved by post-metal annealing (PMA). Using the optimized nitridation and PMA, EOT of the capacitor was scaled down to similar to10 Angstrom with keeping leakage current below 0.1 mA/cm(2) at -1.5 V Interface state density and hysteresis were similar to8.4 X 10(10) eV(-1)/cm(2), and 45 mV, respectively. (C) 2004 American Vacuum Society.