Improved C–V characteristics of metal-oxide-semiconductor capacitors with tantalum nitride gate electrodes grown by ultra-low-pressure chemical vapor deposition

Tantalum nitride (TaN) films have been grown for metal gate electrode applications by ultra-low-pressure chemical vapor deposition using a Ta[=NC(CH3)2C2H5][N(CH3)2]3 precursor. TaN films deposited at 450 °C had a resistivity of 4 mΩ cm. The Ta:N:C ratio of the deposited films was about 1:1:1, as measured by Rutherford backscattering spectroscopy. TaN/SiO2/p-Si capacitors subjected to postdeposition annealing (PDA) showed distorted capacitance–voltage (C–V) curves, although no apparent reaction layer was observed at the interface between TaN and SiO2. The distortion of the C–V curves could be eliminated by depositing a 200-nm-thick SiO2 capping layer onto the TaN gate electrodes prior to PDA. The PDA-induced distortion can be ascribed to mechanical stress due to the difference in thermal expansion coefficients between TaN and Si. It is suggested that control of the mechanical stress during PDA is important for scaled metal-oxide-semiconductor devices using metal gate electrodes.