Oxygen incorporation and dipole variation in tantalum nitride film used as metal-gate electrode

Abstract

Tantalum nitride (TaN) films were used as gate electrodes in MOS capacitors fabricated with 8-nm-thick SiO2 as gate dielectric, and also used in Schottky diodes on n-type Si (100) substrates. TaN films with 20- and 100-nm-thick layers presented electrical resistivity of 439 and 472 μΩ cm, respectively. XPS measurements on these TaN film surfaces show oxygen incorporation, which can be related to air exposure. MOS capacitors with TaN/SiO2/Si/Al and Al/TaN/SiO2/Si/Al structures, and Schottky diodes with TaN/Si/Al and Al/TaN/Si/Al structures, were fabricated on the same substrates. These devices were electrically characterized by capacitance–voltage (C–V) and current–voltage (I–V) measurements after sintering in a conventional furnace in a forming gas environment at 450 °C, for different times between 0 and 30 min. From C–V measurements of the MOS capacitors, the extracted TaN work function, effective charge densities, and flatband voltage values were found to be between 4.23 and 4.42 eV, −1011 and −1012 cm−2, and −0.12 and 0.25 V, respectively. From I–V measurements of the Schottky diodes, work function and ideality factor values between 4.40 and 4.53 eV, and 1.0 and 1.9, respectively, were extracted. The variation of the TaN work function (extracted from C–V and I–V curves), flatband voltage, and ideality factor values were related to dipole variations (at the TaN/SiO2 interface), Ta and N vacancies in the TaN film, and oxygen incorporation on the TaN film surface. These results can contribute to work function engineering area for MOS technology.