Investigation of the thermal stability of reactively sputter-deposited TiN MOS gate electrodes

The effective work function of TiN, deposited by reactive magnetron sputtering, was found to be unaltered at ∼5 eV after rapid thermal processing (RTP) annealing in nitrogen atmosphere at temperatures below 700°C. However, further increase in the RTP temperature lowered the extracted work function by 0.4-0.5 eV to midgap values. In this brief, RTP anneals of TiN/SiO₂/p-Si MOS capacitors were evaluated by extracting the metal gate TiN work function from capacitance-voltage measurements of MOS capacitors with multiple SiO₂ thicknesses. The RTP anneals were performed in nitrogen between 600°C and 1000°C for 30 s. The effective oxide charge density in the capacitors increased by a factor of five at RTP temperatures exceeding 800°C. The resistivity seems to decrease slightly with increasing RTP temperature. The crystallographic orientation of the TiN films remain (111) after annealing up to 900°C and is apparently not responsible for the change in work function. Analysis by X-ray photoelectron spectroscopy indicates no significant change in the binding states of titanium and nitrogen in the TiN/SiO₂ interface with increasing temperature.