Reactive radio frequency sputter deposition of higher nitrides of titanium, zirconium, and hafnium

Abstract

Higher nitrides of Ti, Zr, and Hf have been prepared by reactive rf sputtering of Ti, Zr, and Hf metals in a pure nitrogen atmosphere. The electrical and optical properties of these films are highly dependent on two deposition parameters, namely, the substrate temperature and the target voltage. We find that at each particular target voltage, there exists a critical temperature below which the higher nitride phase can be deposited and above which the phase cannot form. This suggests that the higher nitride phase (which is speculated to be an ordered defect structure) is metastable and is not energetically favored at high processing temperature or at high input power. At 2000 V target voltage, this critical temperature is determined to be approximately 200 °C for Hf–N, 25 °C for Zr–N, and is unknown for Ti–N system. The optical band gap of the ZrNx films decreases from 5.31 to 1.66 eV as the substrate temperature varies from −196 to 750 °C. Thermal analyses, using modulated beam mass spectrometry for monitoring the desorption rate of N2 gas, show that the principal decomposition reaction for TiNx, ZrNx, and HfNx films peak at 753, 773, and 788 °C, respectively.