Properties of atomic layer deposited HfO ₂ films on Ge substrates depending on process temperatures

The effect of deposition temperature and post deposition annealing (PDA) on the electrical properties of HfO ₂ films grown on a Ge substrate by atomic layer deposition (ALD) was investigated. The HfO ₂ films deposited at 280°C (280°C-HfO ₂) showed a large capacitance-voltage (C-V) hysteresis, but it was significantly reduced at 200°C (200°C-HfO ₂). Further reduction of deposition temperature to 160°C resulted in the abrupt increase of C-V hysteresis. The reduction of C-V hysteresis was originated from the smaller degree of intermixing between the HfO ₂ and Ge substrate with decreasing temperature, while the increase of C-V hysteresis comes from the low density of films grown at low temperatures. The C-V hysteresis characteristics were also strongly influenced by PDA temperatures. PDA temperatures higher than 550°C induced a large C-V hysteresis regardless of deposition temperature. Interestingly, after the PDA process, the HfO ₂ grown at 200°C is crystallized to the tetragonal phase, while the HfO ₂ grown at 280°C is crystallized to the monoclinic phase. These different crystalline phases result in a lower equivalent oxide thickness in the 200°C-HfO ₂ compared to the 280°C-HfO ₂