Properties of Atomic Layer Deposited HfO2 Films on Ge Substrates Depending on Process Temperatures

The effect of deposition temperature and post deposition annealing (PDA) on the electrical properties of HfO2 films grown on a Ge substrate by atomic layer deposition (ALD) was investigated. The HfO2 films deposited at 280°C (280°C-HfO2) showed a large capacitance-voltage (C-V) hysteresis, but it was significantly reduced at 200°C (200°C-HfO2). 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 HfO2 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 HfO2 grown at 200°C is crystallized to the tetragonal phase, while the HfO2 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-HfO2 compared to the 280°C-HfO2