Effect on passivation mechanism and properties of HfO2/crystalline-Si interface under different annealing atmosphere

Hafnium oxide (HfO2) thin film has received tremendous research interests as a passivation layer of crystalline silicon (c-Si) due to its thermal stability and positive fixed charges. HfO2 films were prepared both on P-type and N-type polished c-Si via a remote plasma atomic layer deposition process. Post annealing was carried out in oxygen, atmosphere (Air) and nitrogen (N2) at temperature of 500 °C. Electrical characterization was done through a regular metal-insulator-semiconductor structure and capacitance-voltage measurements. The oxide fixed charge (Qf) and density of interface traps (Dit) between HfO2 and c-Si were extracted. Qf and Dit reveal the potential of HfO2 for field effect and chemical passivation, respectively. Effective lifetime measurements by microwave photoconductivity decay in Si wafers passivated with HfO2 were applied to characterize surface recombination velocity to directly evaluate the overall passivation quality. The impacts of post-annealing gas ambient on passivation qualities on Si by HfO2 thin films are systematically studied. The results show that N2-annealed sample possesses the highest Qf of 1.73 × 1012 cm−2 and therefore provides the best field effect passivation. Air-annealed sample has lowest Dit of 1.0 × 1012 eV−1cm−2 and therefore provides the best chemical passivation. Air-annealed sample possesses the highest effective lifetime of 290 μs at injection level of 1 × 1015 cm−3, which means that good passivation was obtained for N-type Si wafer passivated with HfO2 after annealing in Air.