Investigation of c-Si surface passivation using thermal ALD deposited HfO2 films

Abstract

Thermal Atomic Layer Deposition (ALD) based Hafnium oxide (HfO2) films grown on n-type Float Zone (FZ) c-Si are investigated as passivation layers. In order to reach optimum passivation, one needs an adequate choice of film growth variables, preceded by the proper pre-growth surface conditioning and the post deposition thermal treatment of the film. Provided a set of deposition parameters, annealing of the film grown on OH-terminated Si surfaces in air led to the lowest Surface Recombination Velocity (SRV) value reported in the literature using a single layer of HfO2, namely a value of 1.2 cm/s for a 15 nm thick HfO2. The SRV is extracted from the measured carrier's effective lifetime. Field effect passivation accounts for this performance as shown by the oxide charges density (Qtot) values extracted from the C-V measurements. The chemical passivation contribution, although suspected to be as important, cannot be established in a definite manner due to inherent limitations of the experimental method (high frequency C-V) used to extract the reported Dit values corresponding to the interface state density of defects at the interface HfO2/Si.