Effect of ozone concentration on silicon surface passivation by atomic layer deposited Al2O3

•The ALD Al2O3 passivation quality can be controlled by the ozone concentration.•Ozone concentration affects the Si/Al2O3 interface charge and defect density.•A surface recombination velocity of 7cm/s is reached combining ozone and water ALD.•Carbon and hydrogen concentrations correlate with the surface passivation quality. We study the impact of ozone-based Al2O3 Atomic Layer Deposition (ALD) on the surface passivation quality of crystalline silicon. We show that the passivation quality strongly depends on the ozone concentration: the higher ozone concentration results in lower interface defect density and thereby improved passivation. In contrast to previous studies, our results reveal that too high interface hydrogen content can be detrimental to the passivation. The interface hydrogen concentration can be optimized by the ozone-based process; however, the use of pure ozone increases the harmful carbon concentration in the film. Here we demonstrate that low carbon and optimal hydrogen concentration can be achieved by a single process combining the water- and ozone-based reactions. This process results in an interface defect density of 2×1011eV−1cm−2, and maximum surface recombination velocities of 7.1cm/s and 10cm/s, after annealing and after an additional firing at 800°C, respectively. In addition, our results suggest that the effective oxide charge density can be optimized in a simple way by varying the ozone concentration and by injecting water to the ozone process.