Process control of reactive sputter deposition of AlO _x and improved surface passivation of crystalline silicon

In this paper, we investigate the relationship between the deposition-process parameters of reactively sputtered aluminium oxide films and the passivation of silicon surfaces. A method of tuning the deposition process has been established that results in a reduced level of surface recombination, where surface recombination velocities as low as 8.5 cm/s have been achieved on 1 Ω·cm n-type monocrystalline silicon. We find that in order to achieve good surface passivation, the deposition need to be conducted at low power density and at high deposition pressure. We have found that effective passivation is achieved when a sputtering target is close to being fully oxidized-indicated by deposition rate-likely resulting in films that are less aluminium rich. Additionally, Fourier-transform-infrared spectroscopy measurements were used for film characterization; the correlation between effective lifetime and the integrated absorption of all Al and O related bonds shows that films with lower absorption in the wavenumber range 500-1060 cm ^-1 result in better passivation.