Impurity gettering effect of atomic layer deposited aluminium oxide films on silicon wafers

We present experimental evidence for the impurity gettering effect of atomic layer deposited aluminium oxide (Al₂O₃) films on silicon wafers, during typical surface passivation activation at 425 °C. Iron was used as a model impurity in silicon to study the gettering effects. Dissolved iron concentrations were determined by carrier lifetime measurements, allowing the iron loss kinetics in silicon wafers with Al₂O₃ coatings to be monitored during annealing. The redistribution of iron to the surface layers and the sub-surface regions was examined by secondary ion mass spectrometry depth profiling. The results show that the atomic layer deposited Al₂O₃ films generate a strong gettering effect, removing 50% of the iron after 30 min at 425 °C for a 160-μm thick silicon wafer. The iron reduction process is largely diffusion-limited in the initial stages. The gettering effect is caused by the accumulation of iron at the Al₂O₃/Si interface.