Deposition temperature dependence of material and Si surface passivation properties of O3-based atomic layer deposited Al2O3-based films and stacks

The material composition and the Si surface passivation of aluminum oxide (Al2O3) films prepared by atomic layer deposition using Al(CH3)3 and O3 as precursors were investigated for deposition temperatures (TDep) between 200 °C and 500 °C. The growth per cycle decreased with increasing deposition temperature due to a lower Al deposition rate. In contrast the material composition was hardly affected except for the hydrogen concentration, which decreased from [H] = 3 at. % at 200 °C to [H] < 0.5 at. % at 400 °C and 500 °C. The surface passivation performance was investigated after annealing at 300 °C–450 °C and also after firing steps in the typical temperature range of 800 °C–925 °C. A similar high level of the surface passivation performance, i.e., surface recombination velocity values <10 cm/s, was obtained after annealing and firing. Investigations of Al2O3/SiNx stacks complemented the work and revealed similar levels of surface passivation as single-layer Al2O3 films, both for the chemical and field-effect passivation. The fixed charge density in the Al2O3/SiNx stacks, reflecting the field-effect passivation, was reduced by one order of magnitude from 3·1012 cm−2 to 3·1011 cm−2 when TDep was increased from 300 °C to 500 °C. The level of the chemical passivation changed as well, but the total level of the surface passivation was hardly affected by the value of TDep. When firing films prepared at of low TDep, blistering of the films occurred and this strongly reduced the surface passivation. These results presented in this work demonstrate that a high level of surface passivation can be achieved for Al2O3-based films and stacks over a wide range of conditions when the combination of deposition temperature and annealing or firing temperature is carefully chosen.