Impact of the deposition and annealing temperature on the silicon surface passivation of ALD Al₂O₃ films

The effect of the deposition and annealing temperature on the surface passivation of atomic layer deposited Al₂O₃ films was investigated on n-type Cz silicon wafers. The deposition temperature was varied between 200 and 500°C and the annealing temperature between 300 and 450°C, respectively. Films prepared at 200 and 300°C showed an improvement of surface passivation with increasing anneal temperature. The Al₂O₃ films grown at 400 and 500°C did not improve by annealing. By corona charging experiments it was revealed that the improvement in surface passivation with increasing anneal temperature of films grown at 300°C can be attributed to a significant increase in chemical passivation with a minor increase in field-effect passivation. For Cz and FZ wafers an identical surface passivation was achieved with the chemical passivation being lower for Cz wafers due to the surface morphology and the field-effect passivation being quite similar. Consequently the field-effect passivation was found to be the more important passivation mechanism.