Passivation mechanism of thermal atomic layer-deposited Al2O3 films on silicon at different annealing temperatures

Thermal atomic layer-deposited (ALD) aluminum oxide (Al 2 O 3 ) acquires high negative fixed charge density ( Q f ) and sufficiently low interface trap density after annealing, which enables excellent surface passivation for crystalline silicon. Q f can be controlled by varying the annealing temperatures. In this study, the effect of the annealing temperature of thermal ALD Al 2 O 3 films on p-type Czochralski silicon wafers was investigated. Corona charging measurements revealed that the Q f obtained at 300°C did not significantly affect passivation. The interface-trapping density markedly increased at high annealing temperature (>600°C) and degraded the surface passivation even at a high Q f . Negatively charged or neutral vacancies were found in the samples annealed at 300°C, 500°C, and 750°C using positron annihilation techniques. The Al defect density in the bulk film and the vacancy density near the SiO x /Si interface region decreased with increased temperature. Measurement results of Q f proved that the Al vacancy of the bulk film may not be related to Q f . The defect density in the SiO x region affected the chemical passivation, but other factors may dominantly influence chemical passivation at 750°C.