Plasma-assisted atomic layer deposition (PA-ALD) is more suitable than thermal atomic layer deposition (ALD) for mass production because of its faster growth rate. However, controlling surface damage caused by plasma during the PA-ALD process is a key issue. In this study, the passivation characteristics of Al2O3 layers deposited by PA-ALD were investigated with various O-2 plasma exposure times. The growth per cycle (GPC) during Al2O3 deposition was saturated at approximately 1.4 angstrom/cycle after an O-2 plasma exposure time of 1.5 s, and a refractive index of Al2O3 in the range of 1.65-1.67 was obtained. As the O-2 plasma exposure time increased in the Al2O3 deposition process, the passivation properties tended to deteriorate, and as the radio frequency (RF) power increased, the passivation uniformity and the thermal stability of the Al2O3 layer deteriorated. To study the Al2O3 /Si interface characteristics, the capacitance-voltage (C-V) and the conductance-voltage (G-V) were measured using a mercury probe, and the fixed charge density (Q(f)) and the interface trap density (D-it) were then extracted. The Q(f) of the Al2O3 layer deposited on a Si wafer by PA-ALD was almost unaffected, but the D-it , increased with O-2 plasma exposure time. In conclusion, as the O-2 plasma exposure time increased during Al2O3 layer deposition by PA-ALD, the Al2O3/Si interface characteristics deteriorated because of plasma surface damage.