Aluminum oxide(Al2O3) film deposited by atomic layer deposition (ALD) is known to supply excellent surface passivation properties on crystalline Si surfaces. Since Al2O3 has fixed negative charge, it forms effective surface passivation by field effect passivation on the rear side in p-type silicon solar cell. However, Al2O3 layer formed by ALD process needs very long process time, which is not applicable in mass production of silicon solar cells. In this paper, plasma-assisted ALD(PA-ALD) was applied to form Al2O3 to reduce the process time. Al2O3 synthesized by ALD on c-Si (100) wafers contains a very thin interfacial SiO2 layer, which was confirmed by FTIR and TEM. To improve passivation quality of Al2O3layer, the deposition temperature was changed in range of 150∼350℃, then the annealing temperature and time were varied. As a result, the silicon wafer with aluminum oxide film formed in 250℃, 400℃ and 10min for the deposition temperature, the annealing temperature and time, respectively, showed the best lifetime of 1.6ms. We also observed blistering with nanometer size during firing of Al2O3 deposited on p-type silicon.