Aluminum oxide thin films were deposited by plasma-assisted atomic layer controlled deposition method in the temperature range of 100-125℃ using DMEAA (Dimethylethylamine alane [(CH₃)₂(C₂H_5)N:AlH₃]) as a source gas. Al was deposited by plasma-assisted ALD(Atomic Layer Deposition) method. And then, the Al films were oxidized into Al₂O₃ by the plasma oxidation in the same chamber without breaking the vacuum. For physical and electrical measurements, Al₂O₃ thin films of 15 ㎚ thickness were prepared by repetition of the above mentioned process. Thus prepared Al₂O₃ thin films showed a refractive index of 1.68. The thickness and the refractive index fluctuation of the film over a 4 in. wafer were ±2.3% and ±1.9%, respectively, for atomic layer controlled film, while those were ±7.8%, ±6.4% for all the sputter-deposited film. The leakage current density and breakdown field were measured to be about 10^(-8) Ａ/㎠ at 1 ㎹/㎝ and 7 ㎹/㎝, respectively. Considerable improvement of the electrical properties could be realized by the post oxygen-plasma annealing at 200℃.