Tantalum oxide thin films were prepared by photo-assisted atomic layer deposition (Photo-ALD) in the substrate temperature range of 170-400 degreesC using Ta(OC2H5)(5) and H2O as precursors. The constant growth rates of 0.42 and 0.47 Angstrom per cycle were achieved for the films grown by normal ALD and Photo-ALD, respectively. The increased growth rate in Photo-ALD is probably due to the reactive surface by photon energy and faster surface reaction. In Photo-ALD, however, the constant growth rate started at lower temperature of similar to30 degreesC and one cycle time shortened up to 5.7 s than that of normal ALD. The films grown by normal ALD and Photo-ALD were amorphous and very smooth (0.21-0.35 run) as examined by X-ray diffractometer and atomic force microscopy, respectively. Also, the refractive index was found to be 2.12-2.16 at the substrate temperature of 190-300 degreesC, similar to that of the film grown by normal ALD. However, the remarkably low leakage current density of 0.6 x 10(-6) A/cm(2) to 1 x 10(-6) A/cm(2) at applied field of 1 MV/cm is several order of magnitude smaller than that of normal ALD, probably due to the presence of reactive atom species. (C) 2004 Elsevier B.V. All rights reserved.