Preparation of tantalum oxide thin films by photo-assisted atomic layer deposition

摘要

Tantalum oxide thin films were prepared by photo-assisted atomic layer deposition (Photo-ALD) in the substrate temperature range of 170-400℃ using Ta(OC_2H_5)_5 and H_2O as precursors. The constant growth rates of 0.42 and 0.47 A 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 ～30℃ 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 nm) 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℃, 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.