Effect of rapid thermal annealing on the structure and the electrical properties of atomic-layer-deposited Ta2O5 films

Abstract

Tantalum oxide films were grown using atomic layer deposition with the precursors of Ta(OEt)(5) and H2O on ITO and Si substrates at 300 degreesC. The changes of the structure and the electrical properties of the films were investigated fur various rapid-thermal-annealing (RTA) temperatures. The thicknesses and compositions were analyzed using Rutherford backscattering spectroscopy and were found to be invariable under our RTA processes of 500 similar to 700 degreesC. As-deposited and RTA-processed samples under 550 degreesC were amorphous and had a dielectric constant of epsilon (r)approximate to 24. For these specimens, the leakage current density for the [Al/Ta2O5/ITO] capacitors gradually decreased with increasing the annealing temperature and was as low as 5x10(-8) A/cm(2) at an electric field of 1 MV/cm. This improvement of the leakage current characteristics is thought to result from a reduction of impurities, such as hydrogen remaining in the films, as observed from the depth analysis of secondary ion mass spectroscopy. The films annealed above 600 degreesC showed a polycrystalline structure. This crystallization leads to an increase in the permittivity, up to 52, and a high leakage-current level.