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

Tantalum oxide films were grown using atomic layer deposition with the prec ursors 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 in vestigated fur various rapid-thermal-annealing (RTA) temperatures. The thic knesses and compositions were analyzed using Rutherford backscattering spec troscopy and were found to be invariable under our RTA processes of 500 sim ilar to 700 degreesC. As-deposited and RTA-processed samples under 550 degr eesC 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 temperatu re 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 fr om a reduction of impurities, such as hydrogen remaining in the films, as o bserved from the depth analysis of secondary ion mass spectroscopy. The fil ms annealed above 600 degreesC showed a polycrystalline structure. This cry stallization leads to an increase in the permittivity, up to 52, and a high leakage-current level.