ATOMIC LAYER EPITAXY GROWTH OF TANTALUM OXIDE THIN-FILMS FROM TA(OC2H5)(5) AND H2O

The deposition of thin Ta2O5 films by atomic layer epitaxy (ALE) was investigated in the temperature range of 150 to 450 degrees C using Ta(OC2H5)(5) and water as precursors. Because of the thermal self-decomposition of Ta(OC2H5)(5) the self-limiting ALE growth was achieved only below 350 degrees C. Ah the films grown were amorphous as examined by x-ray diffraction analysis. The films grown at 250 and 325 degrees C were stoichiometric within the accuracy of Rutherford backscattering spectrometry and contained 4 and 0.6 atom percent (a/o) hydrogen as determined by nuclear reaction analysis, respectively. Except for the outermost surface, the content of carbon residues was below 3 a/o as analyzed by x-ray photoelectron spectroscopy. The films exhibited smooth surfaces as observed by scanning electron microscopy and relatively uniform thicknesses with 7% deviation in the gas flow direction. The refractive index of the films increased with deposition temperature stabilizing at 2.23 at temperatures higher than 300 degrees C. The permittivities for the films grown at 250 and 325 degrees C were 21 and 25, respectively, and leakage current densities at 1 MV/cm electric field were 4.0 and 2.3 mA/cm(2), respectively.