Thickness dependence of structural and electrical characteristics of ZrO2 thin films as grown on Si by chemical-vapor deposition

Microstructural and electrical characteristics of as grown ZrO2 thin films having different thicknesses of 1.2-10 nm were investigated. The films were grown on a p-Si substrate by chemical-vapor deposition at 275 degreesC using zirconium t-butoxide as the precursor. The structural characterization showed that the ZrO2 films had a microstructure that changed from amorphous to polycrystalline with increased film thickness over 3.2 nm, along with a SiOx interfacial layer similar to1.5 nm thick, irrespective of the film thickness. From the hysteresis in the capacitance-voltage (C-V) relation of the Al/ZrO2/SiOx/p-Si metal-oxide-semiconductor capacitors, it was found that the density of the oxide-trapped charge drastically increased from 2.22 x 10(10) to 3.54 x 10(12) cm(-2) as the films change from amorphous to polycrystalline. Furthermore, the shift of flatband voltage in the C-V curves revealed that the fixed charges changed sign from negative to positive. An increase of interface-state density was also found from the stretch-out of the C-V curves and the increase of turnaround voltage in the current-voltage (I-V) relation. In addition, an analysis of the I-V relation indicated that the negatively biased leakage current in the ultrathin stacked dielectrics followed the direct tunneling of holes from substrate to gate before hard breakdown. However, for the thicker films, the leakage current changed to Fowler-Nordheim tunneling of electrons from the gate to the substrate. (C) 2004 American Vacuum Society.