Effects of plasma nitridation of Al2O3 interlayer on thermal stability, fixed charge density, and interfacial trap states of HfO2 gate dielectric films grown by atomic layer deposition

HfO 2 / Al 2 O 3 gate dielectric thin-film stacks were deposited on Si wafers using an atomic-layer-deposition technique. A 2.3-nm-thick Al2O3 interlayer was grown at 450 °C using Al(CH3)3 and O3, and (4–5)-nm-thick HfO2 films were grown at 400 °C using HfCl4 and H2O as precursors. Because the Al2O3 interlayer was not an effective Si-diffusion barrier layer on its own, the Al2O3 interlayer was plasma treated under an NH3 atmosphere at 790 °C for 40 s. The plasma treatment increased the Al2O3 interlayer thickness by approximately 1 nm and decreased the overall capacitance density of the film stack. However, the thermal stability of the capacitance density was greatly improved as a result of the treatment resulting in a similar capacitance density after postannealing at 800 °C in a N2 atmosphere to that observed in nontreated samples after similar annealing conditions. The signs and amount of the fixed charges of the Al2O3/Si and HfO2/Al2O3 interfaces greatly depend on the nitridation of the Al2O3 layer. Furthermore, the interface trap density of the sample with the plasma-treated Al2O3 interlayer decreased from that of the nontreated sample by almost one order of magnitude.