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

HfO2/Al2O3 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 450degreesC using Al(CH3)(3) and O-3, and (4-5)-nm-thick HfO2 films were grown at 400degreesC 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 790degreesC for 40 s. The plasma treatment increased the Al2O3 interlayer thickness by approximately 1 mn 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 800degreesC in a N-2 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. (C) 2003 American Institute of Physics.