High-resolution x-ray photoelectron spectroscopy (XPS) was applied to characterize the electronic structures for a series of high-k materials (HfO2)x(Al2O3)1−x grown on (100) Si substrate with different HfO2 mole fraction x. Al 2p, Hf 4f, O 1s core levels spectra, valence band spectra, and O 1s energy loss all show continuous changes with x in (HfO2)x(Al2O3)1−x. These data are used to estimate the energy gap (Eg) for (HfO2)x(Al2O3)1−x, the valence band offset (ΔEν) and the conduction band offset (ΔEc) between (HfO2)x(Al2O3)1−x and the (100) Si substrate. Our XPS results demonstrate that the values of Eg, ΔEν, and ΔEc for (HfO2)x(Al2O3)1−x change linearly with x.

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The effect of postdeposition annealing (PDA) of the Al2O3 blocking layer in a charge-trap type memory device is investigated. Significant improvements are achieved by high temperature PDA at 1100 °C, achieving faster operation speed, good charge retention, and a wide program/erase window. Experimental evidence shows that the underlying mechanism is not the changes in the band gap of the crystallized Al2O3 but is due to the higher trap density in the Si3N4 trapping layer at a deeper energy level by the intermixing between Al2O3 and Si3N4. The reduced trapping efficiency of the annealed Al2O3 also helps improve the retention property.

Thermal instability of effective work function and its material dependence on metal/high-gate stacks is investigated. It is found that thermal instability of the effective work function of metal electrode on a gate dielectric is strongly dependent on the gate electrode and dielectric material. Thermal instability of a metal gate is related to the presence of silicon at the interface, and the Fermi-level pinning position is dependent on the location of silicon at the interface. The silicon-metal or metal-silicon bond formation by thermal anneal at the metal/dielectric interface induces the donor-like or acceptor-like interface states, causing a change of effective work function. Index Terms-Fermi-level pinning, high-, metal gate, thermal instability, work function.