Interface optimization and modification of band offsets of ALD-derived Al2O3/HfO2/Al2O3/Ge gate stacks by annealing temperature

Abstract

Interfacial thermal stability and band alignment of ALD-derived Al2O3/HfO2/Al2O3/Ge gate stacks have been investigated by X-ray photoelectron spectroscopy (XPS) and spectroscopy ellipsometry (SE) as a function of annealing temperature. It has been found that reduction in interfacial GeOx component and formation of HfAlO alloy layer have been detected with increasing the annealing temperature from 500 to 700°C. Combined with analysis from XPS and SE, the increase in conduction band offset and reductions in band gap and valence band offset have been observed. When annealing temperature reaches 700°C, the valence band offset has been reduced to 0.88eV, which is smaller than the minimal requirement of ΔEv values for high-k dielectrics and, thus, leads to unacceptably high leakage currents. Therefore, annealing temperature should be carefully controlled to guarantee excellent properties of Al2O3/HfO2/Al2O3/Ge gate stacks in future Ge-based MOS devices.