Development of X-ray Photoelectron Spectroscopy under bias and its application to determine band-energies and dipoles in the HKMG stack

In this paper, we present for the first time specific methodology and test structures authorizing an accurate analysis of XPS under bias measurements. Such analysis which identifies effective biasing across the device, allows to determine the absolute energy levels of the different layers in the HKMG stack at any bias. This enables an accurate band diagram identification and it is applied to analyze the physical mechanisms at work in the threshold voltage (VT) engineering of HKMG stacks. We demonstrate that VT shift induced by La and Al additives or metal gate thickness variations originates by the modifications of the dipole at SiO2/high-k interface.