Abstract
An interface dipole model explaining threshold voltage (V-t) tuning in HfSiON gated n-channel field effect transistors (nFETs) is proposed. The magnitude of nFET Vt tuning tuning depends on rare earth (F-E) type and diffusion in Si/SiOx/HfSiON/REOx cap layer/metal gated nFETs as follows: Sr < Er <Sc+Er < La < Sc < no cap layer. This V-t ordering is very similar to the trends in dopant clectronegativity (EN, dipole charge transfer) and ionic radius (r, dipole separation) expected for a interfacial dipole mechanism. The resulting V-t dependence on RE dopant allows distinction between a dipole model (dependent on EN and r) and an oxygen vacancy model (dependent on valence).