Systematic analysis of silicon oxynitride interfacial layer and its effects on electrical characteristics of high-k HfO2 transistor

High-k hafnium oxide dielectric metal-oxide-semiconductor field-effect transistors with several physical thicknesses of silicon oxynitride interfacial layers were investigated to understand the relationship of their effects to electrical properties. Both flatband voltage and threshold voltage were negatively shifted with reduction of leakage current density as the thickness of silicon oxynitride interfacial layer increased. Charge pumping measurement revealed that the density of interface states were proportional to the physical thickness of the interfacial layer. The large amount of positive charge and interface state density for the thick interfacial layer affected the effective channel electron mobility, resulting in 20% of low-field peak mobility degradation. In addition, less stress immunity under stress was observed when silicon oxynitride interfacial layer increased.