Effect of Composition in Ternary La–Al–O Films on Flat-Band Voltage for Application to Dual High-k Gate Dielectric Technology

Abstract

We examined the relationship between the flat-band voltage (Vfb) and the La/(La+Al) atomic ratio in a La–Al–O ternary oxide film for stacks with and without a SiO2 interfacial layer. A clear dependence of Vfb on La/(La+Al) atomic ratio was observed for both stacks. However, the dependence for the stack with the SiO2 layer was particularly large at La/(La+Al) atomic ratios below 40%, leading to a large maximum difference in Vfb (ΔVfb) of 1.2 eV. The results obtained indicate that dipoles with opposite orientations at La–Al–O/SiO2 interfaces contribute substantially to the large ΔVfb. These findings imply that precise control of Al concentration and the use of an interfacial layer with low permittivity are important in achieving both the threshold voltage (Vth) control of p-metal insulator semiconductor field effect transistors (p-MISFETs) and equivalent oxide thickness (EOT) scaling.