Influence of the Surface Pretreatment on the Electrical Properties of MgO and Al2O3 Gate Stacks grown by MBE

Abstract

For CMOS devices, the interface between the dielectric and the semiconductor is of crucial importance for the electrical properties. This paper is devoted to examining the role of different substrate preparation procedures on the interface properties. After the surface treatment 5 nm amorphous oxide films were deposited by molecular beam epitaxy (MBE). MgO on Si was chosen as our main model system. Additionally, a higher k dielectric, Al2O3, was also studied. The electrical properties were investigated through measurements of MOS capacitor structures. Mainly capacitance density measurements as a function of voltage C-V were performed and analysed. Moreover, post-metal annealing experiments were performed in order to change the interface configuration and to optimize the electrical properties. The results demonstrate that the interface properties can be well controlled by the pretreatment of the substrates. Surprisingly it was also found that an identical surface pretreatment – despite the different dielectrics – induced a systematic, reproducible and substantial VFB shift of the C-V curves while most other parameters remain unaffected. This opens additional possibilities to fine-tune the flat-band voltage in such high-k transistors.