La–silicate gate dielectrics fabricated by solid phase reaction between La metal and SiO2 underlayers

Abstract

La-based high- k gate dielectrics were fabricated by reoxidation of thin La layers deposited on SiO 2 underlayers. Interface reaction that causes metal diffusion through the oxide underlayer increases permittivity of the oxide and forms high-quality La–silicate films. We successfully fabricated ultrathin La–silicates of equivalent oxide thickness ranging from 0.75 to 1.6 nm with low-leakage current by controlling the interface solid phase reaction. We characterized degradation in the silicate film caused by electrical stressing and demonstrated the effectiveness of high-temperature annealing to improve the reliability of silicate dielectrics. Moreover, it was found that water absorption during exposure to air causes positive fixed charge in the silicate (flatband voltage shift), but degradation can be annealed out at relatively low temperatures.