X-ray photoemission studies of praseodymium thin films on SiO 2/Si(100)

Pr overlayers, with thicknesses of about 1.8 and 0.6 nm, were deposited on 1.2 nm SiO2/Si(100) at room temperature and x-ray photoelectron spectroscopy (XPS) was used to investigate the reactions at the Pr/SiO2/Si interfaces as a function of annealing temperature. The results show that the Pr overlayers reduce SiO2 at room temperature, forming Pr2O3 and a Pr silicate (Pr-O-Si). For the 1.8 nm Pr/SiO2/Si system, the 1.2 nm SiO2 layer is mostly reduced at room temperature and a Pr silicide was also observed. The Pr-O-Si silicate increases in intensity while the Pr2O3 intensity decreases with annealing temperature. Angle-dependent XPS, taken after annealing, indicates that the silicate is located at the top surface. In the case of the 0.6 nm Pr/SiO2/Si system, the Pr overlayer is almost oxidized after annealing, and some SiO2 remains even after annealing at 1090 K, which can serve as a low-defect-density buffer layer between the high-kappa film (Pr2O3 and Pr-O-Si) and the silicon.