XPS/LEIS STUDY OF HIGH-K RARE EARTH (LU, YB) OXIDES AND SILICATES ON SI: THE EFFECT OF ANNEALING ON MICROSTRUCTURE EVOLUTION

Abstract

Thin Lu₂O₃ and Yb₂O₃ layers grown on Si using Atomic Layer Deposition (ALD) were studied with x-ray photoelectron spectroscopy (XPS) and low energy ion spectroscopy (LEIS). Our results show that ALD grown Lu2O3 and Yb₂O₃ films subsequently annealed in N₂ are polycrystalline, and that their oxygen “subsystems” are very sensitive to further heat treatments in various atmospheres. In particular, it is evident that two chemically nonequivalent oxygen states are present in the oxides at equilibrium conditions. The one with the higher binding energy (BE_O1s ≈ 531.8 eV) is loosely bound, desorbs from the subsurface region upon vacuum annealing at T>300°C, and reappears upon annealing in O₂ (T≈500°C, P_O2=10^-1 Torr). ALD can provide a variety of Lu silicates, depending on precursor combination and growth conditions. As grown ultrathin (≤5 nm) continuous Lu₂O₃ and Yb₂O₃ films on Si exhibit an interfacial layer from ~1 to 3 nm thick and a hydroxide layer on top. Upon annealing in N₂, both components of the stacks transform into amorphous silicates. In situ XPS and LEIS analyses show that ultrathin Lu silicate films are further stable on Si at least up to T=900°C, while for ultrathin Yb silicate layers the valence band structure appears sensitive to the annealing environment, and the Yb silicates eventually decompose and desorb from the surface upon vacuum annealing at T=900°C.