Many-Electron Multiplet Theory Applied to O-Vacancies in (i) Nanocrystalline HfO2 and (ii) Non-crystalline SiO2 and Si Oxynitride Alloys

Abstract

AbstractPerformance and reliability in semiconductor devices are limited by electronically active defects, primarily O-atom vacancies. Synchrotron X-ray spectroscopy results, interpreted in the context of multiplet theories, have been used to analyze conduction band edge, and O-vacancy defect states in nanocrystalline transition metal oxides such as HfO2, and the non-crystalline oxides including SiO2, and Si3N4 and Si oxynitride alloys. Multiplet theory provides the theoretical foundation for an equivalentd 2 model for O-vacancy transitions and negative ion states as detected by X-ray absorption spectroscopy in the O K pre-edge regime. Comparisons between theory and experiment have relied on Tanabe-Sugano energy level diagrams for identifying the symmetries and multiplicities of transition energies for an equivalent d2 ground state occupancy. The equivalent d2 model has been applied to nanocrystalline thin films of ZrO2,HfO2,TiO2 and Lu2O3 and provides excellent agreement with X-ray absorption spectroscopy data. The model has also been applied to SiO2 and other Si based dielectrics where very good agreement with multiplet theory has also been demonstrated. The spectra indicate both triplet and singlet final states indicating that the two electrons in the vacancy sites have singlet and triplet ground states that are within a few tenths of an eV of each other. For the transition metal oxides, this is explained by relatively small distortions in the vacancy geometry in which the separation between the respective transition metal atoms is 1.6 times the bond-length in an ideal tetrahedral geometry, or the same factor for two fold coordination in O-atom bonding sites in SiO2 andGeO2. These distortions minimize the exchange energy in triplet spin states, and reduce the radial wave function overlap in singlet spin states.KeywordsTransition Metal OxideTransition Metal AtomJahn TellerNegative Bias Temperature InstabilityEdge SpectrumThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.