Degradation of thin oxides during electrical stress

A bond-breaking phenomenon responsible for oxide degradation during electrical stress is considered as a multi-step process that includes generation of precursor breakdown defects by the injected electrons directly in the bulk oxide and the subsequent breakdown of the defect's bonds. Precursor defect generation is attributed to the capture/scattering of the injected electrons by the localized gap states associated with oxide structural imperfections. These precursor defects, represented by significantly elongated Si-O bonds or Si-Si bonds are shown to be unstable due to their vibrational excitation and polarization induced by temperature and an applied electric field. respectively; breakdown of the weak precursor defect's bonds results in the formation of the E' centers. The proposed model suggests that new precursor defects are preferentially created in the vicinity of the previously generated E' centers. This leads to the formation of defect clusters, which can grow and coalesce throughout the oxide, contributing to oxide leakage Current and eventual oxide breakdown. The model describes the charge-to-breakdown dependence on the electron fluence and energy, electric field, temperature and oxide thickness. (C) 2001 Elsevier Science Ltd. All rights reserved.