Electron-spin resonance (ESR) experiments show that the interface degradation induced in thermal (111)Si/SiO2by postoxidation annealing (POA) in vacuum—previously isolated by ESR as a permanent creation ofPb(&convolu;Si≡Si3)interface defects—is strongly enhanced(∼6 times)when performed inH2ambient. It, thus, appears that theH2POA step, standardly applied to passivate interface states (preexistingPbs) naturally introduced during oxidation, effectively creates additional defect entities; the process initiates from∼550 °Conward vis-a`-vis∼640 °Cfor vacuum. The results unveil the atomic nature of one of the mechanisms of the electrically long-known H-induced POA generation of adverse interface states. ©1998 American Institute of Physics.