Comparison of defect structure in N2O- and NH3-nitrided oxide dielectrics

Abstract

Electron spin resonance spectroscopy is used to identify and compare point defects in N2O-nitrided, NH3-nitrided, and conventional SiO2 films. We detect only three types of defects in these dielectrics. Pb centers, the primary source of interface states in Si/SiO2 systems under all technologically significant circumstances, appear in all three dielectrics. Both N2O and NH3 nitridation result in higher as-processed Pb interface defect densities, but lower radiation-induced Pb defect generation. Thus N2O nitridation appears capable, as does NH3 nitridation, of providing reduced radiation-induced interface state generation. In addition, both nitridations appear capable of lowering the number of radiation-induced E′ centers, the dominant hole trap in conventional thermal oxides. NH3 nitridation, however, appears to offer greater resistance to radiation-induced generation of these traps. NH3 nitridation also results in a large number of bridging nitrogen centers, and strong evidence indicates that the bridging nitrogen centers are the dominant electron trap in NH3-nitrided and -reoxidized nitrided oxide films. These defects are absent in N2O-nitrided films, which are known to exhibit reduced levels of electron trapping.