Excess silicon at the Si3N4/SiO2 interface

Using electron energy loss spectroscopy, X-ray photoelectronic spectroscopy, and ellipsometry measurements, a large number of Si-Si bonds at the Si3N4/thermal SiO2 interface is confirmed, After etching away the surface SiO2 of reoxidized Si3N4, we found at the Si3N4/SiO2 interface that the plasmon energy on the surface is 20 eV which is smaller than the bulk plasmon of either Si3N4 (24.0 eV) or SiO2 (23.0 eV). From ellipsometric measurement. a large value of the refractive index (II =2.1) in the Si3N4/wet SiO2 interface layer was obtained. The effective width of the Si-rich interfacial layer is estimated to be in the range of 6-5 Angstrom. We propose that the excess silicon at the Si3N4/SiO2 interface is created by replacing nitrogen atoms with the oxygen atoms during the oxidation of Si3N4. Based on these observations and on numerical simulation, a hypothesis is proposed to explain the abnormally large electron capturing at the Si3N4/SiO2 interface observed previously and the accumulation of positive charge at the top interface of the nitrided oxide under ionizing irradiation. (C) 1998 American Institute of Physics.