EXCESS SILICON AT THE SI(3)N4 SIO2 INTERFACE

Using electron energy loss spectroscopy, X-ray photoelectronic spectro scopy, 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 interfac e that the plasmon energy on the surface is 20 eV which is smaller tha n the bulk plasmon of either Si3N4 (24.0 eV) or SiO2 (23.0 eV). From e llipsometric 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 atom s during the oxidation of Si3N4. Based on these observations and on nu merical simulation, a hypothesis is proposed to explain the abnormally large electron capturing at the Si3N4/SiO2 interface observed previou sly and the accumulation of positive charge at the top interface of th e nitrided oxide under ionizing irradiation. (C) 1998 American Institu te of Physics.