GROWTH AND STRUCTURE OF RAPID THERMAL SILICON-OXIDES AND NITROXIDES STUDIED BY SPECTROELLIPSOMETRY AND AUGER-ELECTRON SPECTROSCOPY

Rapid thermal oxidation of Czochralski-grown silicon in either O-2 or N2O atmospheres have been studied using spectroellipsometry and Auger electron spectroscopy. Multiwavelength ellipsometric data were process ed in order to separately derive the thicknesses and refractive indexe s of rapid thermal dielectrics. Results revealed a significant increas e of the mean refractive index as the film thickness falls below 20 nm for both O-2 or N2O oxidant species. A multilayer structure including an about 0.3-nm-thick interfacial region of either SiOx or nitroxide in the case of O-2 and N2O growth, respectively, followed by a densifi ed SiO2 layer, was found to accurately fit the experimental data. The interfacial region together with the densified state of SiO2 close to the interface suggest a dielectric structure in agreement with the con tinuous random network model proposed for classical thermal oxides. Au ger electron spectroscopy analysis confirmed the presence of noncrysta lline Si-Si bonds in the interfacial region, mostly in the case of thi n oxides grown in O-2. It was speculated that the initial fast growth regime was due to a transient oxygen supersaturation in the interfacia l region. Besides, the self-limiting growth in N2O was confirmed and e xplained in agreement with several recently published data, by the ear ly formation of a very thin nitride or oxynitride membrane in the high ly densified oxide beneath the interface. The beneficial effect of dir ect nitrogen incorporation by rapid thermal oxidation in N2O instead o f O-2 for the electrical behavior of metal-oxide-semiconductor capacit ors is likely a better SiO2/Si lattice accommodation through the reduc tion of stresses and Si-Si bonds in the interfacial region of the diel ectric.