THICKNESS MEASUREMENT OF ULTRA-THIN SI OXIDE-FILMS BY ESCA

Ellipsometry has been widely used for measuring Si oxide thickness in semiconductor industry. However, as the gate oxide (SiO2) thickness for MOS (Metal-Oxide-Semiconductor) ULSI's (Ultra-large-scale Integrations) decreases with the increasing integration density, the error in measuring the thickness has become a problem. In this study, it is shown on the basis of the ESCA studies of the oxide concentration, chemical state and SiO2/Si interface structure that the oxide thickness can be defined and obtained from Si2p (oxidized) intensity as measured by ESCA (Electron Spectroscopy for Chemical Analysis). This thickness is that of SiO2, and unlike that of ellipsometry, the conventional method, it contains no effects of an adsorption layer. This thickness is defined from the results on thermal oxide films less than several nm thick formed in O2/N2 atmosphere at several hundred-degrees-C. However, it is considered that the same definition can also be used for the evaluation of the thickness of "natural" oxide films formed at room temperature.