Application of spectroscopic ellipsometry for investigations of compaction and decompaction state in Si-SiO2 systems

Abstract

In the modern microelectronics technologies, stresses and strains are known to affect process yield and microelectronic device reliability. Therefore, better understanding of generation mechanisms of elastic and non-elastic strains (compaction and decompaction) in the Si-SiO2 system is needed. The main goal of the work was the elaboration of the analytical functional relationship between refractive index n and density ρ of SiO2 layers on silicon substrates. Such ρ(n) relationship will allow determination of elastic and non-elastic strains in SiO2 layers on silicon substrates. For the sake of the quality and shape of silicon substrates surface, before thermal oxidation, all substrate wafers were subjected to interferometric measurements by means of Fizeau interferometer. But, ellipsometric measurements by using Variable Angle Spectroscopic Ellipsometer of J.A. Woollam Company allowed determination of thicknesses and refractive indexes of silica layers. Measured SiO2 masses and calculated volumes of the layers gave possibility to determine the degree of densification of the oxide layers on silicon substrates. The Hill approximation function curve turned out to be the best fitting curve for the experimental data. The obtained Hill curve indicates saturation for the density of the oxide equalled c.a. 4.53 g/cm3. This value corresponds to the value near by the one of the crystalline polymorph of silica (stishovite). It seems to be physically established that degree of densification tends to the limiting value. © 2009 IOP Publishing Ltd.