Measurement of the interface layer thickness in SiO2/Si structures by single-wavelength null ellipsometry

Abstract

A procedure for the determination of the interface layer thickness between the bulk SiO2 film and the Si substrate from single‐wavelength null ellipsometric data is described. The effect of the angular errors in the angle of incidence is eliminated because it is found along with the film and interface layer thicknesses. Optimum film thickness ranges minimizing the propagation of angular errors in measured ellipsometric quantities are deduced from error analyses. Immersion ellipsometry is thus shown to reduce further the effect of these errors. A 10 Å interface layer can thus be determined within 10±2 Å under these conditions. The dominant uncertainty produced in the interface layer thickness obtained from the ellipsometric angles measured to one or a few hundredths of a degree under these conditions is only due to the inaccurate knowledge of the interface layer refractive index. A minimum thickness for the interface layer may be specified at a particular value of the refractive index irrespective of its real value. The procedure is illustrated regarding these results with determining the interface layer thickness from simulated and experimental data on SiO2/Si structures. © 1998 John Wiley & Sons, Ltd.