Ellipsometric characterization of shallow damage profiles created by Xe-implantation into silicon

Shallow damage profiles created by Xe-implantation into Si were characterized using spectroscopic ellipsometry (SE). 100 keV Xe ions with doses ranging from 1 × 10
¹³
to 1.6 × 10
¹⁴
cm
^-2
caused damage peaks at about 30 nm from the surface. The SE measurement is based on the fact that the ion implantation induced disorder changes the complex refractive index of the implanted material, therefore, it can be measured by optical methods. Because SE is an indirect technique, the sample properties are determined using proper optical models, and parameter fitting. The optical models and the fitting algorithms are crucial for getting reliable results. In this study we also present improved models and algorithms for the evaluation of the SE spectra. In the improved model the thicknesses of the sublayers are automatically calculated from the four parameters of the coupled half-Gaussian profile, while the number of the layers are held constant. This ensures that the calculation time does not increase when using the improved optical model. A new fitting algorithm, which we call multi point random search, was applied to minimize the probability of getting in a local minimum. The improved fit quality and the results from Rutherford backscattering spectrometry measurements used as cross-checking basically supported the new optical model.