Nondestructive determination of damage depth profiles in ion-implanted semiconductors by multiple-angle-of-incidence single-wavelength ellipsometry using different optical models

Abstract

Several-parameter fitting of multiple-angle-of-incidence ellipsometry data is developed to characterize near-surface layers on semiconductors damaged by implantation. The damage depth profiles were described by either rectangular, trapezoid-type, or coupled half-Gaussian (realistic) optical models. The rectangular model has three parameters: the average damage level and effective thickness of the implanted layer, plus the thickness of the native oxide. The trapezoid-type model is enhanced with a fourth parameter, the width of the back (a/c) interface. The realistic optical model consists of a stack of layers with fixed and equal thicknesses and damage levels determined by a depth profile function (presently the coupled half-Gaussians). Five parameters were used: the center, the height, and two standard deviations of the profile, plus the thickness of the native oxide. The complex refractive index of each layer is calculated from the actual damage level by the Bruggeman effective medium approximation. The method was tested on Ge-implanted silicon layers (at a wavelength of 632.8 nm) and was cross checked with high depth resolution Rutherford backscattering spectrometry and channeling.