Quantification of Ge in Si1‐xGex by using low‐energy Cs+ and O2+ ion beams

Abstract

Several studies have been reported on the quantification of Ge in Si1‐xGex using SIMS with oxygen or cesium primary ions. Most of them were limited to lower Ge concentrations. In this paper, we discussed procedures to quantify Ge content in Si1‐xGex with x ranging from 0.11 to 0.70 by using low‐energy Cs+ and O2+ primary beams. The results showed that at impact energy of 250 eV, the Ge secondary ion yield changed dramatically against the SiGe matrix composition with a Cs+ primary beam, whereas the change was minimal with an O2+ primary beam. As a result, quantification by using the reference signal inside Si substrate became difficult as no linear correlation exists between the Ge intensity and the Ge concentration in the case of Cs+ primary ions. However, the correlation between the ratios of secondary intensities I(Ge)/I(Si) within the SiGe layers and the composition ratio [Ge]/[Si] is monotonic (although nonlinear). Hence, quantification based on the ratios of the secondary ion intensities versus the ratios of the corresponding contents worked for both Cs+ and O2+ primary beams to quantify the Ge content of an unknown SiGe sample. In addition to this, we reported the angular (incidence angles between 0° and 70°) dependence of the sputter yield of SiGe as a function of Cs+ primary ion energy (150–500 eV). Copyright © 2012 John Wiley & Sons, Ltd.