APPLICATION OF ANGLE-RESOLVED XPS ALGORITHMS TO OVERLAYERS AND CONCENTRATION GRADIENTS

Angle-resolved XPS data from three different sample types was used to compare algorithms for the determination of overlayer thickness and/or concentration gradients. Samples included SiO2 on Si, epitaxial Si0.862Ge0.138 on Si and As implanted in Si. Two algorithms for the determination of overlayer thickness (the relative ratio and patchy overlayer algorithms) and two algorithms based on Laplace transform or regularization methods for the evaluation of concentration gradients were evaluated. For the SiO2 and As-implanted samples, results representative of the sample type were obtained. However, the composition profiles from the Laplace algorithms showed the expected sharp interface between the Si substrate and the SiGe overlayer, while the regularization algorithm did not. All of the algorithms have correlating parameters, and absolute results depend upon the normalization method, electron attenuation length values and other algorithm-dependent terms. A comparison of angle-resolved XPS data from different samples thus requires careful and consistent choices for algorithm parameters.