SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 2002; 33: 238–244 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/sia.1206 Comparison of the Tougaard, ARXPS, RBS and ellipsometry methods to determine the thickness of thin SiO 2 layers B. S. Semak 1 , C. van der Marel 2 and S. Tougaard 1∗ 1 Physics Department, University of Southern Denmark, SDU, Campusvej 55, DK-5230 Odense M, Denmark 2 Philips CFT/WY42, Prof.Holstlaan 4, 5656 AA Eindhoven, The Netherlands Received 1 November 2001; Revised 18 December 2001; Accepted 18 December 2001 The Tougaard and angle-resolved x-ray photoelectron spectroscopy (ARXPS) methods were compared with ellipsometry and Rutherford backscattering (RBS) for their ability to determine the amount of SiO 2 on an Si substrate. The Tougaard and ARXPS methods give generally consistent results (root-mean-square deviation ∼12%), whereas the deviation between the other techniques is significantly larger (∼30–40%). The Tougaard method gives consistent results for all angles of emission q ≤ 60 ◦ . It is found also that the amount of SiO 2 determined by the two methods depends approximately linearly on the inelastic mean free path. The ARXPS method also depends on the accuracy with which one can separate the peak area of the bulk and the oxide part of the peaks. The correction for elastic scattering in the ARXPS method gives a reduction of only 5 – 7% in the determined amount of SiO 2 . Copyright  2002 John Wiley & Sons, Ltd. KEYWORDS: XPS; ARXPS; RBS; ellipsometry; Tougaard method; SiO 2 layers INTRODUCTION Measurement of the thickness of oxide overlayers on silicon is very important from a technological point of view. 1 In the present paper we study two computational methods for determining the thickness and surface morphology of thin SiO 2 overlayers on Si using x-ray photoelectron spectroscopy (XPS) spectra, the Tougaard method and the angle-resolved x-ray photoelectron spectroscopy (ARXPS) method. The Tougaard method 2–6 relies on the fact that the energy distribution of the emitted electrons depends strongly on the travelled path lengths and thereby also on the in-depth concentration profile. Quantification then is possible by analysis of the peak shape and background of inelastically scattered electrons. In the Tougaard method, the in-depth concentration profile is determined from analysis of a spectrum taken at a single emission angle. In this paper we study also the consistency in depth profiles obtained from spectra taken at various emission angles. The ARXPS method 7–9 relies on the phenomenon that the angular dependence of the peak intensity varies characteristically with the depth of excitation. Commercial software packages QUASES-Tougaard 11 and QUASES-ARXPS 13 were used for data analysis of the overlayer thickness of five different SiO 2 samples. These samples had also been characterized using Rutherford backscattering spectroscopy (RBS) and ellipsometry. These results will be compared with the results presented here. The paper presents also a discussion on Ł Correspondence to: S. Tougaard, Physics Department, SDU-Odense, Campusvej 55, DK-5230 Odense M, Denmark. E-mail: svt@fysik.sdu.dk. the influence of the uncertainty of the inelastic mean free path (IMFP)  on the analysis results. The effect of elastic scattering also is studied because the QUASES-ARXPS method provides the possibility of correcting for elastic scattering effects by an algorithm proposed by Nefedov. 10 EXPERIMENTAL X-ray photoelectron spectra of the O 1s peak were used in the QUASES-Tougaard analysis and XPS spectra of the Si 2s and Si 2p peaks were used in the QUASES-ARXPS analysis. The photoelectrons were excited with monochromatic Al K˛ x-rays and recorded with a Quantum 2000 (Phi) analyser. The O 1s spectra were taken at different emission angles, with 117 eV pass energy and a step size of 0.25 eV. The acquisition window for these spectra was 400–700 eV (binding energy). These wide-scan spectra at relatively low energy resolution were used in the QUASES-Tougaard analysis method (see next section for details). Spectra were recorded at emission angles 0, 30, 45 and 60 ° and at an analyser acceptance angle of š20 ° . The Si 2p and Si 2s spectra were recorded at emission angles 0, 30, 45, 60, 70, 76, 80, 82 and 84 ° , with a pass energy of 47 eV, a step size of 0.2 eV and an analyser acceptance angle of š4 ° . The acquisition windows were 140–170 eV (Si 2s) and 90–120 eV (Si 2p) and contained both the bulk and oxide part of the Si 2p and Si 2s peaks. These spectra were decomposed to determine the peak areas of the bulk and oxide Si peaks, which are needed for the QUASES-ARXPS analysis (see next section). Table 1 summarizes the samples studied and shows the thicknesses determined by RBS and ellipsometry. Sample A Copyright  2002 John Wiley & Sons, Ltd.