Elsevier

Applied Surface Science

Volume 432, Part B, 28 February 2018, Pages 72-77
Applied Surface Science

Full Length Article
Quantitative analysis of Si1-xGex alloy films by SIMS and XPS depth profiling using a reference material

https://doi.org/10.1016/j.apsusc.2017.08.136Get rights and content

Highlights

  • Quantitative analysis methods of multi-element alloy films were investigated.

  • The RSFs were determined from a reference alloy film by the conventional method, average intensity method and total number counting method.

  • In XPS analysis, the measurement uncertainty was highly improved by the AI method and TNC method.

Abstract

Quantitative analysis methods of multi-element alloy films were compared. The atomic fractions of Si1-xGex alloy films were measured by depth profiling analysis with secondary ion mass spectrometry (SIMS) and X-ray Photoelectron Spectroscopy (XPS). Intensity-to-composition conversion factor (ICF) was used as a mean to convert the intensities to compositions instead of the relative sensitivity factors. The ICFs were determined from a reference Si1-xGex alloy film by the conventional method, average intensity (AI) method and total number counting (TNC) method. In the case of SIMS, although the atomic fractions measured by oxygen ion beams were not quantitative due to severe matrix effect, the results by cesium ion beam were very quantitative. The quantitative analysis results by SIMS using MCs2+ ions are comparable to the results by XPS. In the case of XPS, the measurement uncertainty was highly improved by the AI method and TNC method.

Introduction

Quantitative analysis of alloy films has been one of the most important analytical issues for international standardization. The quantification of AuCu and CoNi alloy films was the subject of Versailles Project on Advanced Materials and Standards – Surface Chemical Analysis (VAMAS-SCA) [1], [2], [3], [4] By Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM) two key comparisons K-67 and K-129 have been performed for the quantification of FeNi alloy films and Cu(In,Ga)Se2 films, respectively [5], [6], [7]. The degrees of equivalence uncertainty of K-129 (0.0228 mol/mol for Se in Cu(In,Ga)Se2 films) by total number counting (TNC) method for was much better than that of K-67 (0.0330 mol/mol for Fe in FeNi alloy films) by the conventional method [5], [7].

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are the general methods for the quantitative surface compositional analysis of multi-element alloy films [8], [9], [10]. The relative sensitivity factors (RSFs) determined from pure metals are generally used for the quantification of alloy materials. However, the matrix effects due to the atomic density, the attenuation lengths of electrons and the electron backscattering factor (for AES) in the matrix materials must be taken into account [11], [12], [13].

A calibration method using an alloy reference material is recommended for the quantitative analysis of binary alloys to minimize the matrix effects. The ideal method for the quantification of binary alloys is to use alloy certified reference materials (CRM) with the same composition. In a pilot study P-98, it showed that the RSFs of Fe and Ni determined from a certified alloy film are much more quantitative than those determined from the pure elements [5].

Recently, the atomic fractions and depth distributions of the constituent elements in multi-element alloy films could be quantitatively analyzed by secondary ion mass spectrometry (SIMS) and AES using the RSFs determined from a multi-element alloy reference film by TNC method [14], [15].

In this study, the quantitative analysis of multi-element alloy films was systematically investigated for the Si1-xGex alloy films. The measurement uncertainties for the quantitative analysis of binary alloy films were compared for the results by a conventional method, average intensity (AI) method and TNC method.

Section snippets

Fabrication of alloy films

Si1-xGex alloy films were grown by ion beam sputter deposition (IBSD) using a 1 keV Ar+ ion beam produced by a Kaufmann-type DC ion gun [16]. The target material was sputtered and deposited on 6” Si (100) substrates rotating with a speed of 30 revolutions per minute to improve the thickness uniformity. The composition of the alloy thin films was controlled by varying the relative sputtering areas of the two adjacent target materials using a movable target holder. The growth rate was calibrated

Measurement method

The quantification of multi-element alloy films was studied by SIMS and XPS depth profiling. The intensities of the secondary ions and the peak areas of the core level photoelectons are the signals to monitor in depth profiling analyses by SIMS and XPS, repectively. The average-matrix relative sensitivity factors (AMRSF) determined from the pure-element RSFs (PERSF) and theoretically determined matrix correction factors are the general relative sensitivity factors for the quantification of

SIMS depth profiling

The SIMS quantitative analysis of Si1-xGex alloys was performed with a IMS 7F SIMS instrument (Cameca, France). Depth profiling was performed by oxygen and cesium ion beams. Fig. 3 shows the quantitative analysis results by O2+ ion beam with the energy of 1 keV. There is no great difference in the slope and offset value between the results by AI and TNC methods. The relations between the measured atomic fractions and the nominal values are not so linear due to the severe matrix effect.

The

Conclusion

The atomic fractions of Si1-xGex alloy films measured by SIMS and XPS were compared with the certified values by RBS. The intensity-to-composition conversion factors were determined from a reference Si1-xGex alloy film by the conventional method (CM), average intensity (AI) method and total number counting (TNC) method. The atomic fractions measured by SIMS using oxygen ion beams are not so quantitative due to severe matrix effect. However, the results by SIMS using cesium ion beam are very

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