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