ISO/TC 201/SC 7/WG 2 - Quantification and interpretation of data in electron spectroscopy

This document is intended to aid the operators of X-ray photoelectron spectrometers in their analysis of typical samples. It takes the operator through the analysis from the handling of the sample and the calibration and setting-up of the spectrometer to the acquisition of wide and narrow scans and also gives advice on quantification and on preparation of the final report.

This document specifies the necessary information required in a report of analytical results based on measurements of the intensities of peaks in Auger electron and X-ray photoelectron spectra. Information on methods for the measurement of peak intensities and on uncertainties of derived peak areas is also provided.

This document is designed to allow the user to assess, on a regular basis, several key parameters of an X‑ray photoelectron spectrometer. It is not intended to provide an exhaustive performance check, but instead provides a rapid set of tests that can be conducted frequently. Aspects of instrument behaviour covered by this document include the vacuum, measurements of spectra of conductive or non-conductive test specimens and the current state of the X‑ray source. Other important aspects of the instrument performance (e.g. lateral resolution) fall outside the scope of this document. The document is intended for use with commercial X‑ray photoelectron spectrometers equipped with a monochromated Al Kα X‑ray source or with an unmonochromated Al or Mg Kα X‑ray source.

This document specifies several methods for measuring the oxide thickness at the surfaces of (100) and (111) silicon wafers as an equivalent thickness of silicon dioxide when measured using X-ray photoelectron spectroscopy. It is only applicable to flat, polished samples and for instruments that incorporate an Al or Mg X-ray source, a sample stage that permits defined photoelectron emission angles and a spectrometer with an input lens that can be restricted to less than a 6° cone semi-angle. For thermal oxides in the range 1 nm to 8 nm thickness, using the best method described in this document, uncertainties, at a 95 % confidence level, could typically be around 2 % and around 1 % at optimum. A simpler method is also given with slightly poorer, but often adequate, uncertainties.

ISO 19668:2017 specifies a procedure by which elemental detection limits in X-ray photoelectron spectroscopy (XPS) can be estimated from data for a particular sample in common analytical situations and reported. This document is applicable to homogeneous materials and is not applicable if the depth distribution of elements is inhomogeneous within the information depth of the technique.

ISO 17973:2016 specifies a method for calibrating the kinetic energy scales of Auger electron spectrometers with an uncertainty of 3 eV, for general analytical use in identifying elements at surfaces. In addition, it specifies a method for establishing a calibration schedule. It is applicable to instruments used in either direct or differential mode, where the resolution is less than or equal to 0,5 % and the modulation amplitude for the differential mode, if used, is 2 eV peak-to-peak. It is applicable to those spectrometers equipped with an inert gas ion gun or other method for sample cleaning and with an electron gun capable of operating at 4 keV or higher beam energy.

ISO/TR 18394:2016 provides guidelines for identifying chemical effects in X-ray or electron-excited Auger-electron spectra and for using these effects in chemical characterization.

ISO 19830:2015 Standard is to define how peak fitting and the results of peak fitting in X-ray photoelectron spectroscopy shall be reported. It is applicable to the fitting of a single spectrum or to a set of related spectra, as might be acquired, for example, during a depth profile measurement. This International Standard provides a list of those parameters which shall be reported if either reproducible peak fitting is to be achieved or a number of spectra are to be fitted and the fitted spectra compared. This International Standard does not provide instructions for peak fitting nor the procedures which should be adopted.

ISO 15472:2010 specifies a method for calibrating the binding-energy scales of X‑ray photoelectron spectrometers, for general analytical purposes, using unmonochromated Al or Mg X‑rays or monochromated Al X‑rays. It is only applicable to instruments which incorporate an ion gun for sputter cleaning. It further specifies a method to establish a calibration schedule, to test for the binding-energy scale linearity at one intermediate energy, to confirm the uncertainty of the scale calibration at one low and one high binding-energy value, to correct for small drifts of that scale and to define the expanded uncertainty of the calibration of the binding-energy scale for a confidence level of 95 %. This uncertainty includes contributions for behaviours observed in interlaboratory studies but does not cover all of the defects that could occur. ISO 15472 is not applicable to instruments with binding-energy scale errors that are significantly non-linear with energy, to instruments operated in the constant retardation ratio mode at retardation ratios less than 10, to instruments with a spectrometer resolution worse than 1,5 eV, or to instruments requiring tolerance limits of ±0,03 eV or less. It does not provide a full calibration check, which would confirm the energy measured at each addressable point on the energy scale and which would have to be performed in accordance with the manufacturer's recommended procedures.

ISO 17974:2002 specifies a method for calibrating the kinetic energy scales of Auger electron spectrometers used for elemental and chemical state analysis at surfaces. It also specifies a calibration schedule for testing the kinetic energy scale linearity at one intermediate energy, for confirming the uncertainty of the scale calibration at one low and one high kinetic energy value, for correcting for small drifts of that scale and defining the expanded uncertainty of the calibration of the kinetic energy scale for a confidence level of 95 % (with this uncertainty including contributions for behaviours observed in interlaboratory studies but not covering all possible defects). It is applicable only to those instruments incorporating an ion gun for sputter cleaning. It is not applicable to instruments with kinetic energy scale errors significantly non-linear with energy, those operated at relative resolutions poorer than 0,2 % in the constant delta E/E mode or 1,5 eV in the constant delta E mode, those requiring tolerance limits of plus or minus 0,05 eV or less, nor those with an electron gun that cannot be operated in the energy range 5 keV to 10 keV. It does not provide a full calibration check for confirming the energy measured at each addressable point on the energy scale, this being performed according to the manufacturer's recommendations.

ISO 14701:2011 specifies several methods for measuring the oxide thickness at the surfaces of (100) and (111) silicon wafers as an equivalent thickness of silicon dioxide when measured using X-ray photoelectron spectroscopy. It is only applicable to flat, polished specimens and for instruments that incorporate an Al or Mg X-ray source, a specimen stage that permits defined photoelectron emission angles and a spectrometer with an input lens that can be restricted to less than a 6° cone semi-angle. For thermal oxides in the range 1 nm to 8 nm thickness, using the best method described in the standard, uncertainties, at a 95 % confidence level, could typically be around 2 % and around 1 % at optimum. A simpler method is also given with slightly poorer, but often adequate, uncertainties.

ISO 17973:2002 specifies a method for calibrating the kinetic energy scales of Auger electron spectrometers with an uncertainty of 3 eV, for general analytical use in identifying elements at surfaces. In addition, it specifies a method for establishing a calibration schedule. It is applicable to instruments used in either direct or differential mode, where the resolution is less than or equal to 0,5 % and the modulation amplitude for the differential mode, if used, is 2 eV peak-to-peak. It is applicable to those spectrometers equipped with an inert gas ion gun or other method for sample cleaning and with an electron gun capable of operating at 4 keV or higher beam energy.