ISO 13424:2013 pdf free download.Surface chemical analysis — X-iy photoelectron spectroscopy — Reporting of results of thin-film analysis.
X-ray photoelectron spectroscopy (XPS) is widely used for the characrenzation of surfaces of materials, especially (or overlayer thin films on a substrate. The chemical composition of the near-surface region of a thin film can be determined by XPS. If the film has a uniform thickness and the thickness is less than about three times the mean escape depth (MED) for the measured photoelectrons, the film thickness and the depth distribution of elements or chemical stales of elements In the film can be determined by angle- resolved XPS or peak-shape analysLs. For thicker films, the depth distributions of elements in the film can be obtained by sputter-depth profiling. Possible lateral inhomogeneities in film thicknesses or depth profiles can be determined if the XPS system has sufficient lateral resolution. These XPS applications are particularly valuable for characterizing thin-film nanostructures since the MED Is typically less than 5 nm for many materials and common XPS measurement conditions.
Clauses 6 and Z of ISO 13424 provide guidance to the operator of an XPS instrument in making efficient measurements for determi fling meaningful chemical compositions and film thicknesses for overbyer films on a substrate. Clause 8 of ISO 13424 shows the information to be included In reports of the measurements and the analyses of the XPS data. Annex A. Annex B. Annex C. and Annex D provide supplementary Information on methods of data analysis for different types of XPS measurements on thin-film samples.
1 Scope
ISO 13424 specifies the minimum amount of information required in reports of analyses of thin films on a substrate by XPS. These analyses involve measurement of the chemical composition and thickness of homogeneous thin films, and measurement of the chemical composition as a function of depth of inhomogeneous thin films by angle-resolved XPS, XPS sputter-depth profiling. peak-shape analysis, and variable photon energy XPS.
2 Normative references
The following documents. in whole or in part, are normatively referenced In this document and are indispensable for Its application. For dated references, only the edition cited applies. For undated references, the Latest edition olihe referenced document (including any amendments) applies.
ISO 18115-1:2010, Surface chemical analysis — Vocabulary — Part 1: General terms and terms used in spectrascopy
3 Terms and definitions
For the purposes of ISO 13424., the terms and definitions In ISO 18115-1:2010 apply.
4 Abbreviated terms
AES AuRer electron spectroscopy
ARXPS Angle-resolved X-ray photoelectron spectroscopy
IMFP lnebslic mean free path
MED Mean escape depth
RSF Relative sensitivity factor
TRMFP Transport mean free path
XPS X-ray photoelectron spectroscopy
5 OvervIew of thin-film analysis by XPS
5.1 Introduction
XPS analyses of thin films on substrate can provide information on the variation of chemical composition with depth and on film thicknesses.Several XPS methods can be used ifthe total film thickness Is less than three times the largest MED for the detected photoelectrons. The MED for particular photoelectrons is a function oIthe IMFP and the emission angle of the photoelectrons with respect to the surface normal. The IMFP depends on the photoelectron energy and the material. MED values can be obtained from a database.tlI A simple analytical formuLa for estimating MEDs has been published for emission angles 506IZl For such emission angles, the MED is less than the product of the IMFP and the cosine of the
XPS is typically performed with laboratory Instruments that are often equipped with monochromated Al Ka or non-monochromated Al or Mg Ku X-ray sources. For some applications, XPS with X-rays from synchrotron-radiation sources is valuable because the energy of the X-ray exciting the sample can be varied. XPS with Ag X-rays Is also used to observe deeper regions compa red to excitation with Al X-rays. In some cases. X-ray energies less than the Mg or Al Ku X-ray energies can be selected to gain enhanced surface sensitivity while In other cases, higher energies are chosen to gain greater bulk sensitivity and to avoid artefacts associated with the use of sputter-depth profiling.
Analysts should he aware of possible artelacts in XPS analyses. These artefacts include sample degradation during X-ray irradiation, reactions of the sample with gases in the ambient vacuum, and many effects that can occur during sputtering-depth profiling.131
5,2 General XPS
Fora uniform thin film ona flatsubstrate.the film thicknesscan bedetermined from a ratio of a photoelectron peak intensity of an element in the substrate for a particular emission angle when an overlayer film is present to the corresponding intensity when the film Is absent. Alternatively, the thickness can be obtained from a ratio olpitotoelectron peak Intensity for an element In the film to the corresponding intensity for a thick film (i.e. a film with a thickness much greater than three times the MED). The composition of the film can be determined by the RSF method, Additional Information Is In Annex A.
For multiple thin-film analysis, it is important to determine the relative order of the Layers above the substrate. We can estimate the layerorder, thicknesses, and compositions by measuring the changes of peakintensity ratios of components at tivo widely separated emission angles. Further details are in AnnezA.
53 Angle-resolved XPS
Angle-resolved XPS (ARXPS)141 can be utilized to determine composition as a function of depth fordepths up to three times the largest MED of the detected electrons. The composition can be found for each film ola multilayer film on a substrate or the distribution of composition with depth can be determined for samples with no phase boundaries, For the former type of sample, film thicknesses can be estimated. Further details are In &nnex.j.
5.4 Peak-shape analysis
Peak-shape analysls,lil the analysis of a photoelectron peak and its associated region of inelastlcally scattered electrons, can be utilized to determine composition as a function of depth for depths up to three times the largest MED of the detected electrons. The analyst can know the expected morphology olthc sample (i.e. the distribution of composition with depth) or can often deduce the likely morphology from peak-shape analysis. Further details are in AnnczC.
5.5 Variable photon energy XPS
Variable photon energy XPS can be employed to determine composition as a function of depth for depths up to three times the largest MM) of the detected electrons.l61 XPS measurements of this type are typically performed with synchrotron radiation over a sufficiently wide photon energy range to give a useful range of MEDs of the detected photoelectrons.
5.6 XPS with sputter-depth profiling
Since 1985. small-spot XPS systems have been developed with lateral resolutions of commercial Instruments less than 10 im. Ion guns with focused beams have also become available so that faster sputtering of smaller regions on a sample became possible. Recent materials developments (e.g. the development of new gate oxides for semiconductor devices and the development of many types of nanostructures) have stimulated the growing use of XPS with sputter-depth profiling, It has also become necessary to obtain composition-depth profiles for Inorganic and organic thin films without causing significant damage. XPS with sputter-depth profiling of such materials has now become possible with the development of buckminsterfullerene (C60), argon cluster, water cluster, and other cluster.