BS ISO 16531:2020 Surface chemical analysis — Depth profiling — Methods for ion beam alignment and the associated measurement of current or current density for depth profiling in AES and XPS.
4.2 Limitations
This document is an important part of the setting up of depth profiling generally; nevertheless, depending on the material of the sample and its structure, there are several depth profiling procedures that may be applied to achieve the best depth resolution, not all of which are aided by this document. Some of the most popular procedures are:
a) ion bombardment of fixed position samples at angles of incidence in the range 00 to 600 with respect to the surface normal;
b) ion bombardment at grazing angles of incidence;
c) sample rotation during ion bombardment;
d) simultaneous ion bombardment applying two ion guns;
e) sample rotation and grazing angle of incidence for ion bombardment.
This document will assist in the use of procedure a). Some aspects could relate to the other procedures hut further considerations might be required that are not necessarily included in this document.
5 Ion beam alignment methods
5.1 General
This document describes six simple methods for ion beam alignment, all easily applied. These methods and a summary of their advantages are set out in Table 1. Also indicated are which methods are best for ion beam current or current density measurement.
Each method has different advantages and requires different instrumental capabilities. The analyst needs to select the method based on requirements and equipment capabilities. Some issues depend on the raster size of the ion beam. A small raster is good, since little material is consumed or sputter deposited in the spectrometer. Additionally, for industrial samples, the material to be profiled may only occupy a small area. A very small raster is possible in AES where the electron beam is small and some users may deliberately use higher ion beam energies where ion beams tend to be better focused to obtain small sputtered areas with a faster sputtering rate. In these cases, and for systems with smallarea XPS analysis, particular care needs to he taken with alignment. For broader ion beams, such as for some XPS instruments, the alignment accuracy may be more relaxed. If more than one method is suitable, tests with each will show which is most convenient for the sputtering conditions intended.
The effects of good and poor ion beam alignment in sputter depth profiling are illustrated in Annex A.BS ISO 16531 pdf download.