ISO/TC 201/SC 4 - Depth profiling

This document specifies a method for the calibration of the sputtered depth of a material from a measurement of its sputtering rate under set sputtering conditions using a single- or multi-layer reference sample with layers of the same material as that requiring depth calibration. The method has a typical accuracy in the range of 5 % to 10 % for layers 20 nm to 200 nm thick when sputter depth profiled using AES, XPS and SIMS. The sputtering rate is determined from the layer thickness and the sputtering time between relevant interfaces in the reference sample and this is used with the sputtering time to give the thickness of the sample to be measured. The determined ion sputtering rate can be used for the prediction of ion sputtering rates for a wide range of other materials so that depth scales and sputtering times in those materials can be estimated through tabulated values of sputtering yields and atomic densities.

This document provides guidelines for measuring the sputtered depth in sputtered depth profiling. The methods of sputtered depth measurement described in this document are applicable to techniques of surface chemical analysis when used in combination with ion bombardment for the removal of a part of a solid sample to a typical sputtered depth of up to several micrometres. The depth typically determined by this approach is between 1 nm to 500 µm.

This document specifies methods for the alignment of the ion beam to ensure good depth resolution in sputter depth profiling and optimal cleaning of surfaces when using inert gas ions in Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). These methods are of two types: one involves a Faraday cup to measure the ion current; the other involves imaging methods. The Faraday cup method also specifies the measurements of current density and current distributions in ion beams. The methods are applicable for ion guns with beams with a spot size less than or equal to 1 mm in diameter. The methods do not include depth resolution optimization.

ISO 14606:2015 gives guidance on the optimization of sputter-depth profiling parameters using appropriate single-layered and multilayered reference materials in order to achieve optimum depth resolution as a function of instrument settings in Auger electron spectroscopy, X-ray photoelectron spectroscopy and secondary ion mass spectrometry. ISO 14606:2015 is not intended to cover the use of special multilayered systems such as delta doped layers.

ISO/TR 22335:2007 describes a method for determining ion-sputtering rates for depth profiling measurements with Auger electron spectroscopy (AES) and X‑ray photoelectron spectroscopy (XPS) where the specimen is ion-sputtered over a region with an area between 0,4 mm2 and 3,0 mm2. The Technical Report is applicable only to a laterally homogeneous bulk or single-layered material where the ion-sputtering rate is determined from the sputtered depth, as measured by a mechanical stylus profilometer, and sputtering time. The Technical Report provides a method to convert the ion-sputtering time scale to sputtered depth in a depth profile by assuming a constant sputtering velocity. This method has not been designed for, or tested using, a scanning probe microscope system. It is not applicable to the case where the sputtered area is less than 0,4 mm2 or where the sputter-induced surface roughness is significant compared with the sputtered depth to be measured.

ISO 17109:2015 specifies a method for the calibration of the sputtered depth of a material from a measurement of its sputtering rate under set sputtering conditions using a single- or multi-layer reference sample with layers of the same material as that requiring depth calibration. The method has a typical accuracy in the range 5 % to 10 % for layers 20 nm to 200 nm thick when sputter depth profiled using AES, XPS, and SIMS. The sputtering rate is determined from the layer thickness and the sputtering time between relevant interfaces in the reference sample and this is used with the sputtering time to give the thickness of the sample to be measured. The determined ion sputtering rate can be used for the prediction of ion sputtering rates for a wide range of other materials so that depth scales and sputtering times in those materials can be estimated through tabulated values of sputtering yields and atomic densities.

ISO 16531:2013 specifies methods for the alignment of the ion beam to ensure good depth resolution in sputter depth profiling and optimal cleaning of surfaces when using inert gas ions in Auger electron spectroscopy and X-ray photoelectron spectroscopy. These methods are of two types: one involves a Faraday cup to measure the ion current; the other involves imaging methods. The Faraday cup method also specifies the measurements of current density and current distributions in ion beams. The methods are applicable for ion guns with beams with a spot size below ~1 mm in diameter. The methods do not include depth resolution optimization.

This Technical Report gives guidelines for measuring the sputtered depth in sputtered depth profiling. The methods of sputtered depth measurement described in this Technical Report are applicable to techniques of surface chemical analysis when used in combination with ion bombardment for the removal of a part of a solid sample to a typical sputtered depth of up to severalmicrometres.