Certified ion implantation fluence by high accuracy RBS

Abstract

From measurements over the last two years we have demonstrated that the charge collection system based on Faraday cups can robustly give near-1% absolute implantation fluence accuracy for our electrostatically scanned 200 kV Danfysik ion implanter, using four-point-probe mapping with a demonstrated accuracy of 2%, and accurate Rutherford backscattering spectrometry (RBS) of test implants from our quality assurance programme. The RBS is traceable to the certified reference material IRMM-ERM-EG001/BAM-L001, and involves convenient calibrations both of the electronic gain of the spectrometry system (at about 0.1% accuracy) and of the RBS beam energy (at 0.06% accuracy). We demonstrate that accurate RBS is a definitive method to determine quantity of material. It is therefore useful for certifying high quality reference standards, and is also extensible to other kinds of samples such as thin self-supporting films of pure elements. The more powerful technique of Total-IBA may inherit the accuracy of RBS.

On the traceably accurate voltage calibration of electrostatic accelerators

“…This calibration method has been validated at both universities of Surrey and Namur by comparison to other calibration methods: namely, the 27 Al(p,) 28 Si resonant reaction [1] & the non-resonant 16 O(p,γ) 17 F proton capture [3] at Surrey, and the use of a triple-alpha source [7,8] at Surrey & Namur. We will show that these new measurements enable us to significantly reduce the uncertainty on the position of this 16 O() 16 O resonance.…”

“…However, the standard calibration points such as the important 27 Al(p,) 28 Si resonant reaction at 992 keV [1] or neutron thresholds such as the 7 Li(p,n) 8 Be at 1881 keV [2] are mostly for a proton beam at various energies. Analysts using an alpha beam (for an enhanced depth resolution) have not conveniently been able to verify their energy calibration.…”

Accurate electronics calibration for particle backscattering spectrometry

“…Figure 1 shows spectra taken from our programme for the quality assurance (QA) of our quantitative implantation, which is discussed in detail elsewhere 2 . The statistics in these spectra are very good since the signals of interest are rather small and we want a 1% measurement accuracy.…”

“…We have recently demonstrated that high accuracy RBS can be used for validating the accuracy of our implanted fluence measurement both by charge collection and also by sheet resistance measurements 1,2 . This is an important result showing that RBS and quantitative implantation are both suitable for certifying new ion implanted or other standards for the quantification of other analytical techniques such as secondary ion mass spectrometry (SIMS) or Xray fluorescence (XRF).…”

“…A 2 The whole dataset (18 pairs of spectra) is fitted using DataFurnace, that is, all spectra are automatically fitted one after the other where the incident energy and PHD are fixed to nominal values and the electronic gain (± 2%) and offset (±10 channels) are fitted to minimise the chi-squared (²) function for each spectrum. Other parameters such as the collected charge (±20%), the detector resolution (±10 keV) and the sample depth profile are also allowed to vary during the ² minimisation.…”