Influence of heavy ion irradiation damage on silicon charged particle detector calibration

The full analytical potential of heavy ion backscattering and elastic recoi l detection analysis (ERDA) depends critically on establishing a reliable e nergy calibration. In order to make accurate measurements of thin film samp les we have investigated the changes in the energy calibration of a Si p(+) -n-n(+) charged particle detector subjected to heavy ion irradiation over 2 4 h in a time of flight-energy elastic recoil detection analysis (ToF-E ERD A) measurement. In this study a set of similar Al/ZrO2/Zr samples were anal ysed sequentially with 60 MeV I-127(11+) ions. The calibration change for O -16, Al-27 and Zr-90-92,Zr-95:96 were monitored by tagging individual recoi ls with their energy derived from the ToF. The calibration parameters for a wider range of elements (Li-Ag) were measured before and after the sequent ial irradiation with O, Al, Zr and I atoms. The results show that the change in the calibration could be characterised by an increase in the energy interval spanned by one channel and a slight d ecrease in the channel zero energy. The calibration shift for a given proje ctile atomic number depends linearly on the fluence of heavy particles impi nging on the detector and the consequential increase in detector leakage cu rrent. This indicates that for similar irradiation conditions, a correction to account for the calibration shift may be simply determined for each sam ple from the number of heavy recoil counts registered or from the change in leakage current. Furthermore, the silicon charged particle detector calibr ation depends on recoil atomic number both before, and after, the heavy ion irradiation. The fluence-induced calibration shift for different recoils c an be described by a linear dependence on recoil atomic number. (C) 2000 El sevier Science B.V, All rights reserved.