Threshold stoichiometry for beam induced nitrogen depletion of SiN H. Timmers a,b, * , T.D.M. Weijers a,b , R.G. Elliman a , J. Uribasterra a,b,c , H.J. Whitlow c , E.-L. Sarwe d a Department of Electronic Materials Engineering, Australian National University, Canberra, ACT 0200, Australia b Department of Nuclear Physics, R.S. Physical S.E, Australian National University, Canberra, ACT 0200, Australia c Division of Nuclear Physics, Lund Institute of Technology, Lund, Sweden d Division of Solid State Physics, Lund Institute of Technology, Lund, Sweden Abstract Measurementsofthestoichiometryofsiliconnitridefilmsasafunctionofthenumberofincidentionsusingheavy ion elastic recoil detection (ERD) show that beam-induced nitrogen depletion depends on the projectile species, the beamenergy,andtheinitialstoichiometry.Athresholdstoichiometryexistsintherange1:3 > N=Si P 1,belowwhich thefilmsarestableagainstnitrogendepletion.Abovethisthreshold,depletionisessentiallylinearwithincidentfluence. The depletion rate correlates non-linearly with the electronic energy loss of the projectile ion in the film. Sufficiently longexposureofnitrogen-richfilmsrendersthemechanism,whichpreventsdepletionofnitrogen-poorfilms,ineffective. Compromising depth-resolution, nitrogen depletion from SiN films during ERD analysis can be reduced significantly by using projectile beams with low atomic numbers. Ó 2002 Published by Elsevier Science B.V. PACS: 61.18.Bn; 81.70.Jb; 81.70.Yp Keywords: Ion beam analysis; Elastic recoil detection; Nitrogen depletion 1. Introduction An ideal application of elastic recoil detection (ERD) analysis with heavy ion beams such as 197 Au or 127 I is the compositional analysis of ma- terials, which include the low-Z elements H, B, C or N in combination with heavier elements. Silicon nitride films belong to this group of materials.Itiswellknown[1–3],however,thatthe measurement of their stoichiometry is affected by beam-induced nitrogen depletion, an effect shared with other insulators containing this element. The depletion is attributed to the production of chemically stable yet volatile N 2 molecules fol- lowing the breaking of chemical bonds due to the electronic energy loss of the projectile ion. Thedepletionratecanbe1–2ordersofmagnitude larger than the sputtering rate. Detailed measure- ments of depletion rates, their dependence on ion species, ion energy, and on the initial stoichiome- try are not available. The correction of nitrogen Nuclear Instruments and Methods in Physics Research B 190 (2002) 428–432 www.elsevier.com/locate/nimb * Corresponding author. Address: Department of Electronic Materials Engineering, Australian National University, Canb- erra, ACT 0200, Australia. Tel.: +61-2-6249-8887/+49-2-6125- 8887; fax: +61-2-6249-0511/+49-2-6125-0748. E-mail address: heiko.timmers@anu.edu.au (H. Timmers). 0168-583X/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. PII:S0168-583X(01)01217-4