Nuclear Instruments and Methods in Physics Research B 119 (1996) 533-542 zyxwvutsrqponmlkjihgfedcbaZYXW a __ f!!!El zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA __ ELSEVIER NOMB Beam Interactions with Materials&Atoms Comparison of TOF-ERDA and nuclear resonance reaction techniques for range profile measurements of keV energy implants J. Jokinen * , J. Keinonen, P. Tikkanen, A. Kuronen, T. Ah&en, K. Nordlund Acceleraror zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Laboratory, Uniuersity of Helsinki, P.O. Box 43, FIN-00014 Helsinki, Finland Received 17 May 1996; revised form received 26 July 1996 zyxwvutsrqponmlkjihgfedcbaZY Abstract A comparative study on the range measurements of keV energy implants by the Time-of-Flight Elastic Recoil Detection Analysis (TOF-ERDA) and conventionally used nuclear resonance reaction methods has been performed for 20-100 keV ‘TN+ ions implanted into crystalline silicon. Range profiles of “N atoms were chosen because they can be measured accurately using a very strong and narrow resonance at Ep = 429.6 keV in the reaction “N(p,ay)‘*C which provides a challenging test for other methods. The measured range profiles were simulated by molecular dynamics calculations where the interatomic N-Si pair potential is deduced from first principles calculations. The electronic stopping power for 20-100 keV nitrogen ions in silicon is deduced from the comparison of the measured and simulated range profiles. The results are discussed in the framework of the applicability of the TOF-ERDA technique for keV energy ion range measurements. 1. Introduction Elastic Recoil Detection Analysis * (ERDA) [1,2] is a method by which the observation of recoiled target atoms yjelds the most direct information about target composi- tipn. In conventional ERDA measurements, recoiling atoms of different elements are separated with stopping foils. The f&ls cause, however, energy straggling and are not very easy to use when several elements need to be separated. Therefore, many different types of ERDA set-ups have b+en constructed [3-lo]. One of the most promising tech- niques is Time-of-Flight ERDA (TOF-ERDA) [9-141 where, in addition to traditional energy measurement, time-of-flight over a known distance is measured for each atom. The mass of each detected atom can be calculated from the classical formula for kinetic energy. Furthermore, when the mass of a particle has been identified, the same equation with a tabulated accurate mass can be used to obtain the energy from the measured time-of-flight [15,16]. Accurate time calibration is more straighforward than en- ergy calibration and using the time-of-flight signal instead of the signal from the energy detector can give a better energy resolution, especially for heavier particles. TOF- ERDA systems have been widely used mainly for analyz- ing thin films and layered structures. In the Accelerator Laboratory we have systematically studied stopping power and employed range profiles of keV energy implants to deduce stopping power values at these energies [17-211. In this work we present a TOF- ERDA measurement system and its application to depth profiling of ion-implanted concentration distributions. Range profiles of implanted “N in crystalline silicon (c-Si) were measured with the TOF-ERDA spectrometer and results are compared with those obtained with the 429 keV resonance in the reaction 15N(p,ay)12C. This reso- nance reaction provides one of the best tools for the range measurements of keV energy light ions with the Nuclear Resonance Broadening (NRB) method 1221. The measured range profiles are compared with those obtained in Molec- ular Dynamics (MD) simulations [19]. From this compari- son, the electronic stopping power of silicon for low energy nitrogen ions is deduced. In order to take into account the damage structure of implanted c-Si in the MD simulations, RBS channeling measurements were also per- formed. 2. Set up for TOF-ERDA measurements * Corresponding author. Fax: +358 9 191 40042; email: Janne.Jokinen@Helsinki.FI. 2.1. Apparatus design ’ Also known as Elastic Recoil Detection (ERD), Elastic Recoil Apalysis (ERA), Forward Recoil Spectrometry (FRES) and Recoil Spectromehy (RS). A schematic diagram of the TOF-ERDA measurement system constructed at the Accelerator Laboratory is shown 0168-583X/96/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved PII SO168-583X(96)00469-7