Molecular dynamics and Monte-Carlo simulation of sputtering and mixing by ion irradiation T. Aoki a, * , S. Chiba a , J. Matsuo a , I. Yamada a,1 , J.P. Biersack b a Ion Beam Engineering Experimental Laboratory, Kyoto University, Sakyo, Kyoto 606-8501, Japan b Hahn-Meitner Institute, Glienicker Strasse 100, D-14109 Berlin, Germany Abstract Molecular dynamics (MD) and Monte-Carlo (MC) simulations of low-energy (<500 eV) Ar ion irradiation on Si substrates were performed in order to investigate the mixing and sputtering eects. Both MD and MC simulatio similar results in sputtering yield, depth pro®le of projectile and mixing of substrate. For these incident energi depth of the mixed region is determined by the implant range of incident ions. For example, when the incident 500 eV, the Ar ions reach a depth of 40 A so that the Si atoms that reside shallower than 40 A are fully mixed at an ion dose of about 5:0 10 16 atoms=cm 2 . The resolution of secondary ion mass spectrometry (SIMS) was also studied. It was found that the resolution of SIMS depends on the depth of mixing, which depends in turn on the implant r the probe ions. This is because the mixing of substrate atoms occurs more frequently than sputtering, so that formation about the depth pro®le in the mixing region is disturbed. Ó 2001 Elsevier Science B.V. All rights res PACS: 79.20.Rf; 71.15Pd Keywords: Molecular dynamics simulation; Monte-Carlo simulation; SIMS resolution; Ion mixing; Sputtering 1. Introduction Secondary ion mass spectrometry (SIMS) is a usefultechnique to measure the depth pro®le of components in target materials [1]. Improving the resolution of SIMS analysis is required more and more recently because of the rapidly shrinking design rules in LSIfabrication. It is considered that the resolution of SIMS depends on the inci- dent energy. In the collisional process of the probe atom, the incident atom induces a large number of collisions, so that the original distribution of sub- strate atoms is disturbed. With increasing incident energy, the disturbance of the original coordinates in the targetbecomesmorefrequent,and this causes a decrease in SIMS resolution. To perform high-resolution SIMS, it is necessary to use low- energy probe ions. However, as the incident energy decreases, it becomes dicult to obtain a sputter- ing yield which is suciently high for measure- ments.Therefore, the proper energy of the probe atom should be selected according to the required resolution. In this paper, the collisional processes Nuclear Instruments and Methods in Physics Research B 180 (2001) 312±316 www.elsevier.nl/locate/nimb * Corresponding author. Fax: +81-75-751-6774. E-mail address: t-aoki@kuee.kyoto-u.ac.jp (T. Aoki). 1 Presentaddress:Laboratory ofAdvanced Scienceand Technologyfor Industry, Himeji Institute of Technology, CAST, Ako, Hyogo 678-1205, Japan. 0168-583X/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PI I : S 0 1 6 8 - 5 8 3 X ( 0 1 ) 0 0 4 3 7 - 2