Nuclear Instruments and Methods in Physics Research B 85 (1994) 167-170 North-Holland NOM zyxwvutsrqpo B Beam Interactions with Materials&Atoms Use of a rastered microbeam to study lateral diffusion of interest to microelectronics P.J. Ding, R. Talevi and W.A. Lanford * zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG Physics Department, University at Albany, Albany, NY 12222, USA S. Hymes and S.P. Murarka Center for Integrated Electronics, Rensselaer Polytechnic Institute, Troy, NY 12180, USA The use of the Albany MeV rastered microbeam to study lateral diffusion of interest to microelectronics is discussed. As an illustration of this technique, a study is presented of the lateral transport that occurs near the edge of a Ni film deposited on Si when this sample is heated. Used in an imaging mode, these measurements show the formation of a series of distinct regions composed of different stable Ni silicides, starting with the Ni,Si and forming progressively less Ni rich silicides as one moves away from the Ni region. 1. Introduction As microelectronic feature sizes shrink, with lateral dimensions decreasing more rapidly than vertical di- mensions, phenomena associated with the edges of microelectronic structures become increasingly impor- tant. The present paper explores the use of a rastered microbeam of MeV He ions to study what happens when an initially sharp edge of a Ni overlaying film on a blanket film of Si is annealed. This is intended as an illustration of what phenomena can be studied with this ion beam method and how the use of ion beams compares other methods available to study such sys- tems, most importantly electron microscopy. The basic geometry of the “lateral diffusion couple” is illustrated in Fig. 1. An understanding of what occurs as such a couple is heated will rely partly on knowledge of silicide growth kinetics, which have been well studied in a more standard geometry [l-3]. Lat- eral diffusion couples have also been studied [4-91, including work on aluminides and silicides [7-121. The main experimental approach has been to use electron microscopy either transmission electron micrography (TEM) or scanning electron micrography GEM) with energy dispersive X-ray analysis. On general grounds, Rutherford backscattering (RBS) with an MeV ion microbeam is a natural ap- * Corresponding author, phone +l 518 442 4480, +l 518 442 4486. preach with which to study lateral diffusion. RBS has clearly demonstrated its unique power in the study of film/film interdiffusion kinetics. The ability of RBS to give quantitative compositional information, quantita- tive depth distribution information, and quantitative film thickness information without use of reference standards suggest its application to the lateral diffusion problem. Indeed, some of the SEM studies of this problem have used RBS to calibrate their electron beam X-ray analysis data [9]. It would seem natural to apply the RBS technique directly. The Albany microbeam is described in detail else- where [13]. This facility rasters a 2 pm diameter beam with a current in the order of 1 nA over the sample and collects the secondary electrons emitted as the beam is scanned across the sample. The intensity of these electrons as a function of beam position is used to form an image of the sample (electron micrograph), very similar to the usual SEM micrograph. In addition to the secondary electron detector, there are detectors to record X-rays emitted from the sample (PIXE) and backscattered particles (RBS). zyxwvutsrqponmlkjihgfedc NI I SIOZ Fig. 1. A schematic representation of a side view of the lateral diffusion couple used in this study. The Ni film was 240 nm thick and the Si was 90 nm thick. 0168-583X/94/$07.00 0 1994 - Elsevier Science B.V. All rights reserved SSDI 0168-583X(93)E0448-P III. INTERFACES/MULTILAYERS