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In this chapter we summarize reactions that take place when an energetic ion impinges on a target surface. The results based on equations that are usually used to estimate ion range and ion sputtering in amorphous materials are presented. A discussion on ion channeling and ion damage in crystalline materials is presented. The problems of redeposition associated with an increase in sputtering yield within a confined trench are presented. Knowledge of ion - solid interactions may be used to prepare excellent quality FIB milled surfaces.

Ion channeling, backscattering and ion-induced X-ray measurements have been done to study the effects of dual implantation and annealing atmosphere on lattice locations and atom profiles of Sn and Sb implanted in GaP.

Whenever an ion beam penetrates a crystalline lattice, strong directional effects, commonly known as “channeling”, may occur. Indeed, some of the more interesting and useful applications of ion beams in materials characterization are based on this channeling effect. The first lecture, therefore, will consist of a general description of the channeling phenomenon in order to provide a basis for the subsequent series of more specialized lectures by Mazzoldi, Rimini and myself on specific solid state applications. For those seeking a more detailed and comprehensive treatment of ion channeling and its applications, excellent reviews by Gemmell1 and by Morgan2 have recently been published.

Ion implantation has been extensively used to prepare radioactive sources of impurities in metals for hyperfine interaction studies. However, it has been found that the hyperfine field (hf) at implanted impurities may vary according to the implantation conditions as well as the processing of the host (see, for example, Reis. 1–3). Factors which can influence the measured hf include radiation damage, the concentration and location of the impurity atoms in the host lattice, and their migration or precipitation on annealing. The impurity lattice location (as well as certain types of radiation damage) can be investigated by the technique of ion channeling. In order to understand better the various factors on which the hf may depend, it was decided to make a combined channel-ing-hf study on a suitable system.

He ion channeling experiments have been performed on molecular beam grown Si/Si0.5Ge0.5 superlattices and n-channel Si/Si0.5Ge0.5 MODFET structures. Angular yield scans provide directly the tetragonal strains in the layers. The strain fields in Si/Si0.5Ge0.5 superlattices grown directly on (100) Si and on Si1-yGey buffer layers were compared experimentally. In the first case only the Si0.5Ge0.5 layers are tensilly strained whereas on a Si0.71Ge0.29 buffer layer with a thickness of 230 230 nm almost equal but opposite strains have been found. Strain sym-metrization yields the minimum elastic energy and thus to the most stable structure. An example of strain measurements on an n-channel MODFET structure will be shown. Ion channeling is probably the only technique which allows strain measurements in structures, like the MODFET structure investigated, where the thicknesses vary from layer to layer.

Previous lectures by Mazzoldi and Rimini have discussed the use of channeling to pinpoint the location of foreign atoms and displaced lattice atoms within the bulk of a single crystal. In this final lecture, we will consider a simple extension of these atom-locating techniques that permits similar studies to be performed on surface atoms1,2. Of particular interest is the possibility of using single- and double-alignment techniques for studying changes in structure and lattice spacing of surface atoms relative to the underlying lattice. Such information is of basic interest in understanding the nature of surface adsorption on various crystal surfaces and hence has obvious application in the field of catalysis and in testing theoretical models for estimating interatomic potentials.

The lattice location of Au implanted to high doses at room temperature into single crystal Ni, Cu, Pd and Ag has been determined using 4He ion channeling and backscattering. In all cases the Au atoms are found to be 100% substitutional for room temperature implants without annealing. Au implants in Cu at 15°K are found to be 100% substitutional. High dose implants of W in Cu, a reportedly insoluble impurity, are also found to be highly substitutional.

Historically, the first use of ion backscattering for material analysis was by Geiger and Marsden1 (1909), whose effects were explained by the Rutherford2 atomic model (1911). This was followed immediately by suggestions of ion channeling in single crystals by Stark and Wendt (1912). Recently, the most widely publicized example of nuclear backscattering was the first atomic compositional analysis of the moon by Surveyor 5 (1967). This first soft-landing package contained a radioactive source of 5MeV α-particles which were backscattered from the moon’s surface and provided information on the elemental composition of the moon’s surface.4,5

Ion implantation and ion channeling are used to study hydrogen in metals. Deuterium implanted at room temperature into Cr and W is found to be localized at distinct positions, predominately near the octahedral and tetrahedral interstitial sites respectively. Irradiation of the implanted W by the 750 keV3He analysis beam results in the movement of the deuterium to a new location.