The influence of the deposition energy on thin film formation: Co on Si(111)
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The influence of the deposition energy on thin film formation: Co on Si(111) Koen Vanormelingen, Bart Degroote and André Vantomme Katholieke Universiteit Leuven, Instituut voor Kern- en Stralingsfysica, Celestijnenlaan 200 D, 3001 Leuven, Belgium ABSTRACT The deposition of a thin film on a substrate surface can be achieved with a wide variety of techniques. Deposition using low energy ion beams is not a common technique, but it yields promising features, due to the hyperthermal nature of the deposited ions. With low energy ion deposition, it is possible to grow films with good characteristics at significantly lower temperatures compared to thermal deposition. The quality of these films critically depends on the energy of the impinging ions. We investigated the influence of the energy on the surface morphology for the deposition of Co onto Si(111). The roughness of this surface decreases significantly when the ion energy is increased, until it reaches a minimum at 25 eV. When the ion energy is further increased, the surface roughness increases again. This behavior can be explained by taking into account the interplay between the beneficial and detrimental effects due to the ion energy. Beneficial effects such as enhanced mobility and improved layer-by-layer growth cause a decrease in surface roughness when the deposition energy is increased from thermal to 25 eV. For energies above that value, undesirable effects such as defect creation and pileup dominate, leading to an increase in surface roughness. This study shows that low energy ion deposition can be used to improve the surface quality of a thin film by choosing the optimal deposition energy.
INTRODUCTION Due to the continuously shrinking size of electronic components, the knowledge of interactions at the atomic scale, when growing thin films, is gaining importance. Moreover, for many applications it is important to grow flat films with a good crystalline quality. A particular group of materials under investigation are silicides, such as CoSi2, on a silicon substrate. Conventional techniques to grow such thin silicide layers (e.g. solid phase reaction, reactive deposition or coevaporation) all incorporate an annealing step to supply sufficient energy to induce the kinetic and thermodynamical processes necessary for the silicide formation [1]. This annealing step can have detrimental effects on the film structure, such as roughening, pinhole formation, etc and should therefore be avoided. An alternative way of supplying the necessary energy is the use of hyperthermal deposition energies, in contrast to atoms with thermal energies between 10 and 100 meV, which are deposited in a conventional growth technique such as molecular beam epitaxy (MBE). Theoretical calculations as well as experimental data reveal a significant decrease in the temperatures needed for compound formation and the growth of crystalline films when using hyperthermal deposition energies [2-5]. However, as shown by several groups [6-9], the deposition energy has a strong influence on t
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