Morphology modification by high energy ion beam bombardment concurrent with TiN film growth

Abstract

Ion bombardment during film growth has been shown to be useful in controlling the growth kinetics and thus the physical properties of the film. One of the more spectacular aspects of how ion beams modify the growing film concerns topographical changes. There have been a number of reports in the literature concerning the development of surface morphology of films growing under concurrent low energy (<1 keV) ion bombardment [1, 2], but few works dealing with morphology modification by high energy ion beam bombardment concurrent with film growth. There are remarkable differences between low energy ion/surface interaction and high energy ion/surface interaction in terms of range and energy deposition etc. In assessing the role of low energy ion irradiation on the surface morphology, ion energy and ion flux were often considered, but the effect of ion species was usually neglected, because the mean ion ranges in the film for different ions at low energies are very similar. However, at higher energies, ions with different masses penetrate to quite different depths, and thus their influence on topography modification should be detectable. On the other hand, there are also differences between morphology modification by high energy ion bombardment concurrent with film growth and after film deposition [3-5]. The present authors have reported the fabrication of TiN films by vapour deposition of Ti in a N2 atmosphere concurrent with high energy inert Xe + ion beam bombardment [6] and studied the effect of ionic mass on the intrinsic stress of the formed TiN films [7]. In this letter, the morphologies of the synthesized TiN films were examined by atomic force microscopy (AFM), which can provide quantitative three-dimensional surface morphological information with high resolution. In order to investigate the mechanism of surface morphology modification by high energy ion beam irradiation during film growth, both Xe + ions and lighter Ne + ions were employed to prepare TiN films. A detail description of the film synthesis facility has been given elsewhere [6]. The TiN films were deposited onto optically polished silicon substrates by electron beam evaporation of Ti at a rate of 1 nms -a in a N2 atmosphere. The angle of incidence of the vapour stream to the substrate was 45 °. During deposition the substrates were water-cooled and did not reach atemperature greater than 200 °C.