Mechanism of in-plane texture development by ion-beam-assisted deposition
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Mechanism of in-plane texture development by ion-beam-assisted deposition H. Ji Physics Department, The University of Michigan, Ann Arbor, Michigan 48109
G. S. Wasa) Department of Nuclear Engineering and Radiological Sciences, The University of Michigan, Ann Arbor, Michigan 48109 (Received 31 July 1998; accepted 26 January 1999)
The objective of this work was to determine the mechanism of in-plane texture development in films made by ion-beam-assisted deposition (IBAD). Both in-plane texture and surface roughness were studied as functions of film thickness. A phenomenological growth model based on the preferential growth of aligned grains due to channeling was proposed, linking the surface roughness evolution and texture development. Good correlation was found between the measured roughness and the model prediction, as well as between the roughness evolution and the in-plane texture development. A critical thickness was introduced at which in-plane texture is completed. Both surface roughness and texture results gave a critical film thickness of 114–250 nm for an ion energy of 1000 eV and an R ratio of 0.4. This range of critical film thickness was far beyond the nucleation stage, providing evidence that the development of in-plane texture in IBAD Nb films was growth-controlled.
I. INTRODUCTION
Ion beam bombardment during film deposition has been found to have a pronounced effect on the establishment of texture in thin films.1–5 It is believed that the preferential growth of grains with open channeling orientation aligned with the ion beam due to ion channeling is responsible for the established texture.6,7 The difference in sputtering yields between grains with their channeling direction aligned with the ion beam and those which are not can be as high as a factor of 5 in some materials.8 This difference leads to a larger net growth rate for aligned grains than for misaligned grains. The newly deposited layer grows epitaxially on grains with low sputter yield orientation, and these grains will eventually dominate the film. However, there is argument over whether in-plane texture is established in the nucleation stage or in the growth stage. Yu et al.3 suggested that the influence of IBAD on in-plane texture formation in the films started from the early stage of growth. They deposited a Nb film of several hundred nanometers thick without ion bombardment onto a 50 nm Nb layer that was bombarded with the ion beam during deposition. They found that this film was highly in-plane textured, and the texture a)
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http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 6, Jun 1999
Downloaded: 14 Mar 2015
was slightly less developed than films grown under steady ion bombardment. In work on yttrium stabilized zirconia (YSZ),5 a 60 nm film was first deposited under ion bombardment. The ion beam was then turned off, but the deposition continued to a film thickness of 1 mm. The pole figure exhibited a stro
