Two critical thicknesses in the preferred orientation of TiN thin film
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Two critical thicknesses in the preferred orientation of TiN thin film U. C. Oha) and Jung Ho Jeb) Department of Materials Science and Engineering, Pohang University of Science & Technology, Pohang 790-784, Korea
Jeong Y. Lee Department of Materials Science and Engineering, Korea Advanced Institute of Science & Technology, Korea (Received 31 May 1995; accepted 29 June 1996)
The preferred orientation of the TiN film grown by sputter-deposition was studied by the cross-sectional TEM. The preferred orientation was changed from the (200) through the (110), and then finally to the (111) with the film thickness. The cross-sectional microstructure also shows that the film consists of three layers which are all columnar structure. The (111) preferred orientation was observed in the top layer, and the (110) in the middle layer, and finally the (200) in the bottom layer. It is very surprising that the (110) preferred orientation could be observed in a medium thickness region and there are two kinds of critical thicknesses. These results surely show the strong dependence of the change in the preferred orientation on the strain energy in TiN thin films.
I. INTRODUCTION
TiN films have been studied extensively for the interest of surface protective coating. For TiN films grown from the vapor phase, preferred orientations are generally observed and vary with growth conditions.1–6 The control of the preferred orientation of TiN films is important from the viewpoint of applications. For example, the wear resistance of tool materials depends on the orientations of TiN films, and the films with the (111) preferred orientation are known to have the highest value of wear resistance.2 However, the mechanism of choosing a preferred orientation is not well understood. Most explanations suggested on the preferred orientation in thin films were given in terms of the surface energy of the film and kinetic factors.2,6 It was proposed in the case of TiN films that the atoms would be arranged by themselves into the plane with the lowest surface energy, i.e., the (111) plane in equilibrium conditions, and into the plane with higher energy, i.e., the (200) plane in nonequilibrium conditions.3,6 However, such explanations have some problems. The first is that the plane of the lowest surface energy is not the (111), but the (200) in TiN crystal with the NaCl-type structure.7 The second problem is that the change in the preferred orientation with the film thickness cannot be explained from the viewpoint of the surface energy and kinetics.8
a)
Current address: Department of Materials Science, Division of Thin Film Technology, University of Science and Technology, Beijing, People’s Republic of China. b) Corresponding author. J. Mater. Res., Vol. 13, No. 5, May 1998
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Therefore, another driving force to cause the preferred orientation of TiN films should be investigated. Pelleg et al.7 suggested that the preferred orientation of TiN thin films was
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