Ta films were obliquely deposited on glass substrates by magnetron sputtering method using the parameters: deposition angleaα = 60^o; deposition temperature T_S = 298, 373, 473, and 573 K; Ar working gas pressure P_AR = 2, 7.5, and 15 mTorr; film thickness t_f =100 nm. From X-ray diffraction, atomic force microscopy, cross-section transmission electron microscopy, and Auger depth profile analysis, we conclude that: [1] the axis of each columnar grain is inclined at an angle β ≈35^o with respect to the film normal; [2] in-plane grain aggregates show some vestiges of the chain-like structure, whose long axis is perpendicular to the plane of incidence (i.e. the transverse or width direction of the sample); [3] oxygen atoms are found inside the film; especially located in the columnar gaps (or micro-voids) between neighboring grains. The stress of each film was measured via Stoney equation. The main results in regard to the stress behavior of this series of Ta films are summarized below: [a] the intrinsic stress S_i is always tensile and dominant over the thermal stress S_T; [b] the total stress is anisotropic with the longitudinal stress being larger than the transverse stress; [c] as T_S increases, Sibecomes less tensile. Result [a] is reasonable because Ta is a high melting point material.¹ Especially, in the oblique-deposition case, the formation of gaps becomes more obvious. Hence, much larger tensile stress (than in the normal-deposition case) arises from the attractive interaction of oxygen atoms across the gaps. Result [b] is a consequence of the self shadowing effect, which is already manifested in the conclusion [2] above. Result [c] is due to the fact that as T_S is higher, there is a structure transition from zone 1 to zone T, and oxygen atoms are less likely to be incorporated into the film.

^1. G. Guisbiers, O. Van Overschelde, M. Wautelet, Acta Materialia 55, 3541(2007).