Oblique angle co-deposition of nanocolumnar tungsten thin films with two W sources: Effect of pressure and target current
Résumé
Two series of tungsten thin films are sputtered on silicon and glass substrates by oblique angle co-deposition technique with an original configuration. Two opposite distinct tungsten targets are simultaneously used, both tilted with an oblique angle of 80°. The growth is performed at low (0.33 Pa) and high (1.5 Pa) argon sputtering pressure and the current intensity applied to the targets varies between 50 and 250 mA. The effect of these deposition parameters on the films microstructure and electrical properties is investigated by scanning and transmission electron microscopy, X-ray diffraction and pole figures, and van der Pauw method. Due to self-shadowing effect, all tungsten sputtered thin films are porous and columnar. At low pressure, the columnar tilt angle β can be tuned with the target current intensity until obtaining vertical columns. X-ray diffraction and pole figure analyses point out a A15 crystal structure (β-W) and a uniaxial fiber texture with a <100> growth direction. In contrast, tungsten thin films deposited at high pressure present a cauliflower structure and are poorly crystallized. Both deposition parameters also affect the films electrical resistivity and anisotropy. These behaviors are discussed and linked to the microstructure and crystallography.
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