Evaluating substrate bias on the phase-forming behavior of tungsten thin films deposited by diode and ionized magnetron sputtering

This work employs diode and inductively coupled plasma ionized magnetron sputtering to deposit tungsten thin films of thickness 40 nm. The effect of varying the deposition parameters, particularly, substrate bias on the phase-forming behavior and related film properties was investigated using glazing incidence and high-resolution scanned X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electrical resistivity evaluation. Over a broad deposition window using the optimal substrate bias, −75 Vdc, diode sputtering can only lead to the formation of β-W dominated films with resistivities from ∼60 μΩ cm up to hundreds of μΩ cm, whereas ionized sputtering is capable of depositing quasi-pure α-W thin films that have a markedly reduced resistivity of only ∼20 μΩ cm. Finally, the impact of varying the sputtering-gas and base pressures on phase distribution, microstructure and crystallinity of the films is discussed in terms of energy-enhanced deposition mechanism, the role of absorbed impurities and the zone-structure model proposed previously.