New insights on the effect of hydrogen to tungsten hexafluoride partial pressure ratio on plasma deposited tungsten thin films

Abstract

Resistivities of tungsten thin films deposited by plasma enhanced chemical vapor deposition are very sensitive to the H2/WF6 partial pressure ratio, while the resistivities of tungsten films deposited by low pressure chemical vapor deposition are insensitive to the H2/WF 6 ratio. The reason is investigated with x-ray diffraction, transmission electron microscopy, Auger electron spectroscopy and optical emission spectroscopy. As a result, when the H2/WF6 partial pressure ratio is higher than 15, plasma deposited tungsten has a low resistive (11 μΩcm) bcc structure without F impurities. However, if the H2/WF6 ratios are decreased, porous and β-phase W films are formed due to the incomplete reduction of F concentrations.