Aspects of the methods and apparatus described herein relate to deposition of tungsten nucleation layers and other tungsten-containing films. Various embodiments of the methods involve exposing a substrate to alternating pulses of a tungsten precursor and a reducing agent at low chamber pressure to thereby deposit a tungsten-containing layer on the surface of the substrate. According to various embodiments, chamber pressure may be maintained at or below 10 Torr. In some embodiments, chamber pressure may be maintained at or below 7 Torr, or even lower, such as at or below 5 Torr. The methods may be implemented with a fluorine-containing tungsten precursor, but result in very low or undetectable amounts of fluorine in the deposited layer.