The effects of thin (chemical) oxide grown during the chemical cleaning of silicon wafers on the silicon reduction of tungsten hexafluoride have been investigated. Unlike tungsten deposition on samples without the chemical oxide, deposition thickness on those with the chemical oxide was found to be unlimited. Inspection by cross‐sectional SEM and TEM revealed the existence of microchannels penetrating the tungsten film, reaching all the way from the surface of the film to the tungsten/silicon interface. These channels enable tungsten hexafluoride to reach the substrate, thus causing unlimited tungsten growth.