The effects of diborane (B2H6) pretreatment on atomic layer deposition (ALD) of tungsten (W) thin film using a sequential supply of WF6 and SiH4 on thermally grown SiO2 and TiN films at 300 degrees C were investigated. The results show that the B2H6 pretreatment reduces the incubation time for film growth. X-ray photoelectron spectroscopy and scanning electron microscopy analysis suggest that elemental B on SiO2, released during B2H6 pretreatment, induce rapid W nucleation. The drastically improved step coverage of ALD-W film is achieved at the ultrahigh aspect ratio contact (height: 2.23 mu m and top diameter: 0.14 mu m) by the enhanced nucleation and growth via B2H6 pretreatment. The effects of B2H6 pretreatment on the properties of ALD-W films such as roughness, phase, microstructure, and resistivity are also investigated. (c) 2005 The Electrochemical Society.