Chemical vapor deposition of tungsten silicide into high aspect ratio trenches has been investigated using a commercial 8-inch Applied Materials Centura single wafer deposition tool. For an in-depth study of both step coverage and stoichiometry, a combined chemistry/topography simulator has been developed. Dichlorosilane reduction of tungsten hexafluoride (WF6) has been identified as a suitable chemistry to fill deep trenches with tungsten disilicide, while for WF6 reduction with silane (SiH4) or disilane (Si2H6) fundamental drawbacks have been identified for extreme aspect ratios. In the process range under study, good agreement is observed between the simulated step coverages and those obtained from scanning electron microscope images. The simulations predict a deposition regime in which both good step coverage and a suitable stoichiometry are achieved inside deep trenches. (C) 2003 Elsevier B.V. All rights reserved.