On the Mechanism of Step Coverage of Blanket Tungsten Chemical Vapor Deposition

In this study, computer modeling of the contact fill process with chemical vapor deposition, (CVD) of tungsten is usedto show the importance of several details on the quality of the fill process. The effect of surface curvature on the stepcoverage of CVD-W has been investigated. It is shown that for contacts with an aspect ratio smaller than one, the effect ofsurface curvature is substantial and actually improves step coverage. Therefore, surface curvature for features with aspectratios smaller than one, should be accounted for in computer simulations of the fill process. For contacts with aspect ratioslarger than one the effect of surface curvature is negligible. It is shown that the size of the void (which will be formed incases of step coverage less than 100%) is a better way to describe the quality of the deposition and the repercussions of thevoid on subsequent process steps such as tungsten etch back. In addition, the size of the void depends for a given set ofdeposition conditions solely on the depth of the contact rather than the contact diameter (for aspect ratios larger than 1.0).