On the mechanism of the step coverage of blanket tungsten chemical vapor deposition

In this study, computer mode l ing of the contact fill process with chemical vapor deposition, (CVD) of tungsten is used to show the importance of several details on the quality of the fill process. The effect of surface curvature on the step coverage of CVD-W has been investigated. It is shown that for contacts with an aspect ratio smaller than one, the effect of surface curvature is substantial and actually improves step coverage. Therefore, surface curvature for features with aspect ratios smaller than one, should be accounted for in computer simulations of the fill process. For contacts with aspect ratios larger than one the effect of surface curvature is negligible. It is shown that the size of the void (which will be fo rmed in cases of step coverage less than 100%) is a better way to describe the quality of the deposition and the repercussions of the void on subsequent process steps such as tungsten etch back. In addition, the size of the void depends for a given set of deposition conditions solely on the depth of the contact rather than the contact diameter (for aspect ratios larger than 1.0). Blanket chemical vapor deposition of tungsten (CVD-W) deposited under optimum conditions is known to be capa-ble of voidless filling of high aspect ratio contact and via windows in sub-micron (very large scale integrated/ultra large scale integrated) (VLSI/ULSI) circuits. This tech