Reliability improvement in blanket tungsten CVD contact filling process for high aspect ratio contact

The reliability improvement of submicron contacts filled by a blanket tungsten process is studied. It is found that, for contacts with an aspect ratio around 2.0, the contact resistance is initially high and increases drastically with additional heat treatment, finally resulting in open failure. This failure mode is caused by chemical reaction on the interface through a previously deposited, porous, glue layer of sputtered tungsten during high-pressure blanket tungsten CVD processing. This reaction occurs at the bottom corner of the contact. A few minutes of hydrogen annealing, followed by a low-pressure hydrogen reduction CVD tungsten nucleation step, suppresses the failure mode drastically. A mechanism for this process in which hydrogen annealing induces selective growth of CVD tungsten only around weak spots in the sputtered tungsten film, thus suppressing WF/sub 6/ intrusion, is proposed. >