Performance and failure mechanisms of TiN diffusion barrier layers in submicron devices

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Abstract
Defects in reactively sputtered titanium nitride diffusion barriers in submicron devices were investigated. Four different failure mechanisms could be extracted, two originating from the production of the layers, two related to foregoing process steps. The latter are contact hole overetch and topology inside the contact hole, i.e., edges, created by deviating isotropic etch ratios of different dielectric layers in a post-treatment after the contact etch. The insufficiencies related to the preparation of the TiN films are microcracks due to excessive stress incorporated and encroachment caused by a Ti-rich titanium nitride on the contact hole walls, proved by an Auger electron spectroscopy analysis. Accidental accumulation of two or more of these defects in a production line can cause the barrier to fail. The process of contact degradation was investigated by transmission electron microscopy and energy-dispersive x rays. It was found that after aluminum penetration the destruction of the contact area proceeds via a ternary AlxTiySiz reaction until all titanium is consumed, followed by the growth of a pure Al spike and the fatal breakdown of the contact.