Evaluation of Air Gap structures produced by wet etch of sacrificial dielectrics: Critical processes and reliability of Air Gap formation

Two Air Gap technologies were investigated concerning critical process steps. Both approaches use SiO₂ for sacrificial material and buffered HF wet etch chemistry. These critical processes include pre-wet-etch-concerns and wet-etch-concerns. The results of a special spacer etch-back process are shown. A buffer layer of SiO₂ was introduced to relax the requirements on the dry back-etch process. The oxidation of SiC and SiCN films during dry etching and resist stripping is an issue of both technologies, because this may lead to an undercut of the interconnect lines during the buffered HF treatment. Nevertheless, this can be successfully avoided by the application of appropriate oxygen (O₂) free process media. Furthermore, the shifting of mechanical behaviour of such structures as a result of wet-etch treatment is investigated. The intrinsic stress of cantilever SiC films has the capability to cause pull-off forces to interfaces which may result in film delamination.