Environment-friendly PVD Al-plug process for submicron multilayer interconnection

IC industries are now under heavy pressure to develop electronics that lessen the environmental pressure. Green electronics calls for more environment-friendly manufacturing processes. An aluminum reflow process for metallization simply employing a PVD cluster tool, instead of CVD-tungsten fixtures, was successfully applied to fabricate IC wafers of narrow line width. Compared with tungsten, aluminum plugs can be formed in vias and contacts by PVD method which contributes to no precursor and little by-products. It also benefits the environment by saving process steps and equipment. Moreover, unlike refractory metals, aluminum is among the selected materials for electronic products for its recyclability after disposal. This paper will show how this green process can realize multilayer interconnection in submicron scope that used to be achieved only by tungsten. Voids in contacts and vias are eliminated by the thermal diffusion of aluminum atoms. Different conditions including two-step process are used to treat device wafers. The step coverages of contacts are tested to investigate both temperature and power dependence of the ability of aluminum to diffuse into the void during reflow steps. The mechanism of reflow is demonstrated theoretically and experimentally. The optimal processing condition is. also obtained through the experiments.