Controlling void formation in WSi2polycides

Polycides, composite wiring/electrode films formed by depositing a refractory metal silicide such as WSi2, MoSi2, or TaSi2atop a polysilicon film [1]-[4], are finding their way into IC technologies as low-resistivity electrodes/interconnects. One of the desirable features of polycide composite films is their ability for self-passivation through thermal oxidation. In some cases, however, oxidation of the two-layer materials results in the formation of large "voids" in the polysilicon film (bottom layer in the polycide) [5], [6]. A method for preventing this void formation has been found. The solution involves deposition of a thin silicon layer onto the existing two-layer material. The additional layer is designed to provide some of the silicon required for oxidation during the initial stages of self-passivation. In cases where over 200 nm of SiO2were grown atop a WSi2polycide, a silicon layer as thin as 15-nm prevented void formation.