Effects of oxidant additives for exact selectivity control of W- and Ti-CMP process

Tungsten is widely used as a plug for the multi-level interconnection structures. However, due to the poor adhesive properties of tungsten (W) on SiO2 layer, the Ti/TiN barrier layer is usually deposited onto a SiO2 layer in order to increase the adhesion ability with the tungsten film. Generally, for the tungsten chemical mechanical polishing (W-CMP) process, the passivation layer on the tungsten surface during CMP plays an important role. In this paper, the effects of oxidants controlling the polishing selectivity of the W/Ti/TiN layer were investigated. The alumina (Al2O3)-based slurry with H2O2 oxidizer was used for CMP applications. As an experimental result, for the case of 5% oxidizer added, the removal rates were improved and a polishing selectivity of 1.4:1 was obtained. Therefore we conclude that the W and Ti metal CMP characteristics are strongly dependent on the amounts of H2O2 oxidizer additive.