Following the ashing and cleaning of high-aspect-ratio contact holes, the structure requires a conductive interface to connect the silicon active areas to the subsequent tungsten plug P3.The Ti/TiN stack serves a critical dual purpose: the titanium (Ti) layer acts as an oxygen-gettering and adhesion layer, while the titanium nitride (TiN) layer acts as a diffusion barrier P2.Without this TiN barrier, the highly corrosive WF6 precursor used in the subsequent tungsten deposition step aggressively