After the contact hole is etched, cleaned, and ashed, the silicon or silicide surface at the bottom is exposed P1.The Ti deposition step is the critical first stage of the middle-of-the-line (MOL) contact plug metallization P1.Ti serves as an adhesion layer and an oxygen-scavenging agent that prepares the contact bottom for subsequent barrier formation P2.In the process flow, it directly precedes the TiN diffusion barrier and the chemical vapor deposition (CVD) of tungsten (W) P1.By establishing