Following the deposition of the primary Ti liner, the TiN deposition step serves as a critical diffusion barrier and adhesion layer in the contact module P3. Its fundamental purpose is to protect the underlying Ti layer and substrate silicon from the highly corrosive tungsten hexafluoride ($WF_6$) precursor utilized in the subsequent tungsten chemical vapor deposition (CVD) step P3. In the absence of this protective barrier, $WF_6$ aggressively attacks the Ti liner to form volatile titanium tetr