The effect of the chemical vapor deposition of tungsten on shallow n ⁺p and p⁺n junctions using titanium-tungsten as a barrier

The effect of blanket chemical vapor deposition (CVD) of tungsten (SiH ₄ reduction) on shallow CoSi₂ junctions using 450-1800 Å of titanium-tungsten (TiW) as a diffusion barrier has been investigated. Thermal stability of W/TiW and Al/W/TiW is studied by measuring the reverse leakage current at 25 °C anneal intervals. The Al/TiW structure has been used as a reference. W/TiW junctions with ≤700 Å of TiW are less stable than Al/TiW junctions. The addition of Al on top of CVD W enhances the junction degradation considerably. p⁺n junctions are more sensitive to the barrier failure. The effect of CVD W deposition temperature has been studied. Junctions exposed to 480 °C CVD W deposition temperature showed a lower leakage than those at 300 °C.