The effect of CVD W/TiW metallization on very shallow CoSi2 junctions

The effect of Al/CVD W deposition on shallow junctions below CoSi ₂ using 450-1800-Å sputtered TiW as a barrier/glue layer is investigated. The thermal stability of the Al/CVD W/TiW/CoSi ₂ structure is studied by comparing the reverse bias current of the initial diodes with that after annealing the structure. The results for the deeper n⁺(P)/p diodes ~1000 Å below ~700-Å CoSi₂ are different from those for the p⁺ (BF₂)/n diodes ~500 Å below CoSi₂. When the TiW is >450 Å thick, Al/CVD W does not degrade the n ⁺/p diodes. The reverse bias current is <10 nA/cm² when the Al/CVD W/900-Å TiW is annealed at up to 450°C for 60 min. The n⁺/p diode sport population increases when CVD W is deposited on 450-Å TiW. The diodes are severely degraded after 3000-Å Al is sputtered at 300°C. The temperature of CVD W deposition affected the degradation of the p⁺/n diodes. Higher-temperature depositions at ~500°C degraded these diodes less than depositions at ~300°C. However, annealing the Al/CVD W/900-Å TiW/CoSi₂ p⁺/n structures at 400°C for 30 min degrades the diodes independently of the CVD W temperature where 300<T<500°C