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

The effect of Al/CVD W deposition on shallow junctions below CoSi₂ using 450-1800-angstrom sputtered TiW as a barrier/glue layer is investigated. The thermal stability of the Al/CVD W/TiW/CoSi₂ 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 approximately 1000 angstrom below approximately 700-angstrom CoSi₂ are different from those for the p⁺(BF₂)/n diodes approximately 500 angstrom below CoSi₂. When the TiW is >450 angstrom 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-angstrom 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-angstrom TiW. The diodes are severely degraded after 3000-angstrom Al is sputtered at 300°C. The temperature of CVD W deposition affected the degradation of the p⁺/n diodes. Higher-temperature depositions at approximately 500°C degraded these diodes less than depositions at approximately 300°C. However, annealing the Al/CVD W/900-angstrom 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.