Kinetics of copper drift in low-κ polymer interlevel dielectrics

This paper addresses the drift of copper ions (Cu⁺) in various low-permittivity (low-κ) polymer dielectrics to identify copper barrier requirements for reliable interconnect integration in future ULSI. Stressing at temperatures of 150-275°C and electric fields up to 1.5 MV/cm was conducted on copper-insulator-silicon capacitors to investigate the penetration of Cu⁺ into the polymers. The drift properties of Cu⁺ in six industrially relevant low-κ organic polymer insulators-parylene-F, benzocyclobutene, fluorinated polyimide, an aromatic hydrocarbon, and two varieties of poly(arylene ether)-were evaluated and compared by capacitance-voltage, current-time, current-voltage, and dielectric time-to-failure measurements. Our study shows that Cu⁺ drifts readily into fluorinated polyimide and poly(arylene ether), more slowly into parylene-F, and even more slowly into benzocyclobutene. Among these polymers, the copper drift barrier property appears to be improved by increased polymer crosslinking and degraded by polar functional groups in the polymers. A thin nitride cap layer can stop the drift. A physical model has been developed to explain the kinetics of Cu⁺ drift