Kinetics of copper drift in low-kappa polymer interlevel dielectrics

This paper addresses the drift of copper ions (Cu+) in various low-permitti vity (low-k) polymer dielectrics to identify copper barrier requirements fo r reliable interconnect integration in future ULSI. Stressing at temperatur es of 150-275 degrees C and electric fields up to 1.5 MV/cm was conducted o n copper-insulator-silicon capacitors to investigate the penetration of Cu into the polymers. The drift properties of Cu+ in six industrially relevan t low-k; organic polymer insulators-parylene-F; benzocyclobutene, fluorinat ed polyimide, an aromatic hydrocarbon, and two varieties of poly(arylene et her)-were evaluated and compared by capacitance-voltage, current-time, curr ent-voltage, and dielectric time-to-failure measurements, Our study shows t hat Cu+ drifts readily Into fluorinated polyimide and poly(arylene ether), more slowly into parylene-F, and even more slowly into benzocyclobutene, Am ong these polymers, the copper drift barrier property appears to be improve d by increased polymer crosslinking and degraded by polar functional groups in the polymers, A thin nitride cap layer can stop the drift. A physical m odel has been developed to explain the kinetics of Cu+ drift.