Misalignment-Free Air-Gap (MFAG) Interconnect with Via Base Structure for 45/65nm Node and Below

A misalignment-free air-gap (MFAG) interconnect with via base was proposed to overcome a via misalignment issue. A conventional via structure is fabricated at limited areas around via sites, whereas the other wires have air-gaps. The good yield in 800k vias' chains was confirmed. The reliability of SIV, EM and TDDB were studied. There was no via degradation after thermal stress of 200degC/500hrs. The EM lifetime of an air-gap interconnect corresponds to that of a conventional damascene interconnect. Also an air-gap interconnect has longer TDDB lifetime by a factor of 1 to 2 than conventional damascene. A wire capacitance can be controlled by etched-back thickness, and capacitance reduction by about 17 to 32% was confirmed. The frequency of the ring oscillator in the air-gap interconnect was higher by 17% on average than that in a conventional damascene interconnect