Evidence for metastable defects in airgap interconnects

Electrical measurements demonstrate that some metastable defects are present inside airgap interconnect structures realized with the close-off approach. Leakage and capacitance strongly depend on sweep conditions and temperature, which suggests the presence of traps. Compared to homologous full structure, the relative increase of defect states in airgap structures can reach up to ∼5000 for 0.6 μm spacing in the Poole-Frenkel regime. TVS spectra also suggests the presence of mobile species like surface states, trapped charges or mobile ions. These defects gradually evolve with electric and thermal stress, therefore they could be reduced by proper post-growth processing steps.