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Stress-induced voids can form in Cu interconnects, due to either thermal expansion mismatch between the metal and the dielectric or due to confined grain growth in the Cu. The fail rate due to stress-induced voids increases as device dimensions decrease, because the critical void size to cause a fail decreases. Good process control is required for trench and via profiles, barrier and seed layer coverage, Cu fill, and cap layer adhesion, to prevent fails from stress-induced voids.

In this study, intralevel dielectric breakdown is studied for copper interconnects in an SiOF dielectric, capped with either SiN or SiCN. The leakage current is higher and the failure time of dielectric breakdown is shorter for an SiCN capping layer compared to an SiN capping layer. It is proposed that the dielectric breakdown of the integrated structure is limited by the interface between the capping layer and the SiOF dielectric. Lower lifetime for dielectric breakdown is observed for structures with an SiCN cap compared to structures with an SiN cap, due to higher leakage current in the SiCN. The higher leakage for an SiCN cap is consistent with results from planar metal-insulator-semiconductor capacitors.

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