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Implementation of air-gaps in the trench dielectric levels has been demonstrated as a potential effective solution to further reduction of the capacitance coupling in the Cu/low-k interconnects.[1-4] In this paper, the critical issue of mechanical stability in such air-gap interconnect structures during thermal processing and under chip packaging interaction (CPI) is investigated using 3D multilevel finite element analysis (FEA) models. Introduction Implementation of air-gaps in the trench dielectric levels has been demonstrated as a potential effective solution for dielectric scaling beyond 32nm with an achievable dielectric constant below 2.0.[1-4] However, air-gap interconnect confronts serious challenges concerning its structural integrity and mechanical stability. Bridging low-k cap (or hard mask) was observed to collapse over wide gaps during thermal decomposition of the gapforming material.[2,4] Crack initiation in keyhole-shaped gaps [5] formed by etchback and nonconformal refill schemes can also be a potential reliability concern. As packaging assembly exerts additional stresses to the fragile interconnect structures, chip packaging interaction (CPI) has been recognized as a serious reliability issue for air-gap structures. In this paper, we analyzed the mechanical stability issues of air-gap interconnect structures during thermal processing and subsequent packaging assembly using 3D multilevel finite element analysis (FEA) models. Structural and Mechanical Stability of as-Processed Air-gap Interconnects A 3D five-level finite element model was developed to simulate processinduced stresses in an air-gap interconnect (see Figure 1). To catch the representative features, FSG was used in the first two metal levels and the global level. Air-gaps were implemented in levels three and four. With varying line widths and dielectric materials, only slight reduction of the stress levels was observed in Cu wires as a result of air-gap implementation. This is not unexpected, as Cu wires are primarily confined by the silicon substrate. The introduction of air-gaps only further weakens the already weak confinement of Cu wires by the interlevel dielectrics. These results indicate that air-gap implementaMechanical Stability of Air-gap Interconnects Xuefeng Zhang, Suk-Kyu Ryu, Rui Huang, Paul S. Ho, Junjun Liu, Dorel Toma University of Texas, Austin; Tokyo Electron US Holdings. PRINT E-MAIL