A Study of Mechanical Stability Issues in Multilevel Air-Dielectric Interconnect Schemes for ULSIs

Abstract

Air-dielectric interconnect schemes are under active consideration for use in high performance LSIs because they can improve speed significantly. However, mechanical stability is the biggest engineering issue in these schemes. In this paper, an investigation of mechanical stability issues is presented. It is found that the deflection of the wires due to their own weight is unlikely to be a problem. For a typical long wire cross-section of 2 µm×2 µm, wires of length slightly more than 1mm can be allowed without appreciable sag. On the other hand, it is found that the initial tensile stress in the metal wires produces significant bending stresses at the bottom of the via plugs. The dependence of the bending stress on various geometrical parameters is studied in detail. It is found that bending stresses of more than 1 GPa can result even for a very low initial tensile stress in the wire of 20 MPa.