Numerical analysis of airgap stability under process-induced thermo-mechanical loads

In order to understand the state of process induced stresses in air-gap interconnect structures fabricated by means of etch-back procedure, finite element (FE) models of a 90nm pitch interconnect were developed and stress analysis of the structure was conducted as a function of the dielectric liner and metal barrier (MB) thicknesses in a parametric study in order to minimize the risk of mechanical failure. The results identified the sidewall dielectric liner as the critical location where high stresses can result in failure of structures under thermo-mechanical loads. Simulations suggest that optimal mechanical stability is achieved by minimizing the MB thickness and maximizing the thickness of the conformal dielectric liner. The upper limit of the liner thickness however, is dictated by restrictions imposed by interline capacitance which can lead to RC delay.