Interface Instability of Integrated Circuit Layers under Electric Current and Mechanical Stress

Abstract

The paper proposes a theory describing the effect of ion migration induced by electric current at initially plane interfaces of integrated circuit (IC) conducting layers on the interface stability with account of mechanical (residual) stress from IC wafers. A system of equations is derived and solved to trace the relation between the interface profile and mechanical stress induced at the interface by ion electromigration due to spatially periodic interface perturbation. Criteria are formulated to judge the buildup of perturbation with time, i.e., the interface profile instability under external conditions. The theory is applied to two practically significant cases: to interfaces between identical materials and between dissimilar materials of which one can be taken free of ion diffusion. Analytical expressions are presented for the influence of external conditions (temperature, current density, residual mechanical stress from wafers) on the range of perturbation wavelengths at which interface instability occurs and for the characteristic time of exponential perturbation buildup. Our estimates show that the interface of IC layers can get unstable via electromigration under typical acceleration conditions. For example, at T ~ 100–500°C, |j| ~ 10¹⁰–10¹² A/m², the perturbation (e.g., vibration) wavelength responsible for instability measures λ ~ 10–1000 μm. The results of this study can be useful for increasing the reliability of micro- and nanoelectronic structures.