Derivation of film characteristic constants of polycrystalline line for reliability evaluation against electromigration failure

Abstract

Increases in electric current density and temperature due to scaling down of IC deteriorate the reliability of the metal line. Electromigration might be one of the main damage mechanisms of the interconnecting metal line. Electromigration is a phenomenon that metallic atoms are transported by electron wind. The metal lines in IC are often connected by vias and multi-level interconnections are constructed. In such lines, it is well known that there is a threshold current density of electromigration damage. When the metal line is subjected to the electric current beyond the threshold current density, electromigration damage occurs as a drift of cathode edge of the line. Recently, a parameter governing electromigration damage at the ends of passivated polycrystalline line, AFD gen | end ∗ , was expressed for reliability evaluation of the polycrystalline line connected with via. In this study, velocity of the edge drift is theoretically expressed by utilizing AFD gen | end ∗ to construct the derivation method of film characteristic constants. By this derivation method, the film characteristic constants included in the parameter formula can be determined only from the measurement of the drift velocity. Next, the test specimen modeled on the via-connected line is treated, and the drift velocity in the line is actually measured under accelerated condition. By equating the theoretical drift velocity expressed by AFD gen | end ∗ with experimental one, the film characteristic constants are obtained. Through the discussion on the validity of film characteristics obtained based on AFD gen | end ∗ , the adequateness of the parameter is verified. And, the usefulness of the derivation method of the film characteristic constants is shown.