Extensive analysis of resistance evolution due to electromigration induced degradation.

Electromigration failure kinetic has been studied with resistance evolution versus time of interconnects during degradation. Tests were performed on dual damascene copper lines, issued from the 65 nm technology node, of various widths and lengths. All samples exhibit similar resistance evolution: an initial step, characterized by its height called Rstep, follows a linear kinetic characterized by its slope called Rslope. These two parameters were systematically extracted; Rstep is proportional to the critical volume of a void spanning the whole section of the line, and Rslope to the copper drift velocity. On one hand, the linewidth does not affect these two parameters. On the other hand, Rslope is highly dependent on the line length because of the Blech effect, while Rstep remains constant. Consequently, it was demonstrated that the classical linear function L/TTF=f(jL), where TTF is the time to failure, j is the current density, and L is the line length, used to study the Blech effect in interconnects could be substituted with the linear function RslopeL=f(jL), confirming that Rslope is a suitable parameter to study void growth kinetics. At 300 °C and 2 MA/cm2, a void growth velocity of 1.15×10-8 μm3/s was thus determined on long lines, and an activation energy of 0.95 eV was found. Finally based on the resistance analysis, an explanation is proposed concerning the larger spread observed on the TTF measured on short lines at low current density. [ABSTRACT FROM AUTHOR]