Effect of reservoir on electromigration of short interconnects

As the interconnect cross-sections are ever scaled down, a particular care must be taken on the tradeoff between increase of current density in the back end of line and reliability to prevent electromigration (EM). Some lever exists as the well-known Blech effect. One can take advantage of the EM induced backflow flux that counters the EM flux. As a consequence, the total net flux in the line is reduced and additional current density in designs can be allowed in short lines. However, the immortality condition is most of the time addressed with a standard test structures ended by two vias. Designs present complex configurations far from this typical case and the Blech product (jL)c can be deteriorated or enhanced. In the present paper, we present our study of EM performances of short lines ended by an inactive end of line (EOL) at one end of the test structure. Significant differences on the median time to failure (MTF) are observed with respect to the current direction, from a quasi deletion of failure to a significant reduction of the Blech effect. Based on the resistance saturation, a method is proposed to determine effective lengths of inactive EOL configurations corresponding to the standard case.