Electromigration failure modes and Blech effect in single-inlaid Cu interconnects

This work demonstrates that we can prevent electromigration failures in single-inlaid copper during DC electromigration testing by taking advantage of the Blech effect. This effect, also known as stress-induced backflow, was coined after I.A. Blech, who first reported this phenomenon for aluminum metal lines.(1) As the metal ions move toward the anode end of the line, a stress buildup occurs opposing the electron wind, thus constraining the void growth. Therefore, a critical length exists for which no electromigration occurs for a specific current density in metal lines. This Blech effect is evident in lines short enough for the stress to fully inhibit the void evolution. We performed electromigration testing of single-inlaid copper metal lines ranging from 5 to 250 mum in length. The testing was performed at 300 degreesC with a stress current density of 1.4x10(6) A/cm(2). The shorter lines did not show any resistance increase even after hundreds of hours of testing, while the longer lines failed at the same time, independent of the line length. The critical product (jl)(c) was calculated to be between 2800 and 3500 A/cm at 300 degreesC for single-inlaid copper.