Electromigration behavior of hot-sputtered Al(Cu) versus chemical vapor deposition W vias

Abstract

The electromigration behavior of hot-sputtered aluminum-copper (Al-Cu) vias is compared to that of chemical vapor deposition (CVD) tungsten (W) vias. Al(Cu) vias were prepared by one of two processes: (1) the via was filled and then defined by chemical mechanical polish (CMP) and (2) the via and top metal line were deposited in the same step (this is referred to as the "Sprint" process). During electromigration testing, the W via chains exhibited more uniform resistance changes with time than the CMP Al(Cu) via chains. This had a direct impact on the shape parameter of the log-normal lifetime distribution, where σ was higher for the CMP Al(Cu) via chains. A closer examination of the failure distributions revealed the need to describe the CMP Al(Cu) via lifetimes by a three-parameter log-normal distribution as opposed to the conventional two-parameter log-normal distribution. Failure analysis of the CMP Al(Cu) samples indicated electromigration failures downstream from the via in the direction of the electron flow. Samples prepared by the Sprint process showed >5× electromigration lifetime improvement as compared to either the CVD W or CMP Al(Cu) via samples. © 1997 American Vacuum Society.