ELECTROMIGRATION BEHAVIOR OF HOT-SPUTTERED AL(CU) VERSUS CHEMICAL-VAPOR-DEPOSITION W VIAS

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 v ia 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 tes ting, 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 s hape parameter of the log-normal lifetime distribution, where a was hi gher for the CMP Al(Cu) via chains. A closer examination of the failur e distributions revealed the need to describe the CMP Al(Cu) via lifet imes by a three-parameter log-normal distribution as opposed to the co nventional 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 b y the Sprint process showed >5 x electromigration lifetime improvement as compared to either the CVD W or CMP Al(Cu) via samples. (C) 1997 A merican Vacuum Society.