Mechanism of via failure in copper/organosilicate glass interconnects induced by oxidation

Annealing for copper/organosilicate glass (Cu/OSG) dual damascene (DD) structure resulted in via resistance increase when Ta or TaNx film by ionized physical vapor deposition (iPVD) method was used as a barrier metal. The percentage increase in via resistance was higher in smaller vias. In spite of the huge increase of more than 50% in via resistance during annealing, any Cu voids in a single via or via chains of the DD structure were not observed. Instead, large amount of oxygen was detected at the interface between the barrier metal and Cu in the bottom of the vias. It was found that via resistance increase during annealing was caused by oxidation of the barrier metal at the via bottom. Improvement of the step coverage of the barrier metal inhibited the via resistance increase even after the high temperature annealing at 500 °C. It means that the oxygen atoms diffused out from the OSG film were blocked by the barrier metal covering the side wall of the vias.