A new reliability problem associated with Ar ion sputter cleaning of interconnect vias

The cleanliness of a sputter-etched surface of an aluminum alloy in interconnect vias has been investigated. In situ Auger analysis of the sputter-etched vias indicates that sputter-etch cleaning prior to metallization removes the natural oxide on the aluminum surface, but leaves a thin insulating layer due to redeposition of the atoms sputtered out of the intermetal dielectric. Existence of the redeposited layer was also confirmed by scanning electron microscopy (SEM) cross-sectional observation of the vias. The redeposited insulating layer causes contact failure of vias during life testing including high-temperature storage and operation. A multipinhole contact model is proposed to explain the failure mechanism