Nickel silicide encroachment formation and characterization

The stability of nickel-based silicides integrated in CMOS circuits has been studied. The evolution of transistor electrical failures is then reported, linked to Ni abnormal migration through different process steps. We have found in our studies that Ni encroachment is not only due to NiSi2 clusters formation but also to NiSi precipitates formation. Silicon substrate doping, surface preparation, nickel film thickness and the thermal treatments were identified to modify occurrences of this randomly localized phenomenon. Ni-rich phase initial formation is preferable to prevent Ni encroachment even though other upstream process steps for CMOS integration are also key for Ni migration control.