LOCALIZATION OF SOFT TUNGSTEN CONTACT FAILS WITH RELIABILITY IMPLICATIONS BY INNOVATIVE REVERSE ENGINEERING TECHNIQUES

Tungsten contacts mostly fail because of a defective bottom barrier wh ich in turn may find its origin in technological problems with contact etch, barrier or tungsten deposition. Owing to the often unstable ele ctrical properties of those contacts, detection in electrical test or non-destructive localization techniques is time-consuming or even unsu ccessful. The reverse engineering techniques presented here supply 100 % identification and localization of the failing contacts. They reveal a disturbed region under a barrier defect produced by the aggressive chemical reaction of fluorine radicals from WF6 deposition with silico n to the gaseous SIF4. The market contacts exceed the detection fails by far. Some failing contacts may slip through relaxed test conditions -the majority of them, though, still work and indicate a potential of reliability problems as could be demonstrated on chips failing the bur n-in. Thus, an analysis and classification of the contacts at the wafe r level in the presented way allows an identification and first step t o estimation of reliability yield risks.