Inline Defect Root Cause Analysis of Cu CMP Shorts Using Dual Beam FIB

Copper (Cu) line shorts defects have a high potential of becoming yield killers for device manufacturing. As design rules shrink the importance of a process free of metal shorts becomes essential to increase FAB yield performance. One of the main challenges of analyzing short defects caused by various physical mechanisms is that when reviewed by top view SEM image after the CMP process step, all of them show similar characteristics. From these top-view images one can only learn that the shorts were due to extra pattern in Cu structures, without a clear insight of the root cause of these defects. Three different mechanisms generating short defects were identified during the time of this study. The first mechanism is related to dual damascene litho process that could not correctly define the Cu line, thus creating shorts between metal lines of the same layer (e.g. Metal 2). The second mechanism is related to Cu line thinning (over dishing) at the Metal 1 level, where as a result a crater is created. During the following Metal 2 insulating deposition process, Cu is deposited into this crater and remains there after the CMP process causing a short between neighboring metal structures. The third mechanism is cracking in Metal 1 that creates shorts between the metal lines at Metal 2 which could not be removed by the Cu CMP process.