An evaluation of electrolytic repair of discontinuous PVD copper seed layers in damascene vias

Abstract

This paper presents a study of electrolytic repair of PVD seed using alkaline baths. The test features used were 6:1 aspect ratio (AR) 0.18 μm vias seeded with 250–1500 Å PVD. A wide variety of electrolytic repair process chemistry compositions and plating parameters were studied. The results showed that electrolytic repair of PVD seeds as thin as 500 Å could largely eliminate the bottom voids which otherwise result during subsequent plating in acidic baths. However, repair bath compositions and conditions conducive to optimum fill improvement have also resulted in rough (possibly pitted) wafer surfaces. It is believed that the electrolytic repair requirement of a high cathodic overpotential is in conflict with conditions yielding a smooth and defect-free surface on the submicron scale. Hydrogen evolution, corrosion of seed by complexing agent, and variable behaviour of copper oxide in the complexed alkaline repair baths are believed to contribute to the correlation of increased pitting and repair capability improvement. Therefore, electrolytic seed repair process appears to be a difficult and unpromising process for practical implementation.