Electroless and electrolytic seed repair effects on Damascene feature fill

Damascene metallization processes utilizing PVD seed and electroplated copper are demonstrating the capability to provide void free fill in sub 0.1 micron generation features. Ultimately, the extendibility of this metallization sequence is limited by the trade-off between pinch-off of very small features at higher PVD thickness, and the lack of seed coverage near the feature base at lower PVD thickness. When very thin PVD seeds are augmented by a conformal copper deposition process, the pinch-off and poor seed coverage issues which limit filling during bottom-up electrodeposition are potentially reduced, while the adhesion properties of PVD deposition are maintained. This paper presents a study of electrolytic and electroless seed repair in 6:1 aspect ratio 0.18 micron vias seeded with PVD thickness of 250-1500 A Cu. Filling performance and copper coverage in vias after seed repair were studied. Results suggest that PVD thickness in the range of 500 A can be combined with both electroless and electrolytic film thickness in the range of 200 A to improve overall fill performance.