A Study on Seed Damage in Plating Electrolyte and Its Repairing in Cu Damascene Metallization

Abstract

In this study, we observed the changes in the film properties of a Cu seed layer with its damage and repair. The immersion of the Cu seed layer in a sulfuric-acid-based plating electrolyte can result in damage to the Cu seed layer by the dissolution of the native Cu oxide and corrosion of Cu, leading to defects in the subsequent electrodeposited layer. The damaged seed layer was repaired using electroless plating. Cu re-covered the surface and the crystal structure of the seed layer was rebuilt and, finally, the filling characteristic was improved into superfilling in Cu electroplating for the damascene process. Electroless repairing, however, increased the seed roughness due to the low nucleation on the exposed barrier surface and the accompanying three-dimensional Cu growth. To refine the repairing process by inducing the nucleation on the barrier surface, Sn-Pd activation was adopted before the repair, and it reduced the surface roughness and improved the continuity of the seed layer effectively. © 2010 The Electrochemical Society. ͓DOI: 10.1149/1.3291985͔ All rights reserved.Manuscript submitted October 27, 2009; revised manuscript received December 11, 2009. Published February 9, 2010 Cu electroplating has been used in the damascene process for forming interconnects in microprocessors, mainly due to the superior capability in filling the recessed region. Generally, it requires a Cu seed layer, which provides nucleation sites for the formation of a continuous film.1,2 Additionally, it reduces the potential drop originating from its own resistance and, accordingly, prevents a higher deposition rate on the substrate near the points electrically connected to the electron supplier for electroplating.3,4 Moreover, the nature of the seed layer affects the resistivity, crystallinity, and adhesion of the electrodeposit. 5-8In submicrometer technology generations, the Cu seed layer is usually deposited using a physical vapor deposition ͑PVD͒ method. As the trench width decreases to the tens of nanometers range, it becomes more difficult to obtain a continuous and conformal seed layer on the trench wall, especially at the trench base. This is due to the directional deposition of PVD, which results in a "bottom void" during trench filling. 4 Moreover, the coverage of the seed layer becomes worse by the damage in the acidic plating electrolyte. The native Cu oxide formed on the seed layer is dissolved in the acidic electrolyte, resulting in defects in the seed layer. 4,[8][9][10] Martyak and Ricou 2 observed seed layer damage in a sulfuric-acid-based electrolyte by applying 100 A/cm 2 of anodic current on the seed layer. Before adopting methods such as atomic layer deposition and electroless plating in the seed layer fabrication, seed layer repair has been suggested as a bridge between PVD and the methods mentioned. Seed layer repair is a technique that improves the continuity of the seed layer by connecting sparse parts of Cu seed through the addition of a few Cu layers. Electroless plating, 11 alkaline-based electropl...

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