In semiconductor wafer fabrication, the contamination issue by halogens (such as F, Cl, and Br) brings great challenges to metallization processes in the back end of line (BEOL). For aluminum (Al) back-end process, severe metal corrosion may occur by halogens, forming aluminum halide defects. Such halogen-induced metal corrosion issue creates the defects on Al metal lines, Al bondpads and Vias, causing direct device failure, resulting in low yield and reliability issue. In this paper, we reported failure analysis and mechanism studies of the Worm-like defects in Via holes, which was caused by Cl contamination and the subsequent Al metal corrosion. With this study, a corrosion mechanism was proposed in which a Cl-based chemical chain-reaction resulted in repeated/continuously enhanced chemical corrosion even with a small amount of Cl ions. The chemical chain-reactions caused more serious corrosion with corrosive by-products. Such Cl-induced Al metal corrosion and the worm-like defect formation resulted in the process integrity issues related to Al metallization processes, such as voiding in Via structures, opening or bridging in between metal lines.

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