Slurry Chemical Corrosion and Galvanic Corrosion during Copper Chemical Mechanical Polishing

Abstract

Copper (Cu) corrosion during chemical mechanical polishing (CMP) was controlled in order to improve the Cu damascene interconnect process. Slurry chemical corrosion was found to be enhanced when the slurry was diluted by deionized (DI) water during rinsing just after CMP. Since the corrosion inhibitor, benzotriazole (BTA), reduces the Cu removal rate, adding it to the rinse solution prevents chemical corrosion more effectively than adding it to the slurry. On the other hand, galvanic corrosion occurs at the interface between Cu and the barrier metal, and it can be prevented by selecting appropriate barrier metals. Because the difference between the electrochemical potentials of Cu and the barrier metal is small in the slurry, refractory metals such as Ta, TaN, and TiN were found to be appropriate barrier metals. On the other hand, W, WN, and Ti have large potential differences, so galvanic corrosion was clearly observed when Cu/W damascene interconnects were fabricated.

Review on copper chemical–mechanical polishing (CMP) and post-CMP cleaning in ultra large system integrated (ULSI)—An electrochemical perspective

“…Further increase in H 2 O 2 concentration resulted in copper dissolution rate reduction [40,48]. It was suggested by Zeidler et al [45,48,[50][51][52][53], Nguyen et al [49], Wang et al [40] and Kondo et al [46] that this observation was a result of copper passivation. Similar explanation was suggested by Molodov et al [57], describing copper behavior in HClO 4 -H 2 O 2 media.…”

Defects Observed on the Wafer after the CMP Process

“…Massive electrochemical attack known as galvanic corrosion [58,59] is the most severe form of copper corrosion. It can completely remove the copper from the structures (Figs.…”

Post‐CMP Cleaning

“…As a result, the less noble metal will suffer from accelerated corrosion [58]. When excess copper is polished away by copper CMP, copper and barrier metal are exposed to the CMP slurry simultaneously.…”