Metal Corrosion Mitigation in Fine Geometries during Chemical Mechanical Planarization

Abstract

In the Si semiconductor industry, aggressive device geometry scaling has given rise to new processing challenges to each new technology nodes over the past 6 decades. When the feature size shrinks to nanometer regime, new phenomenon emerges whereby significant loss in metal vias and lines can be observed after CMP. Findings from our previous studies suggest just a few nanometers of metal loss imposes serious yield loss in sub-5nm technology nodes MOL and BEOL metallization. Post CMP clean process can be responsible for ~ 50% of the metal loss after CMP. The phenomenon was observed with W, Co, and Cu alike. It affects conductors as well as liner/barrier metals, and exhibits strong dependence on pattern density, feature size, and even underlying layer. [1, 2]. Properly formulated slurries and post CMP clean chemicals can modulate the amount of metal loss and partially alleviate the issue. In this study, we continue to assess how post CMP clean chemicals and modified de-ionized water can influence the amount of metal loss for Cu interconnects. As a starter, blanket wafers resembling several different Cu/liner/low-k stacks were evaluated. The were subjected to polish with the same alkaline slurry followed by various alkaline post clean chemicals (Clean 1, pH ~ 10.2; Clean 2, pH 9.8). It was observed on the attached figure that brush clean only process with DIW alone can induce small amount of Cu loss. For wafers with polish and post clean, on a comparison basis, Clean1 resulted in slightly more Cu loss than Clean2. However, when dilute NH4OH solution (pH ~ 9.6) was introduced to replace DIW during brush clean with Clean1, the amount of Cu loss is reduced, on par with that of Clean2. The observation suggests $NH_4OH$-treated DIW can help alleviate part of Cu loss during post CMP clean process. Patterned wafers with various combination of liner stacks will be subjected to clean process with various combinations of chemistries and/or NH4OH-treated DIW. The amount of Cu or liner loss will be characterized. References: [1] R. Patllola et al., “Copper Metal Loss in Nanometer Fine Features during Chemical-mechanical Planarization”, ICPT (2022). [2] W.-T. Tseng et al., “Nano-scale Metal Loss during Chemical-mechanical Planarization”, ICPT (2023).