Supramolecular Abrasive-free System for Cu CMP
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Supramolecular Abrasive-free System for Cu CMP Jason Keleher1, Ken Rushing1, Joe Zhao1, Bill Wojtczak2, and Yuzhuo Li1 1 Center for Advance Materials Processing, Department of Chemistry, Clarkson University, Potsdam, NY 13699 2 SACHEM, 821 East Woodward, Austin, Texas 78704 Abstract Key issues in CMP today include reduction of surface defectivity and enhancement of planarization efficiency. More specifically, the polished surface should be free of defects such as scratches, pits, corrosion spots, trench copper loss, and residue particles. For copper/low k CMP, one of the most promising strategies to accomplishing these goals is an Abrasive-Free Process (AFP). By eliminating abrasive particles from the process, either free or fixed to the pad, it has been anticipated and realized that defects such as severe scratching, particle contamination and slurry instability via particle aggregation or settling will be significantly reduced. In addition, with proper formulation, an abrasive free process can also yield an excellent over polishing window and desired step function of pressure for material removal rate. Coupled with a supramolecular design, some of the characteristic advantages seen in abrasive containing system such as step height reduction efficiency can be realized without the side effects often introduced from solid particles. In this presentation, some designing principles for an abrasive free system will be first presented. The potential advantages of a supramolecular design for copper CMP will be illustrated. The CMP performance on a set of testing blanket and patterned wafers will be discussed. Introduction For copper CMP, an abrasive free system (AFS) may have many potential advantages over conventional abrasive systems, such as higher selectivity of copper to barrier in removal rate, lower dishing and erosion, longer over-polishing window, lower defectivity, easier post CMP clean, more straight forward treatment of the waste stream, and no slurry handling issues. [1-2] In addition, an abrasive free system can be easily integrated into the existing polishing tools.[3-4] Unlike other proposed schemes such as electrochemical polishing[5], there is no need to modify the existing polishing tools. In copper CMP development, dishing or total copper loss on lines greater than 50 um is often used as one of the most important performance metrics in evaluating of a potential polishing slurry or solution. The cause of dishing can be grouped into two categories: chemical and mechanical. The dishing introduced by chemical attack is often originated from an inadequate protection of lower area in the feature. The passivation layer is either too fragile or too slow to regenerate after the removal of the previous layer. As a result, the formulation is unable to protect the copper in the valley, which in turn, translates to low step height reduction efficiency. When such a slurry/solution is used in copper CMP, the initial step height may propagate throughout the polishing process and leave significant dishing after
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