Novel Pure Organic Particles for Copper CMP at Low Down Force
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Novel Pure Organic Particles for Copper CMP at Low Down Force K. Cheemalapati1, A. Chowdhury1, V. Duvvuru1, Yong Lin,1 Kwok Tang2, Guomin Bian2 Lily Yao3, and Yuzhuo Li1 1 Center for Advanced Materials Processing, Clarkson University, Potsdam, NY 13699 2 Dynea, Mississauga, Ontario L5R 1B8 Canada 3 Strasbaugh, San Luis Obispo, CA 93401 Abstract It is generally accepted that there is a minimum hardness requirement for abrasive particles to be used in CMP (Chemical Mechanical Polishing) slurries. For copper CMP, the common abrasives are various types of alumina and silica. It has also long been suspected that a softer organic based abrasive could significant reduce the defects during polishing. In this study, for the first time, we demonstrated the usefulness of an organic particle as abrasive in formulating copper CMP slurry. The unexpected consequence of using such soft hydrophilic particles is its low sensitivity of material removal rate for copper towards polishing down force and platen speed. In addition, due to its unique particle surface properties, the slurry gives high selectivity in removal rate for copper over barrier, cap, and dielectric materials. In this paper, some basic physical and chemical characteristics of the particles and slurry will be first presented. The performance of this new slurry in relation to conventional slurries on blanket and patterned wafers will be discussed. Introduction With the integration of copper as interconnect and low k materials as dielectric, the CMP community is facing an ever increasing demand on reducing defectivity without scarifying production throughput. One approach to meet such challenge is to lower the polishing pressure to below 1 psi.1 Such a move has placed tremendous challenges to the tool manufactures, consumable suppliers (especially the slurry vendors), and end-users. It is generally difficult to remain high throughput (MRR and selectivity) at low down force without using harsh abrasives. It is commonly accepted that a minimum hardness is required for the abrasive particles in order to achieve the desirable performance in removal rate.2 In addition, the colloidal stability of the particles are also very important in reducing surface defects.3 For these and other reasons, the commonly used abrasive particles are those inorganic abrasive particles including silica, alumina, ceria, etc. Soft organic particles have not been considered as a key component in slurry formulation except previous work on the use of vesicles and micelles in an abrasive free systems.4 It is important to point out that the function of particles in slurry is not limited the enhancement of the abrasiveness of the pad. A more prominent role of the particles, at least in some cases, is related to its ability to interact with key chemical components found in the slurry due to its high surface area. For example, at pH = 5, a simple analysis based on isoelectric points (IEP) for a silica based copper CMP slurry indicates that the negatively charged silica particles and slightly positi
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