Characterization of the Chemical Effects of Ceria Slurries for Chemical Mechanical Polishing
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Characterization of the Chemical Effects of Ceria Slurries for Chemical Mechanical Polishing 1,3 J. T. Abiade , S. Yeruva1, B. Moudgil1, D. Kumar3, and R. K. Singh2, 1 Department of Materials Science and Engineering and Particle Engineering Research Center, University of Florida, Gainesville, FL 32611 2 Microelectronics Research Center, University of Texas, Austin, TX 78712 3 Center for Advanced Materials and Smart Structures and Department of Mechanical Engineering, North Carolina A&T State University, Greensboro, NC 27411 Abstract For highly selective particle-based slurries or fixed abrasive pads, ceria has been identified as the abrasive of choice for the chemical mechanical polishing (CMP) step for shallow trench isolation (STI). The advantageous performance of ceria-based CMP consumables is usually attributed to enhanced chemical reactivity between ceria and oxide materials. In fact, this reaction is a central theme of all ceria polishing models from glass polishing to STI CMP. Previously, experimental evidence in support of the ceria-silica reaction during CMP was virtually non-existent. Recently, we proposed a pH-dependent ceria-silica polishing mechanism based on polishing results, in-situ friction force measurements, and spectroscopic and microscopic investigations. In this report, we have studied the chemical interactions between ceria and silica in the absence of particles using an atomic force microscope (AFM) and a scanning electron microscope (SEM). AFM silicon tapping mode cantilevers were functionalized by depositing a silica coating via chemical vapor deposition (CVD) and thermal oxidation. SEM imaging and compositional analysis was conducted on the cantilevers before and after wear against a ceria thin film, which was grown by pulsed laser deposition. The cantilever wear profile and elemental composition as a function of pH confirms our earlier polishing results and the pH-dependent CMP model for ceria-silica CMP. Introduction In recent years, ceria based slurries have been extensively investigated for polishing of STI structures. Ceria slurries rapidly achieve preferential removal and planarization of the oxide layer with minimal polishing of the underlying nitride. Several studies have shown the rapid removal of oxide using ceria-based slurries, however the mechanisms for this removal process are not well understood. One model termed the chemical tooth, is based on results from glass polishing [1]. The second,
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proposed specifically for ceria-silica CMP, is more mechanical in nature and has been given the label ‘particulate generation’ model [2]. Neither model conclusively explains the particle-surface interactions during CMP that lead to silica removal with ceria-based slurries. In this paper, we conduct investigations to understand the fundamental mechanisms prevalent during ceria-based silica polishing. Why do ceria abrasives polish silica so much faster than silica-based slurries? This is the fundamental question in ceria-silica CMP. For STI applications, understanding the o
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