Characterization of the chemical effects of ceria slurries for dielectric chemical mechanical polishing

In a little over a decade, chemical mechanical polishing (CMP) has grown from a niche application to an enabling technology for global planarization of virtually any material. Initially, CMP was limited to planarization of the silicon substrate during integrated circuit (IC) manufacturing. However, CMP has been successfully implemented in all phases of IC manufacturing. Since CMP is materials insensitive and the only process capable of producing globally planar surfaces, it is being investigated for new processing techniques like shallow trench isolation (STI), micro electromechanical systems (MEMS) fabrication, and a variety of other applications where the surface properties control device performance.; Despite the widespread acceptance of CMP, it remains the least understood step in the microelectronic device fabrication process. The emergence of novel technologies like STI that demand tighter control over the CMP process have stimulated increased interest in the fundamentals of the CMP process. In this work, the fundamental properties of ceria abrasives for STI CMP were studied.; Ceria slurries are promising for STI CMP because of their intrinsic preferential polishing of oxides over nitrides or polysilicon. This advantageous behavior has been attributed to a chemical reaction between the ceria abrasive and the oxide substrate. To date, ceria-silica polishing mechanisms have been supported by little to no experimental evidence. As a result of fundamental investigations, the silica polish rate and surface finish has been found to be a strong function of the ceria slurry pH, with the maximum polish rate occurring near the isoelectric point of ceria. An assortment of complementary surface analytical techniques was used to study the proposed abrasive-surface reaction that is widely attributed to ceria-silica CMP. The ceria-silica reaction has been confirmed by x-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). Finally, the surface chemistry of ceria has been reviewed and correlated with ceria-silica CMP observations.