In this study the effects of oversize particle contamination in chemical mechanical polishing (CMP) slurries were investigated on the silica CMP process. The limits of light scattering technique were established in detecting coarse particles in a commercial silica CMP slurry using two different methods. The detection limits were set by observing the shift in particle size distribution curve or by the appearance of an additional peak in the particle size distribution curve of the baseline slurry when a known amount of coarser particles were added to it. Simultaneously, polishing tests were conducted by spiking the base slurry with coarser sol-gel silica particles at the established detection limits. It was observed that the contamination of larger particles not only created surface damage but also changed the material removal rate. The mechanism of polishing in the presence of larger size particles is discussed as a function of particle size and concentration.
The formulation of slurries for chemical–mechanical planarization (CMP) is currently considered more of an art than a science, due to the lack of understanding of the wafer, slurry, and pad interactions involved. Several factors, including the large number of input variables for slurries and the synergistic interplay among input variables and output parameters, further complicate our ability to understand CMP phenomena. This article provides a fundamental basis for the choice of chemical additives and particles needed for present-day and next-generation slurry design. The effect of these components on nanoscale and microscale interaction phenomena is investigated. Methodologies are suggested for the development of next-generation slurries required to overcome CMP challenges related to defectivity and the surface topography of soft materials such as Low-κ dielectrics and copper.
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