Investigating the partial plastic formation mechanism of typical scratches on silicon wafers induced by rogue particles during chemical mechanical polishing

The occurrence of scratches on silicon wafers during chemical mechanical polishing (CMP) is a common phenomenon that significantly affects the structural stability and electrical characteristics of integrated circuits. The complex interplay between abrasives, inorganic and organic substances in an aqueous environment, and the iterative evolution of surface morphology, collectively contribute to the limited understanding of CMP-induced scratches. This paper explores the full-plane scratch shape, directions, and number density on different crystal orientations, the microscopic form of scratches with plastic and brittle features for Si(111), Si(110), and Si(100) by the diamond particle doping method. The CMP scratches observed by profilometry display a plastic-like morphology and show no directional preference, irrespective of crystal orientation. The Si(110) exhibits the fewest scratches, while Si(111) has the most, with the volume modulus being a significant factor in this variation. The nature of CMP scratches, the material removal process due to polishing slurries, and the smoothing effect of hillock abrasion and by-product refilling are substantiated by an atomic force microscope and a high-resolution transmission electron microscope. During CMP, the relaxation effect of water solvent and hydrated oxide layer mitigates the hard touching between abrasives and silicon wafer, reducing the brittleness of silicon and the depth of sub-surface damage. The height of scratch hillocks is reduced through continuous scratching of polishing abrasives, and the bottom of scratches is covered by amorphous silica and a small amount of polycrystal silicon. The Fourier transform of transmission electron microscopic images shows the quasi-plastic nature of CMP scratches, indicating the disparity of filling materials between CMP scratches and scratches generated in dry air. This work highlights the distinct nature of CMP scratches, offering insights for guiding the manufacturing of defect-free ultrasmooth silicon wafers.