Damage assessment of 6H-SiC under repeated nano-scratching

Abstract

Monocrystalline silicon carbide (SiC) is a promising next-generation semiconductor material, and ultra-precision machining techniques such as grinding, polishing, and lapping are essential in the fabrication of SiC-based devices. During these processes, randomly dispersed abrasive grains interact with the SiC wafer through contact sliding, removing material via repeated nano-scale scratching. This study investigates the underlying mechanisms of material removal, aiming at minimal subsurface damage, through detailed nano-scale experimental analyses using atomic force microscopy (AFM). Experiments were performed on 6H-SiC surfaces under a constant AFM tip load of 8 μN. The surface and subsurface microstructural evolution were analyzed using scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Results show that as the number of nano-scratching cycles increases under consistent loading conditions, the thickness of the amorphous layer stabilizes without further phase transformations or defect formation. A uniform amorphous layer, 3–5 nm thick, develops in the top subsurface, with no lattice defects present beneath it. Due to tip wear and changes in the ratio of undeformed chip thickness to tip radius, the material removal mechanism shifts from extrusion-shearing dominated cutting to plowing. The complex stress field and stress gradient, combined with the material's anisotropic microstructure, introduces multifaceted plastic deformation in the top subsurface during plowing, resulting in irregular amorphization and lateral lattice distortions. This leads to material pile-ups containing both crystalline and amorphous phases along the nanogroove.