Deformation characteristics and subsurface damage of monocrystalline silicon under repeated nano-scratching

In the context of grinding and polishing of monocrystalline silicon, abrasive particles repeatedly scratch the surface. The resultant subsurface damage significantly degrades the performance of monocrystalline silicon as a semiconductor substrate or optical component. However, the exact mechanism of material removal in monocrystalline silicon subjected to repeated nano-scratching remains inadequately understood. To address this gap, we conducted an in-depth study of the deformation characteristics of monocrystalline silicon via repeated nano-scratch tests. The nano-scratching was performed using atomic force microscopy (AFM) with a diamond tip, which had a radius of approximately 62 nm, under a normal load of about 23 μN. We employed scanning electron microscopy and transmission electron microscopy to analyze the states of the removed material, focusing on the mechanisms of material removal in ductile-regime machining. Our findings indicated that the monocrystalline silicon surface was removed through the formation of continuous curved chips composed of amorphous phase structures. Subsurface deformation from a single nano-scratching was through amorphization and machining defects, including dislocations, stacking faults, and lattice distortions. With repeated nano-scratching, these defects further underwent amorphization and became randomly distributed, rather than occurring in the <111> direction. Moreover, the subsurface defects exhibited a tendency not to expand or penetrate deeper with increasing nano-scratching cycles. This study provides crucial insights into the evolution of subsurface damage under repeated nano-scratching, offering valuable guidance for optimizing grinding and polishing processes to achieve high-quality subsurface and further enhance the performance of monocrystalline silicon.