Investigation of surface integrity and material removal mechanism of single-crystal Si subjected to micro-laser-assisted machining

Abstract

Single-crystal Si, which is one of the best infrared optics materials and an important semiconductor substrate, is difficult to process owing to its inherent brittleness and hardness. Micro-laser-assisted machining (μ-LAM) has the potential for improving surface integrity by combining the advantages of LAM and conventional ultra-precision machining. However, its material removal mechanism differs from that of conventional machining (CM) technology owing to the interaction between LAM and the diamond turning action. In this study, a three-dimensional transient thermal model based on the finite element method was developed to investigate the temperature responses under different machining conditions. To examine the material removal mechanism and feasibility of high-efficiency machining with μ-LAM, the machining parameters, including laser power and rotation speed, were considered. Furthermore, the surface integrity was systematically characterised and analysed. It was observed that the dislocation motion velocity increased to approximately 2.57 × 109 times that of CM, thereby facilitating ductile deformation of single-crystal Si in μ-LAM. Based on the X-ray diffraction (XRD) pattern analysis, the residual stress significantly decreased with μ-LAM. Furthermore, it was revealed that increasing the rotation speed facilitated ductile mode machining and suppressed the occurrence of micro-pits, and the surface roughness and amorphous layer thickness decreased with increasing rotation speed. Thus, this study provides an important reference for μ-LAM of hard and brittle materials.