Feasibility investigation on ductile machining of single-crystal silicon for deep micro-structures by ultra-precision fly cutting

Single-crystal silicon is a widely used brittle material in infrared optics and optoelectronics industries. However, due to its extremely low fracture toughness, it is difficult to obtain deep micro-structures on single-crystal silicon with ultra-smooth surface quality using previous ductile machining models based on plunge cutting, diamond milling and grinding. Current methods to enhance the machinability of silicon include laser-assisted machining, ion implantation modification and vibration-assisted machining. However, the increase of the ductile machining depth using these methods is still very small in the fabrication of deep micro-structures with a depth over tens of micrometers on silicon. This paper proposes a novel ductile machining model for ultra-precision fly cutting (UPFC) to efficiently fabricate deep micro-structures on silicon. The modeling results show that through configuring a large swing radius, much deeper ductile machining depth can be reached by UPFC. To confirm this proposed model, micro-grooves with different depths were machined, and the surface micro-topographies, form error, tool wear patterns and material phase transformation were analyzed and compared with that acquired by diamond sculpturing method. The experimental results demonstrated that much deeper micro-grooves (over tens of micrometers) with better surface quality were acquired by UPFC. Moreover, compared with the sculpturing method, UPFC prolonged the tool life, and generated less amorphous silicon on the machined surface.