6. Ductile Mode Cutting of Silicon

In wafer fabrication, most machining processes such as slicing, edge grinding, finishing, lapping, polishing, back thinning and dicing, are based on grinding or/and abrasive process, which always generate micro cracks and subsurface damage. In this chapter, theoretical analysis on ductile mode cutting of silicon wafer shows that machined silicon surface with free of fracture and nanometer scale surface roughness can be achieved when dislocation dominates its chip formation rather than crack propagation. Nanometric cutting of silicon wafers using an ultra-precision CNC lathe with single crystal diamond cutters are carried out to investigate the tool edge radius effect on critical undeformed chip thickness and verify ductile mode cutting performance of silicon wafer. Machined workpiece surfaces and used diamond tools are examined using a scanning electron microscope (SEM), transmission electron microscopy (TEM) and atomic force microscope (AFM). Experimental results from the nanometric cutting tests indicate that in cutting of silicon wafers, there is a critical undeformed chip thickness, at or below which chip formation is under ductile mode cutting generating continuous chips. And critical undeformed chip thickness differs when cutting of silicon wafers using diamond cutters with different tool edge radius. Larger diamond tool edge radius, larger critical undeformed chip thickness. But there is an upper bound for diamond tool edge radius, above which chip formation is changed from ductile mode to brittle mode even though undeformed chip thickness remains to be smaller than tool edge radius. Experimental results are found to well substantiate the analytical findings and nanometric ductile mode cutting of silicon wafer is successfully achieved under certain cutting conditions.