Evaluation of surface and subsurface cracks in nanoscale-machined single-crystal silicon by scanning force microscope and scanning laser microscope

Abstract

Studies of nanoscale machining of brittle materials, such as silicon, have come into prominence in recent years. Material removal with plastic deformation, known as ductile mode machining, has been achieved by a very small depth of cut. When surface cracks occurred with increasing cut depth, the machining has been commonly considered to be of brittle mode. In the present study, the ductile–brittle transition point in the nanoscale machining of single-crystal silicon was examined by the observations not only on the surface cracks but also on the subsurface cracks. A scanning force microscope was used to measure the depth of the grooves and to observe the surface cracks. The distance from the surfaces to the deepest point of the subsurface cracks on obliquely sectioned and then etched surfaces were measured by a scanning laser microscope. The transition point determined by the subsurface cracks was found to occur at a shallower depth of cut compared with the transition point from the surface cracks. Therefore, evaluation of subsurface cracks is important especially in the finish shape of machining.