ORIGINS OF THE DUCTILE REGIME IN SINGLE-POINT DIAMOND TURNING OF SEMICONDUCTORS

A germanium surface and the chips produced from a single-point diamond turning process operated in the ''ductile regime'' have been analyzed by transmission electron microscopy and parallel electron-energy-loss spectroscopy. Lack of fracture damage on the finished surface and con tinuous chip formation are indicative of a ductile removal process. Pe riodic thickness variations perpendicular to the machining direction a lso are observed on these chips and are identified as ductile shear la mellae. The chips consist of an amorphous, elemental germanium matrix containing varying amounts of microcrystalline germanium fragments. Th e relative orientation of machining marks and crystallographic fragmen t texture are used to position individual chips with respect to the in itial angular cutting zone on the wafer. Chips with high fragment cont ent correlate directly to cutting zones subject to the highest resolve d tensile stress on cleavage planes. These findings are explained in t he context of a high-pressure metallization (brittle to-ductile) trans formation with ductility limited by the onset of classical brittle fra cture.