Surface damage and mechanical strength of silicon wafers

The fracture strength of silicon wafers used for photovoltaic and microelectronic applications mainly depends on the damage structure, which is introduced on the surface during processing of the wafers. The present paper investigates the formation and development of the damage structure by scratching, which occurs during grinding processes or when sawing with diamond coated wires. The basic scratching process has been studied with a newly developed scratch technique, where test parameters comparable to a real process could be used. Single scratch tests have been performed with diamond particles on monocrystalline silicon wafers with a defined surface orientation and under different applied forces. The resulting microcrack structure, which develops under the surface, has been investigated by confocal laser scanning microscopy, scanning electron microscope and Raman spectroscopy. Details of the shape, depth and distance of the cracks have been obtained by high quality sample cross sections. The orientations of the main microcrack planes are determined.