Effects of avalanche injection currents on the endurance of Si MOS devices

A new bulk donor defect in the silicon surface space charge layer is identified as a major limitation on the endurance of avalanche injection type nonvolatile MOS memory transistors. This donor is generated during heavy avalanche injection of holes and electrons and it reduces the silicon surface electric field and the injection current or efficiency at constant injection voltages. Generation-annealing kinetics data and process dependences are summarized which suggest that the donor is an oxygen complex which can be annealed by hydrogen bonding and activated when the hot avalanche holes and electrons break the oxygen-hydrogen bond. The oxygen donor model is consistent with our current knowledge of bulk oxygen properties in silicon such as solubility, diffusivity, outdiffusion and surface denudation. A design example is presented to give the threshold voltage endurance as a function of the number of write/erase cycles. Process variables to reduce the donor density and to increase the endurance are delineated.