Hot-electron injection into the oxide in n-channel MOS devices

In recent years, interest in hot-electron injection current in MOS devices has increased due to advances in device concepts and technology. The injection current to the gate is the mechanism for programming FAMOS devices and determines the potential degradation of short-channel MOS devices due to electron trapping in the oxide. This work presents an accurate indirect current measurement technique based on charge transport to the floating gate in a FAMOS structure. The measurement bypasses effects of trapping and local heating, allowing full characterization of parameter, voltage, and temperature dependence down to gate current levels of 10^-16A. Based on this characterization, a new qualitative model of hot-electron injection into the oxide is proposed. The basic assumption in the model is the spherical symmetry of the momentum distribution function of the hot electrons. This assumption leads to the experimentally observed dominant role of the lateral electric field in the pinchoff region in determining gate current behavior. The model provides an explanation of gate current parameter and voltage dependence, and suggests correlation between gate current and substrate impact ionization current in a range of operating voltages. This correlation is substantiated experimentally for a range of device parameters and voltages.