Device Simulation of Mechanical Stress Effects on Electrical Characteristics of nMOSFETs: Impact of Local Stress in nMOSFETs

An electrical characteristic of a semiconductor device suffers from a residual stress during various packaging processes. Very few attempts have been made at developing a numerical method for evaluating such problems. Therefore, the objective of this study is to evaluate stress-induced effects by numerical simulation. That is, the effects of stress on the electrical characteristics of n-type Metal Oxide Semiconductor Field Effect Transistors (nMOSFETs) with a 85nm gate length were evaluated by mechanical stress simulation and drift-diffusion device simulation (multi-physics simulation). The device simulation model used includes the electron mobility model that considers the stress-induced effects. This study focused on the impact of the stress distribution in the nMOSFETs. The stress distribution in the nMOSFETs was considered in conducting the multi-physics simulation. As determined by mechanical stress simulation, stress concentrated around the STI, and the effect of such stress concentration reached the channel region of the nMOSFETs. Then, the drift-diffusion device simulation was carried out. The stress distribution in the nMOSFETs obtained by mechanical stress simulation was used as the stress effect in the device simulation model. As determined by device simulation, the drain current decreased under the estimated residual stress. The drain-current shift corresponded quantitatively to the stress at the region of the channel. It was demonstrated that the multi-physics simulation is essential for evaluating the effect of stress on electrical characteristics of a semiconductor device.