Influence of different isolation technologies on threshold voltage of parasitic MOSFETs

Two technological structures of parasitic MOSFETs for the isolation processes LOCOS and SILO are simulated. Existence of bird´s beak in LOCOS process and its absence in SILO is obtained. The field threshold voltage of both parasitic devices is calculated as a function of the isolation length and substrate concentration by numerical device simulations. The variation of the field threshold voltage with the substrate concentration and isolation process is explained. Both short-channel and reverse short-channel effects are obtained and, then, explained by calculating potential distribution along the silicon/oxide interface in the gate region.