Effects of field boron dose on substrate current in narrow channel LDD MOSFETs

Effects of field boron dose on substrate currents in narrow channel LDD NMOSFET's are investigated. When field boron is heavily introduced, the substrate peak currents show marked increase. Through experiments and simulation, it was found that the increase of the substrate peak current in wide channel device is due to the generation of hot carrier at the isolation edges and that a marked hump of substrate peak current in narrow channel device is mainly due to the increase of impact ionization rate at the center of channel region. These phenomena are explained by the field boron penetration toward the channel region. It is also shown that the increase of substrate peak current in narrow channel LDD MOSFET's gives rise to the degradation of current drive capability.