The effects of channel boron-doping on the performance and hot electron reliability of N-channel trench UMOSFETs

Abstract

We report on the effects of channel doping on the performance and hot electron stress (HES) reliability of U-shaped trench gate metal-oxide–silicon field-effect transistors (UMOSFETs). The boron-doped n-channel UMOSFETs are examined using transistor parameters and charge pumping current measurements. It is shown that increasing boron doping of the channel degrades UMOSFETs performance via decreasing the effective electron mobility in the channel and increasing the electron drift resistance in the drain region of the device. It is shown that increasing the boron doping of the channel does not increase interface trap density, which is a major cause for mobility reduction in MOSFETs: instead, ionized impurity scattering in the channel as well as the electric field transverse to the device channel, both of enhanced by doping, are argued to primarily cause the observed degradation in the electron mobility. The UMOSFETs response to HES is observed to be dependent on the doping level of the channel and is discussed in terms of the hot electron energy and its influence by channel doping.