High-k shallow traps observed by charge pumping with varying discharging times

Abstract

In this paper, we investigate the influence of falling time and base level time on high-k bulk shallow traps measured by charge pumping technique in n-channel metal-oxide-semiconductor field-effect transistors with HfO2/metal gate stacks. NT-Vhigh level characteristic curves with different duty ratios indicate that the electron detrapping time dominates the value of NT for extra contribution of Icp traps. NT is the number of traps, and Icp is charge pumping current. By fitting discharge formula at different temperatures, the results show that extra contribution of Icp traps at high voltage are in fact high-k bulk shallow traps. This is also verified through a comparison of different interlayer thicknesses and different TixN1−x metal gate concentrations. Next, NT-Vhigh level characteristic curves with different falling times (tfalling time) and base level times (tbase level) show that extra contribution of Icp traps decrease with an increase in tfalling time. By fitting discharge formula for different tfalling time, the results show that electrons trapped in high-k bulk shallow traps first discharge to the channel and then to source and drain during tfalling time. This current cannot be measured by the charge pumping technique. Subsequent measurements of NT by charge pumping technique at tbase level reveal a remainder of electrons trapped in high-k bulk shallow traps.