Analysis of trap distribution in polysilicon channel transistors using the variable amplitude charge pumping method

Abstract

The trap distribution of a polysilicon (poly-Si) channel in a metal-oxide-semiconductor field effect transistor (MOSFET) was extracted successfully using a variable amplitude charge pumping method (VACP) and an energy band bending model. Compared to single crystal Si channels, the poly-Si channels exhibited a high density of bulk channel traps due to the presence of grain boundaries. The densities of the trap states existing in the poly-silicon channel with various grain sizes and channel thicknesses were extracted and compared. The grain size of poly-Si was found to have a stronger impact on the trap distribution than the channel thickness. After hot carrier stress, the trap density in the poly-silicon channel increases and the generated traps are located both at mid gap energy level and near the conduction band energy level.