Effects of hot carrier and irradiation stresses on advanced excimer laser annealed polycrystalline silicon thin film transistors

The effects of hot carrier and gamma-irradiation stresses on thin film transistors fabricated in polysilicon films crystallized using the advanced sequential lateral solidification excimer laser annealing (SLS ELA) process, as well as the polycrystalline silicon film quality, are investigated. The TFT drain current transients after a gate bias pulsing in the OFF state were similar at room temperature at dark or under illumination and exhibited a marked fall, due to generation freezeout, at cryogenic temperatures. This behavior is indicative of low defect density and good crystal quality. The application of DC hot carrier stress, with a condition of V-GS = V-DS/2, was found to induce threshold voltage, subthreshold slope and electron mobility degradation, which, for all these parameters, is significantly higher for thicker polysilicon films. A stress condition with higher vertical field resulted in increased V-th shift but decreased s and mu degradation. The gamma-irradiation of the ELA TFTs resulted in a negative V-th shift, which is higher for thicker polysilicon films, and a small s and mu degradation, while the oxide and interface charge densities increased. (C) 2004 Elsevier Ltd. All rights reserved.