Effect of multiple scans and granular defects on excimer laser annealed polysilicon TFTs

A thorough investigation of excimer laser annealed polycrystalline silicon thin film transistors fabricated from single and multiple laser scan processes has been completed. Our results show that even though multiple scans can enhance the grain size in the polycrystalline silicon film, the production of intragrain defects and interface trapping states have adverse effects on the performance of the corresponding devices and in particular, on the leakage current, threshold voltage and subthreshold swing. Further investigation revealed substantial changes in the source-drain current activation energy, as a function of the number of scans. Using our experimental data, coupled with theoretical analysis, we were able to examine to what degree intragrain and grain boundary mobilities determine the overall field effect mobility of the device. A transition region, based on the grain boundary barrier height, was identified separating annealing conditions for which the carrier scattering in the grains or the carrier scattering at the grain boundaries dominated the conduction process. (C) 1998 Elsevier Science Ltd. All rights reserved.