Assessment of the performance of laser-based lateral-crystallization technology via analysis and modeling of polysilicon thin-film-transistor mobility

In this work, we present a comprehensive set of mobility data for poly-Si thin-film-transistors (TFTs), laser-crystallized by sequential-lateral-solidification. We studied the effect of film thickness and device orientation and employed mobility measurements over a wide temperature range to evaluate how the crystal quality of laterally-crystallized (LC) poly-Si films is affected by various process-related factors. Based on this evaluation, we proposed a simple mobility model introducing crystal-defect scattering as an additional scattering mechanism affecting the TFT mobility. The sub-boundary spacing was used as a measure of the crystal quality of the LC poly-Si material and as the main variable for the purposes of modeling crystal-defect scattering. The model was found to account correctly for the experimentally observed mobility variation and yield a reasonable agreement with a wide variety of independent data. Observed inconsistencies between model predictions and some literature data were discussed in terms of an additional factor that was assumed to be laser-process specific. This factor was speculated to relate to the heating/cooling rate of the film, which drives the material propensity for defect generation. In that sense, excimer-laser-based lateral crystallization appears to enable more control over the poly-Si material crystal quality, hence, seems most effective in producing the highest performance LP poly-Si TFTs, with the most uniform characteristics.