Polycrystalline silicon/dielectric/substrate material systems for thin film transistor applications: The impact of material properties on transistors' characteristics

Polycrystalline silicon (poly-Si) thin film transistors (TFTs) are currently attracting a great deal of attention for use as pixel switching elements and as driving elements in active matrix liquid crystal displays. For these applications, high quality poly-Si films on glass substrates associated with low thermal budget are necessary for fabricating high performance and long-term reliable poly-Si TFTs. We report herein on a comprehensive study of material qualities of poly-Si produced by low temperature solid-phase crystallization (SPC) and metal-induced SPC (MISPC). We subsequently fabricate n-channel TFTs on the SPC and MISPC crystallized poly-Si and study their properties. The parameter space investigated includes a-Si:H deposition conditions, substrate type, glass substrate coating, glass substrate treatment, metal type, and metal/coating film thickness. Mechanisms for SPC and MISPC kinetics are proposed and variations in TFT's leakage current, threshold voltage, subthreshold swing are interpreted in terms of models incorporating generation/population of traps in the poly-Si channel, bulk gate-oxide, or poly-Si/gate-oxide interface coupled with field emission of carriers from these traps.