Optimization of silicon-germanium TFT´s through the control of amorphous precursor characteristics

Polycrystalline thin-film transistors (TFT´s) are promising for use as high-performance pixel and integrated driver transistors for active matrix liquid crystal displays (AMLCD´s). Silicon-germanium is a promising candidate for use as the channel material due to its low thermal budget requirements. The binary nature of the silicon-germanium system complicates the optimization of the channel deposition conditions. To date, little work has been done to perform this optimization, resulting in poor performance for SiGe TFT´s. We report on optimization studies done on the low-pressure chemical vapor deposition of SiGe and its effect on TFT performance. We detail the results of a response surface characterization of SiGe deposition, and explain the obtained results in terms of atomistic models of deposition. Optimization strategies to enable the fabrication of high-performance SiGe TFT´s are explained, Using these strategies, SiGe TFT´s fabricated using solid phase crystallization and a 550°C process are demonstrated, with mobility greater than 40 cm²/V-s. Analysis is also performed on the effect of Ge-catalysis on the maximum optimization range. Results suggest that SiGe may offer enhanced optimization ranges over Si, as a result of this catalysis