Low thermal budget polycrystalline silicon thin-film transistors fabricated by metal-induced lateral crystallization

It is well known that amorphous TFTs should be replaced by poly TFTs in order to obtain high resolution and fast response in liquid crystal display (LCD) devices. In a previous work, high performance poly-Si TFTs were fabricated by furnace annealing with metal-induced lateral crystallization (MILC) (Lee and Joo, IEEE Electron Device Lett. vol. 17, no. 4, p. 160, 1996). In this paper, polysilicon TFTs were fabricated by RTA-MILC with a tungsten-halogen lamp. A line-shaped beam, which was focused with an elliptical reflector, was scanned on the sample, which was preheated to 500°C. The annealing temperature, which was measured in Si wafers for reference using a thermocouple, was lower than 750°C, and the real temperature of the glass substrate was likely to be much lower. In order to improve crystallization uniformity and crystallization rate, capping oxide was deposited before RTA. Furnace annealed TFTs were prepared for comparison. In the case of RTA-MILC TFTs, dopant activation and crystallization were carried out in just a few seconds of annealing at over 500°C. RTA-MILC TFTs show higher electron mobility than that of furnace-MILC TFTs. The differences in electrical properties can be attributed to the different thermal profiles which can induce differences in microstructure and defect concentrations.