Effects of the Second Step Annealing Time and Temperature in Two Steps Annealing on Low Temperature Poly-Silicon Film Fabrication

This study fabricates large grain low temperature poly-crystalline silicon film which can be applied to solar cell. The first annealed poly-crystalline silicon film is used as the seeding layer in the crystallization of the next thicker amorphous silicon film. The thickness of the silicon film is over 1 mum. The annealing temperature is set at 500degC and last for 1 hour in the first annealing stage. The crystallinity of the first annealed silicon film is discussed in this paper. In the second annealing stage, two different annealing temperatures (450 and 500 degC) and five different annealing time periods (15, 30, 60, 120 and 240 minutes) are chosen to see the effects of annealing temperature and time period on the crystallization of poly silicon film. Leakage current and surface topography are also being studied. XRD and Raman spectra analysis are used to identify the crystallinity of specimens made under different annealing time periods and temperatures. The surface and cross-section are observed and discussed via scanning electron micrographs. The I-V characteristic is tested to see the magnitude of leakage current of poly silicon film in our study. The leakage current of the poly-silicon film fabricated in this study falls in about 10^-7 A/cm². The resistivity of the poly-silicon film falls between 10³~10⁶ H-cm. The lateral grain size observed from SEM graph is about 3~5 mum The maximum carrier mobility obtained in this study is about 23.4 cm²/V.s.