An investigation of laser annealed and metal-induced crystallized polycrystalline silicon thin-film transistors

We report results on thin-film transistors (TFTs) made from a new hybrid pr ocess in which amorphous silicon (a-Si) is first converted to polycrystalli ne silicon (poly-Si) using Ni-metal-induced lateral crystallization (MILC), and then improved using excimer laser annealing (laser MILC or L-MILC), Wi th only a very low shot laser process, we demonstrate that laser annealing of MILC material can improve the electron mobility from 80 to 170 cm(2)/Vs, and decrease the minimum leakage current by one to two orders of magnitude at a drain bias of 5 V, Similar trends occur for both p and n-type materia l. A shift in threshold voltage upon laser annealing indicates the existenc e of a net positive charge in Ni-MILC material, which is neutralised upon l aser exposure. The MILC material in particular exhibits a very high generat ion state density of similar to 10(19) cm(-3), which is reduced by an order of magnitude in L-MILC material, The gate and drain held dependences of le akage current indicate that the leakage current in MILC transistors is rela ted to this high defect level and the abruptness of the channel/drain junct ion. This can be improved with a lightly doped drain (LDD) implant, as in o ther Poly-Si transistors.