Integrated Amorphous and Polycrystalline Silicon Thin-Film Transistors in a Single Silicon Layer

Using a masked hydrogen plasma treatment to spatially control the crystallization of amorphous silicon to polycrystalline silicon in desired areas, amorphous and polycrystalline silicon thin-film transistors (TFTs) with good performance have been integrated in a single film of silicon without laser processing. Both transistors are top gate and shared all process steps. The polycrystalline silicon transistors have an electron mobility in the linear regime of 15 cm/Vs, the amorphous silicon transistors have a linear mobility of 0.7 cm/Vs and both have an ON/OFF current ratios of 10. Rehydrogenation of amorphous silicon after the 600 C crystallization anneal using another hydrogen plasma is the critical process step for the amorphous silicon transistor performance. The rehydrogenation power, time, and reactor history are the crucial details that are discussed in this paper.