Annealing effect of low-temperature (<150°C) Cat-CVD gate dielectric silicon nitride films diluted with atomic hydrogen

The effect of in-situ hydrogen pretreatment on dielectric properties of silicon nitride (SiN_x) thin films for a gate dielectric layer has been studied. SiN_x thin films were grown at a low temperature (150°C) by Catalytic CVD followed by conventional furnace annealing at 150°C for 2 hours. The in-situ hydrogen pretreatment was performed without vacuum break before the samplewas transferred to the furnace for thermal annealing. Capacitance-voltage (C-V) and current-density-voltage (J-V) measurement showed that the hydrogen pretreatment was effective in reducing the hysteresis in the C-V curve and in increasing the breakdown voltage.Without the treatment, the 150°C annealing failed to produce reliable C-V and I-V characteristics. The C-V hysteresis and the threshold voltage shift of SiN _x were improved by furnace annealing as the hydrogen dilution ratio increased. Also, addition of hydrogen to the deposition gas mixture helped to improve the dielectric properties of the SiN_x films after thermal annealing. The combination of hydrogen dilution of the source gas and the in-situ hydrogen treatment was successful in producing low-temperature SiN _x films applicable to a-Si TFTs. The TFT fabricated by using these films showed a field-effect mobility of 0.23 cm²/V-sec and a V _th of 3.1 V.