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 sample was 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 cm 2 /V‐sec and a Vth of 3.1 V.