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

Abstract

Abstract— The effect of in‐situ hydrogen pretreatment on dielectric properties of silicon nitride (SiNx) thin films for a gate dielectric layer has been studied. SiNxthin 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 SiNx 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 SiNx 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 SiNx 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 Vth of 3.1 V.