A comparative study of hydrogen and deuterium plasma treatment effects on the performance and reliability of polysilicon TFTs

Polycrystalline silicon (poly-Si) thin-film transistors (TFTs) provide the capability to integrate display driver circuitry directly on display substrates, offering improved reliability and lower cost. However, long-term stability under DC bias stress is a critical issue for TFTs. Previous studies have shown that hydrogen, introduced into the channel film during the device fabrication process to passivate defects and thereby improving device performance, is the cause of the performance instability (Wu et al., 1990). Recent publications on deuterium post-metal annealing have demonstrated that deuterium passivated single crystalline MOSFETs exhibit superior reliability to MOSFETs passivated with hydrogen (Kizilyalli et al., 1997). Results indicated that, prior to hot carrier stress, deuterium and hydrogen anneals give identical improvement in device performance. In this study, we compare the performance and reliability of conventional top-gate, self-aligned polysilicon (poly-Si) thin-film transistors (TFTs) after passivation by plasma hydrogenation and plasma deuteration. We show that deuterium passivated poly-Si TFTs exhibit generally poorer pre-stress device characteristics than hydrogen passivated TFTs. In addition, reliability testing indicates that deuterium passivation does not provide greater resistance to performance degradation than hydrogen passivation for poly-Si TFTs.