| Summary: | 博士 === 國立臺灣大學 === 電機工程學研究所 === 87 === The characteristics of amorphous silicon hydrogen and deuterium thin film transistors (a-Si:H/a-Si:D TFT) were studied. The D2 or H2 plasma was applied to treat the amorphous silicon layers. It was found that substitution of hydrogen with deuterium improved the field-effect mobility of the thin film transistor. A new process of bottom-gate polysilicon thin film transistors was developed. The transistors were passivated by hydrogen/deuterium (poly-Si:H/poly-Si:D TFT) using D2 or H2 plasma. The polysilicon layers were crystallized by irradiating the amorphous silicon film with KrF excimer laser at room temperature. It was found that Si nanoclusters are formed in amorphous silicon (a-Si) thin film by the irradiation of pulsed KrF excimer laser. To the best of our knowledge, this is the first time, KrF excimer laser has been used to prepare Si nanoclusters (nc-Si). It was found that substitution of hydrogen with deuterium improved the electrical characteristics and stability of the polysilicon thin film transistor.
The silicon dioxide deposited by liquid phase deposition (LPD) was used as the gate insulator of the thin film transistor. Liquid phase deposition (LPD) is a special and potential technique for deposition of silicon dioxide. However, the quality of LPD-SiO2 grown on metal is not good. The reason for the poor deposition of SiO2 on metal is probably due to the difficulty of forming nucleation centers on metal. To solve this problem, the metal can be covered by 10 nm thick undoped hydrogenated amorphous silicon layer (a-Si:H) before depositing LPD-SiO2 film. It is found, however, that the liquid phase deposition tends to oxidize the underlying a-Si:H layer. The thickness of oxidized amorphous silicon has been found to be around 15 nm for a deposition of 200 nm thick SiO2. This fact suggests that the liquid phase expitaxial SiO2 can be deposited on any surface by first depositing an a-Si:H sacrificial layer with thickness less than 15 nm. In this thesis, we present evidence that both a-Si:H and poly Si TFTs using LPD-SiO2 layer as a gate insulator can be fabricated with good electrical performance.
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