| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 95 === In this thesis, fluorine and nitrogen ions with different dosage and energy were implanted into polycrystalline silicon of thin film transistor with the gate-last process in all low temperature process < 600oC. After deposition of HfO2 high-k gate dielectric and metal gate, the Low-Temperature-Poly-Si Thin Film Transistors which have excellent sub-threshold swing were fabricated. In order to find out the best device with proper implant dosage and energy, we use the method of positive bias temperature instability, which could help us to find out the best defect-passivation condition.
After finding out the best implant dosage and energy conditions, hot carrier stress method was used to qualify the fluorine and nitrogen passivation ability in the drain-side junction. It is found that the gate dielectric HfO2 which fabricated by the e-gun exhibited the worse performance to resist the hot carrier damage. After stress, transferred curves show serious gate leakage, which means hot carriers create damage inside the HfO2, resulting in a path for electron to tunnel through gate dielectric. It is found that a lower gate leakage current was found in the F-implanted devices, which maybe due the passivation of defects by fluorine. On the other hand, strong Si-F bonds exhibit good resistance to hot carrier, causing less threshold voltage shift which is strongly defect-related. After hot carrier stress, devices were evaluated by using positive bias temperature instability test. With different trends in the time evolution of threshold voltage shift and sub-threshold swing degradation, it is found that electron trapping in the HfO2 is the major reason for the threshold voltage variation. Compared to control devices, devices with fluorine and nitrogen exhibit good passivation at the interface. Devices were measured at an elevated temperature. The transferred curves measured at higher temperature show that fluorine implantation reduces the thermionic emission current at the drain junction. Finally, from the shift of the threshold voltage, it is found that the electron trapping in the HfO2 could easily be de-trapped at high temperature. This can be explained by that interfacial oxide layer between gate dielectric and channel can be suppressed with F-incorporation, so that trapping electrons could easily escape at high temperature for devices with F-incorporation.
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