| Summary: | 碩士 === 國立交通大學 === 電機學院微電子奈米科技產業專班 === 98 === In this thesis, advanced High-κ materials were employed to fabricate high performance low-temperature polycrystalline silicon thin film transistors (TFTs). High performance n-channel poly-Si thin film transistors (TFTs) are demonstrated using the different High-κ dielectric with hafnium dioxide (HfO2), hafnium silicate (HfSiOx) and hafnium aluminum oxide (HfAlOx) layer are demonstrated by metal organic chemical vapor deposition system with low temperature processing. We compare with different composition ratio High-κ materials layer for our main shaft and the effect and reliability are also studied.
It is found the electrical characteristic of High-κ dielectric TFTs that improve obviously：including the lower threshold voltage, the better subthreshold swing, the higher driving current.
However, the large leakage current would be caused by the polycrystalline structure of HfO2 film. In contrast, HfSiOx films exhibit better thermal stability and retain the amorphous structure even after high temperature annealing. In addition, as Al content increasing of HfAlOx films that could be to raise crystalline temperature. Certainly, the lower κ compared with HfO2 film is the disadvantage of the HfSiOx films. Besides, the native interfacial layer with lower κ value always exists between the High-κ gate dielectric and Si substrate, which defeats the purpose of EOT lowering.
Moreover, the higher leakage current of poly-Si TFTs using High-κ gate dielectric was also studied. Aggravated gate-induced drain leakage (GIDL) current was thought to arise from the higher induced electric field by the introduction of High-κ films, and field-emission current would be the dominant leakage mechanism. We found the HfSiOx dielectric TFTs have the better reliability due to it has the better interface, higher crystalline temperature and lower density of states.
Finally, we also tried to apply the newly-developed High-κ films to the Metal-oxide semiconductor field-effect transistors (MOSFETs). And the structural and electrical properties of the thinner High-κ films were discussed.
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