There are some interesting and important topics that are valuable for the future works. First of all, SPC process is used to crystallize a-Si layer in this thesis. Low mobility and high trap state density are the two major disadvantages. With excimer laser crystallization (ELC), better device performance can be expected. Besides active layer crystallization, there are some imperfect processes in the fabrication of MSB TFTs. First of all, because the un-silicided Si layer of gate electrode is almost undoped, gate depletion becomes unavoidable. Replacing undoped Si-gate by heavily doped Si-gate or fully silicided gate, the device performance will be improved further.
On the other hand, micro-trenching effect during the plasma etch of gate oxide may affect device performance and integrity. In order to avoid this effect, gate oxide should be etched at the process step of sidewall spacer anisotropic etching. Besides the improvement of fabrication process steps, it is known that plasma treatment can passivate trap states so that device characteristics such as threshold voltage, subthreshold swing, mobility, off-state current, DIBL-like subthreshold current, as well as geometric effect are expected to be improved. The doping profile of the ultra-short SDE form by the ITS process is hard to be measured. Novel nano-analysis techniques are required. Once the doping profile can be determined precisely, device optimization becomes possible.
The key process of HfO2 remove after gate patterning has been developed in this thesis. The integration of HfO2 into TFT devices is practicable. With the application of high-k gate dielectric, device performance can be improved furthermore. Certainly, side effects such as mobility degradation, FIBL effect, and hot carrier reliability due to the incorporation of high-k dielectric may be generated. Real devices must be fabricated to under stand all possible issues. It is optimistic that combining MSB S/D junction, high-k gate dielectric, and fully silicided gate, high performance LTPS TFTs is not a dream.
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