| Summary: | 碩士 === 國立暨南國際大學 === 電機工程學系 === 91 === Due to high melting point, high stability and low resistivity of metal silicide, the use of metal silicide to replace the conventional poly-silicon gate has become a necessary trend in recent development in integrated circuit fabrication. In the past, hydrogen played an important role in the integrated circuit processing, particularly in the improvement of the reliability of metal-oxide-semiconductor (MOS) devices. Recently, deuterium, the isotope of hydrogen, has also been applied in the integrated circuit fabrication to reduce the damage caused by interface trap density and hot carrier effect in MOS devices.
Although post-metallization anneal in either hydrogen or deuterium environment can improve the damage caused by electrical stress, impact ionization caused by irradiation when the device is exposed to a radiation will be a different story because the damage mechanism is not necessarily the same as electrical stress. In addition to application in outer space, device may also be subjected to radiation during the fabrication process such as ion implantation and reactive ion etching. Especially, when metal silicide is used as the gate contact in MOS devices, antenna effect could possibly aggravate the radiation effect.
In this thesis, we aim at the radiation effect, post-irradiation annealing in deuterium, hydrogen, or nitrogen environment, the second irradiation effect of MOS devices with two of the most commonly used metal silicides — cobalt silicide (CoSi) and tungsten silicide (WSi), as gate metal contact. The Hi-Lo frequency C-V curves were used to determine the interface trap density Dit shift and flatband voltage shift before and after irradiation, and the effect of interface trap charge generation during irradiation was discussed.
We found that after-irradiation annealing in deuterium or hydrogen cannot improve the radiation-induced oxide trap charges and interface trap charges. On the contrary, deuterium and hydrogen would increase the radiation sensitivity of MOS devices. We also found that the radiation sensitivity of the polycrystalline silicon was increased after post-metallization anneal. Therefore, in this thesis we discussed the radiation effect and the relation between post-metallization annealing in deuterium, hydrogen, and nitrogen and the impact ionization of MOS devices with CoSi and WSi as the gate contact.
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