| Summary: | 碩士 === 國立中興大學 === 電機工程學系所 === 97 === Although the BCE-type TFTs of bottom-gate have the advantage of more easier procedure, but the channel is exposed to the dry etching of high energy plasma, which would destroy the a-Si:H bonding in the channel causing lower on current、higher leakage current and worse reliability, and also decrease the optical performance of the display. Therefore we need to research and study the improving mechanism of the BCE-type TFTs after the different plasma treatment conditions.
In this thesis, we take the asymmetrical a-Si:H TFTs which have completed three masks processes and the active layer is exposed.And then then they are applied by different RF power (13.56MHz and 40.68MHz) for plasma treatment. We use different gas sources (NH3、Ar、H2、CF4). Process pressure and ratio of mixed gases to improve device’s performance, and then compare the electric at characteristics of Ion､Ioff､Gm､Vth between before-process and after-process. From experiment results, under 40.68MHz RF power at the 1 torr pressure, the electrical characteristics of NH3 plasma
treatment are significantly improved as compared with other gas plasma conditions.Because the NH3 plasma will create the N ion and H ion to fill the dangling bond (form
N-H bonding､S-H bonding or S-N bonding), it makes the active layer strong and reduces the state creation in the active layer and the interface of dielectric layer and
active layer. About the mixing ratio of Ar in the NH3 plasma treatment experiment, Ar ratio is very important to improve device’s performance. At the different RF power, and mixing ratio of Ar, this ion plasma will directly bombardment the active layer or helpfully ion the gas to affect TFTs’ electric characteristics. In addition, when we used Ar gas only, it is no assistance to fix the defect in the active layer of TFTs owing to the inert property of Ar. The significant improve ment of the Gm is due to that Ar plasma directly bombards the surface of the active layer and makes surface flattened. When increasing the treatment time of Ar plasma, the Gm improvement will reduce.
The BCE-type of bottom-gate asymmetrical a-Si:H TFTs usual have five-masks process, but it has the possibility the use four-masks to fabricate.If we achieve the optimal condition at the plasma treatment process, it will have the profit of cost down, increasing throughput and yield.
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