Dependences of Structural Parameters on the Characteristics of Poly-Si Thin-Film Transistors after Plasma Passivation
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A18.8.1
Dependences of Structural Parameters on the Characteristics of Poly-Si Thin-Film Transistors after Plasma Passivation Cheng-Ming Yu , Tiao-Yuan Huang2, Tan-Fu Lei2, Horng-Chih Lin1 2
1
National Nano Device Labs, 1001-1 Ta-Hsueh Road, Hsinchu, Taiwan, 30050, R.O.C.
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Institute of Electronics, National Chiao Tung University, 1001Ta-Hsueh Road, Hsinchu, Taiwan, ROC. ABSTRACT The effects of NH3 and H2 plasma passivation on the characteristics of poly-Si thin-film transistors with source/drain extensions induced by a bottom sub-gate were studied. Our results show that significant improvements in device performance can be obtained by both passivation methods. Moreover, NH3-plasma-treatment appears to be more effective in reducing the off-state leakage, subthreshold swing, compared to H2 plasma passivation. NH3 plasma treatment is also found to be more effective in reducing the anomalous subthrehold hump phenomenon observed in non-plasma-treated short-channel devices. Detailed analysis suggests that all these improvements can be explained by the more effective passivation of the traps distributed in both the front and back sides of the channel by NH3 plasma treatment. INTRODUCTION With their higher mobility, the use of polycrystalline silicon (poly-Si) thin-film transistors (TFT) allows the integration of the active switching element and the peripheral driver circuitry on the same substrate, which further improves system performance and reliability.1,2 However, defects at the grain boundaries as well as inside the grains are known to cause device degradation.3, resulting in poor device performance including low mobility and high off-state leakage current.4,5 In order to obtain high-performance poly-Si TFTs, it is essential to reduce the trap density in the poly-Si channel. To this end, hydrogen plasma passivation is a well-known technique.6,7 The atomic hydrogen can passivate defects in the poly-Si channel, thereby improves the device characteristics. In addition, nitrogen-containing plasma treatments in combination with hydrogen (e.g., H2/N2 mixture plasma8, nitrogen implantation with H2-plasma9, and pre-oxidation NH3 annealing with H2-plasma10, and NH3 plasma11) have also been shown to further improve the device performance. The additional nitrogen passivation and/or the enhanced hydrogen passivation effects in the presence of nitrogen are presumably responsible for the observed improved characteristics. Concurrently, an effective method for reducing the off-state leakage current by employing an electrical drain junction induced by a sub-gate
Downloaded from https://www.cambridge.org/core. UNSW Library, on 28 Oct 2017 at 00:25:41, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-762-A18.8
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has been proposed.12,13 It is shown that, with proper device structure design and operation conditions, the leakage current can be dramatically reduced without significantly compromising the drive current. Recently, we have proposed a nov
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