Impacts of Ammonia Gas Plasma Surface Treatment on Polycrystalline-Silicon Junctionless Thin-Film Transistor

• Published in: IEEE transactions on plasma science 2021-01, Vol.49 (1), p.26-32
• Main Authors: Ma, William Cheng-Yu, Luo, Shen-Ming, Tsai, Cai-Jia, Lin, Jiun-Hung, Li, Ming-Jhe, Jhu, Jhe-Wei, Chang, Ting-Hsuan, Chen, Po-Jen, Chang, Yan-Shiuan
• Format: Article
• Language: English
• Subjects: Ammonia; Carrier transport; Degradation; Gas plasmas; Grain boundaries; Integrated circuits; Junctionless (JL) transistor; Logic gates; Passivation; Performance enhancement; Performance evaluation; Plasma; plasma passivation; Plasmas; Polycrystals; Polysilicon; positive gate bias stress (PGBS); Semiconductor devices; Silicon; Surface treatment; Thin film transistors; Thin films; thin-film transistors (TFTs); Threshold voltage; Transconductance; Transistors
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/TPS.2020.3010483

The impacts of ammonia gas (NH 3 ) plasma treatment on the performance and positive gate bias stress (PGBS) of polycrystalline-silicon (poly-Si) junctionless thin-film transistor (JL-TFT) are studied. A −0.785-V threshold voltage ( V_{\mathrm {TH}} ) shift of JL-TFT due to the NH 3 plasma treatment is observed, which is attributed to the fixed oxide charge effect of the plasma-induced interfacial layer (PIL). In addition, the transconductance of JL-TFT with the NH 3 plasma treatment is enhanced by ~2.73 times due to the trap state passivation of grain boundaries in the poly-Si, and the ON-state current ( I_{\mathrm {ON}} ) is enhanced by ~2.91 times. In addition to the performance enhancement of JL-TFT by the plasma process, the V_{\mathrm {TH}} shift of poly-Si JL-TFT under PGBS is suppressed from −0.240 to −0.063 V after the plasma treatment. It is attributed to the less degradation of insulator/channel interface due to the growth of PIL by the plasma process. Moreover, the I_{\mathrm {ON}} degradation of JL-TFT after PGBS is also improved from −19% to −16% after the plasma treatment. As the carrier transport of JL-TFT is the bulk conduction rather than the surface conduction of conventional inversion-mode TFT, the degradation of insulator/channel interface would exhibit less impacts on the I_{\mathrm {ON}} . The improvement of performance and PGBS of JL-TFT by the NH 3 plasma treatment would be beneficial to the application of 3-D integrated circuits.