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

The impacts of ammonia gas (NH3) 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-TH) shift of JL-TFT due to the NH3 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 NH3 plasma treatment is enhanced by similar to 2.73 times due to the trap state passivation of grain boundaries in the poly-Si, and the ON-state current (I-ON) is enhanced by similar to 2.91 times. In addition to the performance enhancement of JL-TFT by the plasma process, the V-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-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-ON. The improvement of performance and PGBS of JL-TFT by the NH3 plasma treatment would be beneficial to the application of 3-D integrated circuits.