The Study of Ta2O5 Dielectric in Thin Film Transistors

• Main Authors: Jun Son Chen, 陳俊生
• Other Authors: C. H. Kao
• Format: Others
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/04424145845239692291

碩士 === 長庚大學 === 電子工程學研究所 === 96 === In this thesis, we apply a new high-K material Ta2O5 as the dielectric layer in low temperature Poly-Si TFT. The post plasma treatment was combined to passivate the interface states of grain boundary between the Ta2O5 and polysilicon layer. Furthermore, the characteristics of the LTPS TFT’s transistors were improved. At first, Ta2O5 and TaN materials were used to fabricate the capacitors deposited on the polysilicon layer. Those high-K polyoxide capacitors after the hydrogen post plasma treatment can obtain larger breakdown fields and lower leakage currents. The is due to the released hydrogen ion can passivate the traps and defects existed in high-K material and the interface states in the grain boundary to form more strong Si-H bondings for the quality improvements. On the other hand, another post NH3 plasma treatment was used to apply in the high-K polyoxide capacitors for improvements. Using the NH3 post plasma treatment, the growth of interfacial layer can be suppressed to get thinner effective oxide thickness (EOT); and the formation of strong Si-N bondings can improve the electrical characteristics such as lower leakage currents, higher breakdown voltages and larger charg-to-breakdown. Finally, we also demonstrated that the Ta2O5 as the gate insulator combined with NH3 post plasma treatment can improve the performances of the poly-Si TFT transistors, which including off-state leakage currents, on-state driving currents, threshold voltages and grain-boundary trap-state densities. These improvements are also attributed to be due to the hydrogen and nitrogen ions can passivate the trap-states existed in the Ta2O5/polysilicon interface and grain-boundary effectively and form more strong bondings for performance improvements.