We report a new fluorine passivation method without ion implantation and additional annealing
step by low-temperature process and its effects on p-channel polycrystalline silicon (poly-Si) thin
film transistors (TFTs). The proposed method is not post-passivation, but in-situ passivation
because fluorine passivation is simultaneous with excimer-laser-induced crystallization by
employing excimer laser annealing of fluorine-doped silicon oxide (SiO
x
F
y
) on amorphous silicon
(a-Si) structure. From experimental results, it has been shown that in-situ fluorine passivation is
effective to improve the electrical characteristics, specially field-effect mobility, and the stability of
p-channel poly-Si TFTs. The improvement is due to fluorine passivation, which reduces the trap
state density and forms the strong Si-F bonds in place of the weak Si-H bonds in poly-Si channel
and SiO2/poly-Si interface.
A 12.1-in. tablet liquid-crystal-display (LCD) panel with integrated amorphous-silicon row driver circuits has been developed using a standard TFT process and Advanced Fringe-Field Switching (AFFS) technology. An XGA-resolution 768-stage shift-register circuit with two-phase clocks has been designed and fabricated. The circuit parameters were optimized in order to obtain a highly reliable a-Si row-driver-circuit structure. Thermal Humidity Operation (THO) test results at 50°C and 80% humidity during 500 hours of operation shows that the fabricated panel is reliable during long-term operation and any abnormal display phenomenon was not observed at 0°C.
A new poly-Si TFT has been fabricated by employing laser-induced in-situ fluorine passivation and laser-doping method. With only one excimer laser annealing, we have successfully fabricated the device using one step to crystallize, passivate and dope simultaneously. Although any additional plasma post-passivation was not performed, the on-state and the off-state leakage properties of TFTs with fluorine passivation were improved compared with those without fluorine passivation. The device with in-situ fluorine passivation has the maximum transconductance of 13.3 A/V for a C 2 F 6 flow rate of 100 sccm, while the device without fluorine passivation has that of 8.4 A/V. The device reliability under electrical stress was remarkably improved in the in-situ fluorine-passivated devices due to the fluorine passivation effects of trap states in the poly-Si channel and SiO 2 /poly-Si interface.
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