| Summary: | 碩士 === 國立中興大學 === 電機工程學系 === 90 === The major application of hydrogenated amorphous silicon nitride (a-SiNx:H) film is gate dielectric material and passivation layer for thin film transistors (TFTs). A good quality a-SiNx:H film has those characteristics including low leakage current, low hydrogen content, high breakdown voltage, high dielectric constant and lower interface trapping density. Because the properties of a-SiNx:H film effects the performances of TFT.
Pulse-wave modulation RF plasma with changing frequency and duty cycle can alternate the radicals generated in the plasma. It is excepted that the N/Si ratio in a-SiNx:H can be adjusted precisely and the bonding quality of the a-SiNx:H can be modified by this unique technology.
The range of SiH4/NH3 ratio, total flow, pulse-on time/pulse-off time, RF peak power, and hydrogen dilution was set as 1/3.75 to 1/15, 220cssm to 266sccm, 25ms/500ms, 100W to 400W, 50%.
A-SiNx:H can be characterized with FTIR and N&K analyzer to analysis its characteristics, such as bonding structure, hydrogen content, thickness, refractive index, and optical energy gap. The C-V and I-V measurements were made with MIS Al/a-SiNx:H /N-type Si wafer/Al structure. The electrical, optical, and material properties of the a-SiNx:H films was discussed to find out influence of the different deposition conditions and the relation of those properties. The modification of the quality of the a-SiNx:H films using pulse-wave modulation RF plasma will be improved.
The major deposition conditions to influence the characteristics of a-SiNx:H films are NH3/SiH4 ratio, RF power, and hydrogen dilution ratio. The a-SiNx:H films deposited using higher NH3/SiH4 ratio (1/15), higher pulse-on time (23.33ms), lower RF peak power (100 W), and 50％ hydrogen dilution has the smallest leakage current density of 1.97×10-9 A/cm2(at 1 MV/cm)、the largest dielectric constant of 7.93, refractive index of 1.460, breakdown filed of 6.96 MV/cm (at J = 1μA/cm2), and energy bandgap of 5.46 eV。
A-Si:H TFT devices are fabricated using Channel-Passivated(CHP) structures. In CHP structure, the increasing of leakage current in the a-Si:H activation layer can be reduced due to the a-Si:H film passivated by the upper a-SiNx:H layer. The best a-Si:H TFT device in this study has the characteristics of Ion/Ioff = 2.48×106, threshold voltage VT = 3.01V, and field-effect mobility μ = 0.86 cm2/V-s.
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