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Vol.46, No.11, 762 ~ 770, 2008
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| Title |
| Property of Nickel Silicides with Hydrogenated Amorphous Silicon Thickness Prepared by Low Temperature Process |
| 김종률 Jong Ryul Kim , 최용윤 Young Youn Choi , 박종성 Jong Sung Park , 송오성 Oh Sung Song |
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| Abstract |
| Hydrogenated amorphous silicon(a-Si : H) layers, 120 nm and 50 nm in thickness, were deposited on 200 nm SiO2/single-Si substrates by inductively coupled plasma chemical vapor deposition(ICP-CVD). Subsequently, 30 nm-Ni layers were deposited by E-beam evaporation. Finally, 30 nm-Ni/120 nm a-Si:H/200 nm-SiO2/single-Si and 30 nm-Ni/50 nm a-Si:H/200 nm-SiO2/single-Si were prepared. The prepared samples were annealed by rapid thermal annealing(RTA) from 200℃ to 500℃ in 50℃ increments for 30 minute. A four-point tester, high resolution X-ray diffraction(HRXRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and scanning probe microscopy(SPM) were used to examine the sheet resistance, phase transformation, in-plane microstructure, cross-sectional microstructure, and surface roughness, respectively. The nickel silicide on the 120 nm a-Si:H substrate showed high sheet resistance(470 Ω/□) at T(temperature) < 450℃ and low sheet resistance (70 Ω/□) at T > 450℃. The high and low resistive regions contained ζ-Ni2Si and NiSi, respectively. In case of microstructure showed mixed phase of nickel silicide and a-Si:H on the residual a-Si:H layer at T < 450℃ but no mixed phase and a residual a-Si:H layer at T > 450℃. The surface roughness matched the phase transformation according to the silicidation temperature. The nickel silicide on the 50 nm a-Si:H substrate had high sheet resistance(~1 kΩ/□) at T < 400℃ and low sheet resistance (100 Ω/□) at T > 400℃. This was attributed to the formation of δ-Ni2Si at T > 400℃ regardless of the siliciation temperature. An examination of the microstructure showed a region of nickel silicide at T < 400℃ that consisted of a mixed phase of nickel silicide and a-Si:H without a residual a-Si:H layer. The region at T > 400℃ showed crystalline nickel silicide without a mixed phase. The surface roughness remained constant regardless of the silicidation temperature. Our results suggest that a 50 nm a-Si:H nickel silicide layer is advantageous of the active layer of a thin film transistor(TFT) when applying a nano-thick layer with a constant sheet resistance, surface roughness, and δ-Ni2Si temperatures > 400℃. |
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| Key Words |
| nickel silicide, ICP-CVD, hydrogenated amorphous silicon, nano-thick process, RTA |
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