Control of Threshold Voltage on the Excimer Laser Annealed Poly-Si TFTs by Oxygen Plasma Treatment on Poly-Si Surface
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SIMS and ESCA analysis. IR spectroscopy was used to measure the structural properties of the oxide films. The excimer laser annealed poly-Si TFTs (figure 1) were fabricated to investigate the effect of oxygen plasma treatment prior to deposition of inter-layer SiO, drain gate the gate insulator. The poly-Si films were formed on glass ayer insulator gate r ayger :imnntersubstrates with buffer oxide films. The recrystallization of i n poly-Si poly-Si n' poly-Si SiO a-Si films was performed with XeCI excimer laser. The gate buffer oxide oxide films were deposited with oxygen plasma treatment. Both the treatment and the Fig. 1. The cross-sectional view of poly-Si TFT fabricated in the deposition temperature were present work. The oxygen plasma treatment was performed on 450'C, which was the poly-Si surface. maximum processing temperature for fabricating poly-Si TFT. After gate metal patterning, the source and drain region was formed by an ion doping technique. The inter-layer oxide deposition, contact hole opening, Al sputtering, and sintering were performed.
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RESULTS Prior to deposition of Si0 2 film on the Si wafer, the oxygen plasma treatment was performed for 6 min. The hydrogen and carbon impurity profiles in Si0 2 film and silicon wafer were measured by SIMS with the results shown in figure 2. There exist some more impurities, such as carbon or hydrogen, at the SiO 2/Si interface. With oxygen plasma treatment, the hydrogen profiles are not varied significantly, but the carbon content at the Si0 2 /Si interface decreases. The relative carbon content at the SiO2/Si interface measured by SIMS is shown in figure 3 as a function of oxygen plasma treatment time. With increasing oxygen plasma treatment time, the carbon content decreases and subsequently saturates. Figure 3 also shows the deposition rate of Si0 2 films with respect to oxygen plasma treatment time. lci
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Fig. 2. Depth profiles of LPCVD Si0 2 films with silicon substrate. (a) untreated, (b) 7 miin treated by oxygen plasma.
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Fig. 3. The relative carbon content obtained in the SiO2/Si interface from SIMS depth profiles and deposition rates of Si0 2 films as a function of oxygen plasma treatment time
Fig. 4. Infrared absorption spectra of oxygen p
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