| Summary: | 碩士 === 國立交通大學 === 電子工程系 === 90 === High-performance low-temperature polycrystalline silicon thin film transistors fabricated by metal induced lateral crystallization (MILC) method have been widely studied. But, all related papers just discuss the effects of MILC method on the performance of poly-Si TFTs. However, from experiments we find that the dimension of device, the active layer thickness, the dimension of nickel pattern, the distance between channel region and nickel pattern would also affect the performance of poly-Si TFTs. Additionally, MILC with post excimer laser annealing (ELA) called L-MILC method will also be investigated. In this report, these effects will be discussed and a reasonable model will be proposed to explain them.
First, we stepped in the material analyses of the MILC poly-Si thin films. According to the optical microscopic inspection, we find that the thickness of a-Si thin film and the dimension of the nickel pattern would affect the crystallization rate of MILC. From the micro-Raman spectrographs, we find that the thickness of a-Si thin film, dimension of nickel pattern and the distance from nickel pattern also influence the crystallinity of poly-Si thin film. On the other hand, from the TEM analysis, the crystallinity would obviously increase as the selected region shrunk. It means that MILC poly-Si thin film has excellent crystallinity in the local areas. Moreover, from cross section TEM image, it is obviously that the thickness of a-Si thin film would affect the orientation of grain growth and the micro structure of the poly-Si tihn film. We also find that low-angle grain boundaries exhibited between grains and few amorphous residues remaining in the poly-Si thin film from the SEM image after Secco etching. In addition, amorphous residues would increase with the distance from the nickel pattern. When we introduce L-MILC method, such misoriented grains are merged and the defects can be eliminated. As the occurrence of large-scale vertical regrowth, giant grain sizes are achieved at least 10um from SEM graphs.
Then, high-performance and high-uniformity poly-Si TFTs are fabricated according to the results of the material analyses. Mobility of the n-channel MILC TFTs can attain to 80 cm2/V*s. For TFTs with post excimer laser annealing, the mobility would attain to above 250 cm2/V*s.
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