Investigation of Electrical Properties, Reliability and Uniformity Issues in Metal-Induced Lateral Crystallization Poly-Si TFTs
Wu, Yew-Chung Sermon
|關鍵字:||薄膜電晶體;複晶矽;金屬誘發側向結晶;離子佈植;電漿處理;驅入;thin film transistors;poly-Si;metal-induced lateral crystallization;ion implantation;plasma treatment;drive-in|
Low-temperature processed polycrystalline silicon thin-film transistors (LTPS TFTs) as pixel active elements and in peripheral driver circuits has been an important issue in the development of active matrix flat panel displays (AMFPDs). This dissertation studies a number of processing techniques for the high performance poly-Si TFTs. The main focus of this dissertation can be divided into four parts. Initially, continuous-wave (CW) laser crystallization (CLC) of amorphous Si (α-Si) has previously been employed to fabricate high-performance low-temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs). Unfortunately, their uniformity was poor because the shape of beam profiles was Gaussian. Therefore, α-Si film was replaced by Ni metal-induced laterally crystallized Si (MILC-Si). After irradiation by a CW laser (λ ~532 nm and power ~3.8W), it was found that the performance and uniformity of the MILCLC-TFTs were much better than those of the CLC-TFTs. Therefore, the MILCLC-TFT is suitable for application in a system on panel. Next, the effect of fluorine-ion (F+) implantation on the performance of metal-induced lateral crystallization (MILC) polycrystalline silicon thin film transistors (poly-Si TFTs) was investigated. It was found that fluorine ions minimize effectively the trap-state density, leading to superior electrical characteristics such as high field-effect mobility, low threshold voltage, low subthreshold slope, and high on/off current ratio. F+-implanted MILC TFTs also possess high immunity against the hot-carrier stress and thereby exhibit better reliability than that of typical MILC TFTs. Moreover, the manufacturing processes are simple (without any additional thermal annealing step), and compatible with typical MILC poly-Si TFT fabrication processes. As discussed in part of second, fluorine ion (F+) implantation was employed to improve the electrical performance of MILC TFTs. It was found that fluorine ions effectively minimize the trap state density, leading to superior electrical characteristics and better reliability. However, the minimum off-state currents were nearly unchanged. This might because the Ni concentration was unchanged. Therefore, in the part of third, MILC poly-Si TFTs with etching channel surface by CF4 plasma etching treatment were use to improve the electrical properties and reliability in this study. It was found that CF4 plasma etching treatment effectively minimized the trap state density, leading to superior electrical characteristics. Besides, the leakage current was also suppressed with the increase on etching time. Moreover, CF4 plasma-treated MILC TFTs also possess high immunity against the hot-carrier stress and thereby exhibit better reliability than that of conventional MILC TFTs, which is due to the storng Si-F bonds formed in the MILC poly-Si channel region. At the last part of the thesis, a new manufacturing method for polycrystalline silicon thin film transistors (poly-Si TFTs) using Ni drive-in induced laterally crystallization (DILC) was proposed. The DILC poly-Si was prepared by collision between F ion implantation and Ni film through the designed pattern into amorphous-Si (α-Si). It was found that the drive-in by F atoms effectively suppresses the nucleation of solid phase crystallization grain and reduces trap-state density, and lead to improve electrical characteristics. Moreover, the manufacturing processes are simple and compatible with MILC TFT processes.
|Appears in Collections:||Thesis|
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