鎳金屬誘發側向結晶複晶矽薄膜電晶體中電特性、可靠度與均勻性課題之研究

Abstract

低溫複晶矽薄膜電晶體用來製作畫素元件與周邊驅動電路已成為發展主動式平面顯示器的重要技術。本論文主要在於深入討論並製作有關高性能複晶矽薄膜電晶體的研究，主要分為以下四個部份來探討。 首先，利用固態連續波雷射將非晶矽薄膜再結晶為複晶矽薄膜已成功製作出高效能的低溫複晶矽薄膜電晶體，但是受限於雷射能量的高斯分佈而導致元件的均勻性變差。因此，我們在此提出利用鎳金屬誘發側向結晶的複晶矽薄膜取代傳統的非晶矽薄膜，接著利用不同能量的固態連續波雷射進行再結晶，從實驗的結果得知在較小的照射能量(3.8W)的條件下，就可獲得比傳統CLC結晶技術高的性能與均勻性。 在論文的第二個部份，我們探討離子佈植方式下氟離子對於金屬誘發側向結晶複晶矽薄膜電晶體的影響。從實驗的結果得知，經由氟離子佈植後的金屬誘發側向結晶複晶矽薄膜電晶體可獲得較佳的電特性，其主要原因為氟離子於複晶矽薄膜內可有效的降低缺陷密度，因而獲得較好的元件特性。除此之外，與傳統的金屬誘發側向結晶技術相較下，氟離子的佈植也可使得元件在熱載子劣化下具有較好的對抗能力，使元件具有較佳的可靠度，並且在製作的過程不需額外的熱退火。 經由論文的第二部份的實驗結果得知，利用離子佈植將氟離子植入金屬誘發側向結晶複晶矽薄膜內可使得元件特性與穩定性獲得改善，但是此方式在漏電流的方面並沒有獲得改善，其原因有可能為殘留在薄膜的鎳金屬濃度並沒有改變。因此在論文的第三個部分我們提出利用四氟甲烷(CF4)電漿蝕刻金屬誘發側向結晶複晶矽薄膜的表面，經由電漿處理後的元件也可獲得電性與可靠度的提升，其主要原因為電漿蝕刻表面後可有效的降低複晶矽薄膜缺陷密度使得元件特性提升，並且有效的產生矽氟鍵結(Si-F bond)因而改善元件的可靠度。除此之外，隨著電漿蝕刻表面時間增加，元件在漏電流方面的表現也可獲得改善。 在論文的最後一部份，我們提出一種新的製作複晶矽薄膜電晶體的技術－”鎳驅入誘發側向結晶”，主要利用氟離子佈植的方式撞擊鍍在非晶矽薄膜表面的鎳金屬，透過圖形的設計形成鎳金屬驅入側向結晶區，由此方式發現，利用氟離子驅入的過程，可有效抑制退火再結晶時所產生的固相結晶，並降低薄膜中的缺陷密度導致電晶體性能的提升。此外，在與傳統的金屬誘發側向結晶技術相較下，鎳驅入側向結晶技術的實行步驟並沒有複雜化。

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.