結合準分子雷射與金屬誘導方式製作低溫複晶矽薄膜電晶體之研究

Abstract

利用鎳金屬矽化物誘導側向結晶的方式來製作高效能低溫複晶矽薄膜電晶體已廣泛地被討論。但目前相關的論文均只是在討論鎳金屬矽化物誘導側向結晶的現象對於複晶矽薄膜電晶體特性之影響，而從實驗中我們發現元件尺寸、主動層的厚度乃至於鎳金屬圖樣的大小以及鎳金屬沉積區域距離元件通道的遠近與位置均會影響到複晶矽薄膜電晶體的特性。另外，我們也發現，結合準分子雷射與金屬誘導兩種方式，能更有效的改善單純以金屬誘導方式製作之複晶矽薄膜的結晶性，進而製作高性能的低溫複晶矽薄膜電晶體。在報告中，我們將就這些因素進行討論，並且對於實驗結果，提出合理的模型來加以解釋。 我們首先就鎳金屬矽化物催化側向結晶後的複晶矽薄膜做材料上分析。從顯微鏡觀察得知，非晶矽薄膜的厚度以及金屬沉積區域圖樣的形狀大小會影響鎳金屬矽化物催化側向結晶的速率；從微拉曼光譜分析上發現非晶矽薄膜的厚度、鎳金屬沉積區域圖樣的形狀大小、以及距離鎳金屬沉積區域的遠近皆會影響結晶後複晶矽薄膜的結晶性；而從穿透式電子顯微鏡影像亦發現隨著圈選區域的縮小，複晶矽薄膜的結晶性將有明顯增加，這意味著鎳金屬矽化物催化側向結晶後的複晶矽薄膜在局部的區域具有極佳的結晶性；而從縱剖面穿透式電子顯微鏡影像發現不同厚度的非晶矽薄膜厚度將影響晶粒成長的方向以及結晶後薄膜的微結構；此外，從Secco etch後複晶矽薄膜的掃描式電子顯微鏡影像中亦可發現複晶矽薄膜中晶粒間呈現低角度的晶界，且複晶矽薄膜中亦殘存些許非晶矽相，隨著距鎳金屬沉積區域越遠，非晶矽相的分布越趨增加。而從掃描式電子顯微鏡的影像中發現，當我們結合準分子雷射技術，原本存在於中的低角度晶界將相互融合，並利用大範圍的側向成長的機制，使得晶粒的大小可以達到至少10um。最後，我們將提出合理的模型解釋這些現象，並提出以鎳金屬矽化物催化側向結晶的機制。 接著我們再以材料分析上的結果作為依據，製作出具有高性能、高均勻性之鎳金屬誘導低溫複晶矽薄膜電晶體，N型通道低溫複晶矽薄膜電晶體之載子移動率可達80cm2/V*s以上，而若再結合準分子雷射處理，低溫複晶矽薄膜電晶體的載子移動率將可達到250cm2/V*s以上。

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.