非結晶碳於複晶矽雷射再結晶之應用

Abstract

複晶矽薄膜電晶體的效能受到元件通道中的晶粒邊界（Grain Boundaries, GBs）劇烈影響，這些晶粒邊界會降低載子遷移率並增加元件關閉狀態下的漏電流。為了降低以上的效應，我們利用外加的熱儲存層（H-REC），來加大雷射退火後的晶粒尺寸，以減少元件通道中的晶界數量。首先，我們使用數值分析的方法來模擬雷射結晶時，熱流在薄膜中流動的情形。並藉由有限元素分析軟體(Femlab)來計算熱能於材料中隨時間之流動狀況，我們改變熱儲存層的吸收係數、組成成分以及結構，在不同的雷射能量下來模擬雷射退火的過程。因此，我們可以找出雷射退火結晶的最佳狀況。 含氫之非晶碳膜(a-C:H)在寬廣的波段中顯示出非常高的光學吸收性。可在許多的雷射退火機台上做為熱儲存層材料，如:準分子雷射(351nm)與固態雷射(532nm)。在研究中，我們以XeF準分子雷射搭配a-C:H熱儲存層，進行複晶矽雷射結晶。由於熱儲存層的加入，複晶矽融熔時間將因而大幅度的提升，並且可成長出較大的晶粒。而由拉曼光譜分析，最佳化的峰值的位置及半高寬分別為516.7 cm-1和3.51cm-1。由電子顯微鏡的圖像可發現外加儲熱層的矽膜具有較大的晶粒。此外，拉曼分析在本論文中亦將被用來討論a-C:H被雷射退火之後的鍵結改變。

Grain boundaries(GBs) in channel region will influence the poly-Si TFT performance severely, GBs will lower the carrier mobility and increase the off state leakage-current. In order to reduce these effects, we utilized an additional heat retaining enhanced crystallization (H-REC) layer to enlarge the grain size, which can reduce the numbers of GBs in channel region. First, we use the numerical analysis to simulate the heat flux inside the thin film during laser crystallization. With the aid of the software of finite element modeling laboratory (FEMLAB), we change the heat absorption coefficient, components, and structure of the H-REC layer to model the process of laser annealing under different laser intensity. Hence, we can find out the optimized condition for laser recrystallization. The hydrogen contained amorphous carbon film (a-C:H) shows a highly absorbent property during a wide wavelength. It can be used as an H-REC layer in several process of laser recrystallization, such as excimer laser (351nm) and solid state laser (532nm). In this study, we utilized the XeF excimer laser and the a-C:H film as the H-REC layer to process the experiment of poly-Si laser recrustalization. With the insertion of H-REC layer, the melting time of Si film and the grain size will be prolonged and enlargered, respectively. The optimized poly-Si signal of Raman spectrum, is at 516.7 cm-1and the full width at half maximum(FWHM) is 3.51cm-1. From the scanning electron microscope (SEM) images, it is found that the larger poly-Si grains will appeared with the insertion of H-ERC layer. Besides, the change of a-C:H layer is also analyzed by Raman spectrum after the laser irradiation.