超大橫向長晶應用於多晶矽鍺薄膜電晶體之研究

Abstract

在此論文裡，我們以準分子雷射結晶法為基礎，探討超大橫向長晶對於多晶矽鍺薄膜電晶體電特性的影響。依據結晶結構以及元件通道材料兩個觀點去改善多晶矽鍺薄膜電晶體之特性。 矽原子與鍺原子具有不同的溶點以及4%差異的晶格常數。這結果會造成鍺原子的偏析和矽鍺薄膜的應力。這兩者可借由拉曼頻譜來決定晶粒中合金的組合成份以及殘留的應力。根據材料分析的結果，經過連續橫向結晶後，多晶矽鍺薄膜具有不同濃度的鍺原子分布在晶粒中，起因在於橫向結晶的期間，薄膜開始橫向長晶的位置到晶粒邊界的位置之間發生鍺原子的偏析。實驗結果，超大橫向長晶對於矽鍺薄膜應力的釋放具有很好的功效。至於結構性質也將透過原子力顯微鏡與掃描式電子顯微鏡來描述。 鍺原子的偏析會造成鍺含量高與鍺含量低兩種區域。當鍺濃度逐漸增加地分佈在電晶體的通道之中會造成通道能隙的改變。鍺含量高的區域相對於鍺含量低的區域具有較低的價電帶。假如鍺含量高的區域落於源極處，將會加速電洞的排出而改善浮體效應。因為浮體效應的改善，扭結效應也會改善。

In this thesis, based on the excimer laser crystallization technique, the influences of the super lateral-growth crystallization on the electrical characteristics of polycrystalline SiGe thin film transistors have been investigated. From the two viewpoints of crystallization structure and channel material have been proposed to improve the performance of polycrystalline SiGe TFTs. Si and Ge atoms have different melting point and 4% difference in the lattice constants. The results to make the Ge segregation and the strain of SiGe thin film. Both the alloy composition and residual strain in the grains were determined from the Raman shift. According to the material analysis results, poly-Si1-xGex thin film can be grading the Ge content across the grain after sequential lateral solidification due to the Ge segregation occurs at film initiate later growth to the grain boundary during lateral-growth crystallization. The experimental results are in good agreement with the strain relaxation of SiGe thin film by the super lateral-growth crystallization. Structural properties were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The Ge segregation to make the Ge-rich and Ge-poor region. By grading the Ge content across the transistor channel region, the band gap will be different. The Ge-rich region has lower valence band than Ge-poor region. If the Ge-rich region at the source, the floating body effect will be improve by accelerate the hole emission. The kink effect will be improve due to improve the floating body effect.