超臨界流體技術應用於非晶矽薄膜電晶體之研究

Abstract

在此論文裡，我們研究了非晶矽薄膜電晶體在超臨界二氧化碳流體混合水的熱處理下其電性的改變。非晶矽薄膜電晶體已經被廣泛的使用在液晶平面顯示器的製造上。電漿輔助化學氣相沉積用來達到在低溫下製造非晶矽薄膜電晶體，但不可避免地，非晶矽薄膜在沉積過程中因為懸鍵和晶格的錯位，會產生電性上的缺陷，這些缺陷會捕捉載子而使電流降低。而如何減少這些缺陷密度在非晶矽薄膜電晶體的製造中是很重要的。 我們發現在超臨界流體的處理下，非晶矽薄膜電晶體有較好的元件特性，其漏電流、臨界電壓和次臨界擺幅以及場效移動率都有顯著的提升。這些改善是因為氧原子護佈住了懸鍵。 為了驗證超臨界流體混合水能有效的使矽與氧鍵結，我們使用了紅外線光譜儀量測薄膜的吸收光譜。除此之外還使用了接觸角量測以及熱脫附常壓游離質譜儀來分析與比較。 這些結果均顯示，藉由超臨界流體中的氧護佈，能減少薄膜的缺陷密度。可預期的，超臨界流體的特殊特性將使其整合在TFT-LCD製程上具有其優勢。

In this thesis, the changes in electrical properties induced by heat treatment with supercritical CO2 fluid interfuse H2O are researched for amorphous TFTs. Amorphous silicon thin film transistors (a-Si TFTs) have been widely applied to fabrication of liquid crystal flat-panel display. Plasma enhancement chemical vapor deposition (PECVD) have been used for fabrication of a-Si TFTs at low temperatures. Inevitable amorphous silicon films among deposition have electrically active defect states because of dangling bonds and lattice disorder. The defects reduce electrical current due to trapping carriers. One of most important problems on fabrication of a-Si TFTs is the reduction of densities of those defect states. It is found that the a-Si TFTs after supercritical fluid passivation could achieve better device performances, including the off-current and the threshold voltage and the subthreshold swing, and also better filed effect mobility. These improvements were attributed to the oxygen atoms passivation of the dangling bonds.

In order to demonstrate the incorporation of oxygen in silicon films by the supercritical fluid passivation interfuse H2O, infrared absorption spectra were measured using fourier transform infrared spectroscopy (FTIR). In addition, contact angle and thermal desorption spectroscopy (TDS) were also been used.

These results show that the supercritical fluid passivation interfuse H2O reduces the defect density in the silicon films with oxygen incorporation. With the excellent characteristic, supercritical fluids will have advantages of integrating into the fabrication of TFT-LCD’s.