非晶矽與微晶矽薄膜電晶體製程及其特性之研究

Abstract

本論文以電漿輔助化學氣相沉積法及陽極氧化法製造了氧化鋁/氮化矽雙 層介電層非晶矽薄膜電晶體,以用於大面積液晶顯示器. 並嘗試以微晶矽 取代非晶矽,來改善薄膜電晶體之電特性。陽極氧化鋁在此是用來疏解鋁 電極及氮化矽之間的壓應力,以防止在熱處理製程中所產生的丘狀及鬚狀 物。然而為了進一步提昇其電特性, 選擇適當的氧化鋁/氮化矽厚度比,以 得到平坦的表面形態是必要的。我們發現非晶矽薄膜電晶體的電特性與其 介電層表面形態有密切的關係,選擇最佳的氧化鋁 /氮化矽厚度,可得到最 平坦的介電層表面形態, 此時電晶體有最高的載子移動率及最佳的穩定度 。 這是由於越平坦的介電層表面可使隨後成長的非晶矽層有較佳的結構 。另外本論文亦探討了壓力對成長的磷摻雜微晶矽薄膜之影響,透過拉曼 光譜,穿透式電子顯微鏡, 傅立葉轉換紅外線光譜及電導值的量測, 我們 檢視了磷摻雜微晶矽薄膜的結構,並提出了" 離子撞擊輔助氫選擇性蝕刻" 的模型來解釋薄膜成長受壓力影響的機制。我們利用無摻雜微晶矽膜為材 料,製成薄膜電晶體, 發現它具有較低的次臨界漂移值但載子移動率亦較 低。最後,我們有系統地研究了 ,非晶矽及微晶矽薄膜電晶體的不穩定特 性。並探討了氮化矽陷阱及位階增量兩種機制。 在溫度及電壓變化下我 們發現主要的不穩定性是來自位階增量的機制。 由本論文的研究顯示,微 晶矽薄膜電晶體的電特性除了照光漏電流較低外,在各方面仍不及非晶矽, 最後我們說明了其原因及可能改善之方法。 Al2O3/SiNx double-layered dielectric films suitable for large size amorphous silicon thin film transistor liquid crystal display(a-Si:H TFT LCD) have been prepared by anodization and plasma enhanced chemical vapor deposition (PECVD). Aluminum oxide film is used as a protective interlayer to release the compressive stress between Al/SiNx interface and suppress the formation of hillocks and whiskers during heat process. A hydrogenated amorphous silicon(a-Si:H)thin film transistors with an aluminum gate electrode and Al2O3/SiNx double layered gate insulator has been developed. Phosphorus-doped microcrystalline silicon (P-doped 甥-Si:H) has been prepared by radio frequency glow discharge method Effects of pressure on the formation of microcrystalline Si film have been explored. An ion-bombardment assisted model is proposed to explain the experimental results. The static behavior of a-Si:H and Mc-Si:H TFT`s have been studied. The original physics of nitride- trapping and metastable state creation are introduced. Our results indicate that the performance of microcrystalline silicon TFTs is infer to that of amorphous silicon except the lower photo-leakage current.