超臨界流體技術應用於新穎式透明非晶態氧化鋁鋅錫薄膜電晶體之研究

Abstract

選擇使用鋁錫取代銦鎵之非晶隙透明導電四元氧化物半導體，當作薄膜電晶體之主動層，再利用超臨界流體同時具有氣體高擴散性與液體高負載能力，將氧化劑帶入濺鍍沉積的薄膜內，成功地在150°C低溫的環境下鈍化薄膜內的缺陷，改善非晶態氧化鋁鋅錫薄膜電晶體的電特性，並藉由一系列可靠度分析與材料分析的探討，驗證薄膜電晶體效能之提升。 先是分析材料的變化趨勢，經過退火(Thermal Annealing)、超臨界流體(Supercritical Fluid)、水氣(H2O Vapor)三種後製處理後，薄膜的材料成分與表面狀態並沒有受太大影響。再來是元件可靠度分析，在基本電性方面，經過退火後再做超臨界流體處理的元件特性，相較於其他處理有明顯改善，進而萃取出的缺陷能態密度(Density of states)也因此有大幅下降。緊接探討環境穩定性，經過一個高溫450°C退火的元件可降低對環境中水氧之吸附；在常壓與真空環境下做電性可靠度測試(Gate bias stress)，元件皆較不受閘極負偏壓應力(Negative Gate bias stress)的影響，而經過超臨界流體處理後的元件，在閘極正偏壓之劣化程度最小；最後是對光敏感度量測(Illumination)，元件皆不受可見光範圍之波長影響，但在照光環境下做閘極負偏壓應力測試(Negative bias illumination stress)，元件都有受到劣化，但經過超臨界處理的元件受影響程度最小。 最後，使用氫電漿處理在主動層(Active Layer)、閘極絕緣層(Gate Insulator)，與兩層都處理，成功降低原本元件的退火溫度，從450°C到300°C。

Quaternary compound semiconductors which had no indium and no gallium were chose as active layer of thin film transistors. In this study, a-AlZnSnO was chose. Due to supercritical fluid simultaneously possess gas-like high diffusivity and liquid-like high density; oxidant was carried into thin films which were deposited by supercritical fluid. It was used to successfully terminate the defect states in thin films at 150 °C, and the quality of thin films were improved. Furthermore, electrical stability and material analysis were used to verify that a-AZTO TFTs performances were improved. Frist, material components and surface structure of a-AZTO thin films were scarcely changed by thermal Annealing, supercritical fluid, and H2O vapor post-treatments. Next, basic electrical characteristics of a-AZTO TFTs were enhanced by supercritical fluid, and H2O vapor post-treatments. Effect of H2O and oxygen molecules were adsorbed on the backchannel of a-AZTO TFTs, which was decreased by a high temperature 450 °C thermal annealing. The a-AZTO TFTs were scarcely affected under negative gate bias stress. After supercritical fluid post-treatment, the migration of threshold voltage shifts was smaller under positive gate bias. Finally, treated a-AZTO TFTs were scarcely affected under illumination. Nevertheless, threshold voltage was shifted under negative bias illumination stress, and a-AZTO TFTs were treated by supercritical fluid post-treatment had the smallest threshold voltage shifts. At last, active layers, gate insulators, and both of layers of a-AZTO TFTs were treated by hydrogen plasma. That was successfully that decreased the post-annealing temperature from 450 °C to 300 °C.