非晶態氮摻雜氧化銦鎵鋅薄膜電晶體特性之研究

Abstract

非晶態氧化半導體(Amorphous Oxide Semiconductors: AOSs) 具有高載子遷移率而且可低溫沉積、可撓曲、透明性以及均勻度佳等特點已受到廣泛的重視。目前被研究的氧化半導體有ITO、IZO、TiO2、ZnO、In2O3、Ga2O3、IGO、a-IGZO等。其中以透明非晶態氧化銦鎵鋅(Amorphous InGaZnO: a-IGZO)薄膜當作主動層(Active layer)的薄膜電晶體(Thin Film Transistors: TFTs)，具有載子遷移率與可靠度比傳統氫化非晶矽薄膜電晶體(a-Si:H TFT)高、均勻性優於低溫複晶矽薄膜電晶體(Low Temperature Polycrystalline Silicon TFT: LTPS TFT)，而且可低溫製程。因此非晶態氧化銦鎵鋅薄膜(IGZO)電晶體具有取代氫化非晶矽薄膜電晶體與低溫複晶矽薄膜電晶體來製作主動矩陣有機發光顯示器(Active Matrix Organic Light Emitting Display: AMOLED)的潛力。但是氧化銦鎵鋅(IGZO)薄膜存在著一些本質上的缺點。例如對環境中的水、氧很敏感進而影響元件的穩定性。並且，氧化銦鎵鋅薄膜電晶體長時間操作的可靠度也是需要探討。文獻得知，非晶矽薄膜摻入氮後，本身對環境變得較不敏感。因此本研究中我們使用直流濺鍍(DC Sputtering)沉積氧化銦鎵鋅薄膜薄膜，並於薄膜沉積過程中混入氮氣製成非晶態含氮氧化銦鎵鋅(a-IGZO:N)薄膜，之後分別進行進行電特性與材料特性的分析與探討。 由實驗結果顯示隨著通入氮氣量增加，元件的電特性及可靠度都隨之下降。分析實驗數據我們推論電特性下降可能原因為主動層(a-IGZO:N)和介電層(SiO2)間的通道品質不穩定。藉由低頻雜訊分析儀(Low-Frequency Noise measurement)的分析結果證實通道缺陷密度隨通氮量增加而上升。之後我們選擇於薄膜沉積前先以氧化亞氮(N2O)電漿處理介電層表面，實驗結果顯示電特性獲得顯著改善。並進一步發現於薄膜沉積過程中通入適量的氮氣，可以增加薄膜的導電性，提高載子遷移率並且有效的提升元件在長時間操作下的可靠度。研究中，我們發現先以電漿處理介電層而後於氧化銦鎵鋅薄膜沉積製程通入適量氮氣形成非晶態含氮氧化銦鎵鋅薄膜電晶體，成功將載子遷移率提升至19.21 cm2/V s，因此極有潛力成為下個世代的主流顯示技術。

Amorphous oxide semiconductors (AOSs) are attracted much attention due to high mobility, low temperature deposition, flexible, transmission, and uniformity. It has been investigated of AOSs, such as ITO, IZO, TiO2, ZnO, In2O3, Ga2O3, IGO, a-IGZO, etc. Especially, the thin film transistors (TFTs) with a-IGZO thin film as active layer perform higher mobility and better reliability than conventional hydrogenated amorphous silicon TFT (a-Si:H TFT). Therefore, the a-IGZO TFTs have the potential to replace a-Si: H TFT and LTPS TFT forming Active Matrix Organic Light Emitting Display (AMOLED). However, a-IGZO there are some inherent defect, such as sensitive to water and oxygen in ambient environment thereby affect the device stability. The device reliability under GBS also has to be considered. In this work, we presents the electrical characteristics of the nitrogenated amorphous InGaZnO thin film transistor (a-IGZO:N TFT) for the first part. The a-IGZO:N film acting as a channel layer of a thin film transistor (TFT) device was prepared by DC reactive sputter with a nitrogen and argon gas mixture at room temperature. Experimental results show that TFT electric parameters and reliability degrade with increasing nitrogen flow rate due to in situ N doping method during a-IGZO:N film preparation may form an unstable interface between dielectric and channel layer and average interfacial trap density (Nt) increases with increasing nitrogen flow rate confirmed by Low-Frequency measurement analysis. For the second part, N2O plasma treatment is executed on the SiO2 dielectric surface to improve the instability behavior of the a-IGZO:N TFTs. The superior device characteristics of IGZO:N-based TFTs can be achieved. Moreover, the role of nitrogen doping has been investigated. With a proper amount of in situ nitrogen doping, nitrogen doped TFT can reduce the oxygen vacancy and total trap densities then demonstrate superior electric characteristics, improved reliability, and smaller falling-rate (FR). These results showed the application potentials of a-IGZO:N TFT device on flat panel display technology.