使用氮氣中性粒子束電漿處理於大氣常壓電漿輔助化學氣相沉積製備氧化鎵鋅薄膜電晶體之研究

Abstract

具有高解析度、快速畫面更新率、大尺寸的螢幕是未來平面顯示器的趨勢，從一開始的非晶矽薄膜電晶體(α-Si TFTs)到近代的低溫多晶矽薄膜電晶體(LTPS TFTs)與非晶氧化物薄膜電晶體(AOS TFTs)，非晶矽薄膜電晶體(α-Si TFTs)雖然可以大面積製造且擁有好的均勻度但存在著較高的臨界電壓、較低的場效遷移率、較大的操作電壓及次臨界擺幅等缺點，低溫多晶矽薄膜電晶體(LTPS TFTs)有較快的反應速度、較高的場效遷移率、較佳的穩定性但也有均勻度不佳、高成本等缺點，非晶氧化物薄膜電晶體(AOS TFTs)則兼具上述二者的優點。 在本篇論文中，我們使用大氣常壓電漿輔助化學氣相沉積(AP-PECVD)來沉積氧化鎵鋅薄膜通道層，大氣常壓電漿系統是在常壓的環境下操作，因此可降低成本，且能大面積製造。 但氧化鎵鋅薄膜電晶體的電特性不如銦鎵鋅氧薄膜電晶體(IGZO TFTs)，我們透過使用中性粒子束氮氣電漿處理於氧化鎵鋅薄膜，來改善其特性。中性粒子束電漿與傳統電漿不同，它可以隔絕傳統電漿中可能對元件造成缺陷的紫外光和帶電粒子。透過中性粒子束電漿的處理，我們成功改善其漏電流、電流開關比及場效遷移率。 我們發現經500W中性氮氣電漿處理過的氧化鎵鋅薄膜電晶體擁有最佳的電特性，場效遷移率10.8 cm2/V‧S，電流開關比9.55×104，優於未處理的元件。

Whether the amorphous-silicon thin film transistors (α-Si TFTs) in the beginning, or the low-temperature polycrystalline-silicon thin-film transistors (LTPS TFTs) and amorphous oxide semiconductor thin-film transistors (AOS TFTs) in recent years. There is a tendency to have higher resolution, faster frame rate and larger panel size for the flat-panel display in the future. Although the amorphous-silicon thin film transistors (α-Si TFTs) could be applied to large area manufacturing and have nice uniformity, it still have many drawbacks like higher subthreshold voltage, lower field effect mobility, larger operating voltage and worse subthreshold swing. By comparison, low-temperature polycrystalline-silicon thin-film transistors (LTPS TFTs) have faster response speed, higher field effect mobility and better stability, but have some disadvantage like poor uniformity and high cost. The amorphous oxide semiconductor thin-film transistors (AOS TFTs) take advantages of both. In this research, we used atmospheric-pressure PECVD (AP-PECVD) to deposit Ga-doped ZnO thin film channel layer. Atmospheric-pressure PECVD (AP-PECVD) is operating under atmospheric pressure. Consequently, we can deposit large area thin film with lower cost. We used neutral nitrogen plasma to improve our Ga-doped ZnO thin film by neutral beam system, because the electrical characteristics of Ga-doped ZnO thin-film transistors aren't as good as In-Ga-Zn-O thin-film transistors'. Neutral beam plasma is different from the conventional plasma. It could eliminate ultraviolet and charged particles which might cause defects on device in conventional plasma. After neutral beam plasma treatment, we improved its leakage current, on-off ratio and field effect mobility. We found that the Ga-doped ZnO thin film transistors treated with 500W of neutral nitrogen plasma had the best electrical characteristic： field effect mobility 10.8 cm2/V‧S, on-off ratio 9.55×104, better than the initial case.