低熱預算後續處理製程於透明氧化物薄膜電晶體技術之應用

Abstract

近年來，透明非晶態氧化物半導體因具有高載子移動率、高透明度、室溫沉積以及可與現有顯示器製程配合等特性，普遍被認為是下個世代的顯示器主流技術之一。在眾多的氧化物半導體中，又以氧化銦鎵鋅材料最被廣為研究，然而在先前所發表的技術文獻中，氧化銦鎵鋅至少須經過300℃且30分鐘以上的退火過程，才可展現出較好的電性表現與可靠度，但是此種長時間高溫的退火製程，將會造成額外的熱能消耗以及限制此種材料的應用範圍，是故本研究提出一種可應用於氧化銦鎵鋅薄膜電晶體製程中的低熱預算退火技術-微波退火，由於微波退火技術具有：(1) 低熱預算；(2) 快速加熱；(3) 對加熱材料具有針對性，僅有會吸收微波的材料才會被加熱，因此可減少薄膜電晶體中其他材料受到高溫所造成的影響；(4) 相較於傳統退火方式，熱能是從外層傳遞至內層，會有較多的熱能損失在此過程中，微波退火技術則是直接將熱能傳遞至欲加熱之材料，除了可以減少能論損失外，也具有較佳的均勻性。…等特性，十分適合應用於氧化銦鎵鋅薄膜電晶體製程技術中。在本研究中，我們成功利用微波退火技術製作出在基本電性與可靠度方面可與傳統高溫爐管退火450℃1小時製成之氧化銦鎵鋅薄膜電晶體匹配之元件，其載子移動率高達13.5 cm2/Vs、臨界電壓為3.28 V、以及次臨界擺幅為0.43 V/decade。 雖然氧化銦鎵鋅薄膜電晶體具有良好的電性表現，然而從材料觀點出發，氧化銦鎵鋅中含有稀散元素-銦與鎵，除了會增加製程成本外，在未來的發展上也勢必會受到限制，因此開發不含貴重及稀有元素的氧化物半導體便成為工業界與學術界共同努力的目標，是故本研究也發展不含貴重及稀有金屬的氧化物半導體-氧化鋁鋅錫薄膜電晶體技術，並針對其特性進行詳細的探討。在本研究中，首先探討不同錫含量對於氧化鋁鋅錫薄膜電晶體特性的影響，而後進一步利用低熱預算的電漿處理改善薄膜電晶體的可靠度。由實驗結果顯示，利用氧電漿及一氧化二氮電漿可有效使得薄膜背通道中的錫離子氧化，並增強背通道對外在環境的抵抗性，進而改善氧化鋁鋅錫薄膜電晶體的可靠度與穩定度。此外，我們也成功的利用氫電漿處理的方式，將製程溫度由原本的450°C降低至350°C，並且保持住氧化鋁鋅錫薄膜電晶體良好的電性表現。最後，本論文利用一低熱預算薄膜缺陷鈍化技術-超臨界流體技術，改善氧化鋁鋅錫薄膜電晶體之特性，由於超臨界流體同時具有氣體高擴散性與液體高負載能力，可有效將氧化劑帶入濺鍍沉積的薄膜內，並成功地在150°C低溫的環境下鈍化薄膜內的缺陷，提升氧化鋁鋅錫薄膜電晶體的基本電特性與可靠度。

Recently, transparent metal oxide semiconductor attracts great attention due to the characteristics of high mobility, high transparency, room temperature deposited, and high process compatibility with present solid-state semiconductor technologies. Among several novel oxide semiconductors, amorphous InGaZnO (a-IGZO) thin film received considerable attention for their use in next-generation active matrix liquid crystal display (AMLCD) and active-matrix organic light-emitting diode display (AMOLED) technologies. The sputter-deposited a-IGZO active layer typically requires thermal annealing at around 300℃ for 30 min or longer to achieve a satisfactory device performance and stability. In this study, we presents a novel microwave annealing process for a-IGZO TFT fabrication with low thermal budget process. Microwave heating process can transfer the energy directly to the target materials by absorption of microwave energy throughout the volume of the material. Among its advantages include low thermal budget, rapid heating process, thermal uniformity, suppression of unexpected species diffusion, and selective heating of materials, which is impossible with the typical furnace annealing process, microwave annealing is highly promising for a-IGZO TFT manufacturing. The performance of a-IGZO TFTs with microwave annealing are well competitive with its counterpart with furnace annealing at 450℃ for 1 hour with a carrier mobility of 13.5 cm2/Vs, threshold voltage of 3.28 V, and subthreshold swing of 0.43 V/decade. Although a-IGZO TFTs performed good electrical performance, containing the rare-dispersive elements will increase the cost and be a critical issue for the long-term applications. Therefore, rare elements-free transparent metal oxide semiconductors are considered to be the promising candidates for the next generation display technologies. In this work, we developed a novel rare elements-free oxide semiconductor, amorphous AlZnSnO (a-AZTO), TFT technologies. The band-gap of a-AZTO is larger than 3.6 eV, therefore it shows high transparency in visible light region. We have investigated the effects of SnO2 content on performance of a-AZTO TFTs. Moreover, we employed the plasma treatment to enhance the electrical reliability of a-AZTO TFTs. The experiment results showed that the O2 and N2O plasma could effectively oxidize Sn in back channel of a-AZTO thin film and improve the reliability and stability of a-AZTO TFTs. Furthermore, we decreased the fabrication temperature from 450°C to 350°C by H2 plasma process and remained great performance of a-AZTO TFTs. In the end of this study, a supercritical fluid (SCF) technology is proposed at 150°C to enhance the electrical performance and reliability of a-AZTO TFTs. The SCF provides good liquid-like solvency and high gas-like diffusivity, giving it excellent transport capacity to take the H2O molecules into metal oxide films and terminate the traps in metal oxide films by the oxidization reaction.