電漿優化之透明氧化鋁鋅錫薄膜電晶體特性研究

Abstract

近年來，非晶態銦鎵鋅氧薄膜電晶體(InGaZnO-TFT)因具備高透光性及高載子驅動電流特性，受到極大的矚目。但在降低成本與環保為訴求的技術目標下，銦鎵鋅氧組成的金屬氧化物半導體材料(IGZO)中含有稀有貴重元素-銦(In)與鎵(Ga)，未來將會受到發展的限制。因此，開發不含貴重及稀有元素(In/ Ga free)的氧化物半導體便成為工業界與學術界共同的研究目標。本研究中，我們開發出不含貴重及稀有元素(In/Ga free)的氧化物半導體---氧化鋁鋅錫(Al-Zn-Sn-O)，對非晶態氧化鋁鋅錫薄膜電晶體來進行電特性與材料特性的分析與探討。氧化鋁鋅錫薄膜的光學能隙高達3.5eV以上，僅會吸收波段小於360nm的紫外光，在可見光的波段具有高穿透性。我們先藉由改變退火的溫度來改善薄膜，進一步以不同電漿處理，來探討不同電漿處理對於薄膜修補的影響。 由實驗結果顯示隨著退火溫度增加，氧的鍵結增強，缺陷減少，元件臨界電壓變小，其他電特性也隨之改善。薄膜經過退火之後我們藉由氧氣電漿以及氧化亞氮電漿處理，修補薄膜中缺陷態的氧，更進一步增強氧的鍵結，有效的提升元件在長時間操作下的可靠度，以及長時間照光操作下的可靠度。另一方面，我們希望藉由電漿處理來降低退火的溫度，以減少製程的熱預算。研究中，我們發現低溫退火(350oC)的元件，再透過氨氣電漿處理薄膜，可以增加薄膜的導電性，提高載子遷移率，成功將載子遷移率由0.48 cm2/V s提升到1.2 cm2/V s，因此極有潛力成為下個世代的主流顯示技術。

Recently, 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). In addition, the uniformity of a-IGZO TFT is also superior to low temperature polycrystalline silicon TFT (LTPS TFT). Therefore, the a-IGZO TFTs have been widely considered to be the most promising candidate for the next generation display technology. a-IGZO TFTs showed good electrical performance, however, containing the rare-dispersive elements(In, Ga), will be an important issue for the long-term application. In this work, we developed rare elements-free oxide semiconductors--- amorphous Al-Zn-Sn-O thin film transistor (a-AZTO TFT). We investigated on the physical characteristics and electrical performance of a-AZTO TFT under temperature effect of annealing process and plasma post treatment. The higher annealing temperature could strengthen the oxygen bonding, therefore the quality of the a-AZTO film improves. The electrical performance enhanced under high temperature of annealing process, as well. Moreover, O2 and N2O plasma could oxidize the AZTO film and eliminate some of the oxygen deficient. As a result, the reliability of the devices under GBS improved significantly after O2 and N2O plasma post treatment. The optical energy gap of a-AZTO films untreated and with O2 or N2O plasma treatment were about 3.5 eV which indicated that all of the a-AZTO films were insensitive to visible light. On the other hand, the electron mobility of a-AZTO TFTs enhanced after NH3 plasma post treatment. The improved device parameters could be attributed to H+ ions doping. These results showed the application potentials of a-AZTO TFT device on flat panel display technology.