氫電漿處理銦鎵鋅氧主動層應用於大氣壓電漿輔助化學氣相沉積薄膜電晶體之研究

Abstract

傳統的薄膜電晶體存在較高的臨界電壓、次臨界擺幅與較大的操作電壓等缺點，在現今追求高效能、高精細度與低溫製程和節能的環境下，這些缺點突顯示了傳統型的薄膜電晶體已逐漸不符合這些要求。 在近幾年非晶銦鎵鋅氧薄膜電晶體得到了相當大的注目，相對傳統非晶矽薄膜電晶體（a-Si:H TFTs）有較佳的電子遷移率(>10 cm2/V•S)，較大的開關電流比(>106)，較小的次臨界擺幅，且不需像低溫多晶矽薄膜電晶體(LTPS)得經過再結晶，活化摻雜等高溫的製程步驟。低製程溫度及高穿透率使得非晶銦鎵鋅氧薄膜電晶體可以用來製造透明且具可隢性的顯示器。 為了改善非晶銦鎵鋅氧薄膜電晶體的特性，大部份的研究著重於調整參數，例如氣體的分壓、化學靶材的成分。在這篇論文的研究中，我們選擇氫電漿處理，是個好的方法在於改善開關電流比、次臨界擺幅和電子遷移率。隨著莫爾定律的演進，氧化層的厚度也越來越薄，當傳統二氧化矽厚氧化層厚度薄到1.4奈米時會導致不可避免得漏電流飆高，造成電性上的影響。因此我們採用高介電係數材料二氧化鋯來當我們的氧化層，藉此我們可以獲得較薄的等效氧化層厚度(4.05奈米)，以及較高的驅動電流，卻又不會造成漏電的上升。 在這次的研究論文裡，我們採用了大氣壓電漿輔助化學氣相沉積(AP-PECVD)來沉積我們的銦鎵鋅氧主動層。藉由大氣壓電漿輔助化學氣相沉積的幫助，我們可以不需要真空腔體或真空系統便可以沉積我們的銦鎵鋅氧主動層，因此可以降低我們的成本，提高產率，並且利用再大面積的製造上。 我們成功的藉由大氣壓電漿輔助化學氣相沉積製作出經電漿處理的主動層之非晶銦鎵鋅氧薄膜電晶體。未經過電漿處理它的電子遷移率有2.82 cm2/(V•S)，臨界電壓 1.38 伏特，次臨界擺幅 116 mV/decade，開關電流比 3.4×106。而採用經電漿處理過的銦鎵鋅氧當主動層的薄膜電晶體表現出更佳的電性，它擁有更高的電子遷移率20.12 cm2/V•S，臨界電壓 1.11伏特，更小的次臨界擺幅 93 mV/decade，更高的開關電流比 5.34×107。

Conventional thin film transistor suffered from high threshold voltage, poor subthreshold swing, high operation voltage. These shortcomings make the traditional thin film transistor does not comply with the high-performance, high-resolution, low temperature and energy conservation nowadays. In the past few years, amorphous In-Ga-Zn-O (IGZO) thin film transistors had attracted attention that compared with the conventional a-Si:H TFTs, due to its better field-effect mobility (>10 cm2/V．S), larger Ion/Ioff ratio (>106), smaller subthreshold swing (SS) and better stability against electrical stress. On top of that, compared with low temperature ploy-Si (LTPS) TFTs, the a-IGZO TFT did not need high temperature process to recrystallize and activate the dopant. Furthermore, the a-IGZO TFTs had low process temperature, high transmittance that can be applied to fabricate the full transparent TFT on flexible substrate. To improve the performance of practical a-IGZO applications, most of the studies focused on adjusting process variables such as gas partial pressure, chemical components of target. In this investigation, we chose hydrogen plasma treatment which was a good way to improve Ion/off, subthreshold swing and field-effect mobility. As the scaling to Moore’s law, it is terrible that gate oxide is so thin (1.4nm) which caused an intolerable gate leakage due to direct tunneling current. We use the high-k material ZrO2 as our oxide to achieve the thinner EOT (4.05nm) and high on current but not degrade the leakage current. In this study, we used atmospheric-pressure PECVD (AP-PECVD) to deposit our IGZO active layer. With AP-PECVD, we could deposit IGZO thin film without vacuum system, thus, it could lower our cost, improved the throughput, and applied to large area manufacturing. Successfully, we fabricated a-IGZO TFT by plasma treatment with AP-PECVD. Without plasma treatment, it exhibited comparable mobility of 2.82 cm2/V•S, VT of 1.38 V, subthreshold swing of 116 mV/decade, Ion/Ioff is 3.4×106. With the post plasma treatment on IGZO active layer, the a-IGZO TFT exhibited higher mobility of 20.12 cm2/V•S, VT of 1.11 V, lower subthreshold swing of 93 mV/decade, higher Ion/Ioff of 5.34×107.