二維材料之轉印製程的可靠度研究及應用;Reliability Study and Applications of the Transfer Process for Two-Dimensional Materials

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題名:	二維材料之轉印製程的可靠度研究及應用;Reliability Study and Applications of the Transfer Process for Two-Dimensional Materials
作者:	呂可安;Lu, Ke-An
貢獻者:	機械工程學系
關鍵詞:	石墨烯;二維材料;轉印;六方氮化硼;Graphene;Two-dimensional material;Transfer;Hexagonal boron nitride
日期:	2025-11-12
上傳時間:	2026-03-06 19:00:15 (UTC+8)
出版者:	國立中央大學
摘要:	石墨烯(Graphene)因具備高載子遷移率、優異的熱傳導性與機械強度，自被成功製備以來便成為二維材料研究的核心。同時，六方氮化硼(Hexagonal boron nitride, hBN)具備寬能隙、化學穩定性與熱傳導性，常應用在理想的介電層或阻隔層。然而，將石墨烯與hBN導入元件製程的關鍵在於如何有效整合至功能基板，故轉印這道製程必不可少。轉印過程中常伴隨裂縫、皺褶與汙染等缺陷，因此發展高效且可控的轉印方法，對於維持材料品質並提升元件性能至關重要。本實驗利用獨有的真空壓印機進行轉印，初步將現有轉印製程更加優化：在蝕刻前利用電漿處理生長基板背面石墨烯，改善轉印後的潔淨度，並將加熱失去黏性後的熱解黏膠帶(Thermally released tape, TRT)與聚對苯二甲酸乙二酯(Polyethylene terephthalate, PET)加入緩衝層堆疊，提升轉印的完整性，並進一步調整熱壓公斤數至8公斤轉印石墨烯，使完整性與潔淨度皆可有效提升至超過99 %，片電阻降低至900 ohm/sq。此外，也進一步調整雙層石墨烯的轉印方式，將貼合第二層石墨烯至目標基板的壓力降低，避免材料破損，使片電阻可以從850 ohm/sq降低至640 ohm/sq。更利用電漿改質目標基板，增加其對材料的吸附力，無論是氧電漿或是氮電漿可提高完整性與潔淨度至超過99.5 %，並在XPS分析發現C-O與COO鍵結的強度有明顯上升，而氮電漿處理後發現產生了新的碳與氮的鍵結，顯示電漿使基板受到摻雜，產生懸鍵與石墨烯作用得到新的鍵結，增加附著力而提高完整性。再來討論石墨烯的應用：利用真空平壓法轉印至不同深寬比複雜結構中，進一步討論其貼合狀況：當深寬比為1.5×10-1時，因懸空面積占比大，有機率產生完全懸空之情況；而深寬比到3.8×10-2時，石墨烯即能夠連續無破損的轉印至圖形中，並服貼邊壁。此外，將石墨烯轉印至GaN元件作為中界層，並以Ti/Al/Ti金屬接觸，可以於低溫(700℃)轉化為TiC(111)，藉此可將元件的接觸電阻從5.12×10-5 Ω·cm2大幅降低至5.09×10-6 Ω·cm2。除此之外，也研究轉印後改質之氟化石墨烯作為元件閘極下方絕緣層，使蕭特基能障上升、理想因子降低，也發現氟化石墨烯的增加可以使元件的導通電阻及汲極飽和電流得到改善。最後討論hBN在不同生長基板的分離方法，並轉印至目標基板於評估其可靠度。 ;Graphene, owing to its high carrier mobility, excellent thermal conductivity, and mechanical strength, has become the core of two-dimensional (2D) material research since its successful fabrication. Meanwhile, hexagonal boron nitride (hBN), with its wide bandgap, chemical stability, and thermal conductivity, is widely employed as an ideal dielectric or barrier layer. A critical step for introducing graphene and hBN into device fabrication lies in their effective integration with functional substrates, making transfer processes indispensable. However, defects such as cracks, wrinkles, and contamination frequently occur during transfer, highlighting the importance of developing efficient and controllable transfer methods to maintain material quality and enhance device performance. In this work, we employed a customized vacuum lamination system to optimize the transfer process. Plasma treatment of the growth substrate backside prior to etching was used to improve post-transfer cleanliness. A buffer stack consisting of thermally released tape (TRT) and polyethylene terephthalate (PET) was introduced to enhance transfer integrity after TRT lost adhesion upon heating. Furthermore, by adjusting the hot-pressing force to 8 kg during graphene transfer, both integrity and cleanliness were improved to over 99%, while the sheet resistance was reduced to 900 Ω/sq. For bilayer graphene transfer, lowering the pressure during the lamination of the second graphene layer onto the target substrate minimized material damage, reducing the sheet resistance from 850 Ω/sq to 640 Ω/sq. Plasma modification of target substrates further enhanced adhesion; both oxygen and nitrogen plasma treatments improved integrity and cleanliness to over 99.5%. XPS analysis revealed enhanced intensities of C–O and COO bonds after oxygen plasma treatment, while nitrogen plasma treatment introduced new C–N bonds, indicating plasma-induced doping of the substrate, formation of dangling bonds, and improved adhesion through interfacial bonding. Applications of the developed transfer process were also explored. Graphene was successfully transferred onto structures with varying aspect ratios using vacuum lamination. For an aspect ratio of 1.5×10-1, suspended regions occasionally formed due to the large unsupported area, whereas at an aspect ratio of 3.8×10-2, graphene could be transferred continuously and defect-free, conforming well to the sidewalls. In addition, when transferred onto GaN devices as an interfacial layer with Ti/Al/Ti metal contacts, graphene enabled the formation of TiC(111) at a relatively low annealing temperature (700 °C), thereby reducing the specific contact resistance significantly from 5.12×10-5 Ω·cm² to 5.09×10-6 Ω·cm². Moreover, fluorinated graphene was investigated as a post-transfer modified insulating layer beneath the gate electrode, resulting in an increased Schottky barrier height, reduced ideality factor, and improved device performance, including lower on-resistance and enhanced drain saturation current. Finally, separation methods of hBN grown on different substrates and subsequent transfer to target substrates were examined to evaluate their reliability.
顯示於類別:	[機械工程研究所] 博碩士論文

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