| 摘要: | 石墨烯具有出色的電導率和高載流子遷移率，讓其成為高效半導體材料的潛在選擇。然而，由於石墨烯本身缺乏帶隙，其開關特性不如傳統半導體，因此在邏輯電路應用中受限。此外，石墨烯與其他材料的界面控制困難，也增加了製造挑戰。相比之下，二硫化鉬 (MoS₂) 作為具有本質之能隙帶的二維材料，展現了優異的半導體特性，使其在低功耗、高效能電子元件中具備潛力。MoS₂ 的能帶有助於提升開關性能，適用於場效電晶體和光電元件等應用。但其機械穩定性和製備技術面臨挑戰，特別是在大面積製造和一致性控制上。因此，二維材料的轉印技術在克服基板限制和解決半導體製程中的高溫問題上，扮演了關鍵角色。轉印方法也在持續進步，從濕式轉印法發展到真空壓印法，後者能改善薄膜破裂和殘留問題，並適用於大面積轉印。
本實驗採用我們設計的真空奈米壓印機進行轉印。六吋載台可用於大面積轉印，其真空腔體設計和平壓貼合方式有效減少氣泡與污染，並能轉印至具有凹陷結構的材料表面。第一部分研究二維材料的大面積轉印，利用優化的實驗配置，將雙面熱解黏膠帶與玻璃基板作為二維材料的支撐層，解決了單面熱解黏膠帶支撐不足的問題，並用受熱脫附的 TRT 取代 PDMS，解決 PDMS 因老化而平坦度降低的問題。此外，氧電漿基板改質技術也增強了材料與基板的附著性。第二部分則著重於石墨烯的應用，使用真空壓印技術將石墨烯轉印至不同深寬比結構中，並透過金屬退火形成的中介層降低接觸阻抗，進而改善元件電性。同時，將石墨烯轉印至不同身寬比的金屬結構並進行氟化，可作為絕緣層以解決漏電流問題。
本研究結果顯示，利用新配置的真空壓印技術在大面積二維材料轉印方面有顯著提升。對二吋 MoS₂ 轉印，其完整性從原配置的 74.92% 提升至 94.26%，表面潔淨度由 98.82% 提升至 99.99%；對四吋石墨烯轉印而言，氧電漿蝕刻石墨烯背面可減少表面殘留，潔淨度從 97.75% 提升至 99.96%。此外，對於 MoS₂ 表面的高分子殘留和表面粗糙度，使用氫氣與氬氣混合氣體進行熱退火處理可達到最佳表面粗糙度 0.35 nm。在石墨烯於元件應用的實驗中，主要討論化合物半導體GaN的接觸阻抗改善的研究，利用真空壓印法使石墨烯能轉印至深寬比為 8.3×10⁻² 的結構中，且在水平線條蝕刻深度為 2 µm 的結構中，作為介面層的歐姆接觸電阻達到最佳值約為 10⁻⁸ Ω⋅cm²；在 2 µm 深的蝕刻圓孔圖案中，使用氟化石墨烯作為絕緣層，達到最低的漏電流關閉電流 (ID,off)，約為 7.1×10⁻³ mA/mm。
;Graphene exhibits excellent electrical conductivity and high carrier mobility, making it a promising candidate for efficient semiconductor materials. However, due to the lack of a bandgap, its switching characteristics are inferior to traditional semiconductors, limiting its use in logic circuits. Additionally, challenges in interface control between graphene and other materials add complexity to the manufacturing process. In contrast, molybdenum disulfide (MoS₂), a two-dimensional material with a natural bandgap, shows exceptional semiconductor properties, giving it substantial potential in low-power, high-performance electronic devices. The bandgap of MoS₂ enhances switching performance, making it suitable for applications such as field-effect transistors and optoelectronic devices. However, MoS₂ faces challenges in terms of mechanical stability and fabrication techniques, especially in large-scale manufacturing and consistency control. Therefore, transfer techniques for two-dimensional materials play a crucial role in overcoming substrate limitations and addressing high-temperature issues in semiconductor processes. Transfer methods have advanced from wet transfer to vacuum imprinting, with the latter helping to mitigate film breakage and residue issues while enabling large-area transfers.
This experiment uses a vacuum nano-imprinter designed by us to carry out the transfer process. The six-inch platform can be used for large-area transfers, and its vacuum chamber design and pressure-aligning method effectively reduce bubbles and contamination, allowing transfer onto surfaces with recessed structures. The first part of the study focuses on large-area transfer of two-dimensional materials. Using optimized experimental configurations, we utilize double-sided thermal release tape and a glass substrate as a support layer for two-dimensional materials, addressing the inadequate support of single-sided thermal release tape. Additionally, TRT, which is thermally desorbed, replaces PDMS to overcome the flatness issues caused by PDMS aging after repeated use. Furthermore, oxygen plasma substrate modification improves the adhesion between the material and the substrate. The second part focuses on graphene applications. Using vacuum imprinting technology, graphene is transferred onto structures with different depths, and the interfacial layer formed by annealing with metals reduces contact resistance, improving device performance. Simultaneously, transferring graphene onto metal layers of varying heights and fluorinating it enables it to act as an insulating coating layer to address leakage current issues.
The results of this study show significant improvements in large-area transfer of two-dimensional materials using the newly configured vacuum imprinting technology. For the two-inch MoS₂ transfer, the integrity increased from 74.92% in the original configuration to 94.26%, while the surface cleanliness improved from 98.82% to 99.99%. For the four-inch graphene transfer, oxygen plasma etching of the graphene backside to reduce surface residues improved surface cleanliness from 97.75% to 99.96%. In addition, for polymer residues and surface roughness on MoS₂, annealing with a hydrogen-argon gas mixture achieved an optimal surface roughness of 0.35 nm. In the experiment applying graphene to devices, vacuum imprinting enabled graphene to be transferred into structures with an aspect ratio of 8.3 × 10⁻². In structures with a horizontally etched pattern depth of 2 µm, the ohmic contact resistance of graphene as an interfacial layer reached an optimal value of approximately 10⁻⁸ Ω⋅cm². In etched circular hole patterns with a depth of 2 µm, fluorinated graphene used as an insulating layer achieved the lowest off-state leakage current (ID,off), approximately 7.1×10⁻³ mA/mm. |
