藉由介面改善以優化多層石墨烯與後端製程金屬之接觸性能

Abstract

研究利用感應耦合電漿輔助化學氣相沉積系統，在相對低溫與短時間內成功成長出高品質的石墨烯，並透過精確調控成長時間，達到石墨烯厚度之準確控制。石墨烯經轉移至目標基板後，仍維持良好的結構品質與製程穩定性。此外，本研究藉由 FeCl₃ 插層技術，在不破壞石墨烯原有結構之下，透過強烈的電荷轉移作用，有效提高石墨烯的載子濃度並顯著降低其片電阻。透過插層調控費米能階位置，使石墨烯之導電特性獲得明顯提升，展現成為高性能後端互連（BEOL）材料的潛力。 在金屬緩衝層選擇上，本研究探討了不同功函數與導電率之金屬對接觸電阻之影響。實驗結果顯示，銀（Ag）具有極高導電率（6.3 × 10⁷ S/m）及低功函數（約4.26 eV），可有效使石墨烯費米能階遠離狄拉克點，大幅降低接觸電阻。此外，厚度增加之Ag緩衝層進一步提升此調控效果，且Co覆蓋層可作為有效防氧化保護層，穩定接觸品質。高功函數鉑（Pt）則透過將石墨烯費米能階推向高態密度區域，顯著改善接觸性能與穩定性。相較之下，雖然鈷（Co）具較高導電率，但其功函數不足以有效調控費米能階，致使其接觸電阻偏高，顯示金屬功函數在界面電子傳輸機制中扮演關鍵角色。 在界面品質改善方面，本研究採用熱退火處理與氫氣電漿（H₂ plasma）清潔技術，成功去除微影製程後之光阻與插層殘留物，並透過系統化調整電漿處理參數（例如100 W、30 s），達到最佳的界面潔淨效果。透過X光光電子能譜（XPS）分析可見sp³/sp²比例下降，原子力顯微鏡（AFM）亦顯示表面粗糙度降低，證實此方法可在避免石墨烯結構損傷的同時，有效提升界面品質並降低接觸電阻。

The present study successfully demonstrates the growth of high-quality graphene at relatively low temperatures and short durations via inductively coupled plasma-enhanced chemical vapor deposition. By precisely controlling growth time, accurate thickness management of graphene layers was achieved. Following transfer to the target substrate, graphene retained excellent structural integrity and demonstrated stable process quality. Additionally, FeCl₃ intercalation doping was employed, enabling a significant increase in carrier concentration and a marked reduction in sheet resistance through strong charge transfer effects without compromising graphene’s original structure. By tuning the Fermi-level position through intercalation, graphene's electrical conductivity was notably enhanced, highlighting its great potential as a high-performance back-end-of-line （BEOL） interconnect material. Regarding the choice of metallic buffer layers, the effects of different metal work functions and conductivities on graphene–metal contact resistance were thoroughly investigated. Experimental results reveal that silver （Ag）, exhibiting an extremely high conductivity （6.3 × 10⁷ S/m） and a low work function （~4.26 eV）, effectively shifts graphene’s Fermi level away from the Dirac point, significantly reducing contact resistance. Increasing the thickness of the Ag buffer layer further strengthened this modulation effect. Moreover, the addition of a cobalt （Co） capping layer effectively prevented oxidation, thereby stabilizing the contact interface quality. On the other hand, platinum （Pt）, characterized by a high work function, considerably improved the contact performance and stability by shifting graphene's Fermi level into a higher density-of-states region. In contrast, cobalt （Co）, despite its relatively high conductivity, exhibited higher contact resistance due to its insufficient work function to effectively modulate graphene's Fermi level, highlighting the critical role played by metal work functions in interfacial electron transport. To improve interfacial quality, thermal annealing and hydrogen plasma （H₂ plasma） treatments were implemented, successfully removing photoresist and intercalation residues from the lithography processes. By systematically optimizing plasma parameters （e.g., 100 W, 30 s）, optimal interface cleaning conditions were determined. X-ray photoelectron spectroscopy （XPS） analysis confirmed a reduction in the sp³/sp² ratio, and atomic force microscopy （AFM） demonstrated reduced surface roughness, verifying that this approach effectively improved interface quality and reduced contact resistance without compromising graphene structural integrity.