在元件尺寸不斷微縮下，傳統的矽基電晶體逐漸達到其物理極限，短通道效應造成的元件效能下降亟需解決，因此近年研究著重在尋找能夠取代矽的新興通道材料。過渡金屬二硫屬化物中的二硫化鉬具有接近矽的能隙，以及本身極薄的厚度等特性，在元件微縮的發展上極具優勢。然而二硫化鉬電晶體會受到金屬誘發間隙態的影響，產生強烈的費米能階釘扎現象，因此面臨到非常高的接觸電阻，嚴重降低元件的性能。
為了改善二硫化鉬電晶體的高接觸電阻，本論文探討使用半金屬作為接觸金屬，利用半金屬在費米能階附近之態密度趨近於零的特性，抑制金屬誘發間隙態，進而降低二硫化鉬電晶體的接觸電阻以提升整體元件表現。首先，本論文探討了半金屬銻和一般金屬鈦作為二硫化鉬電晶體金屬接觸的差異，並確認了在頂部接觸的元件中，半金屬銻有較低的接觸電阻，且蕭特基能障為接近理論值的360meV，顯示半金屬銻能夠減緩費米能階釘扎效應。接著，我們使用過氧化氫蝕刻，成功製作出具有邊緣接觸且頂部接觸長度為40奈米之混合接觸元件，並證實此混合接觸元件中，半金屬銻的接觸電阻仍然低於一般金屬鈦。在這兩種接觸方式中，半金屬銻之最大開電流以及接觸電阻都非常接近，而一般金屬鈦混合接觸元件之接觸電阻卻高達頂部接觸元件的50倍，顯示半金屬銻在降低二硫化鉬元件的接觸電阻以及元件微縮方面皆具有非常高的潛力。
為了再更進一步降低半金屬銻接觸元件的接觸電阻，本論文採用快速熱退火製程，期望移除二硫化鉬表面吸附物，並改善金屬接觸和二硫化鉬的介面。將元件個別經過400°C、450°C以及500°C退火30秒後，透過電性及材料分析，確認400°C和450°C退火之元件的場效載子遷移率皆提升，且接觸電阻都大幅降低，其中以450°C退火之元件表現最好，單一顆元件的最低接觸電阻達到1.3kΩ·μm。但是500°C退火之元件因為覆蓋金屬鋁發生了嚴重的擴散，且有可能和二硫化鉬形成了部分的一般金屬鋁的接觸，因此接觸電阻反而提升。
本研究證實半金屬銻作為二硫化鉬電晶體接觸金屬之優勢，且透過適當的退火條件能夠再進一步降低接觸電阻，期望未來能將二維材料成功應用於先進元件中。
關鍵字：二硫化鉬、二維材料、接觸電阻、半金屬、快速熱退火

As the size of transistors continue scaling, silicon-based transistors are approaching their physical limits, necessitating solutions to the performance degradation caused by short-channel effects. Recent researches have focused on finding new channel materials with the potential to replace silicon. Molybdenum disulfide (MoS2), a transition metal dichalcogenide, features a bandgap comparable to silicon and an extremely thin structure, making it advantageous for device scaling. However, MoS2 transistors are significantly affected by metal-induced gap states, which lead to severe Fermi level pinning and consequently high contact resistance, adversely degrades device performance.
For the purpose of reducing the high contact resistance of MoS2 transistors, this study explores the use of semimetal as contact metal, leveraging their near-zero density of states around the Fermi level to suppress metal-induced gap states and thereby reduce contact resistance, enhancing overall device performance. Initially, the differences between the semimetal antimony and titanium as metal contacts for MoS2 transistors were investigated, confirming that the semimetal antimony exhibits lower contact resistance in top-contact devices, and the Schottky barrier height is 360meV, which is close to the theoretical value, indicating that semimetal antimony can reduce the Fermi level pinning effect. Subsequently, we successfully fabricated hybrid contact devices with edge contacts and a top-contact length of 40nm using hydrogen peroxide etching. It was further demonstrated that the contact resistance of the semimetal antimony in hybrid contact devices remains lower than that of titanium. In both contact configurations, the on-state current and contact resistance for the semimetal antimony were comparable, while the contact resistance for the titanium hybrid-contact device was fifty times greater than that of the top-contact device. These results highlight the significant potential of semimetal antimony in reducing contact resistance of MoS2 transistors and facilitating device scaling.
To further reduce the contact resistance of the semimetal antimony devices, rapid thermal annealing was employed to remove surface adsorbates from the MoS2 films and improve the metal-MoS2 interface. Devices were subjected to annealing at 400°C, 450°C, and 500°C for 30 seconds. Electrical and material analyses confirmed that the field-effect mobility of the devices annealed at 400°C and 450°C was enhanced, with their contact resistance significantly reduced. Notably, the devices annealed at 450°C exhibited the best performance, achieving a minimum contact resistance of 1.3kΩ·μm. In contrast, the 500°C annealed devices exhibited increased contact resistance due to severe diffusion of the capping metal aluminum, which potentially formed partial aluminum contacts with MoS2.
This research substantiates the advantages of utilizing semimetal antimony as a contact metal for MoS2 transistors, and demonstrates that appropriate annealing conditions can further reduce contact resistance. It is anticipated that in the future, two-dimensional materials will be successfully applied in advanced devices.
Keywords: Molybdenum disulfide, two-dimensional materials, contact resistance, semimetals, rapid thermal annealing.

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