| 摘要: | 為延續摩爾定律，矽基半導體近年不斷朝向尺寸微縮的方向發展，雖然達到效果，但隨之而來的便是尺寸微縮所帶來的短通道效應、穿隧效應、靜電效應、高接觸阻抗等問題。在這樣的條件下，二維材料便成為了理想的選擇，因為其具有表面沒有懸鍵、厚度僅有數個原子層、載子遷移率不隨厚度變化等優勢，可有效因應目前的困境，因此二維材料也被視為下世代的電子元件材料，而在眾多二維材料中又以過渡金屬硫化物最受矚目，其中二硫化鉬更因可調節能隙及良好的傳輸特性備受關注。
在電晶體應用上由於金屬與半導體材料接觸時會產生費米能階釘扎效應(Fermi-level pinning effect, FLP)；在電子穿隧時會產生蕭特基能障(Schottky barrier)，為了改善這些因不同材料接觸所帶來的接觸阻抗問題，於是便衍生了相位工程(Phase engineering)、邊角接觸(Edge contact)、凡德瓦接觸(Van der Waals)、嵌入緩衝層(Inserting buffer layer)、間隙狀態飽和(Gap-state saturation, GSS)、分子或化學摻雜(Molecular/chemical doping) 等諸多研究方向。
本研究將分成兩部分對雙層硫化鉬進行探討，第一部分針對雙層元件製備的轉印製程進行探討，會分為乾轉印雙層薄膜以及濕轉印雙層單晶兩種不同轉印製程，接著透過拉曼(Raman)、光致發光(Photoluminescene, PL)光譜進行分析，並製作元件探討轉印製程對電性的影響；第二部分則聚焦於氫電漿對二硫化鉬的改質，利用氫電漿對雙層二硫化鉬進行低損傷轟擊，透過氫原子與硫原子的鍵結將上層表面的硫原子剝除，使上層的鉬原子裸露出來，接著用蒸鍍製程沉積金屬電極，使金屬與鉬原子直接接觸，達成金屬-金屬的接觸，藉此降低接觸阻抗達到提升元件性能的目的，透過後續的穿透式電子顯微鏡(Transmission electron microscope, TEM)、原子力顯微鏡(Atomic Force Microscope, AFM)等材料分析方法確認是否成功達成選擇性的硫剝除，並確認鉬原子是否受到損傷，最後進行電漿改質對雙層元件電性表現影響的探討。
經過真空電性量測證明電漿處理後導通電流較處理前提升5倍，由0.137µA/µm升至0.682µA/µm，開關比也提升約0.5個數量級，載子遷移率提升約6.95倍，次臨界擺幅也下降63.16%，足可以證明此項製程對雙層元件電性的有效提升。
;To continue Moore′s Law, silicon-based semiconductors have increasingly focused on size reduction in recent years. Although this approach has yielded considerable results, it has also introduced problems such as short channel effects, tunneling effects, electrostatic effects, and high contact resistance. Under these conditions, two-dimensional (2D) materials have emerged as an ideal choice due to their advantages, including the absence of dangling bonds on the surface, a thickness of only a few atomic layers, and carrier mobility that does not vary with thickness. These properties make 2D materials effective in addressing current challenges, and they are thus considered the next-generation electronic component materials. Among the many 2D materials, transition metal dichalcogenides (TMDs) are particularly noteworthy, with molybdenum disulfide (MoS2) receiving significant attention due to its tunable bandgap and excellent transport properties.
In transistor applications, the Fermi-level pinning effect (FLP) occurs when metals contact semiconductor materials, and Schottky barriers form during electron tunneling. To address the contact resistance issues arising from different material contacts, several research directions have emerged, including phase engineering, edge contact, Van der Waals contact, inserting buffer layers, gap-state saturation (GSS), and molecular/chemical doping.
This study investigates bilayer MoS2 in two parts. The first part examines the transfer process for fabricating bilayer devices, comparing dry transfer of bilayer films and wet transfer of bilayer single crystals. Raman spectroscopy and photoluminescence (PL) spectroscopy are used for analysis, and devices are fabricated to study the impact of the transfer process on electrical properties. The second part focuses on modifying MoS2 with hydrogen plasma, using low-damage bombardment to remove sulfur atoms from the surface of the upper layer by bonding hydrogen atoms with sulfur atoms. This exposes molybdenum atoms, allowing direct contact with metal electrodes via evaporation, achieving metal-metal contact to reduce contact resistance and enhance device performance. Subsequent materials analysis methods, including transmission electron microscopy (TEM) and atomic force microscopy (AFM), confirm the selective removal of sulfur and assess any damage to molybdenum atoms. Finally, the study evaluates the impact of plasma modification on the electrical performance of bilayer devices.
Vacuum electrical measurements demonstrate that after plasma treatment, the on-state current increases fivefold from 0.137 μA/μm to 0.682 μA/μm, the on/off ratio improves by about 0.5 orders of magnitude, carrier mobility increases by approximately 6.95 times, and the subthreshold swing decreases by 63.16%, proving the effectiveness of this process in enhancing the electrical performance of bilayer devices. |
