| 摘要: | 二維材料具原子層級厚度與具有良好的電性表現，在先進奈米元件與柔性電子中展現高度潛力。其中，過渡金屬二硫化物（TMDs）中的二硫化鉬（MoS2），因具直接能隙與優異機械與熱穩定性、高載子遷移率，成為次世代半導體材料的研究重點。單層MoS2具約1.85 eV直接能隙，適用於場效電晶體(Field-Effect Transistor,FET)、感測器與光電元件。然而，傳統化學氣相沉積（Chemical Vapor Deposition,CVD）高於700°C，限制其於玻璃、聚合物等低溫基板的應用，亦不利於與半導體後段製程（BEOL）整合。BEOL中，多層金屬與介電層結構對熱極為敏感，過高溫度可能造成導線熔融或介電層崩解。因此，發展低溫、高品質、可整合於BEOL的二維材料合成技術，是當前關鍵挑戰。
本研究採用金屬有機化學氣相沉積(Metal-Organic Chemical Vapor Deposition,MOCVD)，以 Mo(CO)6與H2S為前驅物，在約350°C下於SiO2/Si基板上直接成長單層MoS2。透過不同的基板處理與不同基板，優化成核並促進晶體均勻生長。藉由控制前驅物流率、反應溫度與反應時間，成功合成具高均勻性與結晶品質之單層MoS2。PL分析顯示激子發光峰位於1.86 eV，半高寬約70 meV，對應高結晶品質；拉曼光譜中E_2g^1與A_1g兩峰間距約18 cm⁻¹，證實為單層。AFM與SEM觀察顯示薄膜厚度約0.7 nm，表面均勻連續，無明顯皺摺與孔洞，顯示製程具良好可靠性與均勻性。研究中我們利用NaCl有助降低成核能障的特性並提升MoS2尺寸，使晶粒尺寸與分布更可控，進一步提升膜質均勻性。此低溫MOCVD製程避免高分子轉印殘留與缺陷，並具製程相容性與大面積可擴展性。本研究成功在低溫MOCVD成長單層的MoS2，並證實其具與半導體BEOL製程整合之潛力，未來可應用於邏輯與記憶體整合、先進封裝與異質整合平台中。
;Two-dimensional (2D) materials, characterized by their atomic-scale thickness and excellent electrical performance, exhibit significant potential in advanced nanoscale devices and flexible electronics. Among them, molybdenum disulfide (MoS2), a type of transition metal dichalcogenide (TMD), has garnered considerable attention as a promising next-generation semiconductor material due to its direct bandgap, outstanding mechanical and thermal stability, and high carrier mobility. Monolayer MoS2 possesses a direct bandgap of approximately 1.85 eV, making it highly suitable for applications such as field-effect transistors (FETs), sensors, and optoelectronic devices.
However, conventional chemical vapor deposition (CVD) processes typically require temperatures exceeding 700°C, which limits their use on low-temperature substrates such as glass and polymers, and poses challenges for integration with semiconductor back-end-of-line (BEOL) processes. BEOL structures contain multiple metal and dielectric layers that are extremely sensitive to thermal stress; exposure to high temperatures can result in metal line melting or dielectric degradation. Therefore, developing low-temperature, high-quality, and BEOL-compatible synthesis techniques for 2D materials is a critical challenge.
In this study, metal-organic chemical vapor deposition (MOCVD) was employed to directly grow monolayer MoS2 on SiO2/Si substrates at approximately 350°C, using Mo(CO)6 and H2S as precursors. By adopting various substrate treatments and using different types of substrates, nucleation behavior was optimized to promote uniform crystal growth. Through precise control of precursor flow rates, reaction temperature, and growth duration, monolayer MoS2 films with excellent uniformity and crystalline quality were successfully synthesized.
Photoluminescence (PL) measurements revealed an excitonic emission peak at 1.86 eV with a full width at half maximum (FWHM) of approximately 70 meV, indicating high crystallinity. Raman spectroscopy showed a peak separation of around 18 cm⁻¹ between the E_2g^1 and A_1g modes, confirming the monolayer nature. AFM and SEM analyses revealed a film thickness of approximately 0.7 nm with a continuous and uniform surface morphology, free of noticeable wrinkles or voids, demonstrating the high reliability and consistency of the growth process.
In this work, we further utilized the property of sodium chloride (NaCl) to lower the nucleation energy barrier and enhance MoS2 domain size. The presence of NaCl enabled more controllable grain size distribution and improved film uniformity. This low-temperature MOCVD approach also eliminates the need for polymer transfer, thereby avoiding associated residues and defects, while maintaining compatibility with semiconductor fabrication and scalability for large-area production.
In conclusion, this study demonstrates the successful low-temperature MOCVD growth of monolayer MoS2 and validates its potential for integration with semiconductor BEOL processes. This technique holds promise for future applications in logic-memory integration, advanced packaging, and heterogeneous integration platforms. |
