藉由3ω法探討sp3/sp2鍵結比 對類鑽碳薄膜結構與熱導性之影響

Abstract

隨著元件微縮與高功率密度的發展趨勢，熱管理逐漸成為限制電子元件效能與可靠度的重要挑戰。類鑽碳薄膜（Diamond-Like Carbon, DLC）因具備高熱穩定性、機械強度與結構可調性，在高熱導絕緣材料的應用上展現高度潛力。本研究使用感應式耦合型電漿輔助化學氣相沉積系統（ICP-CVD）於低熱預算（300~400 °C）條件下沉積DLC薄膜，並搭配掃描式電子顯微鏡（SEM）、拉曼光譜儀、X光光電子能譜儀（XPS）與本實驗自製之3ω熱導率量測系統，探討DLC薄膜厚度、sp²/sp³結構比例與熱導率之間的相互關聯。 在沉積製程方面，透過電漿裂解乙炔氣體作為碳源，並調控氣體流量與沉積時間，以實現厚度與結構可控的DLC薄膜。結果顯示，當乙炔氣體流量提高與沉積時間延長時，DLC薄膜厚度顯著增加，其中以乙炔流量5 sccm、生長時間5分鐘條件所製備樣品最厚。結構分析部分，透過拉曼光譜與XPS技術進行定量分析，確認在高流量條件下，薄膜sp³含量較高，且隨沉積時間拉長，sp²含量逐漸上升。本研究成功製備出sp²/sp³比例變化明顯之樣品組，並觀察到以乙炔流量5 sccm、生長時間30秒條件所成長之樣品具有最低的sp²/sp³比例，顯示結構最接近sp³主導的類鑽碳特性。 熱導率量測方面，透過微影製程將寬度10 μm、長度5 mm之金屬加熱器（200 nm Cu / 10 nm Ti）沉積於樣品表面，並根據文獻指標進行設計。為驗證量測系統準確性，使用藍寶石基板與PECVD生長之SiO₂薄膜進行校正。藍寶石基板熱導率量測值為23.56 W/m·K，與文獻值（25.8 W/m·K）誤差約8.56%；SiO₂薄膜則透過厚度依賴性與介面熱阻回推其本徵熱導率為1.643 W/m·K，與文獻值（1.5 W/m·K）相差9.5%，顯示本系統具備良好準確性。 進一步對DLC樣品進行3ω量測後發現，當薄膜厚度過薄時，介面效應對熱導率產生明顯干擾，因此需回推至本徵熱導率以進行分析。最終結果指出，DLC薄膜之熱導率與sp²/sp³結構比例密切相關，當sp²含量增加時，熱導率呈現快速下降趨勢，並於高sp²比例條件下趨於飽和。其中，乙炔流量5 sccm、生長時間30秒沉積時間所製備之樣品，具備最高熱導率與最低sp²比例，為本研究中熱傳性能最佳樣品。最終本研究亦建立熱導率與結構比例之擬合模型，可用於預測不同成分下DLC薄膜的熱傳行為，為後續功能性碳薄膜材料的設計與應用提供實驗基礎與數據支持。

As electronic devices continue to scale down and power density increases, thermal management has emerged as a critical challenge limiting device performance and reliability. Diamond-Like Carbon (DLC) films, known for their high thermal stability, mechanical strength, and tunable structural properties, have shown significant potential as high thermal conductivity insulating materials. In this study, DLC thin films were deposited using an Inductively Coupled Plasma-Enhanced Chemical Vapor Deposition (ICP-CVD) system under low thermal budget conditions (300–400 °C). The thickness, sp²/sp³ ratio, and thermal conductivity of the films were systematically investigated using Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and a custom-built 3ω thermal conductivity measurement system. The films were deposited by plasma-assisted decomposition of acetylene gas, with variations in gas flow rate and deposition time to control film thickness and structure. The results indicated that higher acetylene flow rates and longer deposition times led to increased film thickness, with the thickest DLC obtained under C2H2 5 sccm for 5 minutes growth time. Structural analysis revealed that higher gas flow led to a lower sp²/sp³ ratio, while longer deposition times increased sp² content. Among all samples, the DLC film deposited at C2H2 5 sccm for 30 seconds growth time exhibited the lowest sp²/sp³ ratio, indicating a highly sp³-rich structure. For thermal measurements, metal heaters composed of 200 nm Cu and 10 nm Ti were fabricated on the samples via lithography, with dimensions of 10 μm in width and 5 mm in length, consistent with established standards. The accuracy of the 3ω system was validated using sapphire substrates and PECVD-grown SiO₂ films. The measured thermal conductivity of sapphire was 23.56 W/m·K, showing an 8.56% deviation from the literature value (25.8 W/m·K), while the intrinsic thermal conductivity of SiO₂, back-calculated using thickness dependence and interface resistance models, was 1.643 W/m·K, with a 9.5% deviation from the reported 1.5 W/m·K. Thermal conductivity measurements of DLC films revealed that thin films were significantly affected by interface thermal resistance, requiring back-calculation to estimate intrinsic values. A clear correlation between thermal conductivity and sp²/sp³ ratio was observed: as the sp² content increased, thermal conductivity rapidly decreased and eventually saturated. The highest thermal conductivity was found in the sample deposited at C2H2 5 sccm for 30 seconds growth time, which also had the lowest sp² content. A fitting model was developed to predict the thermal behavior of DLC films based on their structural composition, providing a foundation for future design and application of functional carbon-based thermal materials.