以電化學原子層沉積法於TaN/Ta基板上製備銅薄膜之熱穩定性研究

Thermal Stability of Copper Film Prepared on a Tantalum Nitride/Tantalum Substrate by Electrochemical Atomic Layer Deposition

陳建豪(Jain-Hao Chen)

指導教授 ： 方昭訓

國立虎尾科技大學/工程學院/材料科學與綠色能源工程研究所/碩士(2015年)

https://doi.org/10.6827/NFU.2015.00109

摘要

銅連導線具有良好的抗電致遷移率及高導電性，已經廣泛應用在超大型積體電路。但銅薄膜容易擴散進入矽晶片，造成深層能階。因此，需要在銅連導線與矽基板中間加上擴散阻障層，以防止銅擴散。隨著元件進入奈米級，高深寬比孔洞需要解決薄膜沉積階梯覆蓋性問題，本實驗之電化學原子層沉積 (Electrochemical Atomic Layer Deposition, EC-ALD) 所製備原子層級薄膜，可有效解填洞問題及改善階梯覆蓋率，更具潛力應用於半導體銅製程。
　　本研究先利用濺鍍法製備TaN (10 nm)/Ta (5 nm)/Si薄膜作為擴散阻障層，再利用欠電位沉積法 (Underpotential deposition, UPD) 鍍上一層鉛鍍層作為犧牲層，接著通入銅溶液，在開路電位的環境下進行表面侷限氧化還原取代反應 (Surface limited redox replacement, SLRR)，銅離子將取代鉛而形成一層銅薄膜。由於鉛鍍層小於一原子層，後續銅置換形成之鍍層也小於一原子層。藉由控制上述步驟之循環次數，即可得到適當厚度之銅薄膜。銅薄膜後續經熱處理後探討其熱穩定性與電性質。以表面輪廓儀 (α-step) 測量薄膜厚度、四點探針 (FPP) 分析電性、X光繞射儀 (XRD) 進行相鑑定、場發射掃描式電子顯微鏡 (FE-SEM) 觀察表面形貌以及使用歐傑電子能譜儀 (AES) 進行縱深成分分佈分析。
　　實驗結果顯示，當鍍液pH值為3.5，Cu以 -1100 mV之還原電位沉積60秒做為晶種層，Pb以 -1150 mV沉積30秒作為犧牲層，為最佳參數設定，初鍍膜具有最低電阻係數7.5 μΩ cm.，沉積速率為1.09 ML/cycle。其在快速高溫退火爐 (RTA) 氬氣+氫氣 (95%+5%)，熱穩定性可達650℃。

關鍵字

銅 ； 氮化鉭 ； 擴散阻障層 ； 電化學原子層沉積 ； 欠電位沉積 ； 表面侷限氧化還原取代反應

並列摘要

Copper has been used as interconnects in ultra-large scale integrated (ULSI) because Cu has a high resistance to electromigration and high electrical conductivity. Generally, Cu interconnection needs a barrier to prevent Cu diffusion due to the fast diffusion of Cu into Si will introduce deep level traps. Furthermore, high-aspect trench/hole makes deposition of a conformal film more difficult as the device continuously scaling down. The Electrochemical atomic layer deposition (EC-ALD) used in this study is highly potential for application in Cu interconnection.
TaN (10 nm)/Ta (5 nm) thin films, as a barrier, were deposited on a silicon substrate by sputtering. Cu thin films were then deposited by EC-ALD. The first Cu seed layer was performed by underpotential deposition (UPD), and a layer of Pb was applied by UPD for use as a sacrificial layer. Finally, the next Cu monolayer was prepared by replacing Pb through a surface limited redox reaction (SLRR). The cycle was repeated 50 times to form a thick film. The sample was annealed at 300-800°C in Ar + H2 (95% + 5%) for 5 minutes. The resistance of the films was measured by four-points probe (FPP). The thickness of films was measured by surface profiler (α-step) and crystal structure was analyzed by X-ray diffraction (XRD). The surface morphology was observed by field-emission scanning electron microscope (FE-SEM) and the depth profiling was analyzed by Auger electron spectrometer (AES).
The results showed that optimal parameters can be obtained at UPD of Cu: -1100 mV, Pb: -1150 mV at a solution of pH 3.5. The lowest resistivity was 7.5 μΩ cm and the deposition rate was 1.09 ML/cycle for as-deposited film. The results showed that film is thermally stable up to 650 °C / 5 min.

並列關鍵字

Copper ； Tantalum nitride ； Barrier ； Electrochemical atomic layer deposition (EC-ALD) ； Underpotential deposition (UPD) ； Surface limited redox replacement (SLRR)

參考文獻

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