銀金屬化製程與鈦基薄膜擴散阻障層之技術開發研究

本研究採用銀金屬做為半導體元件之金屬化製程的導線材料，成功開發單層導電材料(氮化鈦)薄膜，同時兼具擴散阻障層以及電鍍晶種層功能，有效放大後續電鍍銀的製程空間，克服目前銅製程在微縮孔洞填充失敗的缺點，提升製程良率。本研究透過對以原子層沉積技術(ALD)製備的氮化鈦薄膜進行表面改質，一方面採用氣體電漿進行氮化鈦薄膜表面的物理轟擊，另一方面透過化學溶液的處理，希望藉此改善氮化鈦表面潤濕性，探討銀電鍍於其上的成膜行為，對成長於氮化鈦薄膜上的銀薄膜進行結晶型態、表面形貌、電阻值以及高溫退火後之材料擴散縱深分析，以評估氮化鈦薄膜應用於銀金屬化製程之可行性。利用氣體電漿前處理的方式，透過水滴實驗量測接觸角的方式觀察表面改質效果，發現此方式可有效增加表面親水特性，我們推測氣體電漿前處理不僅一方面破壞表面原有的鍵結，提供更多銀成核位置與自由電子供後續電鍍過程銀原子的還原析出，在不需要晶種層(Seed Layer)的情況下就可以讓銀金屬直接電鍍在氮化鈦薄膜上。實驗電漿前處理結果顯示，當電漿功率在100W、持續時間為30s時，電鍍銀薄膜有較低的電阻值3.19μΩ-cm，其中氧氣及氬氣加氫氣電漿前處理對於銀薄膜有良好的熱穩定性。另一方面，我們也發現銀的成長機制也由未經電漿前處理的島狀成長的VW機制轉變成島狀加層狀的SK成長機制，這有助於電鍍銀可在極短的時間內形成連續薄膜，對於未來應用在微小孔洞填充的製程，可連續、平坦的附著在孔洞內緣。由氧氣與氬氣加氫氣電漿前處理所鍍出的銀薄膜於氮氣環境下經過550oC、30分鐘真空退火後，銀薄膜表面無任何聚集球化與破孔產生，透過縱深分析與接面二極體漏電流(junction diode leakage current)檢測結果，顯示氮化鈦薄膜可有效阻擋銀原子於高溫400~600oC的擴散。最後在銀的填洞實驗，結果顯示以底部成長方式製作金屬結構，可以避免微孔洞產生，不需花費升級現有機台或能力，因此可節省成本，在未來小尺寸金屬結構應用方面有極佳的潛力。

關鍵字

金屬導線製程技術；電鍍銀；表面改質；接面電阻；熱穩定性

並列摘要

In this study, we investigated the silver metallization technology and feasibility of Ti-based diffusion barrier for Back-end-of-Line (BEOL) interconnect application. To enlarge the electroplating process window, a single ALD-TiN film with bi-functional diffusion barrier and plating seed layer were proposed. Surface modification of TiN film using plasma bombardment is believed to change the surface energy and bonding condition for better Ag wetting during plating. The used plasma sources were selected from argon, hydrogen, oxygen and mixed argon with hydrogen gases. The surface modification of titanium nitride films were examined by water-drop contact angle measurement. We believed that plasma pre-treatment provide more nucleation sites and free electrons for silver reduction during electroplating process. Better thermal stability behaviors of silver film directly plated on TiN film were also observed when pre-treatment using oxygen plasma and mixed argon/hydrogen plasma. No agglomeration and micro voids were seen even annealed at 550oC for 30min. The electroplating Ag film properties including the crystallinity, surface morphology and electrical properties were characterized. The best result showed the lowest silver film resistance was 3.19μΩ-cm when the condition of plasma pre-treatment was 100W for 30s. Silver/TiN/SiO2/Si stacked structures annealed at elevated temperatures was used to evaluate the barrier capability and no Ag signal was detected in SiO2 layer after 550oC annealing. Depth profile analysis and junction leakage current measurement using n+/p-Si diode showed that the titanium nitride can effectively prevent silver diffusion. Bottom-up Ag electroplating approach avoids the disadvantages, pinch-off, during plating process in damascene approach and can be used in 1X and beyond interconnect technology.

並列關鍵字

Metallization technology ； Silver electroplating ； Surface treatment ； Contact resistance ； Thermal stability

參考文獻

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銀金屬化製程與鈦基薄膜擴散阻障層之技術開發研究

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