細間距印刷電子奈米銀導線電化學遷移及其抗性提升之研究

Electrochemical migration behavior and its improvement of printed fine-pitch Ag interconnects

鄒家弘(Tsou, Chia Hung)

指導教授 ： 歐陽汎怡

國立清華大學/原子科學院/工程與系統科學系/碩士(2016年)

摘要

隨著智慧型電子產品的發展，電子元件朝著輕薄短小的趨勢邁進，元件中的金屬導線的尺寸與間距也將隨之逐漸縮小，因此細間距導線的使用成為了主流。金屬導線的電化學遷移（ECM）是一種在高溫度，濕度和施加偏壓的使用環境中最主要的破壞機制。本研究使用間距尺寸為20至50 um印刷銀導線進行電化學遷移行為的測試，測試方法主要為恆溫恆濕偏壓測試（THB）以及滴水（WD）測試，並且藉由labview程式可以進行其漏電流隨時間變化(CVT)的即時量測。結果顯示，在細間距的銀導線的滴水測試中，電化學遷移破壞在數秒之內就會發生，而且隨著導線間距的增加，電化學遷移破壞的時間會跟著延長。由其表面微結構可觀察到在陰陽極之間會有密集的銀樹枝狀結構生成並且連接陰陽兩極。在THB測試中，其CVT曲線呈現了兩個階段，亦即潛伏期和漏電流快速上升期。此外，在有銀導線突起缺陷的位置會發生強烈的樹枝狀結構偏析，本研究進行了電場分佈的模擬與實驗結果比較。為了瞭解電子產業中常見的氯離子污染對ECM行為所造成的影響，本研究對10 mS/cm NaCl、10 mS/cm HCl、1000 μS/cm NaCl和1000 μS/cm HCl的氯離子水溶液進行了滴水測試。在氯離子水溶液的滴水測試中，陰陽極兩端之間不再有銀樹枝狀結構的生成，取而代之的是氯化銀會在銀導線的陽極端生成並且由於氯化銀的生成會消耗銀導線內部的奈米銀膠而造成導線斷路所產生的破壞。此外，本研究亦提出藉由表面處理的方法以增加銀導線對電化學遷移行為的抗性，我們使用濃度為10 mM的十二烷基硫醇酒精溶液來進行印刷製程試片的表面處理，藉由金屬導線與硫醇溶液之間的自發性反應在試片表面形成自組裝單分子薄膜（SAMs），銀導線上的SAMs層會作為其保護層並且成功增加試片的電化學遷移破壞時間，在進行SAMs處理之後，將再次分別以滴水測試以及THB測試來確認其抵抗電化學遷移破壞的能力，在WD測試中能延長電化學遷移破壞時間達約3～5倍，而在THB測試之中其電化學遷移破壞時間約為原本的兩倍。

關鍵字

電化學遷移 ； 恆溫恆濕測試 ； 滴水測試 ； 自組裝單分子層

並列摘要

With the development of intelligent electronic products, usage of fine-pitch interconnects became mainstream in high performance electronic devices. Electrochemical migration (ECM) of interconnects would be a serious reliability problem under temperature, humidity and biased voltage environments. In this study, ECM behavior of nanopaste Ag interconnects with pitch size from 20 um to 50 um was evaluated by thermal humidity bias (THB) and water drop (WD) tests through in-situ leakage current versus time (CVT) curve. The results indicate that the failure time of ECM in fine-pitch samples occurs within few seconds under WD test and it increases with increasing pitch size. The microstructure examination indicates that intensive dendrite formation of Ag through the whole interface was found to bridge the two electrodes. When samples tested in the THB test, the CVT curve exhibits two stages, incubation and ramp-up stages. Intensive dendrite formation was only observed at the protrusion of Ag interconnects due to the concentration of electric field at the protrusion of Ag interconnects. To understand the effect of chloride pollution in ECM behavior, solutions of 10 mS/cm NaCl、10 mS/cm HCl、1000 μS/cm NaCl and 1000 μS/cm HCl was used to conduct the water drop test. No dendrite was observed, however another failure mechanism caused by silver chloride may lead to open circuit. Also, this study proposed one of the approaches to prevent ECM failure by surface treatment after sample preparation. 10 mM ethanolic solutions of 1-Dodecanethiol was used to treat the samples after preparation to form Self-Assembled Monolayers(SAMs), which would act as the protective thin film for ECM failure. In WD test, the time to failure was increased to about 3~5 times longer while in THB test, it was about two times longer.

並列關鍵字

electrochemical migration ； THB test ； water drop test ； self assembly monolayer

參考文獻

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