鎢奈米點非揮發性記憶體經電漿處理之
元件其製作及研究

研究生：羅元駿 指導教授：楊士禮 博士
張鼎張 博士
國立清華大學
光電工程研究所碩士班

摘要
傳統的非揮發性記憶體是利用複晶矽浮停閘(floating gate)作為載子儲存的單元，而在元件尺寸持續微縮下，此結構將面臨一些瓶頸。為了克服尺寸極限，近年來衍生出之奈米晶體非揮發性記憶體，即利用半導體或金屬奈米點作為電荷儲存的單元，可以減少穿隧氧化層的厚度，而不損失可靠性，進而降低操作電壓及操作速度增快。
金屬奈米點勝過於其他相關材料的優點，包含更高的能態密度，對通道層有更高的耦合，更佳的尺寸設計控制和更自由的功函數搭配選擇來達到最佳的電性。然而，鎢奈米點在所有金屬奈米點中最讓人感興趣，鎢有許多吸引人的優點，例如極高的熔點，很高的製程溫度使元件有優越的熱穩定性，現今超大型積體電路技術應用廣泛，使鎢奈米點非揮發性記憶體在工業上的實際可能生產。
近年來發展了許多方法來形成奈米點，一般而言，大多數的方法都需要長時間高溫的熱製程，這個步驟會影響現階段半導體製程中的熱預算和產能。而電漿處理的方法已經廣泛的應用在多晶矽的薄膜電晶體(poly-Si TFT)製程中，用來減低介面缺陷，進而改善元件的特性和提高其可靠度。因此，在本文中，一個簡單、低溫的電漿處理方法將用來改善金屬奈米點，並應用於非揮發性記憶體中。
在此論文中，將從鎢(W)金屬奈米點的製作方式出發，首先在穿隧氧化層上方沉積矽化鎢(WSi2)薄膜，當試片經過快速熱退火後，金屬鎢成分會向下在靠近穿隧氧化層附近成核析出形成鎢奈米點，同時，成份矽則氧化成二氧化矽而將鎢奈米點包圍，使成為各自獨立的儲存單元。之後，再經由不同電漿的處理，來研究鎢奈米點記憶體在不同電漿處理後的記憶效應以及可靠度分析。由電性分析得知，含有Si-H鍵結的電漿，在處理後可以有效的修補元件的介面缺陷，使鎢奈米點記憶體有更好的儲存能力。而含有Si-O鍵結的電漿，可提供充足的氧，來氧化因為快速熱退火氧化不完全的部分，進而提升奈米點記憶體的元件特性。
最後，我們將針對單元和多元的電漿氣體，對鎢奈米點記憶體的記憶窗口以及電性加以研究。由以上結果，我們將可以得到，不同的電漿處理，可提供傳統的鎢金屬奈米點記憶體不同程度上的貢獻。

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