電鍍銅在化學機械研磨製程中缺陷機制的研究

Defect behaviors of electroplated copper films during chemical mechanical polishing

馮憲平(Hsien Ping Feng)

指導教授 ： 萬其超 ； 王詠雲

國立清華大學/工學院/化學工程學系/博士(2008年)

https://doi.org/10.6843/NTHU.2008.00307

摘要

這篇論文主要探討，(1)化學機械研磨時pits缺陷形成的機制與鍍層結構和雜質的關聯性(2)研磨後extrusion缺陷的氧化機制與光激發反應，這兩部份是以往論文中中較少深入研究的部份，補強對於這兩種缺陷的了解有將助於整體銅製程良率的提昇。
首先，我們改變電流密度與鍍層雜質，發現隨著銅膜(111)/(200)的比例上升，pits缺陷與研磨速率下降，證明fcc中的最密堆積的(111)在化學機械研磨時有較好的抗腐蝕性。再者，銅鍍膜的雜質愈多，pits缺陷亦會增加，但研磨速率的變化不顯著。另外，幾何效應也會造成雜質的集中進而影響到dishing的行為。
其次，extrusion缺陷是銅的氧化物且由銅晶界開始形成，會隨時間長大到一定的大小，數量也會隨時間增加。實驗結果顯示extrusion缺陷數隨著鍍層雜質增加而增加，且光照會提高費米能階以激發更多的電子而加速缺陷氧化的成長速率，還有，晶界必需有一定量的雜質才能被光機發成核成長為缺陷。

關鍵字

電鍍銅 ； 化學機械研磨 ； 缺陷機制 ； 研磨速率 ； 氧化

並列摘要

Knowledge of the defect behaviors of copper-interconnect surface is important for continuous yield improvement. This study is to focus on the defect behavior in copper damascene process, aiming at, (a) pits-formation mechanism related to structure and impurities of deposits during polishing (b) extrusion-formation mechanism for copper oxidation and light illumination after polishing.
First, we investigate the effect of current density and impurities incorporated in blanket and pattern wafer by potentiodynamic polarization method, X-ray diffraction and secondary ion mass spectroscopy. Defect count is decided by optical scan method and SEM reviewing. Removal rate and corroded pits are found to decrease with increasing (111)/(200) ratio because (111), the closed packed plane of the fcc structure, has strong chemical resistance during polishing. Furthermore, incorporated impurities, such as carbon, chloride and sulfur, tend to weaken grain boundaries to generate more corroded pits, but do not affect removal rate. In addition, geometric constraint induces concentrated impurities to restrict copper grain growth and induce fast oxide growth rate, resulting in large dishing effect on the wafer.
Second, copper-extrusion defect is initiated at grain boundary on interconnect surface and its size is enlarged with time and finally reaches a fixed value over a period of time after chemical mechanical polishing. The extrusion is composed of derivatives of copper oxide, not being observed under nitrogen environment, and increases with time after polishing. Auger analysis was used to compare the impure atoms between locations with and without extrusion, which proves that impurity is an important factor for initial growth. It has been verified that growth rate of copper-oxide extrusion increases with increasing impurity content of the copper deposit. Moreover, illumination significantly enhances and accelerates the growth rate of copper-oxide at the initial nucleation stage by providing more electron carriers and acceptors. It has also been discovered that illumination effect is related to impurities of grain boundaries, which need to be sufficiently enhanced by illumination to generate nucleation sites.

並列關鍵字

copper plating ； CMP ； defect ； removal rate ； oxidation

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