化學機械研磨之清洗對銅導線電性的研究

Abstract

雖然銅導線的化學機械研磨在未來的導線製程上最具潛力的製程，然而卻還有許多待解決問題需要去克服。其中，最大的挑戰為研磨後的清洗。經過化學機械研磨後，晶圓表面會殘留大量的污染物，包括研磨過程中所使用的研磨粉體、金屬離子等等。若無有效的清洗製程去除這些污染物，則將影響元件特性和製程良率。 當使用含有粉體的研磨漿料作研磨時，粉體會大量吸附在銅導線表面。我們很難利用傳統的清洗方法去除掉。有論文中提出了使用硝酸和BTA的混合水溶液進行磨光以去除粉體 [1]。在擦光的過程中，藉由硝酸輕微蝕刻去除銅導線表面的之氧化銅鈍化層，而BTA將於銅導線表面形成Cu(Ⅰ)-BTA保護層以防止氧化銅的生成。但是，此Cu(Ⅰ)-BTA保護層會造成表面漏電卻是個未知數。本研究中，將從表面漏電去比較Cu(Ⅰ)-BTA保護層和氧化銅鈍化層對表面漏電的影響，氧化銅鈍化層可以代表著傳統銅導線化學機械研磨後銅表面的狀況。在論文中使用KOH作為磨光，然後浸泡雙氧水，以模擬無粉體，但是卻有氧化銅在銅導線表面的情形。除此之外，Cu(Ⅰ)-BTA保護層的熱穩定性和金屬螯合劑清洗液是否會破壞Cu(Ⅰ)-BTA保護層也將在本論文中討論。 銅金屬化學機械研磨後清洗另一關鍵為去除殘留在介電層表面銅離子。表面殘留大量的銅離子將造成大量的表面漏電[2] [3]。金屬螯合物具有配位基可以和過渡金屬離子形成穩定的錯合物。在本研究中，將探討三種金屬螯何物的清洗效果以及對銅腐蝕的結果。除此之外，清洗溶液若具有好的浸潤能力，則可以確保整個晶圓表面都可以被清洗的很均勻。我們也將討論此三種金屬螯合劑的浸潤能力。同時，也將探討溶液酸鹼度對螯合劑清洗能力的影響。

Although Cu CMP has being the enabling technology for multilevel Cu interconnect manufacturing, there were several challenges to its implementation. One of the serious challenges was post-Cu CMP cleaning. There will be a large amount of contaminants on the wafers after Cu CMP, including particles and chemicals from slurry, debris from the substrate which been polished and Cu residuals. As polishing with colloidal silica based slurry, there was a strong tendency of the absorption of colloidal silica on Cu surface. It was difficult to remove these chemisorbed colloidal silica by conventional chemical clean. A novel process, which was buffing with Nitric acid (HNO3) and 1H-benzotriazole (1H-BTA, C6H4N3H), could remove colloidal silica abrasives from Cu surface [1]. HNO3 would dissolve Cu oxide layer on Cu surface, while 1H-BTA would coordinate with cuprous ions to form a mono-layer Cu(Ⅰ)-BTA on the surface to prevent Cu form oxidation. However, one may suspect whether the Cu(Ⅰ)-BTA layer on Cu surface was stable for thermal and electrical bias stress or not? We would like to explore the mechanism of surface leakage for CuBTA and Cu oxide passivation on Cu surface. Cu oxide on Cu surface could be used to describe the surface condition after conventional CMP. To establish the environment of Cu oxide on the Cu surface without colloidal silica, we used KOH for buffing followed by immersing in hydrogen peroxide (H2O2). In additional, thermal stability and chemical durability of CuBTA layer would be discussed in this study. One of the greatest challenges to the Cu CMP cleaning process was the removal of residual Cu contamination from the dielectric surface. Cu ions remained on the dielectric would cause large leakage current [2] [3]. Metal chelators were known to form stable complexes with Cu ions. Because metal chelators had one or several dentates, they would react as electron-pair acceptors to form coordination compounds or complex ions with metal ions. The metal chelators in solution would form uncharged Cu-chelator complexes by coordination. In this study, three types of chelotors with different structures would be compared from their cleaning efficiency and corrosion effect. In additional, good wetting ability would ensure whole wafer surface would be coved with chelator chemicals, which made Cu ions cleaning uniformly. We also discussed the wetting ability of chelator solutions in this study. Furthermore, the effect of different pH for chelating capability would be discussed.