研磨墊性質對銅化學機械研磨製程的影響

Abstract

化學機械研磨技術已廣泛地被使用在半導體製造上，此製程技術是經由研磨墊、研磨液與晶圓三者的交互作用，將晶圓表面上高低起伏的金屬層予以移除達到完全平坦化的效果。現今半導體先進製程之金屬層多達十層且金屬導線已全部採用銅製程，因此銅製程的化學機械研磨在半導體製程中扮演極重要的角色。研磨墊在CMP製程中最主要的功能是輸送研磨液，而研磨墊的性質亦會影響到晶圓上的缺陷結果，包括微刮傷、淺碟化、磨耗等；這些缺陷若是沒有加以控制，堆疊後的銅導線有可能會發生短路造成製程良率偏低。 此研究主要就不同材料性質的研磨墊，探討樹脂硬度、發泡孔隙密度與孔徑尺寸對銅CMP製程的影響，藉由圖案晶圓與控片量測後之實驗結果，比較不同研磨墊樣本在銅研磨移除速率、缺陷和平坦化效率結果上的差異；此外，使用後的研磨墊經由3D表面粗糙度分析儀器量測，亦可了解研磨墊表面粗糙度的變化與晶圓研磨表現之相互關係。 本論文研究結果顯示，研磨墊性質中以孔隙密度的改變對研磨移除速率和缺陷上的影響較明顯，而孔洞尺寸大小在研磨結果上沒有顯著的差異；此外，降低研磨墊的樹脂硬度對改善晶圓上的微刮傷數量有所助益。

Chemical mechanical planarization (CMP) process has been widely used in integrated circuit(IC) fabrication, by which the deposit film can be removed through the interactive process of polishing pads, slurries and wafers, and to achieve the desired surface planarity. Recently, copper (Cu) has been adopted for multilevel interconnect in the advanced technology node, instead of plasma etching, CMP is an enabling process for realized Cu interconnect manufacturing. Polishing pad plays a critical role in modulating the slurry transportation which significant affects the polishing performance. In this study, polishing pads with different resin hardness, porosity, pore size, were tested in 300mm CMP tool for polishing performance validation, including removal rates, scractching, planarization efficiency, dishing and erosion. In addition, the used pads were analyzed with 3D laserscope surface profiler, for pad surface roughness measurement. The correlation of pad roughness and polishing results were evaluated and discussed in detail. In this study, pad’s porosity shows significant effect on Cu removal rate and defectivity, but no obvious difference was found with pore size. Resin hardness of polish pad is also a dominate factor for the defectivity, reducing resin hardness is able to improve micro scratch count.