Local-topography-induced defects during tungsten chemical mechanical polishing and their impact on back end of line

As very large scale integrated fabrication technology continuously scales down, the requirements for contact tungsten chemical mechanical polishing (CMP) become more and more stringent. In this paper, we reported newly observed surface particle defects which were confirmed to be slurry particles or residues. These particles were trapped among W plugs and were difficult to be removed with existing cleaning methods and chemicals. Consequently, these particles may give rise to shorts between metal 1 (M1) and contact plugs or cause severe reliability problems, which have been directly revealed by failure analysis. A mechanism of defect-induced short was proposed. In addition, defect counts were found to have a strong correlation with tungsten plug protrusion. With the reduction of plug protrusion, defect counts decrease significantly. Oxide buff is found to be able to effectively control the local plug protrusion. However, due to the inversely proportional relationship between oxide buff and erosion, erosion may get worse if the oxide buff amount is reduced for the purpose of diminishing plug protrusion. An optimized topography before the oxide buff plays an important role in widening the process margin of the oxide buff. A correlation study of erosion and local protrusion is envisioned to be applicable to other CMP processes.