Wafer extreme-far edge related study in BEOL (Back-End-of-Line) including BEOL chemical mechanical polishing at 28nm technology node and beyond

In this study, a robust Cu chemical mechanical polishing (CMP) process with better Cu polishing profile, lower defectivity and tighten metal line sheet resistance (Rs) control has been evaluated on a dual wafer polisher to meet the CuCMP process criteria at 28 nm node. As the metal line width kept shrinking to 28 nm node, the CMP correlated performance such as metal line resistance which resulted from the CMP induced surface erosion and dishing, defect resulted from barrier polishing and reliability. However, as the parameter was optimized to gain better performance, others related phenomenon would also be induced especially at wafer extremely far edge. The related study of wafer extremely far edge metrology issues will be introduced: First part is the description of wafer extremely far edge metrology issue. Accordingly, the hypothesis and the partition of wafer extremely far edge metrology issue will be introduced, such as the increasing Cu density which is influenced by pattern deformation around wafer extremely far edge and the different polished wafer extremely far edge topography resulted from different polishing slurry selections. Meanwhile, the metrology issue results from several processes such as Cu plating, photoresist patterning, CMP, etc. Based on mentioned studies, the wafer extremely far edge metrology issues can be solved by implementing suitable Cu plating, lithography and CMP process.