Micro-scratch reduction of replacement metal gate aluminum chemical mechanical polishing at 28nm technology node

The defectivity control of replacement metal gate (RMG) chemical mechanical polishing was important for high-k metal gate (HKMG) process. Micro-scratches of RMG CMP easily caused shorting or open of devices. In this study, the micro-scratch reduction of aluminum chemical mechanical polishing (AlCMP) has been investigated to provide solutions for preventing the formation of micro-scratches. Micro-scratches can be reduced by implementing soft pads at platen 2 and platen 3, pad cleaning chemical, and optimized post cleaning condition. Soft pads can reduce micro-scratch levels of AlCMP process, especially at platen 2. However, AlCMP with soft pads easily suffer serious dishing or erosion. Therefore, the balance between micro-scratches and dishing or erosion was crucial for pad selection of AlCMP. Besides, removal of pad stain was also important. Pad stain removed by pad cleaning chemical could get a lower micro-scratch level of AlCMP. In addition to polishing process, post cleaning process was a source of micro-scratch for AlCMP. An unsuitable post cleaning condition caused a counter effect of micro-scratch reduction.