BEOL Cu CMP Process Evaluation for Advanced Technology Nodes

The back end of the line (BEOL) copper (Cu) interconnect line width and spacing is decreasing with each advancement in technology node. It is important to understand how the decreasing dimensions will impact BEOL chemical mechanical planarization (CMP) process. This study is focused on evaluation of Cu CMP using three categories of slurry formulations (i.e. alumina abrasive, silica abrasive and abrasive-less) by utilizing test structures with dimensions relevant to sub-20 nm technology. The results presented in this study show the key factors driving the performance of slurry formulation (e.g. liner selectivity, defects) are strongly dependent on the copper (Cu) interconnect line width and spacing. The results show the blanket rate selectivity does not translate to equivalent selectivity on patterned structures. In addition, the slurry formulations lost selectivity to liner as interconnect width/spacing is reduced from 40 nm to 32 nm highlighting the need to account for pattern density when predicting selectivity. Furthermore, evaluation of Cu CMP slurry formulations with cobalt (Co) liner indicates that existing formulations exhibit no Cu to Co selectivity. Overall, the results on multiple interconnect dimensions from this study are very important for researchers focused on slurry formulation development and CMP modeling.