Copper CMP evaluation: planarization issues

This paper is focused on planarization evaluation for the copper CMP process. Two alumina slurries with different oxidizers (one hydrogen peroxide based, the other ferric nitrate based) have been evaluated and compared in terms of removal rate, uniformity, copper/oxide selectivity and especially planarization. A high removal rate and selectivity are obtained with the Fe(NO3)(3) based slurry, but planarization is very poor. This seems to be due to the copper etchant action of Fe(NO3)(3). H2O2 based slurry gives better planarization results. The evolution of the planarization versus polishing time has been studied. While the glue layer is not revealed, topologies are well planarized. But when this interface is reached extra polishing time leads to copper dishing and oxide erosion: planarization is degraded. Planarization efficiency was evaluated on different patterns (varying in copper line width and oxide space). Oxide erosion and copper dishing drastically increase with copper density. The remaining copper gets much thinner on areas where copper density is larger than 40%.