Copper CMP with Composite Polymer Core-Silica Shell Abrasives: A Defectivity Study

The results of copper chemical mechanical planarization (CMP) experiments with a model slurry chemistry based on the combination of glycine-water-benzotriazole (Gly-H2O2-BTA), and different types of composite A (silane coupling agents between the polymer core and the silica shell) and B (electrostatic attraction between the polymer core and the silica shell) abrasives, are presented. While the presence of BTA allows a 10-fold reduction in the static etch rate from 95 to 10 nm/min, combining an oxidizer and complexing agent leads to removal rates higher than 400 nm/min. Different surface morphology and root-mean-square (rms) roughness are observed after polishing with composite abrasives combined with different peroxide concentrations. Oxidizer concentrations as low as 0.1 vol % lead to a high nonuniformity and defectivity values. In particular, at pH similar to 6, composite B performs better than pure colloidal silica during copper CMP using the IC-1000 pad, giving a comparable material removal rate (MRR), but a better surface finish due to the contribution of the elasticity of the polymer in gently transferring the applied load to the wafer surface. Cu CMP with pure polymer particles is a promising alternative to the hard inorganic material, especially if combined with suitable surfactants that act from both particle stabilization and friction reduction/lubrication improvement perspectives. The use of a medium/high-hardness pad IC-1000 is compared to the use of a soft Politex pad. In the former case, differences in terms of MRR, rms roughness, and total defects are observed between the composite abrasives A and B; in the latter case, the behavior of the two composites is similar. In the case of a soft pad in combination with composite abrasives, there is a remarkable improvement in the defectivity without any loss in MRR.