Role of the adhesion force during copper chemical mechanical planarization

The adhesion force between slurry particles and the wafer surface has a significant effect on the material removal and ultra-smooth surface formation during the chemical mechanical polishing/planarization (CMP) process. Based on zeta potentials measurements, we calculate the value of adhesion force, which cannot be ignored compared with the Hertz contact force for small sized abrasive particles at low polishing pressures. More over, the impacts of slurry (particle size and pH value) and wafer surface roughness on the adhesion force are evaluated. Theoretical analyses manifest that the adhesion force mainly originates from the van der Waals force and electrical double-layer force, which increases with the increase of the particle size and slurry pH, while decreases with the increase of the wafer surface roughness. The relationships between the adhesion force and scratch depth indicate that scratching would be avoided while enhancing the adhesion force during CMP. These findings would provide some inspirations to understand the CMP technology in depth, and they are also beneficial to engineering super-smooth and super-lubricant surfaces with nano-scaled roughness.