Planarization Efficiency of Copper Protrusion

Planarization efficiency of Cu protrusion on a 0.175/0.175 ??m feature was investigated with polishing tests on a hard pad, a medium pad, and a soft pad. Slurries with two different chemistries and two abrasive particles were formulated to study the planarization efficiency and its improvement. The results proved that the planarization efficiency of Cu protrusion decreased dramatically with decreasing pad hardness. The planarization efficiency on the hard pad was satisfactory and Cu protrusion could be reduced to near zero. The planarization efficiency on the soft pad was low and little improvement was obtained by changing the slurry formulation. The planarization efficiency on the medium pad was intermediate but could be improved significantly by changing chemistry and/or abrasive in the slurry. One of the improved slurries produced planarization efficiency on the medium pad that exceeded the planarization efficiency by a commercial slurry on the hard pad. Effect of H2O2 concentration in the working slurry on planarization efficiency on the medium pad was also observed. It was interpreted by changes in the characteristics of the protective film on Cu surface with H2O2 concentration. Keywords: Chemical-mechanical Polishing (CMP), Cu protrusion, Planarization efficiency