Evolution of Copper Oxide Damascene Structures in Cmp: Ii. Dishing and Overpolishing

Test wafers comprising damascene structures are designed and fabricated to investigate Cu dishing and oxide overpolishing. The mask design coveres a wide range of linewidths and pitches to represent such features as signal and power transmission lines and probing or wirebonding pads. Experiments are conducted to investigate the evolution of pattern profile during polishing and to determine the onset and rates of dishing and overpolishing. The effects of Cu linewidth and area fraction on the rates of pattern planarization, Cu dishing and oxide overpolishing are quantified. The effect of hardness of the composite surface on dishing and overpolishing are examined. An optimization scheme, employing particle size, particle hardness, and pad stiffness to increase MRR, to enhance the selectivity between SiO2 and Cu, and to reduce surface nonplanarity is proposed.