Experimental and theoretical investigation of slurry chemical and mechanical characteristics in copper polishing

Mechanical and chemical rate characteristics of Cabot Microelectronics Corporation iCue 600Y75 and iCue EP-C7092 slurries are examined in this study on IC1000 K-groove pads. Copper polishing was performed on a 200 mm Fujikoshi polisher at polishing pressures of 1, 2 and 3 PSI and sliding velocities of 0.3, 0.75 and 1.2 m/sec. Two slurry flow rates (120 and 200 ml/min) were used. During polishing, the coefficient of friction was measured in real time and the pad leading edge temperature was measured with an IR camera. Data were subsequently modeled with a two-step chemical-mechanical removal rate model in which the reaction temperature is attributed in part to flash heating of asperities involved in pad/wafer contact. The model provides separate estimates of the chemical and mechanical rates. It was assumed that the pre-exponential factor in the Arrhenius expression for the chemical rate depends only on the slurry type and that the flash heating parameters are related only to the pad material properties. A proportionality constant in the mechanical rate, similar to a Preston coefficient, was allowed to vary independently for each slurry/pad/flow rate combination. This constrained and structured model analysis describes the observed non-Prestonian copper removal rates very well.