Method for determining stability of CMP slurry

Increasing exacting requirements for defectivity during chemical mechanical planarization/polishing (CMP) process has led to an increased demand of highly stable CMP slurries. Herein, we describe a novel method to obtain values of stability ratio (SR) denoted as ‘W’, a parameter which defines the ability of slurry particles to resist agglomeration. We found that SR is independent of shear rates, is constant for a given slurry and higher the value of SR, lesser is the inclination of the slurry particles to agglomerate even under intense shear stress conditions. We conclude that for determining slurry stability, evaluation of the SR value is a much better metric than traditional methods such as zeta potential, particle size measurements etc. For a 10 wt% silica slurry depending upon conditions such as pH, addition of salts, particle size; values of SR were in the range 1.26–16.53. Based on comparison with CMP defects data, we concluded that (among the slurry samples studied) 10wt% solids, 35 nm basic pH silica slurry with no salt, having SR value 16.53 is most stable and 35 nm acidic pH silica slurry with KCl salt and 135 nm basic pH slurry having SR value 1.26 are relatively most unstable.