Characterization of the nature of shear-induced agglomerates as hard and soft in chemical mechanical polishing slurries

The nature of agglomerates either hard or soft could determine the kind of defects created during the chemical mechanical planarization/polishing process. To understand the nature of shear-induced agglomerates, the silica slurry at different pH is subjected to high shear rate and time to form agglomerates. Subsequently, these stressed slurry samples are subjected to low shear rates 100–1000 s−1 for time 100–1000 s, corresponding to the conditions for which de-agglomeration is observed. Based on the comparison of percentage de-agglomeration in stressed versus as-received slurries, it is qualitatively shown that agglomerates formed due to shear-induced agglomeration in basic pH slurries are soft agglomerates, whereas those formed in neutral and acidic pH slurries are hard agglomerates. Also, between neutral and acidic pH slurries, shear-induced agglomerates in acidic pH slurry are relatively strongly held than the ones that are formed in neutral pH slurries. Subsequently, the nature of agglomerates was compared to defectivity and surface roughness trend of BD1 low-k wafers in silica slurries at different pH from the previous work.